JP2008037843A - Method for synthesizing methanol - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for synthesizing methanol, with no need of preparing and replenishing any active solvent necessary for the reaction, conducting the reaction at relatively low temperatures and low pressure, needing no recirculation of high-pressure gas, affording high yield in an one-pass step, with a miniaturized reaction vessel. <P>SOLUTION: The method for synthesizing methanol comprises a first synthesis step of bringing a synthesis gas 1 comprising hydrogen and carbon monoxide into contact with a Cu/Zn catalyst in a vapor phase at a temperature and pressure suitable for vapor-phase synthesis process to synthesize a methanol-containing first reaction gas 2, a second synthesis step of bringing the methanol synthesized in the first step into contact with the Cu/Zn catalyst to synthesize a second reaction gas newly containing methanol, and a step of cooling the resultant second reaction gas to isolate the methanol. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for synthesizing methanol from a synthesis gas containing hydrogen and carbon monoxide.

  A typical methanol synthesis process is a gas phase synthesis method. For example, a process by a research and development organization such as ICI, Japan-Topoe, Vulcan, etc. has already been put into practical use (Non-patent Document 1).

The reaction formula of methanol synthesis by the gas phase synthesis method is represented by the following formulas (1) and (2).
CO + 2H ₂ → CH ₃ OH + 21.6 kcal (exothermic reaction) (1)
CO ₂ + 3H ₂ → CH ₃ OH + H ₂ O + 11.8 kcal (exothermic reaction) (2)

FIG. 5 (A) shows theoretical calculation values showing the influence of pressure and temperature on the methanol synthesis rate, and FIG. 5 (B) shows data for actual catalysts.
In order to advance the reaction formulas (1) and (2) to the right side, pressurization is required, and in order to increase the degree of reaction, the temperature must be low and the pressure must be high. However, the reaction rate is faster at higher temperatures.

  FIG. 6 is a configuration diagram of a methanol synthesis apparatus by a gas phase synthesis method. The reaction gas passes through the catalyst in the reaction tower, and a part of the reaction gas is converted to methanol, whereby the reaction gas is cooled to separate methanol, and the unreacted gas is mixed and circulated to the raw material gas while maintaining a high pressure.

  The practical methanol synthesis catalyst in the gas phase synthesis method is copper and zinc, and additives are added to enhance the activity. The activation temperature of the zinc oxide-based catalyst is about 400 ° C., and since the rate of change in equilibrium is low at this temperature, it is used under a very high pressure (several tens of MPa). Copper-based catalysts have high activity and are used at 250 to 300 ° C. and 5 to 15 MPa.

  On the other hand, various liquid phase synthesis methods have been proposed as methanol synthesis methods instead of gas phase synthesis methods (for example, Patent Documents 1 and 2 and Non-Patent Documents 2 and 3).

Patent Document 1 discloses a process for producing methanol in which methanol is produced by reacting a raw material gas composed of hydrogen and carbon oxide (CO, CO ₂ ) in the presence of a catalyst and in the presence of a water-insoluble or hardly water-soluble reaction solvent. The reaction is carried out under a sufficiently high reaction pressure necessary for at least a part of methanol and water in the reactor to exist as a liquid, and the methanol and water produced in the reaction are not converted into an aqueous methanol solution from the reactor. The reaction source gas is discharged independently.

  Patent Document 2 “Methanol Synthesis Catalyst and Methanol Synthesis Method Using the Catalyst” refers to reducing a non-calcined or calcined product of a basic carbonate composed of auricalcite-type copper and zinc with a hydrogen-containing gas. And a catalyst for methanol synthesis obtained by using the catalyst.

  Non-Patent Documents 2 and 3 are the results of research by the inventors of the present invention, and in the absence of a solvent at low temperatures (for example, 170 ° C.), liquid phase synthesis is almost impossible, but methanol, ethanol, 1-butanol, etc. In the presence of the active solvent, it is disclosed that liquid phase synthesis is possible at a high conversion rate even at a low temperature.

“Survey on Energy Conversion Technology Using Biomass Resources (III)”, New Energy and Industrial Technology Development Organization, 2000 Survey Report, NEDO-GET-0004, March 2001 P. Reubroycharoen, et al. , “Continuous Low-Temperature Measurement Synthesis from Synergy Using Alcohol Promoters”, Energy & Fuels 2003, 17, 817-821. J. et al. -Q. Zeng, et al. , “The promoting effect of alcohol in a new process of low-temperature synthesis of methanol from CO / CO2 / H2”, Fuel 81 (2002), 125-127.

