JP4077253B2 - Method for producing carbonyl compound - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a carbonyl compound. More specifically, the present invention reacts a carbonylation raw material such as methanol with carbon monoxide in the presence of a solid catalyst in which a noble metal complex such as a rhodium complex is supported on a carrier such as a pyridine resin containing quaternized nitrogen. The method of producing a carbonyl compound such as acetic acid to suppress elution of the catalytic metal into the reaction solution.
[0002]
[Prior art]
The method of producing acetic acid by reacting methanol and carbon monoxide in the presence of a noble metal catalyst is well known as the so-called “Monsanto method”. Initially, this method is based on a homogeneous catalytic reaction in which methanol and carbon monoxide are reacted in a reaction solution in which a rhodium compound as a catalyst metal and methyl iodide as a reaction accelerator are dissolved in an acetic acid solvent containing water (for example, a special catalyst reaction). No. 47-3334), but as a modified method thereof, a heterogeneous catalytic reaction using a solid catalyst carrying a rhodium compound (for example, JP-A 63-253047) was developed. In the case of homogeneous catalytic reactions, the reaction rate cannot be increased due to the low solubility of the catalytic metal in the solvent, the problem is that the size of the reactor is increased, and the reaction rate and acetic acid selectivity are increased and dissolved. In order to prevent the precipitation of the catalyst, it is necessary to have a certain amount of moisture in the reaction solution, which causes hydrolysis of methyl iodide used as a reaction accelerator, resulting in a decrease in yield and equipment. There is a background that a heterogeneous catalytic reaction with few such problems has been developed.
[0003]
Carbonylation of methanol by heterogeneous catalysis usually uses acetic acid as a solvent and heats methanol and carbon monoxide in the presence of a solid catalyst carrying a rhodium compound and methyl iodide as a reaction accelerator. The reaction is carried out in a reactor under pressure. The reaction product liquid extracted from the reactor is led to a separation system including means such as distillation, the produced acetic acid is separated and recovered, and the remaining liquid after separation is returned to the reactor. At this time, the inside of the reactor is a two-phase system in which solid catalyst particles are contained in a reaction solution composed of acetic acid, methanol, methyl iodide, etc. (more specifically, a three-phase system in which bubbles of carbon monoxide gas are further included). That is, it is a heterogeneous system. The reaction solution contains, in addition to the above components, methyl acetate, dimethyl ether, hydrogen iodide, water, and the like, which are reaction byproducts. As the solid catalyst, a catalyst in which a rhodium complex is supported on insoluble resin particles containing a pyridine ring in the molecular structure is usually used.
[0004]
[Problems to be solved by the invention]
The solid catalyst has a form in which a basic nitrogen atom contained in a pyridine ring of a resin carrier is quaternized with a methyl group, and a rhodium complex ion [Rh (CO) ₂ I ₂ ] ⁻ is adsorbed in an ion exchange manner. Take. This binding is due to an equilibrium reaction that is greatly inclined toward the adsorption side. Even if acetate ions or iodine ions are present in the liquid phase in the reactor, rhodium complex ions are substantially eliminated from the resin carrier. Although there was almost no, it was found that rhodium gradually moved into the liquid phase when the operation was continued for a long time. When the amount of rhodium transferred into the liquid phase increases, it causes inconveniences such as rhodium precipitating with the flasher, accompanying mist, or entering the purge flow from the process, and rhodium is lost from the reactor. As a result, the catalyst function decreases. Furthermore, the loss of expensive rhodium not only reduces productivity, but also significantly increases the cost of the catalyst, and significantly impairs the economics of the process.
