FIELD: membrane treatment of gases. SUBSTANCE: synthesis gas is prepared from methane-containing reactant gas in reactor with mixed- conductance membrane. Reactor conditions are set such as to render outlet gas product temperature higher than starting reactant gas temperature, total gas pressure in membrane oxidant zone being below that in membrane reactant zone. In one embodiment of invention, starting reactant gas temperature is preferably below maximum threshold temperature 760 C and usually ranges between 510 and 760 C. Maximum temperature in reactant zone is superior to 815 C. According to another version, oxygen-containing oxidant gas and methane-containing gas reactant are heated from indirect heat exchange with oxygen-depleted gas oxidant from reaction zone. According to one more version, outlet gas product temperature is maintained higher than starting reactant gas temperature whereas total pressure in any point in reactant zone of reaction zone is higher than total pressure in any point in oxidant zone of reaction zone. EFFECT: reduced power consumption. 24 cl, 6 dwg, 3 ex
