Study On The Isolation Of Lignin And The Effect Of Lignin Content On The Enzymatic Hydrolysis Of Furfural Residues

Efficient conversion of lignocellulosic biomass to fermentable sugars is essential for the realization of economic bioethanol, and also has enormous potential in meeting global food and energy demand via biological route. Currently, enzymatic hydrolysis has attracted increasing attention as an alternative to acid hydrolysis for converting lignocellulosic materials to sugars. Furfural residues are the by-products of furfural industry, which are mainly obtained from corn cobs by acid catalysis at high temperature. They represent the sources having the highest potential for low-cost, high-volume production.The enzymatic saccharification of pretreated furfural residues with different lignin content was studied to verify the effect of lignin removal in the hydrolysis process. The samples investigated here were treated with the sodium chlorite to remove the lignin. The results showed that the glucose yield was improved by increasing the lignin removal. A maximum glucose yield of 96.8% was obtained when the residue with a lignin removal of 51.4% was hydrolyzed for 108 h at an enzyme loading of 25 FPU/g cellulose. However, further lignin removal did not increase the hydrolysis.Sodium chlorite treatment is not environment-friendly and mild enough to be used in chemical industry, so alkaline peroxide pretreatment was studied as an alternate method. The results showed that delignification significantly enhanced the enzymatic hydrolysis yield from furfural residues. The maximum glucose yield of 92.2% was achieved when the pretreated sample with a lignin removal of 56.7% was hydrolyzed for 120 h at an enzyme loading of 25 FPU/g cellulose, which was consistent with the result of sodium chlorite treatment. In a word, furfural residues could improve the hydrolysis most when the lignin was removed by 50%.In addition, further study is in progress on utilizing the lignin isolated from the filtrate during the H2O2 pretreatment, realizing the efficient use of lignocellulosic materials. The physic-chemical properties and structural features of the isolated lignin fractions were characterized by UV, FT-IR, and 2D-'H-13C-NMR spectroscopies as well as GPC. The results are reported that isolated lignin was mainly composed of syringyl (S), p-hydroxyphenyl (H) and guaiacyl(G) units. The lignin preparation also included moreβ-5 linkages thanβ-βandβ-O-4 linkages, which were broken through the H2O2 pretreatment. Compared with the MWL of furfural residues, isolated lignin fraction had fewer functional group such as methylene, hydroxyls, Conjugated carbonyl groups, and the benzene ring was also partly broken. The weight-average (Mw) and number-average (Mn) molecular weights of lignin preparation was 1405 and 735, which was much lower than the MWL of furfural residues. The reason was that the smaller lignin fraction was easier to remove during the H2O2 pretreatment.The effects of lignin content on simultaneous saccharification and fermentation of furfural residues was also explored here. The results showed that lignin remover could effectively increase ethanol yield in fermenting liquid. The ethanol concentration concentration was raised remarkably from 6.8 to 14.5 g/L, as well as the ethanol yield increased from 50.6% to 69.35%, which were much higher the the results of untreated furfural residues.