Kinetic Modeling of Sorbitol Hydrogenolysis over Bimetallic RuRe/C Catalyst

Sorbitol hydrogenolysis kinetics using bimetallic RuRe catalyst is reported based on multiple experiments in parallel batch slurry reactors (H2 pressure: 1.0–6.5 MPa, temperature: 473–503 K) to obtain concentration–time profiles. It is observed that RuRe/C bimetallic catalysts with Ca­(OH)2 as a base promoter show significantly higher activity and selectivity toward liquid phase products such as 1,2-propanediol, lactic acid, ethylene glycol, and linear alcohols compared with monometallic Ru/C catalysts and other base promoters. It is further found that sorbitol hydrogenolysis initiates with dehydrogenation and subsequent C–C cleavage via retro-aldolization to form smaller molecules (C2–C4). Those smaller intermediates undergo dehydration, reorganization, and C–O cleavage to form C2–C3 acids, glycols, and linear alcohols as products, which are very similar to glycerol conversion chemistry. For the kinetic modeling, experimental data on concentration–time profiles were obtained using RuRe/C catalysts with Ca­(OH)2 promoter in which H2 pressure, catalyst loading, and temperature were varied. The analysis of kinetic models employed a batch slurry reactor model with which several rate equations based on different complex multistep reaction mechanisms were fit to the experimental data in order to gain insights into the reaction pathways and mechanisms. Activation energies for sorbitol hydrogenolysis to glycols and further conversion of glycols to corresponding alcohols are found to be in the range 38 kJ/mol to 125+ kJ/mol. The kinetic model from this work provides the framework for developing rational multiphase reactor engineering strategies for upgrading polyol mixtures (e.g., glycerol, xylitol, sorbitol, and mannitol) to value-added glycols and alcohols.