The Research On Fractionation,Purification,Structural Characterization And Chemical Modification Of Lignin

Lignin as the largest amount of renewable aromatic compounds on earth is a potential substitute for petroleum-base energy and chemicals.The property of lignin varies from its material and approach.There is much obstacle to utilize the lignin due to its complex structure.Thus it is of great significance to utilize the lignin with different properties respectively.Corncob residue as by-products of xylose or furfural mill is mainly composed of cellulose and lignin,however most of which were burned for electricity generation.Sodium sulfite pretreatment on corncob residue,not only can get high enzymatic hydrolysis efficiency of cellulose,but also there was lignosulfonate in black liquor after pretreatment.If the lignosulfonate was did fractionation,purification and sulfonation modification,it will be reused for surfactang of concrete water reducer and oilfield coagulant,et al.Lignin is the main component of black liquor that derived from alkaline pulping with wheat straw.It is hard to use lignin with high value due to its complex structure,lower reactivity and high content of ash.In this paper,the corncob residue and the wheat straw soda lignin were fractionated,purified and modified.The effect of xxx on xxx and characterization of different lignin were investigated,which is beneficial to industrial lignin.In this paper,the effects of sodium sulfite pretreatment on corncob residues fractionation,chemical modification and cellulose saccharification by enzymatic hydrolysis were researched firstly.It was showed that sodium sulfite pretreatment can not only obtain lignosulfonate products by efficiently separating the corncob residues,but also can improve the efficiency of cellulose enzymatic hydrolysis.The optimal pretreatment conditions were that: dosage of sodium sulfite was 12%,pH= 7,reaction temperature was 160 oC and the holding time was 20 min.Under this pretreatment condition,the rate of lignin removal was 77.45%,the cellulose content was 85.17% and the sulfonation degree of sodium lignosulfonate was 0.677mmol/g.The corncob residue after sulfite pretreatment was hydrolyzed by cellulase(5 FPU/g)for 48 h.It was showed that the efficiency of enzymatic hydrolysis and the yield of glucose were 92.76% and 84.77% respectively,while they were 72.02% and 70.58% respectively when hydrolyzed by cellulase(20 FPU/g)using corncob residue directly.The whole components of corncob were taken fully use through this technology.The soda lignin of wheat straw has high ash content and complex constituent,which brings difficulty in direct utilization.Fractionation,purification and structural characterization of soda lignin were studied in this paper.Firstly,soda lignin was dissolved in 0.01mol/L HCl solution with adjusting the pH value to 2-3,then it was centrifuged and washed with water to pH value of 5-6,amount of ash can be removed by this way and ash-free soda lignin can be obtained.The ash content of acid precipitated lignin declined from 45.33% to 12.98%.Meanwhile,the acid-insoluble lignin of ash-free soda lignin from 22.79% increased to 78.79%,compared with soda lignin it increased by 56.00%.Secondly,lignin was fractionated by different organic solvents with different molar ratio.The optimized condition for lignin fractionation was that the molar ratio of dioxane and methonal was 1:1 and the ratio of liquid to solid was 6:1.Under this condition the dissolving rate of acid precipitated lignin can reach 79.00%.The ash content of soluble lignin was less than 1%.Elemental analysis,FT-IR,1H NMR and 13 C NMR HSQC were conducted for characterization of soda lignin,acid precipitated lignin and purified lignin.Finally the phenolation modification of purified lignin was conducted.It was showed the optimized modification conditions were that the reaction temperature was 90 oC,phenol:lignin =5:1(w/w),dosage of 98% H2SO4 was 5%(based on total weight of phenol and lignin)and reaction time is 1.5 h.Under the condition,the content of phenolic hydroxyl group in phenolated lignin reached 12.48% while it was only 2.69% before phenolation.