Extent Of Delignification Research Articles

An optimum biomass fractionation strategy into maximum carbohydrates conversion and lignin valorization from poplar

Appropriate fractionation of lignocellulosic biomass into useable forms is a key challenge to achieving an economic bioethanol production. In the present study, four different fractionation strategies of hydrothermal-, NaOH-, ethanol-, and NaOH catalyzed ethanol pretreatment were investigated to compare their abilities of cellulose conversion. Results showed that NaOH catalyzed ethanol pretreatment showed a rather high extent of delignification of 85.92%, which also enhanced the retention of cellulose (92.56%) and hemicellulose (76.57%); while other pretreatments tended to produce cellulose fraction which was insufficient to achieve the whole component utilization. After simultaneous saccharification and fermentation at high solids loading, synergistic maximization of xylose (42.47 g/L) and ethanol (85.74 g/L) output was achieved via alkaline ethanol pretreatment. Lignin characterization information showed that alkaline ethanol pretreatment facilitates the cleavage of β-O-4 linkage and further converts into arylglycerol. Moreover, less condensed substructure units with high processing activity were also generated in S- and G- lignin.

Acidic deep eutectic solvent assisted mechanochemical delignification of lignocellulosic biomass at room temperature

Lignocellulosic biomass is the most abundant natural polymer on Earth, but the efficient fractionation and refinery of all its components remain challenging. Acidic deep eutectic solvents refining is a promising method, while it is likely to cause lignin condensation and carbohydrates degradation, especially at server operation conditions. Here we propose the use of acidic deep eutectic solvent (DES), choline chloride/p-toluenesulfonic acid assisted mechanochemical pretreatment (DM) for efficient lignocellulose fractionation at mild condition. Four representative lignocellulose, wheat straw, moso bamboo, poplar wood and pine wood were selected at varied milling time (3, 6 h) to assess the fractionation ability of this strategy. This DM pretreatment demonstrated a rather high cellulose retentions (∼90 %) and extent of delignification for wheat straw and bamboo biomass, which corresponds to a high extent of enzymatic hydrolysis (∼75.5 %) for sugar platform pursuing. The extracted lignin showed rather high content of β-O-4′ leakages due to the swelling effect of deep eutectic solvent and mild operation conditions. This work provided a promising strategy to fractionate lignocellulose using deep eutectic solvents with the goal of simultaneous cellulose hydrolysis and reactive lignin obtaining that is usually difficult to realize using traditional chemical fractionation approach.

Comparison of various delignification/desilication pre-treatments and indigenous fungal cellulase for improved hydrolysis of paddy straw.

The efficient removal of lignin and silica from paddy straw is essential for its volarization into biofuels and other value-added products. In this work, different chemical pre-treatments viz. acid/alkali, organosolv and deep eutectic solvents were carried out to assess the extent of delignification and desilication of paddy straw. Maximum lignin and silica removal of 96.08 and 95.51% was observed with two step acid (0.5% sulphuric acid) followed by alkali (4% sodium hydroxide) pre-treatment with significantly low total lignin (2.30%) and silica content (0.80%) of the treated straw residue. The treated straw residue contained significantly high holocellulose (91.65%), cellulose (75.01%) and hemicellulose content (16.64%). Among the four indigenous fungal isolates, Penicillium mallochii (JS17) cellulase showed better accessibility for the treated straw residue with maximum release of 504.18mgg-1 of reducing sugars and saccharification efficiency of 56.90%. The two-step acid/alkali pre-treatment of paddy straw was highly effective for removing lignin and silica from paddy straw, thereby, resulting in enhanced enzymatic accessibility of the substrate and more efficient hydrolysis of cellulose into fermentable sugars.

