Apricot kernel shells as a feedstock for second-generation biofuel

This study investigated an oxidative treatment method for apricot kernel shells (AKS) to extract their polysaccharide component for subsequent conversion into liquid biofuel. The aim was to overcome the inherent recalcitrance of lignocellulosic biomass by selectively removing lignin and enriching cellulose content - critical steps for efficient enzymatic hydrolysis. The AKS were treated in an acetic acid medium with hydrogen peroxide under varied conditions, and the resulting substrates were analyzed for yield, cellulose, and lignin content. Mathematical modeling, using regression equations with statistically significant coefficients, accurately described the changes in substrate properties depending on the treatment parameters. Optimization of this multi-criteria process using a generalized Harrington desirability function identified 9% hydrogen peroxide and 120 minutes of treatment as optimal parameters, yielding a composite desirability value of 0.7966. Under these conditions, the obtained substrate exhibited a 50.1% recovery, 54.4% cellulose, and 12.4% lignin, closely matching theoretical predictions. Visual and IR spectroscopic analyses confirmed the efficiency of the treatment: the processed substrate (AKS-S) displayed a lighter color, indicating reduced lignin and increased cellulose content compared to raw AKS. IR spectra further revealed significant lignin removal and degradation of low-molecular-weight hemicelluloses, which is advantageous as it minimizes the formation of inhibitory byproducts during enzymatic hydrolysis. The treatment also doubled the specific surface area and increased porosity six-fold, improving enzyme accessibility. These findings underscore the potential of this oxidative treatment as an effective pretreatment strategy for converting agricultural waste into a high-quality substrate for biofuel production.