Effect of hydrogen donor on glycerol hydrodeoxygenation to 1,2-propanediol

The effect of various biomass-derived hydrogen donors in liquid phase hydrodeoxygenation of glycerol to 1,2-propanediol over Cu:Zn:Al catalyst is investigated. The effectiveness of each H-2 donor (methanol, formic acid, ethanol, ethylene glycol, 2-propanol, 1-propanol, 2-butanol, 1-butanol and tert-butanol) is compared with that of glycerol and water in the feed. When glycerol serves as H-2 source, mostly via aqueous phase reforming, it is converted by 68.1%, showing moderate selectivity to 1,2-propanediol (40.9%). Improved catalytic results are obtained with the addition of a H-2 donor molecule in the feed. Except for ethylene glycol and formic acid, H-2 donors' presence in the feed and especially at increased concentration, enhances the activity and the target product yield, without affecting the distribution of hydrodeoxygenation products. In terms of hydrogen production and 1,2-propanediol formation, methanol is the best H-2 donor (74% 1,2-propanediol yield), followed by 2-propanol (59.6% 1,2-propanediol yield). Formic acid has also potential as H-2 donor, as its activity in the catalytic hydrogen transfer is favored at low H-2 donor/ glycerol molar ratios.