Sulfonation Reactivity Enhancement Of Enzymatic Hydrolysis Lignin Via NaOH/Urea And Formic Acid Pretreatment

Developing bioethanol industry will effectively relieve the serious energy crisis,and produce a large amount of enzymatic hydrolysis lignin(EHL),the most abundant by-product in the bioethanol industrial.The purification and modification of EHL is of great significance to improve the comprehensive benefit of the value chain and reduce the environmental pollution came with the bio-residue.However,due to the mild condition of the enzymatic hydrolysis process,EHL is often mixed with cellulose,hemicellulose and other carbohydrates,which restricts its reactivity to a great extent.Sulfonation is the most convenient method to improve the surface performance and additional value of lignin.Therefore,the pretreatment of EHL to enhance its reactivity is the key to the utilization and application of EHL.In this study,EHL was treated with NaOH / Urea(NU)pretreatment and formic acid(FA)pretreatment to improve its purity,reduce the aggregation so that enhance the reactivity.Sulfomethylated enzymatic hydrolysis lignin(S-EHL)was introduced to investigate the reactivity by its sulfonation degree and efficiency and was applied as the dispersant of the graphite suspension.In order to reveal the enhancement mechanism,the molecular weight,the influence of pretreatment on the structure features and aggregation behavior of EHL were studied.NaOH / Urea(NU)pretreatment in low temperature can enhance the sulfonated reactivity of EHL.When the pretreatment tempreture was-10?,the sulfonation degree and efficiency of S-EHL reached 1.82mmol/g and 85.29%,the phenolic and carboxyl group content increased 19.83% and 8.72% respectively,the methoxy group content decreased 21.01%,molecular weight was lower.NU pretreatment can lead to the higher hydroxyl benzene propane unit(H-unit)content.What's more,the NU pretreatment caused the molecular expansion,elimination of inter and intra aggregation of EHL.Formic acid(FA)pretreatment can enhance the sulfonated reactivity of EHL.When the pretreatment tempreture was 70?,formic concentration was 15%,the sulfonation degree and efficiency of S-EHL reached 1.63mmol/g and 59.86%,the phenolic and carboxyl group content increased51.64% and 25.39% respectively,the methoxy group content decreased 24.06%.The molecular weight dropped remarkblely,more importantly,the G-unit and H-unit in the EHL molecular was increased.Meanwhile,FA pretreatment reduced the association of the EHL aggregates and led to a softer and looser adsorption layer of EHL.Both NU pretreatment and FA pretreatment can enhance the reactivity of EHL due to the increase of reactivity site and the descrease of aggregation which reduced the steric hindrance and improved thse mass transfer rate.NU pretreatment placed emphasis on the disassociation of the hydrogen bond so that the homogeneity improved while the FA pretreatment focused on the degradation of EHL which created more reactivity site.As the result,the sulfonated EHL by NU pretreatment was more homogeneous with much higher sulfonation efficiency while those by FA pretreatment had much higher solubility molecular but lower sulfnation efficiency.