JP-A-6-263666, “Method for Producing Methanol” JP-A-9-187654, “Methanol Synthesis Catalyst and Methanol Synthesis Method Using the Catalyst”

  FIG. 4 is a graph showing the relationship between the temperature and pressure (hydrogen partial pressure) and the equilibrium conversion rate in the methanol synthesis reaction. As can be seen from this figure, the equilibrium conversion rate in methanol synthesis decreases as the temperature increases and the pressure decreases.

However, as described above, methanol synthesis by the gas phase synthesis method is carried out at a high temperature (for example, 250 to 300 ° C.) in order to increase the reaction rate, and a high pressure (for example, to increase the reaction degree (equilibrium conversion)). 5-15 MPa) is used.
Nevertheless, the vapor phase synthesis method has a problem that the conversion rate in one pass is as low as about 10% due to the limitation of the equilibrium conversion rate due to the high temperature.
Therefore, in the gas phase synthesis method, it is necessary to recirculate the high pressure gas to increase the conversion rate to a practical level, the high pressure circulation pump is indispensable, and the reaction tank including the pressure intensifying equipment and the separation equipment becomes large. There was a point.

  In addition, since the methanol synthesis reaction is an exothermic reaction, in the case of the gas phase synthesis method, it is difficult to remove heat from the high-temperature gas, which has a problem of adversely affecting the conversion rate.

  On the other hand, in the production method of Patent Document 1 which is a liquid phase synthesis method, the methanol yield of one pass in the examples is 94 to 97%, and the methanol production amount is 19 to 152 g / kg. h (0.59 to 4.75 mol / kg.h), the reaction temperature was 200 to 250 ° C., the reaction pressure was 9 to 15 MPa, and the temperature was still high and high.

  In addition, in the case of the production method of Patent Document 2 which is a liquid phase synthesis method, the methanol yield in one pass in Examples is 97 to 98.5%, and the methanol production amount is about 1.58 mol / kg per catalyst weight. . h, the reaction temperature was 225 to 230 ° C., the reaction pressure was 6 MPa, and the temperature was still high and high.

  Further, in the methods of Non-Patent Documents 2 and 3 by the inventors of the present invention, a high conversion can be obtained in one pass at a relatively low temperature and low pressure (for example, 170 ° C., 3 MPa), but methanol, ethanol, 1-butanol. There was a problem that preparation and replenishment of active solvents such as.

  The present invention has been developed to solve the above-described problems. That is, the object of the present invention is that preparation and replenishment of the active solvent necessary for the reaction are not required, the reaction can be performed at a relatively low temperature and low pressure, no high-pressure gas recirculation is required, and a high yield can be obtained in one pass. An object of the present invention is to provide a methanol synthesis method capable of miniaturizing a reaction vessel.

According to the present invention, a synthesis gas containing hydrogen and carbon monoxide is brought into contact with a Cu / Zn catalyst in a gas phase at a temperature and pressure suitable for a gas phase synthesis method to synthesize a first reaction gas containing methanol. A first synthesis step;
A second synthesis step of bringing the first reaction gas into contact with a Cu / Zn catalyst and methanol synthesized in the first synthesis step to synthesize a second reaction gas newly containing methanol;
And a separation step of separating the methanol by cooling the second reaction gas after the contact is provided.

The temperature suitable for the second synthesis step is preferably lower than the temperature suitable for the first synthesis step.
According to a preferred embodiment of the present invention, the temperature and pressure suitable for the first synthesis step are 250 to 300 ° C. and 5 to 15 MPa, and the temperature and pressure suitable for the second synthesis step are 100 to 190. The temperature is 3 to 10 MPa.

  It is preferable to have a cooling step for cooling the first reaction gas after the first synthesis step to a temperature suitable for the second synthesis step.

  According to the method of the present invention, since the first reaction gas containing methanol is synthesized in the first synthesis step, the catalytically active substance (methanol) necessary for the reaction can be constantly supplied in the second synthesis step, and the catalyst active substance Preparation and replenishment are not required.

  Further, since the remaining synthesis gas in the first reaction gas is further converted into methanol by contacting the Cu / Zn catalyst with the catalytically active material (methanol) synthesized in the first synthesis step (second synthesis step), 1 The conversion rate in the pass can be increased. Furthermore, since the second synthesis step is a liquid phase synthesis method, it is advantageous for removing reaction heat compared to the gas phase synthesis method.

