Depolymerization And Upgrading Of Polysaccharides Of Corn Cob And Corn Straw

In recent years,renewable biomass has received great attention due to the environmental issues related to the use of fossil fuels.Lignocellulose is the main form of biomass in nature,which is widely distributed,rich in sources and low in price,but its utilization rate is low.The polysaccharide component of lignocellulose accounts for 55%to 70%of the total biomass.The depolymerization and upgrading of polysaccharide components is an important part of realizing efficient utilization of biomass.This work studies the depolymerization and upgrading of polysaccharide components of corn cob and corn straw.At present,corn cob is mainly used to convert its hemicellulose component into furfural.One-pot processing of corn cob is commonly used in industry to produce furfural with a low selectivity of about 30%.In this work,a step-by-step depolymerization strategy was used to study the upgrading of corn cob.In the first step,the corn cob is pretreated with high-pressure CO2-H2O to selectively hydrolyze the hemicellulose components.The main products are xylose and xylo-oligosaccharides.When the corn cob was treated at 185℃ for 1 h,the yields of xylo-oligosaccharides and xylose in the liquid were 57.4%and 19.4%,respectively.The hydrolyzate was converted to furfural using H2SO4(5 wt%)as catalyst at 140℃ for 1 h with the selectivity of 67.9%at the pentose conversion of 57.9%.In the second step,the cellulose component of the corn cob residue after the high-pressure CO2-H2O treatment was converted into glucose by the oxidation-hydrolysis strategy.17.2 g 100 g-1 yield of glucose(calculated based on the cellulose content in the sample,the yield was 29.5%)was given for the hydrolysis of the oxidized sample at 170℃ for 6 h.Oxidation-hydrolysis method was used to convert furfural residue(waste after furfural production).At the optimal conditions,the yield of glucose was 10.5 g 100 g-1 furfural residue(calculated based on the cellulose content,the yield was 26.2%).Corn straw is the biomass with the highest yield among agricultural straws.Therefore,it is of great significance to study the depolymerization and upgrading of polysaccharides of corn straw.The upgrading of corn straw is studied by two step depolymerization strategy.Corn straw was pretreated in the high-pressure CO2-H2O-CH3COOH(0.3 mol L-1)system at 185℃ for 1 h.The yields of xylo-oligosaccharide and xylose in the hydrolysate were 31.9%and 22.6%,respectively.The oxidation-hydrolysis strategy was used to depolymerize the cellulose component of corn straw residue.At the optimal oxidation conditions(200℃,12 h)and hydrolysis conditions(170℃,6 h),the yield of glucose was 17.5 g 100 g-1(calculated based on the cellulose content,the yield was 32.2%).