JPH10114701A - Production of acetic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acetic acid producing process having improved economical efficiency, space time yield, degree of conversion by isomerizing methyl formate under the pressence of a rhodium catalyst, an iodine compound and carbon monoxide by using a specific equipment and a piston flow system. SOLUTION: Acetic acid is obtained by carrying out the isomerization of methyl fomate under the presence of 100-10,000ppm of the rhodium catalyst (e.g. rhodium iodide) in the reaction medium, 5-20wt.%. of the iodine compound (e.g. methyl iodide) in the reaction medium, partial pressure 0.1-50 atmospheric pressure of carbon monoxide, using a pipe and/or tower type reactor, having <0.1% of water, in the piston flow type system, under the condition of 1-100 atmospheric pressure of total pressure, at 100-240 deg.C. Following this process, acetic acid is obtained free from the restriction of high purity production system of carbon monoxide and reducing the energy cost regard for the purification of the product acetic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing acetic acid. More specifically, the present invention relates to a method for producing acetic acid by reacting methyl formate as a raw material under carbon monoxide pressure. Acetic acid is a basic chemical used industrially as a raw material for acetic esters, acetic anhydride, vinyl acetate, and terephthalic acid.

[0002]

2. Description of the Related Art A method for producing acetic acid by reacting methanol with carbon monoxide in the presence of a rhodium compound and methyl iodide in the presence of a rhodium compound and methyl iodide is widely practiced industrially as the Monsanto process. In recent years, as an improved method of the Monsanto method, a technique has been disclosed in which the water concentration in a reaction solution is reduced to 5% by weight or less to suppress a water gas shift reaction which is a side reaction and increase the productivity of acetic acid (Japanese Patent Application Laid-open No. Sho. 60-
239434, JP-A-60-54334). Since then
Described as the improved Monsanto method. However, according to the prior art relating to the carbonylation reaction of methanol, the production of acetic acid requires an amount of high-purity carbon monoxide that is larger than the amount of acetic acid produced. The Monsanto method has a disadvantage in that the cost of generating carbon monoxide is approximately the same as the cost of the carbonylation step. The coexistence of water is essential in the production of acetic acid by the carbonylation reaction of methanol, and even if the water concentration in the reaction solution is reduced to 5% by weight or less as shown in the improved method, it is impossible to completely suppress the water gas shift reaction. In addition, there is a disadvantage that a large amount of energy is required for separating water in a distillation step in order to obtain a product acetic acid. Further, in the carbonylation reaction of methanol, since a complete mixing tank type reactor having a stirrer is used to promote the dissolution of carbon monoxide in the liquid phase catalyst, there is a disadvantage that a stirring power is required.

[0003] There is disclosed a technique in which a mixed raw material of methanol and methyl formate is introduced into a carbonylation reaction condition of methanol so as to be released from the restriction of a facility for producing carbon monoxide (JP-A-7-291892). However, the present inventors have examined that, when methyl formate is introduced in the presence of water under the carbonylation reaction conditions of methanol, hydrolysis of methyl formate occurs to produce methanol and formic acid, and the methanol generated here is Acetic acid is formed by a carbonylation reaction that consumes carbon monoxide. Acetyl iodide, which is produced as an intermediate in the reaction system, preferentially undergoes hydrolysis with water, so no new carbon monoxide is generated in the system due to the reaction with formic acid. Cannot be reduced. (1) Methanol carbonylation reaction CH ₃ OH + CH ₃ COOH → CH ₃ COOCH ₃ + H ₂₀ CH ₃ COOCH ₃ + HI → CH ₃ COOH + CH ₃ I CH ₃ I + CO → CH ₃ COI CH ₃ COI + H ₂₀ → CH ₃ COOH + HI ───────────────────────────── CH ₃ OH + CO → CH ₃ COOH (2) Isomerization reaction of methyl formate HCOOCH ₃ + CH ₃ COOH → CH ₃ COOCH ₃ + HCOOH CH ₃ COOCH ₃ + HI → CH ₃ COOH + CH ₃ I CH ₃ I + CO → CH ₃ COI CH ₃ COI + HCOOH → CH ₃ COOH + CO + HI ────────────── HCOOCH ₃ → CH ₃ COOH also formic acid with some by-produced methyl acetate A process that recycles catalyst and by-products because the amount of by-product formic acid that is converted to acetic acid and methyl formate by the stele exchange reaction but is not consumed in the reaction with acetyl iodide exceeds the amount of by-product methyl acetate. Has the disadvantage that formic acid accumulates and cannot be established as a process.

