AU686189B2

AU686189B2 - Process to produce methanol

Info

Publication number: AU686189B2
Application number: AU71624/94A
Authority: AU
Inventors: Baldur Eliasson; Erik Killer
Original assignee: ABB RESEARCH Ltd
Current assignee: ABB RESEARCH Ltd
Priority date: 1993-09-27
Filing date: 1994-09-01
Publication date: 1998-02-05
Anticipated expiration: 2014-09-01
Also published as: JPH07173088A; DE4332790A1; AU7162494A

Description

1

AUSTRALIA

Patents Act 1990 ABB RESEARCH LTD

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "Process to produce methanol" The following statement is a full description of this invention including the best method of performing it known to us:- I -1 F The present invention concerns a process for producing methanol from carbon dioxide and hydrogen, wherein a mixture of carbon dioxide and hydrogen is introduced into a thermal reactor and converted therein to methanol under pressure and in the presence of a catalyst.

In connection with the invention, we make reference to the state-of-the-art revealed, for example, in the journal "HITACHI REVIEW", December 1990, Vol.39 No.6, pages 318 and 319, in particular Fig.8 on page 318, or in the publication by N. Kanoun et al. "Catalytic properties of new Cu based catalysts containing Zr and/or V for methanol synthesis from a carbon dioxide and hydrogen mixture" in '"CATALYSIS LETTERS" 15, (1992), pages 231-235.

.The carbon dioxide output of fossil fuel combustion 15 processes has reached such an extent, that it causes global changes in the composition of the atmosphere and by means of the greenhouse effect it may lead to serious climatic changes. According to data supplied by the IPCC commission, which conducted the world climate conference in Geneva in October/November 1990, the emission of carbon dioxide should be reduced immediately by 60% to stabilise S.the atmosphere's carbon dioxide content.

At this stage there are only few applications which require larger quantities of carbon dioxide and at the same time contribute to the reduction of emission, e.g.

tertiary oil output (enhanced oil recovery). The suggested concepts for final storage (ocean, natural gas fields) are unlikely to be realised in this century and could remain barred forever, for example, for biological reasons. In contrast to this, the conversion of carbon dioxide into chemical compositions which can be used in large quantities, e.g. as fuel for means of transport or combustion plants, is proposed. Methanol or perhaps methane belong foremost to these compounds.

In principle the synthesis of these substances can 2 take place in accordance with the following summary reactions:

CO

2 3H2

CH

3 oH H 2 0

CO

2 4H 2 v CH 4 2H20 In classical chemical engineering these reactions can be carried out only under elevated pressure by using special catalysts, e.g. rhodium and metallic oxides, copper/zinc and chromium, aluminium, manganese, silver or vanadium or copper/zinc compounds, at temperatures of 230-280 0

C.

In the publication mentioned in the introduction, namely "HITACHI REVIEW", at the place stated, in Fig.8, :two new processes are added in a summary form to the classic processes of synthetic manufacture of methane and methanol, in which water or hydrogen reacts directly with carbon dioxide.

In one process ("photo-electric chemical conversion") the water molecules are dissociated by photo-catalysis.

The protons (H resulting from this reduce the carbon dioxide to methane and methanol. The efficiency achieved during this (energy conversion efficiency) is, however, below In addition, very large electrode surfaces are necessary for this.

In another known process carbon dioxide is hydrogenated catalytically by means of hydrogen produced by solar energy, a process which is already carried out on a commercial scale during the hydrogenation of carbon monoxide. In this case in addition to the provision of cheap hydrogen the main problems are the high pressures and high temperatures necessary for an economical application.

From DE-A-42 20 865 a process for the synthesis of methane or methanol is known, which can be carried out economically at low temperatures and low pressures. In that case in a reaction chamber a mixture of carbon -3dioxide and a hydrogen containing substance are subjected to silent electric discharges.

For the known catalytic processes only vague data exists about the pressure and temperature in the reaction chamber, dwell times of the mixture in the catalyst (bed) and also about the pre-treatment of the catalyst.

The co-ordination of these process parameters is, however, of decisive significance on the achievable methanol field.

The present invention proposes a process for producing methanol, which process can be carried out economically at low temperatures and low pressures and enables a high yield of methanol.

According to the invention, a mixture of carbon dioxide and hydrogen is introduced from above into a reaction chamber and the mixture subsequently penetrates through the catalyst in the lower section of the reaction chamber, wherein the catalyst used is copper based, and further wherein the dwelling time in the catalyst, depending on the temperature in the reaction chamber is regulated, so that the numerical value of the quotient of the t:wdi-eltiXesv and of the temperature t is between and 50, whereby the dwe ii=4nI"- \=-Isv is defined as the volume of gas/hour divided by the total quantity of gas and the temperature is measured in degrees of Celsius.

