The Depolymerization Of Organosolv Lignin:Effect Of Pretreatment Process

Lignin is a renewable biomass raw material.However,It is not fully utilized due to the difficulty in depolymerizing its stable macromolecular structure.The depolymerization of lignin requires C-O and C-C bond breaking.The most frequent type of bond in natural lignin is ?-O-4 aryl ether bond.In the conventional extraction process of organosolv lignin,a large amount of ?-O-4 aryl ether bonds undergo severe polycondensation after the breaking under the action of acid,which makes the depolymerization of lignin more difficult.This paper studied the effect of the addition of formaldehyde,formic acid and methanol compounds in the extraction process to stabilize the aryl ether bond measured by lignin and further inhibit the polycondensation of organosolv lignin.The condensation structure and thermochemical properties of the improved organosolv lignin were characterized with the GPC,FT-IR,HSQC-NMR,TGA and Py-GC / MS techniques.During the pretreatment,the stabilizer can inhibit the cleavage of the aryl ether bond in the lignin.Most of the ?-O-4 linkages still exist in formaldehyde-stabilized lignin,retaining the structural characteristics of natural lignin.Compared to formaldehyde-stabilized lignin,lignin extracted without the addition of stabilizer is more difficult to depolymerize when heated.The stabilizing effect of formaldehyde is that the yield of condensable volatiles during the rapid pyrolysis of the extracted lignin is increased by a factor of two with less coke formed.The improvement in pyrolysis performance can be attributed to the retention of the original aryl ether bond during delignification which inhibits the polycondensation of lignin.The biofuel,which is the liquid product of pyrolysis has the disadvantages of high oxygen content,low calorific value and strong acidity.HZSM-5 molecular sieve catalyst was further used to achieve deoxidation effect.For the catalytic pyrolysis under the action of HZSM-5 molecular sieve,the yield of condensable volatiles is higher than that of non-catalytic pyrolysis.The catalytic pyrolysis of H? molecular sieve has a strong deoxidation effect,but the yield of cold liquid products is low.For non-catalytic pyrolysis,the yield of lignin extracted by formaldehyde treatment is one-third of that without the catalyzation of the H? molecular sieve while the yield of lignin extracted after adding methanol and formic acid treatment is half of that.The effect of adding stabilizer on the hydrogenolysis performance of organic solvent lignin in the extraction process was further investigated.The addition of a small molecule stabilizer during the pretreatment process has a significant effect on the monomer yield of lignin hydrogenolysis.The yield of monomer after adding propionaldehyde can reach 35%,which is nearly three times as much as the yield of hydrogenolysis of lignin extracted without additives.This indicates that the addition of small molecule additives during pretreatment has a relatively large effect on the monomer yield of lignin hydrogenolysis.It is deduced from the selectivity of the monomer after hydrogenolysis that the addition of acetaldehyde and propionaldehyde stabilizes the ?,?-diol structure in guaiacol(G)while the addition of formic acid,methanol and formaldehyde stabilizes the ?,?-diol structure in phenol(H)and eugenol(S).