JP5866051B1 - Method for producing acetic acid - Google Patents

Abstract

Disclosed is a method for producing acetic acid that controls the water concentration in the side stream between two towers. The water concentration is controlled by the light liquid phase recycling rate, and the hydrogen iodide concentration in the side stream is maintained at 50 wppm or less. [Selection figure] None

Description

  [0001] The present invention relates to a method for producing acetic acid, and more particularly to an improved method for controlling the concentration of water and hydrogen iodide fed to a drying tower.

  [0002] One of the most commercially useful methods of synthesizing acetic acid currently employed is carbonylation of methanol with carbon monoxide using a catalyst. This method is taught in US Pat. No. 3,769,329, the entire content of which is incorporated herein by reference. The carbonylation catalyst includes a metal catalyst such as rhodium and a halogen-containing catalyst promoter such as methyl iodide, and the metal catalyst is dissolved or dispersed in a liquid reaction medium or supported on an inert solid. This reaction is performed by continuously bubbling carbon monoxide gas in a liquid reaction medium in which a catalyst is dissolved.

  [0003] Methanol and carbon monoxide are fed to the reactor as raw materials. A portion of the reaction medium is continuously removed and fed to a flash vessel where the product is evaporated and sent as vapor to the purification system. The purification system is equipped with a light fractionation tower in which "light" or low boiling components are removed as overhead and a side stream is obtained for further purification. The purification system may further comprise a column for dehydrating the side stream or for removing “heavy” or high boiling components such as propionic acid from the side stream. In the carbonylation process to produce acetic acid, it is desirable to minimize the number of distillation operations to minimize the energy used in this process.

  [0004] US Pat. No. 5,416,237 discloses a process for producing acetic acid by carbonylation of methanol in the presence of a rhodium catalyst, methyl iodide, and an iodide salt stabilizer. . The improvement described in US Pat. No. 5,416,237 provides a liquid reaction composition while maintaining a finite concentration of water in the liquid reaction composition of about 10 wt% or less and a methyl acetate concentration of at least 2 wt%. The product is passed through a flash zone to produce a vapor fraction that is fed to a single distillation column where the acetic acid product is recovered by removing the acetic acid product. Omitting the distillation step has the disadvantage that the purity of the product is impaired. In particular, distillation towers tend to remove high boiling iodides and aldehyde contaminants. Any of these impurities affects the commercially desired end product.

  [0005] US Patent No. 9,006,483 discloses a method for producing acetic acid for liquid-liquid separation of overhead from a distillation column for the purpose of reducing hydrogen iodide concentration. In the first distillation column (3), a mixture containing hydrogen iodide, water, acetic acid and methyl acetate is distilled to form an overhead and a side stream or bottom stream containing acetic acid, and the condenser is used to cool and condense the overhead. Then, it is separated into an upper phase and a lower phase with a decanter (4) to produce acetic acid. According to this method, the water concentration is an effective amount or more and 5% by weight or less (for example, 0.5 to 4.5% by weight) and the methyl acetate concentration is 0.5 to 9% by weight (for example, 0.5 to 8% by weight). ) Is fed to the distillation column and distilled, a region having a high water concentration is formed above the mixture supply position in the distillation column. In this high water concentration region, hydrogen iodide is reacted with methyl acetate to produce methyl iodide and acetic acid.

  [0006] US Patent No. 7,884,241 distills a mixture containing hydrogen iodide and water and having a water content in the distillation system of 5 wt% or less (especially 3 wt% or less). Preventing the condensation of hydrogen iodide in a distillation system is disclosed. This mixture may contain hydrogen iodide, water, methanol, methyl iodide, acetic acid, methyl acetate. Even if this mixture contains hydrogen iodide at a concentration of 1 to 3000 ppm in terms of weight, a fraction containing hydrogen iodide is taken out from the top of the distillation column, and acetic acid is used as a side stream or a stream from the bottom of the distillation column. By taking out, an acetic acid product having a hydrogen iodide concentration of 50 ppm or less can be obtained. Although this distillation method can suppress condensation of hydrogen iodide in the distillation system and corrosion in the distillation system, the energy loss is large. In order to keep the water concentration low, this method requires a large reflux ratio of 2.35 and consumes a large amount of energy.

  [0007] US Pat. No. 6,657,078 discloses a process for producing acetic acid at low energy by carbonylation of methanol. The process includes a rhodium catalyst system operated with less than about 14% by weight water using up to two distillation columns.

  [0008] US Pat. No. 4,008,131 describes a tendency to reduce the yield of pure acid and increase it in the recycle stream during operation of a distillation system that purifies crude acetic acid containing water and methyl iodide. A method of removing excess water present in Crude acetic acid is introduced into the upper half of the distillation zone. Methyl iodide, most of the water, and an equivalent amount of acid are removed from the distillation zone as overhead. A small amount of water containing a small amount of acetic acid is removed as a liquid side stream near the top of the distillation zone. An essentially dry acid product stream substantially free of methyl iodide is removed from the bottom of the distillation zone. The overhead stream may be stored or discarded, but preferably recycled to the acid production process. The liquid side stream may be discarded or rectified for acid value recovery.

  [0009] US Pat. No. 3,791,935 introduces a monocarboxylic acid stream containing water and halogen contaminants into the upper half of a distillation column, primarily water and alkyl halogen charged to the distillation column. Removing the overhead fraction consisting of fluoride, removing the stream containing the majority of the hydrogen halide present in the distillation column from the middle of the distillation column, substantially free of halogen contaminants input to the distillation column, A method is disclosed in which an essentially dry acid product stream is removed from or near the bottom of the distillation column. This method is particularly applicable to the removal of water and iodine-containing compounds from acetic acid and propionic acid. In these examples, the bottom product containing acetic acid is reported to contain 83-132 wppm water and 0.083 wppm-0.3 wppm hydrogen iodide.

  [0010] In view of this, there is a need for an improved method of acetic acid production to control acetic acid recovery.

[0011] In one aspect, the present invention provides a reaction system comprising a reactor and a flash vessel, forming a reaction medium in the reactor, liquid recycle stream and steam generation in the reaction vessel Separating into a stream, distilling at least a portion of the steam product stream in a first column to obtain a side stream and a low boiling overhead steam stream comprising more than 5 wt% water, Condensing at least a part and separating into two phases to form a heavy liquid phase and a light liquid phase, and controlling the recycling rate of the light liquid phase to the reaction system to control the water concentration in the side stream Is maintained at 1 to 3 wt%, such as preferably 1.1 to 2.5 wt%, and the hydrogen iodide (HI) concentration is maintained at 50 wppm or less, such as preferably 0.1 to 50 wppm, and At least of the side stream in the second tower Parts distilled to include obtaining purified acetic acid product, a method for producing acetic acid. In one embodiment, the sidestream further comprises one or more iodide _C 1 _{-C 14} alkyl 0.1-6 wt%, the methyl acetate from 0.1 to 6 wt%. The light liquid phase may contain 40 to 80% by weight of water. The reaction medium is 0.5-30 wt% methyl acetate, 0.1-14 wt% water, 200-3000 wppm metal catalyst, 1-25 wt% iodide salt, 1-25 wt% methyl iodide. % May be included. The reaction medium may also contain acetic acid and methanol. In addition to recycling the light liquid phase, a portion of the light liquid phase can also be refluxed to the first column. In one embodiment, the first column is operated at a reflux ratio of 0.05 to 0.4. In some embodiments, another portion of the light liquid phase may be fed to a PRC removal system for removing acetaldehyde and / or other permanganate reducing compounds. In other embodiments, a portion of the heavy liquid phase may be refluxed to the first column alone or as a mixture with the light liquid phase reflux.

