Hemicellulose hydrolysis using solid acid catalysts generated from biochar

In an integrated forest biorefinery (IFB), hemicellulose is pre-extracted primarily in oligomeric form (e.g., hot water extraction) and the remaining solids (cellulose and lignin) subsequently treated via the Kraft process. Conceptually, hemicellulose can be used as a bio/chemical building block, but requires hydrolysis to monomeric carbohydrates. Selective hemicellulose hydrolysis using reusable solid acid catalysts, generated as a biorefinery co-product, could improve IFB economics. Solid acid carbon catalysts were synthesized from biochar (pine chip or PCC via slow pyrolysis at 400 degrees C) and wood based activated carbon (AC), and compared with a commercially available sulfonated styrene-divinylbenzene macroreticular resin (Amberlyst 15). The formation of active sites (SO3H) was verified by base titration, CHNS analysis, and attenuated total reflectance (ATR-FTIR) analysis with each technique indicating higher active site density in the biochar based catalyst (e.g., 0.7 and 0.2 mmol/g for PCC and AC, respectively). Catalytic testing using birchwood xylan as a model compound was performed in batch reactors (working volume 12 mL, 16 wt% catalyst) over a range of temperatures (90-120 degrees C). Although the biochar surface area was significantly lower than the activated carbon (365 vs. 1391 m(2)/g, respectively) hydrolysis rates were significantly higher for the biochar derived catalyst; e. g., an 85% conversion of xylan was observed within 2 h using the biochar, compared to 57% at 24 h for AC (7.7 g L-1, 120 degrees C). Kinetic analysis clearly indicated that the hydrolysis reaction rate and conversion increased with temperature (85% in 2 h at 120 degrees C vs. 65% and <5% for 111 degrees C and 93 degrees C, respectively). Catalytic activity declined after one recycling (similar to 14%) and eventually lost all activity after multiple uses (4x). Loss in activity was attributed to a combination of acid site leaching and significant attrition of the biochar. (C) 2012 Elsevier B.V. All rights reserved.