(634b) Conversion of Biomass-Derived Polyols Over Carbon Supported Pt-Re Catalysts
We have studied the conversion of concentrated polyol solutions (80 wt% glycerol and 60 wt % sorbitol) into gas mixtures containing CO/CO2/H2 and light alkanes as well as oxygenated hydrocarbons (e.g., alcohols and ketones) in the liquid phase over a Pt-Re/C catalyst. The conversion of polyols over Pt-Re/C proceeds via reaction pathways that involve C-C and C-O bond scission. High rates of C-C scission lead to the formation of CO and CO2, while high rates of C-O scission result in alkanes, alcohols, diols, and ketones. We show that the relative rates of C-C versus C-O scission can be manipulated by changing process conditions (temperature and pressure). At 503 K and 18 bar, the conversion of 80 wt % glycerol yields COx (40% carbon conversion), C1-C3 alkanes (20%), acetone (5%), and alcohols and diols such as ethanol, ethylene glycol, and acetol (35%). Increasing the temperature to 523 K at constant pressure causes the selectivity to COx to increase to 50% and alkane selectivity to increase to 27%, while the selectivity to alcohols decreases to 18%. Increasing the pressure to 27 bar at constant temperature causes a significant increase in the production of alcohols (50% selectivity) at the expense of alkanes (13%) and COx (30%). We also show that under similar reaction conditions, the conversion of glycerol produces more COx and light alcohol species, whereas sorbitol yields more alkanes and higher molecular weight oxygenates, and that both polyols follow similar pressure and temperature trends with respect to relative rates of C-C to C-O bond cleavage. The results from this study provide a fundamental basis for using Pt-Re catalysts to convert polyols to fuels and valuable chemicals.