Study Of Sulfonation Reactivity Enhancement Of Lignin With Cellulase Hydrolysis

With the global increasing demands of energies, fossil fuel resources are increasingly exhausted. The development of alternatives to fossil fuel resources will become a necessary trend of energy development. Lignin is one of the most abundant natural renewable resources and its comprehensive utilization is of great positive significance to relieve the energy crisis and improve the environment. Alkali lignin coming from the pulp and paper industry and enzymatic hydrolysis lignin generating from bio-ethanol industry process have high-volume production annually. But due to its incompleteness of the extraction process, lignin is often mixed with cellulose, hemicellulose and other carbohydrates, which greatly restricts its reactivity and water solubility. However, among all the chemical modification methods, sulfonation is the most convenient method to improve the water solubility and surface activity of lignin. Therefore, it’s necessary to have industrial lignin pretreated and modificated with sulfonation for further applications.In the present study, enzymatic hydrolysis lignin(EHL), pine alkali lignin(PAL) and wheat straw alkali lignin(WAL) were chosen as raw material. EHL was treated with cellulase hydrolysis under different Ctec2 loading to remove cellulose impurities and improve EHL’s reactivity. Then the pretreated EHL was sulfomethylated with sulphite to obtain sulfomethylated enzymatic hydrolysis lignin(SEHL) to investigate the influence of cellulase hydrolysis pretreatment on the sulfomethylated reactivity of EHL and obtained optimum Ctec2 loading. Then PAL and WAL was treated with cellulase hydrolysis under optimum Ctec2 loading to improve their reactivity and further modificated with sulfonation to prepare sulfomethylated alkali lignin(SAL) to explore the effect of cellulase hydrolysis pretreatment on the sulfomethylated reactivity of alkali lignin(AL). With the use of Elemental Analyzer, Gel Permeation Chromatography, Automatic Potentiometric Titrator, Rheometer, AFM, Infrared Spectrometerand Ultraviolet Spectrograph, this research preliminarily revealed the effect of cellulose-removal on lignin reactivity by detecting the cellulose content, the molecular weight, the content of functional groups, the solution viscosity and structure characteristics of lignin and the molecular weight, sulfonation degree and adsorption property of sulfomethylated lignin. And furthermore investigated the application performance of sulfomethylated lignin used as graphite dispersant and polyaniline dopant.Cellulase hydrolysis pretreatment was used to enhance the reactivity of EHL. The results showed that cellulase hydrolysis pretreatment could significantly lead to the drop cellulose content of EHL and its optimum Ctec2 loading was 20 FPU·g-1. Then, the cellulose removal rate reached 28.86% and the content of lignin reached 87.86%. The pretreatment caused the increase of phenolic hydroxyl and carboxyl content and the decrease of the methoxy group. After pretreatment, the sulfonation efficiency increased from 38.53% to 92.03%, while the amount of sulfonic group of SEHL kept constant. Meanwhile molecular weight of SEHL increased slightly. The effects of concentration on aggregation behaviors of EHL in concentrated solutions were investigated by means of rheology. The results showed that the aggregation degree of EHL in aqueous solution decreased after the pretreatment. Besides, pretreatment can significantly improve the adsorption properties of SEHL. The application performance of SEHL used as graphite dispersant and polyaniline dopant were effectively improved. It can be comparable to CMC and SDBS which were industrial commonly used graphite dispersant and polyaniline dopant, respectively.Cellulase hydrolysis pretreatment was used to activate the reactivity of PAL and WAL. The results showed that cellulase hydrolysis pretreatment could significantly lead to the drop of cellulose content of alkali lignin. The cellulose removal rate of PAL and WAL reached 37.71% and 24.22%, respectively. Meanwhile the content of PAL increased from 64.73% to 71.04%, while the content of WAL increased from 69.91% to 75.49%. IR, UV and 1H-NMR analysis showed that pretreatment did not break the main structure of AL, but caused the decrease of the methoxy group and the increase of phenolic hydroxyl content and carboxyl content. Meanwhile molecular weight of AL increased slightly. Besides, the sulfonic group content of AL kept constant, while the sulfonation efficiency of SPAL increased from 70.08% to 85.57% and sulfonation efficiency of SWAL increased from 64.61% to 81.13%. Cellulase hydrolysis pretreatment could increase the surface charge density of SAL and its adsorbing capacity to hydrophobic surfaces obviously. The application performance of polyaniline composite prepared by doping with SAL was significantly improved. What’s more, conductivity of polyaniline composite prepared by doping with sulfomethylated WAL was the highest, which reached 8.2-fold of that of polyaniline composite prepared by doping with proton acid.This work not only could provide theoretical foundation for the pretreatment and application performance improvement of industrial lignin, but also expands the application of sulfomethylated lignin in conductive material field, which gives a new way for the high-value applications of industrial lignin.