WO2019211904A1 - 酢酸の製造方法 - Google Patents
酢酸の製造方法 Download PDFInfo
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- WO2019211904A1 WO2019211904A1 PCT/JP2018/017508 JP2018017508W WO2019211904A1 WO 2019211904 A1 WO2019211904 A1 WO 2019211904A1 JP 2018017508 W JP2018017508 W JP 2018017508W WO 2019211904 A1 WO2019211904 A1 WO 2019211904A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J39/00—Cation exchange; Use of material as cation exchangers; Treatment of material for improving the cation exchange properties
- B01J39/04—Processes using organic exchangers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
- B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
- B01J31/06—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides containing polymers
- B01J31/08—Ion-exchange resins
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J47/00—Ion-exchange processes in general; Apparatus therefor
- B01J47/02—Column or bed processes
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/10—Preparation of carboxylic acids or their salts, halides or anhydrides by reaction with carbon monoxide
- C07C51/12—Preparation of carboxylic acids or their salts, halides or anhydrides by reaction with carbon monoxide on an oxygen-containing group in organic compounds, e.g. alcohols
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/42—Separation; Purification; Stabilisation; Use of additives
- C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
- C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/42—Separation; Purification; Stabilisation; Use of additives
- C07C51/47—Separation; Purification; Stabilisation; Use of additives by solid-liquid treatment; by chemisorption
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C53/00—Saturated compounds having only one carboxyl group bound to an acyclic carbon atom or hydrogen
- C07C53/08—Acetic acid
Definitions
- the present invention relates to a method for producing acetic acid.
- Methanol method carbonylation process (methanol method acetic acid process) is known as an industrial production method of acetic acid.
- methanol and carbon monoxide are reacted in the presence of a catalyst in a reaction vessel to produce acetic acid, the reaction mixture is evaporated in an evaporation vessel, and the vapor phase is removed from a low boiling tower followed by dehydration.
- Acetic acid is commercialized by purification in the column, or acetic acid is commercialized through the dehydration column and further through the dehigh boiling column and further through the product column.
- organic iodine compounds such as hexyl iodide are by-produced in the reaction system and are contained as trace impurities in the product acetic acid.
- acetic acid containing an organic iodine compound is used as a raw material for vinyl acetate production, the palladium catalyst is deteriorated, so the concentration of the organic iodine compound in acetic acid must be reduced to the order of several ppb. Therefore, conventionally, the concentration of the organic iodine compound in acetic acid is reduced to the limit by using a cation exchange resin exchanged with silver ions.
- the method for adsorbing and removing organic iodine compounds using such a silver-substituted ion exchange resin is iron, nickel, chromium, molybdenum present in the process stream.
- Corrosion metal also called corrosive metal
- derived from the corrosion of equipment such as ion exchange with silver in the ion exchange resin effective silver dissolves in acetic acid and flows out of the system, ion exchange resin
- the organic iodine compound removal life of the product is reduced.
- the concentration of corrosive metals or the like in the product acetic acid or the silver concentration is increased, and the quality of the product acetic acid is deteriorated.
- Patent Document 1 describes a metal-activated exchange resin containing a specific amount of a metal-functionalized active site and a non-metal-functionalized active site for the purpose of suppressing a reduction in the lifetime of the ion exchange resin due to corrosive metals.
- a process for the purification of acetic acid using an ion exchange resin composition comprising a nonmetal-functionalized exchange resin comprising Further, Patent Document 2 discloses a method of adding and mixing an alkali component for neutralizing hydrogen iodide that causes apparatus corrosion in a dehydration tower or a liquid supplied to the dehydration tower in order to suppress corrosion of the dehydration tower. ing.
- an object of the present invention is to provide a method for producing acetic acid capable of greatly improving the life of a silver-substituted ion exchange resin (IER) for removing organic iodine compounds in acetic acid.
- IER silver-substituted ion exchange resin
- the present inventor has focused on the dehydration tower material and impurities in the dehydration tower charge, and as a result, made the dehydration tower a specific material and in the dehydration tower charge
- the concentration of specific metal ions By controlling the concentration of specific metal ions, the concentration of metal ions in acetic acid obtained from the dehydration tower can be maintained at a low level, and the concentration of metal ions in acetic acid charged in the IER in the subsequent adsorption removal step can be reduced to a low level. It has been found that it can be controlled, and therefore, the life of the IER can be greatly improved, and as a result, the quality degradation of the acetic acid product can be prevented.
- the present inventor first examined the relationship between the composition of the bottom liquid (also referred to as the bottoms) of the distillation tower and the bottom temperature.
- a metal catalyst such as a rhodium catalyst is used as a catalyst, and methyl iodide is used as a co-catalyst. Therefore, hydrogen iodide is by-produced in the reaction system.
- Most methyl iodide and hydrogen iodide are separated by distillation in the dehydration tower, but hydrogen iodide in the order of ppb and ppm exists in the bottoms of the dehydration tower.
- alkali such as potassium hydroxide is charged in the dehydration tower or in the bottoms to neutralize the remaining hydrogen iodide.
- the produced alkali metal salt (alkali metal iodide, alkali metal acetate) is removed by distillation equipment in the next step (for example, a deboiling tower).
- Such an alkali metal salt is concentrated at the bottom of the distillation column and is discarded along with acetic acid from the take-out line, but the amount of waste has been reduced as much as possible to improve the usage rate of acetic acid. For this reason, the alkali metal salt concentration in the bottom liquid of the distillation tower is increased, the boiling point rises due to the salt, and the bottom temperature (bottom temperature) of the distillation tower rises.
- acetic anhydride is generated by the dehydration reaction of acetic acid.
- This acetic anhydride is produced in a larger amount by its catalytic action in the presence of a metal iodide (for example, iron iodide) produced by corrosion of the distillation equipment by hydrogen iodide. Therefore, a large amount of acetic anhydride is present in the bottom liquid of this distillation tower, and the bottom temperature rises.
- a metal iodide for example, iron iodide
- the present invention relates to a catalyst system comprising a metal catalyst and methyl iodide, and a carbonylation reaction step in which acetic acid is produced by reacting methanol and carbon monoxide in a reaction vessel in the presence of acetic acid, methyl acetate and water.
- acetic acid is produced by reacting methanol and carbon monoxide in a reaction vessel in the presence of acetic acid, methyl acetate and water.
- the reaction mixture obtained in the carbonylation reaction step is converted into a stream containing a metal catalyst, an acetic acid stream rich in acetic acid, and a lower boiling component than the acetic acid stream using one or more evaporation tanks and / or distillation towers.
- a method for producing acetic acid comprising: The acetic acid distillation step has at least one distillation step in which the acetic acid stream is distilled under a condition where the distillation column bottom temperature is less than 175 ° C., and the material of the distillation column in the distillation step is nickel-based alloy or zirconium, Production of acetic acid, wherein the concentration of metal ions in the feed solution of the distillation column in the distillation step is less than 10,000 mass ppb of iron ions, less than 5000 mass ppb of chromium ions, less than 3000 mass ppb of nickel ions, and less than 2000 mass ppb of molybdenum ions
- the acetic acid concentration in the distillation column charge is preferably 90% by mass or more.
- the liquid charged in the distillation column in the distillation step includes at least one compound selected from the group consisting of acetate, acetic anhydride, and propionic acid, for example.
- the acetate concentration in the bottom liquid of the distillation column in the distillation step is preferably 34% by mass or less.
- the acetic anhydride concentration in the bottom liquid of the distillation column in the distillation step is preferably 90% by mass or less.
- the propionic acid concentration in the bottom liquid of the distillation column is preferably 90% by mass or less.
- the zinc ion concentration in the feed solution of the distillation tower in the distillation step is less than 1000 mass ppb.
- the stage interval between the feed liquid supply stage of the distillation column and the top vapor extraction stage is preferably 1 or more in terms of the actual number of stages.
- the material of the supply pipe to the distillation tower in the distillation step is a nickel base alloy or zirconium.
- the acid distillation step has at least one distillation step in which the acetic acid concentration in the acetic acid stream to be subjected to distillation is 97% by mass or more. In all such steps, the distillation of the acetic acid stream is performed in the column of the distillation column. It is preferable to carry out under conditions where the bottom temperature is less than 175 ° C.
- the present invention also provides a catalyst system comprising a metal catalyst and methyl iodide, and a carbonylation reaction step in which acetic acid is produced by reacting methanol and carbon monoxide in a reaction vessel in the presence of acetic acid, methyl acetate and water.
- An evaporation step for separating the reaction mixture obtained in the carbonylation reaction step into a vapor stream and a residual stream in an evaporation tank Subjecting the vapor stream to distillation to separate an overhead stream rich in low boiling components into a first acetic acid stream rich in acetic acid; Subjecting the first acetic acid stream to distillation to separate a water-rich overhead stream and a second acetic acid stream richer in acetic acid than the first acetic acid stream; An adsorption removal step of treating the second acetic acid stream or an acetic acid stream richer in acetic acid further refined from the second acetic acid stream with an ion exchange resin;
- a method for producing acetic acid comprising:
- the material of the distillation column in the dehydration step is nickel-based alloy or zirconium, and the metal ion concentration in the feed solution of the distillation column in the dehydration step is less than 10,000 mass ppb iron ions, less than 5000 mass ppb chromium ions
- the iron ion concentration in the second acetic acid stream is preferably less than 21000 mass ppb.
- the metal ion concentration in the second acetic acid stream is less than 21,000 mass ppb of iron ions, less than 7100 mass ppb of chromium ions, less than 4000 mass ppb of nickel ions, less than 3000 mass ppb of molybdenum ions, and less than 1000 mass ppb of zinc ions. Is preferred.
- the iron ion concentration is less than 10000 mass ppb in a distillation column whose material is a nickel-base alloy or zirconium, and the stage interval between the feed liquid supply stage and the tower top steam extraction stage is one stage or more.
- Chromium ion concentration less than 5000 mass ppb, nickel ion concentration less than 3000 mass ppb, molybdenum ion concentration less than 2000 mass ppb, zinc ion concentration less than 1000 mass ppb, hexyl iodide concentration less than 510 mass ppb, acetic acid concentration of 80 mass% or more Acetic acid is charged into the above-mentioned feed liquid supply stage through a feed pipe made of a nickel-base alloy or zirconium, distilled under conditions of a tower bottom temperature of less than 175 ° C., water-rich overhead, iron ion concentration of less than 21000 mass ppb, chromium Ion concentration less than 7100 mass ppb, nickel ion concentration 4000 quality Less ppb, less than molybdenum ion concentration 3000 mass ppb, obtain a purified acetic acid of less than zinc ion concentration 1000 mass ppb, it provides a process for the production of acetic acid.
- the distillation column in the acetic acid distillation process (for example, dehydration process, dehigh boiling process, etc.) is specified.
- the distillation is performed under the condition that the bottom temperature of the distillation column is less than 175 ° C., and the specific metal ion concentration in the liquid charged into the distillation column is regulated to a specific value or less.
- the concentration of metal ions in acetic acid can be reduced, and therefore the concentration of metal ions in acetic acid used for the subsequent adsorption removal process can also be reduced.
- the lifetime of the silver-substituted ion exchange resin (IER) used in the adsorption removal process can be significantly improved, and the metal ion concentration in the product acetic acid can also be reduced.
- Acetic acid having a low metal ion concentration thus obtained can be used as a low metal acetic acid used for electronic materials.
- a catalyst system containing a metal catalyst and methyl iodide, and a carbonyl that produces acetic acid by reacting methanol and carbon monoxide in a reaction vessel in the presence of acetic acid, methyl acetate, and water.
- An adsorption removal step of treating the purified acetic acid stream to be treated with an ion exchange resin wherein the acetic acid distillation step performs distillation of the acetic acid stream under conditions where the bottom temperature of the distillation column is less than 175 ° C. Fewer processes And the material of the distillation column in the distillation step is nickel-based alloy or zirconium, and the metal ion concentration in the charged solution of the distillation column in the distillation step is less than 10000 mass parts of iron ions and 5000 masses of chromium ions. Control is made to be less than ppb, nickel ion less than 3000 mass ppb, and molybdenum ion less than 2000 mass ppb.
- the zinc ion concentration in the dehydration tower charge is less than 1000 mass ppb.
- the distillation column feed liquid refers to the entire flow supplied to the distillation column, and an acetic acid stream sent from the distillation column immediately before the distillation column (for example, the distillation column in the de-low boiling step of the distillation column immediately before the distillation column). In this case, at least a part of the first acetic acid stream) is included, and a stream other than the acetic acid stream (for example, the first acetic acid stream) (for example, a recycle stream from a downstream process) is added. Good.
- the catalyst system may further contain ionic iodide.
- the separation step includes, for example, an evaporation step of separating the reaction mixture obtained in the carbonylation reaction step into a vapor stream and a residual liquid stream in an evaporation tank, and subjecting the vapor stream to distillation to obtain a low boiling point component.
- a deboiling step that separates into a rich overhead stream and a first acetic acid stream rich in acetic acid, and subjecting the first acetic acid stream to distillation to produce a first stream that is richer in acetic acid than the water rich overhead stream and the first acetic acid stream; And a dehydration step of separating into two acetic acid streams.
- the separation step the reaction mixture obtained in the carbonylation reaction step is replaced with a stream containing the catalyst, an overhead stream rich in low-boiling components, acetic acid, instead of the evaporation step and the de-low boiling step.
- a step of separating the first acetic acid stream rich in water evaporative de-low boiling step.
- the separation step is a delowing boiling step (so-called delowing low boiling dehydration step) having a function of the dehydration step instead of the delowing low boiling step and dehydration step, that is, subjecting the vapor stream to distillation.
- the method may further comprise a step of separating the overhead stream rich in low boiling components and the acetic acid stream dehydrated to the same water concentration as the second acetic acid stream.
- the evaporative de-low boiling step may be a step (evaporative de-low boiling dehydration step) having the function of the dehydration step.
- the acetic acid stream rich in acetic acid obtained from the de-low boiling dehydration step and the evaporation de-low boiling dehydration step corresponds to the second acetic acid flow.
- the acetic acid distillation step may be a step included in the separation step or may be a step provided separately from the separation step.
- the dehydration step, the de-low boiling dehydration step, and the evaporative de-low boiling dehydration step are included in the “acetic acid distillation step” in the present invention.
- the acetic acid distillation step provided separately from the separation step include a dehigh boiling step described later and a distillation step in a product tower.
- the nickel-based alloy is an alloy based on nickel, and includes Hastelloy (Hastelloy B2, Hastelloy C, etc.), Monel, Inconel, Incoloy and the like.
- iron ions, chromium ions, nickel ions and molybdenum ions are metal ions (corrosion metal ions) generated by corrosion of the apparatus.
- zinc ions are derived from zinc ions contained as impurities in methanol used as a reaction raw material.
- the acetic acid distillation step includes a distillation step in which the bottom temperature of the distillation column is lower than 175 ° C. (for example, 173 ° C. or lower).
- a distillation step in which the bottom temperature of the distillation column is lower than 175 ° C. (for example, 173 ° C. or lower) may be referred to as “distillation step (A)”.
- the tower bottom temperature refers to the temperature of the tower bottom liquid.
- the bottom temperature of the distillation tower is 175 ° C. or higher, the corrosion rate of stainless steel and some nickel-based alloys is high even when acetate, acetic anhydride, and propionic acid are not present in the bottom liquid. These materials are not suitable as materials for the distillation column apparatus.
- zirconium-based alloy or zirconium which has higher corrosion resistance than nickel-based alloy, in the acetic acid distillation process, it is a device that uses hydrogen iodide or acetic acid that is produced in the reaction system and contained in the liquid charged in the distillation column. Corrosion of metal and accompanying metal ion elution are greatly suppressed. Further, by setting the bottom temperature of the distillation column to less than 175 ° C. (for example, 173 ° C. or less), corrosion of the distillation column apparatus can be remarkably suppressed.
- the regulation of the bottom temperature of the distillation column in the distillation step (A), the regulation of the amount of the specific metal ion flowing into the distillation column, and the suppression of elution of the specific metal ion in the distillation column are combined,
- the specific metal ion concentration in the purified acetic acid obtained in the distillation column can be greatly reduced. Therefore, the amount of specific metal ions flowing into the subsequent adsorption removal step can be reduced, and the life of the silver-substituted ion exchange resin (IER) used in the step can be greatly improved.
- IER silver-substituted ion exchange resin
- the metal ion concentration in the purified acetic acid obtained in the adsorption removal step can be reduced, and high-quality product acetic acid can be produced over a long period of time without exchanging the IER for a long period of time.
- the material of the distillation column is made of stainless steel, for example, the inside of the distillation column is corroded by hydrogen iodide or acetic acid, and if the column bottom temperature of the distillation column is 175 ° C.
- the iron ion concentration in the distillation column charge in the distillation step (A) is preferably less than 9000 mass ppb, more preferably less than 5000 mass ppb, even more preferably less than 3000 mass ppb, particularly preferably less than 1500 mass ppb, especially It is less than 800 mass ppb (for example, less than 400 mass ppb).
- the chromium ion concentration in the feed solution is preferably less than 4000 mass ppb, more preferably less than 2500 mass ppb, still more preferably less than 1500 mass ppb, particularly preferably less than 750 mass ppb, especially less than 400 mass ppb (for example, less than 200 ppb). ).
