JPH0121138B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an industrially useful method for producing dimethoxyethane from dimethyl ether, which is an intermediate product, in the process of synthesizing ethylene glycol from methanol via dimethyl ether and dimethoxyethane. Methanol is produced in large quantities from natural gas using established technology, and thanks in part to the decline in the price of raw natural gas, it is easily and inexpensively available and has a wide range of uses, including as a fuel. development is being considered. As part of this effort, the synthesis of ethylene glycol from methanol has attracted attention, and several methods have already been proposed. (1) Method by dimerization of methanol Since the dimerization of methanol by dehydrogenation corresponds to ethylene glycol,
Studies are underway to perform this reaction directly. For example, a method of dehydrogenating and dimerizing methanol by irradiating it with radiation (B.Ya.Ladygin et al.,
Kinetics and Catalysis, 6 , 779 (1960)),
A method in which methanol is dehydrogenated and dimerized by using a platinum group metal complex such as rhodium or palladium as a catalyst and further irradiated with light (Yamamoto et al., 50th Catalyst Symposium, P290 (1982)), or at 800°C without a catalyst.
A method of coupling oxidation and dehydrogenation by reacting methanol and oxygen at high temperatures (JB
Cropley, US Pat. No. 4,345,104), etc. have been proposed. Although these methods are simple because methanol is reacted as is, the highly reactive hydroxyl group is not protected, so side reactions tend to proceed, and high selectivity cannot be obtained. Furthermore, since this reaction is not a chain reaction, light, radiation, etc. are extremely disadvantageous from an economic standpoint and at the same time not desirable from a safety standpoint. In an attempt to couple the highly reactive hydroxyl group after protecting it, we synthesized methyltrialkylsilyl ether consisting of methanol and trialkylsilanol, and reacted it with di-tert-butyl peroxide to perform oxidative coupling (Japanese Patent Application Laid-open No. 53-73506), but it is economically impractical due to the stoichiometric consumption of expensive peroxides and the recycling of large amounts of trialkylsilanol during the production of ethylene glycol from methanol. It's hard to hold. (2) Method via formaldehyde Several methods are known in which methanol is dehydrogenated to form formaldehyde and then converted to ethylene glycol, but these methods require high pressure or the catalytic action of a strong acid, so they have not been commercialized. It is difficult. Under these circumstances, there is a strong desire to develop an industrially advantageous method for synthesizing ethylene glycol from methanol. An object of the present invention is to provide an industrially advantageous method for producing dimethoxyethane from dimethyl ether in the process of synthesizing ethylene glycol from methanol. In the ethylene glycol synthesis process to which this invention is applied, methanol is converted to ethylene glycol through a process represented by the following formula. 2CH ₃ OH→CH ₃ OCH ₃ +H ₂ O …(1) 2CH ₃ OCH ₃ +1/2O ₂ →CH ₃ OCH ₂ CH ₂ OCH ₃ +H ₂ O …(2) CH ₃ OCH ₂ CH ₂ OCH ₃ +2H ₂ O →HOCH ₂ CH ₂ OH +2CH ₃ OH …(3) or CH ₃ OCH ₂ CH ₂ OCH ₃ +2CH ₃ OH → HOCH ₂ CH ₂ OH + CH ₃ OCH ₃ In the reaction of formula (1), dimethyl ether is produced by dehydration of methanol. This reaction can be carried out very easily using known methods. Further, the reaction of formula (3) is a hydrolysis reaction of dimethoxyethane, and proceeds relatively easily. The feature of this inventive method is that, unlike various routes studied in the prior art, methanol is first dimerized and converted into dimethyl ether, this dimethyl ether is oxidatively coupled to form dimethoxyethane, and then this dimethoxyethane is converted into dimethyl ether. The key point is that it uses a new route of hydrolyzing ethane to produce ethylene glycol. As mentioned above, since the reactions of formulas (1) and (3) proceed relatively easily, the reaction of formula (2) is a key step in the method of this invention. In the method of this invention, the reaction of formula (2), ie, the reaction of oxidatively coupling dimethyl ether to produce dimethoxyethane, is carried out using a special catalyst. The catalyst used in the method of this invention is one in which an oxide of a metal belonging to group b of the periodic table, ie, tin, lead, etc., is supported on MgO. According to the results of numerous experiments conducted by the present inventors, the above-mentioned catalyst exhibited a unique selectivity for the production of dimethoxyethane, whereas other known redox catalysts, such as chromium oxide, manganese oxide, etc. No formation of dimethoxyethane was observed.
It was also confirmed that oxides such as tin and lead do not produce dimethoxyethane when combined with carriers other than MgO. Although there are no particular restrictions on the conditions for carrying out the reaction of formula (2), it has been found that the reaction proceeds advantageously at a temperature of 150°C or higher and under slight pressure. It has been determined that the optimum temperature is about 200-230°C and the optimum pressure at this temperature is about 10-20 atm.
At temperatures below 150℃, the reaction rate naturally slows down.
In addition, under high temperature conditions exceeding 250℃, CO ₂ , CO,
By-products including methane and methanol increase, and the selectivity to dimethoxyethane decreases. Moreover, if the pressure is too high, the catalyst activity will decrease. However, the temperature and pressure conditions are not limited, and optimal conditions can be easily selected by those skilled in the art. Furthermore, it has been found that depending on the reaction conditions, the reaction of formula (2) may proceed more favorably by using a catalyst prepared by adding a small amount of an alkali metal compound to the above catalyst. Example Using a general fixed bed flow reactor, experiments were conducted using various catalysts to oxidatively couple dimethyl ether to produce dimethoxyethane according to the reaction of equation (2). The catalyst is MgO
The desired metal oxide (along with Na, if used) was supported on a porous carrier consisting of the following materials, and then activated by firing in air. The catalysts used, reaction conditions and results are summarized in Table 1.

[Table] Comparative Example An oxidative coupling experiment of dimethyl ether was conducted under the same conditions as in the example using a known redox catalyst outside the scope of the present invention. The catalyst used, reaction conditions and results are shown in Table 2. As is clear from the results of the above Examples and Comparative Examples, according to the method of the present invention, it is possible to effectively carry out the reaction of oxidative coupling of dimethyl ether to produce dimethoxyethane, and the dehydration coupling of methanol is possible. An industrially viable method for synthesizing ethylene glycol from methanol is provided by combining the reaction for producing dimethyl ether by hydrolysis of dimethoxyethane and the reaction for producing ethylene glycol by hydrolysis of dimethoxyethane.

【table】

Claims (1)

[Claims] 1. Production of dimethoxyethane from dimethyl ether, characterized in that dimethoxyethane is produced by oxidative coupling of dimethyl ether in the presence of a catalyst in which tin or lead oxide is supported on MgO. How to do it. 2. The method according to claim 1, wherein a small amount of an alkali metal compound is added to the catalyst.