WO1996006064A1

WO1996006064A1 - Process for the production of methanol from waste gas

Info

Publication number: WO1996006064A1
Application number: PCT/KR1995/000109
Authority: WO
Inventors: Sung Jin Uhm; Seong Hwan Han; Suk Mok Song; Oh Shim Joo
Original assignee: Korea Institute Of Science And Technology
Priority date: 1994-08-19
Filing date: 1995-08-19
Publication date: 1996-02-29
Also published as: KR0138587B1; JPH09510734A; KR960007519A

Abstract

Methanol is economically produced from carbon dioxide in a high yield by a process which comprises compressing a gaseous mixture of carbon dioxide and hydrogen; introducing the compressed gaseous mixture into a conversion column; converting a part of the carbon dioxide contained in the mixture to carbon monoxide in the presence of a catalyst in the conversion column to produce a gas phase mixture and a liquid phase mixture; removing the liquid phase mixture in a gas-liquid separator; introducing the gas phase mixture from the gas-liquid separator into a reactor while recycling, optionally, a part thereof into the conversion column; reacting the compressed gas phase mixture introduced into the reactor in the presence of a catalyst to produce a mixture containing methanol; and recovering methanol as a liquid phase product from the mixture.

Description

PROCESS FOR THE PRODUCTION OF METHANOL FROM WASTE GAS

Field of the Invention

The present invention relates to a process for the production of methanol from carbon dioxide by way of employing a reverse water gas shift reaction.

Description of the Prior Art

Today's prevalent industrial developments throughout the world together with the increasing use of fossil fuels generate vast amounts of waste gas or carbon dioxide emitted into the air, spawning a host of environmental pollution problems including the green house effect which may alter, among other things, weather patterns. Alarmed by the dire consequences which may stem from the air pollution, governmental agencies and international organizations have striven to regulate the emission of carbon dioxide; and yet the level of waste gas emission continues to escalate. One of the ideas proposed to solve the waste gas problem is to recycle it; and, in this connection, methanol has been named as one of the useful substances which can be produced from carbon dioxide. Specifically, it has been proposed to prepare methanol by compressing a mixture of carbon dioxide and hydrogen and introducing the compressed gas into a reactor to provide a product mixture containing methanol. However, this method of producing methanol directly from carbon dioxide has a number of inherent difficulties including the problem that the reaction becomes suppressed by water produced during the reaction. In an effort to ameliorate the difficulties and improve the yield of methanol, Goehna et al. recently reported a two-step process for producing methanol from waste carbon dioxide gas (see Goehna, H. et al., "Producing methanol from C0₂", CHEMTECH, pp 36-39 (June, 1994)). As illustrated in Fig. 1, this process employs a mixture of C0₂ and H₂ as feed gas to a fixed-bed reactor (20) in a once-through operation. The output from the fixed-bed reactor (20) is then fed to a synthesis loop incorporating a second reactor (30) wherein methanol is eventually produced. However, the Goehna method still suffers from the disadvantage in that a large quantity of water present in the output from the first reactor undermines the whole process. Further, the molar ratio of C0₂ in the gaseous mixture to be fed into the second reactor is too high; and, consequently, the volume of the C0₂ gas recycled into the second reactor and the amount of the purge gas remain excessively high, rendering the process commercially impracticable.

Summary of the Invention

It is, therefore, a primary object of the invention to provide a process for economically producing methanol in a high yield by employing a reverse water gas shift reaction of carbon dioxide with hydrogen.

In accordance with the present invention, there is provided a process for preparing methanol, which comprises: (a) compressing a gaseous mixture of carbon dioxide and hydrogen;

(b) introducing the compressed gaseous mixture into a conversion column;

(c) converting a part of the carbon dioxide contained in the mixture to carbon monoxide in the presence of a catalyst in the conversion column to produce a gas phase mixture and a liquid phase mixture;

(d) removing the liquid phase mixture in a gas-liquid separator; (e) introducing the gas phase mixture from the gas-liquid separator into a reactor while recycling, optionally, a part thereof into the conversion column;

(f) reacting the gas phase mixture introduced into the reactor in the presence of a catalyst to produce a mixture containing methanol; and

(g) recovering methanol as a liquid phase product from the product mixture.

Brief Description of the Drawings

The above and other objects and features of the present invention will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawings, in which:

Fig. 1 provides a schematic flow diagram showing a two- step prior art process for the production of methanol from C0₂ and H₂; and Fig. 2 presents a schematic flow diagram illustrating the inventive process for the production of methanol.

Detailed Description of the Invention

In accordance with the present invention, methanol can be economically produced from carbon dioxide, which may be recovered in vast amounts from various industrial processes as a by-product. In the inventive process, a part of carbon dioxide is first converted into carbon monoxide by a reverse water gas shift reaction at a high temperature; water produced during the conversion process is removed; and then the remaining gaseous mixture thereof is subjected to a methanol synthesis reaction to produce methanol.

