JPH07324055A - Production of acetic anhydride and acetic acid - Google Patents

Abstract

PURPOSE:To efficiently obtain the compounds with a series of production equipment by efficiently recovering low-boiling components and entrainment catalyst while reducing the energy cost through a specific process. CONSTITUTION:Firstly, in a reaction zone, both methanol and methyl acetate are reacted with CO in the presence of a catalyst, and the resultant carbonylated mixture is depressurized in a gas-liquid separation zone and the volatile components evaporated and the catalyst solution are fed to 1st distillation zone and the reaction zone, respectively. Second, the low-boiling components from the column top in the 1st distillation zone, the catalyst-contg. high-boiling components from the column bottom, and the medium-boiling components obtained by side cut and consisting mainly of acetic anhydride and acetic acid, are fed to the reaction zone, the reaction zone, etc., and 2nd distillation zone, respectively. Subsequently, the residual low-boiling components from the column top in the 2nd distillation zone, and the components obtained from the side cut or column bottom and consisting mainly of acetic anhydride and acetic acid, are fed to the reaction zone and 3rd distillation zone, respectively. Finally, in the 3rd distillation zone, the objective acetic acid and acetic anhydride are obtained from the column top and from the side cut or column bottom, respectively.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a process for producing acetic anhydride and acetic acid from methanol and methyl acetate and optionally dimethyl ether in a continuous series of production facilities.

[0002]

BACKGROUND OF THE INVENTION Acetic acid is used in large amounts as a raw material for acetic acid esters, acetic anhydride, vinyl acetate, and terephthalic acid, and is a basic substance necessary for many industries including polymer industry and chemical industry. Compound.
On the other hand, acetic anhydride is a compound that is used in large quantities as a raw material for producing cellulose acetate and is also useful as a raw material for chemical products such as pharmaceuticals, fragrances and dyes. Further, acetic acid and acetic anhydride are chemical substances that are related to each other for practical use. For example, in the cellulose acetate industry, acetic anhydride is produced from acetic acid, and acetic anhydride and cellulose are reacted to form cellulose acetate and acetic acid, and acetic acid is reused.

As a method for obtaining acetic acid and acetic anhydride, there has been disclosed a method of reacting methyl acetate and methanol or dimethyl ether and methanol with carbon monoxide in a continuous series of manufacturing facilities.

Above all, as a method for separating and purifying the acetic acid and acetic anhydride obtained in the reaction zone, JP-A-2-10455 is used.
No. 1 discloses a process in which two gas-liquid separation zones having different pressures are used to separate a catalyst solution, while a carbonylation product and a low-boiling raw material are separated in a single-stage distillation zone under normal pressure. Have been described. In the above process, not only two gas-liquid separation zones are required to circulate the catalyst solution into the reactor, but also the second gas-liquid separation zone is controlled under reduced pressure, which makes the catalyst unstable. However, there is a problem in that it precipitates. Furthermore, it is managed under reduced pressure. 2
The need arises to pressurize the components evaporating from the second gas-liquid separation zone before feeding them to the distillation zone. Further, according to the method described in the above publication, the control pressure of the distillation zone in which the low boiling point components such as methyl iodide, methyl acetate and dimethyl ether and the product acetic acid and acetic anhydride are separated is atmospheric pressure,
The cooling recovery capacity of low boiling point components such as methyl iodide, methyl acetate and dimethyl ether at the top of the distillation column is low,
The heat exchanger required at the top of the distillation column is large,
It is pointed out that there are problems such as an increase in the amount of energy required for cooling and an increase in the equipment for recovering waste gas from the top of the distillation column. Further, in the distillation zone, the catalyst entrained in droplets is not recovered from the gas-liquid separation zone, and there is a problem that it is not economically feasible when an expensive catalyst is used.

The object of the present invention is to produce low-boiling components such as methyl iodide, methyl acetate, and dimethyl ether when producing acetic acid and acetic anhydride in a series of continuous production facilities.
Provided is a method for producing acetic acid and acetic anhydride, which efficiently recovers a catalyst entrained from a gas-liquid separation zone.