[0005]
According to the understanding of the inventors, the cause of the transfer of rhodium into the liquid phase is that the pyridine ring decomposes and desorbs from the resin carrier and moves into the liquid phase during long-time operation. That is, the rhodium complex ion and the quaternized nitrogen atom of the pyridine ring are in an ion exchange equilibrium relationship, and since this quaternized nitrogen atom has a high affinity for the rhodium complex ion, even if other anions exist. The rhodium complex ion does not easily desorb from the resin carrier. However, when a pyridine ring is present in the liquid phase, a part of the rhodium complex ion bonded to the resin carrier is part of the pyridine ring in the liquid phase. In some cases, it binds to the quaternized nitrogen atom of the resin and deviates from the resin carrier. As a result, if the concentration of the pyridine ring in the liquid phase can be suppressed, the migration of rhodium into the liquid phase can also be suppressed.
[0006]
In view of the above problems and considerations, an object of the present invention is to effectively prevent a noble metal such as rhodium from desorbing from a solid catalyst during operation and transferring to a liquid phase. Therefore, an object of the present invention is to provide a measure for preventing the concentration of a basic nitrogen compound such as pyridine in the liquid phase from increasing during operation.
[0007]
[Means for Solving the Problems]
The present invention provides a reaction step of reacting a carbonylation raw material with carbon monoxide to form a carbonyl compound in a liquid phase containing a solid catalyst having a noble metal complex supported on a resin carrier containing quaternized nitrogen, A method for producing a carbonyl compound comprising: a distillation step for recovering a gas phase fraction containing a carbonyl compound by distilling the reaction product solution from the reaction step; and a circulation step for circulating the bottoms from the distillation step to the reaction step. The present invention provides a method characterized in that at least a part of the bottoms is brought into contact with an acidic cation exchange resin, thereby solving the above-mentioned problems.
[0008]
A resin carrier containing quaternized nitrogen is typically a pyridine resin, that is, a resin containing in its structure a pyridine ring in which a nitrogen atom can be quaternized. For example, a copolymer of 4-vinylpyridine and divinylbenzene. Coalescence is typical. However, the present invention is not limited to this specific resin, and it is intended to comprehensively include resins containing basic nitrogen that can be quaternized to adsorb and support a noble metal complex. Accordingly, instead of 4-vinylpyridine, those containing various basic nitrogen-containing monomers such as 2-vinylpyridine having a different vinyl group position, substituted vinylpyridines such as vinylmethylpyridine, or vinylquinolines, or Instead of divinylbenzene, those containing various crosslinkable monomers having two or more groups containing an ethylenically unsaturated bond can be used. Furthermore, in addition to the basic nitrogen-containing monomer and the crosslinkable monomer, those containing other polymerizable comonomers such as styrene and methyl acrylate can also be used.
[0009]
The degree of cross-linking of the resin carrier (the content of the cross-linking monomer expressed in weight%) is preferably 10% or more, and more preferably 15 to 40%. If the degree of crosslinking is lower than 10%, swelling and shrinkage due to the composition of the liquid phase will be remarkable, and if the degree of crosslinking is too high, the content of basic nitrogen for supporting the noble metal complex will be too small. The content of basic nitrogen contained in the resin may be about 2 to 10 meq / g, more preferably 3.5 to 6.5 meq / g, in terms of basic equivalent. In general, basic nitrogen can exist in a form such as a free base form, an acid addition salt form, and an N-oxide form. In the present invention, a noble metal complex is adsorbed in an ion-exchange manner in a state where they are quaternized. Carry. The resin carrier is usually used in the form of spherical particles, and its particle size is generally 0.01 to 2 mm, preferably 0.1 to 1 mm, more preferably 0.25 to 0.7 mm.
[0010]
The noble metal complex supported on the resin carrier refers to a noble metal complex exhibiting a catalytic action for the carbonylation reaction, which is ion-exchanged and adsorbed on the quaternized nitrogen of the resin carrier. As such a noble metal, rhodium and iridium are known, but rhodium is generally preferably used. When a resin carrier and a rhodium halide are brought into contact with each other under a pressure of carbon monoxide (0.7 to 3 MPa) in a solution containing methyl iodide, the resin carrier can carry rhodium. At this time, the nitrogen atom in the resin carrier is quaternized, and the rhodium complex ion produced by the reaction of rhodium halide, methyl iodide and carbon monoxide, that is, rhodium carbonyl complex [Rh (CO) ₂ I _2] ^- ion exchange binds the solid catalyst used in the present invention is obtained.
