JP2764114B2 - Method for producing methanol - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing methanol. More specifically, the present invention relates to a method for producing methanol from carbon dioxide and hydrogen in a solvent.

Methanol is one of the most basic general-purpose chemicals used for synthesis raw materials such as formaldehyde and carboxylate.

In recent years, the concentration of carbon dioxide in the atmosphere has been increasing remarkably, and it is the carbon source that is most concerned about the impact on the destruction of the global environment, such as the greenhouse effect caused by it.

[Prior Art] Industrial methanol synthesis methods include high-pressure synthesis (320-380 ° C, 340-400 atm) using carbon monoxide and hydrogen as raw materials and a zinc-chromium-based catalyst, and copper-zinc. A low-pressure synthesis method using a system catalyst (250 to 300 ° C., 50 to 150 atm) is known. This reaction is an equilibrium reaction in which the number of moles decreases with exotherm, and the lower the temperature and the pressure, the more advantageous the chemical equilibrium. Therefore, if the reaction heat is not sufficiently removed and the reaction temperature is not properly controlled, the conversion decreases, and the reaction cannot be advantageously advanced. The above-mentioned conventional processes are all gas-phase flow-type catalytic reaction processes, and have a problem that it becomes very difficult to design a reactor especially when the process is enlarged.

As a method for overcoming such problems, a method for synthesizing methanol from carbon monoxide and hydrogen in a liquid phase has been studied. For example, Chem Systems and Air Pr
A liquid phase fluidized bed reaction system has been developed by oducts and has been implemented until pilot testing. This method disperses a heterogeneous catalyst in an inert medium and directly converts the raw material gas to methanol.Since heat removal is easy, temperature control is simple, and a uniform temperature distribution can be obtained, this method is better than the gas phase method. Is also said to be excellent. The Brookhaven National Laboratory in the United States is also developing a process for synthesizing methanol from a synthesis gas obtained by the partial oxidation of natural gas as a raw material by a low-temperature liquid-phase reaction using a volatile liquid catalyst. Since the reaction system has a very low reaction temperature of 120 ° C., a high one-pass conversion can be obtained in terms of chemical equilibrium, and there is no need to recycle unreacted gas. It is called a process.

On the other hand, methanol synthesis by hydrogenation of carbon dioxide is often studied in parallel with a synthesis method from synthesis gas. That is, it is known that the synthesis gas contains a considerable amount of carbon dioxide, and that the synthesis of methanol sometimes proceeds more advantageously in the presence of carbon dioxide. For example, Applied Catalysis, Vol. 4, pp. 281 to 286 (1982) (Appl. Catal., 4,
To 281-6 (1986)), the synthesis of methanol vapor phase from the carbon dioxide and hydrogen using a Cu-ZnO-La ₂ O ₃ catalyst has been reported. Bull Chem Sos Japan, Volume 60, 26
63-2664 (1987) (Bull. Chem. Soc. Jpn., 60,
(7), 2663-2664 (1987)), the reaction between carbon dioxide and hydrogen is more advantageous for methanol synthesis than the reaction between carbon monoxide and hydrogen. A reaction mechanism for the generation via carbon dioxide is also provided.

However, in these vapor phase processes, the above-mentioned problems cannot be essentially solved unless the reaction heat is removed and the reaction temperature is not sufficiently controlled. There is also a limit to the temperature drop, and thus a limit to the solution of the problem.

Thus, an idea of synthesizing methanol by reacting carbon dioxide and hydrogen in a liquid phase is conceivable, but there have been few studies on this and little is known. Izvesta Academy Nauk S.S.S.S.S. Seriya Chemichskaya, No. 12.2669-2770 (19
79 years) (Izv.Akad.Nauk.SSSR Khim., No. 12, 2769-2770
(1979)), as a reaction example, using benzene as a reaction solvent, in the presence of a tin tetrachloride catalyst, at 200 ° C. and 100 atm (CO ₂ / H ₂ = 1 /
3) After 12 hours of reaction, a conversion rate of only 9% and a methanol yield of 8% were obtained. However, tin tetrachloride generates hydrochloric acid due to the generated water, which may significantly corrode the apparatus, and still has problems such as insufficient yield.

Chemical Engineering Science, Vol. 43,
No. 8, pages 2161 to 2168 (1988) (Chemical Enginee
Kinetics of methanol synthesis by hydrogenation of carbon dioxide in the liquid phase compared to hydrogenation of CO as in the gas phase method, as in Ring Science, 43 (8), 2161-2168 (1988). As a source gas, carbon dioxide in excess of CO is used as a source gas, and it is practically unknown whether methanol is obtained directly from carbon dioxide. It is merely examining the effect of adding carbon dioxide on the synthesis. In addition, Fuel Science and Technology International,
Vol. 6, No. 5, pp. 569-589 (1988) (Fuel. Sci. T.
echnol. Int., 6, (5), 569-589 (1988))
In a zinc-based liquid phase slurry reaction, methanol can be obtained from carbon dioxide-free synthesis gas raw material, but in the reaction of carbon dioxide and hydrogen without CO, only the water gas shift reaction proceeds, and only water is obtained. Reaction examples have been reported.

