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Kinetic Modeling of Sorbitol Hydrogenolysis over Bimetallic RuRe/C Catalyst
journal contribution
posted on 2016-09-28, 00:00 authored by Xin Jin, Prem S. Thapa, Bala Subramaniam, Raghunath V. ChaudhariSorbitol 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.