Study On The Modification Of Lignin And Its Adsorption Behavior For Phenol And Methylene Blue

Lignin is an important biological resource,which has been extended to a wide range of applications in materials,energy,and medicine.However,there are still problems such as low conversion and poor economic benefits.In order to improve the application value of lignin,based on the modification of alkaline lignin and its adsorption of organic matter as the research background,the effects of amination modification of alkaline lignin on the structure of lignin-based activated carbon and the adsorption capacity of phenol are studied respectively,Demethylation modification,Sulfur methylation modification.The structure and thermal stability of alkaline lignin before and after modification were analyzed by FTIR,BET,TG and other instruments,so as to carry out the above modification and adsorption mechanism.Discussed.Mannich reaction was used to aminate lignin,and diethylenetriamine(DETA)was used as aminating reagent to investigate the effects of the ratio of aminating reagent,reaction temperature,reaction time,and solution pH on the nitrogen content of lignin.The results show that when the reaction temperature is 60℃,the reaction time is 4h,the pH is 11,the mass ratio of DETA to alkali lignin is 1.5,and the mass ratio of formaldehyde to DETA is 3,the nitrogen content of amino lignin is the highest It can reach 6.16%.Activators and precursors are important factors affecting the adsorption performance of activated carbon.This article examines the effects of potassium carbonate and urea as activators,and alkali lignin and amino lignin as precursors on the adsorption performance of phenol.The results show that potassium carbonate and urea are used as precursors.When urea is used as a co-activator,the adsorption capacity of amino-lignin-based activated carbon for phenol can reach 339.47 mg/g(when C0 is 500 mg/L),which is an increase of 17.37%compared with alkali-lignin-based activated carbon.Compared with lignin activated carbon,the activated carbon prepared by amination modified lignin has increased surface area,micropore volume,and nitrogen content.In addition,the preparation process of activated carbon and the adsorption behavior of phenol were studied,and its mechanism was discussed,and the influence of regeneration on the adsorption performance of phenol was investigated.In order to increase the content of phenolic hydroxyl and carboxyl groups,lignin was modified by demethoxylization and carboxymethylation.The sodium sulfite method was used to demethylate the alkali lignin,and the results showed that the modified lignin increased 25.06%of the phenolic hydroxyl content of the original alkali lignin.Demethylated lignin(DL)was modified by carboxymethylation with sodium chloroacetate,and the carboxyl content of the modified lignin was twice that of the original alkali lignin.The methylene blue adsorption experiment was carried out with the modified lignin,and the results showed that increasing the phenolic hydroxyl and carboxyl content of lignin can increase the adsorption capacity of methylene blue.The lignin obtained by the two-step modification of demethylation and carboxymethylation is used as the adsorbent(Phenolic hydroxyl group and carboxyl group were 1.06 and 2.33 times of alkali lignin,respectively).When the initial concentration of methylene blue is 1000 mg/L,the amount of adsorbent is 1 g/L,and the pH is 7,the adsorption capacity of methylene blue can reach 826.76 mg/g.The modified lignin contains more oxygen-containing functional groups and higher charge density,which is prone to hydrogen bond and electrostatic interaction with methylene blue,so as to achieve the purpose of removing methylene blue.The adsorption of methylene blue by the demethylated-carboxymethylated modified lignin(DL-CL)conforms to the Langmuir adsorption model,which is mainly monolayer adsorption.The theoretical maximum adsorption capacity obtained by simulation is 1028.45 mg/g.