Integrated biorefinery for cellulosic ethanol and spherical nanolignin production from coconut waste

Abstract

Green coconut waste was subjected to different fractionation methods to obtain integrated lignin nanoparticles and cellulosic ethanol. Pretreatment with gradual addition of dilute sulfuric acid provided a higher structural hemicellulose precursor yield (68.2%). Alkaline treatment resulted in the highest extraction and recovery of lignin from coconut waste, at 79.5% and 25.3%, respectively. Separate hydrolysis and fermentation indicated that slow acid addition followed by alkaline treatment rendered the coconut biomass more susceptible to enzymatic digestion, achieving sugar yields above 60% and an ethanol yield of 0.48 (w/w). Alkaline lignin from coconut fibers was successfully converted into nanometric structures of spherical conformation ( Ø  = 80–600 nm) with a high degree of uniformity, homogeneous dispersion, and colloidal stability, with weight yields of 30% to 50%. Thus, utilizing coconut waste to obtain cellulosic ethanol and lignin nanoparticles is feasible and results in value‐added products and an environmentally sustainable alternative to waste disposal.