New Methods and New Processes for the Synthesis of DMAC

US DuPont patented technology

In patent US3300531, DuPont introduced the process of producing N, N-dimethylacetamide from acetic acid and dimethylamine. This process adopts special reaction device and process flow, in order to avoid reverse mixing of reactants, using the reactor length tube with length ratio greater than 500:1, using two distillation towers to separate the refined products, to solve the problem of acetic acid and N, N-dimethylacetamide difficult to separate the products due to azeotropic, and obtain DMAC products with high purity. In addition to the acetic acid process, DuPont also developed the process of trimethylamide synthesis, conducted a small trial of the process and applied for the patent CA1304408.

The route uses nitrogen as the protective gas, CO 2 (CO) 8 as the catalyst, trimethylamine and carbon monoxide, water as the hydrogen donor, and synthesize N, N-diethylacetamide at pressure 2.7~27.5MPa and temperature 220~250℃. The reaction equation is as follows:

In the production rate of this process, CH3Co (CO) 4 actually plays a catalytic role, and with water as the hydrogen donor, the conversion rate of trimethylamine can reach 94%.

Mitsubishi Liyang Technology

Mitsubishi Riyang Corporation of Japan has invented a new production process to synthesize N, N-dimethylacetamide from acetic acid and dimethylamide. And applied for a patent in Japan in 1998 with public number JP123853; and in China in 1995 with patent number CN1298382A.

This process is at atmospheric pressure and low temperature (30~60℃), acetic acid and dimethyine salt solution, and then the liquid into the mediation reactor, add dimethylamine, at 1~3MPa, temperature of 150~250℃, molybdic acid, tungstic acid, partial vanadium acid as catalyst, reaction for 1~2 hours, the upper recovery of the excessive dimethylamine gas is recycled, and the product is discharged from the bottom.

The advantages of this process are simple equipment, short reaction time and high product yield; the disadvantages are high equipment, material and high operating cost.

South Korea Samsung Technology

South Korea Samsung Patent KR1019990044579 introduces a method for producing N, N-diethylacetamide.

In this process, acetic acid and diamine are neutralized into diamine acetate salt in the temperature range of 50 to 160℃, and the neutralization salt is dehydrated under 130 to 180℃ under the action of catalyst to produce N, N-diethylacetamide. The patented technology uses aluminum salt as the catalyst, but it is unstable in the reaction.

Low pressure catalytic method

Southwest Chemical Industry Research and Design Institute has designed and developed a new technology for catalytic synthesis of DMAC under low pressure conditions. This technology uses a series reaction of liquid phase kettle reactor, first passing dimethylamine into the acetic acid solution, the two quickly neutralize the diamine acetate salt, then lift the pressure of the system, and condense the diamine acetate salt under low pressure to produce the product. Excess dimethylamine was recovered, and the product was dehydrated and refined to obtain DMAC.

The best material ratio for this process is n (acetic acid): n (dimethylamine) =1:1.2. The amount of catalyst is 0.6%~1.2% (measured by the quality of acetic acid). The yield of acetate conversion and DMAC can be over 95% under the optimal reaction conditions.

Catalytic reaction by the distillation method

Wang Xiaoli, Wang Ru et al. of Fushun Vocational and Technical College, [32] of Liaoning Petrochemical University improved the reaction process on the basis of the traditional acetic acid catalytic condensation method, combined the reaction and distillation technology to directly synthesize DMAC, so that the acetic acid reaction heat could be used and reduce the energy consumption in the reaction process. At the same time, because the reaction and distillation are in the same equipment, the equipment is reduced, and the process flow is shortened. But the study is an intermittent process and is still in the small trial stage.

Jiangsu Institute of Technology has successfully carried out a small test of DMAC synthesis, and achieved good results. In this method, Lewis acid is used as the catalyst, acetic acid and diamidine are used to form acylation solution, amidation in the atmosphere of excessive dimethylamine, continuously feed and extract crude products. The pure product was obtained by secondary distillation.

The small test process realizes the partial coupling of reaction and distillation, simplifies the process, and solves the problem of incomplete separation of acetic acid and DMAC due to zeolization. It has the advantages of low production cost, good product quality, less pollutants and simple post-treatment.

Methyl acetate method

DMAC was synthesized with dimethylamine and methyl acetate, patent US3342862 applied by Monsanto, and reacted in a packing tower to separate DMAC and methanol. Southwest Chemical Industry Research and Design Institute of China synthesized DMAC with dimethylamine and methyl acetate as raw materials, selected the kettle reactor for intermittent reaction, and continuously refined DMAC. However, by this method, methyl acetate is prone to hydrolysis under this process condition, and the production cost of the product is high.

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