[0011]
The carbonylation raw material refers to a material that reacts with carbon monoxide in the presence of the catalyst to form a carbonyl compound. Typically methanol, which reacts with carbon monoxide to produce acetic acid. At this time, a reaction accelerator such as methyl iodide is preferably added. This reaction is usually carried out using acetic acid as a reaction solvent. In this case, acetic acid is a reaction product and also serves as a reaction solvent. In this reaction, methyl acetate, dimethyl ether, water, and the like are produced as by-products, and these are returned to the reaction step as a residual liquid obtained by separating and recovering acetic acid as a product together with the solvent, reaction accelerator and unreacted raw material. The liquid phase in this reaction step consists of a mixture of all these components. The reaction step of the present invention can be carried out using various types of reactors such as a fixed bed, an expanded bed, a mixing tank, and any of batch operation and continuous operation may be employed. In particular, a continuous mixing tank in which the reaction conditions can be easily controlled is preferable.
[0012]
The reaction product liquid from the reaction process (in the case of a continuous mixing tank, the same composition as the liquid phase in the reaction process) is subjected to a separation operation in the next distillation process, and the produced acetic acid is separated and recovered as a product, and the remaining residue. The liquid is returned to the reaction step, except that a portion is purged from the process. In the distillation process, first, a part of the gas is vaporized in a flash evaporation section and separated into a gas phase and a liquid phase (flash evaporation process), and then the gas phase fraction is led to a light-end distillation column section to acetic acid from the lower part. A technique of separating and collecting (light end separation process) is taken. As described above, the reaction solution is a mixture of various components, and acetic acid is a component having a low volatility among them. This is because acetic acid cannot be recovered from the bottoms as a product because impurities (or non-volatile) are mixed. The flash evaporation section and the separation column section can be integrally provided at the bottom and upper part of a single tower, or can be configured as separate towers by dividing into a flasher and a light end distillation column. Since the carbonylation reaction is generally an exothermic reaction, by partially evaporating in the flash evaporation section, the liquid phase fraction returned to the reaction step can be cooled, and the heated reaction product liquid can be flushed. By introducing it into the evaporation section, it can function as an evaporator for the light end distillation column section.
[0013]
The bottoms from the distillation step (that is, the liquid phase fraction from the flash evaporation section) is returned to the reaction step, but the bottoms come into contact with the acidic cation exchange resin in the middle of the return path. The bottoms are mainly composed of acetic acid as a solvent. When basic nitrogen-containing molecules such as pyridine rings are decomposed and eluted from the resin medium of the solid catalyst, they are also included in the bottoms. When the bottoms containing such basic nitrogen-containing molecules (these are quaternized) are directly returned to the reaction step, such molecules accumulate in the liquid phase in the reaction step, and the solid catalyst resin Partitioning occurs between the basic nitrogen-containing sites in the support and the basic nitrogen-containing molecules in the liquid phase based on the ion exchange adsorption equilibrium of the noble metal complex. That is, the noble metal complex is liberated in the liquid phase, causing the problems described above.
[0014]
However, in the present invention, since the bottoms returning to the reaction step contacts the acidic cation exchange resin, the basic nitrogen-containing molecules in the bottoms are adsorbed and removed by the acidic cation exchange resin. In addition, there may be a concern that acetic acid contained in the bottoms may regenerate the acidic cation exchange resin and elute the adsorbed basic nitrogen-containing molecules. In addition to the large adsorption affinity of acidic cation exchange resins for molecules, acetic acid in the bottoms is hardly dissociated, and the hydrogen ion concentration does not have a regenerative effect. Is totally useless. Moreover, even if the noble metal complex ion moves into the liquid phase due to the dissolution and dissolution of the basic nitrogen-containing molecule, the basic nitrogen-containing molecule is adsorbed and removed by the acidic cation exchange resin, and then the process returns to the reaction step. At this point, it is supported again by ion exchange on the resin carrier of the solid catalyst.
