Gas-Phase Hydrogenolysis of Dimethyl Maleate to 1,4-Butanediol and γ-Butyrolactone over Copper/Zinc Oxide Catalysts

Abstract

The gas-phase hydrogenolysis of dimethyl maleate has been studied over copper/zinc oxide catalysts at temperatures between 473 and 513 K in the pressure range from 2 to 35 bar. A Cu/ZnO catalyst with a low copper content of 15 mol % was found to be the most active for the conversion of dimethyl maleate. At very low residence times, significant amounts of dimethyl maleate isomerize to dimethyl fumarate. The reaction then proceeds via the saturated ester, dimethyl succinate, until 1,4-butanediol and γ-butyrolactone are formed together with methanol. Furthermore, the chosen catalyst produces low amounts of tetrahydrofuran and water and only traces of undesirable butanol and CO2. It was found that the production of high amounts of 1,4-butanediol in one step is not possible, because the simultaneous presence of diesters and butanediol gives rise to the formation of a polymeric material via transesterification. Therefore, a two-step process including the complete conversion of dimethyl maleate to γ-butyrolactone, carried out at high temperature and moderate pressure, without formation of butanediol followed by the hydrogenation of γ-butyrolactone to 1,4-butanediol at low temperature and high pressure was proposed. It could be shown by systematic investigation of the hydrogenation of γ-butyrolactone that the amount of 1,4-butanediol formed is limited by thermodynamic constraints. The dependence of the equilibrium constant for the reaction between γ-butyrolactone and 1,4-butanediol was determined as a function of temperature and pressure.

Demonstration of CO2 Conversion to Synthetic Transport Fuel at Flue Gas Concentrations

“…Hydrogenation of the produced acetoacetate ester to directly yield butanol had not been previously reported in the scientific literature but similar hydrogenation processes using supported Cu(0) catalysts have been reported, particularly in the reduction of highly oxidized species such as low-molecular weight esters, glycerol, dimethyl maleate, and carbon dioxide (Figure 6) (van de Scheur and Staal, 1994;Brands et al, 1999;Schlander and Turek, 1999;Bienholz et al, 2011).…”

Extrusion of Cu/ZnO catalysts for the single-stage gas-phase processing of dimethyl maleate to tetrahydrofuran

“…This comparison indicates that the magnitude of the copper surface area is negatively affected by the catalyst formulation and forming. On the basis of earlier results reported by Schlander and Turek [8], one should expect that the activity of the catalysts in the conversion of dimethyl maleate follows the same trend as the copper surface area. The following proportionality should hold for equal modified residence time and equal temperature:…”

“…So far, only one gas-phase process has been established by Davy McKee Ltd. [6] which consists of two stages. A potential problem in gas-phase operation comprises fouling and plugging of the fixed-bed by polymeric material [7,8]. The polymeric deposits (polyesters) can be formed upon trans-esterification of dialkyl esters of maleic or succinic acid with the product BDO.…”

“…The role of ZnO as an adsorbent for succinic anhydride has been elucidated recently by Herrmann and Emig who investigated the hydrogenation of maleic acid anhydride in the liquid (slurry) phase [10,11]. The gas-phase conversion of dimethyl maleate has been studied by Turek and coworkers [8,12]. These authors found that the hydrogenolysis of dimethyl succinate rather than the hydrogenation of the double bond in dimethyl maleate is the rate-limiting step.…”

“…At conversions of dimethyl succinate above ca. 80%, the temperature-and pressuredependent thermodynamic equilibrium in the hydrogenation of γ -butyrolactone (GBL) to BDO is attained over Cu/ZnO catalysts [8,9]. The subsequent dehydration of BDO to THF plays a minor role because Cu/ZnO does not exhibit sufficient acidity.…”