Effect Of Residual Lignin Research Articles

Further insights into the solubilization and surface modification of lignin on enzymatic hydrolysis and ethanol production

In this study, the effect of residual lignin and its structural modification of pretreated sugarcane bagasse (SCB) on enzymatic hydrolysis and fermentation was comprehensively evaluated by alkali and alkaline hydrogen peroxide (AHP) pretreatment. It was found that the AHP pretreatment had a negative influence on lignin dissolution compared with alkali pretreatment accompanied by a relatively low NaOH concentration (≤1%, w/v). However, there was less significance of enzymatic hydrolysis efficiency between NaOH and AHP pretreatment with >1% NaOH loading due to a high lignin removal above 78%. In addition, PEG 6000-assisted pretreatment was also performed to stabilize the enzymatic activity and further promote enzymatic digestibility and fermentability. The highest ethanol concentration of 59.96 g/L (61.22%) was obtained with PEG 6000-assisted 1% NaOH pretreated SCB at 30% solid loading. The structural features of the residual lignin indicated that most of the side chain structures were oxidized and that some aryl-ether bonds were dissociated after the pretreatments, especially in alkali pretreatment. The reduction of molecular weight and the breaking of lignin substructures help to achieve a more effective yield of enzymatic hydrolysis and fermentation.

Production of xylo-oligosaccharides from poplar by acetic acid pretreatment and its impact on inhibitory effect of poplar lignin

Recently, efficient production of xylo-oligosaccharides (XOS) from poplar by acetic acid (AA) pretreatment was developed; but the effect of residual lignin on subsequent cellulase hydrolysis was unclear. Herein, XOS was produced from poplar by AA pretreatment and the effect of AA pretreatment on lignin inhibition to cellulase hydrolysis was investigated. The results indicated that a high XOS yield of 55.8% was obtained, and the inhibition degree of lignin in poplar increased from 1.0% to 6.8% after AA pretreatment. Lignin was acetylated and its molecular weight decreased from 12,211 to 2871 g/mol after AA pretreatment. The increase of S/G ratio, phenolic hydroxyl, and condensed units of lignin after AA pretreatment might be reasons for this intensified inhibition. The results advanced our understanding of the structural and inhibitory properties of lignin after production of XOS from poplar with AA pretreatment, and provided references for efficient cellulase hydrolysis of poplar after AA pretreatment.

Effect of lignin and hemicellulose on the properties of lignocellulose nanofibril suspensions

Lignocellulose nanofibrils (LCNFs) are nano-objects produced in aqueous suspension by industrially adaptable methods, with a high yield, low production cost and the potential to replace or complement delignified cellulose nanofibrils in their current applications. To this end, it is necessary to understand how their constituents affect the production and characteristics of the final product. This review explores the most recent results on the effect of the residual amount of lignin and hemicelluloses on the properties of LCNF suspensions. In the current literature, there is a consensus on hemicelluloses, a larger amount of which favors the mechanical fibrillation process, with mannans providing the greatest benefits. Meanwhile, there is no consensus on the effect of residual lignin on mechanical fibrillation, since it can act as an antioxidant, which promotes fibrillation, or as a cementing agent, which hinders fibrillation and, therefore, the production of LCNFs.

Effect of residual extractable lignin on acetone\u2013butanol\u2013ethanol production in SHF and SSF processes

BackgroundLignin plays an important role in biochemical conversion of biomass to biofuels. A significant amount of lignin is precipitated on the surface of pretreated substrates after organosolv pretreatment. The effect of this residual lignin on enzymatic hydrolysis has been well understood, however, their effect on subsequent ABE fermentation is still unknown.ResultsTo determine the effect of residual extractable lignin on acetone–butanol–ethanol (ABE) fermentation in separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) processes, we compared ABE production from ethanol-washed and unwashed substrates. The ethanol organosolv pretreated loblolly pine (OPLP) was used as the substrate. It was observed that butanol production from OPLP-UW (unwashed) and OPLP-W (washed) reached 8.16 and 1.69 g/L, respectively, in SHF. The results showed that ABE production in SHF from OPLP-UW prevents an “acid crash” as compared the OPLP-W. In SSF process, the “acid crash” occurred for both OPLP-W and OPLP-UW. The inhibitory extractable lignin intensified the “acid crash” for OPLP-UW and resulted in less ABE production than OPLP-W. The addition of detoxified prehydrolysates in SSF processes shortened the fermentation time and could potentially prevent the “acid crash”.ConclusionsThe results suggested that the residual extractable lignin in high sugar concentration could help ABE production by lowering the metabolic rate and preventing “acid crash” in SHF processes. However, it became unfavorable in SSF due to its inhibition of both enzymatic hydrolysis and ABE fermentation with low initial sugar concentration. It is essential to remove extractable lignin of substrates for ABE production in SSF processes. Also, a higher initial sugar concentration is needed to prevent the “acid crash” in SSF processes.

Effect of residual lignin and heteropolysaccharides in nanofibrillar cellulose and nanopaper from wood fibers

Unbleached (UN), oxygen-delignified and fully-bleached (FB) birch fibers with a residual lignin content of ca. 3, 2 and <1 %, respectively, were used to produce nanofibrillated cellulose (NFC) and nanopaper by using an overpressure device. The tensile index, elongation and elastic modulus of nanopaper were compared and the effect of residual cell wall components accessed. Under similar manufacturing conditions, UN NFC produced nanopaper with a density of 0.99 g/cm3, higher than that from FB NFC (0.7 g/cm3). This translated in much lower air permeability in the case of UN nanopaper (1 and 11 mL/min for UN and FB samples, respectively). Fundamentally, these observations are ascribed to the finer fibrils produced during microfluidization of UN fibers compared to those from lower yield counterparts (AFM roughness of 8 and 17 nm and surface areas of 124 and 98 m2/g for NFC from UN and FB fibers, respectively). As a result, values of stress at break and energy absorption of nanopaper from high yield fibers are distinctively higher than those from fully bleached NFC. Interactions of water with the surface and bulk material were affected by the chemical composition and structure of the nanofibrils. While UN nanopaper presented higher water contact angles their sorption capacity (and rate of water absorption) was much higher than those measured for nanopaper from FB NFC. These and other observations provided in this contribution are proposed to be related to the mechanoradical scavenging capacity of lignin in high shear microfluidization and the presence of residual heteropolysaccharides.