KR950005191B1 - Improved production of carboxylic acids from carbobylation of alcohol - Google Patents

Abstract

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Description

Method for producing carboxylic acid by carbonylation of alcohol

The present invention relates to a process for the synthesis of carboxylic acids by carbonylation of alcohols. More specifically, the present invention relates to a method of promoting the reaction rate by adding trihaloacetic acid to the rhodium catalyst system. The alcohol used in the reaction system has a general formula of ROH, wherein R is a saturated C ₁ -C ₄ -hydrocarbon radical.

The use of Group VIII transition metals as carbonylation catalysts for the production of carbonylation products is known in the art, and most of these catalysts are cobalt based and use halide promoters. However, rhodium series has become the most important thing in recent years. As far as is known, until now, rhodium-based carbohydrates containing trihaloacetic acid using carbon monoxide at normal pressure and temperature and as promoters for the production of carboxylic acids such as acetic acid by carbonylation of alcohols such as methanol There was no description of the carbonylation catalyst system. The rhodium catalyst system described will be described below and the relationship between the process and the present invention will be described.

Among the methods of synthesizing acetic acid, the most commercially useful ones are described in US Pat. Nos. 3,769,329 and 4,690,912, both issued to Polik et al. On October 30, 1973 and September 1, 1987, respectively. And carbobolic of methanol with carbon monoxide. The reaction is carried out at 180 ° C. and 35-70 kg / cm 2 Co. The catalyst system, together with a halogen-containing catalyst promoter such as methyl iodide, consists of rhodium dissolved or otherwise dispersed in a liquid reaction medium or supported on an inert solid phase. The patent suggests that the preferred solvent and liquid reaction medium for the process is the preferred carboxylic acid itself, ie acetic acid, when methanol is carbonylated to produce acetic acid. The selectivity is very high, typically 95% or more. However, the rate of carbonylation is highly dependent on the water concentration in the reaction medium. When the water concentration is reduced to about 14-15% by weight or less, the reaction rate decreases. In addition, by reducing the moisture content, byproducts such as esters are produced. EP 00556618 describes, typically, that about 14-15% water is present in the reaction medium of a typical acetic acid-generating system using the carbonylation technique. Ind.Eng.Chem., Prod, Res.rev. 16,281 (1977), written by Hjortkjaer and Jensen, shows that with an increase in water content of 0 to 14% by weight, It is described that the reaction rate of methanol carbonylation increases. At 14% by weight or more, the reaction rate is unchanged. In addition, the catalyst is better deactivated and precipitated when the partial pressure and / or moisture content of carbon monoxide is low. In this prior document, it is explained that water must be present in the reaction system in order to obtain a satisfactory reaction rate.

U.S. Pat.Nos. 606730 and 699525, both issued to Celanese Corporation, use high concentrations of LiI as a stabilizer for rhodium catalyst systems in the presence of a limited amount of water, resulting in a system having a high concentration of water. It is described that it is necessary to add methyl acetate as an accelerator in order to obtain approximately the same productivity. The purpose of the Celanese patent is to reduce the amount of water, but this also reduces the reaction rate.

From the above-mentioned prior documents, it can be seen that the catalyst systems have the disadvantage of requiring a high moisture content, or the reaction rate is reduced if the amount of water is reduced. The documents do not mention the use of trihaloacetic acid.

Therefore, the main purpose of the present invention is to find suitable additives that can increase the reaction rate while reducing the amount of water. By using the palpation of the present invention, very high productivity can be obtained under reduced moisture content of 4 to 11%, to the extent that the problems resulting from water can be avoided. Even if dissolved in a system containing a small amount of water, the catalyst system of the present invention is still resistant to precipitation. Also, in view of the separation of acetic acid from a small amount of water, the consumption of energy during distillation can be reduced compared to the separation of acetic acid from a large amount of water. Other processes, such as solvent extraction, can be straightforward and expansion of the device can be prevented. Completion of the present invention, i.e., incorporation of trifluoroacetic acid into the catalyst system to achieve high productivity and reaction rate under low moisture content may be superior to the prior art. According to the invention, in low moisture content environments and in the absence of methyl acetate, the reaction rate is much higher than that of the prior art in which methyl acetate is used.

