A process for preparing butanediol

The present invention relates to a process for the preparation of optionally alkyl-substituted 1,4-butanediol by two-stage catalytic hydrogenation in the gas phase of C¶4¶-dicarboxylic acids and / or derivatives thereof comprising the steps of: DOLLAR A a) introducing a gas stream of a C¶ 4¶-dicarboxylic acid or a derivative thereof at from 200 to 300 ° C and 10 to 100 bar product into a first reactor or into a first reaction zone of a reactor and catalytic gas-phase hydrogenation at a mainly optionally alkyl-substituted gamma-butyrolactone containing solution; DOLLAR A b) introducing the product stream thus obtained into a second reactor or into a second reaction zone of a reactor at a temperature of 140 DEG C to 260 DEG C and catalytic gas phase to optionally alkyl-substituted 1,4-butanediol, DOLLAR A wherein the steps a) and b) are carried out at the same pressure; DOLLAR A c) separating the desired product from intermediates, by-products and any unconverted reactant; DOLLAR A d) optionally recycling unconverted intermediates into one or both hydrogenation stages, DOLLAR A being used in both hydrogenation each A catalyst containing 95 wt .-%, preferably 5 to 95 wt .-%, in particular 10 to 80 wt. -% of CuO and> = having 5 wt .-%, preferably 5 to 95 wt .-%, in particular 20 to 90 wt .-% of an oxidic support, and the product mixture taken from the first hydrogenation stage without further purification in the second ...