Plasma Electrolytic Liquefaction Lignocellulosic Biomass Under Acidic Conditions

Plasma electrolytic liquefaction(PEL)is a novel liquefaction technology which combines the plasma technology with the conventional solvent-catalytic liquefaction.During the PEL process,the solvent can be heated by electric field and plasma without extra heating devices.Additionally,the free radicals produced by discharge can not only accelerate the liquefaction of sawdust,but also promote the quality of products.PEL has the desirable feature of short time,high efficiency,simple device and low energy consumption.In this paper,we investigated the mechanism and universality of PEL.In the first place,the plasma electrolytic technology was successfully employed to achieve the fast liquefaction of sawdust when polyethylene glycol 200(PEG 200)and glycerol were used as liquefacient in the presence of the catalyst sulfuric acid.The results show that H+ ions not only heat the solution effectively,but also accelerate the protonation process in the electric field generated during the PEL process.Besides,the free radicals produced by discharge can accelerate the liquefaction of sawdust and promote the quality of products.The influence of some key parameters such as the catalyst percentage,the liquefacient/sawdust mass ratio,and PEG 200/glycerol molar ratio on the liquefaction yield were investigated in detail in our work.Under the optimal conditions such as sawdust mass of 5 g,reaction time of 5.10 min,liquefacient/sawdust mass ratio of 7.12:1,PEG 200/glycerol molar ratio of 1.40 and catalyst mass percentage of 1.02%,the liquefaction yield of sawdust reached 99.48%.Then,we compared the discharge characteristics and catalytic efficiency of sulfuric acid,p-toluenesulfonic acid,and their respective sodium salts(sodium sulfate and sodium p-toluenesulfonate)and found that sulfuric acid was the optimal catalyst and that the liquefaction yield was inversely proportional to the water content when glycerol was used as the liquefacient during the PEL process.When a salt was used as the only catalyst without adding additional H+ ions,the liquefaction yield reached 83.51%after 25 min in the presence of the catalyst,sodium p-toluenesulfonate.This yield was higher than the yield obtained using sodium sulfate as the catalyst(60.63%)because different concentrations of H+ ions were produced during the PEL process.In order to investigate the universality of PEL,the cellulose,lignin,and holocellulose were extracted from sawdust;then each was liquefied using PEL.In addition,cellulose and lignin,as well as holocellulose and lignin,were blended in different proportions and were also liquefied using PEL.The results showed that cellulose,the most recalcitrant fragment in PEL,and lignin,the most vulnerable in PEL,were efficiently liquefied at the high temperatures produced during the PEL process,illustrating the universality of PEL.Of particular note,condensation reactions occurred during the process of liquefying single or proportionate compositions,leading to a decline in the liquefaction yield.In summary,PEL created a new field for the conversion of biomass and improved the industrialization potential of biomass liquefaction.