[0015]
The acidic cation exchange resin used in the present invention is not particularly limited, but a porous one (macroporous type) having pores having a pore diameter of 20 nm or more is preferable. In addition, acidic cation exchange resins include strong acidic resins having sulfonic acid type ion exchange groups and weak acidic resins having carboxylic acid type ion exchange groups. However, they have selective adsorption properties for basic nitrogen-containing molecules. In view of this, a strongly acidic resin is preferable. As such, for example, Amber List 15 manufactured by Rohm and Haas is commercially available and can be suitably used. The type of apparatus for bringing the bottoms into contact with the cation exchange resin is not particularly limited, but in order to reliably remove the basic nitrogen-containing molecules, the can is placed in a column packed with the cation exchange resin. A fixed bed system for flowing out the effluent is preferred. In this case, if a plurality of columns are provided in parallel and adsorption and regeneration are performed cyclically, the bottoms can be processed continuously. The liquid passing temperature during the adsorption operation is preferably 30 to 100 ° C., and the residence time is preferably about 0.5 to 5 hours.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings, but it should be noted that the following description does not limit the present invention in any way.
[0017]
In FIG. 1, methanol and carbon monoxide, which are carbonyl raw materials, are introduced into a reactor 1. The distillation apparatus 2 has a flash evaporation section 2a at the bottom and a light-end distillation column section 2b at the top, and acetic acid as a reaction solvent circulates between the reactor 1 and the flash evaporation section 2a. The path where the bottoms mainly composed of acetic acid return from the flash evaporation section 2a to the reactor 1 branches in the middle, and a part of the bottoms passes through the acidic cation exchange resin column 3 and then returns to the reactor 1. It has become. The gas phase fraction from the flash evaporation section 2a flows into the light end distillation column section 2b, and gas-liquid contact separation is performed inside. Acetic acid is separated and recovered from the lower part of the light end distillation column part 2b, and components other than acetic acid and the unrecovered part of acetic acid are distilled from the top.
[0018]
In the reactor 1, a granular pyridine resin in which the pyridine portion is quaternized with an alkyl iodide and a resin catalyst composed of a rhodium carbonyl complex supported by ion exchange are dispersed in the liquid phase. The liquid phase contains acetic acid as a solvent, methyl iodide as a reaction accelerator, methanol as a reaction raw material, and various reaction byproducts. Carbon monoxide gas is blown into the reaction solution in which the resin catalyst is dispersed, and methanol reacts with carbon monoxide in the presence of a rhodium catalyst under the conditions of a reaction temperature of 100 to 200 ° C. and a reaction pressure of about 1 to 5 MPa. To produce acetic acid. Some methanol reacts with each other or with the produced acetic acid to produce by-products such as dimethyl ether, methyl acetate, and water.
[0019]
Only the reaction liquid is taken out from the reactor 1 through a screen or the like, and flows into the flash evaporation section 2a of the distillation apparatus 2. Here, a part of the reaction solution is vaporized by flash evaporation to become a gas phase fraction and flows into the upper light-end distillation column section 2b. In the light-end distillation column part, the gas phase fraction is separated, but by making a part of acetic acid having the lowest volatility among the components constituting the gas phase fraction be included in the overhead fraction, All other gas phase components can be included in the overhead fraction. Most of the acetic acid contained in the gas phase fraction in the flash evaporation section 2a is taken out from the lower part of the light end distillation column section, subjected to a necessary purification treatment, and then separated and recovered as a product. On the other hand, the column top fraction is returned to the reactor 1 after undergoing necessary adjustment and treatment such as separation and purging.