- the nickel ion concentration in the feed liquid is preferably less than 2500 mass ppb, more preferably less than 2000 mass ppb, still more preferably less than 1000 mass ppb, particularly preferably less than 500 mass ppb, especially less than 250 mass ppb (for example, 150 mass). less than ppb).
- the molybdenum ion concentration in the feed liquid is preferably less than 1700 mass ppb, more preferably less than 1200 mass ppb, still more preferably less than 700 mass ppb, particularly preferably less than 350 mass ppb, especially less than 170 mass ppb.
- the zinc ion concentration in the charged solution is preferably less than 800 mass ppb, more preferably less than 650 mass ppb, still more preferably less than 500 mass ppb, particularly preferably less than 410 mass ppb, especially less than 200 mass ppb. .
- Examples of the method for controlling the concentration of the specific metal ion in the liquid charged in the distillation column in the distillation step (A) within the specific range include, for example, (i) a nickel-base alloy as the material of the supply pipe to the distillation column, (Ii) an ion exchange resin (especially a cation exchange resin) for adsorbing and removing the specific metal ion at an appropriate location from the outlet of the reaction tank to the inlet of the distillation column. And (iii) a method of using methanol with extremely low metal ion content (for example, zinc ion content) as methanol to be supplied to the reaction tank.
- methanol with extremely low metal ion content for example, zinc ion content
- the feed pipe to the dehydration column is easily corroded.
- a highly corrosion-resistant metal such as nickel-base alloy or zirconium as the material of the feed pipe, it is possible to suppress corrosion inside the feed pipe and the resulting dissolution of corrosive metal ions into the dehydration tower feed liquid. The metal ion concentration inside can be reduced.
- the ion exchange resin treatment tower for adsorbing and removing the specific metal ions at appropriate locations from the outlet of the reaction tank to the inlet of the dehydration tower, the ion exchange resin treatment tower from the reaction system is provided.
- the metal ions that have flowed in or generated by the route up to immediately before the tank can be removed, and the specific metal in the liquid charged into the dehydration tower and the subsequent distillation tower (for example, the distillation tower in the deboiling step)
- the concentration of ions can be reduced to the above specific range.
- the inner surfaces of tankers and tanks used for transporting and storing methanol are coated with an inorganic zinc-based paint to prevent iron rust from being generated during drying.
- the zinc ion concentration in the raw material methanol used in the reaction system is, for example, less than 10 mass ppm, preferably less than 1 mass ppm, more preferably less than 500 mass ppb, and particularly preferably less than 100 mass ppb.
- zinc ions derived from raw material methanol can be obtained by providing an ion exchange resin (particularly cation exchange resin) tower (or tank) at an appropriate location from the outlet of the reaction tank to the inlet of the dehydration tower. It can also be removed.
- the bottom temperature of the distillation column in the distillation step (A) is preferably 173 ° C. or lower (for example, less than 173 ° C.), more preferably 172 ° C. or lower, further preferably 170 ° C. or lower, particularly preferably 168 ° C. or lower, especially 165 ° C. It is as follows. If the bottom temperature of the distillation column is 165 ° C or lower, especially 164 ° C or lower, even if a considerable amount of acetate, acetic anhydride, or propionic acid is present in the bottom liquid, corrosion inside the distillation column is further suppressed. can do. Furthermore, if the bottom temperature of the distillation column is 163 ° C. or lower, particularly 162 ° C. or lower, corrosion inside the distillation column can be remarkably suppressed.
- the lower limit of the tower bottom temperature is, for example, 125 ° C, preferably 130 ° C, more preferably 135 ° C.
- the top temperature of the distillation column in the distillation step (A) is, for example, less than 170 ° C., preferably 168 ° C. or less, more preferably 167 ° C. or less (for example, less than 167 ° C.), still more preferably less than 165 ° C., and even more preferably 163 Less than 160C, in particular less than 161C, in particular less than 160C.
- the lower limit of the top temperature of the distillation column is, for example, 90 ° C., preferably 100 ° C., more preferably 110 ° C.
- the acetic acid distillation step has at least one distillation step in which the acetic acid concentration in the acetic acid stream to be subjected to distillation (that is, the charged solution of the distillation column) is 97% by mass or more.
- the acetic acid stream is preferably distilled under the condition that the bottom temperature of the distillation column is less than 175 ° C. (that is, the distillation step (A)).
- the stage interval (stage number) between the feed liquid supply stage (feed stage) of the distillation column (particularly the dehydration tower) and the top vapor extraction stage is preferably 1 or more, more preferably 3 stages. As described above, more preferably 5 stages or more, particularly preferably 8 stages or more (in particular, 10 stages or more).
- the feed solution of the distillation column in the distillation step (A) contains impurities having a boiling point higher than that of acetic acid and acetic acid, and preferably contains acetic acid as a main component.
- the acetic acid concentration in the feed solution is preferably It is 90% by mass or more (for example, 95% by mass or more), more preferably 97% by mass or more, further preferably 98% by mass or more, and particularly preferably 99% by mass or more.
- the impurity having a higher boiling point than that of acetic acid is not particularly limited, but the present invention particularly includes at least one compound selected from the group consisting of acetate, acetic anhydride, and propionic acid as the high boiling point impurity.
- the acetate include alkali metal acetates such as potassium acetate.
- the acetate concentration in the bottom liquid of the distillation column (particularly dehydration column) in the distillation step (A) is, for example, 34% by mass or less (for example, 30% by mass or less), preferably 23% by mass or less (for example, 15% by mass). Or less), more preferably 13% by mass or less (eg 12% by mass or less), more preferably 10% by mass or less (eg 5% by mass or less), particularly preferably 1% by mass or less (eg 0.5% by mass or less), Especially, it is 0.3 mass% or less (for example, 0.1 mass% or less), and may be 0.05 mass% or less, 0.01 mass% or less. The lower the acetate concentration in the bottom liquid, the slower the corrosion rate.
- the lower limit of the acetate concentration in the tower bottom liquid is, for example, 0 mass ppm (or 1 mass ppm).
- alkali such as potassium hydroxide is added to neutralize highly corrosive hydrogen iodide by-produced in the reaction system.
- the added alkali not only reacts with hydrogen iodide, but also reacts with acetic acid to form an acetate salt (for example, potassium acetate).
- corrosive metals such as iron, nickel, chromium, manganese, and molybdenum (hereinafter sometimes referred to as “corrosive metals”) generated by corrosion of the apparatus, and other metals such as cobalt and zinc , Copper and the like may be included.
- the corrosive metal and other metals may be collectively referred to as “corrosive metal or the like”.
- acetate metal acetate
- acetic acid When the crude acetic acid solution containing such an acetate salt is distilled, it is stored at the bottom of the distillation column. Therefore, the acetate concentration in the bottom liquid of the distillation column can be adjusted, for example, by adjusting the amount of alkali added or suppressing corrosion inside the distillation column.
- the acetic anhydride concentration in the bottom liquid of the distillation column (particularly dehydration column) in the distillation step (A) is, for example, 90% by mass or less (for example, 80% by mass or less), preferably 74% by mass or less (for example, 60% by mass). Or less), more preferably 45% by mass or less (eg 20% by mass or less), further preferably 10% by mass or less (eg 5% by mass or less), particularly preferably 1% by mass or less (eg 0.5% by mass or less), Especially, it is 0.2 mass% or less (for example, 0.1 mass% or less), and may be 0.05 mass% or less, 0.02 mass% or less, or 0.01 mass% or less.
- the concentration of acetic anhydride in the bottom liquid of the distillation column can be adjusted by, for example, adding water to the piping or device located upstream of the distillation column or adding water into the distillation column to hydrolyze the acetic anhydride. it can.
- the propionic acid concentration in the bottom liquid of the distillation column (particularly dehydration column) in the distillation step (A) is, for example, 90% by mass or less (for example, 80% by mass or less), preferably 75% by mass or less (for example, 65% by mass). Or less), more preferably 55% by mass or less (eg 35% by mass or less), further preferably 29% by mass or less (eg 20% by mass or less), particularly preferably 10% by mass or less (eg 5% by mass or less), especially 3 It is not more than mass% (for example, not more than 1 mass%), and may be not more than 0.1 mass%, not more than 0.05 mass%, or not more than 0.03 mass%.
- the concentration of propionic acid in the bottom liquid of the distillation column may be a cause of propionic acid by-product when, for example, reaction conditions are changed to reduce propionic acid by-products or when a part of the process liquid is recycled to the reaction system. This can be reduced by separating and removing the acetaldehyde from the process liquid and recycling it to the reaction system, or by providing a distillation column or an evaporator (depropionic acid column) for separating and removing propionic acid upstream of the distillation column.
- the column bottom pressure of the distillation column (particularly dehydration column) in the distillation step (A) is appropriately adjusted according to the desired column bottom temperature and column bottom liquid composition.
- the tower bottom pressure is, for example, less than 0.255 MPaG, preferably 0.24 MPaG or less, more preferably 0.23 MPaG or less, and particularly preferably 0.21 MPaG or less. “G” indicates a gauge pressure.
- the higher the concentration of high-boiling impurities in the bottom liquid the higher the boiling point.
- the concentration of high-boiling impurities in the bottom liquid the lower the bottom pressure is. There is.
- the lower limit of the bottom pressure of the distillation column is, for example, 0.01 MPaG, preferably 0.02 MPaG, more preferably 0.03 MPaG, and particularly preferably 0.05 MPaG.
- the present invention since the column bottom temperature is adjusted to a specific value or less, acetic acid can be purified by distillation while preventing corrosion of the apparatus even under pressure. Therefore, the present invention is particularly useful when distillation is performed under pressure in order to increase the production efficiency of acetic acid.
- the material of the distillation column (particularly the dehydration column) in the distillation step (A) is a specific material
- the bottom temperature of the distillation column is less than 175 ° C.
- the concentration of metal ions in the acid stream (for example, the second acetic acid stream) obtained as a side stream or a bottom stream of the distillation column can be reduced.
- the iron ion concentration in the acetic acid stream (for example, the second acetic acid stream) is, for example, less than 21000 mass ppb, preferably less than 16000 mass ppb, more preferably less than 6000 mass ppb, still more preferably less than 2000 mass ppb, particularly preferably. Less than 200 mass ppb.
- the chromium ion concentration in the acetic acid stream is, for example, less than 7100 mass ppb, preferably less than 5000 mass ppb, more preferably less than 3000 mass ppb, still more preferably less than 1000 mass ppb, particularly preferably. It is less than 100 mass ppb.
- the nickel ion concentration in the acetic acid stream is, for example, less than 4000 mass ppb, preferably less than 3000 mass ppb, more preferably less than 1800 mass ppb, still more preferably less than 700 mass ppb, particularly preferably. It is less than 70 mass ppb.
- the concentration of molybdenum ions in the acetic acid stream is, for example, less than 3000 mass ppb, preferably less than 2500 mass ppb, more preferably less than 1500 mass ppb, still more preferably less than 500 mass ppb, particularly preferably. It is less than 50 mass ppb.
- the zinc ion concentration in the acetic acid stream is, for example, less than 1000 mass ppb, preferably less than 850 mass ppb, more preferably less than 710 mass ppb, still more preferably less than 410 mass ppb, particularly preferably. It is less than 150 mass ppb.
- the distillation method may be either batch distillation or continuous distillation, but continuous distillation is more preferable in terms of production efficiency.
- the material is a nickel-base alloy or zirconium
- the stage interval between the feed liquid supply stage and the tower top steam extraction stage is one stage or more (the number of theoretical stages is, for example, 0.5 stage).
- the iron ion concentration is less than 10000 mass ppb
- the chromium ion concentration is less than 5000 mass ppb
- the nickel ion concentration is less than 3000 mass ppb
- the molybdenum ion concentration is less than 2000 mass ppb
- the zinc ion concentration is less than 1000 mass ppb
- iodide the number of theoretical stages
- Crude acetic acid having a hexyl concentration of less than 510 mass ppb and an acetic acid concentration of 80 mass% or more is charged into the above-mentioned feed solution supply stage through a feed pipe made of a nickel-based alloy or zirconium, and distilled at a column bottom temperature of less than 175 ° C.
- FIG. 1 is an example of an acetic acid production flow diagram (methanol carbonylation process) showing an embodiment of the present invention.
- the acetic acid production apparatus includes a reaction tank 1, an evaporation tank 2, a distillation tower 3, a decanter 4, a distillation tower 5, a distillation tower 6, an ion exchange resin tower 7, and a scrubber system 8. And acetaldehyde separation and removal system 9, condensers 1a, 2a, 3a, 5a and 6a, heat exchanger 2b, reboilers 3b, 5b and 6b, lines 11 to 56 and pump 57, and acetic acid is continuously added.
- reaction tank 1 the reaction tank 1, the evaporation tank 2, the distillation tower 3, the distillation tower 5, the distillation tower 6, and the ion exchange resin tower 7, respectively.
- a reaction process an evaporation process (flash process), A 1st distillation process, a 2nd distillation process, a 3rd distillation process, and an adsorption removal process are performed.
- the first distillation step is also called a delow boiling step
- the second distillation step is also called a dehydration step
- the third distillation step is also called a dehigh boiling step.
- the second distillation process and the third distillation process are included in the “acetic acid distillation process” in the present invention.
- a process is not restricted above, Especially, the installation of the acetaldehyde separation-removal system 9 (deacetaldehyde tower etc.) may not be attached. Further, as will be described later, a product tower may be provided downstream of the ion exchange resin tower 7. This product column is also included in the “acetic acid distillation step” in the present invention.
- the reaction tank 1 is a unit for performing a reaction process.
- This reaction step is a step for continuously generating acetic acid by a reaction (methanol carbonylation reaction) represented by the following chemical formula (1).
- a reaction mixture that is stirred by, for example, a stirrer exists in the reaction tank 1.
- the reaction mixture contains methanol and carbon monoxide as raw materials, a metal catalyst, a cocatalyst, water, acetic acid for production purposes, and various by-products, and the liquid phase and the gas phase are in an equilibrium state. It is in. CH 3 OH + CO ⁇ CH 3 COOH (1)
- the raw materials in the reaction mixture are liquid methanol and gaseous carbon monoxide.
- Methanol is continuously supplied at a predetermined flow rate from the methanol reservoir (not shown) to the reaction tank 1 through the line 11.
- methanol in the market often contains zinc. This zinc becomes a factor that decreases the life of the silver-substituted ion exchange resin (IER) used in the subsequent adsorption removal step. Therefore, it is preferable to use methanol having a high zinc content for the reaction after previously treating with cation exchange resin to lower the zinc ion concentration in methanol.
- IER silver-substituted ion exchange resin
- Carbon monoxide is continuously supplied from the carbon monoxide reservoir (not shown) through the line 12 to the reaction tank 1 at a predetermined flow rate.
- Carbon monoxide is not necessarily pure carbon monoxide, and contains a small amount (for example, 5% by mass or less, preferably 1% by mass or less) of other gases such as nitrogen, hydrogen, carbon dioxide, and oxygen. Also good.
- the metal catalyst in the reaction mixture is for accelerating the carbonylation reaction of methanol.
- a rhodium catalyst or an iridium catalyst can be used.
- a rhodium catalyst for example, a rhodium complex represented by the chemical formula [Rh (CO) 2 I 2 ] ⁇ can be used.
- a iridium catalyst for example, an iridium complex represented by the chemical formula [Ir (CO) 2 I 2 ] ⁇ can be used.
- a metal complex catalyst is preferable as the metal catalyst.
- the concentration of the catalyst in the reaction mixture (in metal conversion) is, for example, 200 to 5000 ppm by mass, preferably 400 to 2000 ppm by mass with respect to the entire liquid phase of the reaction mixture.
- the cocatalyst is an iodide for assisting the action of the above-described catalyst.
- methyl iodide or ionic iodide is used.
- Methyl iodide can exhibit an action of promoting the catalytic action of the above-described catalyst.
- the concentration of methyl iodide is, for example, 1 to 20% by mass with respect to the entire liquid phase of the reaction mixture.
- the ionic iodide is an iodide (in particular, an ionic metal iodide) that generates an iodide ion in the reaction solution, and can exhibit an effect of stabilizing the above-described catalyst and an effect of suppressing side reactions.
- the ionic iodide examples include alkali metal iodides such as lithium iodide, sodium iodide, and potassium iodide.
- concentration of the ionic iodide in the reaction mixture is, for example, 1 to 25% by mass, preferably 5 to 20% by mass, based on the entire liquid phase of the reaction mixture.
- a ruthenium compound or an osmium compound can also be used as a promoter.
- the total amount of these compounds used is, for example, 0.1 to 30 mol (metal conversion), preferably 0.5 to 15 mol (metal conversion) with respect to 1 mol of iridium (metal conversion).
- Water in the reaction mixture is a component necessary for generating acetic acid in the reaction mechanism of the carbonylation reaction of methanol, and is also a component necessary for solubilizing water-soluble components in the reaction system.
- the concentration of water in the reaction mixture is, for example, 0.1 to 15% by mass, preferably 0.8 to 10% by mass, more preferably 1 to 6% by mass, based on the entire liquid phase of the reaction mixture.
- the amount is preferably 1.5 to 4% by mass.
