Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Patent
1996-07-24
1998-06-30
Burn, Brian M.
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
564470, C07C20916
Patent
active
057736596
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE ART
The present invention relates to a process for producing dimethylamine, utilizing the gas phase catalytic reaction between methanol and ammonia. More particularly, the present invention relates to a process for producing dimethylamine, characterized by using a specific catalyst.
Dimethylamine is an important chemical intermediate useful in the production of a variety of solvents, pharmaceuticals, rubber chemicals and surface active agents.
BACKGROUND ART
Typically, dimethylamine is produced by carrying out the reaction between methanol and ammonia in the gaseous phase at a high temperature (approximately 400.degree. C.) in the presence of a solid acid catalyst, such as alumina or silica alumina, capable of causing dehydration and amination. In addition to dimethylamine (hereinafter referred to as DMA), monomethylamine (hereinafter referred to as MMA) and trimethylamine (hereinafter referred to as TMA) are produced as by-products by this reaction. The demand for these by-product methylamines is considerably smaller than that for DMA. For this reason, after being separated from the reaction product, these by-products are transferred to the reaction system and reused.
Distillation is conducted in order to isolate dimethylamine from the methylamine reaction product. However, TMA forms complicated azeotropic mixtures with ammonia, MMA and DMA, so that a very intricate, large-scale distillation operation is needed. As a result, the cost for energy to be consumed by the process of recovering DMA amounts extremely high. The recovery process is shown in detail, for instance, in "Manufacturing Process Charts, Revised Edition" (in Japanese) (published by Kabushiki Kaisha Kagaku Kogyo-Sha on Apr. 25, 1978).
In order to reduce the production cost of DMA and to make the size of the equipment smaller, it is essential to suppress, as much as possible, the formation of the by-product methylamines, especially the formation of TMA, and to promote the formation of DMA. However, the selectivities of the three methylamines are thermodynamically determined on the above-described conventional amorphous solid acid catalyst such as alumina or silica alumina. Under the typical reaction conditions, the rate of TMA formation is considerably higher than that of DMA formation.
For instance, in the case where the reaction temperature is 400.degree. C. and the ratio of ammonia to methanol at the inlet of a reactor is 1:1 (weight ratio), the weight ratio of the amines formed at equilibrium, calculated thermodynamically is MMA:DMA:TMA=0.284:0.280:0.436. It is therefore necessary to continually separate a large amount of MMA and TMA, and to recirculate, in the reaction system, these two methylamines along with a large amount of excess ammonia which is to exist so that the reaction can proceed favorably to DMA from the viewpoint of equilibrium.
In recent years, various zeolite catalysts have been proposed in order to solve the above problem. For example, there can be mentioned Japanese Laid-Open Patent Publication No. 69846/1981 which relates to zeolite A; Japanese Laid-Open Patent Publications Nos. 148708/1979 and 69846/1983 which relate to FU-1; U.S. Pat. No. 4,082,805 which relates to ZSM-5; Japanese Laid-Open Patent Publication No. 113747/1981 which relates to ferrierite and erionite; Japanese Laid-Open Patent Publications Nos. 178951/1986 and 8358/1988 which relate to rho, ZK-5 and chabazite; and Japanese Laid-Open Patent Publications Nos. 46846/1981, 210050/1984 and 049340/1983 which relate to mordenite.
Although all of the processes using the above zeolite catalysts may give DMA selectivities higher than the thermodynamical equilibrium values, the DMA selectivities and the suppression of TMA formation are not always sufficient. In addition, there is still remaining such a problem that the DMA selectivity is, in general, drastically lowered when the conversion of methanol exceeds 95-96%, so that it is required to continually keep a considerable amount of unreacted methanol so as to maintain the DMA selectivity high.
REFERENCES:
patent: 4918233 (1990-04-01), Deeba et al.
Fukatsu Michio
Nakamura Toshio
Narita Takeshi
Nishijima Katsumasa
Niwa Kiyonobu
Burn Brian M.
Nitto Kagaku Kogyo Kabushiki Kaisha
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