[0006]

Means for Solving the Problems As a result of intensive studies made by the present inventors in order to achieve the above object, a method for producing acetic anhydride and acetic acid by reacting methanol and methyl acetate and optionally dimethyl ether with carbon monoxide. In, the separation of low-boiling components mainly consisting of methyl iodide, methyl acetate and dimethyl ether is carried out in two or more distillation zones, and the entrainment catalyst from the gas-liquid separation zone is used in the reaction zone and / or gas-liquid separation. By returning to the zone, and further by controlling the gas-liquid separation zone and the distillation zone under a pressure of 5 bar or less, a method for efficiently producing acetic anhydride and acetic acid in a series of production facilities was found. .

That is, the present invention provides a method for producing acetic anhydride and acetic acid by reacting methanol and methyl acetate and optionally dimethyl ether with carbon monoxide, in which: a) methanol and methyl acetate and optionally dimethyl ether in the presence of a catalyst. 150 to 250 in the reaction zone with carbon monoxide or a mixture of carbon monoxide and hydrogen.
At a temperature of ℃ and a pressure of 5 to 120 bar, b) releasing the carbonylation mixture leaving the reaction zone in a gas-liquid separation zone under a pressure of 5 bar or less, to evaporate the main amount of volatile components, The catalyst solution that was supplied to the first distillation zone and did not evaporate in the gas-liquid separation zone was returned to the reaction zone. C) In the first distillation zone, low boiling point components were obtained from the top of the column and returned to the reaction zone, and sprayed. A high boiling point component containing a part of the catalyst mixed by entrainment is obtained from the bottom of the column and returned to the reaction zone and / or the gas-liquid separation zone to obtain a medium boiling point component mainly containing acetic anhydride and acetic acid by side-cutting. D) The acetic anhydride, a medium boiling point component mainly containing acetic acid, obtained by side-cutting in the first distillation zone, is further fed to the second distillation zone, and e) in the second distillation zone, In addition, residual low boiling point components are obtained from the top of the column. And then returned to the reaction zone, and f) a component mainly consisting of acetic anhydride and acetic acid is side-cut or obtained from the bottom of the column and further fed to the third distillation zone, or partially containing a catalyst by entrainment of droplets. To obtain a high boiling point component from the bottom of the column, return to the reaction zone and / or gas-liquid separation zone, to obtain a component mainly consisting of acetic anhydride and acetic acid by side-cut, further fed to the third distillation zone, G) Acetic acid was obtained from the top of the column in the third distillation zone,
Provided is acetic anhydride and a method for producing acetic acid, which comprises obtaining acetic anhydride from a side cut or a column bottom.

As the catalyst used in the reaction, each metal of Group VIII of the Periodic Table of the Elements can be used together with methyl iodide. For example, palladium, iridium, rhodium, nickel, cobalt and the like can be mentioned, but rhodium and nickel are particularly preferable. Of these, rhodium has the highest activity. The catalyst may be used in any form, but one that is soluble under the reaction conditions is preferable, and one that forms a carbonyl complex species in the reaction system is particularly preferable.

The alkali metal salt used as a co-catalyst may be any one as long as it is soluble under the reaction conditions, but iodide salts and acetates are preferable, and among them, lithium iodide, sodium iodide, Potassium iodide,
Lithium acetate, sodium acetate, potassium acetate and the like are preferable. Further, as a cocatalyst, a salt of each element having Lewis acidity of Group III of the Periodic Table of Elements can be used. Any form of salt may be used as long as it is soluble under the reaction conditions, but iodide salt and acetate are preferable,
Of these, iodide salts such as aluminum and boron, acetates, aluminum chloride, boric acid, and metaboric acid are particularly preferable.

The rhodium catalyst will be described below as an example.

