| Producing fuel ethanol from lignocellulose has become an important industry route because of its remarkable environmental advantage.However,it is difficult to degrade the lignocellulose,which restricts the development of the industry.The main components of lignocellulose are cellulose,hemicellulose and lignin,and cellulose is embedded in lignin and hemicellulose.This complex space structure of lignocellulose hindered the degradation of cellulose by microorganisms or enzymes.Pretreatment can destroy the complex structure to some extent,and thus improve the utilization efficiency of lignocellulose.In this paper,corn straw and salix psammophila were pretreated by physical methods,chemical methods and ionic liquid methods to improve the conversion of lignocellulose to fuel ethanol.Firstly,the effect of high temperature and high pressure,high temperature and normal pressure,high hydrostatic pressure,ultrasonic and mechanical grinding on ethanol production from corn straw and Salix psammophila were studied.The results showed that high temperature and normal pressure method was superior to the other four kinds of pretreatment method.Compared with untreated corn straw,cellulose digestibility was increased 12%,hemicellulose digestibility was increased 14%,ethanol production was increased 21% when corn straw was pretreated by high temperature and normal pressure method(solid-liquid ratio1:10,120 min,80?).Compared with untreated Salix psammophila,cellulose digestibility was increased 9%,hemicellulose digestibility was increased 13%,ethanol production was increased 17% when Salix psammophila was pretreated by high temperature and normal pressure method(solid-liquid ratio1:30,120 min,80?).X-diffraction(XRD)analysis showed that the crystallinity of cellulose was increased gradually due to the removal of disordered lignocellulosic in the amorphous region.The crystallinity index of pretreated corn straw and Salix psammophila was increased 11.7% and 8.2% respectively.Fourier transform infrared(FT-IR)analysis showed that the absorption peak of corn straw and Salix psammophiladid not change significantly.Scanning electron microscopy(SEM)showed that there were obvious cracks on pretreated corn straw and Salix psammophila.Secondly,the effect of dilute sulfuric acid and sodium hydroxide on ethanol production from corn straw and Salix psammophila were studied.The results showed that the pretreatment effect of sodium hydroxide was better than dilute sulfuric acid.The optimal conditions of sodium hydroxide method on corn straw and Salix psammophila were 180 min,solid-liquid ratio 1:10,the concentration of sodium hydroxide 10%,temperature 80 ?.Compared with untreated corn straw,there are an increase of 49% in cellulose digestibility,an increase of 160% in hemicellulose digestibility,an increase of92% in ethanol production when corn straw was pretreated under those conditions.Compared with untreated Salix psammophila,there are an increase of 48% in cellulose digestibility,an increase of 100% in hemicellulose digestibility,an increase of 75% in ethanol production when Salix psammophila was pretreated under those conditions.XRD analysis showed that the crystallinity index of pretreated corn straw and Salix psammophila were increased 29% and 45% respectively.FT-IR analysis showed that the absorption peak of corn straw and Salix psammophila was weakened significantly.SEM showed that the structure of pretreated corn straw and Salix psammophila changed loose and curly.Finally,the effect of different kinds of ionic liquids pretreatment on ethanol production from corn straw and Salix psammophila was studied.The results showed that the pretreatment of [Emim][DEP] was better than [Emim]Ac,[Bmim]Cl and[Bhy][HSO4].Further research found that the best pretreatment condition of corn straw and Salix psammophila were 50% [Emim][DEP] mixed with 50%water,treatment time24 h,and temperature 100 ?.Compared with untreated corn straw,there are an increase of 44% in cellulose digestibility,an increase of 45% in hemicellulose digestibility,an increase of 75% in ethanol production when corn straw was pretreated under those conditions.Compared with untreated Salix psammophila,there are an increase of 38% in cellulose digestibility,an increase of 48% in hemicellulose digestibility,an increase of53% in ethanol production when Salix psammophila was pretreated under those conditions.XRD analysis showed that because of the dissolution of cellulose in ionicliquid,the crystallinity of lignocellulose was decreased,when Salix psammophila was pretreated by those conditions.The crystallinity index of pretreated corn straw and Salix psammophila were reduced 43% and 39% respectively.FT-IR analysis showed that the absorption peak of corn straw and Salix psammophila did not change significantly.After the treatment,new chemical groups and functional groups were not produced.SEM showed that the structure of pretreated corn straw and Salix psammophila became uneven and appeared fragment.In summary,sodium hydroxide pretreatment was than ionic liquid pretreatment and high temperature and normal pressure.The cost of Sodium hydroxide pretreatment method is low,but it is easy to corrode the equipment and pollute the environment.Ionic liquid pretreatment method can effectively avoid environmental pollution and high equipment requirements,but the cost is high.In this study,considers ionic liquids was considered as the best pretreatment method. |
PDF Full Text Request