H2SO4 and microwave assisted ethylene glycol pretreatment of recalcitrant softwood coupled with fast pyrolysis for platform chemical and porous carbon production

The recalcitrance of softwood biomass resulting from its compact three-component network and high guaiacyl lignin content hinders sugar release through saccharification processes. This study proposes a process integrating H 2 SO 4 -assisted ethylene glycol (EG) pretreatment of softwood pine under microwave heating with subsequent fast pyrolysis saccharification process, which enables efficient fractionation of pine and facilitated targeted conversion of fractionated cellulose into pyrolytic sugar levoglucosan (LG), also the fractionated lignin was converted into porous carbon by activated pyrolysis. The effect of H 2 SO 4 dose (0–3 wt%) on the fractionation efficiency under microwave heating, as well as pyrolytic product distribution was systematically investigated. Moreover, the mechanism that regulates the pore structure development of lignin-derived carbon through a HCl deashing-K₂CO₃ activation strategy was explored. The results show that the dose of H 2 SO 4 plays a significant role in the fractionation of pine, the cellulose-rich fraction yield of 39.93% was achieved when applying 2 wt% H₂SO₄ under microwave heating, which achieves substantial removal of lignin, hemicellulose and AAEMs while preserving the structural integrity of the majority of cellulose. This considerably facilitated the alleviation of biomass recalcitrance and reduction in catalytic effect of AAEMs, enhancing the cleavage of cellulosic glycosidic bonds to form LG during fast pyrolysis saccharification process, with the yield increased from 4.87% of pine sawdust to 47.44% of the 2 wt% H₂SO₄ assisted EG pretreated feedstock. Additionally, pre-deashing pretreatment of feedstock was found to promote the formation of submicron pores in carbon during K₂CO₃-activated pyrolysis of the fractionated lignin, with the carbon specific surface area increased from 30.24 m²/g of pine sawdust derived lignin to 933.14 m²/g of demineralized pine derived one, and microporosity from 68.4% to 93.4%. This biorefinery scheme provides a theoretical and technical basis to overcome softwood biomass recalcitrance for its total valorization into value-added chemicals and porous carbon material.