On the other hand, as a method for producing acetic acid by heating and isomerizing methyl formate under carbon monoxide pressure, a method using rhodium as a catalyst (JP-A-49-3513) and a method using rhodium metal atom and iodine are disclosed. When using a homogeneous catalyst system comprising a mixture of lithium iodide and methyl iodide
149542) is known. However, according to the prior art relating to these methyl formate isomerization reactions, a space-time yield comparable to the Monsanto method cannot be obtained,
Since the conversion of methyl formate was not sufficient, the amount of unreacted methyl formate recycled increased. In addition, formic acid and methyl acetate, which are by-products that can be converted into acetic acid, are produced in large amounts, and they have a disadvantage that their recycling requires a large amount of energy.

[0005]

The production of acetic acid by isomerization of methyl formate is different from the carbonylation reaction of methanol in that the coexistence of water is not an essential condition. Does not require energy. An object of the present invention is to overcome the drawbacks of the method for producing acetic acid by isomerization of methyl formate and to provide a more economical method for producing acetic acid over the Monsanto method and the improved Monsanto method.

[0006]

Means for Solving the Problems The present inventors have conducted various studies, and found that methyl formate is used as a raw material,
In the production of acetic acid, the inventors have found a method for producing acetic acid which is free from the restrictions of the production equipment for high-purity carbon monoxide and minimizes the energy cost required for purifying the product acetic acid. In addition, to sufficiently increase the space-time yield and conversion, which were problems,
The minimization of the production of formic acid and methyl acetate, which are convertible by-products, was made possible by changing the reactor and the reaction mode to those suitable for the isomerization reaction of methyl formate.

That is, the present invention relates to a method for producing acetic acid, comprising reacting methyl formate as a raw material in the presence of a rhodium catalyst, an iodine compound and carbon monoxide. Methods for producing methyl formate include carbonylation with methanol and carbon monoxide, dehydrogenation of methanol, esterification of formic acid with methanol, dimerization of formaldehyde, and methanol /
A co-production method of methyl formate and a co-production method of methanol / methyl formate from carbon dioxide and hydrogen are known. Although any method may be used for producing methyl formate, the use of methyl formate produced by a dehydrogenation method of methanol is most preferable for the application of this method. If methyl formate produced by the present invention and the methanol dehydrogenation method is used as a raw material, a large-scale high-purity carbon monoxide production facility required for methanol carbonylation reaction is not required. Further, by applying both methods, a production process of acetic acid using only methanol as a raw material is obtained. Dehydrogenation Methyl formate is produced adjacent to a methanol production plant, and the raw material methyl formate may be transported to a remote acetic acid plant, or methanol may be transported from a remote location and dehydrated adjacent to the acetic acid plant. Methyl formate may be produced in the methyl formate production plant of the elementary method.

BEST MODE FOR CARRYING OUT THE INVENTION

As the catalyst for the production of acetic acid in the present invention, metals of Group 8 of the periodic table can be used, but rhodium is particularly preferred because of its high activity. Rhodium may be used in any form as long as it is soluble under the reaction conditions and can form a rhodium carbonyl complex species in the reaction system. Industrially, rhodium iodide and the like are exemplified, but not limited thereto. The rhodium concentration in the reaction solution is 100 to 10,000.
0 ppm, preferably 200 to 3,000 ppm.