  [0012] The concentration of hydrogen iodide in the side stream can be determined by potentiometric titration using lithium acetate as a titration reagent. Depending on the measured hydrogen iodide concentration, if the measured hydrogen iodide concentration is greater than a predetermined threshold, for example, greater than 50 wppm, the light liquid phase recycle rate may be increased. In one embodiment, additional steps may be performed to further reduce the iodide concentration of the purified acetic acid product removed from or near the bottom of the second column. For example, the present invention further includes contacting the purified acetic acid product with a guard bed to remove residual iodide contaminants when the total iodide concentration of the purified acetic acid product is 5 wppm or less, such as 1 wppm or less. Removing may also be included.

  [0013] In another aspect, the present invention provides a reaction system comprising a reactor and a flash vessel, forming a reaction medium in the reactor, liquid reaction stream and steam in the flash vessel Separating into a product stream, distilling at least a portion of the vapor product stream in a first column to obtain a side stream and a low boiling overhead vapor stream, condensing at least a portion of the low boiling overhead stream, and Separating into two phases to form a heavy liquid phase and a light liquid phase, measuring the hydrogen iodide concentration in the side stream, and reacting the light liquid phase according to the measured hydrogen iodide concentration To control the recycle rate to maintain a hydrogen iodide concentration in the sidestream of 50 wppm or less, for example, preferably 0.1-50 wppm, and at least a portion of the sidestream in the second column. Distilled to obtain purified acetic acid product Comprising relates to a process for producing acetic acid.

[0014] In yet another aspect, the invention provides a reaction system comprising a reactor and a flash vessel, forming a reaction medium in the reactor, and supplying the reaction medium as a liquid recycle stream in the flash vessel. Separating into a steam product stream, distilling at least a portion of the steam product stream in a first column, a low boiling overhead steam stream, 1-3 wt% water, 0.1-6 wt% To obtain a C ₁ -C ₁₄ alkyl iodide and a side stream containing 50 wppm or less of hydrogen iodide, for example, 1 to 50 wppm hydrogen iodide, and purifying by distilling at least a part of the side stream in the second column. It relates to a process for producing acetic acid comprising obtaining an acetic acid product and contacting the purified acetic acid product with a guard bed when the total iodide concentration of the purified acetic acid product is 5 wppm or less.

  [0015] The invention will be more fully understood from the accompanying non-limiting drawings.

[0016]
It is the schematic which shows the acetic acid manufacturing method which concerns on this invention.

Introduction
[0017] The acetic acid recovery method usually involves distilling the crude acetic acid product in the first column to form a side stream and distilling this side stream in the second column to form the purified acetic acid product. Including doing. This side stream contains acetic acid and water, and various small amounts of impurities such as hydrogen iodide. In the first column, a low boiling overhead vapor stream is also formed. This low boiling overhead vapor stream is usually condensed and separated into two phases, a light liquid phase and a heavy liquid phase.

[0018] The present invention provides a method of controlling water concentration and indirectly controlling the sidestream hydrogen iodide concentration. As an advantage, the sidestream water concentration can be maintained in the desired range by controlling the recycle rate of the light liquid phase recovered from the first column to the reaction system comprising the reactor and flash vessel. In one aspect, 0-20% of the total light liquid phase condensed from the low boiling overhead stream is recycled. The remainder may be used as the reflux liquid in the first column or may be fed to the PRC removal system. In some embodiments, the light liquid phase recycle rate may be 0%, but this is not recycled to the reaction system, and the light liquid phase is used as the reflux liquid in the first column or the PRC removal system. It is shown to be supplied to. Since the light liquid phase can be refluxed to the first column, changes in the reflux ratio also affect the recycle rate to the reactor and ultimately the sidestream water and hydrogen iodide content. Effect. Reducing the sidestream hydrogen iodide content reduces the total iodide content in the second column and ultimately in the purified acetic acid product . If the total iodide concentration in the purified acetic acid product is low, such as 5 wppm or less, such as 1 wppm or less, residual iodide contaminants can be effectively removed using a guard bed. This greatly improves the quality of the purified acetic acid product.

  [0019] In one aspect, the present invention provides a reaction system comprising a reactor and a flash vessel, forming a reaction medium in the reactor, generating a liquid recycle stream and vapor generation of the reaction medium in the flash vessel Separating into a stream, distilling at least a portion of the steam product stream in a first column to obtain a side stream and a low boiling overhead steam stream comprising more than 5 wt% water, Condensing at least a part and separating into two phases to form a heavy liquid phase and a light liquid phase, controlling the recycling rate of the light liquid phase to the reaction system, and the water concentration in the side stream Is maintained at 1 to 3% by weight, the hydrogen iodide concentration in the side stream is maintained at 50 wppm or less, and at least a part of the side stream is distilled in the second column to obtain a purified acetic acid product. Who produce acetic acid, including On.

  [0020] In another aspect, the present invention provides a reaction system comprising a reactor and a flash vessel, forming a reaction medium in the reactor, and recycling the reaction medium into a liquid recycle stream and steam in the flash vessel Separating into a product stream, distilling at least a portion of the vapor product stream in a first column to obtain a side stream and a low boiling overhead vapor stream, condensing at least a portion of the low boiling overhead stream, and Separating into two phases to form a heavy liquid phase and a light liquid phase, measuring the hydrogen iodide concentration in the side stream, and depending on the measured hydrogen iodide concentration, the light to the reaction system Control the recycle rate of the liquid phase to maintain the hydrogen iodide concentration in the side stream at 50 wppm or less, for example, preferably 0.1 to 50 wppm, and at least part of the side stream in the second column The distillation Te and obtaining purified acetic acid product, a method for producing acetic acid.

[0021] In yet another aspect, the invention provides a reaction system comprising a reactor and a flash vessel, forming a reaction medium in the reactor, and supplying the reaction medium as a liquid recycle stream in the flash vessel. Separating into a steam product stream, distilling at least a portion of said steam product stream in a first column, a low boiling overhead steam stream, 1-3 wt% water, 0.1-6 wt% 1 Obtaining a side stream comprising at least _one species of C ₁ -C ₁₄ alkyl iodide and 50 wppm or less, for example 1 to 50 wppm hydrogen iodide, and distilling at least a portion of said side stream in a second column to produce purified acetic acid The present invention relates to a process for producing acetic acid comprising obtaining a product and contacting the purified acetic acid product with a guard bed when the total iodide concentration of the purified acetic acid product is 5 wppm or less.