- the water concentration is preferably 15% by mass or less in order to suppress the energy required for water removal during the purification process of acetic acid and promote the efficiency of acetic acid production.
- a predetermined flow rate of water may be continuously supplied to the reaction tank 1.
- Acetic acid in the reaction mixture contains acetic acid that is charged in advance in the reaction tank 1 before the operation of the acetic acid production apparatus, and acetic acid that is generated as a main product of the carbonylation reaction of methanol. Such acetic acid can function as a solvent in the reaction system.
- the concentration of acetic acid in the reaction mixture is, for example, 50 to 90% by mass, preferably 60 to 80% by mass, based on the entire liquid phase of the reaction mixture.
- Examples of main by-products contained in the reaction mixture include methyl acetate. This methyl acetate can be generated by the reaction of acetic acid and methanol.
- the concentration of methyl acetate in the reaction mixture is, for example, 0.1 to 30% by mass, preferably 1 to 10% by mass, with respect to the entire liquid phase of the reaction mixture.
- Examples of by-products contained in the reaction mixture include hydrogen iodide. This hydrogen iodide is inevitably generated due to the reaction mechanism of the carbonylation reaction of methanol when the above-described catalyst or promoter is used.
- the concentration of hydrogen iodide in the reaction mixture is, for example, 0.01 to 2% by mass with respect to the entire liquid phase of the reaction mixture.
- Examples of by-products include hydrogen, methane, carbon dioxide, acetaldehyde, crotonaldehyde, 2-ethylcrotonaldehyde, dimethyl ether, alkanes, formic acid, and propionic acid, and hexyl iodide and decyl iodide. Examples thereof include alkyl iodide.
- the concentration of hexyl iodide is, for example, 0.1 to 10000 mass ppb, usually 0.5 to 1000 mass ppb, and 1 to 100 mass ppb (for example 2 to 50 mass) with respect to the entire liquid phase of the reaction mixture. ppb) in many cases.
- the reaction mixture includes metals such as iron, nickel, chromium, manganese, and molybdenum (hereinafter sometimes referred to as “corrosive metals”) generated by corrosion of the apparatus, and other metals such as cobalt, zinc, and copper. Can be included.
- the corrosive metal and other metals may be collectively referred to as “corrosive metal or the like”.
- the reaction temperature is set to 150 to 250 ° C., for example, and the reaction pressure as the total pressure is set to 2.0 to 3.5 MPa (absolute pressure), for example.
- the carbon monoxide partial pressure is set to, for example, 0.4 to 1.8 MPa (absolute pressure), preferably 0.6 to 1.6 MPa (absolute pressure), more preferably 0.9 to 1.4 MPa (absolute pressure). Is done.
- carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether can be used as the vapor in the gas phase in the reaction tank 1 when the apparatus is in operation.
- Methanol, acetaldehyde, formic acid, propionic acid, and the like This vapor can be extracted from the reaction vessel 1 through the line 13. It is possible to control the pressure in the reaction tank 1 by adjusting the amount of steam extracted. For example, the pressure in the reaction tank 1 is maintained constant.
- the steam extracted from the reaction tank 1 is introduced into the condenser 1a.
- the condenser 1a divides the vapor from the reaction vessel 1 into a condensed component and a gas component by cooling and partially condensing.
- the condensate includes, for example, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, propionic acid, and the like, and is introduced from the condenser 1a to the reaction tank 1 through the line 14, Recycled.
- the gas component includes, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, and formic acid.
- useful components for example, methyl iodide, water, methyl acetate, acetic acid, etc.
- a wet method is used for this separation and recovery, which is performed using an absorbent for collecting useful components in the gas component.
- an absorbing solvent containing at least acetic acid and / or methanol is preferable.
- the absorbing solution may contain methyl acetate.
- a condensate of vapor from the later-described distillation column 6 can be used as the absorbing liquid.
- a pressure fluctuation adsorption method may be used.
- the useful components separated and recovered (for example, methyl iodide and the like) are introduced from the scrubber system 8 into the reaction tank 1 through the recycling line 48 and recycled.
- the gas after collecting useful components is discarded through line 49.
- the gas discharged from the line 49 can be used as a CO source to be introduced into the bottom of the evaporation tank 2 described later or the residual liquid flow recycling lines 18 and 19.
- the processing in the scrubber system 8 and the subsequent recycling and disposal to the reaction tank 1 are the same for the gas components described later supplied to the scrubber system 8 from other capacitors.
- the production method of the present invention preferably has a scrubber step of absorbing off-gas from the process with an absorption solvent containing at least acetic acid to separate a stream rich in carbon monoxide and a stream rich in acetic acid.
- acetic acid is continuously generated as described above.
- a reaction mixture containing such acetic acid is continuously withdrawn from the reaction tank 1 at a predetermined flow rate and introduced into the next evaporation tank 2 through a line 16.
- the evaporation tank 2 is a unit for performing an evaporation process (flash process).
- a vapor stream (volatile phase) and a residual liquid stream (low volatile phase) are obtained by partially evaporating the reaction mixture continuously introduced into the evaporation tank 2 through the line 16 (reaction mixture supply line). It is a process for dividing into. Evaporation may be caused by reducing the pressure without heating the reaction mixture, or evaporation may be caused by reducing the pressure while heating the reaction mixture.
- the temperature of the vapor stream is, for example, 100 to 260 ° C., preferably 120 to 200 ° C.
- the temperature of the residual liquid stream is, for example, 80 to 200 ° C., preferably 100 to 180 ° C.
- the pressure in the tank is, for example, 50 to 1000 kPa (absolute pressure).
- the ratio of the vapor flow and the residual liquid flow separated in the evaporation step is, for example, 10/90 to 50/50 (vapor flow / residual liquid flow) in mass ratio.
- the vapor generated in this step is, for example, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, and propionic acid, and ethyl iodide, propyl iodide, butyl iodide, It contains alkyl iodide such as hexyl iodide and decyl iodide and is continuously extracted from the evaporation tank 2 to the line 17 (vapor flow discharge line).
- alkyl iodide such as hexyl iodide and decyl iodide
- the acetic acid concentration of the vapor stream is, for example, 40 to 85% by mass (preferably 50 to 85% by mass), more preferably 50 to 75% by mass (for example 55 to 75% by mass), and the methyl iodide concentration is, for example, 2 to 50% by mass (preferably 5 to 30% by mass), water concentration is, for example, 0.2 to 20% by mass (preferably 1 to 15% by mass), and methyl acetate concentration is, for example, 0.2 to 50% by mass (Preferably 2 to 30% by mass).
- the concentration of hexyl iodide in the vapor stream is, for example, 0.1 to 10000 mass ppb, usually 0.5 to 1000 mass ppb, and is often 1 to 100 mass ppb (eg 2 to 50 mass ppb).
- the residual liquid stream generated in this step is the catalyst and co-catalyst (methyl iodide, lithium iodide, etc.) contained in the reaction mixture, water remaining without volatilization in this step, methyl acetate, acetic acid, formic acid, And propionic acid, etc., are continuously introduced from the evaporation tank 2 to the heat exchanger 2b through the line 18 using the pump 57.
- the heat exchanger 2b cools the remaining liquid stream from the evaporation tank 2.
- the cooled residual liquid stream is continuously introduced from the heat exchanger 2b to the reaction tank 1 through the line 19 and recycled.
- the line 18 and the line 19 are collectively referred to as a residual liquid recycle line.
- the acetic acid concentration in the residual stream is, for example, 55 to 90% by mass, preferably 60 to 85% by mass.
- the condenser 2a divides the vapor flow from the evaporation tank 2 into a condensed component and a gas component by cooling and partially condensing.
- the condensate contains, for example, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, propionic acid, and the like, and is introduced from the condenser 2a into the reaction tank 1 through lines 22 and 23. And recycled.
- the gas component includes, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, etc., and capacitor 2a
- the acetic acid production reaction in the above reaction step is an exothermic reaction, and part of the heat accumulated in the reaction mixture is transferred to the vapor generated from the reaction mixture in the evaporation step (flash step).
- the condensed matter generated by the cooling of the steam in the condenser 2 a is recycled to the reaction tank 1. That is, in this acetic acid production apparatus, heat generated by the carbonylation reaction of methanol is efficiently removed by the capacitor 2a.
- the distillation column 3 is a unit for performing the first distillation step, and is positioned as a so-called deboiling tower in this embodiment.
- the first distillation step is a step of separating and removing low boiling components by subjecting the vapor stream continuously introduced into the distillation column 3 to a distillation treatment. More specifically, in the first distillation step, the vapor stream is distilled and separated into an overhead stream rich in at least one low-boiling component selected from methyl iodide and acetaldehyde, and an acetic acid stream rich in acetic acid. .
- the distillation column 3 is composed of, for example, a rectification column such as a plate column and a packed column.
- the theoretical plate is, for example, 5 to 50 plates, and the reflux ratio is, for example, 0.5 to 3000 depending on the number of theoretical plates.
- the column top pressure is set to 80 to 160 kPaG, for example, and the column bottom pressure is set higher than the column top pressure, for example to 85 to 180 kPaG.
- the column top temperature is set to 90 to 130 ° C., for example, lower than the boiling point of acetic acid at the set column top pressure
- the column bottom temperature is set to, for example, the set column bottom pressure.
- the temperature is equal to or higher than the boiling point of acetic acid and is set to 120 to 165 ° C. (preferably 125 to 160 ° C.).
- the vapor flow from the evaporation tank 2 is continuously introduced through the line 21, and the vapor as an overhead flow is continuously extracted from the top of the distillation column 3 to the line 24. From the bottom of the distillation column 3, the bottoms are continuously extracted into the line 25.
- 3b is a reboiler.
- An acetic acid stream (first acetic acid stream; liquid) as a side stream is continuously extracted from the line 27 from a height position between the top and bottom of the distillation column 3.
- the steam withdrawn from the top of the distillation column 3 contains a larger amount of components having a lower boiling point than that of acetic acid (low-boiling components) compared to the bottoms and side stream from the distillation column 3, such as methyl iodide, Including hydrogen iodide, water, methyl acetate, dimethyl ether, methanol, acetaldehyde, and formic acid. This vapor also contains acetic acid.
- acetic acid low-boiling components
- the condenser 3a cools and partially condenses the vapor from the distillation tower 3 to divide it into a condensed component and a gas component.
- the condensate contains, for example, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, and the like, and is continuously introduced from the capacitor 3a to the decanter 4 through the line 28.
- the condensed matter introduced into the decanter 4 is separated into an aqueous phase (upper phase) and an organic phase (methyl iodide phase; lower phase).
- the aqueous phase includes water and, for example, methyl iodide, hydrogen iodide, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, and formic acid.
- the organic phase includes, for example, methyl iodide and, for example, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, and formic acid.
- a part of the aqueous phase is refluxed to the distillation column 3 through the line 29, and the other part of the aqueous phase is introduced into the reaction tank 1 through the lines 29, 30, and 23 and recycled.
- Part of the organic phase is introduced into the reaction vessel 1 through lines 31 and 23 and recycled.
- the other part of the organic phase and / or the other part of the aqueous phase is introduced into the acetaldehyde separation and removal system 9 through the lines 31, 50 and / or the lines 30, 51.
- acetaldehyde contained in the organic phase and / or the aqueous phase is separated and removed by a known method, for example, distillation, extraction, or a combination thereof.
- the separated acetaldehyde is discharged out of the apparatus through a line 53.
- useful components for example, methyl iodide contained in the organic phase and / or the aqueous phase are recycled to the reaction tank 1 through the lines 52 and 23 and reused.
- FIG. 2 is a schematic flow diagram showing an example of an acetaldehyde separation and removal system.
- the organic phase is fed to the distillation tower (first deacetaldehyde tower) 91 through the line 101 and distilled, and an overhead stream rich in acetaldehyde is obtained. (Line 102) and a residual stream rich in methyl iodide (line 103).
- the overhead stream is condensed in the condenser 91a, a part of the condensate is refluxed to the top of the distillation column 91 (line 104), and the other part of the condensate is supplied to the extraction tower 92 (line 105).
- the condensate supplied to the extraction tower 92 is extracted with water introduced from the line 109.
- the extract obtained by the extraction process is supplied to a distillation tower (second deacetaldehyde tower) 93 through a line 107 and distilled, and an overhead stream rich in acetaldehyde (line 112) and a residual liquid stream rich in water (line 113) To separate.
- the overhead stream rich in acetaldehyde is condensed by the condenser 93a, a part of the condensate is refluxed to the top of the distillation column 93 (line 114), and the other part of the condensate is discharged out of the system (line 115). ).
- a methyl iodide-rich residual liquid stream that is the bottoms of the first deacetaldehyde column 91, a methyl iodide-rich raffinate obtained in the extraction column 92 (line 108), and a second deacetaldehyde column 93 can
- the water-rich residual liquid stream that is the effluent is recycled to the reaction vessel 1 through lines 103, 111, and 113, respectively, or recycled to an appropriate location in the process and reused.
- the methyl iodide rich raffinate obtained in the extraction column 92 can be recycled to the distillation column 91 through line 110.
- the liquid 113 is usually discharged to the outside as waste water.
- the gas (lines 106, 116) that has not been condensed by the condensers 91a, 93a is either absorbed by the scrubber system 8 or discarded.
- the aqueous phase is supplied to the distillation column (first deacetaldehyde column) 91 through the line 101 and distilled to enrich the acetaldehyde.
- the overhead stream (line 102) is separated into a water-rich residual liquid stream (line 103).
- the overhead stream is condensed in the condenser 91a, a part of the condensate is refluxed to the top of the distillation column 91 (line 104), and the other part of the condensate is supplied to the extraction tower 92 (line 105).
- the condensate supplied to the extraction tower 92 is extracted with water introduced from the line 109.
- the extract obtained by the extraction process is supplied to a distillation tower (second deacetaldehyde tower) 93 through a line 107 and distilled, and an overhead stream rich in acetaldehyde (line 112) and a residual liquid stream rich in water (line 113) To separate. Then, the overhead stream rich in acetaldehyde is condensed by the condenser 93a, a part of the condensate is refluxed to the top of the distillation column 93 (line 114), and the other part of the condensate is discharged out of the system (line 115). ).
- a water-rich residual stream that is the bottoms of the first deacetaldehyde tower 91, a methyl iodide-rich raffinate obtained in the extraction tower 92 (line 108), and a bottoms of the second deacetaldehyde tower 93
- the water-rich residual liquid stream is recycled to the reaction tank 1 through the lines 103, 111, and 113, or recycled to an appropriate part of the process and reused.
- the methyl iodide rich raffinate obtained in the extraction column 92 can be recycled to the distillation column 91 through line 110.
- the liquid 113 is usually discharged to the outside as waste water.
- the gas (lines 106, 116) that has not been condensed by the condensers 91a, 93a is either absorbed by the scrubber system 8 or discarded.
- Acetaldehyde derived from a process stream containing at least water, acetic acid (AC), methyl iodide (MeI), and acetaldehyde (AD) can be separated and removed using extractive distillation in addition to the above method.
- the organic phase and / or the aqueous phase (feed solution) obtained by separating the process stream is supplied to a distillation column (extraction distillation column), and methyl iodide and acetaldehyde in the distillation column are concentrated.
- An extraction solvent usually water
- is introduced into the concentration area for example, the space from the top of the column to the feed liquid supply position
- the liquid descending from the concentration area extraction liquid is extracted as a side flow (side cut flow).
- Acetaldehyde can be discharged out of the system by separating the side stream into an aqueous phase and an organic phase and distilling the aqueous phase.
- the liquid descending from the concentration zone may be withdrawn as a side stream without introducing the extraction solvent into the distillation column.
- a unit such as a chimney tray
- the introduction position of the extraction solvent is preferably above the feed liquid supply position, and more preferably near the top of the column.
- the side stream extraction position is preferably lower than the extraction solvent introduction position and higher than the feed liquid supply position in the height direction of the column.
- a high concentration of acetaldehyde can be extracted from the concentrate of methyl iodide and acetaldehyde with an extraction solvent (usually water), and the area between the extraction solvent introduction site and the side cut site is used as an extraction zone. Therefore, acetaldehyde can be extracted efficiently with a small amount of extraction solvent. Therefore, for example, the number of stages of the distillation column can be greatly reduced and the steam load can be reduced as compared with a method of extracting the extract by extraction distillation from the bottom of the distillation column (extraction distillation column).
- the ratio (MeI / AD ratio) of methyl iodide with respect to acetaldehyde in a water extract can be made smaller than the method of combining the dealdehyde distillation and water extraction of FIG. 2 using a small amount of extraction solvent, Acetaldehyde can be removed under conditions that can prevent loss of methyl iodide to the outside of the system.
- the concentration of acetaldehyde in the side stream is much higher than the concentration of acetaldehyde in the feed solution and bottoms (column bottom liquid).
- the ratio of the acetaldehyde with respect to the methyl iodide in the said side stream is larger than the ratio of the acetaldehyde with respect to the methyl iodide in the preparation liquid and the bottom liquid.
- the organic phase (methyl iodide phase) obtained by separating the side stream may be recycled to this distillation column.
- the recycling position of the organic phase obtained by separating the side stream is preferably lower than the side stream extraction position and higher than the feed liquid supply position in the height direction of the tower.