Comparative examples of chemical reactions using fine particles as a catalyst as in the present invention are relatively few, and examples of liquid-phase methanol synthesis by hydrogenation of CO are only known in JP-A-60-94931. .

It is estimated that the increase in atmospheric concentration of carbon dioxide is the main principle of global warming, which has recently become a problem, and the development of energy-saving technologies to reduce emissions associated with the massive consumption of fossil fuels, or It is highly desired to develop a technology for converting this carbon dioxide into other useful substances by chemical means or the like.

[Problem to be Solved by the Invention] An object of the present invention is to provide a method for producing methanol from carbon dioxide and hydrogen.

[Means for Solving the Problems] The present inventors have proposed a new reaction method for synthesizing methanol from carbon dioxide and hydrogen, which is also required to be chemically converted. As a result of intensive studies on catalysts for realizing a reaction in the liquid phase where the heat of reaction necessary for keeping the reaction temperature low in terms of chemical equilibrium was easily studied, the fine particles mainly composed of copper and zinc were By reacting in an inert solvent in the presence of methanol, it has been found that methanol can be synthesized quite efficiently, and the present invention has been completed.

That is, the present invention provides a method for synthesizing methanol, in which a metal mainly composed of copper and zinc is heated and evaporated to obtain an average particle diameter of 10%.
This is a method for producing methanol, comprising suspending fine particles of Å to 1 μm in an inert solvent and reacting carbon dioxide and hydrogen substantially free of carbon monoxide.

 The present invention will be described in more detail.

The carbon dioxide referred to here is mainly the one generated by burning fossil fuels or chemical reaction and separating and recovering it by absorption. It does not mean gas itself, but refers to carbon dioxide that is substantially free of carbon monoxide. However,
For example, the combustion gas contains a small amount of carbon monoxide, and carbon dioxide obtained by the water gas shift reaction of carbon monoxide contains carbon monoxide in a chemical equilibrium amount. The present invention is directed to the use of carbon dioxide containing these small amounts of carbon monoxide. Carbon dioxide whose carbon monoxide content is generally 10% or less is used as a raw material, and a small amount of carbon monoxide contained in the carbon dioxide essentially inhibits the reaction in the present invention. is not. Further, other inert substances such as nitrogen, methane, and water vapor may be contained in the carbon dioxide.

As for hydrogen, which is a gaseous raw material, any hydrogen obtained by various production methods can be used. That is, hydrogen obtained by coal gasification, steam reforming of natural gas or naphtha, or hydrogen obtained by a partial oxidation method can be used in addition to hydrogen obtained by the electrolytic method. Further, a gas obtained by a water gas shift reaction of carbon monoxide is also convenient. In the future, if a large amount of hydrogen can be obtained by the photoelectrode reaction of water, this is also considered to be an effective hydrogen source.

The metal mainly composed of copper and zinc used in the present invention may be composed of only copper and zinc, but may contain a reinforcing agent such as aluminum or chromium as required. The fine particles having an average particle diameter of 10 angstrom to 1 micron and comprising a metal mainly composed of copper and zinc used in the present invention can be usually obtained by heating and evaporating each metal.

Fine particles, helium, argon, inert gas such as nitrogen, hydrogen, CO, and under the atmosphere of one or two or more mixed gas selected from the group consisting of carbon dioxide, pressure 10 ^-5
It can be obtained by heating and evaporating metal at mmHg or atmospheric pressure. Adjustment of the particle size of the obtained fine particles, metal evaporation rate or metal supply rate, type of atmosphere gas,
This can be done by setting pressure conditions and the like. If the particle size of the fine particles is smaller than 10 angstroms, catalytic performance cannot be obtained, which is not preferable. If it exceeds 1 micron, the catalytic performance will decrease.

As a heating method, copper, zinc, or a compound thereof may be directly heated and evaporated in a high-temperature plasma, or a resistance heating method using a tungsten board or the like may be used. The collection of the fine particles can be performed by adhering or coagulating on the wall of the fine particle producing apparatus or adhering in a viscous medium.

The resulting fine particles are not a mixture of different component particles, but it is desirable that the component metals of copper and zinc coexist in the individual fine particles or on the surface, and may be in an alloy state. The ratio of copper to zinc is 80-80% zinc to 20-95% by weight copper.
~ 10% by weight is preferred. As a reinforcing agent for the catalyst, one containing 0 to 50% by weight of aluminum or chromium may be used.

A precipitate is obtained from an aqueous solution of each metal salt of copper and zinc by pH adjustment, and a conventional methanol synthesis catalyst obtained by calcining this as a precursor needs to be subjected to a reduction treatment prior to the reaction. No processing such as calcining reduction is required for the fine particle catalyst obtained by
In particular, there is an advantage that a large rationalization and improvement in operation can be achieved when starting a large plant or reinforcing a catalyst.