  [0022] By controlling the recycling of the light liquid phase, the water concentration in the side stream between the two towers may be maintained within a predetermined concentration limit. The side stream may contain 1 to 3% by weight of water, for example 1 to 2.5% by weight, more preferably 1.1 to 2.1% by weight. It was found that the hydrogen iodide concentration in the side stream is maintained at 50 wppm or less, for example, 0.1 to 50 wppm, or 5 to 30 wppm if the water concentration is within this range. Hydrogen iodide is soluble in an acetic acid-water mixture containing 3 to 8% by weight of water, and the solubility of hydrogen iodide decreases as the water concentration decreases. This correlation promotes hydrogen iodide volatilization, resulting in a reduction in the amount of hydrogen iodide recovered in the tower overhead. Although hydrogen iodide may be corrosive under certain circumstances, it may beneficially act as a catalyst under certain conditions of a given amount of hydrogen iodide. Such catalysts include the catalysts for forming dimethyl ether described in US Pat. No. 7,223,883 (which describes the advantages of forming dimethyl ether by a predetermined acetic acid separation method). The entire contents of the patent are incorporated herein by reference.

  [0023] Controlling the recycling rate of the light liquid phase to the reaction system is another method for controlling the content of hydrogen iodide, such as the method described in US Pat. No. 9,006,483. It is improved compared to this. For that reason, the present invention controls hydrogen iodide without introducing additional components into the first column and / or without maintaining a predetermined concentration in the vapor product feed sent to the first column. This is because it has the advantage of being able to. Also, the method described in US Pat. No. 9,006,483 does not include control of the recycling of the light liquid phase to the reaction system, thus controlling the sidestream water and hydrogen iodide concentrations independently. I can't.

  [0024] The main component of the side stream is acetic acid, and the side stream preferably contains more than 90% by weight, such as more than 94% by weight, or more than 96% by weight acetic acid. In terms of range, the side stream may contain 90-99% by weight acetic acid, for example 91-98% by weight. With such a concentration, most of the acetic acid supplied to the first column can be withdrawn into the side stream and further purified in the second column. Acetic acid is preferably not recovered in the low boiling vapor stream or high boiling residue stream of the first column.

[0025] In addition to acetic acid and water, the side stream may also contain from 0.1 to 6% by weight of one or more C ₁ -C ₁₄ alkyl iodides, especially methyl iodide. Other alkyl iodides such as hexyl iodide may be formed from carbonyl impurities such as acetaldehyde. More preferably, the side stream comprises one or more iodide _C 1 _{-C 14} alkyl 0.5-3 wt%. Due to the presence of water, the side stream may also contain 0.1 to 6% by weight, for example 0.5 to 3% by weight of methyl acetate.

[0026] The concentration of hydrogen iodide in the side stream is determined by potentiometric titration using lithium acetate as a titration reagent. As another method, there is a method of obtaining the content of hydrogen iodide indirectly by calculation. For example, in U.S. Patent Publication No. 2013/0310603, the iodide ion concentration is determined from the iodide ion concentration derived from the iodide salt form (including iodide derived from a cocatalyst and metal iodide). It has been shown that it may be calculated by subtracting from the total concentration of I ⁻ ). Such indirect calculation techniques are usually inaccurate, and the actual ion concentration measurement method is inaccurate, so that the actual hydrogen iodide concentration is not sufficiently shown. Also, this indirect calculation technique does not account for other iodide forms. The reason for this is that measuring metal cations assumes that all of these cations bind only to iodide anions, but this is incorrect, and in fact these metal cations are acetate anions. This is because it may bind to other anions such as catalyst anions. On the other hand, the direct measurement of the hydrogen iodide concentration according to the present invention can reflect the actual hydrogen iodide concentration in the system, and has an advantage that an accuracy as low as 0.01% can be obtained.

[0027] The light liquid phase recycle rate may be controlled by detecting the sidestream hydrogen iodide concentration. For example, when the hydrogen iodide concentration exceeds a predetermined threshold, such as 50 wppm, the light liquid phase recycling rate may be increased. Once the hydrogen iodide concentration falls below a predetermined threshold, such as 10 wppm, the light liquid phase recycle rate may be reduced. Throughout this specification, the light liquid phase recycle rate is the ratio of the recycled light liquid phase to the total amount of light liquid phase condensed from the overhead of the first column. The light liquid phase may be recycled to the reaction system.
Reaction process
[0028] An exemplary reaction and acetic acid recovery system 100 is shown in FIG. As shown, a methanol-containing feed stream 101 and a carbon monoxide-containing feed stream 102 are charged to a liquid phase carbonylation reactor 105 and subjected to a carbonylation reaction to form acetic acid.

  [0029] The methanol-containing feed stream 101 may comprise at least one selected from the group consisting of methanol, dimethyl ether, methyl acetate. The methanol-containing feed stream 101 may be partially derived from a new supply or may be recycled from the system. At least some of the methanol and / or reactive derivatives thereof are converted to methyl acetate in a liquid solvent by an esterification reaction with acetic acid.

  [0030] The usual reaction temperature for carbonylation is 150-250 ° C. A preferred temperature range is 180-225 ° C. The carbon monoxide partial pressure in the reactor may vary greatly, but is usually 2-30 atm, for example 3-10 atm. The hydrogen partial pressure in the reactor is usually 0.05 to 2 atm, for example 0.25 to 1.9 atm. Due to the partial pressure of by-products and the vapor pressure of the liquid contained, the total pressure in the reactor is in the range of 15-40 atm. The production rate of acetic acid may be 5 to 50 mol / L · h, for example 10 to 40 mol / L · h, preferably about 15 to 35 mol / L · h.

  [0031] The carbonylation reactor 105 is preferably a stirred vessel or bubble column vessel with or without a stirrer. In this, the content of the reaction liquid or slurry is maintained at a predetermined value, preferably automatically, and preferably substantially constant during normal operation. If necessary, fresh methanol, carbon monoxide, and a sufficient amount of water are continuously introduced into the carbonylation reactor 105 to maintain a suitable concentration in the reaction medium.