The concentration of rhodium in the reaction solution is 100 to 1
10,000 ppm, preferably 300-3,000 pp
m. The concentration of methyl iodide in the reaction solution is 10 to 30.
wt%, concentration of methyl acetate and / or dimethyl ether is 5-40 wt%, concentration of acetic anhydride is 10-40 wt
%, The concentration of acetic acid is 0 to 40 wt%. methanol,
The concentrations of methyl acetate and dimethyl ether can be changed at any time depending on the production ratio of acetic anhydride and acetic acid. Also, water can be charged as a raw material. Literature (Adv.Ch
em. Ser. , 230, 377-394 (199
As shown in 2)), the rate-determining step of this reaction in the high promoter concentration and high methyl acetate concentration regions is the reaction step of rhodium and methyl iodide. In the obtained high rhodium concentration and high methyl iodide concentration regions, the rate-determining step of this reaction is the reaction step of the iodide salt of the promoter and methyl acetate.

The carbon monoxide used for the reaction does not necessarily have to be pure. If the carbon monoxide partial pressure is kept constant in the reactor, then very small amounts of inert gases such as carbon dioxide, nitrogen or methane do not interfere with the carbonylation. Hydrogen content has a positive effect on the catalytic activity, but it can reduce the selectivity of the process by forming hydrogenation products such as ethylidene diacetate. Therefore, the hydrogen partial pressure in the reactor is 0-10.
Atmospheric pressure is preferred.

The reaction pressure in the reactor is 5 to 120 bar,
The reaction temperature is 150 to 250 ° C, and the carbon monoxide partial pressure is 5 to 7
It is carried out at 0 atm.

A reaction crude liquid obtained by reacting in the presence of a catalyst and a cocatalyst is withdrawn from the reactor and flash-evaporated into a gas-liquid separation zone controlled to a reaction pressure or less, and a circulating catalyst liquid that does not evaporate. It is separated into vapor containing acetic acid and acetic anhydride produced. At this time, the pressure of the gas-liquid separation zone may be any pressure as long as it is a pressure equal to or lower than the reaction zone, but when the difference from the pressure of the reaction zone is small, the amount of vaporized vapor due to flash decreases, The amount of circulating catalyst liquid increases, which is disadvantageous in the process. As a method of earning the amount of vaporized vapor, for example, a method of heating a gas-liquid separation zone, CO, H
A method of heating the gas-liquid separation zone in the presence of ₂ can be considered.
However, when heated, there is a problem that the catalyst becomes unstable and precipitates in the gas-liquid separation zone. On the other hand, CO,
When heating the gas-liquid separation zone in the presence of H _2, CO, H
There are problems that _two gases are required, and that low boiling point raw materials and the like are lost from the distillation zone when they are entrained in the supplied CO and H ₂ gases, and the recovery equipment becomes enormous. On the other hand, when the difference between the pressure in the reaction zone and the pressure in the reaction zone is large, the pressure in the gas-liquid separation zone is so small that it is necessary to raise the pressure before supplying vapor to the distillation zone after the gas-liquid separation zone. ,
There is a problem that the catalyst becomes unstable and precipitates in the gas-liquid separation zone. However, it is preferable that the pressure in the gas-liquid separation zone is controlled under a pressure of 5 bar or less, and more preferably, 4 bar or less and 1.5 bar or more.
Further, if necessary, it may be introduced CO and / or H ₂ gas.

In the gas-liquid separation zone, the catalyst solution separated without evaporation is returned to the reaction zone as it is or after some treatment. The catalyst solution that did not evaporate in the gas-liquid separation zone contains high-boiling impurities such as tar and ethylidene diacetate. Therefore, if necessary, the impurities may be decomposed and removed, separated and purified, and then returned to the reaction zone. When the catalyst solution separated without evaporating in the gas-liquid separation zone is returned to the reaction zone after decomposition and removal or separation and purification, the treatment amount may be the whole amount of the catalyst solution, or a part thereof. May be only.

The vapor containing acetic acid and acetic anhydride flash-evaporated in the gas-liquid separation zone is supplied to the first distillation zone. When the control pressure of the first distillation zone is higher than the control pressure of the gas-liquid separation zone, not only is it necessary to pressurize the vapor before supplying it from the gas-liquid separation zone to the first distillation zone, The equipment cost of the first distillation zone itself and the energy cost required for separation increase, which is disadvantageous in the process. On the other hand, if the control pressure in the first distillation zone is too low, the cooling recovery capacity of methyl iodide, methyl acetate, dimethyl ether, etc. at the top of the distillation column will decrease. This means that the heat exchanger required at the top of the distillation column is large, the amount of energy required for cooling is increased, the waste gas recovery facility from the top of the distillation column is large, and the entrained catalyst is It becomes unstable and causes problems such as precipitation in the distillation column. However, the pressure in the first distillation zone should be controlled under a pressure of 5 bar or less, especially 4
It is preferably controlled to below bar and above 1.5 bar.