Specifically, a gaseous mixture of carbon dioxide and hydrogen is compressed and introduced into a conversion column wherein a part of the carbon dioxide contained in the mixture is converted to carbon monoxide.

The gaseous feed mixture may contain carbon dioxide and hydrogen in a molar ratio ranging from 1:0.1 to 1:100, preferably from 1:1 to 1:10, and, more preferably, from 1:2 to 1:4.

The conversion process may be carried out at a temperature ranging from 100 to 1,000 °C, preferably from 300 to 800 °C, and, more preferably, from 400 to 600 °C under a pressure ranging from 1 to 200 atm, preferably, from 10 to 100 atm, and, more preferably, from 10 to 50 atm, in the presence of a catalyst. The catalyst which may be used in the present invention includes those used conventionally for the water gas shift reaction, e.g., metallic compounds of such metals as Cu, Mo, Fe, Cr, Ni, Zn, W, V, Ni, Pd, Co, Rh, Sn or Al, or a mixture thereof supported on various supporting materials such as ZnO, A1₂0₃, SiO, ZnO/Al₂0₃, lanthanide oxide, actinide oxide, MgO and the like.

Since the conversion process is an endother ic reaction with the heat of reaction being 9064 kcal/kg-mole at 400 °C and 8090 kcal/kg-mole at 800 °C, the inlet temperature of the conversion column is preferably controlled to be higher than the outlet temperature of the conversion column. For example, the inlet temperature of the conversion column may range from 100 to 1,000 °C, preferably, from 300 to 800 °C, and, more preferably, from 400 to 600 °C; and the outlet temperature may range up to 900 °C, preferably, from 200 to 700 °C, and, more preferably, from 350 to 550 °C.

In accordance with the present invention, the rate of conversion from carbon dioxide to carbon monoxide may lie in a range from 10 to 90 %. That is, the partial molar ratio of carbon dioxide to the sum of carbon dioxide and carbon monoxide (hereinafter called "A" value) may be in the range of 0.1 to 0.9. The conversion rate may range preferably from 20 to 80 %, and, more preferably, from 40 to 60 %. The conversion rate may be controlled by adjusting the conversion condition such as the outlet temperature of the conversion column, flow rate of the gas recycled into the conversion column and content of water in the feed gas. Specifically, the conversion rate becomes lowered as the outlet temperature or the flow rate of the recycled gas becomes higher, or as the water content becomes higher.

Subsequently, the resulting product mixture, which comprises a gas phase mixture containing carbon monoxide produced by the conversion process, non-converted carbon dioxide and hydrogen, and a liquid phase mixture containing water is introduced into a gas-liquid separator to remove the liquid phase mixture or water.

The gas phase mixture so separated is then introduced into a reactor via a compressor to produce a mixture containing methanol. The reaction of the compressed gas phase mixture in the synthesis reactor may be conducted at conventional reaction conditions well known in the art, i.e., at a temperature ranging from 100 to 800 °C, preferably, from 150 to 400 °C, and, more preferably, from

200 to 250 °C, under a pressure ranging from 1 to 200 atm, preferably, from 10 to 100 atm, and, more preferably, from

30 to 50 atm, in the presence of a catalyst. The inlet and outlet temperatures of the reactor may range from 150 to 250 °C and from 200 to 300 °C, respectively.

The catalyst which may be used in the reaction includes those used conventionally in the art, e.g., a copper compound supported on a supporting material. If desired, a part of the gas phase mixture separated at the separator may be recycled into the conversion column via a compressor so as to increase the conversion rate.

From the production mixture of the reactor, methanol may be easily recovered as a liquid phase product by, e.g., passing it through a gas-liquid separator. The remaining gaseous mixture may be recycled into the reactor via a compressor or vented off as a purge gas.

As an exemplary embodiment of the inventive process for the production of methanol from carbon dioxide, referring to Fig. 2, a gaseous mixture of carbon dioxide and hydrogen is compressed by a compressor (10) and then the compressed gaseous mixture is introduced into a conversion column (20) with or without the gas phase mixture recycled from a gas- liquid separator (30), to convert a part of the carbon dioxide contained in the mixture to carbon monoxide, thereby producing a gas phase mixture and a liquid phase mixture containing water. The production mixture is then introduced into the gas-liquid separator (30) to remove the liquid phase contained therein at the bottom of the separator and recover the gas phase mixture from the top of the separator. A part or all of the gas phase mixture recovered is introduced as a feed gas into a reactor (60) via a compressor (50) to produce a mixture containing methanol; and, if desired, a part of the gas phase mixture is recycled into the conversion column (20) via a compressor (40). The mixture containing methanol is introduced into a separator (70) to recover methanol as a liquid phase product at the bottom part of the separator while the remaining gaseous mixture is recycled into the synthesis reactor (60) via a compressor (80) or vented off as a purge gas.

