Yingjuan Fu

Lignosulfonate-mediated cellulase adsorption: enhanced enzymatic saccharification of lignocellulose through weakening nonproductive binding to lignin

BackgroundThermochemical pretreatment of lignocellulose is crucial to bioconversion in the fields of biorefinery and biofuels. However, the enzyme inhibitors in pretreatment hydrolysate make solid substrate washing and hydrolysate detoxification indispensable prior to enzymatic hydrolysis. Sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) is a relatively new process, but has demonstrated robust performance for sugar and biofuel production from woody biomass in terms of yield and energy efficiency. This study demonstrated the advantage of SPORL pretreatment whereby the presentation of lignosulfonate (LS) renders the hydrolysate non-inhibitory to cellulase (Cel) due to the formation of lignosulfonate-cellulase complexes (LCCs) which can mediate the Cel adsorption between lignin and cellulose, contrary to the conventional belief that pretreatment hydrolysate inhibits the enzymatic hydrolysis unless detoxified.ResultsParticular emphasis was made on the formation mechanisms and stability phase of LCCs, the electrostatic interaction between LCCs and lignin, and the redistributed Cel adsorption between lignin and cellulose. The study found that LS, the byproduct of SPORL pretreatment, behaves as a polyelectrolyte to form LCCs with Cel by associating to the oppositely charged groups of protein. Compared to Cel, the zeta potential of LCCs is more negative and adjustable by altering the molar ratio of LS to Cel, and thereby LCCs have the ability to mitigate the nonproductive binding of Cel to lignin because of the enlarged electrostatic repulsion. Experimental results showed that the benefit from the reduced nonproductive binding outweighed the detrimental effects from the inhibitors in pretreatment hydrolysate. Specifically, the glucan conversions of solid substrate from poplar and lodgepole pine were greatly elevated by 25.9% and 31.8%, respectively, with the complete addition of the corresponding hydrolysate. This contradicts the well-acknowledged concept in the fields of biofuels and biorefinery that the pretreatment hydrolysate is inhibitory to enzymes.ConclusionsThe results reported in this study also suggest significant advantages of SPORL pretreatment in terms of water consumption and process integration, that is, it should abolish the steps of solid substrate washing and pretreatment hydrolysate detoxification for direct simultaneous saccharification and combined fermentation (SSCombF) of enzymatic and pretreatment hydrolysate, thereby facilitating bioprocess consolidation. Furthermore, this study not only has practical significance to biorefinery and bioenergy, but it also provides scientific importance to the molecular design of composite enzyme-polyelectrolyte systems, such as immobilized enzymes and enzyme activators, as well as to the design of enzyme separation processes using water-soluble polyelectrolytes.

Performance and efficiency of old newspaper deinking by combining cellulase/hemicellulase with laccase-violuric acid system

Performance and efficiency of old newspaper (ONP) deinking by combining cellulase/hemicellulase with laccase-violuric acid system (LVS) were investigated in this study. Brightness, effective residual ink concentration (ERIC) and physical properties were evaluated for the deinked pulp. Fiber length, coarseness, specific surface area and specific volume were also tested. The changes of dissolved lignin during the deinking processes were measured with UV spectroscopy. The fiber morphology was observed with environmental scanning electronic microscopy (ESEM). Experimental results showed that, compared to the pulp deinked with each individual enzyme, ERIC was lower for the cellulase/hemicellulase-LVS-deinked pulp. This indicated that a synergy existed in ONP deinking using a combination of enzymes. After being bleached by H(2)O(2), enzyme-combining deinked pulp gave higher brightness and better strength properties. Compared with individual enzyme deinked pulp, average fiber length and coarseness decreased a little for the enzyme-combining deinked pulps. A higher specific surface area and specific volume of the pulp fibers were achieved. UV analysis proved that more lignin was released during the enzyme-combining deinking process. ESEM images showed that more fibrillation was observed on the fiber surface due to synergistic treatment.

Specific lignin precipitation for oligosaccharides recovery from hot water wood extract.

Hot water extraction is an important strategy of wood fractionation, by which the hemicelluloses can be separated for value-added products, while the residual solid can still be processed into traditional wood products. In this study, a combined process consisting of specific lignin precipitation and dialysis was proposed to recover hemicellulosic oligosaccharides (OS) from hot water extract (HWE). The results showed that polyaluminium chloride (PAC) precipitation was highly specific to large molecular lignin, leading to 25.1% lignin removal with negligible OS loss through charge neutralization mechanism. The separation was further enhanced by dialysis, reaching 37.6% OS recovery from HWE with remarkable purity of 94.1%. By the proposed process, 56.36 g OS, mainly xylooligosaccharides with two fractions of 5.2 and 0.51 kDa was recovered from one kg dried wood. This process can be envisaged as a great contribution to wood biorefinery.

Nanocrystalline cellulose from aspen kraft pulp and its application in deinked pulp.

Nanocrystalline cellulose (NCC) isolated from bleached aspen kraft pulp was characterized, and its application as pulp strengthening additive and retention aid was investigated. Results showed that NCC with high crystallinity of more than 80% can be obtained using 64 wt% sulfuric acid. The structure of nanocrystalline cellulose is parallelepiped rod-like, and their cross-sectional dimension is in the nanometer range with a high aspect ratio. The formation of microparticle retention systems during the application of NCC together with cationic polyacrylamide and cationic starch in deinked pulp was able to further improve pulp retention and strength properties without negative influence on the drainage.

Effect of bio-treatment on the lipophilic and hydrophilic extractives of wheat straw.