- a miscible solvent for components (for example, methyl acetate) constituting the organic phase obtained by separating the process stream may be introduced into this distillation column (extraction distillation column).
- miscible solvent examples include acetic acid and ethyl acetate.
- the introduction position of the miscible solvent is preferably lower than the side flow extraction position and higher than the feed liquid supply position in the height direction of the tower.
- the position where the miscible solvent is introduced is preferably lower than the recycling position when the organic phase obtained by separating the side stream is recycled to the distillation column.
- the organic phase obtained by separating the side stream can be recycled to the distillation column, or the methyl acetate concentration in the extract extracted as the side stream can be reduced by introducing the miscible solvent into the distillation column.
- concentration of methyl acetate in the aqueous phase obtained by separating the extract can be reduced, so that mixing of methyl iodide into the aqueous phase can be suppressed.
- the theoretical column of the distillation column is, for example, 1 to 100 plate, preferably 2 to 50 plate, more preferably 3 to 30 plate, more preferably 5 to 20 plate, and is used for conventional deacetaldehyde.
- acetaldehyde can be separated and removed efficiently with a small number of stages.
- the mass ratio (the former / the latter) of the flow rate of the extraction solvent and the flow rate of the feed liquid (the organic phase and / or the aqueous phase obtained by separating the process stream) is in the range of 0.0001 / 100 to 100/100.
- the top temperature of the distillation column is, for example, 15 to 120 ° C., preferably 20 to 90 ° C., more preferably 20 to 80 ° C., and further preferably 25 to 70 ° C.
- the tower top pressure is an absolute pressure, for example, about 0.1 to 0.5 MPa.
- Other conditions of the distillation column may be the same as those of the conventional distillation column and extraction distillation column used for deacetaldehyde.
- FIG. 3 is a schematic flow diagram showing an example of an acetaldehyde separation and removal system using the above extractive distillation.
- the organic phase and / or aqueous phase (feed solution) obtained by separating the process stream is supplied to the middle stage of the distillation column 94 (position between the top and the bottom) through the supply line 201.
- water is introduced from the vicinity of the top of the column through the line 202, and extractive distillation is performed in the distillation column 94 (extraction distillation column).
- a chimney tray 200 for receiving a liquid (extracted liquid) descending from a concentration area where methyl iodide and acetaldehyde in the tower are concentrated is disposed above the feed liquid supply position of the distillation tower 94.
- the entire amount of the liquid on the chimney tray 200 is preferably withdrawn and introduced into the decanter 95 through the line 208 for liquid separation.
- the aqueous phase (including acetaldehyde) in the decanter 95 is introduced into the cooling cooler 95 a through the line 212 and cooled, and the two phases of methyl iodide dissolved in the aqueous phase are separated and separated in the decanter 96.
- the aqueous phase in the decanter 96 is fed to the distillation column 97 (deacetaldehyde column) through the line 216 and distilled, and the vapor at the top of the column is led to the condenser 97a through the line 217 to be condensed and condensed (mainly acetaldehyde and methyl iodide). ) Is refluxed to the top of the distillation column 97 and the rest is discarded or supplied to the distillation column 98 (extraction distillation column) through the line 220. Water is introduced from the vicinity of the top of the distillation column 98 through the line 222, and extractive distillation is performed.
- the vapor at the top of the column is led to the condenser 98a through the line 223 to be condensed, a part of the condensate (mainly methyl iodide) is refluxed to the top of the column, and the rest is recycled to the reaction system through the line 226.
- the entire amount of the organic phase (methyl iodide phase) in the decanter 95 is preferably recycled below the position of the chimney tray 200 in the distillation column 94 through lines 209 and 210.
- a part of the aqueous phase of the decanter 95 and the organic phase of the decanter 96 are recycled to the distillation column 94 through lines 213 and 210 and lines 214 and 210, respectively, but may not be recycled.
- a part of the aqueous phase of the decanter 95 may be used as an extraction solvent (water) in the distillation column 94.
- a portion of the aqueous phase of the decanter 96 may be recycled to the distillation column 94 through line 210.
- a miscible solvent for example, methyl acetate
- Distillation efficiency can also be improved by charging acetic acid, ethyl acetate, etc.) into the distillation column 94 through the line 215.
- the supply position of the miscible solvent to the distillation column 94 is above the feed liquid supply part (connection part of the line 201) and below the connection part of the recycle line 210.
- the bottoms of the distillation column 94 is recycled to the reaction system.
- the vapor at the top of the distillation column 94 is led to the condenser 94a through the line 203 to condense, the condensate is separated by the decanter 99, the organic phase is refluxed to the top of the distillation column 94 through the line 206, and the water phase is the line.
- Guide to decanter 95 through 207 is described by decanter 95 through 207.
- the bottoms of the distillation column 97 (water is the main component) and the bottoms of the distillation column 98 (extraction distillation column) (water containing a small amount of acetaldehyde) are removed from the system through lines 218 and 224, respectively, or the reaction system. Recycle to. Gases (lines 211, 2221 and 227) which have not been condensed by the condensers 94a, 97a and 98a are absorbed by the scrubber system 8 or disposed of.
- FIG. 4 is a schematic flow diagram showing another example of an acetaldehyde separation / removal system using the above extractive distillation.
- the vapor condensate at the top of the distillation column 94 is led to the hold tank 100, and the entire amount is refluxed to the top of the distillation column 94 through the line 206.
- the rest is the same as the example of FIG.
- FIG. 5 is a schematic flow diagram showing still another example of the acetaldehyde separation and removal system using the above-described extractive distillation.
- the entire amount of the liquid on the chimney tray 200 is extracted, and is directly introduced into the cooling cooler 95 a through the line 208 without passing through the decanter 95, and is supplied to the decanter 96.
- the rest is the same as the example of FIG.
- the gas generated in the capacitor 3a is, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde. , And formic acid, etc., and supplied to the scrubber system 8 through the lines 32 and 15 from the condenser 3a.
- Methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, and the like in the gas component that has reached the scrubber system 8 are absorbed by the absorbing solution in the scrubber system 8.
- Hydrogen iodide is produced by reaction with methanol or methyl acetate in the absorbing solution. Then, the liquid containing useful components such as methyl iodide is recycled from the scrubber system 8 to the reaction tank 1 through the recycling lines 48 and 23 and reused.
- the bottoms extracted from the bottom of the distillation column 3 contains a larger amount of components having a higher boiling point than acetic acid (high-boiling components) compared to the overhead stream and side stream from the distillation column 3 such as propionic acid.
- the above-mentioned catalyst and cocatalyst accompanied by droplets are included.
- the bottoms include acetic acid, methyl iodide, methyl acetate, water and the like.
- a part of such bottoms is continuously introduced into the evaporation tank 2 through the lines 25 and 26 and recycled, and the other part of the bottoms is passed through the lines 25 and 23. It is continuously introduced into the reaction tank 1 and recycled.
- the first acetic acid stream continuously withdrawn from the distillation column 3 as a side stream is richer in acetic acid than the vapor stream continuously introduced into the distillation column 3. That is, the acetic acid concentration of the first acetic acid stream is higher than the acetic acid concentration of the vapor stream.
- the concentration of acetic acid in the first acetic acid stream is, for example, 90 to 99.9% by mass, preferably 93 to 99% by mass.
- the first acetic acid stream includes, for example, methyl iodide, hydrogen iodide, water, methyl acetate, dimethyl ether, methanol, acetaldehyde, formic acid, and propionic acid, and ethyl iodide, propyl iodide, And alkyl iodides such as butyl iodide, hexyl iodide, and decyl iodide.
- the methyl iodide concentration is, for example, 8% by mass or less (eg, 0.1-8% by mass), preferably 0.2-5% by mass
- the water concentration is, for example, 8% by mass or less (eg, 0% 0.1-8% by mass), preferably 0.2-5% by mass
- the methyl acetate concentration is, for example, 8% by mass or less (eg, 0.1-8% by mass), preferably 0.2-5% by mass.
- the concentration of hexyl iodide in the first acetic acid stream is, for example, 0.2 to 10000 mass ppb, usually 1 to 1000 mass ppb, and often 2 to 100 mass ppb (eg 3 to 50 mass ppb).
- the connecting position of the line 27 to the distillation column 3 may be higher than the connecting position of the line 21 to the distillation column 3 in the height direction of the distillation column 3, as shown in the figure. It may be lower than the connection position of the line 21 with respect to, or may be the same as the connection position of the line 21 with respect to the distillation column 3.
- the first acetic acid stream from the distillation column 3 is continuously introduced into the next distillation column 5 through the line 27 at a predetermined flow rate. Note that the first acetic acid stream extracted as a side stream of the distillation column 3, the bottom liquid of the distillation column 3, or the vapor condensate at the bottom of the distillation column 3 remains as it is without passing through the distillation column 5 (dehydration step).
- the material of the line 27 and the material of the distillation column 5 may be stainless steel, but in order to suppress corrosion inside the piping and distillation column by hydrogen iodide or acetic acid It is preferable to use a highly corrosion-resistant metal such as a nickel-base alloy or zirconium.
- Potassium hydroxide can be supplied or added to the first acetic acid stream flowing through the line 27 through a line 55 (potassium hydroxide introduction line). Potassium hydroxide can be supplied or added as a solution such as an aqueous solution. Hydrogen iodide in the first acetic acid stream can be reduced by supplying or adding potassium hydroxide to the first acetic acid stream. Specifically, hydrogen iodide reacts with potassium hydroxide to produce potassium iodide and water. As a result, corrosion of a device such as a distillation tower caused by hydrogen iodide can be reduced. In addition, potassium hydroxide can be supplied or added to an appropriate place where hydrogen iodide is present in this process. Note that potassium hydroxide added during the process also reacts with acetic acid to produce potassium acetate.
- the distillation column 5 is a unit for performing the second distillation step, and is positioned as a so-called dehydration column in this embodiment.
- the second distillation step is a step for further purifying acetic acid by subjecting the first acetic acid stream continuously introduced into the distillation column 5 to a distillation treatment.
- the distillation column 5 as defined in the present invention, it is preferable to obtain purified acetic acid by distilling the first acetic acid stream supplied through the line 27 under the condition that the column bottom temperature is less than 175 ° C.
- the material of the distillation column 5 (at least the material of the liquid contact and gas contact part) is a nickel-based alloy or zirconium. By using such a material, corrosion inside the distillation column due to hydrogen iodide or acetic acid can be suppressed, and elution of corrosive metal ions can be suppressed.
- the feed liquid of the distillation column 5 includes at least a part of the first acetic acid stream (line 27), and a flow other than the first acetic acid stream [for example, a recycle stream from a downstream process (for example, line 42)] is added. Also good.
- the metal ion concentration in the charged solution of the distillation column 5 is less than 10,000 mass ppb of iron ions, less than 5000 mass ppb of chromium ions, less than 3000 mass ppb of nickel ions, and less than 2000 mass ppb of molybdenum ions. .
- the distillation column 5 is made of the above-mentioned specific material, the bottom temperature is less than 175 ° C., and the metal ion concentration in the liquid charged to the distillation column 5 is controlled within the above range, thereby obtaining the purification obtained in this step.
- the concentration of corrosive metal in acetic acid can be remarkably reduced, and consequently the metal concentration in acetic acid used in the subsequent adsorption and removal step can also be reduced, and the life of the silver-substituted ion exchange resin (IER) can be greatly improved.
- IER silver-substituted ion exchange resin
- the iron ion concentration in the feed solution of the distillation column 5 is preferably less than 9000 mass ppb, more preferably less than 5000 mass ppb, still more preferably less than 3000 mass ppb, particularly preferably less than 1500 mass ppb, especially 800 mass ppb. (For example, less than 400 mass ppb).
- the chromium ion concentration in the feed solution is preferably less than 4000 mass ppb, more preferably less than 2500 mass ppb, still more preferably less than 1500 mass ppb, particularly preferably less than 750 mass ppb, especially less than 400 mass ppb (for example, less than 200 ppb). ).
- the nickel ion concentration in the feed liquid is preferably less than 2500 mass ppb, more preferably less than 2000 mass ppb, still more preferably less than 1000 mass ppb, particularly preferably less than 500 mass ppb, especially less than 250 mass ppb (for example, 150 mass). less than ppb).
- the molybdenum ion concentration in the feed liquid is preferably less than 1700 mass ppb, more preferably less than 1200 mass ppb, still more preferably less than 700 mass ppb, particularly preferably less than 350 mass ppb, especially less than 170 mass ppb.
- the zinc ion concentration in the charged solution is, for example, less than 1000 mass ppb, preferably less than 800 mass ppb, more preferably less than 650 mass ppb, still more preferably less than 500 mass ppb, particularly preferably less than 410 mass ppb, especially Less than 200 mass ppb.
- the concentration of hexyl iodide in the above-mentioned feed liquid is, for example, 0.2 to 10000 mass ppb, usually 1 to 1000 mass ppb, 2 to 100 mass ppb (eg 3 to 50 mass ppb, especially 5 to 40 mass ppb). ) In many cases.
- the concentration of acetic acid in the charged solution of the distillation column 5 is, for example, 90% by mass or more (for example, 95% by mass or more), more preferably 97% by mass or more, still more preferably 98% by mass or more, and particularly preferably 99% by mass or more. It is.
- the charging liquid of the distillation column 5 may contain at least one compound selected from the group consisting of acetate, acetic anhydride, and propionic acid.
- the distillation column 5 is composed of, for example, a rectification column such as a plate column and a packed column.
- a plate column is employed as the distillation column 5
- the theoretical plate is, for example, 5 to 50 plates
- the reflux ratio is, for example, 0.2 to 3000 depending on the number of theoretical plates.
- the column top pressure and the column bottom pressure are preferably set according to the column bottom liquid composition so that the column bottom temperature is less than 175 ° C.
- the column top pressure is, for example, 0.10 to 0.28 MPaG, preferably 0.15 to 0.23 MPaG, and more preferably 0.17 to 0.21 MPaG.
- the tower bottom pressure is higher than the tower top pressure, for example, 0.13 to 0.31 MPaG, preferably 0.18 to 0.26 MPaG, and more preferably 0.20 to 0.24 MPaG.
- the column top temperature is, for example, higher than the boiling point of water at the set column top pressure and lower than the boiling point of acetic acid, and is set to 110 ° C. or more and less than 170 ° C.
- the top temperature is, for example, 168 ° C. or less, preferably 167 ° C. or less, more preferably less than 167 ° C., even more preferably less than 165 ° C., even more preferably less than 163 ° C., in particular less than 161 ° C., in particular less than 160 ° C. is there.
- the lower limit of the tower top temperature is, for example, 90 ° C, preferably 100 ° C, more preferably 110 ° C.
- the tower bottom temperature is, for example, a temperature equal to or higher than the boiling point of acetic acid at a set tower bottom pressure and set to 120 ° C. or higher and lower than 175 ° C.
- the tower bottom temperature is preferably 173 ° C. or lower (for example, less than 173 ° C.), more preferably 172 ° C. or lower (for example 170 ° C. or lower), further preferably 168 ° C. or lower (for example 165 ° C. or lower), particularly preferably 165 ° C. or lower ( For example, it is 164 ° C. or lower), particularly 163 ° C.
- the lower limit of the tower bottom temperature is, for example, 125 ° C., preferably 130 ° C., more preferably 135 ° C.
- the stage interval (stage number) between the feed liquid supply stage (feed stage) and the top vapor drawing stage of the distillation tower 5 is the actual number of stages and preferably one or more. More preferably, it is 3 steps or more, more preferably 5 steps or more, particularly preferably 8 steps or more (in particular, 10 steps or more).
- the vapor extracted from the top of the distillation column 5 contains more components having a lower boiling point than that of acetic acid (low-boiling components) compared to the above-mentioned bottoms from the distillation column 5, such as methyl iodide and iodide.
- acetic acid low-boiling components
- iodide methyl iodide
- iodide methyl iodide
- iodide iodide
- Such steam is continuously introduced into the condenser 5a through the line 33.
- the condenser 5a cools and partially condenses the steam from the distillation tower 5 to divide it into a condensed component and a gas component.
- the condensate includes, for example, water and acetic acid.
- a part of the condensate is continuously refluxed from the condenser 5a through the line 35 to the distillation column 5.
- the other part of the condensate is continuously introduced from the condenser 5a into the reaction tank 1 through the lines 35, 36 and 23 and recycled.
- the gas generated in the capacitor 5a is, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, etc. And is supplied from the capacitor 5a to the scrubber system 8 through lines 37 and 15. Hydrogen iodide in the gas component that has reached the scrubber system 8 is absorbed by the absorbing solution in the scrubber system 8, and methyl iodide is generated by the reaction of hydrogen iodide in the absorbing solution with methanol or methyl acetate. The liquid containing useful components such as methyl iodide is recycled from the scrubber system 8 to the reaction tank 1 through the recycling lines 48 and 23 and reused.
- the bottoms (or side stream) withdrawn from the bottom of the distillation column 5 contains more components with a higher boiling point than acetic acid (high boiling point components) compared to the overhead stream from the distillation column 5, for example,
- the acetate include potassium acetate formed when an alkali such as potassium hydroxide is supplied to the line 27 and the like.
- produced and liberated on the inner wall of the structural member of this acetic acid manufacturing apparatus is also mentioned.
