RU2170724C1 - Method of preparing methyl acetate, and catalysts for carrying it through - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: method comprises carbonylation of dimethyl ether in gas phase at elevated pressure at temperature from 200 to 250 C in the presence of catalyst. Catalyst is acid cesium salt of phosphorus-tungsten heteroacid composed of Cs_xH_yPW₁₂O₄₀, wherein 1,5 ≅ x ≅ 2, y = 3-x, with rhodium additives in amount from 0.1 to 2.5 wt %. EFFECT: increased yield of methyl acetate in reaction of carbonylated dimethyl ether without using halogencontaining promoters. 4 cl, 5 ex, 1 tbl

Description

 The invention relates to methods for producing acetic acid ester (methyl acetate) by carbonylation of dimethyl ether in the gas phase in the presence of a catalyst.

 Acetic acid and its esters are large-tonnage products of basic organic chemistry and are widely used in industrial syntheses and processes. World production of acetic acid is 7.0 million tons per year.

Until 1995, more than 60% of acetic acid in the world was obtained according to the well-known technology of liquid-phase carbonylation of methanol on rhodium catalysts in the presence of iodide promoters (Monsanto process, 1970). [MJ Howard, MD Jones, MS Roberts, SATaylor, C ₁ to Acetyls: Catalysis and Process, Catal. Today, 18 (1993) 325].

 This process is carried out only in the presence of halogen promoters, mainly methyl iodide, which require the use of special alloys due to their high corrosivity. A careful separation of the catalyst and iodide from the target product, which is an intermediate for many organic syntheses, is also necessary.

 The advantage of gas phase carbonylation is that the separation of products from the catalyst is easy, but the main problems associated with the use of iodide promoters remain [M.J. Howard, G. J. Sunley, A.D. Poole, R.J. Watt, B.K. Sharma, New Acetyls Technologies from BP Chemicals, Science and Technology in Catalysis (1998) 61.].

 In recent years, several catalytic systems have been proposed for halogen-free gas-phase carbonylation, the main disadvantages of which are very low selectivity and low activity. In the patent [US 4612387, C 07 C 1/20, 09.16.86], copper-containing zeolite catalysts Cu / H-ZSM-5 are proposed. The acetate productivity for this catalyst was 0.03 g / g cath and the selectivity was less than 30%.

 Higher capacities are noted for the cobalt zeolite catalyst, but the reaction proceeds at a pressure not lower than 700 atm [DE 3606169 A1]. Studies by BP Chemical led to the development of a more active catalyst for the synthesis of acetates with selectivity of up to 70%, but the stable operation time of such a catalyst did not exceed 10 hours, after which the reaction direction changed, the main product was dimethyl ether [B. Ellis, M.J. Howard, R. W. Joyner, K.N. Reddy, M.B. Padley, W.J. Smith, Heterogeneous Catalysts for the Direct, Halide-free Carbonilation of Methanol, Stud. Sur. Sci. Catal. 101 (1996) 771].

 Rhodium and iridium salts of phosphor tungsten heteropoly acids supported on silicon oxide showed a rather high selectivity, but low activity [EP 0353722, C 07 C 67/36, 08/01/89]. The productivity of the catalysts did not exceed 50-60 g / l h in the reaction of carbonylation of methanol and 15-20 g / l h in the reaction of carbonylation of dimethyl ether (prototype).

 The problem solved by this invention is to increase the yield of methyl acetate in the carbonylation reaction of dimethyl ether without the use of halogen-containing promoters.

The problem is solved by the method of producing methyl acetate by carbonylation of dimethyl ether in the gas phase at a temperature of 200-250 ^o C in the presence of a catalyst, which is an acidic cesium salt of phosphor tungsten heteropoly acid composition Cs _x H _y PW ₁₂ O ₄₀ , where 1.5 ≅ x ≅ 2, y = 3 -x, with the addition of rhodium, the content of rhodium in the catalyst is not lower than 0.1 wt.%. The process is carried out at a pressure of at least 5 atm.

The problem is also solved by the catalyst for the production of methyl acetate by carbonylation of dimethyl ether at a temperature of 200-250 ^o C, which is an acidic cesium salt of phosphor tungsten heteropoly acid composition Cs _x H _y PW ₁₂ O ₄₀ , where 1.5 ≅ x ≅ 2, y = 3-x, s additives of rhodium, the content of rhodium is not lower than 0.1 wt.%.

