Recycling solvent system in phosphoric acid plus hydrogen peroxide pretreatment towards a more sustainable lignocellulose biorefinery for bioethanol

Pretreating lignocellulosic biomass by phosphoric acid plus hydrogen peroxide (PHP) was integrated with recovering concentrated phosphoric acid (CPA), lignin, and treating phosphorus (P) wastewater. Results indicated no significant effects on cellulose recovery was observed by promoting ethanol addition, but CPA and lignin recovery were improved to 80.0% and 23.3%, respectively. Increasing water addition did not greatly affect CPA recovery (80.0-80.4%), and lignin recovery (22.8-23.6%). Consequently, the ratio of 11:1 (ethanol/PHP solution) and 4:1 (water/de-ethanol liquor) were suggested for solid/liquid separation and lignin precipitation. Average 86.0% CPA was recycled for pretreatment (≥11 runs) with average 96.3% cellulose-glucose conversion. A specially-developed biochar from crab shell was efficient on P removal with maximal adsorption capacity of 261.6 mg/g. Pretreating 1.0 kg wheat straw by 1.1 kg CPA harvested 155.0 g ethanol, 45.0 g high purity lignin and 4.9 kg P-rich biochar fertilizer. Recovering CPA, biochar-fertilizer and lignin, and P wastewater treatment made PHP pretreatment towards more sustainable and cleaner.