Study On Pretreatment And High-solids Enzymatic Hydrolysis Of Cellulosic Materials

Cellulosic materials have great potential to produce chemicals or other materials by physical,chemical or biological methods.Development of cellulosic materials can contribute to environmental protection and high-efficient utilization of nature resources.Sugar,as a middle product,can be obtained from enzymatic hydrolysis of cellulosic materials.Enzymatic hydrolysis of biomass is inhibited by lignin and usually performed at low solids loading.It is difficult to meet with the industry.This study mainly focuses on ways to improve glucose concentration and glucose yield when at high-solids loadings.Alkaline peroxide pretreatment,steam explosion pretreatment,and bisulfite pretreatment were investigated to destroy complex structure of biomass.Ultrasonic-assisted hydrolysis and surfactant-assisted hydrolysis were also discussed for improvement of glucose yield.The main conclusion was shown as below:Ultrasonic-assisted enzymatic hydrolysis of furfural residues(FRs)after alkaline peroxide(AP)pretreatment was first studied.The results showed that ultrasonic-assisted enzymatic hydrolysis after 2 h of saccharification was the optimized condition and glucose yield in this procedure was enhanced from 55.01%to 69.05%in comparison with traditional procedure.Ultrasonic treatment before enzyme addition during enzymatic hydrolysis can improve glucose yield by 33.34%.The mechanical effect of ultrasonic exerted an influence on enzyme adsorption and desorption and was beneficial to enzyme combining with the substrate.Surfactants are popular additives for the prevention of the inhibitory effect of lignin on cellulolytic enzymes.The effect of saponin on the high-solids-loading enzymatic hydrolysis of FRs with a lignin content of 45%was investigated.The addition of 4 g/L Cleditsia saponin(GS)increased the cellulose conversion by up to 52.63%in high-solids-loading enzymatic hydrolysis.Due to the addition of' GS,a maximum cellulose conversion of 74.88%was achieved after FRs had hydrolyzed for 120 h at a solid loading of 20%(w/w)with 30 filter paper unit(FPU)/g-cellulose.The decrease in cellulose conversion was found to exhibit a linear correlation with an increase in the solids loadings from 20.0 to 27.5%(w/w).The carbonyl groups of lignin facilitated the binding of GS to the surface of lignin,which resulted in a decrease in the adsorption of between the enzyme and lignin.Interestingly,GS could maintain enzymatic activity in the supernatants.A combination of steam explosion(SE)and AP pretreatment can improve cellulose conversion of bamboo samples.SE at 224? for 4 min was applied to bamboo,and then the pretreated bamboo was further delignified by alkaline peroxide.This led to remarkable hemicellulose solubilization(63.2%)and lignin solubilization(93.1%).A maximum glucose yield of 90.5%was achieved with a combined steam explosion and alkaline peroxide pretreatment.GS can enhance high-solids enzymatic hydrolysis of steam treated bamboo materials,but there was little improvement of high-solids enzymatic hydrolysis when bamboo was first pretreated with steam and then pretreated with alkaline peroxide.GS has different influence on cellulose conversion of FRs with different lignin content.High lignin content in substrate contributed to high improvement of hydrolysis by the addition of GS.The main reason behind the decreased glucose yield at high-solids loadings was product inhibition.Moreover,the lignin content plays an important role in the enhancement of GS-assisted high-solids enzymatic hydrolysis of AP-treated FRs.Non-detoxified FRs(pH 2-3)had great potential to lower the cost of bioconversion.This study reported four schemes to pretreat acidic FRs with sodium bisulfite for production of fermentable sugar.The optimal process was that unwashed FRs were first pretreated with bisulfite,and the whole slurry was then directly used for enzymatic hydrolysis.A maximum glucose yield of 99.4%was achieved from substrates pretreated with 0.1 g NaHSO3/g dry substrate(DS),at a relatively low temperature of 100?for 3 h.Compared with raw material,enzymatic hydrolysis at a high-solid of 16.5%(w/w)specifically showed more excellent performance with bisulfite treated FRs.Direct bisulfite pretreatment improved the accessibility of substrates and the total glucose recovery(?100%).Lignosulfonate in the non-detoxified slurry decreased the non-productive adsorption of cellulase on the substrate,thus improving enzymatic hydrolysis.Direct pretreatment followed by enzymatic hydrolysis is an environmentally-friendly and economically-feasible method to produce glucose and high-purity lignin,which could be further converted into high-value products.This has great contribution for the further study on corncob biorefinery.