Abstract: The invention relates to a method of carrying out a chemical equilibrium reaction using a permselective membrane, wherein quantitative proportions of at least one product obtained in the reaction are separated and removed from the reaction through the action of the permselective membrane. The chemical equilibrium reaction is carried out in the presence of a water-containing gas mixture, and a permselective membrane made from a material having a porous structure with mean pore sizes of less than 0.45 nm (4.5 ?), which material is hydrophobic at least on the free surfaces thereof is used.