Synthesis Of Graft Copolymers From Enzymatic Hydrolysis Lignin And Amino Acid And Their Adsorbability

Lignin is a renewable natural polymer with a three-dimensional aromaticpolymer structure.The main elements of lignin are C﹑H﹑O. Enzymatic HydrolysisLignin (EHL) was isolated from the residue of enzymatically hydrolyzed cornstalks asa by-product of bioethanol industry. EHL kept the chemical activity of lignin since theenzymatic hydrolysis process of the cornstalks was carried out under relatively mildconditions, many functional groups such as phenolic hydroxyl, alcoholic hydroxyl andmethoxyl are well preserved in EHL. These properties suggest that EHL has potentialto be used to remove heavy metals from wastewaters. Thus, the increase of functionalgroups on EHL chains through graft copolymerization is of great importance.In this thesis, enzymatic hydrolysis lignin grafted glycine (Gly-g-EHL) andenzymatic hydrolysis lignin grafted cystine (Cys-g-EHL) copolymers were preparedvia Mannich reaction with enzymatic hydrolysis lignin glycine (cystine) andformaldehyde as raw materials. The effects of reaction temperature and time, thedosage of formaldehyde on yield and graft rate were investigated. The graftedcopolymers were characterizated by FTIR, TGA and elemental analysis, et al. Theresults showed that the reaction temperature, time and dosage of formaldehyde hadgreat influences on the yield and grafting ratio. High graft ratios of25.6%and13.8%for Gly-g-EHL and Cys-g-EHL, respectively, were achieved at the reactiontemperature of90°C for3h with the mass ratio of amino acids to EHL of1:1themolar ratio of formaidehyde to amino acids of2:1. The TGA results showed thatcarbon residue of the graft copolymers significantly increased. The nitrogen contentof resultant Gly-g-EHL had obvious increase confirmed by elemental analysis.Elemental analysis of Cys-g-EHL showed that the sulfur content of resultantCys-g-EHL was up to2.69%.Furthermore, the adsorption of Cu2+and Co2+from aqueous solution onGly-g-EHL and Cys-g-EHL were studied. Batch experiments were conducted over arange of pH, initial metal concentration，contact time, temperature and ionic strength.Moreover, the equilibrium isotherm data were analyzed using three isotherm models Langmuir,Freundlich and Temkim to determine the best fit equation for the sorptionsof Cu2+and Co2+on Gly-g-EHL and Cys-g-EHL.It was found that the Cu2+adsorption on Gly-g-EHL and Cys-g-EHL wasstrongly dependent on pH and adsorbent dosage but independent of ionic strength andother metal ions. When the initial concentration of Cu2+was of0.1mol/L, theadsorption time was240minute, the pH was6.0, the temperature was40°C, themaximum sorption capacity of Gly-g-EHL and Cys-g-EHL for Cu2+are44.22mg/gand59.34mg/g respectively.It was found that the Co2+adsorption on Gly-g-EHL and Cys-g-EHL wasstrongly dependent on pH and adsorbent dosage also.When the initial concentration ofCo2+was0.1mol/L, the adsorption time was300minute, the pH was6.0, thetemperature was40°C, the maximum sorption capacity of Gly-g-EHL andCys-g-EHL are70.25mg/g and91.09mg/g respectively.This study indicates that Gly-g-EHL, Cys-g-EHL and EHL have the potential tobecome effective and economical adsorbents for the removal of metal ions fromwastewaters.The applications of Gly-g-EHL and Cys-g-EHL to adsorption of metalions are of prime importance from the viewpoint of reproducing the working in natureas materials for human society.