  In addition, the combination of the first synthesis step and the second synthesis step according to the present invention can provide a high yield in one pass as a whole, so that high-pressure gas recirculation is unnecessary and the reaction vessel can be miniaturized.

  Therefore, according to the method of the present invention, the preparation and replenishment of the active solvent necessary for the reaction are unnecessary, the reaction can be performed at a relatively low temperature and low pressure, the high-pressure gas is not recirculated, and the yield is high in one pass. It was confirmed by the Example mentioned later that reaction tank can be reduced in size.

  Hereinafter, preferred embodiments of the present invention will be described.

The methanol synthesis method according to the present invention includes a first synthesis step that is gas phase synthesis, a second synthesis step that is liquid phase synthesis, and a separation step.
In the gas phase synthesis step, a synthesis gas containing hydrogen and carbon monoxide is brought into contact with a Cu / Zn catalyst in a gas phase at a temperature and pressure suitable for the gas phase synthesis method to synthesize a first reaction gas containing methanol. .
In the liquid phase synthesis step, the first reaction gas is brought into contact with the Cu / Zn catalyst and methanol liquid at a temperature and pressure suitable for the liquid phase synthesis method, and catalysis is effected from the unreacted synthesis gas in the first reaction gas. A second reaction gas containing methanol synthesized by the above is synthesized.
In the liquid phase synthesis step, both Cu / Zn and methanol are catalysts. The synthesis formula of this second reaction gas is represented by the following formulas (3) to (5).
CO + H ₂ O → CO ₂ + H ₂ (3)
CH ₃ OH + CO ₂ + H ₂ → HCOOCH ₃ + H ₂ O (4)
HCOOCH ₃ + 2H ₂ → CH ₃ OH + CH ₃ OH (5)
In the formulas (4) and (5), only one CH ₃ OH is circulated as a catalyst.
Expression (6) is obtained as a whole of Expressions (3) to (5).
CO + 2H ₂ → CH ₃ OH (6)
In the separation step, the second reaction gas after contact is cooled to separate methanol.

The temperature and pressure suitable for the gas phase synthesis method are 250 to 300 ° C. and 5 to 15 MPa.
The temperature and pressure suitable for the liquid phase synthesis method are 100 to 190 ° C. and 3 to 10 MPa.

The Cu / Zn catalyst in the present invention is preferably an ICI catalyst (hereinafter abbreviated as ICI) that is commercially available for use in a gas phase synthesis method, but may be any other known Cu / Zn catalyst.
There is no restriction | limiting in particular in the shape of a catalyst, The shape suitable for the process to be used can be selected from various shape products, such as a spherical product, a crushing product, and a cylindrical molded product. Further, the average particle diameter of the catalyst is not limited, but those having a particle size of usually 10 μm to 10 mm, preferably 20 μm to 5 mm are appropriately selected and used depending on the process.
The specific surface area of the catalyst to be used is not particularly limited, but is usually 40 to 400 m ² / g, preferably 200 to 300 m ² / g.

  In the present invention, when the catalyst is subjected to a methanol synthesis reaction, it is preferable to perform a reduction treatment with hydrogen or the like in advance.

The raw material for carrying out the synthesis method of the present invention is not particularly limited as long as it is a synthesis gas mainly composed of hydrogen and carbon monoxide, but the molar ratio of hydrogen / carbon monoxide is usually 1.0 to It is desirable to be in the range of 3.0, preferably 1.8 to 2.2. In addition, it is possible to replace 1/30 to 1/2 of carbon monoxide with CO ₂ (carbon dioxide).
The reaction method of the synthesis method of the present invention can be applied to any process conventionally known as a fixed bed, a supercritical fixed bed, a slurry bed, a fluidized bed and the like, and is not particularly limited. A supercritical fixed bed and a slurry bed can be mentioned, and a slurry bed and a supercritical fixed bed are particularly preferable processes, and a slurry bed is most preferable process.
There is no restriction | limiting in particular in the reaction conditions at the time of using a slurry bed, It can carry out on well-known conditions. Usually, the reaction can be carried out in the range of 1000 to 10,000 h ⁻¹ as the gas space velocity.

  Examples of the present invention will be described below.

