Influence Of Oxygen/Ionic Liquid [EMIM] Ac Pretreatment On Enzymatic Hydrolysis Efficiency Of Wheat Straw

Lignocellulose derivedfuel chemicals and materials are attracting growing concerns for its renewability,sustainability,abundance and carbon-neutral.The main component of lignocellulose is cellulose,which can be hydrolyzed into glucose by cellulase.The performance of enzymatic hydrolysis is affected by porosity(accessible surface area),cellulose crystallinity and lignin content.Therefore,it is very important to develop a pretreatment method which can increase the porosity of the fibers and reduce the crystallinity of the material.1-Ethyl-3-methylimidazolium acetate([Emim] Ac)is a good solvent for cellulose,featuring non-corrosive,non-toxic,low viscosity and liquid at room temperature.Cellulose dissolution and processing using ILs has been reported as a promising application in biorefinery.In this study,ionic liquid([Emim] Ac)and the combined treatment of oxygen with ionic liquid(oxygen/[Emim] Ac)were selected to investigate the enzymatic saccharification of wheat straw,the changes of chemical structure and crystallization of wheat straw's fiber before and after treatment were analyzed by Fourier transform infrared spectroscopy(FT-TR),X-ray diffraction(XRD)and scanning electron microscopy(SEM).Firstly,processing conditions for pretreatment using solely ionic liquid([Emim] Ac)on wheat straw were investigated,the results showed the optimal conditions are as follows: solid-liquid ratio of 1:1.5,temperature of 130 ?,residence time of 6 h.Under this condition,cellulose content of wheat straw increased from 41.4% to 58.2%,hemicellulose content decreased from 23.6% to 18.42% andlignin content decreased by 22.03%.The reducing sugar yield increased to 58.6%,which was 5 times higher than that of the untreated counterpart.SEM and XRD analysis showed that fiber surface became rough,porosity and loose,and fiber crystallinity decreased by 8.81%.after ionic liquid pretreatment.FT-IR result showed that chemical structure of wheat straw changed little after ionic liquid pretreatment.Then,combined oxygen and ionic liquid(oxygen/[Emim] Ac)treatment on wheat straw was conducted,the results showed that the optimal conditions are as follows: solid-liquid ratio of 1:1.5,temperature of 130 ?,processing time of 6 h,and oxygen pressure of 0.4 MPa.Under this condition,cellulose content of wheat straw increased from 41.4% to 61.2% with increase percentage of 47.8%.Hemicellulose content decreased from 23.6% to 17.4% with decrease percentage of 26.2%.Lignin content decreased by 35.1%.Reducing sugar yield increased to 65.1%,which was 6 times higher than that of the unpretreated raw material.SEM and XRD analysis showed fiber surface became rough,porous and loose,crystallinity decreased by 12.6% for pretreated wheat straw.This treatment method not only dissolved wheat straw fiber's surface,also destroyed fiber's pit membrane.This made fiber surface exposed with more spaces,and ionic liquid([Emim] Ac)could get into fiber smoothly.Additionaly,wheat straw fiber became swollen and dissolving with increased contact area between fiber and cellulase,finally improved the efficiency of hydrolysis.FT-IR result showed that opening of benzene ring of lignin occurred after pretreatment.The removal of lignin leaded to wheat straw fiber with more surface area exposed that facilitated the subsequent enzymatic hydrolysis.Comparison of the two studied methods,ionic liquid([Emim] Ac)pretreatment on wheat straw would make fiber surface became rough,porous and loose,while combined oxygen and ionic liquid(oxygen/[Emim] Ac)pretreatment on wheat straw would make fiber surface became even more rough,porous and loose,additional wheat straw's structure also was destroyed.This phenomenon might be caused by oxygen/[Emim] Ac dissolving fiber's surface and destroyed fiber's pit membrane.The crystallinity of the untreatedt wheat straw was 44.5%.After treatment by ionic liquid([Emim] Ac),the crystallinity of wheat straw was 35.7% with decrease percentage of 8.8%.After treatment by combined oxygen andionic liquid(oxygen/[Emim] Ac),the crystallinity of wheat straw was 31.9% with decrease percentage of 12.6%.Therefore,[Emim] Ac had more effect on wheat straw fiber crystallinity at an oxygen atmosphere,made fiber crystallinity reduced.FT-IR results showed that wheat straw's lignin structure changed after by ionic liquid([Emim] Ac)treatment.After treatment by combined oxygen with ionic liquid(oxygen/[Emim] Ac),benzene ring of lignin changed.In summary,combined oxygen and ionic liquid(oxygen/[Emim] Ac)treatment is a promising approach,and these results could provide theoretical guidance on biomass conversion and utilization.