Sustainable conversion of Pinus pinaster wood into biofuel precursors: A biorefinery approach

• Pine wood was subjected to aqueous fractionation to solubilize hemicelluloses.
• Hemicellulosic saccharides were efficiently saccharified by posthydrolysis.
• Solids from fractionation were processed in acidic media under microwave heating.
• The conversion of cellulose into formic acid and levulinic acid was optimized.
• Lignin was recovered as the insoluble residue from acidic processing.

Pinus pinaster wood was fractionated by aqueous treatments to yield a solution containing hemicellulose-derived saccharides (mainly of polymeric or oligomeric nature) and a solid phase enriched in cellulose and lignin. The solution containing polymeric or oligomeric hemicellulosic saccharides was acidified with sulfuric acid (up to 4 wt%) and heated (up to 130 °C) to assess the conversion of substrates into sugars. The interpretation of the experimental data was done on the basis of a mechanism involving 10 first-order, kinetic parameters. Almost total saccharification was achieved under a range of operational conditions, and the hydrolyzates presented compositions favorable for their further utilization as fermentation media. The solid phase coming from aqueous processing was mixed with HCl solutions and reacted under microwave irradiation to yield the target products levulinic acid (precursor of valeric biofuels) and formic acid (suitable for fuel cell devices). The effects of the most influential parameters (temperature, reaction time and acid concentration) were assessed by empirical modeling. The highest cellulose conversion into levulinic acid (61.9% of the stoichiometric value as an average) was achieved at 190 °C operating for 15 min in a medium containing 1 wt% HCl.