Enhancing Enzymatic Hydrolysis Of Lignocellulose By Lignin-based Amphiphilic Polymers And Its Underlying Machanism

Lignocellulosic biomass is the most abundant and renewable source on earth and can be converted to value-add chemicals or bio-fuels through the sugar platform.Enzymatic hydrolysis efficiency of lignocellulose was relative low because of its recalcitrance,and enzymatic hydrolysis lignin(EHL)from biorefinery was usually burned for heat and power directly,lignocellulose had not been efficiently utilized.Lignin-based polyoxyethylene ether(EHL-PEG)and lignosulfonate-based polyoxyethylene ether(LS-PEG)was synthesized from EHL and lignosulfonate(LS)respectively.Effect of the molecular structure of the two amphiphilic polymers on the enzymatic hydrolysis efficiency of Avicel and lignocellulose was investigated,and the enhancing mechanism of enzymatic hydrolysis was proposed.Cationic surfactant cetyltrimethylammonium bromide(CTAB)was used to control the surface charge of LS and LS-PEG,and the formed catanionic surfactant could enchance the enzymatic hydrolysis of lignocellulose.The results are as follows:First,a novel mothed was proposed to synthesize controllable lignin-based polyoxyethylene ether.BF3-Et2 O as Lewis acid catalyst and epichlorohydrin as crosslinker,polyethylene glycol(PEG)was grafted to kraft lignin(KL)in akaline solution and water soluble KL-PEG was obtained,effect of reaction condition on the structure,surface tension and critical aggregation concentration of KL-PEG was investigated.EHL-PEG with various PEG chain lengths,PEG content and average molecular weight was prepared from corn stover EHL,and its effect on the enzymatic hydrolysis of Avicel and corn stover was studied.Quartz crystal microbalance with dissipation monitoring and dynamic light scattering results domenstrated that EHL-PEG bound with cellulase through the hydrophobic interaction and electrostatic interaction,dispersed cellulase aggregates and formed smaller cellulase aggregates(EHL-PEG-Cellulase),thereby,reduced 88% of the nonproductive adsorption of cellulase on lignin and enhanced the enzymatic hydrolysis of corn stover from 16.7% to 70.1%.EHL-PEG-Cellulase started to excavate extensive cavities into the surface of the cellulose film,and the cellulose film became more loose and exposed.When the cellulose film was the most exposed,and the accessibility of cellulase to the cellulose film was the largest,thus,the enzymatic hydrolysis rate reached the maximum.After that,the cellulose film was mainly peeled off layer by layer until equilibrium.Secondly,effect of various structures of LS-PEG amphiphilic polymers prepared from LS on the enzymatic hydrolysis of Avicel and corn stover was studied.CTAB was used to control the surface charge of LS-PEG and further improve the enzymatic hydrolysis of corn stover.Sulfonic group of LS-PEG preferentially interacted with quaternary ammonium group of CTAB by the electrostatic attraction to form catanionic surfactant CTAB-LS-PEG.CTAB-LS-PEG showed weak negative charged and more hydrophobic,and blocked more nonproductive adsorption of cellulase on the lignin,CTAB-LS-PEG enhanced the enzymatic hydrolysis efficiency of lignocelluloses more significantly.Then,various alkyl chain lengths of CnTAB was used to control the surface charge of LS with various molecular weight and improve the enzymatic hydrolysis of Avicel and corn stover from 42.1% and 24.3% to 61.6% and 56.2%,respectively,that performed fairly with PEG4600.LS dispersed cellulase aggregates to form the smaller and more hydrophilic LS-Cellulase aggregates;while CTAB neutralized the electronegative charge of LS and formed LS-CTAB catanionic surfactant,decreased the electrostatic repulsion between LS-Cellulase aggregates and cellulose subtstrate with negative charged,improved the interaction between cellulase and cellulose,and enhanced the enzymatic hydrolysis of cellulose.Finally,found that CnTAB could effectively enhance the enzymatic hydrolysis of Avicel at various conditions.Enzymatic hydrolysis of Avicel increased linearly from 42.1% to 61.4% with the logarithmic increase of the concentration of C16 TAB from 0.0001 mM to 0.01 mM.With the increasing alkyl chain length,CnTAB provides proton more easily and neutralizes the negative charge of cellulase more obviously,the required concentration of CnTAB can be less to enhance enzymatic hydrolysis of Avicel.Anionic surfactant sodium dodecyl sulfate(SDS)could improve the enzymatic hydrolysis of Avicel at the concentration range of 0.1~1 mM,but it did inhibit the enzymatic hydrolysis at higher concentration.CTAB and SDS interacted by positive and negative charge neutralization and formed SDS-CTAB catanionic surfactant,that could enhance the enzymatic hydrolysis of corn stover at high solid content from 33.3% to 62.4%.SDS-CTAB could regulate the surface charge of cellulase in the hydrolyzate and reduce the non-productive adsorption of cellulase on the lignin,thereby improve the enzymatic hydrolysis efficiency of lignocellulose.Both EHL-PEG nonionic amphiphilic polymers directly synthesized from EHL,and LS synthesized from EHL followed by combining with CTAB to form LS-CTAB catanionic surfactant,could be used to enhance enzymatic recation of lignocellulose,that not only improve the enzymatich hydrolysis and decrease the cellulase dosage,but also realize the efficient utilization of enzymatic hydrolysis lignin.