CN100484912C - Method for preparing carboxylic acid - Google Patents

Abstract

The present invention relates to an improved process for the manufacture of organic carboxylic acids of n +1 carbon atoms from alcohols of n carbon atoms and carbon monoxide in the presence of a rhodium catalyst catalytic system. In particular, it relates to a method for producing acetic acid by using rhodium catalyst system to catalyze carbonylation reaction of alcohol such as methanol. The invention is characterised by the addition of a catalyst stabilizer to the reaction medium to avoid precipitation of the catalyst in the liquid phase, the catalyst stabilizer used in the invention being a catalyst stabilizer such as one having ₂) mCOOR and (CH)₂)mSO₃And R (R ═ H, alkyl; m ═ 0-6) substituent pyridine derivatives.

Description

A kind of method for preparing carboxylic acid

technical field

The present invention relates to an improved method for producing an organic acid of n+1 carbon atoms from alcohols of n carbon atoms and carbon monoxide in the presence of a rhodium catalyst catalytic system. In particular it relates to the carbonylation of methanol to acetic acid catalyzed by a rhodium catalyst system.

Background technique

Catalytic carbonylation of methanol to acetic acid using a rhodium catalyst is a well-known and long-established commercial technique. Compared with the early cobalt catalyst system, the rhodium catalyst catalytic system has the advantages of relatively low reaction temperature and low carbon monoxide partial pressure, and its reaction speed is also relatively fast. Typical rhodium-catalyzed carbonylation of methanol is carried out in a liquid phase which contains a dissolved rhodium catalyst and a promoter including methyl iodide. Detailed related technology can be found in Applied Homogeneous Catalysis with Organometallic Compounds, Vol 1, pp 104-138 (1997).

U.S. Patent No. 3,769,329 and No. 4,690,912 disclose a technology for generating acetic acid through carbonylation of methanol. The reaction conditions are: temperature 180° C., carbon monoxide pressure between 35-70 kg/cm ² , the catalyst is a rhodium catalyst, and methyl iodide is used as accelerator. This patent also discloses that the most effective solvent for this acetic acid generating reaction is the product acetic acid itself. The main advantage of this catalytic system is that the conversion and selectivity of the catalyst are very high (>95%), the catalyst life is quite long, the catalyst can be completely recycled to the reactor, and the possible losses are leakage from pipelines, pumps, etc. Although this technology is approaching perfection, the water content in the reaction system needs to be kept at least above 14-15wt%, so as to avoid precipitation of the rhodium catalyst and maintain a relatively high reaction rate. Hjortkjaer (Ind.Eng.Chem.Prod.Res., 1976,15, p46) pointed out that if the water content of this catalytic system increases from 0 to 14wt%, then the carbonylation rate of methanol also increases accordingly, but if the water content is higher than 14wt%, the reaction rate does not change any more. Such a high water content will increase the cost of separation equipment and consume considerable energy during the product purification process. In the last ten years, many patents have proposed different improvement methods for this acetic acid preparation method to improve the stability of the rhodium catalyst at low water content (<14wt%).

European Patent No. 55618 discloses a technique of adding an organic catalyst stabilizer to the reaction solution to reduce precipitation of rhodium catalyst in methanol carbonylation reaction at low water content (<14wt%). The stabilizers disclosed in this patent include several organic compounds containing one or more nitrogen atoms, phosphorus atoms or carboxyl groups simultaneously or independently:

(1) N, N, N ¹ , N ¹ -tetramethyl-o-phenylenediamine (N, N, N ¹ , N ¹ -tetramethyl-o-phenylenediamine) and 2,3 ¹ -bispyridyl (2, 3 ¹ -dipyridyl)

(2) HOOC-Y ₁ -COOH and (HOOC-Y ₂ )(HOOC-Y ₃ )NY ₁ -N(Y ₄ -COOH)(Y ₅ -COOH); Y _1-5 = (CH ₂ ) _m

(3) (R ₁ )(R ₂ )PR ₃ -P(R ₄ )(R ₅ ); R _1-5 = alkyl

U.S. Patent No. 4733006 discloses the use of inorganic salt additive XOAc (X is lithium ion, sodium ion, potassium ion) to reduce the precipitation of rhodium catalyst in methanol carbonylation reaction solution under low water content, but the whole patent does not disclose this The effect of an inorganic salt additive on the reaction rate.

