| Corn stover is a typical agricultural waste with a wide range of sources and a large annual output,the full utilization of corn stover is significant for the replacement of fossil energy and circular economy.However,corn stover has natural biological resistance,and it was usually difficult to directly transform and utilize,so it usually needs to be pretreated to destroy their dense structure.Corn stover presents a low utilization value,there are certain limitations in the commonly used corn straw pretreatment process,especially the single pretreatment technology,so it is of great significance to study the new technology of corn straw pretreatment and realize the high-value utilization of corn stover.In this work,corn stover was pretreated with recyclable p-toluenesulfonic acid(p-TsOH)and green strong oxidizing ozone(Z),and the two pretreatments were further combined.It provides theoretical guidance for efficient and clean conversion and utilization of corn stover.(1)Corn stover was pretreated with p-TsOH,and the effects of three pretreatment factors(p-TsOH concentration,hydrolysis temperature and hydrolysis time)on the dissociation of three components in corn stover were investigated.The effects of the three factors on lignin and hemicellulose removal were analyzed by SIMCA software,and the regression equations of lignin and hemicellulose contents were fitted.The kinetics of lignin and hemicellulose removal during pretreatment were further investigated by using a two-phase model with the introduction of delignification factor(CDF)and combined hydrolysis factor(CHF),and enzymatic hydrolysis with cellulase(C2730)and the enzymatic hydrolysis of pretreated corn stover were explored.It was found that the p-TsOH concentration and hydrolysis temperature had a significant effect on the removal of lignin and the hydrolysis temperature had a significant effect on the removal of hemicellulose during p-TsOH pretreatment of corn stover.Kinetic studies showed that when the CDF value was 0-1500 min·mol/L,it belonged to the fast delignification stage,and 1500-15000 min·mol/L belonged to the slow reaction stage.When the CHF value was less than 100 min·mol/L,the retention rate of hemicellulose was greater than 33%,and when CHF was greater than 300 min·mol/L,the retention rate of hemicellulose was less than23%.The dense structure of corn stover was destroyed after p-TsOH pretreatment.The surface lignin content of corn stover was reduced and enzyme accessibility to the pretreated corn stover was increased,resulting in higher enzymatic yield.After pretreatment with acid concentration of 50 wt%,hydrolysis temperature of 95 °C and hydrolysis time of 40 min,the glucan enzymatic yield of the residue was 72.92%.(2)The process and mechanism of combined p-TsOH and Z pretreatment(Z+p-TsOH)of corn stover were investigated.The effects of Z pretreatment and Z+p-TsOH pretreatment on the separation and enzymatic yield of corn stover components were investigated.It was found that the surface lignin could be removed effectively from corn stover by Z pretreatment,while the effects of Z pretreatment on hemicellulose and cellulose was weak.The lignin and hemicellulose could be removed from corn stover by Z+p-TsOH pretreatment,and the enzymatic yields of the pretreated corn stover were 82.09% after Z10P30 pretreatment processes and 83.21% after Z12P30 pretreatment processes.The enzymatic yield of Z+p-TsOH pretreatment was higher than Z pretreatment.Compared with p-TsOH pretreatment,Z+p-TsOH pretreatment could effectively reduce the amount of p-TsOH at an equivalent lignin removal rate and enzymatic yield.(3)To utilize the pretreatment hydrolysis filtrate,four lignins were isolated from the hydrolysis filtrate of the four pretreatment processes by dilute precipitation and low-speed centrifugation.The microscopic morphology,surface functional groups,elemental composition,hydrophobicity,molecular weight,chemical bond structure,and thermal stability of four lignins were systematically investigated.Besides,the lignin was further used as an additive for the lignin/polyhydroxy fatty acid ester(PHA)composite films.The UV shielding properties and mechanical properties of lignin/PHA composite film materials were investigated.It was found that the average particle size of the lignin powers isolated from the hydrolyzed filtrate of the four pretreatment processes were about 100 nm.The NMR results showed that all four lignins were of GSH type.The oxygen elements proportion and the oxygen-containing functional groups of Lignin-Z10P30 was relatively higher than other three kinds of lignin,and the hydrophilicity of Lignin-Z10P30 was higher.When the addition of lignin in the composite films were 4%,the UV resistance of the lignin/PHA composite films were excellent.The UV transmittance of the films were almost zero at 380 nm wavelength and the tensile strength were almost no decrease compared to pure PHA film. |
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