- the iodide salt include potassium iodide formed when an alkali such as potassium hydroxide is supplied to the line 27 or the like. This bottoms can also contain acetic acid. Such bottoms will be continuously introduced into the next distillation column 6 through line 34 in the form of a second acetic acid stream.
- the bottoms (or side stream) withdrawn from the bottom of the distillation column 5 includes the above corrosive metals and the like (iodide salts) of iodine derived from corrosive iodine and the corrosive metals. Such bottoms are discharged out of the acetic acid production apparatus in this embodiment.
- the concentration of acetate, propionic acid, iodide salt, and acetic anhydride in the bottom liquid of the distillation column 5 is preferably as low as possible.
- the acetate concentration in the bottom liquid of the distillation column 5 is, for example, 0.1 mass ppm to 34 mass%, preferably 1 mass ppm to 10 mass%, more preferably 10 mass ppm to 1 mass% (for example, 20 mass ppm). To 0.5 mass%).
- the propionic acid concentration in the bottom liquid of the distillation column 5 is, for example, 10 mass ppm to 91 mass% (for example, 10 mass ppm to 90 mass%), preferably 50 mass ppm to 75 mass%, more preferably 100 mass ppm to It is 55 mass%, more preferably 150 mass ppm to 29 mass%, particularly preferably 200 mass ppm to 15 mass%.
- the iodide salt concentration in the bottom liquid of the distillation column 5 is, for example, 0.01 mass ppb to 1000 mass ppm, preferably 0.1 mass ppb to 500 mass ppm, more preferably 0.5 mass ppb to 100 mass ppm.
- the concentration of acetic anhydride in the bottom liquid of the distillation column 5 is, for example, 90% by mass or less (for example, 80% by mass or less, 50% by mass or less), preferably 0.1 ppm by mass to 10% by mass, more preferably 0.8% by mass. It is 5 mass ppm to 1 mass%, more preferably 1 to 1000 mass ppm, and particularly preferably 2 to 500 mass ppm.
- the acetate salt concentration and iodide salt concentration in the bottom liquid of the distillation column 5 can be reduced by, for example, reducing the amount of alkali used for neutralizing the hydrogen iodide or making the inside of the distillation column less susceptible to corrosion. Can be reduced.
- the concentration of propionic acid in the bottom liquid of the distillation column 5 is, for example, when propionic acid is reduced in the reaction vessel by changing reaction conditions or when a part of the process liquid is recycled to the reaction system.
- acetaldehyde which is a by-product
- evaporator depropionic acid column
- the acetic anhydride concentration in the bottom liquid of the distillation column 5 can be determined by, for example, adding water to the piping or device located upstream of the distillation column 5 or adding water into the distillation column 5 to hydrolyze the acetic anhydride. Can be reduced.
- the second acetic acid stream is richer in acetic acid than the first acetic acid stream continuously introduced into the distillation column 5. That is, the acetic acid concentration of the second acetic acid stream is higher than the acetic acid concentration of the first acetic acid stream.
- the acetic acid concentration of the second acetic acid stream is, for example, 99.1 to 99.99% by mass as long as it is higher than the acetic acid concentration of the first acetic acid stream.
- the second acetic acid stream can include, for example, propionic acid, hydrogen iodide, etc., in addition to acetic acid, as described above.
- the position for extracting the side stream from the distillation column 5 is lower than the position for introducing the first acetic acid stream into the distillation column 5 in the height direction of the distillation column 5.
- the material of the dehydration tower is a specific material
- the tower bottom temperature is a specific value or less
- the metal ion concentration in the dehydration tower charge is a specific value or less.
- the metal ion concentration in the second acetic acid stream obtained as a bottom stream can be significantly reduced.
- the iron ion concentration in the second acetic acid stream is, for example, less than 21000 mass ppb, preferably less than 16000 mass ppb, more preferably less than 6000 mass ppb, still more preferably less than 2000 mass ppb, and particularly preferably 200 mass. It is less than ppb.
- the chromium ion concentration in the second acetic acid stream is, for example, less than 7100 mass ppb, preferably less than 5000 mass ppb, more preferably less than 3000 mass ppb, still more preferably less than 1000 mass ppb, and particularly preferably less than 100 mass ppb.
- the nickel ion concentration in the second acetic acid stream is, for example, less than 4000 mass ppb, preferably less than 3000 mass ppb, more preferably less than 1800 mass ppb, still more preferably less than 700 mass ppb, and particularly preferably less than 70 mass ppb.
- the molybdenum ion concentration in the second acetic acid stream is, for example, less than 3000 mass ppb, preferably less than 2500 mass ppb, more preferably less than 1500 mass ppb, still more preferably less than 500 mass ppb, and particularly preferably less than 50 mass ppb.
- the zinc ion concentration in the second acetic acid stream is, for example, less than 1000 mass ppb, preferably less than 850 mass ppb, more preferably less than 710 mass ppb, still more preferably less than 410 mass ppb, and particularly preferably less than 150 mass ppb.
- the concentration of hexyl iodide in the second acetic acid stream is, for example, 0.2 to 10000 mass ppb, usually 1 to 1000 mass ppb, and 2 to 100 mass ppb (eg 3 to 50 mass ppb, particularly 5 to 40 mass). ppb) in many cases.
- Potassium hydroxide can be supplied or added to the second acetic acid stream flowing through the line 34 through a line 56 (potassium hydroxide introduction line). Potassium hydroxide can be supplied or added as a solution such as an aqueous solution. Hydrogen iodide in the second acetic acid stream can be reduced by supplying or adding potassium hydroxide to the second acetic acid stream. Specifically, hydrogen iodide reacts with potassium hydroxide to produce potassium iodide and water. As a result, corrosion of a device such as a distillation tower caused by hydrogen iodide can be reduced.
- the distillation column 6 is a unit for performing the third distillation step, and is positioned as a so-called dehigh boiling tower in this embodiment.
- the third distillation step is a step for further purifying acetic acid by purifying the second acetic acid stream continuously introduced into the distillation column 6.
- the material of the line 34 and the material of the distillation column 6 (at least the material of the liquid contact and gas contact parts) be nickel-based alloy or zirconium.
- the feed liquid of the distillation column 6 includes at least a part (line 34) of the second acetic acid stream, and a stream other than the second acetic acid stream [for example, a recycle stream from a downstream process (for example, a column bottom of a product tower described later)
- the recycle stream of the bottoms from can may be added.
- the metal ion concentration in the charged solution of the distillation column 6 is less than 10,000 mass ppb of iron ions, less than 5000 mass ppb of chromium ions, less than 3000 mass ppb of nickel ions, and less than 2000 mass ppb of molybdenum ions. .
- the distillation column 6 is made of the above-mentioned specific material, the bottom temperature is less than 175 ° C., and the metal ion concentration in the liquid charged into the distillation column 6 is controlled within the above range to obtain the purification obtained in this step.
- the concentration of corrosive metal in acetic acid can be remarkably reduced, and consequently the metal concentration in acetic acid used in the subsequent adsorption and removal step can also be reduced, and the life of the silver-substituted ion exchange resin (IER) can be greatly improved.
- IER silver-substituted ion exchange resin
- the iron ion concentration in the feed solution of the distillation column 6 is preferably less than 9000 mass ppb, more preferably less than 5000 mass ppb, still more preferably less than 3000 mass ppb, particularly preferably less than 1500 mass ppb, especially 800 mass ppb. (For example, less than 400 mass ppb).
- the chromium ion concentration in the feed solution is preferably less than 4000 mass ppb, more preferably less than 2500 mass ppb, still more preferably less than 1500 mass ppb, particularly preferably less than 750 mass ppb, especially less than 400 mass ppb (for example, less than 200 ppb). ).
- the nickel ion concentration in the feed liquid is preferably less than 2500 mass ppb, more preferably less than 2000 mass ppb, still more preferably less than 1000 mass ppb, particularly preferably less than 500 mass ppb, especially less than 250 mass ppb (for example, 150 mass). less than ppb).
- the molybdenum ion concentration in the feed liquid is preferably less than 1700 mass ppb, more preferably less than 1200 mass ppb, still more preferably less than 700 mass ppb, particularly preferably less than 350 mass ppb, especially less than 170 mass ppb.
- the zinc ion concentration in the charged solution is, for example, less than 1000 mass ppb, preferably less than 800 mass ppb, more preferably less than 650 mass ppb, still more preferably less than 500 mass ppb, particularly preferably less than 410 mass ppb, especially Less than 200 mass ppb.
- the concentration of hexyl iodide in the above-mentioned feed liquid is, for example, 0.2 to 10000 mass ppb, usually 1 to 1000 mass ppb, 2 to 100 mass ppb (eg 3 to 50 mass ppb, especially 5 to 40 mass ppb). ) In many cases.
- the concentration of acetic acid in the charged solution of the distillation column 6 is, for example, 90% by mass or more (for example, 95% by mass or more), more preferably 97% by mass or more, further preferably 98% by mass or more, and particularly preferably 99% by mass or more. It is.
- the charging liquid of the distillation column 6 may contain at least one compound selected from the group consisting of acetate, acetic anhydride, and propionic acid.
- the distillation column 6 is composed of, for example, a rectifying column such as a plate column or a packed column.
- a plate column is employed as the distillation column 6, the theoretical plate is, for example, 5 to 50 plates, and the reflux ratio is, for example, 0.2 to 3000 depending on the number of theoretical plates.
- the column top pressure and the column bottom pressure are preferably set according to the column bottom liquid composition so that the column bottom temperature is less than 175 ° C.
- the tower top pressure is, for example, 0.005 to 0.24 MPaG, preferably 0.01 to 0.22 MPaG, more preferably 0.02 to 0.20 MPaG, and particularly preferably 0.04 to 0.19 MPaG.
- the tower bottom pressure is higher than the tower top pressure, for example, 0.01 MPaG or more and less than 0.255 MPaG, preferably 0.02 to 0.24 MPaG, more preferably 0.03 to 0.23 MPaG, particularly preferably 0.05 to 0. .21 MPaG.
- the column top temperature is, for example, higher than the boiling point of water at the set column top pressure and lower than the boiling point of acetic acid, and is set to 50 ° C. or higher and lower than 170 ° C.
- the top temperature is, for example, 168 ° C. or less, preferably 167 ° C. or less, more preferably less than 167 ° C., even more preferably less than 165 ° C., even more preferably less than 163 ° C., in particular less than 161 ° C., in particular less than 160 ° C. is there.
- the lower limit of the top temperature of the distillation column is, for example, 50 ° C., preferably 90 ° C., more preferably 100 ° C., and further preferably 110 ° C.
- the tower bottom temperature is, for example, a temperature higher than the boiling point of acetic acid at the set tower bottom pressure, and is set to 70 ° C. or more and less than 175 ° C.
- the tower bottom temperature is preferably 173 ° C. or lower (for example, less than 173 ° C.), more preferably 172 ° C. or lower (for example 170 ° C. or lower), further preferably 168 ° C. or lower (for example 165 ° C. or lower), particularly preferably 165 ° C.
- the lower limit of the tower bottom temperature is, for example, 120 ° C., preferably 125 ° C., more preferably 130 ° C., and still more preferably 135 ° C.
- connection position of the line 46 to the distillation column 6 may be higher than the connection position of the line 34 to the distillation column 6, as shown in the figure. It may be lower than the connection position of 34, or may be the same as the connection position of the line 34 to the distillation column 6.
- the vapor extracted from the top of the distillation column 6 contains a larger amount of components having a lower boiling point than that of acetic acid (low-boiling components) compared to the above-mentioned bottoms from the distillation column 6, and in addition to acetic acid, for example, iodination Including methyl, hydrogen iodide, water, methyl acetate, dimethyl ether, methanol, formic acid and the like.
- acetic acid for example, iodination Including methyl, hydrogen iodide, water, methyl acetate, dimethyl ether, methanol, formic acid and the like.
- Such steam is continuously introduced into the condenser 6a through the line 38.
- the condenser 6a cools and partially condenses the steam from the distillation tower 6 to divide it into a condensed component and a gas component.
- the condensate contains, for example, methyl iodide, hydrogen iodide, water, methyl acetate, dimethyl ether, methanol, formic acid and the like in addition to acetic acid.
- At least a part of the condensate is continuously refluxed from the condenser 6a to the distillation column 6 through the line 40.
- a part of the condensate (distillate) can be recycled from the condenser 6a through the lines 40, 41 and 42 to the first acetic acid stream in the line 27 before being introduced into the distillation column 5. is there.
- a part of the condensate (distillate) is transferred from the condenser 6a through the lines 40, 41, 43 to the steam flow in the line 21 before being introduced into the distillation column 3. And can be recycled. Further, a part of the condensate (distillate) may be recycled from the condenser 6a to the reaction tank 1 through the lines 40, 44, and 23. Further, as described above, a part of the distillate from the condenser 6a can be supplied to the scrubber system 8 and used as an absorbent in the system.
- the gas component after absorbing the useful component is discharged out of the apparatus, and the liquid component containing the useful component is introduced or recycled from the scrubber system 8 to the reaction tank 1 through the recycle lines 48 and 23. Reused.
- a part of the distillate from the condenser 6a may be led to various pumps (not shown) operating in the apparatus through a line outside the figure and used as a sealing liquid for the pump.
- a part of the distillate from the condenser 6a may be regularly extracted out of the apparatus through an extraction line attached to the line 40, or may be extracted out of the apparatus unsteadily when necessary. May be.
- the amount of distillate (distillation) is 0.01 to 30 of the condensate produced in the condenser 6a, for example. % By mass, preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, and more preferably 0.5 to 3% by mass.
- the gas generated in the capacitor 6a is, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, and formic acid. And the like, and is supplied from the capacitor 6a to the scrubber system 8 through lines 45 and 15.
- the bottoms extracted from the bottom of the distillation column 6 through the line 39 contains more components having a higher boiling point than acetic acid (high-boiling components) compared to the overhead stream from the distillation column 6 such as acetate, Contains acetic anhydride, propionic acid and the like.
- acetic acid high-boiling components
- the acetate include potassium acetate formed when an alkali such as potassium hydroxide is supplied to the line 34 or the like.
- the bottoms extracted from the bottom of the distillation column 6 through the line 39 further contains the above corrosive metal and the like, and a compound of iodine derived from corrosive iodine and the corrosive metal. Such bottoms are discharged out of the acetic acid production apparatus in this embodiment.
- the concentrations of acetate, acetic anhydride, and propionic acid in the bottom liquid of the distillation column 6 are as small as possible.
- the concentration of acetate in the bottom liquid of the distillation column 6 is, for example, 1 mass ppm to 34 mass%, preferably 100 mass ppm to 25 mass%, more preferably 0.1 to 20 mass% (for example, 1 to 15 mass%).
- the concentration of acetic anhydride in the bottom liquid of the distillation column 6 is, for example, 1 mass ppm to 91 mass% (eg, 1 mass ppm to 90 mass%), preferably 10 mass ppm to 74 mass%, more preferably 100 mass ppm to It is 44% by mass, more preferably 0.1 to 20% by mass, and particularly preferably 0.2 to 10% by mass (eg 0.5 to 5% by mass).
- the propionic acid concentration in the bottom liquid of the distillation column 6 is, for example, 100 mass ppm to 91 mass% (eg, 1 mass ppm to 90 mass%), preferably 0.1 to 75 mass%, more preferably 0.3 to It is 55% by mass, more preferably 0.5 to 29% by mass, and particularly preferably 1 to 15% by mass.
- concentration of acetate in the bottom liquid of the distillation column 6 can be reduced, for example, by reducing the amount of alkali used for neutralizing the hydrogen iodide or making the corrosion inside the distillation column less likely to occur.
- the concentration of acetic anhydride in the bottom liquid of the distillation column 6 is determined by, for example, adding water to the piping or device located upstream of the distillation column 6 or adding water into the distillation column 6 to hydrolyze the acetic anhydride. Can be reduced.
- the concentration of propionic acid in the bottom liquid of the distillation column 6 is, for example, when propionic acid is reduced in the reaction vessel by changing the reaction conditions or when a part of the process liquid is recycled to the reaction system.
- the side stream continuously extracted from the distillation column 6 to the line 46 is continuously introduced into the next ion exchange resin column 7 as a third acetic acid stream.
- This third acetic acid stream is richer in acetic acid than the second acetic acid stream continuously introduced into the distillation column 6. That is, the acetic acid concentration in the third acetic acid stream is higher than the acetic acid concentration in the second acetic acid stream.
- the acetic acid concentration of the third acetic acid stream is, for example, 99.8 to 99.999% by mass as long as it is higher than the acetic acid concentration of the second acetic acid stream.
- the concentration of hexyl iodide in the third acetic acid stream is, for example, 0.2 to 10000 mass ppb, usually 1 to 1000 mass ppb, and 2 to 100 mass ppb (eg 3 to 50 mass ppb, particularly 5 to 40 mass). ppb) in many cases.
- the position for extracting the side stream from the distillation column 6 is higher than the position for introducing the second acetic acid stream into the distillation column 6 in the height direction of the distillation column 6.
- the side stream extraction position from the distillation column 6 is the same as or lower than the introduction position of the second acetic acid stream into the distillation column 6 in the height direction of the distillation column 6.