U.S. Patent No. 5,001,259 discloses the use of inorganic iodine compound lithium iodide (LiI) as a stabilizer for rhodium catalysts to reduce rhodium precipitation in the carbonylation reaction of methanol with low water content, and to obtain almost similar to high water content (14wt%) the reaction rate. The same patent also discloses the use of a quaternary ammonium salt, N-methyl-picolinium iodide, to increase the carbonylation reaction rate at low water content. However, the experimental results found that the compound N-methyl-picolinium iodide (N-methyl-picolinium Iodide) easily forms an insoluble complex with Rh and precipitates from the reaction solution.

The nitrogen-containing compound N-methylimidazole disclosed in European Patent EP0153834 also easily forms an insoluble complex with Rh and precipitates from the methanol carbonylation reaction solution.

In another U.S. Patent No. 5,442,107, six heterocyclic nitrogen compounds were selected as catalyst stabilizers for carbonylation of methanol with low water content:

(1) 2-Ethyl-4-methylimidazole

(2) 4-Methylimidazole

(3) 4-tert-butylpyridine

(4) 2-Hydroxypyridine

(5) 3-hydroxypyridine

(6) 4-hydroxypyridine

But this patent does not disclose the effect of the additives used on the reaction rate at low water content. The same patent also reveals that pyridine, which has no alkyl substitution at all, is similar to the organic compounds picoline and N-methylimidazole proposed in the prior art, and is also prone to form insoluble complexes with Rh Precipitated from methanol carbonylation reaction solution at low water content. In summary, if there are hydroxyl groups and tert-butyl groups on pyridine, it has a significant effect on reducing the precipitation of rhodium catalysts in methanol carbonylation reaction solutions with low water content, but if there are no substituents or tert-butyl groups on pyridine If the group is a methyl group, it has no appreciable effect on reducing the precipitation of rhodium catalysts at low water contents. The prior art does not mention or suggest the effect of pyridine derivatives bearing other non-hydroxyl and alkyl substituents on reducing the precipitation of rhodium catalysts for methanol carbonylation at low water contents.

The prior art mentioned above provides several organic and inorganic salt additives to reduce or avoid the precipitation of the rhodium catalyst for the carbonylation of methanol to acetic acid at low water content. This technology can save energy consumption in the distillation and separation process of acetic acid products, and reduce other process steps such as solvent extraction, etc., and also avoids increasing the equipment of some separation processes.

Contents of the invention

The present invention provides several organic additives different from the prior art to reduce the precipitation of the rhodium catalyst as methanol carbonylation reaction to acetic acid at low water content. These additives can be carried out in both batch reaction and continuous reactor.

The organic additive used in the present invention is selected from 4-pyridineethanesulfonic acid, pyridine-3-carboxylic acid, pyridine-4-carboxylic acid, pyridine-3,4-dicarboxylic acid or 4-cyanopyridine.

Although US Patent No. 5442107 discloses the use of nitrogen-containing heterocyclic derivatives with alkyl groups and hydroxyl groups, it never mentions nitrogen-containing heterocyclic derivatives with substituents such as formula (A).

The invention relates to an improved method for producing an organic acid with n+1 carbon atoms from alcohols with n carbon atoms and carbon monoxide in the presence of a rhodium catalyst catalytic system, wherein n takes a value within the range of 1-20. In particular, it relates to the carbonylation of methanol with a rhodium catalyst system to produce acetic acid. The process involves feeding an alcohol and/or an ester of the alcohol and an acid along with carbon monoxide to a oxo reaction tank comprising the following components:

(1) rhodium catalyst (2) corresponding to the iodine derivative of raw material alcohol (3) product carboxylic acid and the formed ester of raw material alcohol (4) product carboxylic acid (5) has at least a certain amount of water (6) one or Several catalyst stabilizers selected from 4-pyridineethanesulfonic acid, pyridine-3-carboxylic acid, pyridine-4-carboxylic acid, pyridine-3,4-dicarboxylic acid or 4-cyanopyridine.

