Study On The Degradation Of Bamboo Lignin From Enzymatic Hydrolysis-Mild Acidolysis By Peracetic Acid

With the acceleration of industrialization and urbanization,the problem of rapid consumption of nonrenewable resources and environmental pollution has become to be the biggest bottleneck which restrict the rapid development of mankind.So,how to make use of clean and renewable biomass resources to synthesize energy and chemical products has become one of the research focuses.As one of the important components of biomass,lignin has the advantages of cheap,abundance,biodegradability,renewable and so on.The studies on the efficient synthesis and degradation of lignin,not only help to control environmental pollution caused by the indiscriminate discharge of paper-making black liquid which is rich in lignin,but also do good to prepare clean energy and high economic value chemical products by using lignin as raw material.Finally,to achieve the goal to making full use of lignin resources.In this paper,Zhejiang natural bamboo was chosen as biomass raw materials.First the method of enzymatic hydrolysis-mild acidolysis was used to isolate lignin from the bamboo.The experimental scheme was optimized by single factor experiment.The lignin samples were characterized by FT-IR spectroscopy and ~1H-NMR analysis;For the purpose of avoiding the association of active hydroxyl groups in lignin molecules.acetic anhydride was used as esterification agent to acetylate lignin.the highest acetylation rate was obtained by optimizing the reaction conditions.The changes of lignin morphology before and after acetylation were observed by scanning electron microscopy(SEM).At last,peroxide acetic acid was chosen as degradation agent to degrade acetylated lignin.After the reaction,the degradation rate of lignin was measured by ultraviolet spectrophotometry,the effects of peracetic acid concentration and reaction temperature on the degradation rate were investigated.After the degradation products with the highest degradation rate got by single-factor experiment,the change of lignin before and after degradation was measure by Fourier transform infrared spectroscopy(FT-IR),~1H Nuclear Magnetic Resonance Spectra~1H-NMR,Gel Permeation Chromatography(GPC)?Research conclusions are as follows(1)The optimum reaction conditions of the method enzymatic hydrolysis-mild acidolysis were as follows: namely keeping 50 ? of reaction temperature,1:8 of the ratio of enzyme and substrate,0.025 g/mL of the substrate concentration,48 h of the reaction time in the process of enzymatic reaction,remaining pH as 0.82 in next step mild acidolysis;The lignin samples were characterized by FT-IR spectroscopy and ~1H-NMR analysis.The results showed that bamboo lignin contained typical characteristic peaks of syringyl and guaiacyl units,while the peaks of cellulose,hemicellulose and carbohydrates units were seldom seen.This paper proved that the biorefinery lignin isolated by our method was similar to the original bamboo.(2)Acetic anhydride was chosen as esterification agent to acetylate lignin.The optimum reaction conditions are as follows:reaction time of 90 ?,time of 4 h,At this time,the rate of acetylation was the highest(53.5 %),Scanning electron microscopy(SEM)analysis showed:after acetylation,the lignin structure was gradually changed from spherical to square,and the structural surfaces became rough.(3)Peracetic acid was chosen as degradation agent,and degrade the refined lignin in in homogeneous phase,when the reaction was completed,the degradation rate was measured by ultraviolet spectrophotometry.the optimal reaction conditions are as follow: peracetic acid concentration of 45 g/L,reaction time of 8 h,reaction temperature of 70 ?,at that time,the degradation ratio was the highest(54.7%).The collected deposit in the process of extracting degradation products was characterized by FT-IR,GPC and elemental analysis,the degradation products was characterized by ~1H-NMR and GPC.FT-IR showed : the degradation reaction mainly attracted ether bond,and partly destroyed benzene ring and hydroxy,structure,especially guaiacol.elemental analysis showed: dehydration and carbonization were happened after degradation reaction.~1H-NMR showed: the ether bond and C-C bond which connect lignin units were destroyed.GPC showed: Lignin macromolecule was effectively degraded,and the deposit is the kind of lignin which is incomplete degraded.GC-MC showed: there are many kinds of degradation products,the products which can be identified were p-hydroxy benzoicacid,vanillin,derivative of lilac base,phenol,benzoic acid and so on.