[0032] The metal catalyst may comprise a Group VIII metal. Suitable Group VIII catalysts include rhodium and / or iridium catalysts. When using a rhodium catalyst, as is well known in the _{art, [Rh (CO) 2 I} 2] - any suitable form of rhodium catalyst as rhodium equilibrium mixture containing an anion is present in the catalyst solution May be added. The iodide salt that may be maintained in the reaction mixture of the methods described herein may be in the form of an alkali metal, alkaline earth metal, quaternary ammonium, a soluble salt of a phosphonium salt, or a mixture thereof. Good. In some embodiments, the catalyst co-promoter is lithium iodide, lithium acetate, or a mixture thereof. The salt co-promoter may be added as a non-iodide salt that produces an iodide salt. The iodide catalyst stabilizer may be introduced directly into the reaction system. Alternatively, the iodide salt may be generated in the reaction system. This is because, under the operating conditions of the reaction system, a wide range of non-iodide salt precursors react with methyl iodide or hydroiodic acid in the reaction medium to produce the corresponding co-promoted iodide salt stabilizer. Because. See US Pat. Nos. 5,001,259, 5,026,908, 5,144,068, and 7,005,541 for details on rhodium catalyst and iodide salt formation. The entire contents of which are incorporated herein by reference. Carbonylation of methanol using iridium catalysts is well known and is generally described in U.S. Pat. Nos. 5,942,460, 5,932,764, 5,883,295, 5,877,348, 5, 877,347 and 5,696,284. The entire contents of which are incorporated herein by reference.

  [0033] The halogen-containing catalyst promoter of the catalyst system comprises a halogen compound including an organic halide. Accordingly, alkyl halides, aryl halides, and halogenated substituted alkyls or halogenated substituted aryls can be used. The halogen-containing catalyst promoter is preferably present in the form of an alkyl halide. More preferably, the halogen-containing catalyst promoter is present in the form of an alkyl halide having an alkyl radical corresponding to the alkyl radical of the carbonylated feed alcohol. Thus, in the carbonylation of methanol to acetic acid, the halide promoter includes methyl halide, more preferably methyl iodide.

  [0034] Ensure that a sufficient amount of acetic acid is produced by maintaining the components of the reaction medium within specified limits. The reaction medium contains a predetermined concentration of metal catalyst. For example, the rhodium catalyst is contained in an amount of 200 to 3000 wppm, such as 800 to 3000 wppm, or 900 to 1500 wppm. The concentration of water in the reaction medium is maintained at less than 14% by weight, such as 0.1% to 14%, 0.2% to 10%, or 0.25% to 5%. The reaction is preferably performed under conditions with little water. The reaction medium contains 0.1 to 4.1% by weight of water, for example 0.1 to 3.1% by weight, or 0.5 to 2.8% by weight. The methyl iodide concentration in the reaction medium is maintained at 1 to 25% by weight, such as 5 to 20% by weight, 4 to 13.9% by weight, or 4 to 7% by weight. The concentration of iodide salt, such as lithium iodide, in the reaction medium is maintained at 1-25 wt%, such as 2-20 wt%, or 3-20 wt%. The methyl acetate concentration in the reaction medium is maintained at 0.5-30 wt%, such as 0.3-20 wt%, or 0.6-4.1 wt%. The following amounts are based on the total weight of the reaction medium. The concentration of acetic acid in the reaction medium is generally greater than 30% by weight, for example greater than 40% by weight or greater than 50% by weight.

  [0035] In some embodiments, maintaining the ester concentration in the reaction medium consisting of the desired carboxylic acid, desirably the alcohol used for carbonylation, and another iodide ion in addition to the iodide ion present as hydrogen iodide. Thus, the desired reaction rate can be obtained even when the water concentration is low. The desired ester is methyl acetate. Another iodide ion is desirably an iodide salt, with lithium iodide (LiI) being preferred. At low water concentrations, methyl acetate and lithium iodide act as kinetic promoters only when these components are each present in relatively high concentrations, and are more accelerated when both of these components are present simultaneously. I found it to increase.

  [0036] The carbonylation reaction of methanol to the acetic acid product is carried out under conditions of temperature and pressure suitable to form the carbonylation product, rhodium catalyst, methyl iodide (MeI) promoter, methyl acetate (MeAc), Alternatively, it may be carried out by contacting carbon monoxide gas supplied by bubbling with methanol to an acetic acid reaction solvent containing another soluble iodide salt. In general, what is important is the concentration of iodide ions in the catalyst system, not the concentration of cations bound to iodide, and if the iodide is at a given molar concentration, the nature of the cation is as high as the effect of iodide concentration. It is recognized that it is not important. If the salt is sufficiently soluble in the reaction medium to provide the desired amount of iodide, a metal iodide salt, or a cation based on an organic cation, such as an amine or phosphine compound (tertiary or Any other cation iodide salt, such as a quaternary cation, may be maintained in the reaction medium. When the iodide is a metal salt, from the Group IA and IIA metals of the periodic table as described in “Chemical and Physical Handbook” 2002-03 (83rd edition) published by the Cleveland CRC Press, Ohio A metal iodide salt selected from the group consisting of In particular, alkali metal iodides are useful, and lithium iodide is particularly preferred. In the low water carbonylation process, there is generally another iodide ion present in the catalyst solution in addition to the iodide ion present as hydrogen iodide in an amount such that the total concentration of iodide ions is from 1 to 25% by weight. . Also, methyl acetate is generally present in an amount of 0.5-30% by weight and methyl iodide is generally present in an amount of 1-25% by weight. The rhodium catalyst is generally present in an amount of 200 to 3000 ppm.

  [0037] In a normal carbonylation process, carbon monoxide may be continuously introduced under a carbonylation reactor, preferably a stirrer, and the contents may be stirred using the stirrer. It is preferable that the feed gas is sufficiently dispersed in the reaction solution by this stirring means. It is desirable to discharge the exhaust stream 106 from the reactor 105 to prevent the accumulation of gaseous byproducts and maintain the carbon monoxide partial pressure set at the predetermined total pressure in the reactor. The temperature of the reactor may be controlled and carbon monoxide is fed at a rate sufficient to maintain the desired total pressure in the reactor. A stream 113 containing a liquid reaction medium is sent out of the reactor 105.

  [0038] The acetic acid production system preferably includes a separation system 108 that is used to recover acetic acid and recycle the metal catalyst, methyl iodide, methyl acetate, and other system components within the carbonylation process. One or more recycle streams may be mixed before being introduced into the reactor. Also, the separation system preferably controls the carbonylation reactor and the water and acetic acid content of the entire system to facilitate the removal of the permanganate reducing compound (PRC). Examples of PRC include acetaldehyde, acetone, methyl ethyl ketone, butyraldehyde, crotonaldehyde, 2-ethylcrotonaldehyde, 2-ethylbutyraldehyde, and aldol condensates thereof.

  [0039] The reaction medium is removed from the carbonylation reactor 105 at a rate sufficient to maintain a constant level and fed via stream 113 to the flash vessel 110. The reactor 105 and the flash vessel 110 constitute a reaction system together with related pumps, exhaust ports, pipes and valves. The flash separation may be performed at a temperature of 80 ° C. to 280 ° C. and an absolute pressure of 0.25 to 10 atm, more preferably at a temperature of 100 ° C. to 260 ° C. and 0.3 to 10 atm. In the flash vessel 110, the reaction medium is separated in a flash separation step to obtain a vapor product stream 112 containing acetic acid and a liquid recycle stream 111 containing catalyst-containing liquid.

