Efficient fermentable sugar release from softwood biomass is considerably hampered by the recalcitrant nature of its plant cell wall. Here, we reported an ultrasonic and microwave assisted ethylene glycol pretreatment coupled with fast pyrolysis to make total utilization of softwood (pine sawdust) for pyrolytic sugar (levoglucosan), hemicellulosic sugar and phenol production. Compared with oil bath heating, fractionation of pine sawdust into cellulose rich fraction, hemicellulosic sugars and organosolv lignin was enhanced drastically after applying ultrasonic and microwave heating. Whereas, ultrasonic radiation prior to microwave heating turned out to slightly inhibit the fractionation due to oxygenation of sulfuric acid. Mechanistic insight into levoglucosan formation pathway revealed that microwave heating promoted the cleavage of covalent bonds, aromatic ether linkages and glycosidic bonds in lignocellulose, leading to significant improvement in biomass recalcitrance alleviation as well as alkaline and alkaline earth metal removal. This considerably facilitated the heterolytic cleavage of cellulose into levoglucosan, while inhibiting the formation of microorganism inhibitors (e.g. carboxylic acids and phenols) and other light oxygenates in the pyrolysate. Levoglucosan yield exhibited a drastic increase from 3.53 (pine sawdust) to 48.13 wt.% via single microwave heating at 240 W, which was further enhanced with increasing microwave power. Hemicellulosic sugar derived from organosolvolysis and phenol from fast pyrolysis of organosolv lignin also showed an increase in yields with increasing pretreatment severity. Ethylene glycol pretreatment via single microwave heating at 480 W was a preferable process for achieving high yields of levoglucosan (55.87 wt.%), hemicellulosic sugars (19.96 wt.%) and phenols (14.04 wt.%). These findings help to provide an efficient process for maximizing the conversion of recalcitrant softwood for the production of fermentable sugars and phenols.

从软木生物质中有效释放的可发酵糖受到其植物细胞壁顽强特性的极大阻碍。在这里，我们报道了超声波和微波辅助的乙二醇预处理，再加上快速热解，可以充分利用软木（松木屑）来生产热解糖（左旋葡聚糖），半纤维素糖和苯酚。与油浴加热相比，在施加超声波和微波加热后，松木锯末分馏成富含纤维素的馏分，半纤维素糖和有机溶剂木质素的能力大大提高。然而，事实证明，在微波加热之前的超声辐射稍微抑制了由于硫酸的氧合而引起的分级分离。对左旋葡聚糖形成途径的机理研究表明，微波加热促进了共价键的裂解，木质纤维素中的芳族醚键和糖苷键，可显着改善减轻生物质的抵抗力以及去除碱金属和碱土金属。这极大地促进了纤维素的杂化裂解为左葡萄糖葡聚糖，同时抑制了热解产物中微生物抑制剂（例如羧酸和酚）和其他轻质氧化物的形成。通过以240 W单次微波加热，左旋葡聚糖的产量从3.53（松木屑）急剧增加至48.13 wt。％，随着微波功率的增加，产量进一步提高。来自有机溶剂分解的半纤维素糖和来自有机溶剂木质素的快速热解的苯酚也显示出随着预处理的严重性增加而增加的收率。优选的是通过单微波加热至480 W进行乙二醇预处理，以获得高收率的左旋葡聚糖（55.87 wt。％），半纤维素糖（19.96 wt。％）和苯酚（14.04 wt。％）。这些发现有助于提供一个有效的方法，以最大程度地提高顽固性软木的转化率，以生产可发酵的糖和酚。