Wheat straw, an important papermaking raw material in China, was treated with a white-rot fungus of Phanerochaete chrysosporium ME446, and the lipophilic and hydrophilic extractives from the control and bio-treated samples were analyzed by GC and GC-MS. Bio-treatment of wheat straw could alter the chemical composition of both the lipophylic and hydrophilic extractives. Sugars and phenolic substances such as coniferyl alcohol, 4-hydroxycinnamic acid, 1-guaiacylglycerol and ferulic acid were substantially degraded or consumed by the fungus. More lipophilic substances such as wax, glycerides and steryl esters were degraded into the corresponding components, resulting in much higher concentrations of fatty acids and sterols in the bio-treated samples. Obviously, the bio-treatment of wheat straw was of benefit to pitch control in pulping and papermaking processes, in the view of degradation of the more lipophilic substances. In addition, the bio-treatment could increase the lignin concentration in hot-water extractives of wheat straw.

Fractionation and characterization of saccharides and lignin components in wood prehydrolysis liquor from dissolving pulp production

Saccharides and lignin components in prehydrolysis liquor (PHL) from kraft-based dissolving pulp production was characterized after being fractionated using membrane filtration. The results showed that the membrane filtration provided a method for organics fractionation with considerable recovery rate, but exhibited some disadvantages. Besides the limited ability in purifying oligosaccharides (OS) due to the overlaps of molecular weight distribution with lignin components, the membrane filtration could not improve the homogeneity of OS as indicated by the analysis of chemical compositions and the degree of polymerization (DP), which may be ascribed to the linear conformation of OS. The characterization of lignin components indicated a great potential for polymer industry because of the remarkable content of phenolic hydroxyl groups (PhOH), especially for low molecular weight (LMW) fraction. It was concluded the organics in PHL provided streams of value-added chemicals. However, the practical significance thereof can be realized and maximized only when they are successfully and completely fractionated.

Selective removal of phenolic lignin derivatives enables sugars recovery from wood prehydrolysis liquor with remarkable yield.

The specific elimination of lignin derivatives from wood hydrolysate without sugar loss has great practical significance to biorefinery and bioenergy. In the present study, a process consisting of calcium hydroxide and anion exchange resin treatments was developed for the purpose of selective removal of lignin from wood prehydrolysis liquor (PHL). Particular emphasis was made on the ionization of phenolic lignin, and the subsequent binding to metallic salts. It was observed that phenolic hydroxyl groups (PhOH) in lignin played an important role in lignin removal. The results showed that up to 95.2% lignin was removed from PHL with 78.8% sugar recovery. This suggested that the proposed process is highly specific to lignin, and therefore can be envisaged as a great contribution to wood-sugar production or bioenergy conversion.

Lipophilic Extractives in Populus × euramericana “Guariento” Stemwood and Bark

Abstract The lipophilic extractives in stemwood and bark from three different heights of Populus × euramericana “Guariento” were analyzed. The bark samples, especially from 4 and 8 meters height, contained much more extractives than the stemwood samples. The lipophilic extractives identified by Gas Chromatography–Mass Spectroscopy (GC-MS) were composed of five component groups (i.e. triglycerides, steryl esters, free fatty acids, sterols, and free fatty alcohols both in the stemwood and bark). Besides ferulic acid esters, α-amyrin and its esters, 4-hydroxycinnamic acid esters of fatty alcohols were also identified in the stemwood and bark. Small amounts of alkanes and oligomeric or polymeric material with higher molar mass than triglycerides were present only in the bark. Glycerides, mainly triglycerides, were the largest component group of the lipophilic extractives. The high proportion of short-chain fatty acids released after alkaline hydrolysis are beneficial when removing pitch particles or fatty acid soaps by dispersing and washing during pulping and papermaking.

Saccharide separation from wood prehydrolysis liquor: comparison of selectivity toward non-saccharide compounds with separate techniques

Pre-pulping extraction of hemicellulose from wood produces a prehydrolysis liquor (PHL) rich in monosaccharides and oligosaccharides (OS). However, PHL also contains non-saccharide compounds (NSC), mainly lignin-derived byproducts. A promising usage of PHL is to separate OS from NSC as value-added products. In this work, NSC selectivity was defined as the ratio of NSC removal over the sum of NSC and saccharide removal, and applied to evaluate the performance of several separation techniques. Ultrafiltration (UF) of PHL with a molecular weight cut-off (MWCO) from 50 kDa to 1 kDa showed no selectivity toward NSC because of the equal retention of saccharides and NSC. Polymer flocculation using polyaluminium chloride (PAC) was infeasible due to the conflict between NSC selectivity and NSC removal. Lime treatment showed remarkable selectivity up to 90% due to the specific removal of phenolic lignin derivatives. Adsorption by a macroporous resin attained nearly complete removal of NSC with 78.9% saccharide recovery, but at the expense of massive resin consumption. The comparison of NSC selectivity suggested the combination of lime treatment and resin adsorption as an economic and practical process for saccharide separation from PHL.

Changes in the microstructure and properties of aspen chemithermomechanical pulp fibres during recycling.

The effects of recycling on the microstructure and properties of bleached aspen chemithermomechanical pulp (CTMP) fibres were systematically investigated. The low-temperature nitrogen adsorption and atomic force microscopy results showed that a substantial amount of large pores and most of the very small pores in the fibre wall closed and the fibre surface became less coarse and porous during recycling. The partial cocrystallisation of cellulose microfibrils took place, as reflected in the increment of the cellulose crystallinity and the width of the crystallite in the 0 0 2 lattice plane. These irreversible structural changes caused significant hornification of the recycled fibres, leading to the loss of swelling and bonding capability. The decrease of the tensile index, burst index, and tear index further demonstrated the deterioration of the fibre properties. However, the single-fibre strength considerably increased after recycling, which was mainly due to the enlarged cellulose aggregates in the fibre wall.