Improved processing stability in the hydrogenation of dimethyl maleate to γ-butyrolactone, 1,4-butanediol and tetrahydrofuran

Abstract In the hydrogenation of dimethyl maleate (DMM) to γ-butyrolactone (GBL), 1,4-butanediol (BDO) and tetrahydrofuran (THF), the performance of the process can be negatively affected by (1) fouling and plugging of the unit through deposition of polymeric by-products and (2) activity drop of the Cu/ZnO-based catalysts through structural changes of the active copper phase at reaction conditions. On the basis of thermodynamic data, we calculated the feed compositions required to prevent condensation of reactants and subsequent formation of polyester deposits in the relevant temperature (453– 523 K ) and pressure (1– 7 MPa ) regime. The resulting critical values of the minimum H2/DMM ratios of the feed, when corrected for capillary effects, were found to be in excellent agreement with the limits as experienced in the processing experiments. Conditions for safe and stable gas-phase processing of DMM in a single stage can thus be predicted. The Cu/ZnO-based catalysts were improved by modifying the thermal pre-treatment. As compared to conventional materials of the same composition, they need less runtime to reach stationary performance levels, and their steady state activities are higher. The yield ratio of GBL to BDO can be adjusted through temperature and total pressure because the corresponding hydrogenation attains thermodynamic equilibrium. The subsequent dehydration to THF can be promoted by applying higher temperatures; however, selectivities to tetrahydrofuran remain low over typical Cu/ZnO catalysts unless additional acid sites are implemented.