Process Optimization for Aqueous Ethanosolv Pretreatment of Coffee Husk Biomass Using Response Surface Methodology

This study targeted to optimize process factors using response surface methodology and determining their effect on delignification and cellulose recovery. Optimization of pretreatment conditions with desirability value of 0.828 was done at temperature (A) 150°C, contact time (B) 2 h, and liquid-to-solid ratio (LSR) (C) 15 ml/g. The sample was soaked in an aqueous ethanol solution (48% ethanol). Chemical composition was determined to be 1.87 ± 0.20, 7.03 ± 0.99, 28.05 ± 0.27, 39.29 ± 3.39, and 23.77 ± 3.91 wt% for ash, extractives, lignin, hemicellulose, and cellulose, respectively. Experimental results were validated by comparing actual value with predicted value. The model was verified as the best for improving delignification and cellulose yield. Coefficient of determination (R2), analysis of variance (ANOVA), response plots, and optimization nodes were used to examine the experimental results. The quadratic equation was used to test the model, and ANOVA was used to evaluate the model’s statistical performance and correctness. Temperature, interaction term (BC), and quadratic terms (A2, B2, and C2) showed significance, while contact time, LSR, and interaction terms (AC and AB) indicated insignificance for cellulose recovery. Temperature, contact time, interaction term (AB), and quadratic terms (B2 and C2) showed significance, but LSR, interaction terms (AC and BC), and quadratic term (A2) showed insignificance for delignification. Pretreatment efficacy for delignification (6.0%) and cellulose recovery (151.80%) were achieved at optimal conditions. The pretreatment method is able to produce cellulose-rich coffee husk residues.