Renewable gasoline from aqueous phase hydrodeoxygenation of aqueous sugar solutions prepared by hydrolysis of maple wood

Abstract

In this paper we demonstrate an integrated process for the production of high octane gasoline from maple wood by hydrolysis of maple wood into aqueous carbohydrate solutions followed by aqueous phase hydrodeoxygenation of the sugar solutions. The aqueous carbohydrate solutions were prepared by both hydrolysis in hot water and hydrolysis with dilute acids (H₂SO₄, oxalic acid). The aqueous carbohydrate solutions were a mixture of xylose, water soluble hemicellulose oligomers, acetic acid, glucose, glucose oligomers, and probably some lignin polymers. Hydrolysis with hot water produced primarily hemicellulose oligomers whereas hydrolysis with acids produced mainly xylose and acetic acid. The hydrolysis co-product was a solid enriched in cellulose and lignin. The aqueous streams were hydrodeoxygenated by a two step catalytic process in which the first catalyst bed contained a Ru/C catalyst at 393 K and the second catalyst bed contained a Pt/zirconium phosphate (Pt/ZrP) catalyst at 518 K. The Ru/C catalyst was able to selectively hydrogenate xylose into xylitol but could not selectively hydrogenate the xylose oligomers. The two stage process was able to convert the aqueous carbohydrate streams derived from maple wood into gasoline range products with carbon yields of up to 57% and an estimated octane number of 96.5. No significant catalyst deactivation was observed indicating that the catalysts are very stable. The highest gasoline yield from this two stage process was obtained from the stream produced by acid hydrolysis of maple wood with 0.5 wt% oxalic acid at 433 K for 0.5 h. These results suggest that aqueous phase processing of sugars obtained by hydrolysis is a promising option for the production of fuels and chemicals from lignocellulosic biomass.