Furthermore, the relationship between the pressure in the gas-liquid separation zone (denoted as A) and the pressure in the first distillation zone (denoted as B) is A = B, or
More preferably, A is slightly higher than B.

In the vapor supplied from the gas-liquid separation zone to the distillation zone, low boiling point components such as methyl iodide, methyl acetate and dimethyl ether, acetic acid and acetic anhydride as products, as well as those from the gas-liquid separation zone, are obtained. Part of the catalyst is mixed due to entrainment. Complete separation of low boiling point component vapor consisting of methyl iodide, methyl acetate and dimethyl ether, entrained catalyst from gas-liquid separation zone, acetic acid and acetic anhydride as products in only one distillation zone. Attempting to try causes a problem that the scale of the distillation column required for the separation (the number of plates, the column diameter, the column height) and the energy required for the separation become enormous and unrealistic. However, it is necessary to use two or more distillation zones to separate low boiling point vapors such as methyl iodide, methyl acetate and dimethyl ether supplied from the gas-liquid separation zone into the distillation zone and acetic acid and acetic anhydride as products. preferable.

Further, the vapor supplied from the gas-liquid separation zone to the distillation zone partially contains a catalyst mixed by entrainment. However, in the first distillation zone, it is preferable to obtain a high boiling point component containing a part of the catalyst mixed by entrainment of droplets from the bottom of the column, and to obtain a medium boiling point component mainly containing acetic acid and acetic anhydride by side cut. At this time, the form of the side cut of the medium boiling point component mainly containing acetic acid and acetic anhydride may be liquid or vapor, but is particularly preferably vapor.

The low-boiling components, mainly methyl iodide and methyl acetate, obtained from the top of the column in the first distillation zone are returned to the reaction zone. The medium-boiling-point components containing mainly acetic acid and acetic anhydride, which are obtained by side-cutting in the first distillation zone, are supplied to the second distillation zone. The high-boiling-point component obtained from the bottom of the column in the first distillation zone and partially containing the catalyst mixed by the entrainment of droplets is returned to the reaction zone and / or the gas-liquid separation zone.

During the fractional distillation in the first distillation zone, a waste gas consisting mainly of CO ₂ , CO, CH ₄ , N ₂ is withdrawn via the top of the column, charging methanol and / or
Alternatively, residual methyl iodide is removed by washing with methyl acetate and / or dimethyl ether, and the mixture is fed to combustion, and a mixture containing at least one of methanol, methyl acetate and dimethyl ether is added to the reaction zone. May be supplied. As a method for cleaning the waste gas used here, an ordinary method, for example, the method described in JP-A-61-58803 is used.

The components obtained by side-cutting in the first distillation zone, containing mainly acetic acid and acetic anhydride and a trace amount of methyl iodide, methyl acetate, etc., are fed to the second distillation zone. In the second distillation zone, low-boiling components mainly consisting of methyl iodide and methyl acetate are obtained from the column top, and components mainly containing acetic acid and acetic anhydride are side-cut or obtained from the column bottom. When a high-boiling component partially containing the catalyst remains due to entrainment, a low-boiling component mainly consisting of methyl iodide and methyl acetate is obtained from the top of the column, and a component mainly containing acetic acid and acetic anhydride. Is obtained from the side cut, and the high boiling point component containing a part of the catalyst is obtained from the bottom of the column and returned to the reaction zone and / or the gas-liquid separation zone. The form of the side cut may be liquid or vapor, but vapor is particularly preferable. At this time, if the control pressure of the second distillation zone is higher than the control pressure of the first distillation zone, it is necessary to pressurize the component before supplying it from the first distillation zone to the second distillation zone. In addition to being pressed, the equipment cost of the second distillation zone itself and the energy cost required for separation rise,
It is disadvantageous in the process. On the contrary, if the control pressure in the second distillation zone is too low, the cooling recovery capacity of methyl iodide, methyl acetate, dimethyl ether, etc. at the top of the distillation column will decrease. This means that the heat exchanger required at the top of the distillation column becomes large, the amount of energy required for cooling increases, and the entrained catalyst becomes unstable in the distillation column and precipitates. cause. However, it is preferable that the pressure in the second distillation zone is controlled under a pressure of 5 bar or less, and particularly preferably 4 bar or less and 1.5 bar or more.