  [0040] The liquid recycle stream 111 includes acetic acid, metal catalyst, corrosive metal, and various other compounds. In one aspect, the liquid recycle stream is 60-90 wt% acetic acid, 0.01-0.5 wt% metal catalyst, 10-2500 wppm corrosive metal (e.g., nickel, iron, chromium, etc.), 5-20 wt%. % Lithium iodide, 0.5-5% by weight methyl iodide, 0.1-5% by weight methyl acetate, 0.1-8% by weight water, 1% by weight or less acetaldehyde (eg 0.0001 -1 wt% acetaldehyde), and 0.5 wt% or less hydrogen iodide (e.g. 0.0001-0.5 wt% hydrogen iodide).

  [0041] Each flow rate of the steam product stream 112 and the liquid recycle stream 111 may vary, but in an exemplary aspect, 15% to 55% of the stream to the flash vessel 110 is removed as the steam product stream 112; 45% to 85% of the stream is removed as liquid recycle stream 111. The catalyst-containing liquid is mostly acetic acid containing rhodium and iodide salts and may contain smaller amounts of methyl acetate, methyl iodide, and water, and is recycled to the reactor as described above. . Prior to returning the liquid recycle stream to the reactor, as described in US Pat. No. 5,731,252, the entire contents of which are incorporated herein by reference, the slip stream is ionized. It may be passed through a corrosive metal removal floor such as an exchange floor to remove accompanying corrosive metals such as nickel, iron and chromium. As described in US Pat. No. 8,697,908 (the entire contents of which are incorporated herein by reference), a corrosive metal removal bed may be used to remove nitrogen compounds such as amines. Good.

[0042] In addition to acetic acid, the vapor product stream 112 also includes methyl iodide, methyl acetate, water, hydrogen iodide, and PRCs such as acetaldehyde, crotonaldehyde, and the like. The dissolved gas sent from the reactor 105 and supplied to the flash vessel 110 contains a part of carbon monoxide, but may contain gas by-products such as methane, hydrogen, carbon dioxide and the like. Such dissolved gas is delivered from the flash vessel 110 as part of the vapor product stream 112. In one aspect, carbon monoxide in the exhaust stream 106 may be supplied to the bottom of the flash vessel 110 to enhance rhodium stability.
Acetic acid recovery
[0043] The distillation and recovery of acetic acid is not particularly limited for the purposes of the present invention. As shown in FIG. 1, the steam product stream 112 is supplied to a first column 120 (also referred to as a light fractionation column). In one aspect, the vapor product stream 112 may contain other impurities such as hydrogen iodide, crotonaldehyde, and by-products such as propionic acid in addition to acetic acid, methyl acetate, water, methyl iodide, acetaldehyde. Distillation results in a low boiling overhead vapor stream 122, a purified acetic acid product (preferably removed via side stream 123), and a high boiling residue stream 121. Most of the acetic acid is removed in the side stream 123, but it is preferred that little or no acetic acid is recovered from the high boiling residue stream 121.

  [0044] In one aspect, the low boiling overhead vapor stream 122 comprises greater than 5 wt% water, such as greater than 10 wt%, or greater than 25 wt% water. The amount of water may be 80% by weight or less. With respect to the range, the amount of water may be 5 wt% to 80 wt%, such as 10 wt% to 70 wt%, or 25 wt% to 60 wt%. If the water concentration is lower than 5% by weight, the amount of acetic acid recycled to the reaction system increases, and the amount of recycling of the entire purification system increases, which is not preferable. The low boiling overhead vapor stream 122 may contain carbonyl impurities such as methyl acetate, methyl iodide, and PRC in addition to water. These are preferably concentrated in the overhead and removed from the acetic acid in the side stream 123.

  [0045] As shown, the low boiling overhead vapor stream 122 is preferably condensed and fed to an overhead phase separation unit, shown as an overhead decanter 124. Maintaining conditions so that the low-boiling overhead vapor stream 122 once condensed in the decanter 124 is separated into two phases, a light liquid phase 133 (also referred to as an aqueous phase) and a heavy liquid phase 134 (also referred to as an organic phase). Is desirable. Off-gas components may be exhausted from decanter 124 via line 132. Although the specific composition of the light liquid phase 133 can vary widely, some preferred compositions are shown in Table 1 below.

  [0046] The concentration of water and hydrogen iodide in the side stream 123 is controlled by the recycle rate of the light liquid phase 133 to the reaction system via the line 136. The reflux ratio of the light liquid phase 133 to the first column via line 136 (from the top of column 120 containing both heavy liquid phase 134 (whether or not all recycled) and light liquid phase 133) The mass flow rate of the reflux liquid divided by the total mass flow rate sent out is preferably 0.05 to 0.4, for example, 0.1 to 0.35, or 0.15 to 0.3. In one aspect, the number of theoretical plates between the side stream and the top of the first column is preferably greater than 5, for example greater than 10, in order to reduce the reflux ratio.

  [0047] In one aspect, the recycle rate of the light liquid phase in line 136 to the reaction system is no more than about 20% of the total amount of light liquid phase 133 condensed from the overhead of the first column, such as about 10%. It is as follows. In terms of range, the light liquid phase recycle rate in line 136 is 0-20% of the total amount of light liquid phase 133 condensed from the overhead of the first tower, such as 0.5-20%, or 1- It may be 10%. The remaining portion may be used as a reflux liquid in a light fractionator, or may be supplied to a PRC removal system. As shown in FIG. 1, the recycle stream in line 136 may be mixed with liquid recycle stream 111 and returned to reactor 105. In one aspect, the recycle stream in line 136 may be mixed with other streams that are recycled to the reaction system, such as reactor 105 or flash vessel 110, for example. If the condensation overhead stream 138 from the drying tower 125 is separated into an aqueous phase and an organic phase, it may be preferable to mix the recycle stream in line 136 with the aqueous phase. Alternatively, all or at least a portion of the recycle stream in line 136 may be mixed with the heavy liquid phase 134 and / or the organic phase from the overhead stream 138.

  [0048] For purposes of the present invention, a flow valve (not shown) and / or a flow monitor (not shown) may be used to control the reflux liquid in line 135 and the recycle stream in line 136. Good. In one aspect, the reflux liquid in line 135 and the recycle flow controller in line 136 are each in communication with an on-line analyzer 142 that controls the reflux ratio and recycling to the reactor. Feedback information can be obtained. Changing the reflux ratio can affect the amount of water recycled to the reactor. In some embodiments, the amount may be varied so that light liquid phase 133 is not recycled to the reactor. Decreasing the reflux (and increasing recycling to the reactor) reduces the water content of the side stream. Increasing the reflux increases the sidestream water concentration and decreases the water recycled to the reactor. When the reflux ratio exceeds 0.4, the water concentration in the side stream exceeds 3% by weight, making it difficult to separate in the second column, that is, to remove water, methyl acetate, and methyl iodide from acetic acid. Become. As a result, the total iodide concentration in acetic acid in the bottom stream of the second column may become excessively high and treatment with a guard bed may not be effective.

