Study On Degradation And Structure Of Lignin Sulfonate

Higher purity and homogeneity of lignin are required for its effective utilization.Here,taking sodium lignosulfonate(Na-LS)as an example,we report an optimized homogenous lignin preparation method.Na-LS exhibits reduced molecular weight and dispersity upon degradation and ultrafiltration.On this basis,we screened optimal homogenization conditions based on comprehensive analyses of the structural characterization of degraded Na-LS using multiple strategies,including gel permeation chromatography,gas chromatography,infrared absorption spectroscopy,differential scanning calorimetry analysis,and conductometric titration.The present paper consists of major three components:(1)In the process of Na-LS degradation by H₂O₂,the effects of reaction temperature,sodium hydroxide concentration,and H₂O₂ addition mode were investigated.Both weight-average molecular weight(Mw)and number-average molecular weight(Mn)decreased.The methoxy content and the yield of NBO decreased.After treatment with 2 mol/L Na OH and a four-step addition of H₂O₂ at 170?,the yield of NBO decreased,indicating that the lignin structure was virtually destroyed in this condition,and the methoxy decreased.FTIR results showed that some of the aromatic structures disappeared.The best condition for degradation is that 170?,2 mol/L Na OH solution,hydrogen peroxide is added in four steps.(2)Degrade sodium lignosulfonate at 170?in 1 mol/L with various alkalis and solvents and studied the effect of alkali and solvent on the degradation of Na-LS.In the alkaline solution of Li OH,Na OH,KOH,and Cs OH,as the radius of the counter cation increased,Mw's degradation rate and the removal rate of methoxy groups increase,and the yield of NBO decreased,indicating that the atomic radius is related to degradation rate.Methanol,ethanol,and dioxane in 1mol/L Na OH alkaline solution,the Mw degradation rate in the dioxane solvent system increased,the removal rate of the methoxy group increases,and the yield of NBO decreases,indicating that dioxane promoted the degradation of lignin.The addition of H₂O₂ has generated a higher weight-average molecular weight reduction rate.The higher methoxy removal rate and a lower yield rate of NBO.The addition of organic solvents reduces the molecular weight of degraded sodium lignosulfonate and promotes the degradation of sodium lignosulfonate.(3)Na-LS was purified by gel chromatography and degraded in 2 mol/L Na OH(aq)at 170?.Degraded Na-LS split into levels by ultrafiltration,and molecular weight distribution was researched.After purification,the content of methoxy,sulfonic acid,and phenylpropane unit was improved,and the DP was reduced from 6.3 to 3.8,indicating that sodium lignosulfonate was purified.After degradation and ultrafiltration,two components:10-30 k Da(DP 2.17)and 30 k Da(DP 1.37),have a higher NBO yield rate and lower ash content.The two fractions of Na-LS were evenly distributed,and the yield of 30 k Da up to 17%.