If necessary, during the fractional distillation in the second distillation zone, a waste gas consisting mainly of CO ₂ , CO, CH ₄ , N ₂ is withdrawn via the top of the column, the charge material methanol and / or methyl acetate being used. And / or dimethyl ether to remove residual methyl iodide and feed to the combustion, and a mixture containing at least one of methanol, methyl acetate and dimethyl ether is fed to the reaction zone. Good. In this case, the waste gas cleaning equipment from the second distillation zone may share the waste gas cleaning equipment associated with the first distillation zone.

The components mainly containing acetic acid and acetic anhydride, which are obtained from the side cut or the bottom of the column in the second distillation zone, are supplied to the third distillation column. In the third distillation zone, a component mainly consisting of acetic acid is obtained from the top of the column, and a component mainly consisting of acetic anhydride is obtained from the side cut or the bottom of the column.

At this time, the control pressure of the third distillation zone may be any pressure, but when the control pressure of the third distillation zone is higher than the control pressure of the second distillation zone, In addition to the need to pressurize the component before supplying it from the second distillation zone to the third distillation zone, the equipment cost of the third distillation zone itself and the energy cost required for separation increase, Will be at a disadvantage. However, the control pressure in the third distillation zone is preferably 5 bar or less, and more preferably 1 bar or less.

When the side cut is performed in the third distillation zone, the form of the side cut of the component containing acetic anhydride may be liquid or vapor, but vapor is particularly preferable.

Further, for the purpose of removing trace impurities contained in the fraction composed of acetic acid and acetic anhydride obtained from the second distillation zone, before feeding to the third distillation zone, if necessary, A separation step and a treatment step may be provided.

The acetic acid obtained from the top of the column in the third distillation zone may be directly used as a product or may be reused in the reaction. Further, if necessary, at least one of ozone treatment, ion exchange resin treatment, further distillation purification, etc. may be carried out for commercialization, or two or more of these may be combined for commercialization. . Similarly, acetic anhydride obtained from the side cut in the third distillation zone or from the bottom of the column may be directly used as a product. Further, if necessary, at least one of ozone treatment, ion exchange resin treatment, further distillation purification, etc. may be carried out for commercialization, or two or more of these may be combined for commercialization. .

[0029]

INDUSTRIAL APPLICABILITY According to the present invention, while lowering the equipment cost and the energy cost required for separation, the ability to recover low boiling point components is improved, the entrained catalyst is recovered, and acetic anhydride and acetic acid are efficiently produced. It can be manufactured with a series of manufacturing equipment.

[0030]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by these examples.

[0031]

Example 1 In a test and production facility for acetic acid and acetic anhydride equipped with a reaction zone (reactor) having an internal volume of 500 ml, 0.2 kg / h of product acetic anhydride and 0.2 kg / h of product acetic acid were tested and manufactured. The concentration of rhodium in the reaction solution is 1,000 p
The concentration of pm and methyl iodide is 20 wt% and the concentration of methyl acetate is 17 wt%. The co-catalyst as a reaction promoter is aluminum acetate, lithium iodide, and boric acid at 10 mol times and 20 mol respectively relative to rhodium. Molar times and 20 times by mole were added. The reaction temperature is 190 ° C., and the reaction pressure is 29.
It was 4 bar. The reaction liquid was withdrawn into a gas-liquid separation zone (evaporation tank) controlled at a pressure of 2.4 bar, flash-evaporated, and a liquid component containing a catalyst which was not evaporated by flash evaporation was returned to the reactor.

