Reaction kinetics of the liquid-phase hydrogenation of succinic anhydride on CuZnO-catalysts with varying copper-to-zinc ratios in a three-phase slurry reactor

摘要

The liquid-phase hydrogenation of maleic anhydride is a promising alternative to already established processes (e.g.Reppe process)for the production of 1,4-butanediol.The attractivity of the maleic anhydride hydrogenation results from its efficiency and flexibility since #gamma#-butyrolactone,1,4-butanediol and tetrahydrofuran can be obtained is a single-stage process.The fact that the partial oxidatiion of low value n-butane replaced benzene as a feedstock for maleic anhydride production over the last decades in another major advantage of the maleic anhydride routs.The liquid-phase hydrogenation of maleic anhydride proceeds via succinic anhydride to #gamma#-butyrolactone and 1,4-butanediol in consecutive hydrogenation steps.However,the formation of 1,4-butanediol takes place exclusively on CuZnO-catalysts having a suitable composition,whereas no 1,4-butanediol is formed on zine-free copper catalysts.An excessively high surface coverage of the copper sites with succinic anhydride inhibits the adsorption and thus hydrogenation of #gamma#-butyrolactone to 1,4-butanediol on zinc-free copper catalysts.An eperimentally observed reversible carbon balance deficit in the hydrogenation of succinic anhydride on CuZnO-catalysts led to the assumption,that the catalytically inactive zinc oxide provides additiional sorption sites succinic anhydride whereby the surface coverage of copper is reduced.Furthermore,succinic anhydride is a highly undersirable intermediate since it reacts with 1,4-butanediol to form vaious oligo-and polyesters.Thus,the occurrence of succinic anhydride in the reactor has to be suppressed.According to the mechanistical approach,the copper-to-zinc ratio of CuZnO-catalysts is expected to have an elementray influence on the hydrogenation of succinic anhydride.Therefore,a set of binary CuZnO-catalysts with copper-to-zinc ratios from 0.1 to 9.0 was prepared and applied in kinetic measurements performed in a stirred three-phase slurry reactor.A model discrimination led to a detailed kinetic model for the hydrogenation of succinic anhydride on CuZnO-catalysts,considering the experimentally observed reversible carbon balance deficit.The rate constants of the kinetic model were determined significantly for all copper-to-zinc ratios by performing a numerical parameter estimation.Thus,a kinetic model performing a good agreement between experimental and calculated results was achieved.Moreover,the experimentally observed carbon balance deficit could be predicted by the derived kinetic model.