As the inert solvent used in the reaction, those inert to the reactants and reaction products, for example, aromatic compounds such as benzene, toluene, xylene, and naphthalene, pentane, hexane, heptane, and linear chains such as octane Examples thereof include cyclic aliphatic compounds, higher alcohols such as hexanol, octyl alcohol, and nonyl alcohol, and hydrophobic perfluorocarbons.

The reaction temperature is preferably from 100 to 400 ° C., and the reaction pressure is preferably from ²⁰ to 350 kg / cm ² . The ratio of carbon dioxide to hydrogen, which is the source gas, can be arbitrarily selected, but it is preferable that the ratio be approximately 1:10 to 1: 1 by volume. The reaction time varies depending on the above reaction conditions and reaction type, but is about 30 minutes to 20 hours.

The reaction can be carried out in any of a batch system, a multistage continuous system, and the like.

The concentration of the fine particles in the inert solvent is not particularly limited, but usually 0.01 to 5% by weight is often used.

EXAMPLES Hereinafter, the method of the present invention will be described in more detail with reference to examples.

Example 1 Under an argon atmosphere at a pressure of about 1 mmHg, copper and zinc were heated and evaporated by resistance heating of a tungsten board to produce Cu / Z.
n = 57/24 (weight ratio, balance 19 is mainly oxygen), average particle size
Fine particles of 390 Å were obtained. In a 100 ml autoclave, put 40 ml of benzene and 0.3 g of the above fine particle catalyst, and feed a gas having a carbon dioxide / hydrogen ratio of 1/3 by volume at a total pressure of 100 kg / c.
tension in m ^2, and reacted for 5 hours the temperature was raised to 250 ° C.. The raw material gas was previously prepared from a CO-free liquefied carbon gas and hydrogen in a 3 liter pressure vessel separately from the reaction autoclave at room temperature at a gas volume ratio of 1/3 to 120 kg / cm ^2. Used.

After completion of the reaction, the reaction product was cooled and the reaction product liquid was taken out and analyzed by gas chromatography. As a result, it was found that methanol was produced at a yield of 15% based on the charged carbon dioxide.

Example 2 Cu / Zn = 64/18 (weight ratio, balance 18 being mainly oxygen) by resistance heating of a tungsten board in the same manner as in Example 1,
Fine particles with an average particle size of 340 Å were obtained.
When 0.3 g of the catalyst was reacted under the same conditions as in Example 1, methanol was produced at a yield of 13.5%.

Comparative Example 1 A 1M aqueous solution of copper nitrate trihydrate and a 1M aqueous solution of zinc nitrate hexahydrate were mixed and stirred, and a 1M aqueous sodium carbonate solution was added dropwise while maintaining the temperature at 85 to 90 ° C., and the pH settled to 6.8 to 7.0. After the addition, heating and stirring were continued for another 2 hours. After cooling, the precipitate was filtered, thoroughly washed with distilled water, and dried at 100 ° C. overnight. Further, it was fired in air at 350 ° C. for 4 hours.
At this stage, an oxide of CuO and ZnO having a weight ratio of 75/25 was obtained by adjusting the mixing ratio of the raw material nitrate aqueous solution. Then, the mixture was further reduced at 250 ° C. for 10 hours in a nitrogen gas stream containing 2% hydrogen, crushed in a mortar, and sieved.
A 50 micron powder was obtained.

Except that 5 g of this was used as a catalyst, the reaction was conducted in exactly the same manner as in Example 1 and analysis revealed that methanol was produced in a yield of 3.4%.

Comparative Example 2 The same procedure as in Comparative Example 1 was repeated except that 5 g of a catalyst obtained by adjusting the weight ratio of CuO / ZnO = 55/45 was used. Methanol was obtained at a rate.

[Effects of the Invention] According to the present invention, by using fine particles obtained by heating and evaporating a metal mainly composed of copper and zinc as a catalyst, the reaction temperature can be easily controlled and reaction conditions advantageous in terms of equilibrium can be obtained. Methanol can be obtained with considerable efficiency from CO-free carbon dioxide and hydrogen in an inert solvent that is capable of maintaining.
The present invention provides an industrially useful process as a method for converting carbon dioxide, which is chemically desired to be immobilized, and also as a method for producing methanol as a clean energy source.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C07B 61/00 300 C07B 61/00 300

Claims (4)

(57) [Claims] In a method for synthesizing methanol, fine particles having an average particle size of 10 angstrom to 1 micron obtained by heating and evaporating a metal mainly composed of copper and zinc are suspended in an inert solvent. A method for producing methanol, which comprises reacting carbon dioxide and carbon monoxide-free carbon with hydrogen. 2. The method according to claim 1, wherein the metal mainly composed of copper and zinc contains aluminum or chromium as a reinforcing agent. 3. The method according to claim 1, wherein the inert solvent is selected from the group consisting of aromatic compounds, linear or cyclic aliphatic compounds, higher alcohols and perfluorocarbons. 4. The method according to claim 1, wherein the reaction temperature is 100 to 400 ° C.