Diluted acid-assisted hydrothermal-organosolv fractionation of OPEFB for lignin and sugar recovery

Lignocellulose contains cellulose, hemicellulose, and lignin, each of which can be utilized as valuable products. Due to the complexity of its structure, pretreatments such as sub-critical water and Organosolv are favoured for their environmental friendliness and feasibility in pretreating lignocellulose and isolating lignin. This research aimed to investigate the effects of dilute acid addition in the hydrothermal-organosolv fractionation of OPEFB on total reducing sugars and lignin yields. The hydrothermal process, optimized under conditions of 185.61°C, 60 bar, a solid-to-liquid (S/L) ratio of 1:20, and the addition of 2.62% H2SO4 as a catalyst for 27.3 minutes, yielded a maximum total reducing sugar concentration of 13.52 g/L. This was followed by organosolv pretreatment at a relatively mild severity, with a temperature of 180°C for 60 mins, using 70% ethanol (v/v) as the organic solvent and an S/L ratio of 1:1. The use of a dilute acid catalyst as an additive in the organosolv pretreatment resulted in the higher lignin yield of 16.11%, with a lignin purity of 71.26% and a total reducing sugar yield of 66.25% (14.522 g/L after 72 hours of enzymatic hydrolysis). The combination of sub-critical water pretreatment followed by organosolv was proven to be the most effective, yielding 4.35 grams of sugar and 0.291 grams of lignin per 10 grams of OPEFB.