In the production of acetic acid in the present invention, it is preferable to add an iodine compound to the reaction system. As the iodine compound, methyl iodide and lithium iodide are particularly preferred. It is most preferable to use a mixture of lithium iodide and methyl iodide as known in JP-A-60-149542. Methyl iodide can be directly added to the reaction system, or may be added in such a manner that methyl iodide is generated in the reaction system. When the concentration of methyl iodide in the reaction solution is high, the isomerization reaction of methyl formate is promoted, but it is necessary to recover methyl iodide and recycle it to the reactor. The most economically advantageous concentration of methyl iodide in the reaction solution is 5 to 20 wt.
% Range. Lithium iodide can be directly added to the reaction system, or may be added in such a manner that lithium iodide is generated in the reaction system. When the concentration of lithium iodide in the reaction solution is high, the isomerization reaction of methyl formate is promoted,
It must be below the solubility limit under the reaction conditions. If the concentration is too high, problems such as an increase in the amount of circulating catalyst and an increase in the size of the reactor, an increase in the amount of iodine ions mixed into the product acetic acid, and an increase in the corrosiveness of the entire process are pointed out. Is done. However, the concentration of lithium iodide is 2 to 2
0 wt% is preferred.

In the present invention, the concentration of water in the reaction solution for producing acetic acid is preferably substantially anhydrous under 0.1% by weight. Unlike the carbonylation reaction of methanol, coexistence of water in the reaction system is not essential in the isomerization reaction of methyl formate. The coexistence of water is accompanied by a water gas shift as a side reaction, resulting in the accumulation of substantially unnecessary carbon dioxide and harmful hydrogen in the reaction gas. As a result, it becomes necessary to purge unnecessary reaction gas and increase the reaction pressure to maintain the carbon monoxide partial pressure necessary for holding the rhodium carbonyl complex. When the reaction is carried out under a substantially anhydrous condition with a water concentration of 0.1% by weight or less, the generation of carbon dioxide and harmful hydrogen is almost negligible. Since it is dissolved and discharged out of the reaction system, it does not accumulate in the reactor. In other words, there is no need to purge the reaction gas or increase the reaction pressure, and there is no loss of carbon monoxide or pressure increase of the recycle gas more than necessary. On the other hand, when the water content is high, loss of carbon monoxide due to the water gas shift reaction and many by-products such as carbon dioxide and hydrogen occur. When carbon dioxide or the like accumulates in the system, the carbon monoxide partial pressure decreases. Therefore, a large amount of the reaction gas must be purged as compared with the condition of substantially anhydrous water to supplement carbon monoxide. In addition, in the coexistence of water, methyl formate is hydrolyzed to produce methanol and formic acid. The methanol produced here is converted to acetic acid by carbonylation consuming carbon monoxide. However, under substantially anhydrous conditions having a water concentration of 0.1% by weight or less, hydrolysis of methyl formate does not occur. Do not consume. In addition, accumulation of formic acid in the system can be prevented. The water concentration in the reaction solution in the carbonylation reaction of methanol is 15% by weight in the Monsanto method and 5% by weight in the improved Monsanto method. In the purification of acetic acid from the reaction solution, a large amount of energy is consumed for separating acetic acid and water. It is known. In the production of acetic acid by isomerization of methyl formate according to the present invention, the reaction is carried out under substantially anhydrous conditions, so that the energy required for purification of acetic acid is one-third that of the Monsanto method.
In the following, a significant energy reduction of less than half of the improved Monsanto method can be achieved.

