Study On The Characteristics And Mechanism Of Deoxidizing Products From Biomass Degradative Solvent Extraction

As a kind of renewable energy with low pollution,sustainablility and carbon neutral,biomass energy is expected to play a huge role in the future energy structure as a substitute for traditional fossil energy such as coal and oil.Lignocellulosic biomass is an important component of biomass,which is widely distributed and readily available.Moreover,lignocellulosic biomass can be converted into gas,liquid and solid products with a wide range of uses through thermochemical conversion methods,which is favored by the majority of researchers.Lignocellulosic biomass is an important component of biomass and is favored by researchers because of its wide distribution,availability of raw materials,and its ability to be converted by thermochemical transformation into a wide range of gas,liquid and solid phase products with a broad application.However,lignocellulosic biomass possesses intrinsic disadvantages,such as high oxygen content,high water content,low energy density,high content of alkali and alkali earth metals,strong tendency of moisture adsorption and self-ignition.These intrinsic disadvantages limit its industrial application scale during the thermochemical conversion process.Therefore,in order to achieve the deoxidation and deashing of lignocellulosic biomass,improve its energy density and promote the efficient conversion and utilization,high-efficiency pretreatment of biomass has attracted extensive attention of researchers in recent years.Compared with torrefaction and hydrothermal carbonization pretreatment technologies,degradative solvent extraction can achieve deep deoxidization and deashing of biomass,and extract has excellent properties such as high carbon and low oxygen content and unique thermoplasticity,which can be used in a variety of high value-added applications(such as making carbon fiber).However,the complex composition and structure of lignocellulosic biomass lead to a very complicated transformation process of biomass pyrolysis,and the transformation reaction mechanism is not clear,which restricts the development of degradative solvent extraction.Therefore,the influence of the main components of lignocellulosic biomass on the degradative solvent extraction process and products is of great significance for the in-depth understanding of the reaction mechanism of degradative solvent extraction.In this paper,the influences of torrefaction,hydrothermal carbonization and degradative solvent extraction on the moisture adsorption and self-ignition tendency of biomass were firstly revealed.Then,the interactions between cellulose,hemicellulose and lignin during degradative solvent extraction were investigated.Finally,the influence mechanism of AAEM(alkali and alkaline earth metals)on biomass during degradative solvent extraction was revealed.The main research contents are as follows:(1)The influences of torrefaction,hydrothermal carbonization and degradative solvent extraction on moisture adsorbtion and self-ignition tendency of biomass were studied.The fluctuations of the moisture absorption ratio of samples were obtained through the quality changes of samples in the natural environment,and the moisture absorption characteristics of samples were further acquired.Then,the low temperature oxidation parameters and heat release of biomass and its pretreatment products were obtained by means of the TG-DSC method,on the basis of which the spontaneous combustion tendency of each sample was synthesized and derived.The physical and chemical properties of biomass and its pretreated products were studied to put forward the influence mechanism of torrefaction,hydrothermal carbonization and degradative solvent extraction on moisture absorption and self-ignition tendency of biomass.The research results showed that torrefaction and hydrothermal carbonization could reduce the content of oxygen-containing functional groups in biomass,which could weaken the moisture absorption of biochar and hydrochar.However,the high content of inorganic metal elements and large specific surface area in biochar and hydrochar made their self-ignition tendency not significantly suppressed;The moisture absorption and self-ignition tendency of extract were greatly reduced due to its dense structure and very low content of oxygen-containing functional groups and inorganic metal elements.(2)The interactions between cellulose,hemicellulose and lignin during degradative solvent extraction were studied.In the experiment,the yield distribution law of the three-component degradative solvent extraction products was obtained,and the physical and chemical properties of the single-component and mixed-component extracts were analyzed.The interactions of the three components during degradative solvent extraction process on the extraction products’ yield and their properties were elucidated.The results showed that the interaction between cellulose and hemicellulose was not obvious because the chemical composition and products of low temperature pyrolysis of cellulose and hemicellulose were similar.However,the free radicals generated by cellulose or hemicellulose pyrolysis would promote the degradative solvent extraction of lignin and reduced the condensation reaction between lignin molecules,which led to the decrease of residue yield and the increase of gas and liquid product yield.(3)Firstly,biomass was impregnated with deionizing water,acetic acid and hydrochloric acid,then the biomass obtained after different impregnation pretreatment was subjected to degradative solvent extraction.The AAEM content distribution of biomass and its extracted products were studied.The migrant law of AAEM during degradative solvent extraction was obtained,thereby clarifying the influence law of AAEM on the process of degradative solvent extraction and extracted product properties.The results showed that AAEM(especially K)could catalyze ring-opening fracture and condensation polymerization of macromolecular sugar unit,and the yield of extract after AAEM removal was increased,while that of residue and gas product decreases.The content of AAEM in the extract was very low,and a large amount of AAEM was enriched in the residue.