The catalyst system of the present invention is used in a carbonylation reaction operated as a batch process. The reactor used for the carbonylation reaction in this example consists of a corrosion resistant main reaction vessel, a CO reservoir connected to the main reaction vessel, and a regulator therebetween to maintain a constant pressure in the main reaction vessel. The main reaction vessel is equipped with a magnetic drive stirrer and a methanol reservoir at the top of the sample inlet. Heat is provided by heating the mantle surrounded by the reactor wall. An inlet valve for the liquid reactant is provided at the top of the reactor, and the gaseous reactant enters the reactor through the same inlet. Effluent from the reaction exits through a dip tube.

The temperature at which the reaction is carried out is from 50 ° C. to 300 ° C., with higher temperatures allowing higher rates. Preferred temperatures are from 125 ° C to 195 ° C. The reaction pressure can vary over a wide range. A partial pressure of carbon monoxide of 1 to 70 kg / cm 2 or more may be used. However, this process is particularly advantageous in that it can be carried out at lower carbon monoxide partial pressures of 1 to 21 kg / cm 2 or higher, preferably at carbon monoxide partial pressure of 3 to 71 kg / cm 2. The liquid reaction medium used in the reaction system is acetic acid.

In this operation, the reactants are filled in a reactor containing a liquid catalyst system and then brought to the desired temperature and pressure conditions. For a quantitative comparison of the reaction rates, the reaction rates are reported as space-time yields as set out by the following references: Smith, BL et al. In J. Mol. Cataly. 39, 115, 1987. The space-time yield (STY) is expressed as g gram-mol of acetic acid produced per hour per liter of reaction medium contained in the carbonylation reactor, and the volume of the reaction medium is measured at ambient temperature and non-vented conditions.

Although the invention is illustrated in the following examples, it is not described as limiting the invention as various changes and modifications will become apparent to those skilled in the art within the spirit of the invention.

Comparative Examples 1 and 2

The present invention is repeated in order to show the superiority of the present invention compared to the prior art. The results are shown in Table 1 as comparative examples. In Comparative Examples 1 and 2, no trifluoroacetic acid is used. In Comparative Example 2, 14% LiI is added. The experimental process for both Comparative Examples 1 and 2 is similar to the process for Example 1 and is described below.

TABLE 1

In the examples below, the main reactant used in the experiment is Hastelloy B. % Is by weight.

Example 1

The reactor is charged with rhodium iodide, methyl iodide, water, acetic acid and trifluoroacetic acid (TFAA) at a rate to provide 400 ppm rhodium iodide, 14.0% methyl iodide, 14.0% water and 20.0% TFAA. The reactor is sealed and pressurized to a carbon monoxide partial pressure of about 28.14 kg / cm 2 measured at 25 ° C. Then, slowly remove carbon monoxide from the reactor and add new carbon monoxide (7 kg / cm 2) twice. The reactor is then pressurized to 14 kg / cm <2> with carbon monoxide and heated to 120 [deg.] C. for 2 hours and then stirred at a medium speed (100-200 ppm) by rotating the stirrer. The reactor is then further heated to 194 ° C., stirred at high speed (500-100 rpm) and pressurized to 29 kg / cm 2 using carbon monoxide. When methanol is supplied to the solution and carbon monoxide is continuously introduced at a constant rate so that the pressure in the reactor is maintained at about 29 kg / cm 2, the reactor is maintained at a temperature of 194 ° C. The reaction rate is determined by recording the amount of carbon monoxide consumed over a period of time, and it can be seen that the ideal gas law can be applied to carbon monoxide. The consumption rate of CO is close to the acetic acid production rate because the production of by-products is small as indicated by product analysis.

Analysis of the recovered carbonylation product shows that all methanol has been converted to acetic acid. The selectivity for the production of the carboxylic acid product is at least 95%. Substances such as substantial amounts of aldehyde, dimethyl ether, high boiling carboxylic acids, methane and carbon dioxide are not detected by gas chromatography. The conversion time of 50% methanol to acetic acid is about 10 minutes. The results are shown in Table 1. Compared with Comparative Example 1, it is evident that the STY value of Example 1 with 20% of trifluoroacetic acid added was increased by about 50%.

TABLE 2

Example 2

Acetic acid is prepared by the method of Example 1, except that the water concentration is reduced to 8% and 14% LiI is added. The reaction rate is determined again by recording the amount of carbon monoxide consumed over time. Substantial amounts of byproducts are not detected by gas chromatography. The results are shown in Table 3. It is evident that the value of STY of this example is higher than that of the comparative example and higher than that of Example 1. From the above example, LiI If both and trifluoroacetic acid are added to the reaction system, it can be seen that not only can the water content decrease, but also the reaction rate increases.