  [0049] Although not shown, a portion (preferably an aliquot) of the light liquid phase 133 may be separated and charged into a PRC removal system to recover methyl iodide and methyl acetate. As shown in Table 1, the light liquid phase 133 contains PRC, and the process may include removing carbonyl impurities such as acetaldehyde that impair the quality of the acetic acid product. These carbonyl impurities are disclosed in U.S. Patent Nos. 6,143,930, 6,339,171, 7,223,883, 7,223,886, 7,855,306, 7,884,237. , 8,889,904, and a suitable impurity removal tower or impurity absorber described in US Patent Publication No. 2006/0011462. The entire contents of these patents are incorporated herein by reference. A carbonyl impurity such as acetaldehyde may be reacted with an iodide catalyst promoter to form an alkyl iodide such as ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl iodide, and the like. In addition, since most of the impurities are derived from acetaldehyde, it is desirable to remove carbonyl impurities from the light liquid phase.

  Accordingly, although not illustrated in FIG. 1, as described above, all or part of the light liquid phase 133 and / or the heavy liquid phase 134 may be input to the PRC removal system. Preferably, the reflux ratio of the portion charged into the PRC removal system and the light liquid phase 133 is controlled so that the water in the side stream 123 and hydrogen iodide and the water recycled to the reactor have a desired balance. May be.

  [0051] In some embodiments, all or part of the heavy liquid phase 134 containing more methyl acetate and methyl iodide than the light liquid phase 133 may be recycled to the reactor 105 and / or the first The column 120 may be refluxed. Carbonyl impurities may be further removed from the heavy liquid phase 134 in the same manner as described for the light liquid phase 133.

  [0052] In one aspect, the concentration of hydrogen iodide in the side stream 123 may be determined by supplying the sample stream 141 to the online analyzer 142. The online analyzer 142 provides real-time measurements or near real-time measurements. In one aspect, any suitable analyzer such as a chromatography mass spectrometer, selected ion monitor, mass spectrometer, infrared spectrometer, resonance frequency analyzer, ultrasonic concentration analyzer, etc. may be used, but is not limited thereto. Not.

  [0053] The acetic acid removed via the side stream 123 is further purified by a second tower 125 (also referred to as a drying tower) or the like, and the side stream 123 is converted into an overhead stream 126 mainly composed of water, and mainly acetic acid. Preferably, the bottom stream 127 (also referred to as acetic acid product stream) is separated. Acetic acid may also be recovered from near the bottom of the second column 125 as a side stream. Overhead stream 126 may contain 50 to 75 weight percent water. Also, methyl acetate and methyl iodide are removed from the side stream and concentrated in an overhead stream. The drying tower bottom stream 127 preferably comprises acetic acid or consists essentially of acetic acid. In preferred embodiments, the drying tower bottom stream 127 comprises greater than 90% by weight acetic acid, such as greater than 95% or 98% by weight acetic acid. The drying tower bottom stream 127 may be further processed, such as passing through an ion exchange resin, before being stored or transported for commercial use.

  [0054] Similarly, the overhead stream 126 from the second column 125 contains reaction components such as methyl iodide, methyl acetate, water, etc., but it is preferred to retain these reaction components in the process. As shown, overhead stream 126 is condensed by a heat exchanger to produce stream 138 that is recycled to reactor 105 and / or refluxed to second column 125. Off-gas components may be discharged from the condensed low boiling overhead vapor stream 126 via line 137. Similar to the condensed low boiling overhead vapor stream from the first column 120, the condensed overhead stream 138 may also be separated into an aqueous phase and an organic phase, and these phases can be recycled or refluxed as required. The desired concentration may be maintained in the reaction medium.

  [0055] In particular, these lines may be fed to the scrubber to recover residual liquid from the exhaust streams of lines 106, 132, 137. The scrubber is operated with cold methanol and / or acetic acid to remove methyl acetate and methyl iodide. A suitable scrubber is described in US Pat. No. 8,318,977, the entire contents of which are hereby incorporated by reference.

[0056] The distillation column of the present invention may be a conventional distillation column such as a plate column, packed column, or other column. Examples of the material for the distillation column include, but are not limited to, glass, metal, ceramics, and other suitable materials. In the case of a plate column, the number of theoretical plates depends on the components to be separated, and can be 50 or less, such as 5 to 50, or 7 to 35.
Guard floor
[0057] Carboxylic acid streams (eg, acetic acid streams) contaminated with halides and / or corrosive metals may be contacted with the ion exchange resin composition of the present invention under a variety of operating conditions. This ion exchange resin composition is preferably provided in the guard bed. Purifying a contaminated carboxylic acid stream using a guard bed is described, for example, in US Pat. Nos. 4,615,806, 5,653,853, 5,731,252, and 6,225,498. The entire contents of which are incorporated herein by reference. Generally, a contaminated liquid carboxylic acid stream is contacted with the ion exchange resin composition of the present invention, which is preferably provided in a guard bed. For example, halide contaminants such as iodide contaminants react with metals to form metal iodides. In some embodiments, hydrocarbon moieties that may bind to iodide, such as methyl groups, may esterify carboxylic acids. For example, in the case of acetic acid contaminated with methyl iodide, methyl acetate is produced as a byproduct of iodide removal. This esterification formation usually does not deleteriously affect the treated carboxylic acid stream.

  [0058] The pressure in the contacting step is limited only by the physical strength of the resin. In one aspect, the contacting is performed at a pressure in the range of 0.1 MPa to 1 MPa, such as 0.1 MPa to 0.8 MPa, or 0.1 MPa to 0.5 MPa. However, for convenience, it is preferred to treat both the contaminated carboxylic acid stream as a liquid by defining both pressure and temperature. Thus, for example, in operation at atmospheric pressure, which is generally preferred from an economic point of view, the temperature may range from 17 ° C. (freezing point of acetic acid) to 118 ° C. (boiling point of acetic acid). It is within the purview of those skilled in the art to determine equivalent ranges for product streams containing other carboxylic acid compounds. It is preferable to keep the temperature of this contact step relatively low to minimize resin degradation. In one aspect, the contacting step is performed at a temperature in the range of 25 ° C to 120 ° C, such as 25 ° C to 100 ° C, or 50 ° C to 100 ° C. Some cationic macroreticular resins usually begin to degrade at temperatures of 150 ° C. (due to the reaction mechanism of acid-catalyzed aromatic desulfonation). Carboxylic acids having 5 or less carbon atoms, such as 3 or less, remain liquid at temperatures in this range. Therefore, the temperature at the time of contact must be kept lower than the deterioration temperature of the resin used. In some embodiments, the operating temperature is kept below the temperature limit of the resin to match the liquid phase operation and the desired reaction rate for halide removal.