Specifically, the object of the present invention is to provide a method for producing an organic carboxylic acid with n+1 carbon atoms from alcohols with n carbon atoms and carbon monoxide, wherein n takes a value in the range of 1 to 20, and the method is In a liquid reaction medium of a catalytic system containing a rhodium catalyst, carbon monoxide is reacted with alcohols, and then the carboxylic acid is recovered from the resulting reaction product; the rhodium-containing catalytic system is characterized in that the carbonylation reaction tank is maintained during the carbonylation reaction In a liquid reaction medium containing the following composition: (1) rhodium catalyst (2) iodine derivative corresponding to starting alcohol (3) ester formed by product carboxylic acid and starting alcohol (4) product carboxylic acid (5) at least An amount of water (6) selected from the group consisting of 4-pyridineethanesulfonic acid, pyridine-3-carboxylic acid, pyridine-4-carboxylic acid, pyridine-3,4-dicarboxylic acid and 4-cyanopyridine One or more catalyst stabilizers of the following formula (A).

The organic additives selected for the present invention have been shown to not produce rhodium-containing sparingly soluble complexes even under severe test conditions that deliberately promote rhodium precipitation. The selected additive has the additional advantage that it is particularly effective in preventing precipitation at low water contents in the carbonylation tank compared to conventional methods.

In a preferred embodiment of the above-mentioned method, an alcohol carbonylation reaction solution is removed from the carbonylation reaction tank; the carboxylic acid, rhodium catalyst and catalyst stabilizer are then moved to a place where the carbon monoxide pressure is lower than the carbonylation reaction tank. The separation of carboxylic acid and other components is also exemplified here. The rhodium catalyst and stabilizer are thus recycled to recover the carboxylic acid to the carbonylation tank. Such separation and recycle is characterized in the preferred embodiment in that the catalyst and stabilizer are always together in the absence of carbon monoxide.

As far as the water content of the reaction tank is concerned, although the present invention can still be applicable to the 14-15% (weight ratio) of the traditional methanol carbonylation plant, this technology is when the water content of the carbonylation reaction tank is lower than the traditional method. 0.5 to 12%, preferably 1 to 10% by weight are particularly suitable.

Alcohols with n carbon atoms are considered, although in principle any alcohol with 1 to 20 carbon atoms and at least one hydroxyl group is possible, preferred starting materials are monofunctional aliphatics with 1 to 8 carbon atoms Alcohols. The optimal feedstocks are methanol, ethanol, propanol, with methanol being the most important as it is a commercially proven technology.

The overall chemical formula can be represented by the following formula.

ROH+CO→RCOOH

wherein R is the organic chain moiety as described above. The carboxylic acid product obtained from a certain alcohol is also easy to determine. For example, taking methanol (R=CH ₃ ) and ethanol (R=C ₂ H ₅ ) as examples, the products are acetic acid and propionic acid respectively.

Although the process of the present invention can be operated in batch mode, continuous mode is preferred in most cases. During continuous operation, the alcohol and/or the ester of the alcohol and the product carboxylic acid, together with carbon monoxide, and enough water to maintain a certain proportion of the carbonylation tank, rhodium catalyst, iodine derivatives, and catalyst stabilizers are sent into carbonylation reaction tank. The last four components are not consumed in the reaction and are continuously recirculated from the product outlet back to the reaction tank; only occasional additions are required. Corresponding to continuously adding various raw materials into the carbonylation reaction tank, the product effluent includes product carboxylic acid, rhodium catalyst, iodine derivative and catalyst stabilizer. The net effect is that the carbonylation reactor reaches a steady state while the liquid reaction medium that maintains the steady state contains quantities of water, stabilizers, iodine derivatives, alcohols and esters of carboxylic acids, rhodium catalyst and carboxylic acids. In fact, the carbonylation tank contains only a small amount of free alcohol, because the esterification reaction of alcohol and acid is relatively fast.

