Catalysis of Organic..

Marincean et al. 42747. Glycerol Hydrogenolysis to Propylene Glycolunder Heterogeneous ConditionsAbstractSimona Marincean, Lars Peereboom, Yaoyan Xi,Dennis J. Miller and James E. JacksonDepartment of Chemistry, Department of Chemical Engineering and MaterialsScience, Michigan State University, East Lansing, MI 48824-1322In aqueous media, glycerol (GO), a low-cost renewables-based feedstock, can becatalytically converted under mild conditions to the commodity products propyleneglycol (PG), lactic acid (LA) and ethylene glycol (EG). This report chronicles acomparative study of catalysts, solvents, and reaction conditions aimed at optimizingselectivity towards PG and at the same time augmenting our understanding ofcatalyst-substrate interactions. Two catalysts were evaluated: Ni/Re on carbon wasmore active and selective than Ru on carbon for GO hydrogenolysis to PG. Partialreplacement of water with other hydroxylic solvents—the simple alcohols—increased the selectivity and conversion in the order ethanol/water < water < isopropanol/water~ tert-butanol/water, while unmixed solvents yield the followingtrend: water < ethanol < iso-propanol < tert-butanol, with a three-fold increase in PGyield in tert-butanol relative to water. We interpret these results as evidence offacilitated GO access to the catalyst surface in the presence of larger solventmolecules with a hydrophobic carbon backbone. The reaction is also pH limitedbecause of formation of acids such as lactic and formic, which neutralize the basepromoter. We discuss the relationship between solvent structure and PG yield interms of interactions at the catalyst surface.IntroductionDepletion of fossil oil resources and concern about environmental pollution,especially heavy metals and greenhouse gases, have brought biomass into focus as arenewable source of raw materials for large-scale chemicals and energy production(1). The “biomass refinery” of the future will require a powerful toolbox of processesfor converting complex plant matter into useful commodity and specialty products.Since biomass consists mainly of carbohydrates, sugars are the major renewablefeedstock from which economically feasible organic compounds are to be developedto replace the ones traditionally obtained from petrochemical sources. Glucose,fructose and other monosaccharides as well as disaccharides are inexpensive,accessible in large amounts, and suited for transformations into low molecularweight organic commodities. Research endeavors to transform carbohydrates intouseful commodity and specialty products need to develop strategies to selectivelydecrease the oxygen content, introduce unsaturation in the form of C=C and C=O,and cleave C-C bonds. The technology used to convert fossil resources is