- the distillation column 6 can be replaced by a single distillation device (evaporator). If the impurities are sufficiently removed by the distillation column 5, the distillation column 6 can be omitted.
- the ion exchange resin tower 7 is a purification unit for performing the adsorption removal step.
- This adsorption and removal step is mainly performed by alkyl iodide (for example, ethyl iodide, propyl iodide, butyl iodide, hexyl iodide, etc.) contained in a trace amount in the third acetic acid stream continuously introduced into the ion exchange resin column 7.
- alkyl iodide for example, ethyl iodide, propyl iodide, butyl iodide, hexyl iodide, etc.
- an ion exchange resin having an adsorption ability for alkyl iodide is filled in the tower to form an ion exchange resin bed.
- an ion exchange resin for example, a cation exchange resin in which a part of the detachable proton in the sulfonic acid group, carboxyl group, phosphonic acid group or the like which is an exchange group is substituted with a metal such as silver or copper. Is mentioned.
- a third acetic acid stream flows through the inside of the ion exchange resin tower 7 filled with such an ion exchange resin, and in the flow process, the alkyl iodide in the third acetic acid stream is passed. And the like are adsorbed on the ion exchange resin and removed from the third acetic acid stream.
- the internal temperature is, for example, 18 to 100 ° C.
- the acetic acid flow rate [acetic acid treatment amount per m 3 of resin volume (m 3 / h)] is, for example, 3 ⁇ 15 m 3 / h ⁇ m 3 (resin volume).
- the fourth acetic acid flow is continuously led out from the lower end of the ion exchange resin tower 7 to the line 47.
- the acetic acid concentration in the fourth acetic acid stream is higher than the acetic acid concentration in the third acetic acid stream. That is, the fourth acetic acid stream is richer in acetic acid than the third acetic acid stream that is continuously introduced into the ion exchange resin tower 7.
- the acetic acid concentration of the fourth acetic acid stream is, for example, 99.9 to 99.999% by mass or more as long as it is higher than the acetic acid concentration of the third acetic acid stream.
- the concentration of hexyl iodide in the fourth acetic acid stream is usually 1 mass ppb or less, for example, 0 to 30 mass ppb, particularly 0.01 to 10 mass ppb (for example, 0.1 to 5 mass ppb). May be.
- this fourth acetic acid stream can be stored in a product tank (not shown).
- a so-called product tower or finishing tower which is a distillation tower, may be provided as a purification unit for further purifying the fourth acetic acid stream from the ion exchange resin tower 7.
- the product tower is composed of a rectification tower such as a plate tower and a packed tower, for example.
- the theoretical plate has, for example, 5 to 50 plates, and the reflux ratio is, for example, 0.5 to 3000 depending on the number of theoretical plates.
- the column top pressure and the column bottom pressure are preferably set according to the column bottom liquid composition such that the column bottom temperature is less than 175 ° C.
- the tower top pressure is, for example, 0.005 to 0.24 MPaG, preferably 0.01 to 0.22 MPaG, more preferably 0.02 to 0.20 MPaG, and particularly preferably 0.04 to 0.19 MPaG.
- the tower bottom pressure is higher than the tower top pressure, for example, 0.01 MPaG or more and less than 0.255 MPaG, preferably 0.02 to 0.24 MPaG, more preferably 0.03 to 0.23 MPaG, particularly preferably 0.05 to 0. .21 MPaG.
- the column top temperature is set to, for example, a temperature higher than the boiling point of water and lower than the boiling point of acetic acid at a set column top pressure and set to 50 ° C. or higher and lower than 170 ° C., for example, 168 Below 167 ° C, more preferably below 167 ° C, even more preferably below 165 ° C, even more preferably below 163 ° C, especially below 161 ° C, especially below 160 ° C.
- the lower limit of the top temperature of the distillation column is, for example, 50 ° C., preferably 90 ° C., more preferably 100 ° C., and further preferably 110 ° C.
- the tower bottom temperature is, for example, a temperature higher than the boiling point of acetic acid at the set tower bottom pressure and is 70 ° C. or higher and lower than 175 ° C. (preferably 173 ° C. or lower (for example, lower than 173 ° C.)), more preferably 172 ° C. or lower (for example, 170 Or less), more preferably 168 ° C. or less (for example, 165 ° C. or less), particularly preferably 165 ° C. or less (for example, 164 ° C. or less), particularly 163 ° C. or less (for example, 162 ° C. or less).
- the lower limit of the tower bottom temperature is, for example, 120 ° C, preferably 125 ° C, more preferably 130 ° C, and still more preferably 135 ° C.
- the product tower or finishing tower can be replaced by a simple distiller (evaporator).
- all or part of the fourth acetic acid stream (liquid) from the ion exchange resin tower 7 is continuously introduced into the product tower.
- steam as an overhead stream containing trace amounts of low-boiling components (eg methyl iodide, water, methyl acetate, dimethyl ether, crotonaldehyde, acetaldehyde, and formic acid) continuously Extracted.
- This steam is divided into a condensate and a gas by a predetermined condenser. A part of the condensate may be continuously refluxed to the product column, and another part of the condensate may be recycled to the reactor 1 and / or discarded outside the system.
- the gas component is supplied to the scrubber system 8. From the bottom of the product column, the bottoms containing a trace amount of high-boiling components are continuously withdrawn, and this bottoms, for example, into the second acetic acid stream in the line 34 before being introduced into the distillation column 6. And recycled.
- a side stream (liquid) is continuously withdrawn as a fifth acetic acid stream from a height position between the top and bottom of the product tower.
- the extraction position of the side stream from the product tower is lower in the height direction of the product tower, for example, than the introduction position of the fourth acetic acid stream into the product tower.
- the fifth acetic acid stream is richer in acetic acid than the fourth acetic acid stream that is continuously introduced into the product column.
- the acetic acid concentration in the fifth acetic acid stream is higher than the acetic acid concentration in the fourth acetic acid stream.
- the acetic acid concentration of the fifth acetic acid stream is, for example, 99.9 to 99.999% by mass or more as long as it is higher than the acetic acid concentration of the fourth acetic acid stream.
- the concentration of hexyl iodide in the fifth acetic acid stream is usually 1 mass ppb or less, for example, 0 to 30 mass ppb, particularly 0.01 to 10 mass ppb (for example, 0.1 to 5 mass ppb). May be.
- This fifth acetic acid stream is stored, for example, in a product tank (not shown).
- the ion exchange resin tower 7 may be installed downstream of the product tower instead of (or in addition to) the distillation tower 6 to treat the acetic acid stream discharged from the product tower.
- the acetic acid stream to be supplied is distilled under the condition of a tower bottom temperature of less than 175 ° C. to obtain purified acetic acid.
- the material of the pipe and the material of the product tower be a nickel-based alloy or zirconium.
- the concentrations of acetate, acetic anhydride, and propionic acid in the bottom liquid of the product column are smaller.
- the acetate concentration in the bottom liquid of the product column is, for example, 0.1 mass ppb to 1 mass%, preferably 1 mass ppb to 0.1 mass%, more preferably 10 mass ppb to 0.01 mass% (for example, 100 mass ppb to 0.001 mass%).
- the acetic anhydride concentration in the bottom liquid of the product tower is, for example, 0.1 mass ppm to 60 mass%, preferably 1 mass ppm to 10 mass%, more preferably 10 mass ppm to 2 mass% (for example, 50 mass ppm to 0.5 mass%), or 0.2 to 10 mass% (for example, 0.5 to 5 mass%).
- the propionic acid concentration in the bottom liquid of the product column is, for example, 1 mass ppm to 10 mass%, preferably 10 mass ppm to 5 mass%, more preferably 50 mass ppm to 1 mass% (for example, 100 mass ppm to 0.00 mass). 1% by mass).
- the concentration of acetate in the bottom liquid of the product column can be reduced, for example, by reducing the amount of alkali used for neutralizing the hydrogen iodide, or by making it difficult for corrosion inside the distillation column to occur.
- the concentration of acetic anhydride in the bottom liquid of the product tower can be reduced by, for example, adding water to the piping or apparatus located upstream of the product tower or the product tower to hydrolyze the acetic anhydride.
- the concentration of propionic acid in the bottom liquid of the product tower can be reduced by, for example, reducing the by-product of propionic acid in the reaction tank by changing the reaction conditions, or recycling a part of the process liquid to the reaction system.
- the charge liquid in the product tower contains at least a part of the acetic acid stream to be subjected to distillation, and a flow other than the acetic acid stream may be added.
- the metal ion concentration in the liquid charged in the product tower is less than 10,000 mass ppb of iron ions, less than 5000 mass ppb of chromium ions, and 3000 mass of nickel ions. It is preferable to be less than ppb and less than 2000 mass parts ppb of molybdenum ions.
- the material of the product tower is the above-mentioned specific material
- the bottom temperature is less than 175 ° C.
- the metal ion concentration in the liquid charged into the product tower is controlled within the above range.
- the iron ion concentration in the feed liquid of the product tower is preferably less than 9000 mass ppb, more preferably less than 5000 mass ppb, still more preferably less than 3000 mass ppb, particularly preferably less than 1500 mass ppb, especially less than 800 mass ppb. (For example, less than 400 mass ppb).
- the chromium ion concentration in the feed solution is preferably less than 4000 mass ppb, more preferably less than 2500 mass ppb, still more preferably less than 1500 mass ppb, particularly preferably less than 750 mass ppb, especially less than 400 mass ppb (for example, less than 200 ppb). ).
- the nickel ion concentration in the feed liquid is preferably less than 2500 mass ppb, more preferably less than 2000 mass ppb, still more preferably less than 1000 mass ppb, particularly preferably less than 500 mass ppb, especially less than 250 mass ppb (for example, 150 mass). less than ppb).
- the molybdenum ion concentration in the feed liquid is preferably less than 1700 mass ppb, more preferably less than 1200 mass ppb, still more preferably less than 700 mass ppb, particularly preferably less than 350 mass ppb, especially less than 170 mass ppb.
- the zinc ion concentration in the charged solution is, for example, less than 1000 mass ppb, preferably less than 800 mass ppb, more preferably less than 650 mass ppb, still more preferably less than 500 mass ppb, particularly preferably less than 410 mass ppb, especially Less than 200 mass ppb.
- the concentration of hexyl iodide in the above-mentioned feed liquid is, for example, 0.2 to 10000 mass ppb, usually 1 to 1000 mass ppb, 2 to 100 mass ppb (eg 3 to 50 mass ppb, especially 5 to 40 mass ppb). ) In many cases.
- the acetic acid concentration in the liquid charged in the product tower is, for example, 90% by mass or more (for example, 95% by mass or more), more preferably 97% by mass or more, further preferably 98% by mass or more, and particularly preferably 99% by mass or more. is there.
- the feed liquid of the product column may contain at least one compound selected from the group consisting of acetate, acetic anhydride, and propionic acid.
- the column bottom temperature of the distillation column 5 may be set to less than 175 ° C. (for example, 173 ° C. or less). You may set to less than 175 degreeC (for example, 173 degrees C or less), and you may set the tower bottom temperature of the distillation column 5 and the distillation column 6 to less than 175 degreeC (for example, 173 degrees C or less).
- the tower bottom temperature of a product tower May be set to less than 175 ° C.
- the bottom temperature of the distillation column 5 and the product column may be set to less than 175 ° C. (for example, 173 ° C. or less).
- the bottom temperature of the product column may be set to less than 175 ° C. (for example, 173 ° C. or less), and the bottom temperatures of the distillation column 5, the distillation column 6, and all three distillation columns of the product column are less than 175 ° C. ( For example, you may set to 173 degrees C or less.
- the tower bottom temperature is preferably less than 173 ° C, more preferably 172 ° C or less (eg 170 ° C or less), further preferably 168 ° C or less (eg 165 ° C or less), particularly preferably 165 ° C or less (eg 164 ° C). Below), especially 163 ° C. or lower (eg 162 ° C. or lower). As described above, the distillation column 6 and the product column (particularly the latter) may not be provided.
- Comparative Example 1 In a continuous reaction process in acetic acid production, methanol and carbon monoxide are continuously reacted in a carbonylation reaction tank, and the reaction mixture from the reaction tank is continuously supplied to a flasher, and acetic acid and acetic acid produced by flash distillation.
- a volatile component including at least methyl, methyl iodide, water, and hydrogen iodide is supplied to the first distillation column (delow boiling column), and the first low boiling point component is separated as overhead, and has a boiling point higher than that of acetic acid.
- a stream rich in high components was separated from the bottom of the column as bottoms.
- the overhead liquid (first low-boiling component) was directly recycled to the reaction tank, and the bottoms from the tower bottom were mixed with the bottoms from the flasher and recycled to the reaction tank.
- the first liquid stream is extracted from the side stream of the first distillation column, and is made of stainless steel (SUS316: Mn 2% or less, Ni 10 to 14%, Cr 16 to 18%, Mo 2 to 3%, Fe 50% or more).
- SUS316 Mn 2% or less, Ni 10 to 14%, Cr 16 to 18%, Mo 2 to 3%, Fe 50% or more.
- a second distillation column dehydration column
- a second distillation column made of the material of SUS316 (actual stage number: 50 stages, stage interval between the feed stage and the top steam removal stage: 15 stages in the actual stage) is continuously charged. It is.
- the composition of the first liquid stream is as follows: methyl iodide 2%, methyl acetate 2%, water 1%, iron ion 9100 ppb, chromium ion 4000 ppb, nickel ion 2500 ppb, molybdenum ion 1700 ppb, zinc ion 410 ppb, hexyl iodide 51 ppb , And remaining acetic acid (90% by mass or more, including trace amounts of impurities such as acetate, acetic anhydride, and propionic acid).
- distillation is performed under the conditions of a tower top temperature of 165 ° C.
- the second low-boiling component containing water is concentrated on the tower top, and the second liquid stream (purified acetic acid) is canned. Obtained as effluent.
- the distillate from the top of the column was recycled to the reaction tank.
- the amount fed to the dehydration tower was 1, the amount of bottoms was 0.7, and the amount of distillate from the top of the tower was 0.3.
- the composition of the bottoms was 500 ppm water, 21,000 ppb iron ions, 8300 ppb chromium ions, 5200 ppb nickel ions, 2800 ppb molybdenum ions, 590 ppb zinc ions, 50 ppb hexyl iodide, less than 50 ppm acetate, 110 ppm acetic anhydride, 120 ppm propionic acid, remaining acetic acid (However, it contains a trace amount of impurities).
- Silver acetate concentration of the product after silver-substituted ion exchange resin treatment is 41 ppb, iron ion concentration is 100 ppb, chromium ion concentration is 15 ppb, nickel ion concentration is 10 ppb, molybdenum ion concentration is 6 ppb, zinc ion concentration is 7 ppb, hexyl iodide
- the concentration was less than 5 ppb (below the detection limit).
- the IER resin life operation time until the hexyl iodide concentration at the resin outlet exceeds 5 ppb was 1.2 years.
- the corrosion rate which converted the corrosion rate (thickness reduction of thickness) of the test piece (SUS316) per year into mm was 2.69 mm / Y.
- Comparative Example 2 The material of the dehydration tower was changed to a nickel-based alloy [Hastelloy B2 (HB2): Mo 28%, Ni 69%, Cr 1% or less, Fe 2% or less, Co 1% or less, Mn 1% or less], and the operation conditions of the dehydration tower were
- the composition of the feed liquid supplied to the dehydration tower is as follows: methyl iodide 2%, methyl acetate 2%, water 1%, iron ions 13700 ppb, chromium ions 6000 ppb, nickel ions 3800 ppb, molybdenum Experiment similar to Comparative Example 1 except that ion 2600 ppb, zinc ion 620 ppb, hexyl iodide 51 ppb, and remaining acetic acid (90% by mass or more, including trace amounts of impurities such as acetate, acetic anhydride, propionic acid, etc.) went.
- the composition of the bottoms of the dehydration tower is 490 ppm water, 19700 ppb iron ions, 8700 ppb chromium ions, 7000 ppb nickel ions, 4300 ppb molybdenum ions, 890 ppb zinc ions, 51 ppb hexyl iodide, less than 50 ppm acetate, 110 ppm acetic anhydride, 120 ppm propionic acid. , And remaining acetic acid (however, it contains a trace amount of impurities).
- the silver acetate concentration of the product acetic acid after treatment with the silver-substituted ion exchange resin is 30 ppb, iron ion concentration is 80 ppb, chromium ion concentration is 16 ppb, nickel ion concentration is 15 ppb, molybdenum ion concentration is 9 ppb, zinc ion concentration is 9 ppb, iodine
- the hexyl chloride concentration was less than 5 ppb (below the detection limit). With this operation, the IER resin life was 1.1 years and the corrosion rate was 0.39 mm / Y.
- Comparative Example 3 The same experiment as in Comparative Example 1 was performed except that the dehydrating tower was operated at a tower top temperature of 160 ° C and a tower bottom temperature of 170 ° C.
- the composition of the bottoms of the dehydration tower was 490 ppm water, 19800 ppb iron ions, 7900 ppb chromium ions, 4900 ppb nickel ions, 2700 ppb molybdenum ions, 590 ppb zinc ions, 49 ppb iodide, less than 50 ppm acetate, 110 ppm acetic anhydride, 120 ppm propionic acid. , And remaining acetic acid (however, it contains a trace amount of impurities).
