| As energy demand is increasingly tense, bio-ethanol, as a clean and environmentally- friendly substitute for petroleum will become a trend in energy development. However, due to its high cost of the production process, it has been difficult to be polularized. Enzymatic hydrolysis lignin(EHL) is a by-product generated from bio-ethanol industry process. It is also an important raw material to acquire aromatic hydrocarbon compounds from the natural resources. The modification of EHL is of great positive significance to reduce the cost of bio-ethanol industry and extend the biomass energy industry chain. However, due to the incompleteness of biomass hydrolysis process, enzymatic hydrolysis lignin is often mixed with cellulose, hemicellulose, and other carbohydrates, which restrict its reactivity. Therefore it is necessary to have it pretreated to improve its reactivity before its modification. Among the chemical modification methods, sulfonation is the most convenient method to improve the water solubility and surface activity of EHL.As a new type of clean fuel, the coal water slurry(CWS) is one of the key development direction of China’s coal chemical industry. CWS pulping require higher concentrations, while the dispersant is one of the core technology of coal water slurry quality, therefore, there is an urgent need to acquire CWS dispersant with lower cost, higher performance and good adaptability.In the present study, enzymatic hydrolysis lignin was chosen as raw material. Enzymatic hydrolysis lignin was treated with dilute acid(DA) pretreatment and Na OH / Urea(NU) pretreatment to remove carbohydrate impurities and improve EHL’s reactivity. Then the pretreated EHL was sulfomethylated with sulphite to obtain sulfomethylated enzymatic hydrolysis lignin(S-EHL) to investigate the influence of dilute acid and Na OH / Urea pretreatment on the sulfomethylated reactivity of EHL. With the use of Elemental Analyzer, Gel Permeation Chromatography, Ultraviolet Spectrograph, Infrared Spectrometer, Automatic Potentiometric Titrator and Rheometer, this research preliminarily revealed the effect of cellulose-removal on EHL reactivity by detecting the cellulose content, the molecular weight, the content of functional groups, the solution viscosity and structure characteristics of EHL and S-EHL. Furthermore the synthesis of graft sulfonated enzymatic hydrolysis lignin(GSEHL) based CWS efficient dispersant was studied. The effect of sulphite dosage, reaction concentration, the amount of EHL and epichlorohydrin crosslinking on the dispersion performance of GSEHL based CWS dispersants were investigated.Dilute acid pretreatment was used to activate the reactivity of EHL. The results showed that the dilute acid pretreatment(pretreatment time was 2 h, the temperature was 85 ℃, pretreatment solution p H = 2, the solid-liquid ratio was 1:10) could significantly lead to the drop cellulose content of EHL. Cellulose removal rate reached 22.15% and the purity of lignin reached 80.24%. IR, UV and functional group analysis showed no damage to the main structure of enzymatic hydrolysis lignin after the dilute acid pretreatment, but caused the increase of phenolic hydroxyl content and carboxyl content while phenolic hydroxyl content increased from 1.12 mmol/g to 1.40 mmol/g and carboxyl content increased from 1.86 mmol/g up to 2.08 mmol/g. After pretreatment, the amount of sulfonic group of S-EHL increased from 1.13 mmol/g to 1.40 mmol/g while molecular weight of S-EHL did not change significantly. Rheometer and transmission electron microscopy(TEM) results showed that the surface morphology of enzymatic hydrolysis lignin in aqueous solution became loose after pretreatment and aggregation degree of EHL in aqueous solution decreased.Na OH/Urea pretreatment was used to activate the reactivity of EHL. The results showed that Na OH / urea pretreatment significantly caused the decrease of cellulose content of EHL. When solution ratio of pretreatment was 8% Na OH + 12% Urea and the temperature was 30 ℃, the pretreatment performance was most obvious. The removal rate of cellulose reached 33.45%, purity of lignin reached 84.03%. IR, UV and functional group analysis showed that Na OH / Urea pretreatment did not break the main structure of lignin, but led to the increase of carboxyl content(from 1.98 mmol/g to 2.26 mmol/g) and the increase of phenolic hydroxyl content(from 1.12 mmol/g to 1.34 mmol/g). Under the optimal pretreated conditions(8% Na OH + 12% Urea at room temperature for 24 h), the amount of sulfonic group of S-EHL increased from 1.13 mmol/g to 1.33 mmol/g. Rheometer and transmission electron microscopy(TEM) results show that Na OH / Urea pretreatment resulted in the destruction of hydrogen bonds between lignin and cellulose, the surface morphology of EHL became loose, the solution viscosity decreases and the degree of aggregation decreased.The enzymatic hydrolysis lignin pretreated with dilute acid method was selected as raw materials to prepare the graft sulfonation enzymatic hydrolysis lignin(GSEHL) based CWS dispersants. The effect of sulphite dosage, reaction concentration and the amount of EHL on the dispersion performance of GSEHL-based CWS dispersants were investigated. The results showed that the dispersant with medium sulfonation degree and high molecular weight(sulfonation degree was 2.20 mmol/g, the molecular weight was 26821 Da) showed the best dispersion performance in the coal water slurry. When the dispersant content was 1.0% and the CWS concentration was 60%, the apparent viscosity of CWS was 808 m Pa?s. Crosslinking reaction could significantly increase the molecular weight of the graft sulfonated product with medium sulfonation degree(sulfonation degree was 2.26 mmol/g) and enhance its dispersion performance. After crosslinking reaction with epichlorohydrin, molecular weight of graft sulfonated product with medium sulfonation degree increased from 26821 to 41718 Da, the CWS apparent viscosity with this product decreased to 683.2 m Pa?s. |
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