The present invention is carried out in the presence of carbon monoxide. The high-purity carbon monoxide used need not necessarily be pure. Traces of inert gases such as carbon dioxide, nitrogen and methane do not interfere. The partial pressure of carbon monoxide only needs to have a pressure necessary for holding the rhodium carbonyl complex. In the isomerization of methyl formate, which is carried out under substantially anhydrous conditions, there is no loss of carbon monoxide due to the shift reaction, so only the amount dissolved in the product liquid and discharged out of the reaction system can be compensated. Good, almost negligible. Even in large acetic acid production plants,
With such an amount of carbon monoxide, a large-scale facility for producing carbon monoxide is not required. Although the use of a carbon monoxide cylinder can be used, the most suitable industrial method for obtaining small-scale carbon monoxide is a method for obtaining carbon monoxide by decomposition of methyl formate. Using this method, carbon monoxide to maintain the required partial pressure can be prepared without a compressor.

The required carbon monoxide partial pressure in the present invention is:
0.1 to 50 atm. Total reaction pressure is 1-100a
tm, preferably 10 to 50 atm. The reaction temperature is 100 to 240 ° C, preferably 180 to 210 ° C. In a methyl formate isomerization reaction carried out under substantially anhydrous conditions, methanol
Since a shift reaction that rapidly proceeds at a temperature of 5 ° C. or more does not occur, the reaction rate can be improved at a temperature of 185 ° C. or more.

In the methyl formate isomerization reaction of the present invention, formic acid and methyl acetate, which are by-products that can be converted into acetic acid, are produced by a transesterification reaction between methyl formate and acetic acid. These formic acid and methyl acetate are recovered from the reaction solution and circulated to the reactor. The circulating liquid added to the raw material can be returned to methyl formate and acetic acid again by a reverse transesterification reaction. In a steady state, formic acid and methyl acetate are present in the reactor in equimolar with a certain equilibrium concentration. The concentration of formic acid and methyl acetate in the reaction solution, which is economically most advantageous from the equipment scale of the circulation process and the amount of energy used,
0.1 to 10% by weight.

This reaction can be carried out by a batch reaction system or a continuous reaction system, but a continuous reaction system is preferred. In particular, the present inventors have now found that it is optimal to carry out the reaction in the form of an extrusion flow using a tubular and / or column type reactor. In the carbonylation reaction of methanol, it is necessary to dissolve carbon monoxide in the solution, and since the reaction rate is 0th order with respect to the methanol concentration, the reaction is carried out in a complete mixing tank type having a stirrer. On the other hand, in the methyl formate isomerization reaction, carbon monoxide is supplied from formic acid present in the liquid, so that it can be regarded as if molecular carbon monoxide is present in the liquid, There is no need to dissolve carbon monoxide in the solution due to forced agitation. At most, carbon monoxide that can maintain the stability of the rhodium carbonyl complex only needs to be present, and for that purpose, a predetermined carbon monoxide partial pressure is sufficient. In addition, in the methyl formate isomerization reaction, the reaction rate is first order with respect to the methyl formate concentration. Therefore, in the complete mixing tank type reaction which is carried out in the conventionally applied patent, the conversion of methyl formate is low. However, it has not been possible to overcome the drawbacks such as insufficient increase, low space-time yield, and high solution concentration of convertible by-products.

However, by carrying out the reaction in the form of an extrusion flow using the tubular and / or column type reactor applied by the present inventors, a high space-time yield, a high conversion and a convertible by-product can be obtained. It became possible to lower the solution concentration of formic acid and methyl acetate. In the case where the reaction is carried out in the form of an extrusion flow using a tubular and / or column type reactor, the so-called down flow type in which the raw material liquid is supplied from the upper part of the reaction tube and the product liquid is withdrawn from the lower part of the reaction tube, and vice versa. Applicable in upflow format. The carbon monoxide to be coexisted may be supplied to the gas phase at the upper part of the reactor as a dissolved gas, or may be supplied to the liquid phase from the lower part of the reactor as if it were a bubble column reactor. There is no problem in supplying. It is also possible to stop the stirring in the complete mixing tank reactor having a stirrer to carry out the reaction, and the methanol carbonylation reactor can be used as it is.
There is no particular limitation on the diameter and length of the reactor, and it can be applied to reactors of any shape.