[0020]
The portion that has not been vaporized in the flash evaporation section accumulates in the bottom of the flash evaporation section 2a as a liquid phase fraction and is returned to the reactor 1 as a bottoms. A part of the bottoms returned to the reactor 1 passes through the acidic cation exchange resin column 3. Although the composition of the bottoms is mostly acetic acid as a solvent, impurities such as pyridine ring and rhodium carbonyl complex eluted from the solid catalyst in the reactor may be contained in a trace amount. Of these, accumulation of the pyridine ring in the reaction solution leads to elution of the rhodium carbonyl complex supported on the resin support of the solid catalyst as described above. In the present invention, however, the bottom of the pyridine ring is acidic. Since it is removed when it passes through the ion exchange resin column 3, it does not accumulate at a high concentration in the reaction solution. The rhodium carbonyl complex is not removed by the acidic cation exchange resin column 3, but is adsorbed and supported again on the solid catalyst resin carrier in the reactor 1 if no pyridine ring is accumulated in the reaction solution.
[0021]
FIG. 2 shows another embodiment of the present invention. The difference from the embodiment of FIG. 1 is that the distillation apparatus is composed of two columns, a flasher and a light-end distillation column. That is, in FIG. 2, methanol and carbon monoxide, which are carbonyl raw materials, are introduced into the reactor 11. Here, the distillation apparatus is composed of separate towers as the flasher 12 and the light end distillation column 13. Acetic acid as a reaction solvent circulates between the reactor 11 and the flasher 12. The path where the bottoms mainly composed of acetic acid return from the flasher 12 to the reactor 11 branches in the middle, and a part of the bottoms returns to the reactor 11 after passing through the acidic cation exchange resin column 14. ing. A gas phase fraction from the flasher 12 flows into the light end distillation column 13 and gas-liquid contact separation is performed inside. Acetic acid is separated and recovered from the lower part of the light-end distillation column 13, and components other than acetic acid and a portion of the acetic acid that has not been recovered are distilled from the top.
[0022]
The reactor 11, the flasher 12, the light end distillation column 13, and the acidic cation exchange resin column 14 are respectively the reactor 1, the flash evaporation unit 2a, the light end distillation column unit 2b, and the acidic cation exchange resin in FIG. Corresponds to column 3 and functions similarly to them. The embodiment of FIG. 2 is disadvantageous in that the number of columns is increased compared to FIG. 1, but the gas phase fraction from the flasher 12 is introduced into the middle rather than the bottom of the light end distillation column 13. Since the acetic acid recovered as a product is taken out from the bottom, there is an advantage that the recovered acetic acid can be taken out in a higher purity state.
[0023]
【Example】
Example 1
The continuous synthesis test of acetic acid was conducted with the pilot test apparatus shown in FIG. In the reactor 31, a mixed solution consisting of 8% by weight of methyl iodide, 12% by weight of methanol and 80% by weight of acetic acid, 5% by weight of pyridine resin (crosslinking degree 29%) and 0 as Rh. 0.05 wt% rhodium chloride was added, and CO was introduced and the temperature was raised to 180 ° C. while pressurizing to 2 MPa. Thereafter, continuous supply of methanol was started, and the reaction liquid in the reactor was continuously taken out. The taken out reaction liquid was led to the flasher 32 and separated into a gas phase component and a liquid phase component, the gas phase component was further led to a purification system, and the liquid phase component was returned to the reactor. On the other hand, the gas containing unreacted CO taken out from the top of the reactor was separated into CO and condensate by the condenser 33, the CO was burned by an incinerator, and the condensate was returned to the reactor.
[0024]
When the nitrogen concentration in the reaction solution flowing out from the reactor was measured by the chemiluminescence method, the nitrogen concentration gradually increased and reached 200 ppm after 2500 hours. Further, when the Rh concentration in the reaction solution was measured by an atomic absorption method, the Rh concentration gradually increased similarly and reached 50 ppm after 2500 hours. When the form of nitrogen present in the reaction solution was identified by an electrospray ionization mass spectrometer (ESI-MS), it was identified as the nitrogen-containing compound shown in FIG.