  [0059] The configuration of the guard bed within the acetic acid purification system may vary widely. For example, a guard bed may be provided after the drying tower for treating the acetic acid product. In addition or alternatively, a guard bed may be provided after the heavy removal tower or finishing tower. It is preferred to provide a guard bed at a location where the temperature of the acetic acid product stream is low, for example below 120 ° C or below 100 ° C. In addition to the advantages described above, when the operating temperature is low, there is less corrosion than when the operating temperature is high. When the operating temperature is low, formation of corrosive metal contaminants that may reduce the total life of the resin as described above is suppressed. Moreover, since corrosion is suppressed when the operating temperature is low, there is an advantage that the container does not need to be made of an expensive corrosion-resistant metal. For example, a lower grade metal such as general stainless steel may be used.

  [0060] In one aspect, the flow rate at the guard bed ranges from 0.1 bed volumes per hour (BV / hr) to 50 BV / hr, such as 1 BV / hr to 20 BV / hr, or 6 BV / hr. -10 BV / hr. The bed volume of the organic medium is the volume of the medium equal to the volume occupied by the resin bed. A flow rate of 1 BV / hr means that an amount of organic liquid equal to the volume occupied by the resin bed passes through the resin bed in one hour.

[0061] To avoid depleting the resin with a purified acetic acid product having a high total iodide concentration, in one embodiment, the total iodide concentration of the purified acetic acid product is 5 wppm or less, for example, preferably 1 wppm or less. The purified acetic acid product in the bottom stream 127 is contacted with the guard bed. In one exemplary aspect, the total iodide concentration of the purified acetic acid product may be from 0.01 wppm to 5 wppm, such as from 0.01 wppm to 1 wppm. If the iodide concentration exceeds 5 wppm, re-treatment of non-standard acetic acid may be required. The total iodide concentration include iodides from both inorganic sources such as organic sources, and hydrogen iodide, such as iodide C ₁ -C ₁₄ alkyl. As a result of the treatment on the guard bed, a purified acetic acid composition is obtained. In one aspect, the purified acetic acid composition comprises less than 100 wppb iodide, such as less than 90 wppb, less than 50 wppb, or less than 25 wppb. In one aspect, the purified acetic acid composition comprises less than 1000 wppb corrosive metal, such as less than 750 wppb, less than 500 wppb, or less than 250 wppb. With respect to the range, the purified acetic acid composition may comprise 0-100 wppb, such as 1-50 wppb iodide and / or 0-1000 wppb, such as 1-500 wppb corrosive metal. In other embodiments, the guard bed removes at least 25 wt%, such as at least 50 wt%, or at least 75 wt% iodide from the crude acetic acid product. In one aspect, the guard bed removes at least 25 wt%, such as at least 50 wt%, or at least 75 wt% corrosive metal from the crude acetic acid product.

  [0062] Although the present invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those skilled in the art. In view of the above description, all references and disclosures related to relevant knowledge in the field, [Background Art] and [Mode for Carrying Out the Invention] are incorporated herein by reference. It is. It should also be understood that various features recited in aspects and aspects of the present invention, the following description and / or the appended claims may be combined or interchanged in whole or in part. May be. Those skilled in the art will appreciate that, in the above description of various aspects, aspects referring to other aspects may be combined appropriately with other aspects. Further, those skilled in the art will appreciate that the above description is illustrative only and is not intended to limit the invention.

[0063] The invention will be better understood by the following non-limiting examples.
Comparative Example 1-When the light liquid phase is not recycled
[0064] As a typical example, a sidestream HI concentration was determined by titrating a sidestream sample (0.2 g) with 0.01 M lithium acetate in acetone (50 ml). The end point was determined in a dynamic equivalent point titration mode using a pH electrode with a titrator Metrohm 716 DMS Titrino. Based on the consumption amount of the lithium acetate titration reagent, the HI concentration was calculated by weight% from the following formula.

[0065] A side flow composition sample containing about 1.9 wt% water was tested using this HI titration method. The HI concentration varied from 50 wppm to 300 wppm. The light liquid phase from the overhead light fraction is not recycled to the reactor at all. When the light liquid phase is not recycled, the HI concentration tends to be high.
Example 1-Recycling a light liquid phase
[0066] A portion of the light liquid phase from the overhead light fraction is recycled to the reactor to reduce the sidestream water content. The side stream contains 1.5 wt% water and less than 25 wppm HI with the balance being acetic acid, methyl acetate and methyl iodide. The HI concentration was too low to be measured directly by titration. There are other cations that make it difficult to directly measure the HI concentration. The total amount of inorganic iodide, i.e. the maximum possible total HI amount, is measured directly. These other inorganic iodides may contain corrosive metal iodides in addition to lithium iodide.
The description of the scope of claims at the time of filing is shown below.
[Claim 1]
Preparing a reaction system comprising a reactor and a flash vessel;
Forming a reaction medium in the reactor;
Separating the reaction medium into a liquid recycle stream and a vapor product stream in the flash vessel;
Distilling at least a portion of the vapor product stream in a first column to obtain a low boiling overhead vapor stream comprising a side stream and greater than 5 wt% water;
Condensing at least a portion of the low boiling overhead stream and separating it into two phases to form a heavy liquid phase and a light liquid phase;
Controlling the recycling rate of the light liquid phase to the reaction system to maintain the water concentration in the side stream at 1 to 3% by weight, and maintaining the hydrogen iodide concentration in the side stream at 50 wppm or less; And a method of producing acetic acid comprising distilling at least a portion of the side stream in a second column to obtain a purified acetic acid product.
[Claim 2]
The method of claim 1, wherein the reaction medium comprises methyl acetate, water, metal catalyst, iodide salt and methyl iodide.
[Claim 3]
The reaction medium comprises 0.5-30% by weight methyl acetate, 0.1-14% by weight water, 200-3000 wppm metal catalyst, 1-25% by weight iodide salt, and 1-25% by weight. The method of claim 1 comprising methyl iodide.
[Claim 4]
The process according to claim 1, wherein the water concentration in the side stream is maintained at 1.1 to 2.5% by weight.
[Claim 5]
The method of claim 1, wherein the hydrogen iodide concentration in the side stream is maintained between 0.1 and 50 wppm.
[Claim 6]
The method of claim 1, wherein the side stream further comprises 0.1 to 6% by weight of one or more iodide C ₁ -C ₁₄ alkyl.
[Claim 7]
The method of claim 1, wherein the side stream further comprises 0.1 to 6 wt% methyl acetate.
[Claim 8]
The method according to claim 1, wherein the concentration of hydrogen iodide in the side stream is determined by potentiometric titration using lithium acetate as a titration reagent.
[Claim 9]
The method of claim 1, wherein the recycling rate is increased when the hydrogen iodide concentration exceeds a predetermined threshold.
[Claim 10]
The process of claim 1, wherein the first column is operated at a reflux ratio of 0.05 to 0.4.
[Claim 11]
The method of claim 1, further comprising refluxing the heavy liquid phase, the light liquid phase, or a mixture thereof to the first column.
[Claim 12]
The process according to claim 1, wherein the light liquid phase comprises 40-80 wt% water.
[Claim 13]
The method of claim 1, further comprising contacting the purified acetic acid product with a guard bed when the total iodide concentration of the purified acetic acid product is 5 wppm or less.
[Claim 14]
Preparing a reaction system comprising a reactor and a flash vessel;
Forming a reaction medium in the reactor;
Separating the reaction medium into a liquid recycle stream and a vapor product stream in the flash vessel;
Distilling at least a portion of the vapor product stream in a first column to obtain a side stream and a low boiling overhead vapor stream;
Condensing at least a portion of the low boiling overhead stream and separating it into two phases to form a heavy liquid phase and a light liquid phase;
Measuring the hydrogen iodide concentration in the side stream;
Controlling the recycle rate of the light liquid phase to the reaction system in accordance with the measured hydrogen iodide concentration to maintain the hydrogen iodide concentration in the side stream at 50 wppm or less; To produce a purified acetic acid product by distilling at least a portion of the side stream.
[Claim 15]
The method according to claim 14, wherein the concentration of hydrogen iodide in the side stream is measured by potentiometric titration using lithium acetate as a titration reagent.
[Claim 16]
The method of claim 14, wherein the first column is operated at a reflux ratio of 0.05 to 0.4.
[Claim 17]
The process according to claim 14, wherein the hydrogen iodide concentration in the side stream is maintained between 0.1 and 50 wppm.
[Claim 18]
15. A process according to claim 14, wherein the water concentration in the side stream is maintained between 1 and 3% by weight.
[Claim 19]
Preparing a reaction system comprising a reactor and a flash vessel;
Forming a reaction medium in the reactor;
Separating the reaction medium into a liquid recycle stream and a vapor product stream in the flash vessel;
A low-boiling overhead vapor stream by distillation at least a portion of the vapor product stream in the first column, 1 to 3 wt% of water, 0.1 to 6% by weight of one or more iodide C ₁ -C Obtaining a side stream comprising ₁₄ alkyl and 50 wppm or less of hydrogen iodide,
Distilling at least a portion of the side stream in a second column to obtain a purified acetic acid product, and guarding the purified acetic acid product when the total iodide concentration of the purified acetic acid product is 5 wppm or less; A method for producing acetic acid comprising contacting with a floor.
[Claim 20]
19. A process according to claim 18, wherein the hydrogen iodide concentration in the side stream is maintained between 0.1 and 50 wppm.

