Processes for the conversion of methane to synthesis gas

Details Processes for the conversion of methane to synthesis gas Processes for the conversion of methane to synthesis gas

1993-08-20

1995-07-11

Richter, Johann

Compositions

Gaseous compositions

Carbon-oxide and hydrogen containing

C07C 102

Patent

active

054318556

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of GB 91/02323filed Dec. 24, 1991.
In view of the dwindling supplies of fossil fuels and the relative abundance of methane, there is considerable interest in processes which have greater efficiency and selectivity for the conversion of methane to synthesis gas. There are several known reactions for the oxygenation of methane.
There are several known reactions for the oxygenation of methane. +CO+H.sub.2 O (4)
The partial oxidation of methane by dioxygen to synthesis gas, according to the stoichiometry: .increment.S at 298K are.sup.1 -36 kJmol.sup.-1, and +170 JK.sup.-1 mol.sup.-1, respectively, and for which .increment.G=-215 kJmol.sup.-1 at 1050K.
There are also catalysts for the reforming of methane using carbon dioxide.
This reduction of carbon dioxide by methane is an endothermic reaction.sup.1 (.increment.H.sub.298 =+247 kJmol.sup.-1). At high temperatures, its favourable entropy change (.increment.S.sub.298 =+257 JK.sup.-1 mol.sup.-1) makes it a favourable equilibrium, .increment.G=-23 kJmol.sup.-1 at 1050K.
Different catalysts promote these reactions to different extents, but selectivity is normally poor. This patent application results from our discoveries of a class of catalysts that is capable of selectively reforming methane to carbon monoxide and hydrogen according to equation (6) and a class of catalysts capable of combining both the partial oxygenation reaction shown in equation 2 with the reforming reaction shown in (6).
The major commercial process for the utilization of methane (steam reforming) involves a nickel catalysed reaction of methane with steam.
The products of this reaction are four gases which under catalytic conditions are in the equilibrium known as the water-gas shift reaction, namely
The equilibrium concentrations depend on the temperature and pressure at which the catalytic reaction is carried out.
The two gases, carbon monoxide and hydrogen, can be combined under catalytic conditions to give useful chemicals such as methanol or , via Fischer-Tropsch catalysis, higher hydrocarbons or aldehydes and alcohols. In consequence, the steam reforming process is an important industrial source of carbon monoxide and hydrogen, but the technology of steam conversion requires considerable capital investment, and is relatively inefficient since water and carbon dioxide are unwanted by-products of the reaction.
Therefore there is considerable industrial interest in the combined reforming-partial oxidation of methane to give carbon monoxide and hydrogen as the substantially major products.
British Patent Application No. 9018781.6 describes the catalysts for the partial oxidation of methane by oxygen to synthesis gas under relatively mild conditions of 650.degree.-900.degree. C. and pressures of 10-600 KPa without the use of steam. The catalysts include d-block transition metals on a refractory support and d-block transition metal oxides including mixed metal oxides.
Thus, this invention is concerned with essentially two processes. Process 1 is the reaction of CO.sub.2 with methane giving synthesis gas according to Equation 6. Process 2 is the reaction of oxygen and carbon dioxide mixtures with methane also giving synthesis gas.
A potential application of reaction 6, which is endothermic, is to use energy such as solar energy to drive the reaction to form the synthesis gas, which could then be stored and transported. The reverse reaction, namely the reduction of CO to methane, for which there are well-known catalysts, is highly exothermic thus heat stored by the first reaction can be released by the reverse methanation.
Another aspect of the invention concerns the potential application for usage of CO.sub.2, which has environmental implications towards the general problem of the greenhouse effect.
This invention is concerned with the definition of the conditions and catalysts which will give rise to the conversion of the methane and CO.sub.2, O.sub.2 to synthesis gas with greatly improved selectivity and conversions. Accordingly, the present invention provides a met

REFERENCES:
patent: 4833170 (1989-05-01), Agee
patent: 5023276 (1991-06-01), Yarrington et al.
"Nitrogen", No. 187, Sep. 1990, pp. 28-29.

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