The use of catalytic hydrogenation to intercept carbohydrates in a dilute acid hydrolysis of biomass to effect a clean separation from lignin

Biomass carbohydrates are fractionated very cleanly (>99%) from unreacted insoluble lignin by a dilute acid hydrolysis (0.35–1.5% H3PO4), wherein the incipient aldoses are intercepted by catalytic hydrogenation (Ru/C) to produce a solution of C5–C6 polyols (xylitol, sorbitol) and anhydro polyols (sorbitan) in which no phenols could be detected (<100 ppm). A screen removes granular catalyst and lignin is simply filtered from the product slurry. This “intercepted dilute acid hydrolysis” (IDAH) of biomass to polyols affords high conversion for a variety of biomass types within 3–6 h at 185°C. Minimum polyols cost (not including catalyst cost) is calculated to range from $0.055–$0.070 kg−1. Polyols, rather than aldoses, are required for subsequent chemical conversion into hydrocarbon fuels.