Furfural Production From Corn Stover Employing Carbonaceous Solid Acid

Facing the detrimental environmental pollution caused by the abuse of fossil fuels,comprehensively utilizing of lignocellulosic biomass is regarded as one of the most effective method to achieve the sustainable development of both economy and society.Furfural is a versatile platform chemical,which has the potential of being transformed into bio-based polymer,pharmaceutical and liquid fuels.Thus,effectively converting lignocellulosic biomass into furfural is a key step to promote the commercial utilization of biomass.Currently,furfural production mainly relies on the homogeneous acid hydrolysis of corn stover,which has a long history and good reliability,while the process is limited by the high energy consumption and severe equipment corrosion as well as environmental issues related to liquid pollutants and solid residues.As a result,this work aims to develop novel methods employing heterogeneous acid catalytic systems to convert corn stover into furfural efficiently and environmental friendly.Firstly,a novel carbonaceous solid acid catalyst(S-RFC)was synthesized using sulfanilic acid and isopentyl nitrite based on in-situ diazo-reaction,which was characterized by N2 adsorption-desorption(BET),Elemental Analysis(EA),FT-IR,XPS,SEM,TEM.The results indicate that S-RFC possesses well-developed mesoporous structure and good acidity.Then,the performance of S-RFC was tested in xylose dehydration,where the effects of reaction temperature,reaction time,substrate concentration,catalyst dosage and variety on catalyst activity,selectivity and hydrothermal stability were investigated.The highest furfural yield of 80%was obtained at 170? for 15 min.No significant furfural yield loss was discovered in four consecutive recycling experiments.Besides,68.6%furfural yield was achieved from corn stover at 200?for 100 min.These results suggest that S-RFC was highly active and selective for furfural production in xylose dehydration,while its acidity was not strong enough to hydrolyze stable hemicellulose and cellulose in corn stover.Thus,we prepare a highly porous carbon(C-CaC-X,X=600,700,800)by calcining calcium citrate under N2 atmosphere in horizontal furnance,followed by acid wash,which was sulfonated by the in-situ diazo-reaction with sulfanilic acid and isopentyl nitrite in water to obtain the novel carbonaceous solid acid(SC-CaC-X,X=600,700,800).The solid acid was characterized using various equipments such as BET,FT-IR,XPS,SEM,TEM,ICP-AES etc,which suggested that SC-CaC-X(X=600,700,800)possess highly developed mesoporous structure and much stronger acid density.Comprehensively considering structure and acidity,SC-CaC-700 was selected as the optimal catalyst,whose specific surface area,pore volume,average pore diameter and acidity was 921 m2/g,2.57 cm3/g,9.59 nm and 2.36 mmol/g,respectively.Ultimately,a method was proposed to make a sufficient utilization of cellulose and hemicellulose in corn stover employing SC-CaC-700 as acid catalyst in GVL,in which the effects of reaction temperature,reaction time,corn stover concentration,catalyst dosage and solvents were studied.Under optimized conditions(2000?,100 min,150 mg corn stover,45 mg SC-CaC-700,7ml GVL),93%furfural yield can be gained.The yield loss reactions related to furfural were effectively suppressed because furfural yield remained stable even if prolonging time to 180 min.During the conversion of glucose,fructose and cellulose,furfural was the main product and only trace amount of 5-HMF was detected,indicating the cellulose in corn stover was co-converted into furfural in the direct hydrolysis of corn stover,which enhanced the furfural yield further.In addition,SC-CaC-700 can hydrolyse corn stover in pure water,affording a furfural yield of 51.5%.More importantly,SC-CaC-700 can be easily recycled by filtration from solid residues after reaction due to its extremely small particle size.The recyclability of the catalyst is considered good because furfural yield was still 61%after five recycling runs.The developed strategy of co-converting hemicellulose and cellulose into furfural offers a promising approach for the sufficient utilization of raw biomass.