Claims (19)

Preparing a reaction system comprising a reactor and a flash vessel;
Forming in the reactor a reaction medium comprising acetic acid, methyl acetate, water, metal catalyst, iodide salt and methyl iodide ;
In the flash vessel, the reaction medium is a liquid recycle stream containing acetic acid, a metal catalyst and a corrosive metal, and a vapor containing acetic acid, methyl acetate, water, hydrogen iodide, methyl iodide and permanganate reducing compound (PRC). Separating into product logistics,
Distill at least a portion of the vapor product stream in the first column to obtain a side stream comprising acetic acid and a low boiling overhead vapor stream comprising methyl acetate, methyl iodide, PRC, and greater than 5 wt% water. about,
Condensing and separating at least a portion of the low boiling overhead stream into two phases to form a heavy liquid phase that is an organic phase and a light liquid phase that is an aqueous phase ;
Controlling the recycling rate of the light liquid phase to the reaction system to maintain the water concentration in the side stream at 1 to 3% by weight, and maintaining the hydrogen iodide concentration in the side stream at 50 wppm or less; And a method of producing acetic acid comprising distilling at least a portion of the side stream in a second column to obtain a purified acetic acid product.   The method of claim 1, wherein the reaction medium comprises methyl acetate, water, metal catalyst, iodide salt and methyl iodide.   The reaction medium comprises 0.5-30% by weight methyl acetate, 0.1-14% by weight water, 200-3000 wppm metal catalyst, 1-25% by weight iodide salt, and 1-25% by weight. The method of claim 1 comprising methyl iodide.   The process according to claim 1, wherein the water concentration in the side stream is maintained at 1.1 to 2.5% by weight.   The method of claim 1, wherein the hydrogen iodide concentration in the side stream is maintained between 0.1 and 50 wppm. The method of claim 1, wherein the side stream further comprises 0.1 to 6% by weight of one or more iodide C ₁ -C ₁₄ alkyl.   The method of claim 1, wherein the side stream further comprises 0.1 to 6 wt% methyl acetate.   The method according to claim 1, wherein the concentration of hydrogen iodide in the side stream is determined by potentiometric titration using lithium acetate as a titration reagent.   The method of claim 1, wherein the recycling rate is increased when the hydrogen iodide concentration exceeds a predetermined threshold.   The process of claim 1, wherein the first column is operated at a reflux ratio of 0.05 to 0.4.   The method of claim 1, further comprising refluxing the heavy liquid phase, the light liquid phase, or a mixture thereof to the first column.   The process according to claim 1, wherein the light liquid phase comprises 40-80 wt% water.   The method of claim 1, further comprising contacting the purified acetic acid product with a guard bed when the total iodide concentration of the purified acetic acid product is 5 wppm or less. Preparing a reaction system comprising a reactor and a flash vessel;
Forming in the reactor a reaction medium comprising acetic acid, methyl acetate, water, metal catalyst, iodide salt and methyl iodide ;
In the flash vessel, the reaction medium is a liquid recycle stream containing acetic acid, a metal catalyst and a corrosive metal, and a vapor containing acetic acid, methyl acetate, water, hydrogen iodide, methyl iodide and permanganate reducing compound (PRC). Separating into product logistics,
Distilling at least a portion of the vapor product stream in a first column to obtain a side stream comprising acetic acid and a low boiling overhead vapor stream comprising water, methyl acetate, methyl iodide and PRC ;
Condensing and separating at least a portion of the low boiling overhead stream into two phases to form a heavy liquid phase that is an organic phase and a light liquid phase that is an aqueous phase ;
Measuring the hydrogen iodide concentration in the side stream;
Controlling the recycle rate of the light liquid phase to the reaction system in accordance with the measured hydrogen iodide concentration to maintain the hydrogen iodide concentration in the side stream at 50 wppm or less; To produce a purified acetic acid product by distilling at least a portion of the side stream.   The method according to claim 14, wherein the concentration of hydrogen iodide in the side stream is measured by potentiometric titration using lithium acetate as a titration reagent.   The method of claim 14, wherein the first column is operated at a reflux ratio of 0.05 to 0.4.   The process according to claim 14, wherein the hydrogen iodide concentration in the side stream is maintained between 0.1 and 50 wppm.   15. A process according to claim 14, wherein the water concentration in the side stream is maintained between 1 and 3% by weight. 15. The method of claim 14, further comprising contacting the purified acetic acid product with a guard bed when the total iodide concentration of the purified acetic acid product is 5 wppm or less.

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