KR20080020594A - A process for the preparation of p-toluic acid by liquid phase oxidation of p-xylene in water - Google Patents

Abstract

The present invention provides a process for the preparation of p-toluic acid by liquid phase oxidation of p-xylene using oxygen or air as oxidant in the presence of p-toluic acid, water as solvent and cobalt salt or its combinations with salts of Ce, Mn as catalyst. Oxidation is carried out at 130-190‹C and pressure sufficient to keep water in liquid state. Oxidation step is followed by filteration to obtain p-toluic acid as major product. Unreacted p-xylene is recovered and recycled and the catalyst is recovered from aqueous phase and is recycled. ® KIPO & WIPO 2008

Description

A process for preparing ｐ-toluic acid by liquid-phase oxidation of ｐ-xylene in water {A PROCESS FOR THE PREPARATION OF P-TOLUIC ACID BY LIQUID PHASE OXIDATION OF P-XYLENE IN WATER}

The present invention relates to a process for the preparation of p-toluic acid by liquid phase oxidation of p-xylene in water, in particular the binding of p-toluic acid and cobalt acetate (cobaltous acetate) or the catalyst cerium (III) acetate, and cobalt A process for the preparation of p-toluic acid by liquid phase oxidation of p-xylene in water in the presence of a salt or a catalyst composed of a combination of cerium and / or manganese salts. In particular, the present invention relates to a process for preparing p-toluic acid by oxidation of p-xylene in water as a solvent.

P-toluic acid is an important chemical intermediate product and is widely used in the manufacture of finished products in the manufacture of pharmaceuticals, pesticides, dyes, fluorescent emitters and the like. It is also used in the organic synthesis of various chemical compounds. P-toluic acid is produced as a byproduct during the production of terephthalic acid / dimethyl terephthalate, which is produced mainly by the liquid phase oxidation of p-xylene by oxygen / air in acetic acid medium.

The oxidation of p-xylene to terephthalic acid in an acetic acid solvent is widely described in US Pat. No. 2,833,816 where an initiator is a bromine or bromine containing compound and a catalyst comprising cobalt and manganese components. Homogeneous catalyst systems consisting of cobalt, manganese and bromide are the heart of this process. Oxygen compressed in air is used as oxidant and acetic acid as solvent.

It is advantageous to use bromine for this liquid phase oxidation, but there are some disadvantages as well. Highly corrosive bromine acetic acid environments during oxidation require expensive titanium line equipment as part of this process. In addition, bromine produces methyl bromide, a harmful gas. In addition, in the bromine promotion process, the reaction mixture must remain substantially “anhydrous” (US Pat. No. 3,064,044).

Another patent (US Pat. No. 3,046,305) discloses a process for preparing p-toluic acid from toluene, wherein toluene is reacted with chloroformamide under conditions of Friedel and Craft reaction, and the product thus obtained Is hydrolyzed to p-toluic acid. This process is not practical.

There is another patent reporting the oxidation of p-xylene to terephthalic acid in water. The Belof Labofina, SA patent (US Pat. No. 4,334,086) describes a two-step process for the oxidation of p-xylene, in which the Co-Mn catalyst and 10% (wt%) water are present. Oxidation of p-xylene is carried out at 170 ° C in the state. In the second step, some oxidized compounds are further oxidized at 200 ° C. in the presence of 20-70% water. After this oxidation, the water soluble compound is separated from insoluble terephthalic acid at 180-200 ° C., which contains p-toluic acid, a catalyst, and other byproducts and is recycled for later oxidation. The crude terephthalic acid crystals obtained in the sedimentation column have about 4.5% p-toluic acid and 2.5% 4-carboxybenzaldehyde as impurities. Labofina. S. A. (US Pat. No. 4,357,475) also describes the correlation between oxidation temperature and deposition column temperature for a similar oxidation process of p-xylene in the presence of water as described above. Labofina. S. A. (US Pat. No. 4,259,522) also describes a similar process for isophthalic acid by oxidizing m-xylene in the presence of water. Most patents, including the above patents, describe a process for the oxidation of p-xylene to produce terephthalic acid as the main product. Little information is available on the process for selectively producing p-toluic acid by liquid phase oxidation of p-xylene in an aqueous medium. The oxidation of p-xylene to p-toluene in acetic acid medium in the presence of a bromide initiator was described by S. H. Zaidi [Applied Catalysis, 27, 99-106 (1986)]. Thus, the process of producing p-toluic acid as the main product by liquid phase oxidation of p-xylene in water under suitable operating conditions without the use of brominated compounds as initiators is a very economical and commercially feasible and environmentally friendly technique. .