The proposed method for the synthesis of methyl acetate is as follows: dimethyl ether is mixed with carbon monoxide in the required ratio and passed through the catalyst beds at a pressure of at least 5 atm and a temperature of 180-250 ^o C. The reaction products are cooled and separated into gaseous and liquid. Condensate is the target product - methyl acetate. The gas mixture (unreacted dimethyl ether and carbon monoxide) is again fed to the reactor.

 The proposed synthesis method is characterized in that the catalyst for producing methyl acetate is an acid cesium salt of a phosphor tungsten heteropoly acid with rhodium additives, the content of rhodium is not lower than 0.1 wt.%.

The composition of the catalyst is Cs _x H _y PW ₁₂ O ₄₀ , where 1.5 ≅ x ≅ 2, y = 3-x. The catalyst is prepared by precipitation, a solution of cesium salt is poured with constant stirring to a mixture of solutions of phosphor tungsten heteropoly acid and rhodium salt, taken in the required ratio. The resulting precipitate was evaporated, tabletted and crushed. A catalyst fraction of 0.5-1 mm in size is loaded into the reactor. The surface of the obtained samples is 57-100 m ² / g.

 The invention is illustrated by the following examples.

Example 1. The process of carbonylation of dimethyl ether to methyl acetate is carried out by passing a mixture of dimethyl ether with carbon monoxide through a catalyst bed at a temperature of 200 ^° C and a pressure of 10 atm, a ratio of DME: CO = 1:10, a gas feed rate of 3000 h ^-1 , conversion of dimethyl ether is 22%.

The process is carried out on a catalyst, which is an acid cesium salt of a phosphor tungsten heteropoly acid of the composition Cs ₂ HPW ₁₂ O ₄₀ , the rhodium content is 0.1 mass%. The catalyst was prepared by precipitation, a solution of cesium nitrate salt (0.1 M) was added dropwise with constant stirring to a mixture of solutions of phosphor tungsten heteropoly acid (0.1 M) and rhodium chloride (0.1 M) taken in the required ratio. The resulting suspension is stirred for 24 hours, then the precipitate is evaporated, tabletted and crushed. The catalyst fraction 0.5-1 mm in size is loaded into the reactor. The surface, activity and selectivity of the catalyst are shown in the table.

 Example 2. Analogously to example 1, but the content of rhodium is 0.5 wt. %

 Example 3. Analogously to example 1, but the content of rhodium is 1.0 wt. %

 Example 4. Analogously to example 1, but the content of rhodium is 2.5 wt.%.

Example 5. Analogously to example 1, but the cesium salt of the phosphor tungsten heteropoly acid has a composition of Cs _1.5 H _1.5 PW ₁₂ O ₄₀ , the rhodium content is 1.0 wt.%.

 As can be seen from the table, this method provides a yield of methyl acetate 6-9 times higher than the dimethyl ether known in the carbonylation reaction without the use of an iodide promoter.

Claims (2)

1. The method of producing methyl acetate by carbonylation of dimethyl ether in the gas phase at elevated pressure, at a temperature of 200 - 250 ^o C in the presence of a catalyst comprising heteropolyacid salts, characterized in that the carbonylation process is carried out on a catalyst representing a cesium phosphoric tungsten acid salt heteropoly acids of the composition Cs _x H _y PW ₁₂ O ₄₀ , where 1.5 ≅ x ≅ 2, y = 3 - x, with rhodium additives in an amount of from 0.1 to 2.5 wt.%
2. The method according to claim 1, characterized in that the process is carried out at a pressure of at least 5 atm. 3. The catalyst for the production of methyl acetate by carbonylation of dimethyl ether at elevated pressure, at a temperature of 200 - 250 ^o C, which includes salts of heteropoly acids, characterized in that the catalyst is an acidic cesium salt of phosphor tungsten heteropoly acid composition Cs _x H _y PW ₁₂ O ₄₀ where 1.5 ≅ x ≅ 2, y = 3 - x, with rhodium additives in an amount of from 0.1 to 2.5 wt.%.

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