A tandem chemocatalytic-hydrothermal approach for the conversion of lignocellulosic biomass into organic acids

A metal-ion-promoted, tandem chemocatalytic-hydrothermal approach was investigated for the conversion of lignocellulosic rice hull biomass into lactic acid (LA) and glycolic (GA) acid. Preliminary screening of selected metal ion catalysts revealed that lead (II) nitrate produced the highest conversion yield (35.77 %) and lowest product filtrate pH (2.63) relative to nickel sulfate (28.50%, pH=3.26) and zinc sulfate (27.83%, pH=3.18), making it the most suitable catalyst for the conversion. Furthermore, optimization of experimental parameters showed that the most favorable yields for the lead nitrate-promoted conversion were attained when the reaction was done at 170 °C for 30 min, with a catalyst concentration of 3.5 mM and a substrate concentration of 5%. Such conditions gave way to the production of lactic and glycolic acids with 25.6% and 15.0% yields, respectively. Investigation on the effect of sample pretreatment also showed comparable conversion yields for unground (64.6%) and ground (64.0%) samples, but more favorable organic acid yields were observed for ground samples (25.6% LA, 15.0% GA) compared to unground (7.6% LA, 15.0% GA).