Kinetics of hydrogenation of maleic acid in a batch slurry reactor using a bimetallic Ru-Re/C catalyst

Abstract

The hydrogenation of maleic acid was investigated using a bimetallic Ru-Re/C catalyst powder in a semi-batch stirred slurry reactor with the main objective of developing a kinetic model that would provide reliable predictions of the observed reactant and product distributions and selectivities. The combined effects of hydrogen pressure, catalyst loading and initial maleic acid (MAC) concentration on the concentration vs. time profiles were studied over the temperature range of 523-543 K. The direct hydrogenation of aqueous MAC solutions with the Ru-Re/C catalyst powder showed that succinic acid (SAC), γ-butyrolactone (GBL) and tetrahydrofuran (THF) were the major products while n-butanol (BuOH), methane and propane were the principal side products. The selectivities of GBL and THF were found to be strongly dependent on the initial MAC concentration, H₂ pressure, catalyst powder loading and reaction temperature. Kinetic rate equations for the key steps in the reaction sequence were developed using the observed concentration vs. time profiles as the starting basis and the kinetic parameters were estimated using non-linear parameter estimation. The predictions of the semi batch slurry reactor model were found to agree reasonably well with the experimental data. The kinetic data showed a strong substrate inhibition effect for the consecutive reactions sequence with the extent of inhibition decreasing in the order of MAC>SAC>GBL. This observation suggests that a high space-time yield to THF can be obtained in a slurry reactor with significant liquid phase backmixing by the use of elevated temperature and pressure and long slurry residence time. Implications for commercial implementation are also suggested.