[0016]

By carrying out the reaction in the form of an extrusion flow, the stirring power required for a complete mixing tank reactor having a stirrer is no longer required, and the energy consumption can be greatly reduced. It became. In addition, the heat generated by the latent heat of vaporization in the gas-liquid separator was the rate-limiting factor due to the large amount of heat generated in the conventional carbonylation reaction of methanol, and was a major factor in determining the production of the acetic acid plant. In the reaction, the heat of reaction was two-thirds, and it was possible to construct an acetic acid production process that was released from the restriction.

[0017]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0018]

[Preparation of catalyst raw material liquid] Zirconium 5 equipped with stirrer
An L autoclave was charged with 2400 g of acetic acid, 573 g of anhydrous lithium iodide, and 39.6 g of anhydrous rhodium triiodide. 5 kg / cm 2 of carbon monoxide was charged, followed by purging and replacing the gas in the system with carbon monoxide. This operation was performed twice. Subsequently, 2 kg / cm 2 of carbon monoxide was charged at room temperature, and the temperature was raised to 130 ° C. while stirring, and 130 ° C.
The mixture was reacted at ゜ C for 1 hour to produce soluble rhodium carbonyl, and a catalyst raw material liquid was prepared. In the experiments of the following Examples and Comparative Examples, necessary components such as methyl formate were added to the catalyst raw material liquid to adjust the raw material liquid.

Example 1 Necessary components such as methyl formate were added to a catalyst raw material liquid, and the liquid composition was changed to 17.0% by weight of methyl formate and 1 part of methyl iodide.
5.0 wt%, methyl acetate 0.86 wt%, acetic acid
5 wt%, formic acid 0.53 wt%, lithium iodide 5.0
10 kg of a raw material liquid containing wt%, Rh 750 ppm, and water 50 ppm was prepared. Equipped with liquid level detection device, thermometer, gas injection nozzle, stirrer, inner diameter 4 cm, height 20 cm
A zirconium autoclave was prepared. The raw material liquid is fed from the upper part of the reactor, and when the liquid level reaches 200 ml by the liquid level detecting device, the generated liquid is withdrawn from the withdrawal control valve at the lower part of the reactor so that it can be introduced into the gas-liquid separator. Manufactured an apparatus so as to supply the amount of carbon monoxide corresponding to the amount of purge gas from a gas injection nozzle at the bottom of the reactor through a flow rate controller. No stirring was performed, the reaction temperature was 195 ° C, and the total pressure of the reactor was 3
Carbon monoxide was supplied so as to maintain the pressure at 0 kg / cm ² , and the raw material liquid was supplied at a rate of 900 g / hr. When the product liquid at the time of reaching the steady state was extracted from the lower part of the gas-liquid separator and analyzed for composition, 1.70 wt% of methyl formate, 15.0 wt% of methyl iodide, 0.86 wt% of methyl acetate,
Acetic acid was 76.8 wt%, formic acid was 0.53 wt%, and lithium iodide was 5.0 wt%. In addition, 900 g /
hr, the conversion of methyl formate is 90 mol%
Met. The production and consumption of formic acid and methyl acetate were equal, and it was considered that there was no by-product when formic acid and methyl acetate in the produced liquid were recycled to the raw material system. The selectivity of methyl formate to acetic acid is 99% or more, and unreacted methyl formate can be recycled to the raw material system. Space-time yield is 688 g-acetic acid / Lh
r was obtained. A purge gas of 2 L was obtained from the upper part of the gas-liquid separator by a liquid-passing reaction for 10 hours, and a gas analysis was carried out. As a result, the gas composition was 0.28 vol% of carbon dioxide, 0.08 vol% of hydrogen, and 0.06 vol% of methane. %Admitted.