[0025]
Example 2
A pyridine resin quaternized with methyl iodide was immersed in acetic acid at 200 ° C. for several days, and the form of nitrogen eluted in acetic acid was identified by the same method. As in Example 1, the compound of FIG. Identified. Separately, acetic acid and a catalyst resin (in which pyridine resin was loaded with 1% by weight of rhodium) were placed in an autoclave, the gas phase was purged with CO, sealed, and heated to 180 ° C. Acetic acid containing a nitrogen-containing compound obtained as a result of the immersion was sequentially added to this, and the solution was sampled 3 minutes after the addition, and the nitrogen concentration and rhodium concentration were measured. The results are shown in Table 1.
[Table 1]
Rh concentration (ppm by weight) 5 15 30 38
N concentration (ppm by weight) 50 120 180 240
[0026]
From Table 1, it can be seen that the nitrogen concentration and rhodium concentration in the solution are almost proportional, and rhodium in the catalyst resin flows out into the solution due to ion exchange equilibrium with the free nitrogen-containing compound in the acetic acid solvent.
[0027]
Example 3
Acetic acid containing a nitrogen-containing compound obtained by immersion in Example 2 was adjusted so that the nitrogen concentration in acetic acid was 50 ppm, and rhodium chloride was added so that the Rh was 10 ppm. % Of methyl iodide was added. When the prepared acetic acid solution was pressurized with 2 MPa of CO in an autoclave and treated at 180 ° C. for 1 hour, a light yellow transparent solution (color of Rh complex) was obtained. The obtained solution was passed through an adsorption tower packed with a cation exchange resin (Rum & Haas Amberlyst 15) in a column having a heat insulation jacket in a residence time of 1 hour. The results of measuring the nitrogen concentration and Rh concentration in the effluent are shown in FIG. It can be seen that only the nitrogen compound is adsorbed and removed, and the rhodium complex passes through the column.
[Brief description of the drawings]
FIG. 1 shows a preferred mode for carrying out the method of the present invention.
FIG. 2 shows another preferred embodiment for carrying out the present invention.
FIG. 3 shows an apparatus used in an acetic acid synthesis pilot test of an example.
FIG. 4 shows a chemical structural formula of a nitrogen-containing compound eluted from a pyridine resin.
FIG. 5 shows the concentrations of nitrogen and rhodium in the liquid flowing out from the cation exchange resin column.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reactor 2 Distillation apparatus 2a Flash evaporation part 2b Light end distillation column part 3 Acid cation exchange resin column 11 Reactor 12 Flasher 13 Light end distillation column 14 Acid cation exchange resin column 31 Carbonylation reactor 32 Flasher 33 Condenser

Claims (10)

A reaction step in which a carbonylation raw material is reacted with carbon monoxide to form a carbonyl compound in a liquid phase containing a solid catalyst having a noble metal complex supported on a resin carrier containing quaternized nitrogen,
A carbonyl compound comprising: a distillation step of distilling the reaction product solution from the reaction step to recover a gas phase fraction containing a carbonyl compound; and a circulation step of circulating the bottoms from the distillation step to the reaction step. In the manufacturing method,
A method comprising contacting at least part of the bottoms with an acidic cation exchange resin. The method according to claim 1, wherein the resin carrier containing quaternized nitrogen comprises a pyridine resin. The method according to claim 1 or 2, wherein the noble metal complex is a rhodium complex. Complexes of rhodium _{[Rh (CO) 2 I 2} ] - The method of claim 3, wherein. The method according to any one of claims 1 to 4, wherein acetic acid is used as a solvent in the reaction step. The method according to any one of claims 1 to 5, wherein the distillation step comprises a flash evaporation step and a light end separation step. The method of claim 6, wherein the flash evaporation step and the light end separation step are carried out in the same column. The method of claim 6, wherein the flash evaporation step and the light end separation step are carried out in separate columns. The method according to claim 1, wherein the acidic cation exchange resin is a strongly acidic resin. The method according to any one of claims 1 to 9, wherein the acidic cation exchange resin is a macroporous resin having pores having a pore diameter of 20 nm or more.

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