By using this teaching it is feasible for the first time to produce methanol in larger quantities within a justifiable period and to reuse, as it were, the greenhouse gas, i.e. carbon dioxide. At the same time it has proven to be particularly advantageous to use a copper based catalyst, which had previously been conditioned for several hours with a mixture of nitrogen and hydrogen.

Basically all substances listed at the place stated in the "Catalytic properties of new Cu based catalysts..." quoted in the introduction may be considered as material for the catalyst, which, as a rule, are available as pellets.

B

4L 0) 4 The hydrogen as a primary substance can be produced in accordance with a currently used process, e.g. by electrolysis, wherein nuclear energy or renewable energy sources (solar, wind, hydro-energy, biomasses) may be used as energy sources. In addition, the hydrogen could be produced by splitting hydrogen sulphide (H 2 S) with microwaves, by silent electrical discharges, by thermal dissociation or by electrolytic dissociation. Hydrogen sulphide is produced in some chemical processes as a waste product, as it were, it is also a by-product of the natural gas processing industry. The production of hydrogen from hydrogen sulphide has the additional Sadvantage that its binding energy is less in H2S than it is in H 0.

2' 15 The C0 2 which is required for the synthesis of methanol, is released as an undesirable component during the combustion of fossil energy carriers. Prior to the mixing of this carbon dioxide with hydrogen and its subsequent feeding to the thermal reactor, it has to be freed, of course, from other combustion residues. There are several technologies available today for this purpose, which treat the carbon dioxide either for application to foodstuff or for chemical applications (cf. undated pamphlet by the company ABB Lummus Crest, 12141 Wickester, Houston, TDX 77079-9750 USA, "CO 2 recovery from flue gas").

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic illustration of a olant to carry out a process according to the invention to synthesise methanol on a laboratory scale; Fig. 2 is a graph which explains the influence of temperature and of pressure in the thermal reactor on the methanol yield for a specified dwell time.

T ~c To synthesise methanol (CH30H) in the schematically illustrated laboratory set-up of a plant of Fig. 1 pure hydrogen and pure carbon dioxide are introduced to mixer 3 through high-pressure quantity regulators 1 and 2, respectively.

The mixer 3 is equipped with a safety valve 4. The

H

2 /C0 2 mixture travels from the mixer 3 to a cylindrical thermal reactor 5. A catalyst 6 is loosely deposited in the bottom region of the reactor 5. In a laboratory set-up the catalyst extends over 1/10 of the height of the vessel. The catalyst, available commercially in the form of pellets, had been previously ground, and only catalyst material having grains between S.250 and 500 pm diameter have been used. In this case one deals here with a Cu based catalyst, which is distributed by the company Haldor Topsoe A/S, Nymollevej 2800, Denmark, under the designation of MK-101. The reactor has a heating device 7. By means of a pressure regulator 8 in the supply line leading from the reactor, the pressure within the reactor 5 can be adjusted over a wide range. The temperature and the pressure in the reactor 5 are registered by means of a pressure gapge 9 and a thermometer A heated supply line 11 leads from the pressure 25 regulator 8 to a multi-way valve 13; the heater is designated by 12 and prevents the condensation of the methanol produced in the reactor 5. This multi-way valve allows the gas mixture flowing through the supply line 11 to reach the gas chromatograph 14 on the one hand or a condenser device 15 on the other. The qualitative and quantitative composition of the gas mixture leaving the reactor 5 can be determined in the gas chromatograph 14.

The methanol 16 which condensess at about 60 0 C is collected in the condenser device 15. The not converted

H

2

/C

2 mixture (in this laboratory set-up) is released c 6 to the atmosphere.

In the diagram according to Fig. 2 the rate of methanol conversion CR is shown expressed as percentage, as a function of the pressure P inside the reactor 5 at various temperatures. As a general rule, the rate of conversion CR increases with increased pressure. For a while the rate of conversion CR increases also with the '110 0 increasing temperature; between N Xand 250 C it reaches its maximum and then decreases again with increasing temperature.

As far as the applicant knows, two competing processes are responsible for this optimum.

Methanol is formed in the reactor 5 essentially according to the following summary reactions:

CO

2 3H 2 o CH 3 0H H 2 0 (1) The synthesis of the methanol at lower temperatures results in higher rates of conversion; however, the processes take place much more slowly, and the dwelling time in the catalyst bed nas to be correspondingly increased. In contrast, the effect of the catalyst becomes stronger with increasing temperature up to a specified maximum working temperature (310 C for the MK-101 type).

