Application And Recycling Of Ionicl Iquids In Pretreatment Of Lignocellulosic Biomass

Currently,lignocellulosic biomass needs be pretreated to reduce its recalcitrance during biochemical conversion.Certain ionic liquids(ILs)can dissolve cellulose,which forms the basis of ionic liquid pretreatment technology.The chemical and physical structure changes after pretreatment of biomass are the focus of pretreatment studies.Earlier studies were mainly focused on pretreatment at low solid content(biomass concentration in ILs was about 3-5 wt.%).However,to reduce the pretreatment cost,the solid loading in the ILs needs to be increased.The effects of IL concentration on the pretreatment efficiency(enzymatic hydrolysis efficiency)as well as the structure and composition of biomass are not clear.This project involves pretreatment of four kinds of biomass,white poplar,eucalyptus,sorghum and switchgrass,in different concentrations of IL(1-ethyl-3-methylimidazolium acetate).The biomass concentration ranged from 5 to 25 wt.%.The pretreatment time was 3 hours and temperature was 110?.All of the biomass samples after pretreatment were chemically characterized and tested for enzymatic hydrolysis.Enzymatic hydrolysis data showed that the high biomass content in pretreatment is feasible,and the sugar conversion can reach 60-80%.X-ray diffraction(XRD),small angular neutron scattering(SANS)and nitrogen adsorption analysis were used to study the physical structure of cellulose biomass after IL pretreatment.XRD was used to measure the crystal structure of cellulose in biomass.SANS and nitrogen adsorption device were used to study the porosity and specific surface area of biomass.SANS detected pores with a radius of 25 to 625 A in poplar and eucalyptus.The results showed that the porosity increased after pretreatment,and the contribution from small pore to the increased porosity was less than that from larger pores.The dependence of conversion of sugar from white poplar and eucalyptus on solid content was different.The results showed that the change of cellulose crystal structure played a decisive role,not the porosity.In the study of pine wood,the relative change of the porosity of the pine samples measured by SANS was compared with the results obtained by the nitrogen adsorption device for the first time,and the crystal structure of the biomass was measured by XRD.Porosity and XRD data indicated that during pretreatment,pine samples pretreated at higher solid content were better than those at lower solid content,and this anomalous result was found to be due to presence of rosin acid in the pine wood.When the solid content is high,the concentration of rosin acid is also high,which acted as a catalyst in IL pretreatment.The recycle and reuse of ILs in biomass pretreatment is crucial.A new method for recycling and reuse of ionic liquids was proposed here,a distillation apparatus was used and the recycled pretreatment liquor was directly used for biomass pretreatment.In the distillation apparatus,the concentration of the IL in the pretreatment liquor increased with time due to water evaporation.We carried out three cycles of recycling and reuse.We found that sugar conversion decreased with the number of cycles from 80-90%to 50-60%.We believe that the process optimization can further improve the sugar conversion.