TABLE 3

Example 3-6

Acetic acid is prepared by the method of Example 1, except changing the molar ratio of trifluoroacetic acid to acetic acid. The reaction rate is determined again by recording the amount of carbon monoxide consumed over time. Substantial amounts of byproducts are not detected by gas chromatography. The results are shown in Table 4. As can be clearly seen in Table 4, the reaction rate of acetic acid increases with increasing weight percent of trifluoroacetic acid. The STY value is nearly doubled when TFAA increases by weight from 10% to 25%. In a solution that remained clean after exposure to air for about two weeks, no precipitation was observed. The amount of soluble rhodium metal is determined by atomic absorption as described in Examples 13-17 below.

TABLE 4

[Example 7-12]

The purpose of these examples is to test the activity of the catalyst system after continuous use. The batch reactor is charged with a suitable amount of rhodium iodide, methyl iodide, LiI and trifluoroacetic acid. The solvent is acetic acid. The reaction is operated under the conditions as described in Example 1. The reaction rate is determined again by recording the amount of carbon monoxide consumed over time. STY values are listed in Table 5 as STY1. After all of the methanol has been consumed and the CO pressure of the reservoir is kept constant, a first aliquot of methanol is added to test the activity of the catalyst system. Since the concentration of the rhodium catalyst decreases when the production of acetic acid is increased, lower STY values are expected, which are listed in Table 5 as STY2. The STY2 value is the STY value after adjustment for the concentration of Rh (STY2 = STY1 × regulator). Gas chromatographic analysis shows that the resulting reaction mixture contains acetic acid and methyl iodide. From the table below, the activity of the catalyst system after the first aliquot of methanol is completely converted is approximately equal to the initial activity, which can be demonstrated by the small difference between STY2 and STY2.

TABLE 5

Theoretical STY value after control of rhodium concentration decrease and volume increase

Example 13-17

The purpose of these examples is to test the solubility of the rhodium catalyst system. As a result, it can be seen that the reaction system consisting of a suitable concentrate of trifluoroacetic acid and LiI still has the same solubility after being left for a certain period of time. The experimental method is as follows:

Filling the reactor with a mixture of 8% H ₂ O, 17% MeI, 25% trifluoroacetic acid and Rh, where the concentration of Rh is always maintained at 400 ppm, seals the reactor and heats to 194 ° C. for 1 hour. Afterwards, it is kept at room temperature. The solution in the reactor is separated and then sealed in the flask for 5 to 10 days. The concentration of the clean solution is determined using the atomic absorption spectrum. As a result shown in Table 6, it can be seen that the concentration of Rh is in the range of 342 to 394 ppm. It can be seen from Table 6 that the degree of precipitation is very low.

TABLE 6

In short, by adding trifluoroacetic acid, the present invention not only increases the speed almost twice as fast as the conventional speed, but also reduces the moisture content. Another advantage of the present invention is that the catalyst system has high solubility and is very stable even at high temperatures, making it resistant to precipitation.

Claims (11)

The alcohol of the general formula ROH, wherein R is a C ₁ to C ₄ saturated hydrocarbonyl radical, consists essentially of (1) a rhodium mixture, (2) a halogen donor, (3) an iodide, and (4) sequentially A carbonylation method for producing a carboxylic acid, comprising contacting with carbon monoxide in the presence of a catalyst system consisting of a trihaloacetic acid promoter component. The method of claim 1 wherein said halogen providing component is an iodine providing component. The method of claim 1 wherein said iodine providing component is methyl iodide. The method according to claim 1, wherein the trihaloacetic acid component is tripolouroacetic acid. The method of claim 1 wherein the iodide is lithium iodide. The method of claim 1 wherein the alcohol is methanol. The method of claim 1 wherein the method is performed at 180 ° C to 220 ° C. The method of claim 1 wherein the partial pressure of carbon monoxide is 1.4 to 60 kg / cm 2. 5. A process according to claim 4, wherein the concentration of trifluoroacetic acid is 2 to 40% by weight. 6. The method of claim 5 wherein the concentration of lithium iodide is 2 to 40 weight percent. The method of claim 1 wherein the method is carried out at a moisture concentration of 4 to 11% by weight.