The synthesis of the methanol has been carried out in a laboratory set-up using H 2

/CO

2 mixtures with molar ratios from 1:1 to 10:1, with dwell times between 1/10 and 10 sec, pressures between 1 and 30 bar and temperatures between 140 and 300 0 C. The optimum yield has been achieved at a molar ratio of 3:1, a dwell time of approx. 1 sec, a pressure of 20 bar and temperature of 250 0 C. The CO 2 conversion (ratio of converted moles

CO

2 to the introduced moles C0 2 expressed as percentage) was approx. 10%, at the same time the selectivity (ratio of CH 3 0H moles formed to the number Sof converted CO 2 moles, expressed as percentage) was e ,T Rqi T4q

N/C-

.V 0 -7over The invention has been described above by referring to a laboratory set-up and by using a certain catalyst.

In an industrial realisation of the process according to the invention the carbon dioxide would come, for example, from a plant, as described in the company pamphlet "CO 2 recovery from flue gas", mentioned in the introduction.

Nuclear or solar operated water electrolysis plants, for example, could be considered as sources of hydrogen.

Hydrogen sulphide may also be considered as a source of hydrogen.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments 15 without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

1. A process for producing nmethanol from carbon dioxide and hydrogen, wherein a mixture of carbon dioxide and hydrogen is introduced to a thermal reactor and converted therein to methanol under pressure and in the presence of a catalyst, characterised in that the mixture of carbon dioxide and hydrogen is introduced from above into the thermal reactor and the mixture subsequently penetrates through the catalyst in the lower section of the thermal reactor, and wherein the catalyst used is copper based, and further wherein the volume flow-rate (sv) in the catalyst, depending on the temperature in the reaction chamber is regulated, so that the numerical value of the quotient of the volume flow-rate (sv) and of the temperature (T) is between 10 and 50, whereby the volume flow-rate (sv) is defined as the volume of gas/hour divided by the total volume of gas and the temperature is measured in degrees of Celsius.

2. A process according to claim 1, characterised in that the temperature in the reaction chamber is kept in the range of 220 to 250 0 C, 20 3. A process according to claim 1 or 2, characterised in that in the mixture the molar ration of hydrogen to carbon dioxide is between 1 and

4. A process according to claim 3 characterised in that in the mixture the molar ration of hydrogen to carbon dioxide is about 3. A process according to any one of claims 1 to 4, characterised in that the pressure in the reaction chamber is kept in the range of 1 and 30 bar. 30 6. A process according to claim 5 characterised in that the pressure in the reaction chamber is kept in the range of 20 bar.

7. A process according to any one of the claims 1 to 6, characterised in that the dwell time of the mixture in the reaction chamber is between 0,1 and sec.

8. A process according to claim 7 characterised in tl it the dwell time of the mixture in the reaction chamber is about 1 sec.

9. A process according to any one of the claims 1 to 8, characterised in that the carbon dioxide is obtained by processing the waste gas from energy producing plants combusting fossil fuel. A process according to any one of the claims 1 to 9, characterised in that the hydrogen is obtained by dissociating water or hydrogen sulphide.

11. A process according to claim 10, characterised in that the hydrogen is obtained by dissociating hydrogen sulphide with microwaves, silent electrical discharges, thermal dissociation and/or electrolytic dissociation.

12. A process for producing methanol from carbon dioxide and hydrogen substantially as hereinbefore described with reference to the accompanying drawings. Dated this 21st day of October 1997 ABE INANAGEMENT AG Patent Attorneys for the Applicant: F.B. RICE CO. e4 R< L 1 ABSTRACT To produce methanol from carbon dioxide and hydrogen the primary substances of carbon dioxide and hydrogen are introdi:ed to a thermal reactor and converted therein into methanol under pressure and in the presence of a catalyst. Particularly high rates of conversion are achieved by introducing the mixture of carbon dioxide and hydrogen from above into the thermal reactor and the mixture subsequently penetrating through the catalyst in the lower section of the thermal reactor. As catalyst one based on copper is used. The dwelling time in the catalyst, C depending on the temperature in the reaction chamber is regulated, so that the numerical value of the quotient of the dwelling time s- and of the temperature T is between 10 and 50, whereby the dwelling time sv is defined as the volume of gas/hour divided by the total quantity of gas and the temperature T is measured in degrees of Celsius. 1 *CSCCC C C C.e. (Fig. 1)