| Biomass energy is the only carbon source resource that can be converted into conventional three-phase fuel and other chemicals among renewable energy sources.Lignocellulosic biomass also has a natural and unique carbon source advantage,especially after its main components are separated,the targeted high-value utilization and transformation of each component can solve the problem of resource waste.In the biomass component separation method,Deep Eutectic Solvents(DES)not only have similar physical and chemical properties to ionic liquids,but also have low price,non-toxic,biodegradable,easy to prepare and recover,which is a new type of green solvent.The combination of DES and thermochemical transformation can better understand the physical and chemical properties of each component of the substance and its transformation process.Therefore,in this paper,different hydrogen bond donor(HBD)DES was formulated to separate the components of pine with low ash biomass as raw materials.The optimal DES type and separation conditions were selected by component analysis.In addition,the changes of thermochemical products,including the composition distribution of main pyrolysis products and the yield and quality of hydrothermal carbon products,were investigated under different pretreatment conditions.Key findings include:(1)With the increase of the treatment temperature,the yield of solid products from pine decreased,mainly because the removal rate of pine lignin increased with the increase of the pretreatment temperature.After the pretreatment of pine with choline chloride lactic acid(Ch Cl-Lac),the yield of solid decreased from 89.30% to 41.55% when it increased from 80℃ to 140℃.The removal rate of lignin increased from 32.37% to 73.12%.DES system with HBD as acid had better separation effect,and the lignin removal rate ranged from 32.37% to 73.12%.With the prolongation of pretreatment time,the solid was first decreased and then increased,while the lignin was first increased and then decreased.After Ch Cl-Lac pretreatment for 16 h,the lowest solid recovery was 51.04%,and the highest lignin removal rate was 75.62%.(2)DES pretreatment did not change the crystal structure of cellulose(cellulose type Ⅰ).Under the pyrolysis condition of 500℃,the pyrolysis products of pine hydlocellulose are mainly dehydrated sugars(Lglucose),furan(5-hydroxymethylfurfural,furfural,2(5H)furanone),hemicellulose are mainly pyrolyzed into ketones,furans and acids,and lignin is mainly pyrolyzed into phenols.The proportion of pyrolysis products is mainly related to the composition and structure of raw materials,and the proportion of aldehydes ranges from 11.91 to 22.21%.Acids accounted for 1.11-3.09%;Alcohols accounted for 5.56-11.88%;Ketones accounted for 3.38-7.60%;The proportion of phenols was 2.28-13.49%;The proportion of carbohydrate was 6.18-51.87%;The proportion of furans was 2.24~8.99%.The proportion of hydrocarbons is 0.16~1.69%;The proportion of esters was 2.53~10.45%.Nitrogen compounds accounted for 5.66~11.64%.(3)In the hydrothermal carbonization experiment of pine integrated cellulose,the yield of hydrothermal carbon is related to the composition and structure of raw materials,and is also affected by the lignin content and the conversion effect of cellulose.According to the relevant characterization analysis,after the Ch Cl-Lac pretreatment,the hydrothermal carbon morphology of the pine was changed,and carbon microspheres were formed on the surface.Meanwhile,the surface functional groups showed the appearance of typical polymer characteristic peaks and the disappearance of carbohydrate characteristic peaks,indicating that amorphous carbon was formed on the surface.However,the hydrothermal carbon morphology of integrated cellulose of pine treated with choline chloride urea(Ch Cl-Ua)did not change,and the characteristic peak of cellulose still existed.The ID/IG value of the hydrothermal carbon of pine was 0.7676,and the decrease of the ID/IG value of the hydrothermal carbon after the hydrothermal carbonization with DES pretreatment was beneficial to reduce the disordered degree of the hydrothermal carbon and make the carbon structure more orderly.The ID/IG of the hydrothermal carbon of the pine integrated cellulose obtained after the Ch Cl-Lac pretreatment for 12 h was the lowest,which was 0.5941.In addition,the characterization of the specific surface area and pore size of the hydrothermal carbon showed that after Ch Cl-Lac pretreatment,the pore volume and pore size of the hydrothermal carbon of pine integrated cellulose were higher than that of pine charcoal.But the pore volume and pore size of Ch Cl-Ua hydrothermal carbon were lower than that of pine charcoal.The main research results have theoretical significance for further efficient and comprehensive utilization of lignin cellulose biomass. |
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