Cellobiose hydrolysis using acid-functionalized nanoparticles

Mineral acids have been used effectively for the pretreatment of cellulosic biomass to improve sugar recovery and promote its conversion to ethanol; however, substantial capital investment is required to enable separation of the acid, and corrosion-resistant materials are necessary. Disposal and neutralization costs are also concerns because they can decrease the economic feasibility of the process. In this work, three acid-functionalized nanoparticles were synthesized for pretreatment and hydrolysis of lignocellulosic biomass. Silica-protected cobalt spinel ferrite nanoparticles were functionalized with perfluoroalkylsulfonic acid (PFS), alkylsulfonic acid (AS), and butylcarboxylic acid (BCOOH) groups. These nanoparticles were magnetically separated from the reaction media and reused. TEM images showed that the average diameter was 2 nm for both PFS and BCOOH nanoparticles and 7 nm for AS nanoparticles. FTIR confirmed the presence of sulfonic and carboxylic acid functional groups. Ion exchange titration measurements yielded 0.9, 1.7, and 0.2 mmol H+/g of catalyst for PFS, AS, and BCOOH nanoparticles, respectively. Elemental analysis results indicated that PFS and AS nanoparticles had 3.1 and 4.9% sulfur, respectively. Cellobiose hydrolysis was used as a model reaction to evaluate the performance of acid-functionalized magnetic nanoparticles for breaking β-(1→4) glycosidic bonds. Cellobiose conversion of 78% was achieved when using AS nanoparticles as the catalyst at 175℃ for 1 h, which was significantly higher than the conversion for the control experiment (52%). AS nanoparticles retained more than 60% of their sulfonic acids groups after the first run, and 65 and 60% conversions were obtained for the second and third runs, respectively.