- the silver ion concentration of the product acetic acid after the silver-substituted ion exchange resin treatment is 34 ppb
- iron ion concentration is 85 ppb
- chromium ion concentration is 14 ppb
- nickel ion concentration is 9 ppb
- molybdenum ion concentration is 7 ppb
- zinc ion concentration is 5 ppb
- iodine The hexyl chloride concentration was less than 5 ppb (below the detection limit). With this operation, the IER resin life was 1.2 years and the corrosion rate was 2.28 mm / Y.
- Comparative Example 4 An experiment similar to that of Comparative Example 1 was performed except that the operating conditions of the dehydration tower were a tower top temperature of 155 ° C. and a tower bottom temperature of 165 ° C.
- the composition of the bottoms of the dehydration tower is as follows: water 500 ppm, iron ion 16000 ppb, chromium ion 6700 ppb, nickel ion 4200 ppb, molybdenum ion 2600 ppb, zinc ion 590 ppb, hexyl iodide 45 ppb, acetate salt less than 50 ppm, acetic anhydride 110 ppm, propionic acid 120 ppm , And remaining acetic acid (however, it contains a trace amount of impurities).
- the silver ion concentration of the product acetic acid after the silver-substituted ion exchange resin treatment is 29 ppb
- iron ion concentration is 81 ppb
- chromium ion concentration is 13 ppb
- nickel ion concentration is 9 ppb
- molybdenum ion concentration is 8 ppb
- zinc ion concentration is 5 ppb
- iodine ion The hexyl chloride concentration was less than 5 ppb (below the detection limit). With this operation, the IER resin life was 1.4 years and the corrosion rate was 1.00 mm / Y.
- Comparative Example 5 The same experiment as Comparative Example 1 was performed except that the material of the dehydration tower was changed to a nickel-based alloy [Hastelloy B2 (HB2)].
- the composition of the bottoms of the dehydration tower is as follows: water 510 ppm, iron ion 13200 ppb, chromium ion 5800 ppb, nickel ion 6900 ppb, molybdenum ion 3800 ppb, zinc ion 590 ppb, hexyl iodide 43 ppb, acetate salt less than 50 ppm, acetic anhydride 110 ppm, propionic acid 120 ppm , And remaining acetic acid (however, it contains a trace amount of impurities).
- the silver acetate concentration of the product acetic acid after treatment with the silver-substituted ion exchange resin is 30 ppb, iron ion concentration is 80 ppb, chromium ion concentration is 16 ppb, nickel ion concentration is 15 ppb, molybdenum ion concentration is 9 ppb, zinc ion concentration is 9 ppb, iodine
- the hexyl chloride concentration was less than 5 ppb (below the detection limit). With this operation, the IER resin life was 1.3 years and the corrosion rate was 0.82 mm / Y.
- Example 1 The same experiment as Comparative Example 1 was performed except that the material of the dehydration tower was changed to a nickel-based alloy [Hastelloy B2 (HB2)] and the dehydration tower was operated at a tower top temperature of 160 ° C and a tower bottom temperature of 170 ° C. It was.
- HB2 nickel-based alloy
- the composition of the bottoms of the dehydration tower is 490 ppm water, iron ions 13200 ppb, chromium ions 5800 ppb, nickel ions 5200 ppb, molybdenum ions 3100 ppb, zinc ions 590 ppb, hexyl iodide 52 ppb, acetate salt less than 50 ppm, acetic anhydride 110 ppm, propionic acid 120 ppm , And remaining acetic acid (however, it contains a trace amount of impurities).
- the silver acetate concentration of the product acetic acid after treatment with the silver-substituted ion exchange resin is 18 ppb, the iron ion concentration is 25 ppb, the chromium ion concentration is 9 ppb, the nickel ion concentration is 8 ppb, the molybdenum ion concentration is 6 ppb, the zinc ion concentration is 7 ppb, and iodine.
- the hexyl chloride concentration was less than 5 ppb (below the detection limit). With this operation, the IER resin life was 1.8 years and the corrosion rate was 0.39 mm / Y.
- Example 2 A first liquid stream extracted from the side stream of the first distillation column (delow boiling column) was obtained through a pipe made of a nickel-based alloy [Hastelloy B2 (HB2)], 2% methyl iodide, Methyl acetate 2%, water 1%, iron ion 500 ppb, chromium ion 280 ppb, nickel ion 190 ppb, molybdenum ion 110 ppb, zinc ion 410 ppb, hexyl iodide 51 ppb, remaining acetic acid (90 mass% or more.
- HB2 nickel-based alloy
- Example 2 acetate, acetic anhydride, The same experiment as in Example 1 was performed except that a mixed solution of a small amount of impurities such as propionic acid) was used as a feed solution to be supplied to the dehydration tower.
- the composition of the bottoms of the dehydration tower was 490 ppm water, 770 ppb iron ions, 420 ppb chromium ions, 1900 ppb nickel ions, 800 ppb molybdenum ions, 590 ppb zinc ions, 50 ppb hexyl iodide, less than 50 ppm acetate, 110 ppm acetic anhydride, 120 ppm propionic acid.
- the silver ion concentration of the product acetic acid after the silver-substituted ion exchange resin treatment is 5 ppb
- iron ion concentration is 6 ppb
- chromium ion concentration is 6 ppb
- nickel ion concentration is 7 ppb
- molybdenum ion concentration is 4 ppb
- zinc ion concentration is 4 ppb
- iodine The hexyl chloride concentration was less than 5 ppb (below the detection limit).
- the IER resin life was 6.1 years and the corrosion rate was 0.39 mm / Y.
- Example 3 The same experiment as in Example 1 except that the material of the dehydration tower was changed to a nickel-based alloy [Hastelloy C (HC276): Mo 16%, Ni around 57%, Cr 16%, Fe 5%, Co 2.5% or less, Mn 1% or less] Went.
- HC276 nickel-based alloy
- the composition of the bottom of the dehydration tower is 520 ppm water, iron ion 13300 ppb, chromium ion 6400 ppb, nickel ion 5800 ppb, molybdenum ion 3100 ppb, zinc ion 590 ppb, hexyl iodide 48 ppb, acetate salt less than 50 ppm, acetic anhydride 110 ppm, propionic acid 120 ppm , And remaining acetic acid (however, it contains a trace amount of impurities).
- the silver ion concentration of the product acetic acid after treatment with the silver-substituted ion exchange resin is 16 ppb
- iron ion concentration is 28 ppb
- chromium ion concentration is 12 ppb
- nickel ion concentration is 13 ppb
- molybdenum ion concentration is 7 ppb
- zinc ion concentration is 4 ppb
- iodine The hexyl chloride concentration was less than 5 ppb (below the detection limit).
- the IER resin life was 1.7 years and the corrosion rate was 0.67 mm / Y.
- Example 4 The same experiment as in Example 1 was performed except that the operating conditions of the dehydration tower were a tower top temperature of 155 ° C. and a tower bottom temperature of 165 ° C.
- the composition of the bottoms of the dehydration tower is 490 ppm water, iron ions 13200 ppb, chromium ions 5800 ppb, nickel ions 5200 ppb, molybdenum ions 3100 ppb, zinc ions 590 ppb, hexyl iodide 52 ppb, acetate salt less than 50 ppm, acetic anhydride 110 ppm, propionic acid 120 ppm , And remaining acetic acid (however, it contains a trace amount of impurities).
- the silver ion concentration of the product acetic acid after the silver-substituted ion exchange resin treatment is 13 ppb
- the iron ion concentration is 23 ppb
- the chromium ion concentration is 8 ppb
- the nickel ion concentration is 7 ppb
- the molybdenum ion concentration is 5 ppb
- the zinc ion concentration is 5 ppb
- iodine iodine.
- the hexyl chloride concentration was less than 5 ppb (below the detection limit). With this operation, the IER resin life was 2.0 years, and the corrosion rate was 0.39 mm / Y.
- Example 5 The composition of the bottoms of the dehydration tower is 485 ppm water, iron ion 13100 ppb, chromium ion 5800 ppb, nickel ion 3900 ppb, molybdenum ion 2600 ppb, zinc ion 590 ppb, hexyl iodide 53 ppb, acetate salt less than 50 ppm, acetic anhydride 110 ppm, propionic acid 120 ppm , And remaining acetic acid (however, it contains a trace amount of impurities).
- the silver acetate concentration of the product acetic acid after treatment with the silver-substituted ion exchange resin is 12 ppb, the iron ion concentration is 23 ppb, the chromium ion concentration is 9 ppb, the nickel ion concentration is 6 ppb, the molybdenum ion concentration is 5 ppb, the zinc ion concentration is 5 ppb, and iodine.
- the hexyl chloride concentration was less than 5 ppb (below the detection limit). With this operation, the IER resin life was 2.1 years, and the corrosion rate was 0.07 mm / Y.
- Example 6 The same experiment as in Example 1 was performed except that the operating conditions of the dehydration tower were a tower top temperature of 163 ° C. and a tower bottom temperature of 173 ° C.
- the composition of the bottom of the dehydration tower is 495 ppm water, iron ion 13200 ppb, chromium ion 5800 ppb, nickel ion 5600 ppb, molybdenum ion 3300 ppb, zinc ion 590 ppb, hexyl iodide 51 ppb, acetate salt less than 50 ppm, acetic anhydride 110 ppm, propionic acid 120 ppm , And remaining acetic acid (however, it contains a trace amount of impurities).
- the silver ion concentration of the product acetic acid after the silver-substituted ion exchange resin treatment is 23 ppb
- iron ion concentration is 40 ppb
- chromium ion concentration is 13 ppb
- nickel ion concentration is 14 ppb
- molybdenum ion concentration is 8 ppb
- zinc ion concentration is 8 ppb
- iodine The hexyl chloride concentration was less than 5 ppb (below the detection limit). With this operation, the IER resin life was 1.6 years and the corrosion rate was 0.49 mm / Y.
- the metal ions flowing into the dehydration tower can be obtained by setting the concentration of the specific metal ions in the liquid charged to the dehydration tower to a specific value or less and using a nickel-based alloy with high corrosion resistance as the material of the dehydration tower.
- the concentration of metal ions in the purified acetic acid obtained from the dehydration tower can be greatly reduced.
- the amount of metal ions flowing into the subsequent organic iodine compound adsorption / removal step can be reduced, and the exchange amount of silver ions and other metal ions in the silver-substituted ion exchange resin (IER) is reduced, resulting in the lifetime of IER.
- IER silver-substituted ion exchange resin
- Comparative Example 2 the material of the dehydration tower is the same nickel base alloy as in Example 1, but since the amount of metal ions flowing into the dehydration tower is large, there are many metal ions flowing into the adsorption removal process, and IER Has a short lifetime of 1.1 years. Further, in Comparative Example 3, the metal ion concentration in the liquid charged into the dehydration tower is the same as in Example 1, but since the material of the dehydration tower is stainless steel, the corrosion metal is eluted from the dehydration tower and removed by adsorption. The amount of metal ions flowing into the process is large, so that the IER lifetime was as low as 1.2 years. In Comparative Example 4, the operating temperature of Comparative Example 3 was lowered. However, since the material of the dehydration tower is stainless steel, the IER life is as short as 1.4 years.
- Example 2 Even if the dehydration tower is made of the same material, the concentration of the corrosion metal in the purified acetic acid obtained from the dehydration tower is reduced if the concentration of the corrosion metal in the dehydration tower feed liquid is controlled and lowered.
- the service life of the silver-substituted ion exchange resin used in the adsorption removal process was greatly improved.
- the corrosive metal ion concentration and the silver ion concentration in the acetic acid product after the IER treatment are also lowered, the quality of acetic acid is further improved. It should be noted that the metal ion concentration at the ion exchange resin column outlet does not change much despite the fact that the metal concentration in the ion exchange resin column charging solution is wide open.
- Example 1 From Example 1 and Example 3, the use of “HB2”, which is a nickel-base alloy, which has higher corrosion resistance, can suppress the elution of corrosive metals, and the purified acetic acid obtained from the dehydration tower can be used. Corrosion metal ion concentration is reduced, and IER resin life and product acetic acid quality are improved.
- Example 5 when the material of the dehydration tower is HB2, when the bottom temperature of the dehydration tower is lowered from 175 ° C. to 170 ° C., the resin life of the ion exchange resin becomes 0. It extends for five years. Further, according to Example 1, Example 4, Example 5, Example 6, and Comparative Example 5, when the dehydration tower is made of HB2, when the operating temperature of the dehydration tower is lowered, the amount of corrosion metal eluted And the resin life of the ion exchange resin is improved.
- the zinc ion is only increased in concentration according to the concentration ratio due to concentration in the dehydration tower under any condition.
- the absolute amount of zinc ions in the acetic acid was the same.