For the method of the present invention, each component group is preferably in the scope of the following table in the liquid reaction medium under steady state:

Generally Wider Range Better Range

Water 0.5-12% by weight 1-10% by weight

Esters of alcohols and acids 0.1-10% by weight 0.1-4% by weight

Iodine derivatives 5-20% by weight 10-16% by weight

Stabilizer 0.5-50 0.5-30

(to Rh molar ratio)

Rhodium catalyst (ppm) 100-1800 300-1200

Especially for carbonylation of methanol into acetic acid, the preferred components are water (1-10%), methanol acetate (0.1-4%), methyl iodide (10-16%), catalyst stabilizer (0.5-30%) ; With Rh molar ratio), the rhodium catalyst (300-1200ppm) and the rest are acetic acid and a small amount of impurities.

The temperature of the carbonylation reaction tank can be properly maintained at 100-220°C, and the higher the temperature, the faster the reaction rate. A preferred temperature range is 140-200°C. Carbon monoxide pressure was maintained at 10-200 atmospheres. The preferred pressure range is between 10 and 100 atmospheres.

Example

The present invention will be illustrated by the following examples, but these examples do not limit the scope of the invention.

The reactor used in the present invention includes a corrosion-resistant main reactor and a carbon monoxide storage tank, and a control valve is connected between the two to maintain and control the pressure of the main reactor. Reactor pressure was maintained at 400 psi (carbon monoxide partial pressure was 173 psi) in the examples of the present invention. The main reactor is also equipped with a mechanical stirrer and an alcohol storage tank, which is used to input alcohol and other reactants. The main reactor is heated with a heating pack and has a cooling water inlet to control the temperature. The main reactor also has a common inlet and outlet for liquid reactants and gaseous reactants.

In the operation of the reaction, the reactant methanol is directly added to a mixed solution containing a catalyst and an iodine promoter, and the reaction is kept at a constant temperature and a constant pressure. In order to quantitatively compare the reaction rate, the rate data is represented by Space Time Yield (STY) established by Smith B.L. et al. The calculation of reaction productivity is based on the amount of acetic acid formed per unit volume and unit time. The space-time yield can be obtained from the consumption rate of carbon monoxide in the carbon monoxide storage tank, the volume of the carbon monoxide storage tank and the volume of the reaction solution. Therefore, during the reaction, we constantly monitor the change of carbon monoxide pressure in the carbon monoxide storage tank to obtain the consumption rate of carbon monoxide.

After the carbonylation reaction was finished, the temperature was lowered to room temperature, the carbon monoxide was let off, and 25 milliliters of the reaction solution was placed in a sealed bottle. The clarified solution was extracted again, and the rhodium content in the solution was measured by ICP-AES.

Comparative Examples 1 and 2

For comparison with the present invention, we performed a low water carbonylation experiment without any additives. The content of each component in the reaction tank is 500ppm rhodium, 14wt% methyl iodide and 3wt% water. The reaction temperature was 190°C. Its STY value is about 8.1 measured through the above-mentioned experimental procedure, and the amount of rhodium dissolved in the solution after the reaction is 61% of the amount of added rhodium (see Table 1). In addition, we also add known catalyst stabilizer lithium iodide (LiI) under the same conditions, and the mol ratio of its addition and rhodium catalyst is 10, and the STY value measured after the reaction is 9.4, and the amount of dissolved rhodium is added 88% of the amount of rhodium (see Table 1).

Examples 1-6

Under the same conditions as Comparative Examples 1 and 2 (in the reaction tank, each component content is respectively rhodium 500ppm, methyl iodide 14wt%, water 3wt%, and the reaction temperature is 190 ℃, we have carried out a series of additions that have the prompting of the present invention Organic compound 4-pyridineethanesulphonic acid (4-pyridineethanesulphonic acid), pyridine-3-carboxylic acid (pyridine-3-carboxylic acid), pyridine-4-carboxylic acid (pyridine-4-carboxylic acid)), pyridine-3, 4-dicarboxylic acid (pyridine-3, 4-dicarboxylic acid) and 4-cyanopyridine (4-cyanopyridine) carbonylation experiment with low water content. The STY value and the amount of rhodium dissolved in the solution after the reaction can be measured through the above-mentioned experimental steps. It can be seen from Table 1 that the organic compounds suggested by the present invention 4-pyridineethanesulfonic acid, pyridine-3-carboxylic acid, pyridine-4-carboxylic acid, and pyridine-3,4-dicarboxylic acid have outstanding effects in reducing rhodium precipitation. Its reaction rate is also fast (see table 1) than adding any additive or adding equimolar catalyst stabilizer lithium iodide (LiI), and the organic compound 4-cyanopyridine with cyano group (CN) is reducing rhodium The effect on precipitation is not significant.

