The Effect Of Deep Eutectic Solvents Structures And Properties On Bagasse Pretreatment Efficiency

With the development of the global economy,the energy crisis is becoming more serious,so more attention has been paid to the exploitation of biomass based energy.Lignocellulosic biomass has a complex structure,and the development of economical,efficient and environmentally friendly biomass pretreatment technology is the prerequisite for clean separation and efficient conversion of lignocellulosic biomass components.Deep eutectic solvents(DESs)have been used in biomass pretreatment and conversion because of their advantages of easy synthesis,adjustable properties and environmental friendly.At present,the specific role of hydrogen bond acceptors(HBAs)and hydrogen bond donors(HBDs)in the biomass pretreatment with DESs is still limited.Therefore,bagasse was used as the pretreatment object in this thesis.By changing the structure of HBD and HBA,the influence of the structure and properties of DESs on the efficiency of biomass pretreatment(lignin removal and cellulase enzymatic hydrolysis efficiency)and the related mechanism were discussed.In this thesis,the effect of the change of HBA and HBD among DESs on the pretreatment efficiency of lignocellulosic biomass was studied.When choline chloride was used as the HBA and the HBDs(a series of acids and polyols)were changed,the content of the components changed significantly.The cellulose content increased from 35.8%(untreated)to 47.1%-72.9%,and the xylan content decreased from 25.0% to 3.1%-11.6%;When malic acid was used as the HBD and the type of HBA(a series of amino acids)was changed,it was found that the cellulose content increased to 50.9% and the xylan content decreased to 21.4%.The results of this part of the study indicated that both the HBA and HBD can significantly affect the solvent pretreatment efficiency.The pretreatment efficiency is related to the strength of the intermolecular interaction energy in the solvent.Generally speaking,the intermolecular interaction of the solvent is smaller,and the solvent molecules are easier to dissociate and act on the biomass molecules,so the pretreatment efficiency is higher.In addition,the pretreatment efficiency is related to the p Ka value of the HBA and HBD.The xylan removal is negatively linearly related to the p Ka value of HBD and positively linear related to the p Ka value of HBA.The bagasse was further pretreated with the specific DES(choline chloride lactate,molar ratio of 1:2),and the effect of pretreatment conditions on the composition and enzymatic hydrolysis efficiency of bagasse was investigated.It was found that the pretreatment efficiency has an important relationship with temperature,time and biomass loading.When the time and biomass loading are the same,the enzymatic hydrolysis efficiency increased with increasing temperature.At 150?,the polysaccharide digestibility and sugar yield would reach the highest,the cellulose digestibility reached 72.3%,and the glucose yield reached 69.1%.Under the condition of constant temperature and biomass loading,the time is too short,the pretreatment strength is not enough,the degree of breaking of the key link in the biomass is low,and the pretreatment efficiency is lower;and too long time will lead to excessive degradation of biomass components and loss.The pretreatment severity factor was used to comprehensively analyze the pretreatment efficiency of the deep eutectic solvent.It was found that the pretreatment efficiency(removal of lignin and xylan)gradually increased as the in severity factor increased.The increase in pretreatment efficiency is greatly reduced,especially the lignin removal rate does not increase significantly after reaching 3.25,which may be caused by the formation of pseudo-lignin.In addition,at a fixed temperature and time,the pretreatment efficiency is also affected by the biomass loading,which decreased with the increase of the biomass loading.When the solid-liquid ratio was 5%,the pretreatment efficiency was the best.Therefore,the best condition of pretreatment of bagasse with choline chloride and lactic acid(molar ratio 1:2)was 1 h pretreatment at 150? with a biomass loading of 5%.This study provides a theoretical basis for further understanding the mechanism of DESs pretreatment of biomass,and can also promote the efficient conversion and utilization of lignocellulosic biomass resources.