The block diagram of the test apparatus used for FIG. 1 is shown. In this figure, 1 is a synthesis gas, 2 is a first reaction gas, 3 is a second reaction gas, and 4 is a reaction gas after condensation.
Further, 10 is a synthesis gas cylinder, 11 is a mass flow controller, 12 is an upper reactor, 13 is a pressure gauge, 14 is a lower reactor, 16 is a cooler, 17 is a cooling trap, and 18 is a flow meter.

  Table 1 shows the test conditions.

In the upper reactor 12, the synthesis gas 1 containing hydrogen and carbon monoxide is brought into contact with the Cu / Zn catalyst in the gas phase at a temperature and pressure (230 ° C., 5.0 MPa) suitable for the gas phase synthesis method. A first reaction gas 2 containing was synthesized.
In the method of the present invention, the lower reactor 14 converts the unreacted synthesis gas in the first reaction gas 2 into a Cu / Zn catalyst at a temperature and pressure (170 ° C., 5.0 MPa) suitable for the liquid phase synthesis method. Then, it is contacted with methanol and further converted into methanol (Test No. 1). However, in this case, depending on the conditions of the lower reactor 14, the methanol synthesized in the first synthesis step may be in the gas phase instead of the liquid phase, but even in this case, the gas phase methanol and the Cu / Zn catalyst coexist. If so, methanol also acts as a co-catalyst, and a second reaction gas containing new methanol is synthesized.

  As another embodiment of the present invention, in the lower reactor 14, the synthesis gas in the first reaction gas 2 is synthesized from the Cu / Zn catalyst and the first reaction gas at a lower temperature (170 ° C.) than the upper reactor 12. The second reaction gas 3 with increased methanol in contact with phase methanol was synthesized (Test No. 2).

  In the method of the present invention, the cooler 16 is used to cool a temperature suitable for the gas phase synthesis method in the upper reactor 12 to a temperature suitable for the liquid phase synthesis method in the lower reactor 14. However, the cooler 16 is not indispensable depending on the setting of reaction conditions, and is omitted in this embodiment.

In the lower reactor 14, methanol generated in the upper reactor 12 is used as a catalyst, brought into contact with a Cu / Zn catalyst and liquid phase or gaseous phase methanol, and the remaining synthesis gas in the first reaction gas is used at low temperature and low pressure. Perform methanol synthesis.
In this test, the upper reactor 12 has a test no. 1 and 2 both use a commercially available ICI catalyst. 1 uses a catalyst of Cu / ZnO = 1/1. In 2, ICI catalyst was used.

(Test method)
A Cu / Zn catalyst was set in the upper reactor 12 and the lower reactor 14, the inside of the apparatus was replaced with 1.0 MPa of synthesis gas 1 three times, and then the reaction pressure was adjusted to 5.0 MPa using a back pressure valve.
The upper reactor 12 and the lower reactor 14 were heated by an external heater, and when the reaction temperature reached 230 ° C. and 170 ° C., the reaction time was started and reacted for 20 hours. The second reaction gas 3 exiting from the lower reactor 14 was cooled by a cooling trap 17 containing 10 ml of 2-butanol and cooled with ice.
The gas components during the reaction were sampled every hour at the start and end of the reaction, and analyzed using GL Science GC320 (TCD) in which the column was packed with activated carbon.
The liquid component after the reaction was analyzed by Shimadzu GC-8A (FID) with a methanator in which 1-propanol was added as an internal standard and the column was filled with gas clopac 54 and bora pack N.

(Test results)
FIG. 1 is a graph showing the time course of the conversion rates of CO, CO ₂ and total in FIG. It is a figure which shows the same time passage in 2. FIG.
Table 2 shows the results of the gas phase reaction.

  2 and 3, it can be seen that the conversion rate reaches the maximum at about 10 hours out of the reaction time of 20 hours.

Further, as can be seen from Table 2, the highest conversion was found in Test No. The reaction format was 2. The method using only the liquid phase synthesis step is a liquid phase synthesis reaction, that is, a slurry phase reaction. The results show that the conversion rate of the catalyst of Cu / ZnO = 1/1 used in No. 1 is higher than that of the ICI catalyst.
However, test No. 1, which is another example of the method of the present invention. In the gas phase reaction of 1, the opposite result was obtained.

In the slurry phase, a large amount of alcohol is present around the catalyst, but in the gas phase reaction in this lower reactor, the concentration of alcohol is much smaller. Since the rate-determining step of this low-temperature methanol synthesis method is the formation of formate, it seems that the lower alcohol concentration affects the conversion rate.
The product contained a small amount of DME. This is considered to be produced by dehydration condensation of methanol by the action of Al ₂ O ₃ contained in the ICI catalyst.

