Isolation,Modification Of Lignin In Enzymatic Hydrolysis Residue Of Corn Stalk And Its Adsorption Properties Of Cu²⁺

The corn stalk enzymatic hydrolysis residue is a waste produced in the process of production of corn stalk cellulose ethanol.The main component of enzymatic hydrolysis residue is lignin.In this paper,the lignin in the enzymatic hydrolysis residue was separated and purified by alkali,and modified by two-stepe of epoxidation and amination to synthesis diethylenetriamine-lignin(DETA-lignin).The heavy metal Cu2+ adsorption performance of DETA-lignin was anaylyzed.It provided the basic theory for the comprehensive utilization of enzymatic hydrolysis residue.By the single factor experiment and the response surface experiment,the optimum extraction conditions were as follows:concentration NaOH 39.90g/L,liquid-solid 38.75:1(mL:g),61.33°C,2h.The actual extraction rate of enzymatic hydrolysis lignin was 61.84%.The content of lignin was 88.2%.Enzymatic hydrolysis lignin has a large number of syringl and phenolic hydroxyl groups.The number of the guaiacyl base of enzymatic hydrolysis lignin is more than that of enzymatic hydrolysis residue.The enzymatic hydrolysis lignin of corn stalks is GHS type lignin.The relationship between the content of lignin basic structural units was as follows: guaiacyl > p-hydroxylphengl >syringl.The enzymatic hydrolysis lignin was modified by two steps that contain epoxidation and amination modification to synthesis diethylenetriamine-lignin(DETA-lignin).By single factor experiment,the synthesis conditions of DETA-lignin that was synthesized by epoxidized lignin were as follows: epoxidized lignin 1g,16.7% NaOH solution 30 m L,diethylenetriamine 30 mL,50°C and 4.0h.The nitrogen content of DETA-lignin was 3.94%,which increased by 2.82 times than that of the enzymatic hydrolysis lignin.The peak of methyl,methylene and methine at 2937cm-1 was significantly decreased after modification.The C-N swing vibration at 1124cm-1 and the-NH2 swing vibration at 1593cm-1 were significantly enhanced.The peak of-NH2 and-NH-stretching vibration at 3400cm-1 was significantly widened.Under the conditions of adsorption,DETA-lignin 100 mg,pH=7,40°C and 240 min,The adsorption capacity of Cu2+ can reach 42.46mg/g,which is 2.08 times higher than that of the enzymolysis residue.At 20°C,30°C and 40°C,the adsorption isotherm of DETA-lignin on Cu2+ show that the Cu2+ adsorption isotherm of DETA-lignin is more consistent with Langmuir model.At 30°C,the Cu2+ adsorption process of DETA-lignin was more consistent with the second order reaction rate linear kinetic equation,and the adsorption rate was controlled by chemical adsorption.By X-ray photoelectron spectroscopy(XPS)analysis,there are solitary electrons of N and O atoms in DETA-lignin,which can be combined with Cu2+ by electron pair share.Ion exchange and coordination increased the Cu2+ adsorption capacity.