The kinetics of the aqueous-phase hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO) was studied using a bimetallic Ru-Re/C catalyst in a slurry reactor in a temperature range of 493-513 K and a hydrogen pressure of 2.4-9.6 MPa. Glycerol hydrogenolysis to produce 1,2-PDO via C-O cleavage (i) proceeds with parallel C-C cleavage, reforming, water-gas shift, and Fischer-Tropsch reactions, (ii) results in a very complex reaction network with several gaseous-and liquid-phase products, and (iii) poses a challenge to design selective catalysts. It is observed that Ru-Re bimetallic catalyst shows higher hydrogenolysis activity (glycerol conversion of X ) 57.7%) and 1,2-PDO selectivity (S ) 36.6%), compared to the monometallic Ru catalyst (X ) 52.1%; S ) 18.9%) but the monometallic Re catalyst showed no catalytic activity for the reaction. Stirred-batch reactor data on the transient concentrations of reactants and products in both the gas and liquid phases were obtained using a bimetallic Ru-Re/C catalyst under different conditions to understand the reaction pathways, selectivity behavior, and intrinsic kinetics of the different reaction steps. For kinetic modeling, several experiments were performed at different initial pressures of hydrogen, catalyst concentration, and temperatures. The proposed rate equations, along with the regressed kinetic and activation energy parameters, were found to represent the experimental data for the multistep hydrogenolysis reaction very satisfactorily.
A review of multiphase catalytic
processes in biomass conversion is presented, with an emphasis on
the underlying kinetics, mechanism, and reaction engineering aspects.
The distinguishing features and current state of development of catalysts
and processes for a few selected examples of biomass conversion are
presented, including hydrogenolysis and tandem reforming/hydrogenolysis
of polyols to glycols and linear alcohols, hydrodeoxygenation of bio-oils,
and polyols conversion to lactic acid along with possible reaction
pathways. The complexities of multistep and multiphase catalytic reactions
and kinetics modeling associated with hydrogenolysis and hydrodeoxygenation
are discussed with a brief overview of reaction engineering aspects.
Hydrodeoxygenation
(HDO) is a widely used technology to convert
biomass-based feedstock into value-added fuels and chemical products
that usually require high-pressure hydrogen (H2) to remove
excess oxygen in the biomass feedstock. To make this process safer
and more sustainable, we investigated glycerol conversion under an
inert atmosphere in aqueous media using multimetallic catalysts (comprised
of Ru, Re, and Pt) supported on activated carbon. Here we report a
trimetallic Ru-Re-Pt catalyst that converts glycerol to value -added
products such as 1,2-propanediol (1,2-PDO) and linear alcohols with
higher selectivity with in situ formed H2 (without using
external H2). Thus, the proposed system eliminates use
of expensive hydrogen while giving high selectivity unlike the hydrogenation
with external hydrogen. The results of catalyst screening showed high
glycerol conversion (83%) with liquid-phase product selectivity of
72% and 1,2-PDO selectivity of 43% at 493 K and autogenous pressure
with optimized Ru-Re-Pt/C trimetallic catalyst in the presence of
a solid base promoter (MgO). To infer the mechanism of hydrogenation
with in situ-formed H2, temporal concentration-time profiles
at various operating conditions were elucidated using a kinetic model.
Such a model provides valuable mechanistic insights and guidance for
developing optimal catalyst formulations for maximizing hydrodeoxygenation
products with in situ-formed hydrogen.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.