Patent ID: 7169958

Claim:
A process for preparing optionally alkyl-substituted 1,4-butanediol by two-stage catalytic hydrogenation in the gas phase of C 4 -dicarboxylic acids and/or of derivatives thereof having the following steps: a) introducing a gas stream of a C 4 -dicarboxylic acid or of a derivative thereof at from 200 to 300° C. and from 2 to 60 bar into a first reactor and catalytically hydrogenating it to a product which contains mainly optionally alkyl-substituted γ-butyrolactone; b) converting the product stream into the liquid phase; c) introducing the product stream obtained in this way into a second reactor at a temperature of from 100° C. to 240° C. and a pressure of from 20 to 250 bar and catalytically hydrogenating it in the liquid phase to optionally alkyl-substituted 1,4-butanediol; d) removing the desired product from by-products and any unconverted reactant; e) optionally recycling intermediates into one or both hydrogenation stages, said hydrogenation stages both using a catalyst which comprises ≧95% by weight of CuO, and ≦5% by weight of a support, said second reactor having a higher pressure than said first reactor, and the product mixture removed from said first reactor being introduced without further purification into said second reactor.