PNNL

Abstract

Biomass ash can add removal or waste disposal costs to the biorefinery operations; hence, efforts to valorize this otherwise waste material are needed to enhance its economic value. In this study, biorefinery residues and biomass ash were used to develop sulfonated carbon-based, solid-acid catalysts to enhance xylan hydrolysis. Catalyst preparation steps involving impregnation, carbonization, and sulfonation were conducted to introduce acid sites to the catalysts. Metals extracted from the biomass ash were impregnated into a carbon support prepared from biorefinery residues to synthesize sulfonated ash-impregnated carbon-based catalysts (SAIR). Metals present in the ash probably are responsible for the increased acid density in the SAIR catalyst. At reaction conditions of 160°C for 20 min, xylan hydrolysis using the SAIR catalyst produced a 11.4% xylose yield (measured as g per 100 g of initial solid), which is an increase of 171% over the yield obtained from a catalyst without ash impregnation (SR). A xylan-to-catalyst ratio of 1:2 resulted in 72.9% xylose yield, which comparable to the 74.1% yield from using 0.5 wt% sulfuric acid under the same reaction conditions. Moreover, this catalyst significantly inhibited xylose dehydration and formed much less furfural at 0.85%, only 11.3% of that generated using 0.5 wt% sulfuric acid. Hence, these results show the potential for using biomass ash as a metal source to increase the number of acid sites in solid-acid catalysts used for biomass pretreatment.