It is a main object of the present invention to provide a process for the preparation of p-toluic acid by liquid phase oxidation of p-xylene in water.

Another object of the present invention is to provide a process for the oxidation of p-xylene in environmentally friendly solvents such as water and bromine free catalysts, thereby providing a corrosive substance such as alkanoic acid as a solvent and bromine compound as an initiator. The use of can be avoided.

It is another object of the present invention to provide a process in which reaction by-products such as terephthalic acid and carboxybenzaldehyde are produced in the smallest possible amount so that high purity p-toluic acid is obtained.

Another object of the present invention is to provide a method for producing p-toluic acid by oxidizing p-xylene with oxygen, air or N ₂ -O ₂ mixture in the presence of p-toluic acid and water.

According to one aspect of the invention, the present invention is a method for producing p-toluic acid by liquid phase oxidation of p-xylene in water, in a temperature range of 130-190 ℃ for 5-10 hours, the total charge In the presence of a catalytically active salt of a transition metal selected from the group consisting of Co, Mn, Ce and compounds in the range of 1-200 mmol per mole of p-xylene in water in the range 40-85% of Oxidizing p-xylene or a mixture of p-xylene and p-toluic acid to oxygen, air or an oxygen / nitrogen mixture at a release flow rate of 60-80 ml / min at 25 kg / cm 2 pressure; Cooling the reaction mixture; And washing the unreacted p-xylene with an organic solvent followed by filtration to obtain a desired product.

In one embodiment of the invention, the amount of catalyst used is 5-160 mmol per mole of p-xylene.

In another embodiment of the invention, the transition metal salt is selected from the group consisting of cobaltous acetate, manganese acetate, cerium acetate, and compounds thereof.

In another embodiment of the invention, the cobalt acetate used is 5-150 mmol per mole of p-xylene.

In another embodiment of the invention, the concentration of cerium (III) acetate used is at most 6 mmol per mole of p-xylene.

In another embodiment of the invention, the p-toluic acid used is from about 0.1 to about 1.5 mmol per mole of p-xylene.

In another embodiment of the invention, the water consists of about 50 to about 80 weight percent of the reaction mixture.

In another embodiment of the invention, the pressure is preferably sufficient to keep the water in the liquid state in the range of 5 to 20 kg / cm 2.

In another embodiment of the invention, the reaction mixture is substantially free of organic solvents.

In another embodiment of the invention, the reaction product is recovered by filtration and then recovers some of the unreacted p-xylene and solvent (water) by evaporation and washing of the filtrate.

In another embodiment of the invention, the water remaining in the product consisting of a small amount of reaction product and catalyst is recycled in later oxidation.

The process is carried out at 130-190 ° C. temperature and 5-20 kg / cm 2, sufficient to maintain water in the liquid phase in the presence of a catalytically active metal compound selected from its mixture with Mn, Ce and cobalt compounds in a stirred reactor. It is carried out in an aqueous solution containing 50-80% by weight of water at pressure. After this reaction, the product is separated off as a solid material by filtration. Unreacted p-xylene is recovered from the filtrate by distillation and recycled. The remaining aqueous solution containing a small amount of reaction product and catalyst is later recycled in the oxidation.

Various processes are described in the literature for the production of terephthalic acid by liquid phase oxidation of p-xylene in acetic acid solvent in the presence of bromine-containing compounds as initiators and Co / Mn catalysts. Although the effect of water as a diluent in this process has been reported by Hanotier et al. (US Pat. Nos. 4,334,086 and 4,357,475), the main challenge is the oxidation of p-xylene by oxygen molecules in an aqueous medium to produce p-toluic acid. There is little information available about.

When this oxidation reaction is carried out, a catalyst is selected from Co, Mn compounds with or without cerium and the concentration of this catalyst is in the range of 1-200 mmol per mole of p-xylene. The compounds of cobalt and manganese are preferably cobalt acetate and manganese acetate, and the concentration of cobalt acetate is in the range of 5-150 mmol per mole of p-xylene. Cerium compound is cerium (III) acetate.