After the vapor evaporated by flash evaporation in the evaporation tank is once cooled and released to be liquefied, the first distillation zone (distillation column) which is an Older Shaw distillation column with an inner diameter of 40 mm and actual stages of 20 stages is again charged with a charging pump. ) From the top). The composition of the feed liquid to the first distillation zone was methyl iodide 37.2 wt%, methyl acetate 25.3 wt%, acetic acid 1
7.3 wt%, acetic anhydride 18.5 wt%, others 1.7
It was wt%. The first distillation column with a pressure of 2.4 bar,
The reflux ratio was controlled at 3.5. In the first distillation column, a low boiling point component mainly consisting of methyl iodide and methyl acetate was obtained at a distillation rate of 45% from the column top and returned to the reactor, and a medium boiling point component mainly containing acetic acid and acetic anhydride was side-cut by a side cut. A side cut rate of 52% was obtained, and a high boiling point component containing a part of the catalyst mixed by entrainment of droplets was obtained from the bottom of the column. The composition of the low boiling point component obtained from the top of the first distillation column was as follows: methyl iodide 72.9 wt%, methyl acetate 26.0 wt%,
Others were 1.1 wt%. The position of the side cut was the second stage from the bottom (when the tower bottom was counted as the first stage).

Obtained by side-cutting the first distillation column,
The medium boiling point component mainly containing acetic acid and acetic anhydride was supplied to the second distillation zone (distillation column), and the high boiling point component obtained from the bottom of the first distillation column was returned to the reactor. The composition of the medium boiling point component is
The content was 32.0 wt% acetic acid, 32.5 wt% acetic anhydride, 8.1 wt% methyl iodide, 25.8 wt% methyl acetate, and 1.6 wt% other.

The second distillation column has an inner diameter of 40 mm and an actual stage of 30 mm.
The pressure was controlled at 2.4 bar with a reflux ratio of 2.3 in a one-stage Oldershaw distillation column. Further, the charging stage was the 13th stage from the top. In the second distillation column, a low boiling point component mainly consisting of methyl iodide and acetic acid was obtained at a distillation rate of 35% from the column top and returned to the reactor, and a medium boiling point component mainly containing acetic acid and acetic anhydride was side-cut by a side cut. A high boiling point component containing a part of the catalyst mixed by the entrainment of droplets was obtained from the bottom of the column. The composition of the low boiling point component obtained from the top of the second distillation column is methyl iodide 22.9w.
t%, methyl acetate 72.9 wt%, other 4.2 wt%
Met. High boiling point obtained from the bottom of the second distillation column by feeding the middle boiling point component mainly containing acetic acid and acetic anhydride to the third distillation zone (distillation column) obtained by the side cut of the second distillation column. The component liquid was returned to the reactor. The composition of the medium boiling point component was 49.6 wt% acetic acid, 50.3 wt% acetic anhydride, and 0.1 wt% other. The position of the side cut was the second stage from the bottom (when the tower bottom was counted as the first stage).

The third distillation column has an inner diameter of 40 mm and an actual stage of 60.
The pressure was controlled at 0.4 bar with a reflux ratio of 5.0 in a one-stage Oldershaw distillation column. Further, the charging stage was the 37th stage from the top. In the third distillation column, 99.9 wt from the top of the column
% Product acetic acid was obtained, and from the bottom of the column acetic anhydride 99.8w
A component mainly consisting of acetic anhydride of t% and acetic acid 0.1 wt% was obtained. The product mainly containing acetic anhydride obtained from the bottom of the third distillation column was further deboiling and deboiling to obtain acetic anhydride as a product.

When the rhodium concentration in the reactor was continuously measured during the test production, it decreased at a rate of about 1 ppm / day.

[0037]

[Comparative Example 1] The vapor obtained by flash evaporation in Example 1 in the evaporation tank was once cooled and released to liquefy, and then again liquefied by a liquefaction pump to a first distillation column having an inner diameter of 40 mm and 30 actual stages. Was introduced into the 13th stage from the top, and the reflux ratio was controlled to 3.5 at normal pressure. A low boiling point component mainly consisting of methyl iodide and methyl acetate was obtained from the column top and returned to the reactor, and a liquid mainly consisting of acetic acid and acetic anhydride was obtained from the column bottom and fed to the third distillation column. (Indicating that the low boiling components were separated in one distillation zone and that the entrained catalyst was not returned to the reactor).