In the examples shown in FIGS. 1 is about 56%, test No. 2 is about 65%, and in both cases, a high conversion rate is obtained as compared with a conversion rate of about 10% in one pass in the gas phase synthesis method.
Further, in this example, as a comparative example of the method of the present invention, in the lower reactor 14, a gas phase is used instead of the liquid phase synthesis method at the same temperature and pressure (170 ° C., 5.0 MPa) as the liquid phase synthesis method. Although the synthesis method was applied, it is clear that the CO conversion can be further increased by applying the liquid phase synthesis method in the lower reactor 14 as described above.

  That is, as shown in Table 3 of the above-mentioned Non-Patent Document 2 (results of research by the inventors of the present invention), in one reactor in the presence of an active solvent of methanol at low temperature and low pressure (170 ° C., 5.0 MPa). The conversion rate of about 40% is obtained in one pass.

  As described above, the present invention is a method for synthesizing methanol at low temperature and low pressure using a Cu / Zn-based slurry catalyst in an alcohol solvent. Also, in order to increase the conversion rate, the reaction vessel is made up of two stages, methanol is synthesized by the gas phase synthesis method in the first stage, the methanol is used as a solvent in the second stage, and the first stage is unreacted at low temperature and low pressure. In this method, methanol is synthesized at a high conversion rate by synthesizing methanol using the above synthesis gas.

By synthesizing methanol at low temperature and low pressure by the liquid phase synthesis method, the conversion rate in one pass can be increased, and the liquid phase synthesis method is more advantageous for removing reaction heat than the gas phase synthesis method.
In addition, a gas phase synthesis reactor (upper reactor) is installed in front of the liquid phase reactor (lower reactor), where methanol is synthesized and used as the second stage solvent, resulting in high yields of methanol. Can be synthesized.
That is, in the Example mentioned above, the conversion rate rose from about 10% to about 60% in the conventional single-stage gas phase synthesis method by making the reaction tank into two stages.

  Therefore, according to the method of the present invention, the preparation and replenishment of the active solvent necessary for the reaction are unnecessary, the reaction can be performed at a relatively low temperature and low pressure, the high-pressure gas is not recirculated, and the yield is high in one pass. And the reaction vessel can be downsized.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

It is a block diagram of the test apparatus used for the catalyst activity test. Test No. 1 is a graph showing the time course of CO, CO ₂ and total conversion rates in FIG. Test No. 2 is a graph showing the time course of CO, CO ₂ and total conversion rates in FIG. FIG. 3 is a relationship diagram of temperature and pressure (hydrogen partial pressure) and equilibrium conversion rate in a methanol synthesis reaction. It is the theoretical calculation value (A) which shows the influence of the pressure and temperature with respect to a methanol synthesis rate, and the data (B) of an actual catalyst. It is a block diagram of the methanol synthesis apparatus by a gaseous-phase synthesis method.

Explanation of symbols

1 synthesis gas, 2 first reaction gas,
3 Second reaction gas, 4 reaction gas after condensation,
10 synthesis gas cylinders, 11 mass flow controllers,
12 Upper reactor, 13 Pressure gauge,
14 lower reactor, 16 cooler,
17 Cooling trap, 18 Flow meter

Claims (4)

A first synthesis step of synthesizing a first reaction gas containing methanol by contacting a synthesis gas containing hydrogen and carbon monoxide with a Cu / Zn catalyst in a gas phase at a temperature and pressure suitable for a gas phase synthesis method;
A second synthesis step of bringing the first reaction gas into contact with a Cu / Zn catalyst and methanol synthesized in the first synthesis step to synthesize a second reaction gas newly containing methanol;
And a separation step of separating the methanol by cooling the second reaction gas after the contact.   The methanol synthesis method according to claim 1, wherein the temperature suitable for the second synthesis step is lower than the temperature suitable for the first synthesis step.   The temperature and pressure suitable for the first synthesis step are 250 to 300 ° C. and 5 to 15 MPa, and the temperature and pressure suitable for the second synthesis step are 100 to 190 ° C. and 3 to 10 MPa. The method for synthesizing methanol according to claim 1. 2. The methanol synthesis method according to claim 1, further comprising a cooling step of cooling the first reaction gas after the first synthesis step to a temperature suitable for the second synthesis step.

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