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Abstract
Description
上記カルボニル化反応工程で得られた反応混合物を、1以上の蒸発槽及び/又は蒸留塔を用いて、金属触媒を含む流れと、酢酸に富む酢酸流と、上記酢酸流よりも低沸成分に富む流れとに分離する分離工程と、
上記分離工程に含まれていてもよい工程であって、酢酸流を蒸留して酢酸を精製する酢酸蒸留工程と、
上記酢酸蒸留工程で得られる精製酢酸流をイオン交換樹脂で処理する吸着除去工程と、
を備えた酢酸の製造方法であって、
上記酢酸蒸留工程が、酢酸流の蒸留を蒸留塔の塔底温度175℃未満の条件で行う蒸留工程を少なくとも1つ有し、且つ当該蒸留工程における蒸留塔の材質をニッケル基合金又はジルコニウムとし、当該蒸留工程における蒸留塔の仕込液中の金属イオン濃度を、鉄イオン10000質量ppb未満、クロムイオン5000質量ppb未満、ニッケルイオン3000質量ppb未満、且つモリブデンイオン2000質量ppb未満とする、酢酸の製造方法を提供する。
上記カルボニル化反応工程で得られた反応混合物を蒸発槽において蒸気流と残液流とに分離する蒸発工程と、
上記蒸気流を蒸留に付して、低沸成分に富むオーバーヘッド流と、酢酸に富む第1酢酸流とに分離する脱低沸工程と、
上記第1酢酸流を蒸留に付して、水に富むオーバーヘッド流と第1酢酸流よりも酢酸に富む第2酢酸流とに分離する脱水工程と、
上記第2酢酸流、又は上記第2酢酸流をさらに精製したより酢酸に富む酢酸流をイオン交換樹脂で処理する吸着除去工程と、
を備えた酢酸の製造方法であって、
上記脱水工程における蒸留塔の材質をニッケル基合金又はジルコニウムとし、且つ上記脱水工程における蒸留塔の仕込液中の金属イオン濃度を、鉄イオン10000質量ppb未満、クロムイオン5000質量ppb未満、ニッケルイオン3000質量ppb未満、且つモリブデンイオン2000質量ppb未満とし、
上記脱水工程を蒸留塔の塔底温度175℃未満の条件で行う、酢酸の製造方法を提供する。
CH3OH + CO → CH3COOH (1)
酢酸製造における連続反応プロセスにおいて、メタノールと一酸化炭素とをカルボニル化反応槽で連続的に反応させ、上記反応槽からの反応混合物をフラッシャーに連続的に供給し、フラッシュ蒸留により生成した酢酸、酢酸メチル、ヨウ化メチル、水、及びヨウ化水素を少なくとも含む揮発性成分を第1の蒸留塔(脱低沸塔)に供給し、オーバーヘッドとして第1の低沸点成分を分離し、酢酸より沸点の高い成分を多く含む流れを塔底から缶出液として分離した。オーバーヘッド液(第1の低沸点成分)は直接反応槽にリサイクルし、塔底からの缶出液はフラッシャーの缶出液と混合して反応槽にリサイクルした。そして上記第1の蒸留塔の側流から第1の液状流分を抜き取り、ステンレス製(SUS316:Mn2%以下、Ni10~14%、Cr16~18%、Mo2~3%、Fe50%以上)の材質からなる配管を通して、SUS316の材質からなる第2の蒸留塔(脱水塔)(実段数:50段、仕込段と塔頂蒸気抜き取り段との段間隔:実段で15段)に連続的に仕込んだ。上記第1の液状流分の組成は、ヨウ化メチル2%、酢酸メチル2%、水1%、鉄イオン9100ppb、クロムイオン4000ppb、ニッケルイオン2500ppb、モリブデンイオン1700ppb、亜鉛イオン410ppb、ヨウ化ヘキシル51ppb、残り酢酸(90質量%以上。但し、酢酸塩、無水酢酸、プロピオン酸等の微量の不純物を含む)である。脱水塔では、塔頂温度165℃、塔底温度175℃の条件で蒸留し、水を含んだ第2の低沸点成分を塔頂に濃縮し、第2の液状流分(精製酢酸)を缶出液として得た。塔頂からの留出液は反応槽へリサイクルした。脱水塔への仕込量を1としたとき、缶出液の量は0.7、塔頂からの留出液の量は0.3であった。缶出液の組成は、水500ppm、鉄イオン21000ppb、クロムイオン8300ppb、ニッケルイオン5200ppb、モリブデンイオン2800ppb、亜鉛イオン590ppb、ヨウ化ヘキシル50ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。缶出液を40~50℃に冷却した後、長さ2mの銀置換イオン交換樹脂(IER)カラムを通して、酢酸中のヨウ化ヘキシルを吸着除去した。缶出液の通液速度[樹脂容積1m3当たりの缶出液処理量(m3/h)]は、3.8m3/h・m3(樹脂容積)であった。銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は41ppb、鉄イオン濃度は100ppb、クロムイオン濃度は15ppb、ニッケルイオン濃度は10ppb、モリブデンイオン濃度は6ppb、亜鉛イオン濃度は7ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命(樹脂出口のヨウ化ヘキシル濃度が5ppbを超えるまでの運転時間)は1.2年であった。また、一年間あたりのテストピース(SUS316)の腐食速度(厚みの減肉量)をmmに換算した腐食速度は2.69mm/Yであった。
脱水塔の材質をニッケル基合金[ハステロイB2(HB2):Mo28%、Ni69%、Cr1%以下、Fe2%以下、Co1%以下、Mn1%以下]に変更し、脱水塔の操作条件を、塔頂温度160℃、塔底温度170℃とし、脱水塔へ供給する仕込液の組成を、ヨウ化メチル2%、酢酸メチル2%、水1%、鉄イオン13700ppb、クロムイオン6000ppb、ニッケルイオン3800ppb、モリブデンイオン2600ppb、亜鉛イオン620ppb、ヨウ化ヘキシル51ppb、残り酢酸(90質量%以上。但し、酢酸塩、無水酢酸、プロピオン酸等の微量の不純物を含む)とした以外は比較例1と同様の実験を行った。
脱水塔の缶出液の組成は、水490ppm、鉄イオン19700ppb、クロムイオン8700ppb、ニッケルイオン7000ppb、モリブデンイオン4300ppb、亜鉛イオン890ppb、ヨウ化ヘキシル51ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は30ppb、鉄イオン濃度は80ppb、クロムイオン濃度は16ppb、ニッケルイオン濃度は15ppb、モリブデンイオン濃度は9ppb、亜鉛イオン濃度は9ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は1.1年、腐食速度は0.39mm/Yであった。
脱水塔の操作条件を、塔頂温度160℃、塔底温度170℃とした以外は比較例1と同様の実験を行った。
脱水塔の缶出液の組成は、水490ppm、鉄イオン19800ppb、クロムイオン7900ppb、ニッケルイオン4900ppb、モリブデンイオン2700ppb、亜鉛イオン590ppb、ヨウ化ヘキシル49ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は34ppb、鉄イオン濃度は85ppb、クロムイオン濃度は14ppb、ニッケルイオン濃度は9ppb、モリブデンイオン濃度は7ppb、亜鉛イオン濃度は5ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は1.2年、腐食速度は2.28mm/Yであった。
脱水塔の操作条件を、塔頂温度155℃、塔底温度165℃とした以外は比較例1と同様の実験を行った。
脱水塔の缶出液の組成は、水500ppm、鉄イオン16000ppb、クロムイオン6700ppb、ニッケルイオン4200ppb、モリブデンイオン2600ppb、亜鉛イオン590ppb、ヨウ化ヘキシル45ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は29ppb、鉄イオン濃度は81ppb、クロムイオン濃度は13ppb、ニッケルイオン濃度は9ppb、モリブデンイオン濃度は8ppb、亜鉛イオン濃度は5ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は1.4年、腐食速度は1.00mm/Yであった。
脱水塔の材質をニッケル基合金[ハステロイB2(HB2)]に変更した以外は比較例1と同様の実験を行った。
脱水塔の缶出液の組成は、水510ppm、鉄イオン13200ppb、クロムイオン5800ppb、ニッケルイオン6900ppb、モリブデンイオン3800ppb、亜鉛イオン590ppb、ヨウ化ヘキシル43ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は30ppb、鉄イオン濃度は80ppb、クロムイオン濃度は16ppb、ニッケルイオン濃度は15ppb、モリブデンイオン濃度は9ppb、亜鉛イオン濃度は9ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は1.3年、腐食速度は0.82mm/Yであった。
脱水塔の材質をニッケル基合金[ハステロイB2(HB2)]に変更し、脱水塔の操作条件を、塔頂温度160℃、塔底温度170℃とした以外は比較例1と同様の実験を行った。
脱水塔の缶出液の組成は、水490ppm、鉄イオン13200ppb、クロムイオン5800ppb、ニッケルイオン5200ppb、モリブデンイオン3100ppb、亜鉛イオン590ppb、ヨウ化ヘキシル52ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は18ppb、鉄イオン濃度は25ppb、クロムイオン濃度は9ppb、ニッケルイオン濃度は8ppb、モリブデンイオン濃度は6ppb、亜鉛イオン濃度は7ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は1.8年、腐食速度は0.39mm/Yであった。
第1の蒸留塔(脱低沸塔)の側流から抜き取った第1の液状流分を、ニッケル基合金[ハステロイB2(HB2)]の材質からなる配管を通して得た、ヨウ化メチル2%、酢酸メチル2%、水1%、鉄イオン500ppb、クロムイオン280ppb、ニッケルイオン190ppb、モリブデンイオン110ppb、亜鉛イオン410ppb、ヨウ化ヘキシル51ppb、残り酢酸(90質量%以上。但し、酢酸塩、無水酢酸、プロピオン酸等の微量の不純物を含む)の混合液を脱水塔へ供給する仕込液とした以外は実施例1と同様の実験を行った。
脱水塔の缶出液の組成は、水490ppm、鉄イオン770ppb、クロムイオン420ppb、ニッケルイオン1900ppb、モリブデンイオン800ppb、亜鉛イオン590ppb、ヨウ化ヘキシル50ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は5ppb、鉄イオン濃度は6ppb、クロムイオン濃度は6ppb、ニッケルイオン濃度は7ppb、モリブデンイオン濃度は4ppb、亜鉛イオン濃度は4ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は6.1年、腐食速度は0.39mm/Yであった。
脱水塔の材質をニッケル基合金[ハステロイC(HC276):Mo16%、Ni57%前後、Cr16%、Fe5%、Co2.5%以下、Mn1%以下]に変更した以外は実施例1と同様の実験を行った。
脱水塔の缶出液の組成は、水520ppm、鉄イオン13300ppb、クロムイオン6400ppb、ニッケルイオン5800ppb、モリブデンイオン3100ppb、亜鉛イオン590ppb、ヨウ化ヘキシル48ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は16ppb、鉄イオン濃度は28ppb、クロムイオン濃度は12ppb、ニッケルイオン濃度は13ppb、モリブデンイオン濃度は7ppb、亜鉛イオン濃度は4ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は1.7年、腐食速度は0.67mm/Yであった。
脱水塔の操作条件を、塔頂温度155℃、塔底温度165℃とした以外は実施例1と同様の実験を行った。
脱水塔の缶出液の組成は、水490ppm、鉄イオン13200ppb、クロムイオン5800ppb、ニッケルイオン5200ppb、モリブデンイオン3100ppb、亜鉛イオン590ppb、ヨウ化ヘキシル52ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は13ppb、鉄イオン濃度は23ppb、クロムイオン濃度は8ppb、ニッケルイオン濃度は7ppb、モリブデンイオン濃度は5ppb、亜鉛イオン濃度は5ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は2.0年、腐食速度は0.39mm/Yであった。
脱水塔の缶出液の組成は、水485ppm、鉄イオン13100ppb、クロムイオン5800ppb、ニッケルイオン3900ppb、モリブデンイオン2600ppb、亜鉛イオン590ppb、ヨウ化ヘキシル53ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は12ppb、鉄イオン濃度は23ppb、クロムイオン濃度は9ppb、ニッケルイオン濃度は6ppb、モリブデンイオン濃度は5ppb、亜鉛イオン濃度は5ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は2.1年、腐食速度は0.07mm/Yであった。
脱水塔の操作条件を、塔頂温度163℃、塔底温度173℃とした以外は実施例1と同様の実験を行った。
脱水塔の缶出液の組成は、水495ppm、鉄イオン13200ppb、クロムイオン5800ppb、ニッケルイオン5600ppb、モリブデンイオン3300ppb、亜鉛イオン590ppb、ヨウ化ヘキシル51ppb、酢酸塩50ppm未満、無水酢酸110ppm、プロピオン酸120ppm、残り酢酸(但し、微量の不純物を含む)であった。また、銀置換イオン交換樹脂処理後の製品酢酸の銀イオン濃度は23ppb、鉄イオン濃度は40ppb、クロムイオン濃度は13ppb、ニッケルイオン濃度は14ppb、モリブデンイオン濃度は8ppb、亜鉛イオン濃度は8ppb、ヨウ化ヘキシル濃度は5ppb未満(検出限界以下)であった。この操作でIER樹脂寿命は1.6年、腐食速度は0.49mm/Yであった。
実施例1から分かるように、脱水塔への仕込液中の特定金属イオン濃度を特定値以下とし、且つ脱水塔の材質を耐食性の高いニッケル基合金とすることにより、脱水塔に流入する金属イオンの量が少なく、しかも、蒸留塔の塔底温度175℃未満の条件で蒸留することも相まって、脱水塔からの腐食金属の溶出が抑えられるため、脱水塔から得られる精製酢酸中の金属イオン濃度を大幅に低減できる。これにより、その後の有機ヨウ素化合物の吸着除去工程に流入する金属イオンの量を低減でき、銀置換イオン交換樹脂(IER)の銀イオンと他の金属イオンの交換量が低下して、IERの寿命は1.8年と非常に長いものであった。また、IER処理後の製品酢酸中の金属イオン濃度が低下し、併せて銀イオンの溶出も低減されるので、製品酢酸の品質が大きく向上する。これに対し、比較例2では脱水塔の材質は実施例1と同じニッケル基合金であるが、脱水塔に流入する金属イオンの量が多いため、吸着除去工程に流入する金属イオンが多く、IERの寿命は1.1年と短い。また、比較例3では脱水塔への仕込液中の金属イオン濃度は実施例1と同じであるが、脱水塔の材質がステンレス鋼であるため、脱水塔から腐食金属が溶出して、吸着除去工程に流入する金属イオン量が多く、そのためIERの寿命は1.2年と低い結果となった。なお、比較例4は比較例3の操作温度を低くしたものであるが、脱水塔の材質がステンレス鋼であるため、IERの寿命は1.4年と短い。
2 蒸発槽
3,5,6 蒸留塔
4 デカンタ
7 イオン交換樹脂塔
8 スクラバーシステム
9 アセトアルデヒド分離除去システム
16 反応混合物供給ライン
17 蒸気流排出ライン
18,19 残液流リサイクルライン
54 一酸化炭素含有ガス導入ライン
55,56 水酸化カリウム導入ライン
57 触媒循環ポンプ
91 蒸留塔(第1脱アセトアルデヒド塔)
92 抽出塔
93 蒸留塔(第2脱アセトアルデヒド塔)
94 蒸留塔(抽出蒸留塔)
95 デカンタ
96 デカンタ
97 蒸留塔(脱アセトアルデヒド塔)
98 蒸留塔(抽出蒸留塔)
99 デカンタ
200 チムニートレイ
Claims (16)
- 金属触媒及びヨウ化メチルを含む触媒系、並びに、酢酸、酢酸メチル、水の存在下、メタノールと一酸化炭素とを反応槽で反応させて酢酸を生成させるカルボニル化反応工程と、
前記カルボニル化反応工程で得られた反応混合物を、1以上の蒸発槽及び/又は蒸留塔を用いて、金属触媒を含む流れと、酢酸に富む酢酸流と、前記酢酸流よりも低沸成分に富む流れとに分離する分離工程と、
前記分離工程に含まれていてもよい工程であって、酢酸流を蒸留して酢酸を精製する酢酸蒸留工程と、
前記酢酸蒸留工程で得られる精製酢酸流をイオン交換樹脂で処理する吸着除去工程と、
を備えた酢酸の製造方法であって、
前記酢酸蒸留工程が、酢酸流の蒸留を蒸留塔の塔底温度175℃未満の条件で行う蒸留工程を少なくとも1つ有し、且つ当該蒸留工程における蒸留塔の材質をニッケル基合金又はジルコニウムとし、当該蒸留工程における蒸留塔の仕込液中の金属イオン濃度を、鉄イオン10000質量ppb未満、クロムイオン5000質量ppb未満、ニッケルイオン3000質量ppb未満、且つモリブデンイオン2000質量ppb未満とする、酢酸の製造方法。 - 前記蒸留工程における蒸留塔の仕込液中の酢酸濃度が90質量%以上である請求項1に記載の酢酸の製造方法。
- 前記蒸留工程における蒸留塔の仕込液が、酢酸塩、無水酢酸、及びプロピオン酸からなる群より選択された少なくとも1つの化合物を含む請求項1又は2に記載の酢酸の製造方法。
- 前記蒸留工程における蒸留塔の塔底液の酢酸塩濃度が34質量%以下である請求項1~3のいずれか1項に記載の酢酸の製造方法。
- 前記蒸留工程における蒸留塔の塔底液の無水酢酸濃度が90質量%以下である請求項1~4のいずれか1項に記載の酢酸の製造方法。
- 前記蒸留工程における蒸留塔の塔底液のプロピオン酸濃度が90質量%以下である請求項1~5のいずれか1項に記載の酢酸の製造方法。
- 前記蒸留工程における蒸留塔の塔底圧力0.255MPaG未満の条件で蒸留を行う請求項1~6のいずれか1項に記載の酢酸の製造方法。
- 前記蒸留工程における蒸留塔の塔底圧力0.01MPaG以上0.255MPaG未満の条件で蒸留を行う請求項1~7のいずれか1項に記載の酢酸の製造方法。
- 前記蒸留工程における蒸留塔の仕込液中の亜鉛イオン濃度が1000質量ppb未満である請求項1~8のいずれか1項に記載の酢酸の製造方法。
- 前記蒸留工程における蒸留塔の仕込液供給段と塔頂蒸気抜き取り段との段間隔が、実段数で1段以上である請求項1~9のいずれか1項に記載の酢酸の製造方法。
- 前記蒸留工程における蒸留塔への仕込配管の材質がニッケル基合金又はジルコニウムである請求項1~10のいずれか1項に記載の酢酸の製造方法。
- 前記酢酸蒸留工程が、蒸留に付す酢酸流中の酢酸濃度が97質量%以上である蒸留工程を少なくとも1つ有しており、そのような工程全てにおいて、前記酢酸流の蒸留を蒸留塔の塔底温度175℃未満の条件で行う請求項1~11のいずれか1項に記載の酢酸の製造方法。
- 金属触媒及びヨウ化メチルを含む触媒系、並びに、酢酸、酢酸メチル、水の存在下、メタノールと一酸化炭素とを反応槽で反応させて酢酸を生成させるカルボニル化反応工程と、
前記カルボニル化反応工程で得られた反応混合物を蒸発槽において蒸気流と残液流とに分離する蒸発工程と、
前記蒸気流を蒸留に付して、低沸成分に富むオーバーヘッド流と、酢酸に富む第1酢酸流とに分離する脱低沸工程と、
前記第1酢酸流を蒸留に付して、水に富むオーバーヘッド流と第1酢酸流よりも酢酸に富む第2酢酸流とに分離する脱水工程と、
前記第2酢酸流、又は前記第2酢酸流をさらに精製したより酢酸に富む酢酸流をイオン交換樹脂で処理する吸着除去工程と、
を備えた酢酸の製造方法であって、
前記脱水工程における蒸留塔の材質をニッケル基合金又はジルコニウムとし、且つ前記脱水工程における蒸留塔の仕込液中の金属イオン濃度を、鉄イオン10000質量ppb未満、クロムイオン5000質量ppb未満、ニッケルイオン3000質量ppb未満、且つモリブデンイオン2000質量ppb未満とし、
前記脱水工程を蒸留塔の塔底温度175℃未満の条件で行う、酢酸の製造方法。 - 前記第2酢酸流中の鉄イオン濃度が21000質量ppb未満である請求項13に記載の酢酸の製造方法。
- 前記第2酢酸流中の金属イオン濃度が、鉄イオン21000質量ppb未満、クロムイオン7100質量ppb未満、ニッケルイオン4000質量ppb未満、モリブデンイオン3000質量ppb未満、且つ亜鉛イオン1000質量ppb未満である請求項13又は14に記載の酢酸の製造方法。
- 材質がニッケル基合金又はジルコニウムであり、仕込液供給段と塔頂蒸気抜き取り段との段間隔が実段数で1段以上である蒸留塔に、鉄イオン濃度10000質量ppb未満、クロムイオン濃度5000質量ppb未満、ニッケルイオン濃度3000質量ppb未満、モリブデンイオン濃度2000質量ppb未満、亜鉛イオン濃度1000質量ppb未満、ヨウ化ヘキシル濃度510質量ppb未満、酢酸濃度80質量%以上の粗酢酸を、材質がニッケル基合金又はジルコニウムである仕込配管を通じて前記仕込液供給段に仕込み、塔底温度175℃未満の条件で蒸留し、水に富むオーバーヘッドと、鉄イオン濃度21000質量ppb未満、クロムイオン濃度7100質量ppb未満、ニッケルイオン濃度4000質量ppb未満、モリブデンイオン濃度3000質量ppb未満、亜鉛イオン濃度1000質量ppb未満の精製酢酸を得る、酢酸の製造方法。
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