The third distillation column has an inner diameter of 40 mm and an actual stage of 60.
The pressure was controlled at 0.4 bar with a reflux ratio of 5.0 in a one-stage Oldershaw distillation column. In the third distillation column, a product acetic acid was obtained from the top of the column and a component mainly consisting of acetic anhydride was obtained from the bottom of the column. The product mainly containing acetic anhydride obtained from the bottom of the third distillation column was further deboiling and deboiling to obtain acetic anhydride as a product.

Since the entrained catalyst was not recovered from the gas-liquid separation zone, the rhodium concentration in the reaction solution was about 3 p.
It was decreasing at the ratio of pm / day.

Further, not only the amount of methyl iodide mixed in the product acetic acid was increased, but also the amount of methyl iodide discharged in a gaseous state from the vent of the condenser at the top of the first distillation column was increased. However, the concentration of methyl iodide in the reaction solution could not be kept constant.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C07C 51/54 53/12 // C07B 61/00 300

Claims (5)

[Claims] 1. A method for producing acetic anhydride and acetic acid by reacting methanol and methyl acetate, and optionally dimethyl ether with carbon monoxide, comprising: (a) methanol and methyl acetate and optionally dimethyl ether in the presence of a catalyst; 150-250 in the reaction zone with carbon oxide or a mixture of carbon monoxide and hydrogen
At a temperature of ℃ and a pressure of 5 to 120 bar, b) releasing the carbonylation mixture leaving the reaction zone in a gas-liquid separation zone under a pressure of 5 bar or less, to evaporate the main amount of volatile components, The catalyst solution that was supplied to the first distillation zone and did not evaporate in the gas-liquid separation zone was returned to the reaction zone. C) In the first distillation zone, low boiling point components were obtained from the top of the column and returned to the reaction zone, and sprayed. A high boiling point component containing a part of the catalyst mixed by entrainment is obtained from the bottom of the column and returned to the reaction zone and / or the gas-liquid separation zone to obtain a medium boiling point component mainly containing acetic anhydride and acetic acid by side-cutting. D) The acetic anhydride, a medium boiling point component mainly containing acetic acid, obtained by side-cutting in the first distillation zone, is further fed to the second distillation zone, and e) in the second distillation zone, In addition, residual low boiling point components are obtained from the top of the column. And then returned to the reaction zone, and f) a component mainly consisting of acetic anhydride and acetic acid is side-cut or obtained from the bottom of the column and further fed to the third distillation zone, or partially containing a catalyst by entrainment of droplets. To obtain a high boiling point component from the bottom of the column, return to the reaction zone and / or gas-liquid separation zone, to obtain a component mainly consisting of acetic anhydride and acetic acid by side-cut, further fed to the third distillation zone, G) Acetic acid was obtained from the top of the column in the third distillation zone,
A process for producing acetic anhydride and acetic acid, which comprises obtaining acetic anhydride from a side cut or a column bottom. _2. Predominantly CO ₂ , CO, CH ₄ , N ₂ during the fractional distillation in the first and / or the second distillation zone.
The residual methyl iodide is withdrawn via the top of the column and the residual methyl iodide is removed by washing with the charge methanol and / or methyl acetate and fed to the combustion and methanol and / or acetic acid. The method for producing acetic anhydride and acetic acid according to claim 1, wherein a mixture of methyl is supplied to the reaction zone. 3. The process for producing acetic anhydride and acetic acid according to claim 1, wherein the first and second distillation zones are controlled under a pressure of 5 bar or less. 4. The process for producing acetic anhydride and acetic acid according to claim 1, 2 or 3, wherein the third distillation zone is controlled at a pressure of 5 bar or less. 5. The method for producing acetic anhydride and acetic acid according to claim 1, 2 or 3, wherein the third distillation zone is controlled at a pressure of 1 bar or less.