Effects And Mechanism Of Zwitterionic Surfactants On The Fermentation Of High-solids Lignocellulose

Cellulose ethanol plays an important role in optimizing energy structure,improving the ecological environment and promoting agricultural development.China government proposes to strive to achieve large-scale production of cellulosic ethanol in 2025,but there are still many technical bottlenecks in the production of cellulosic ethanol from lignocellulose.The serious problem in the enzymatic hydrolysis and fermentation of lignocellulose is poor efficiency of enzymatic hydrolysis,which has caused expensive cost of enzymatic hydrolysis and low ethanol yield.The addition of surfactants was not only easy to operate to enhance the enzymatic hydrolysis of lignocellulose,but also could greatly reduce the dosage of cellulase.The compound of sodium lignosulphonate(SL)and hexadecyl trimethyl ammonium bromide(CTAB)could reduce nonproductive adsorption of cellulase on lignin and strengthen enzymatic hydrolysis.Besides,lignin amphoteric surfactant and betaine could enhance the enzymatic hydrolysis of lignocellulose and recover cellulase.In this paper,we studied the effects of the compound of SL and CTAB(SL-CTAB),dodecyl dimethyl betaine(BS-12)and lignosulfonate quaternary ammonium salt(SLQA)on enzymatic hydrolysis efficiency,ethanol yield,yeast cell viability and other properties of high solid enzymatic hydrolysis and fermentation of corncob residue,and investigated the mechanism of zwitterionic surfactants on the fermentation of high-solids lignocellulose.The results were summarized as follows,(1)The compound of SL-CTAB could strengthen the enzymatic hydrolysis by reducing the nonproductive adsorption of cellulase on lignin and increase the concentration of glucose.However,the compound of SL-CTAB had an inhibition on glucose fermentation,which was due to that CTAB damaged the yeast cell membrane.During the process of high solid enzymatic hydrolysis and fermentation of corncob residue,CTAB was adsorbed on lignin,which weakened the inhibitory effect of CTAB on the yeast cell viability.Therefore,the compound of SL-CTAB could strengthen high solid enzymatic hydrolysis and fermentation of corncob residue.(2)SLQA could be adsorbed on lignin by hydrophobic interaction and lessened the nonproductive adsorption of cellulase on lignin,which strengthened the enzymatic hydrolysis,and subsequently improved the ethanol yield.Besides,its hydrophilic three-dimensional structure made it difficult to penetrate the cell membrane and damage the cell membrane,thus,SLQA had little effect on yeast cell viability and the cell membrane damage.(3)1 g/L BS-12 could improve the enzymatic hydrolysis efficiency and ethanol yield of lignocellulose.Although 5 g/L BS-12 could improve the enzymatic efficiency,but it reduced the ethanol yield.BS-12 could strengthen the enzymatic hydrolysis by reducing the nonproductive adsorption of cellulase on lignin and increase the concentration of glucose.But BS-12 strongly inhibited glucose fermentation by damaging the yeast cell membrane.At the low-dose of 1 g/L,most BS-12 was adsorbed on lignin,which weakened the inhibitory effect of BS-12 on the yeast cell viability in the process of fermentation and enhanced the ethanol yield of enzymatic hydrolysis and fermentation of lignocellulose.However,at the high-dose of 5 g/L,the lignin in lignocellulose could only adsorb part of BS-12 and most BS-12 was still free in fermentation broth.The free BS-12 could be adsorbed on yeasts and caused the yeast cell membrane damage,and further inhibited the enzymatic hydrolysis and fermentation of lignocellulose.The effects and mechanism of zwitterionic surfactants on the fermentation of high-solids lignocellulose were studied.This research illustrates that though their effects are different,but they still could promote the enzymatic hydrolysis and fermentation of lignocelluloses by choosing appropriate dosage.Researches on developing lignin-based enzymatic auxiliaries like SLQA and SL could not only achieve the comprehensive utilization of lignin,but also be conducive to the development of new biorefinery processes.