COMPARATIVE EXAMPLE 1 Necessary components such as methyl formate were added to a catalyst raw material liquid, and as a liquid composition, 17.0% by weight of methyl formate, methyl iodide 1
5.0 wt%, methyl acetate 0.86 wt%, acetic acid
0 wt%, formic acid 0.53 wt%, lithium iodide 5.0
10 kg of a raw material liquid containing wt%, Rh750 ppm, and water 0.5 wt% was prepared. A reflux condenser was provided in the same reactor as in Example 1, and a device capable of purging gas from above was prepared. While stirring at 500 revolutions / minute, carbon monoxide was supplied at a reaction temperature of 195 ° C. so that the total pressure of the reactor was maintained at 30 kg / cm ² , and 900 g of the raw material liquid was supplied.
/ Hr. At the same time, gas purging was performed from above the reflux condenser. When the product liquid at the time of reaching the steady state was extracted from the lower part of the gas-liquid separator and analyzed for composition, 4.2 wt% of methyl formate, 15.0 wt% of methyl iodide,
Methyl acetate was 1.50 wt%, acetic acid was 72.8 wt%, formic acid was 0.93 wt%, and lithium iodide was 5.0 wt%. The product liquid was obtained at a rate of 900 g / hr.
The conversion of methyl formate was 75.3 mol%, the by-products of formic acid and methyl acetate were each 4.1 mol%, and the acetic acid selectivity was 91.8 mol%. Space-time yield is 529 g-
Acetic acid / L · hr was obtained. In a 10-hour liquid-passing reaction, a total of 50 L of purge gas was obtained from the upper part of the reflux condenser and the upper part of the gas-liquid separator. When gas analysis was carried out, the composition of carbon dioxide was 1.12% by volume and hydrogen was 0.28% by volume.
1% and methane were found at 0.22 vol%. When the water content of the raw material liquid is large, a large amount of shift reaction occurs, and it is necessary to increase the purge gas amount beyond the dissolved gas amount of the product liquid.

Example 2 The same raw material as that prepared in Example 1 was prepared. The reactor used was the same as that used in Example 1, but the device was improved so that carbon monoxide could be supplied to the gas phase at the top of the reactor. No stirring was performed and the reaction temperature was 205
At ゜ C, carbon monoxide was supplied such that the total pressure of the reactor was maintained at 34 kg / cm 2, and the raw material liquid was supplied at a rate of 1300 g / hr. The product liquid at the time of reaching the steady state was withdrawn from the lower part of the gas-liquid separator and subjected to composition analysis. As a result, methyl formate 1.70 wt%, methyl iodide 15.0 wt%, methyl acetate 0.86 wt%, acetic acid 76.8 wt %, Formic acid 0.5
3 wt% and lithium iodide 5.0 wt%. The product liquid was obtained at a rate of 1300 g / hr. The conversion of methyl formate was 90 mol%, and it was considered that there was no by-product of formic acid and methyl acetate. Space-time yield is 994 g-acetic acid /
L · hr was obtained. A purge gas of 3 L was obtained from the upper part of the gas-liquid separator by a 7-hour flow reaction, and gas analysis was carried out. As a result, the gas composition was 0.28 vol% of carbon dioxide, 0.08 vol% of hydrogen, and 0.06 vol% of methane. %Admitted.

Claims (3)

[Claims] 1. A process for producing acetic acid by isomerizing methyl formate in the presence of a rhodium catalyst, an iodine compound and carbon monoxide, wherein the reaction is carried out in an extruded flow system using a tubular and / or column type reactor. A method for producing acetic acid, comprising: 2. The method for producing acetic acid according to claim 1, wherein the water concentration in the reaction solution is 0.1% by weight or less. 3. The process for producing acetic acid according to claim 1, wherein unreacted methyl formate, by-product formic acid and methyl acetate are recycled to the raw material system.