Table 1 Example 1-6 Rhodium 500ppm; Methyl iodide 14wt%; Water 3%; 190°C

Example additive L/Rh STY Dissolved Rh none 8.1 61% lithium iodide 10 9.4 88% 1 4-cyanopyridine 10 7.3 47% 2 4-Pyridineethanesulfonic acid 10 10.9 99% 3 4-Pyridineethanesulfonic acid 15 11.9 99% 4 Pyridine-3-carboxylic acid 10 10.5 99% 5 Pyridine-4-carboxylic acid 10 10.5 99% 6 Pyridine-3,4-dicarboxylic acid 5 9.7 99%

Examples 7-11

The reaction condition of the present embodiment is similar to embodiment 1-6, difference is that rhodium concentration is promoted to 700ppm. The catalyst stabilizer used is 4-pyridineethanesulfonic acid or pyridine-3,4-dicarboxylic acid. The STY value of its carbonylation reaction experiment can be measured through the above experimental steps. It can be seen from Table 2 that when 4-pyridineethanesulfonic acid has 8wt% water, its reaction rate is equivalent to that when the water content is 14wt% without adding any additives (14.9). When the water content is reduced to 6%, its STY value only drops to 14.

Table 2 Embodiment 7-11, Rh: 700ppm; Methyl iodide (MeI): 14%

Example Additives temperature water L/Rh STY 7 4-Pyridineethanesulfonic acid 185 6% 10 14 8 4-Pyridineethanesulfonic acid 185 8% 1 14.7 9 4-Pyridineethanesulfonic acid 190 8% 10 16.2 10 Pyridine-3,4-dicarboxylic acid 190 8% 5 15.1 11 none 185 14% 0 14.9

L/Rh: molar ratio of added amount to rhodium catalyst

Claims (8)

1. A method for producing an organic carboxylic acid of n+1 carbon atoms from alcohols of n carbon atoms and carbon monoxide, wherein, n takes a value in the range of 1 to 20, and the method is based on a catalytic system containing a rhodium catalyst In a liquid reaction medium, carbon monoxide is reacted with alcohols, and then the carboxylic acid is recovered from the resulting reaction product; this rhodium-containing catalytic system is characterized in that the carbonylation reaction tank is maintained in a liquid reaction medium containing the following composition during the carbonylation reaction Middle: (1) rhodium catalyst (2) iodine derivative corresponding to raw material alcohol (3) ester formed by product carboxylic acid and raw material alcohol (4) product carboxylic acid (5) at least 0.5-12% by weight of water (6) One selected from the group consisting of 4-pyridineethanesulfonic acid, pyridine-3-carboxylic acid, pyridine-4-carboxylic acid, pyridine-3,4-dicarboxylic acid and 4-cyanopyridine or multiple catalyst stabilizers. 2. The method according to claim 1, characterized in that the water content is maintained at 1 to 10% by weight. 3. The method according to claim 1, characterized in that the rhodium content is 100-1800 ppm. 4. The method of claim 1, wherein the catalyst stabilizer is 4-pyridineethanesulfonic acid. 5. The method of claim 1, wherein the catalyst stabilizer is pyridine-3-carboxylic acid. 6. The method of claim 1, wherein the catalyst stabilizer is pyridine-4-carboxylic acid. 7. The method of claim 1, wherein the catalyst stabilizer is pyridine-3,4-dicarboxylic acid. 8. The method according to claim 1, characterized in that the molar ratio of the catalyst stabilizer to the rhodium catalyst is within the range of 0.5 to 30.