| The depletion of fossil fuels and climate changes are regarded as important factors driving researchers to develop sustainable and clean energy sources. Biomass resources are the most promising energy sources that can be used to produce biofuels and chemicals, which could be logical choices to replace fossil fuels and have great benefit to the whole environment. Pyrolysis is a potential thermochemical conversion route, converting biomass to energy-dense biofuels as well as chemical feedstocks. It was proposed that pretreatments may modify the chemical structure of biomass or selectively remove lignocellulosic components, thereby improving the thermochemical conversion of biomass during pyrolysis. However, only a limited number of studies have focused on the pretreatment before biomass pyrolysis to promote thermochemical reactions and upgrade oil contents. In this work, the effects of biopretreatment using two fungi with different degradation patterns on chemical composition and thermochemical conversion of corn stover were investigated. Furthermore, changes in thermogravimetric behaviors and pyrolysis products distribution of corn stover varying depending on the different fungal pretreatment were studied for the first time. By isolating the bio-modified lignin and cellulose, the mechanisms and relationships between the fungi deconstruction characteristics and thermogravimetric alteration have been clarified.By studying on the composition, structure changes on FTIR, crystallinity analysis, pore structure analysis and composition analysis of 1% sodium hydroxide extracts, the results indicated that the white-rot fungus Irpex lacteus CD2 and brown-rot fungus Fomitopsis sp. IMER2 had very different deconstruction characteristics on corn stover. The white-rot fungus I. lacteus CD2 has great lignin degrading ability causing the decrease in acid insoluble lignin and the increase in acid soluble lignin. The brown-rot fungus Fomitopsis sp. IMER2 degraded lignin to a limited extent but degraded the amorphous regions of the cellulose to a significant extent.By investigating the influence of different degradation pattern by white-rot fungus I. lacteus CD2 and brown-rot fungus Fomitopsis sp. IMER2 on corn stover and lignocellulose components thermogravimetric characteristics and the pyrolysis products, the results showed that the biopretreatment of fungi favors thermochemical conversion of corn stover while the extents of the increase in weight losses, weight loss rates and the yields of bio-oil varied depending upon the different pretreatment fungi. The weight loss of Fomitopsis sp. IMER2 pretreated acid detergent fiber became greater, and the oil yield increased from 32.7%to 50.8%. After white-rot fungus I.lacteus CD2 biopretreatment,58% weight loss of acid detergent lignin was achieved and the oil yield increased from 16.8% to 26.8%. Moreover, the content of the cellulose pyrolysis products such as carboxylic acid, furans and ketones increased dramatically after brown-rot fungus Fomitopsis sp. IMER2 pretreated. And the content of the lignin pyrolysis products such as phenols and other aromatics increased remarkably after white-rot fungus I. lacteus CD2 pretreated.By isolating the deconstructed lignin pretreated by fungi, the mechanism and relationship between lignin structure alteration and thermogravimetric characteristics were investigated. Results showed that white-rot fungus I. lacteus CD2 can greatly deconstruct the structure of lignin. By degraded the methoxy groups and destroyed the linkages ofβ-5', 5-5'andβ-O-4 ether bond, the content of coniferyl, guaiacyl and syringyl groups decreased. The great lignin-degrading ability and structure alteration of white-rot fungus I. lacteus CD2 can improve lignin thermogravimetric behavior. After biopretreated by I. lacteus CD2, the weight loss of lignin became larger and the thermal degradation processes were accelerated, as well as the decrease in the activation energy was by about 11.14%(based on original untreated corn stover lignin).By isolating the fungi pretreated cellulose and preparation of regenerated microcrystalline cellulose using imidazolium ionic liquids, the mechanism and relationship between the cellulose crystallinity and thermogravimetric characteristics have been clarified. Along with the increase in crystallinity and the crystalline portion of cellulose, the weight loss became larger and the weight loss rates were accelerated.To understand whether the biopretreatment of fungi can promote the thermal decomposition of bamboo and its main components, the changes in lignocellulose components as well as thermal behaviors of bamboo and acid detergent lignin were investigated. The results showed that the white-rot fungi I. lacteus CD2 pretreatment is also advantageous to thermal decomposition of lignin in bamboo.In this work, the relationship between different fungal degradation patterns and biomass thermochemical conversion behaviors was investigated. Furthermore, the mechanism of white-rot fungus I. lacteus CD2 promote the lignin thermochemical conversion and brown-rot fungus Fomitopsis sp. IMER2 promote the cellulose thermochemical conversion were clarified. This may demonstrate the potential of fungal pretreatment in thermochemical conversion of corn stover to obtain biofuels, and also provided theoretical and technical foundation for biological pretreatment of biomass with white-rot and brown-rot fungi.
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