In this process, the presence of p-toluic acid is important and plays an important role during the oxidation of p-xylene in water. During the course of the study, 16.6% p-toluic acid of p-xylene at 130 ° C. resulted in a maximum conversion of xylene (76.87%) with 80.03% and 16-79% selectivity to p-toluic acid and terephthalic acid, respectively. Turned out. The presence of p-toluic acid is necessary to oxidize p-xylene in water and at least 16.6% of p-xylene is necessary to obtain the maximum conversion of p-xylene to the oxidized product. In the process of the present invention, the concentration of p-toluic acid is in the range of about 0.1 to about 1.5 mmol per mole of p-xylene.

In the present invention, the oxidation is carried out in the presence of water as a solvent. The presence of water as a solvent creates a three-phase system for oxidation that makes this reaction more difficult. The present invention shows that 55-80% water as solvent can be conveniently used for oxidation at 130-150 ° C. When a small amount of water is used, i.e. less than 55% of the reaction mixture is used, the reaction mixture becomes a thick slurry which is difficult to stir and proper mixing of the reactants could not be achieved even by mechanical stirring. Poor mixing of the reactants resulted in lower conversion of p-xylene, possibly due to an increase in resistance to diffusion of O _{2 into} the liquid phase. The conversion of p-xylene as well as the selectivity to terephthalic acid increases somewhat with increasing temperature from 130 ° C. to 150 ° C., but the selectivity to p-toluic acid is about the same.

In the present invention, cerium (III) acetate was combined with cobalt acetate at concentrations up to 6 mmol per mole of p-xylene to increase the selectivity of p-toluic acid when used as cocatalyst. The presence of cerium (III) acetate along with cobalt (II) acetate plays an important role during oxidation. Cerium (III) acetate is a catalyst of cobalt (II) acetate [~ 5% (mol%) of Co (II)] and p-xylene when used with p-xylene [6.7% (mol%)] In the presence, it was oxidized in water (77% of charge) at 130 ° C. temperature and 20 kg / cm 2 pressure of oxygen, and the selectivity of p-toluic acid increased from 77.53% to 84.68%.

In the present invention, the reactor contents were cooled, filtered and washed with water. The filtrate and rinse are distilled, where the unreacted p-xylene and the same portion of water are distilled as an azeotropic mixture of p-xylene and water. The p-xylene thus obtained is recycled. The remaining aqueous solution containing the catalyst and a small amount of oxidation product is also recycled later in the oxidation.

The invention is described in detail with reference to the following examples, where different process conditions / reaction parameters are given for the purpose of illustration and should not be construed as limiting the scope of the invention.

Example -One

30 g of p-xylene, 5.0 g of p-toluic acid, 5.0 g of cobalt acetate, and 150 g of water were charged to the autoclave. The reactor was pressurized with oxygen to a pressure of about 15 kg / cm 2 and then heated to 130 ° C. The pressure in this reactor was continuously stirred at 20 kg / cm 2 at 75 ml / min of discharge oxygen flow rate. After 6 hours reaction, the reactor was cooled down and the contents were filtered and washed with toluene. Total unreacted p-xylene was determined from the state of the organism and the contents of the toluene trap (which is maintained after the reactor through which the offgas passed during the reaction) by analyzing them by gas chromatography. The solid product is also p- to 82-39% of p-toluic acid (p-TA), 1.82% of 4-carboxybenzaldehyde (4-CBA), 13.50% of terephthalic acid (TPA), and other products (mol%) combined with oxygen as 1.35%. GC of reaction product / stream as 65.41% conversion of xylene Analyzed by analysis.

Example -2

30.0 g of p-xylene was oxidized with oxygen at 150 ° C. in the presence of 5.0 g p-TA, 5.0 g cobalt acetate, and 150 g water. This reaction was carried out as in Example-1. 78.23% of p-xylene was converted to p-TA 90.56%, 4-CBA 2.75%, TPA 6.32%, and other 0.30%.

Example -3

30.0 g of p-xylene was oxidized with oxygen at 150 ° C. in the presence of 5.0 g of cobalt acetate and 150 g of water as catalyst. This reaction was carried out and processed as in Example-1. In the absence of p-TA, no oxidation occurred and almost all p-xylene recovered to the unreacted state.

Example -4

30.01 g of p-xylene was oxidized with oxygen at 150 ° C. in the presence of 0.3 g cerium (III) acetate and 4.4 g of cobalt acetate as catalyst in 150 g of water. This reaction was carried out as in Example-1. In the presence of cerium with cobalt instead of without p-TA, 20.05% of p-xylene was converted to a compound combined with oxygen. A white solid product was found consisting of 96.62% p-TA, 0.42% terephthalic acid, and 2.96% other.