The following Examples are given for the purpose of illustration only and are not intended to limit the scope of the invention.

Example 1

A gaseous mixture of 25:75 (v/v) of carbon dioxide and hydrogen was treated in accordance with the conversion process of the present invention (see Fig. 2) under various conversion conditions shown in Table 1. The catalyst employed was Zn-Cr/alumina prepared by supporting zinc and chromium compounds on alumina by a coprecipitation method. The resulting products were analyzed by a gas chromatography and the A values thereof were calculated and are shown in Table 1.

Table 1

T : temperature (°C)

P : pressure (atm)

R : (molar amount of gas to be recycled into the conversion column) / (molar amount of gas to be introduced into the methanol synthesis reactor) * Feed gas was employed in a saturated state under operation pressure

Example 2

A gaseous mixture of 25:75 (v/v) of carbon dioxide and hydrogen was introduced to a conversion column filled with 30 m³ of 5% Mo0₃/alumina as a catalyst at a flow rate of 150,000 m³/hr. The conversion process was conducted at 600 °C under 20 atm while maintaining GHSV (Gas Hourly Space Velocity) of the mixture at 5,000 hr^"1. The conversion rate of carbon dioxide to carbon monoxide was 61 %, and water was condensed in an amount of 18.5 wt% of the resulting product mixture.

Subsequently, water produced during the conversion process was removed in a separator and the gas phase mixture was recovered from the conversion column and then charged at a flow rate of 127,000 m³/hr into a tubular reactor filled with 80 m³ of Cu/ZnO/Al₂0₃ (6:3:1) catalyst. The reaction was conducted at an inlet temperature of the reactor of 200 °C and an outlet temperature of the reactor of 270 °C.

The resulting products thus obtained were separated in a separator to produce methanol. 15.2 wt % water based on the weight of methanol was produced together with methanol and the remaining gas was recycled at a flow rate of 506,000 m³/hr. Methanol was produced at a flow rate of 47.87 t/hr in a yield (based on carbon dioxide) of 89 %. The productivity of methanol was evaluated to be 0.6 t/m³ of catalyst- hr. Comparative Example

The same procedures described in Example 2 were repeated, except that the gaseous mixture was introduced directly at a flow rate of 150,000 m /hr into the reactor, and the inlet and outlet temperatures of the reactor were

220 °C and 295 °C, respectively.

38.2 wt % water based on the weight of methanol was produced and the remaining gas was recycled at a flow rate of 620,000 m³/hr. Methanol was produced at a flow rate of 37.01 t/hr in a yield (based on carbon dioxide) of 69 %. The productivity of methanol was evaluated to be 0.46 t/m³ of catalyst- hr.

As can be seen from the above, in accordance with the inventive process, methanol can be efficiently produced from carbon dioxide in a higher yield and productivity than the prior art process. Consequently, emission of waste carbon dioxide into environment can be minimized, thus reducing air pollution.

While the invention has been described in connection with the above specific embodiments, it should be recognized that various modifications and changes may be made to the invention by those skilled in the art without departing from the scope of the invention as defined by the appended claims .

Claims

What is claimed is:

1. A process for producing methanol from a gaseous mixture of carbon dioxide and hydrogen, which comprises: (a) compressing a gaseous mixture of carbon dioxide and hydrogen;

(b) introducing the compressed gaseous mixture into a conversion column;

(d) removing the liquid phase mixture in a gas-liquid separator; (e) introducing the gas phase mixture from the gas- liquid separator into a reactor while recycling, optionally, a part thereof into the conversion column; and

(f) reacting the gas phase mixture introduced into the synthesis reactor in the presence of a catalyst to produce a mixture containing methanol; and

(g) recovering methanol as a liquid phase product from the product mixture.

2. The process of claim 1, wherein the gaseous feed mixture contains carbon dioxide and hydrogen in a molar ratio of 1:0.1 to 1 : 100.

3. The process of claim 1, wherein the conversion in step (c) is carried out at a temperature ranging from 100 to 1,000 °C under a pressure ranging from 1 to 200 atm.

4. The process of claim 3, wherein the temperature ranges from 300 to 800 °C and the pressure ranges from 10 to

100 atm.

5. The process of claim 1, wherein the rate of conversion in step (c) is at least 10 %.

6. The process of claim 1, wherein the catalyst used in step (c) is a compound of a metal selected from the group consisting of Cu, Mo, Fe, Cr, Ni, Zn, W, V, Ni, Pd, Co, Rh, Sn, Al and a mixture thereof.

7. The process of claim 1, wherein the reaction in step (f) is carried out at a temperature ranging from 100 to 800 °C under a pressure ranging from 1 to 200 atm.

8. The process of claim 1, wherein the catalyst used in step (f) is a copper compound.