Effect of liquid hot water pretreatment severity on properties of hardwood lignin and enzymatic hydrolysis of cellulose

Abstract

Lignin, one of the major components of lignocellulosic biomass, plays an inhibitory role on the enzymatic hydrolysis of cellulose. This work examines the role of lignin in pretreated hardwood, where extents of cellulose hydrolysis decrease, rather than increase with increasing severity of liquid hot water pretreatment. Hardwood pretreated with liquid hot water at severities ranging from log Ro = 8.25 to 12.51 resulted in 80-90% recovery of the initial lignin in the residual solids. The ratio of acid insoluble lignin (AIL) to acid soluble lignin (ASL) increased and the formation of spherical lignin droplets on the cell wall surface was observed as previously reported in the literature. When lignins were isolated from hardwoods pretreated at increasing severities and characterized based on glass transition temperature (Tg ), the Tg of isolated lignins was found to increase from 171 to 180°C as the severity increased from log Ro = 10.44 to 12.51. The increase in Tg suggested that the condensation reactions of lignin molecules occurred during pretreatment and altered the lignin structure. The contribution of the changes in lignin properties to enzymatic hydrolysis were examined by carrying out Avicel hydrolysis in the presence of isolated lignins. Lignins derived from more severely pretreated hardwoods had higher Tg values and showed more pronounced inhibition of enzymatic hydrolysis.

Xylose production from corn stover biomass by steam explosion combined with enzymatic digestibility

“…The possible reason was that the lignin-like compounds were generated by recondensation reactions among carbohydrates, DPs and water extractives (Liu et al, 2013a,b). Lignin content in pretreated solid is a main factor affecting the enzyme activity and hence the digestibility efficiency (Zeng et al, 2014;Ko et al, 2015), implying that the holding temperature of 170, 180 and 200°C may be adverse for the conversion of corn stover biomass.…”

“…Lignocellulosic biomass, which can be converted into alternative fuels such as ethanol, should be the primary energy resource due to its high annual production worldwide (1 Â 10 10 MT/year) (Alvira et al, 2010;Chen and Qiu, 2010). It can be obtained as the wastes of the agriculture and forestry industries, or from energy crops especially cultivated for the purpose (Chen and Liu, 2015;Ko et al, 2015). Corn stover is a potential feedstock for ethanol production due to high sugar content and low price of preparation (Ou et al, 2014;Luo et al, 2009).…”

Enhancement of enzymatic saccharification of corn stover with sequential Fenton pretreatment and dilute NaOH extraction

“…After the pretreatment combined Fenton pretreatment and dilute NaOH extraction (AE-FT and FT-AE), both lignin and hemicellulose were reduced significantly. Removal of lignin by NaOH is important, since the NaOH would then serve to also remove a component that otherwise adsorbs or inhibit cellulase Ko et al, 2015a), thereby increasing the amount of enzyme required (Ko et al, 2015b). Notably, the FT-AE pretreatment resulted in the higher ratio of glucan/xylan than AE-FT pretreatment did, and FT-AE-CS had higher content of cellulose and lower content of lignin than AE-FT-CS.…”

Hydrolysate-Recycled Liquid Hot Water Pretreatment of Reed Straw and Corn Stover for Bioethanol Production with Fed-Batch, Semi-Simultaneous Saccharification and Fermentation

“…However, economic and environmental requirements limit the applicability of these methods. Thus, other highly promising pretreatment processes, such as liquid hot water (LHW) (Lu et al 2013b;Ko et al 2015a), have been established for lignocellulosic biomass.…”