Example -5

30.0 g p-xylene was oxidized with oxygen molecules at 130 ° C. in the presence of 10.04 g p-TA, 5.0 g cobalt acetate as catalyst, and 150 g water as solvent. This reaction was carried out as in Example-1. 72.2% of p-xylene was converted to compounds combined with oxygen such as p-TA 77.53%, 4CBA 4.75%, TPA 16.98%, and other 0.73%.

Example -6

Under the experimental conditions of Example-5, 30.0 g of p-xylene was oxidized with oxygen molecules at 130 ° C. except that a mixture of 0.31 g of cerous acetate and 4.48 g of cobalt acetate was used as a catalyst. 67.34% of p-xylene was converted to compound combined with oxygen as p-TA 84.68%, 4-CBA 2.04%, and TPA 13.22%.

Example -7

30.0 g p-xylene was oxidized with oxygen at 130 ° C. in the presence of 10.0 g p-TA, 5.0 g cobalt acetate as catalyst, and 150 g water as solvent. This reaction was performed at 10 kg / cm 2 pressure as in Example-1. 73.38% of p-xylene was converted to compound combined with oxygen as p-TA 82.88%, 4-CBA 2.87%, and TPA 14.25%.

Example -8

30.0 g of p-xylene was oxidized with oxygen at 130 ° C. in the presence of 5.0 g p-TA, 5.02 g cobalt acetate, and 50 g water as solvent. This reaction was carried out at 20 kg / cm 2 pressure as in Example-1. 67.46% of p-xylene was converted to compound compounded with oxygen as p-TA 78.99%, 4-CBA 1.46%, TPA 16.24%, other 3.3%.

According to the present invention, the advantages of the process for producing p-toluic acid by liquid phase oxidation of p-xylene in an aqueous medium are as follows.

The most important advantage is that it is very safe, nonflammable, non-toxic, readily available and inexpensive because it uses water as the solvent.

2. This production method is safe due to the rapid heat transfer from the reactor during the exothermic oxidation reaction in an aqueous medium.

3. Due to the elimination of bromine-free catalysts and acetic acid solvents, this manufacturing method is not corrosive, requiring no particularly expensive equipment.

4. High conversion of p-xylene and high yield of p-toluic acid are comparable to those using acetic acid as a solvent.

Claims (11)

In the process for producing p-toluic acid by liquid phase oxidation of p-xylene in water, With Co, Mn, Ce and compounds thereof in the temperature range of 130-190 ° C. for 5-10 hours in the range of 1-200 mmol per mole of p-xylene in water in the range of 40-85% of the total charge. In the presence of a catalytically active salt of a transition metal selected from the group consisting of p-xylene or a mixture of p-xylene and p-toluic acid at a release flow rate of 60-80 ml / min at a pressure of 3-25 kg / cm 2 Oxidizing with oxygen, air or oxygen / nitrogen mixture; Cooling the reaction mixture; And And washing the unreacted p-xylene with an organic solvent followed by filtration to obtain the desired product. The method of claim 1, The amount of catalyst used is 5-160 mmol per mole of p-xylene. The method of claim 1, The transition metal salt used is selected from the group consisting of cobaltous acetate, manganese acetate, cerium acetate and compounds thereof. The method according to claim 1 or 2, Cobalt acetate is 5-150mmol per mole of p-xylene. The method according to any one of claims 1 to 4, The concentration of cerium (III) acetate used is up to 6 mmol per mole of p-xylene. The method according to any one of claims 1 to 5, The p-toluic acid used comprises from about 0.1 to about 1.5 mmol per mole of p-xylene. The method according to any one of claims 1 to 6, Water comprises about 50 to about 80 weight percent of the reaction mixture. The method according to any one of claims 1 to 7, The pressure is preferably enough to keep the water in the liquid state in the range of 5 to 20kg / ㎠. The method according to any one of claims 1 to 8, Wherein said reaction mixture is substantially free of foreign organic solvents. The method according to any one of claims 1 to 9, The reaction product is recovered by filtration, and then recovers some of the unreacted p-xylene and solvent (water) by evaporation and washing of the filtrate. The method according to any one of claims 1 to 10, Water remaining in the product consisting of a small amount of the reaction product and the catalyst is subsequently recycled in oxidation.