Graft Modification Of Alkali Lignin As An Adsorbent And Its Applied Basic

Lignin is an important constituent of biomass and, degradable aromaticpolymer. It is exceeded in natural abundance only by cellulose. Alkali lignin is abyproduct in large quantities in the process of pulp and biofuel production, whichhas been labeled “environmental pollutant”. In order to effectively utilize alkalilignin, advanced adsorption materials were prepared through incorporating somefunctional groups by means of simple chemical modification. The modified alkalilignin was used to treat trinitrotoluene (TNT) or aniline wastewater. The resultswere concluded as follows:(1) Chlorinated lignin was prepared using anhydrous aluminum chloride as acatalyst via Friedele-Crafts alkylation reaction with1,2-dichloroethane. Theinfluences of the reaction conditions were investigated by single factorexperiments, and the optimum reaction time and reaction temperature were6hand60°C, respectively. Aminated lignin (AmL) containing ethylenediaminefunctional groups were prepared by Nucleophilic substitution of aminationreaction on chlorinated lignin with ethylenediamine. The influences of thesubstitution reaction conditions were also researched by single factorexperiments, and the optimum reaction time and reaction temperature were8hand80°C, respectively. The structure and morphology of chlorinated lignin andAmL were characterized by several modern testing techniques.(2) A comprehensive study on the adsorption of TNT by AmL wasconducted regarding the effects of various experimental parameters. Theadsorption equilibrium was achieved in24hours and the kinetic data were welldescribed by pseudo-second-order model. It was found that the equilibrium datawas better represented by the Freundlich isotherm model. The saturatedadsorption capacities could reach56.7mg/g at pH7.0. The positive values of ΔHand negative value of ΔG indicated that adsorption of TNT onto aminated ligninis an endothermic and spontaneous process. Finally, excellent reusability of thematerial was observed after8desorption-adsorption cycles.(3) A fixed bed column of AmL was used for the adsorption of TNT from aqueous solution. It was found that higher bed heights, higher initialconcentration and lower flow rate would enhance the adsorption efficiency andadsorption quantity for TNT on the AmL column. The results were best describedby the BDST model, and also were fitted better to the Thomas and Yoon–Nelsonmodels. The breakthrough time of adsorption column was calculated andforecasted by BDST mode, and a good agreement was found between modelpredictions and experimental data.(4) The modified lignin adsorbent for aniline was synthesized by freeradical graft copolymerization of acrylic acid (AA) onto the backbone of alkalilignin molecule. The effect of initiation system, medium, reaction time,temperature, and concentration of evocator and monomer on graft effect wereinvestigated. Such a condition was optimized, as initiation systems of ferrousammonium sulfate and hydrogen peroxide, methanol of medium, acrylic acid ofmonomer, reaction time and reaction temperature were8h and70°C, respectively.The surface structure and thermal properties were analyzed by IR, SEM, XPS andTG.(5) Lignin-graft-acrylic acid (L-g-AA) for aniline removal was investigatedthrough batch experiments. The results showed that L-g-AA possessed strongadsorption ability for aniline on account of hydrogen bond and electrostaticinteraction. The equilibrium adsorption data were well represented by theFreundlich isotherm model and the saturated adsorption capacity could reach amaximum of79.1mg/g at15°C. The adsorption process was found to followpseudo-second-order kinetics. The activation energy (Ea) was found to be8.09kJ/mol. The negative value of ΔH and positive value of ΔG shownexothermic and non-spontaneous nature of adsorption, respectively. It was alsoobserved that L-g-AA possessed excellent reusability for aniline removal after8adsorption-desorption cycles in0.1mol/L hydrochloric acid which acted as adesorption medium.