玉米秸秆纤维素乙醇残渣木素碱溶/酸析分级与表征

Fractionation and characterization of lignin extracted by alkaline extraction/acid precipitation of residual corn stalk in ethanol production

采用常温、大液比氢氧化钠抽提玉米秸秆纤维素乙醇炼制残渣中木素,以盐酸为沉淀剂,通过逐级酸析分离木素的方法,在pH(10、8、6、4、2)酸析条件下进行木素分级制备。采用用离子色谱、凝胶色谱、红外光谱和热重分析手段对木素样品进行分析表征。结果表明,碱溶/酸析沉淀制备木素中含有碳水化合物,随着酸析pH的降低,木素分离级分中的碳水化合物含量增加,木素纯度降低,木素的平均分子量随酸析pH的降低呈现逐渐降低的趋势,分散系数在酸析pH为6时的达到最低值1.67。在低pH下分级沉淀制备的木素热稳定性低于高pH时分级制备的木素。红外光谱显示,木素各级分结构的官能团基本相同,含有紫丁香基、愈疮木基和对羟基苯基3种结构单元。

Lignin was extracted from corn stalk residues of cellulosic ethanol refining by large liquid ratio sodium hydroxide at room temperature,using hydrochloric acid as precipitation agent.The lignin precipitation was fractionated sequentially by acidification at different pH（10,8,6,4and 2）.The lignin samples were analyzed and characterized by ion chromatography,GPC,FT-IR,TG and DSC.The results showed that lignin fractionation by alkali-soluble/acid precipitation contained carbohydrate,and the carbohydrates content increased but the purity of lignin decreased with the decrease of pH.The average molecular weight of lignin decreased gradually with pH decrease.The polydispersity indices in acid precipitation reached to the lowest that was 1.67 at pH 6.The lignin prepared by fractional precipitation has lower thermal stability at lower pH than that of higher pH.FT-IR spectrum result showed that the functional groups of lignin fractions structure are similar,which contain three kinds of structural units such as syringyl,guaiacyl and p-hydroxy phenyl.