A hybrid pretreatment strategy for delignification of Aloe vera processing waste and its effectiveness towards saccharification

A copious amount of rigid Aloe vera leaf rind (AVLR) has been produced from the aloe gel processing industries are majorly disposed as wastes since it has no commercial value. The cell wall compositional analysis revealed that significant quantity of cellulose (46% ± 0.76, w/w) and hemicellulose (18.5% ± 0.24, w/w) which justifies as potent source for bioethanol production. However, high lignin content (13.95% ± 0.45, w/w) hinders depolymerization of polysaccharides into fermentable sugars and subsequent fermentation for ethanol production. In the present study, microwave-assisted alkali (MAA) pretreatment of AVLR biomass was carried out by varying the power level (160 W, 320 W and 480 W) which showed a maximum delignification (66.38%) at 320 W. Scanning Electron Microscope (SEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD) based characterization were performed to study the extent of delignification in AVLR biomass. The Gas Chromatography-Mass Spectrometry (GC-MS) analysis was performed for the liquid hydrolysate obtained after MAA pretreatment at 320 W indicated that the hydrolysate contained more of oxidized phenolic hydrocarbons that can be potentially utilized for other value-added product synthesis. A comparison of saccharification efficiency was performed using two different cellulase producers namely Aspergillus niger and Aspergillus sp. A maximum saccharification of 68.5% ± 0.34 was achieved by Aspergillus sp., that was 2.8% higher on comparing with untreated AVLR biomass. This indicates the feasibility of MAA pretreatment for AVLR biomass in order to improve the accessibility of fermentable sugars available for ethanol production.

Obtaining Cellulose-Available Raw Materials by Pretreatment of Common Agro-Forestry Residues With Pleurotus spp.

The goals of the present study were to characterize the profile of ligninolytic enzymes in five Pleurotus species and determine their ability to delignify eight common agro-forestry residues. Generally, corn stalks were the optimal inducer of Mn-dependent peroxidase activity, but the activity peak was noted after wheat straw fermentation by P. eryngii (3066.92 U/L). P. florida was the best producer of versatile peroxidase, especially on wheat straw (3028.41 U/L), while apple sawdust induced the highest level of laccase activity in P. ostreatus (49601.82 U/L). Efficiency of the studied enzymes was expressed in terms of substrate dry matter loss, which was more substrate-than species-dependent. Reduction of substrate dry mass ranged between 24.83% in wheat straw and 8.83% in plum sawdust as a result of fermentation with P. florida and P. pulmonarius, respectively. The extent of delignification of the studied substrates was different, ranging from 51.97% after wheat straw fermentation by P. pulmonarius to 4.18% in grapevine sawdust fermented by P. ostreatus. P. pulmonarius was also characterized by the highest cellulose enrichment (6.54) and P. ostreatus by very low one (1.55). The tested biomass is a highly abundant but underutilized source of numerous value-added products, and a cocktail of ligninolytic enzymes of Pleurotus spp. could be useful for its environmentally and economically friendly transformation.

Properties of densified poplar wood through partial delignification with alkali and acid pretreatment

Poplar trees can be grown on marginal land to conserve water and recycle nutrients, but the wood has poor mechanical properties for structural applications. This study evaluated the feasibility of densifying poplar wood through delignification to improve mechanical properties. Delignification was conducted using a commercial soda pulping process under various NaOH concentrations of 0–6% with a reduced liquor-to-wood ratio of 3, along with a novel hydrotropic fractionation process using maleic acid. Delignified wood was pressed with or without stop bars at a low pressure of 1 MPa at 150 °C for 15 min or 100 °C for 2 or 10 h. Results indicate that wood density is the key variable dictating wood strength properties rather than extent of delignification. Pressing with stop bars resulted in similar wood densities for samples with different levels of delignification. Wood modulus of rupture (MOR), modulus of elasticity (MOE), and Brinell hardness (HB) all increased linearly with wood density, in agreement with literature results from pure hydrothermal compression. When removing stop bars in pressing, MOR, MOE, and HB were increased to 150 MPa, 20.7 GPa, and 43.2 MPa, respectively, from 88.5 MPa, 6.5 GPa, and 14.8 MPa for undensified poplar when wood density was increased to 0.81 g/cm3 from 0.46 g/cm3. Low-pressure densification with delignification is advantageous to significantly improve wood properties.

Studies on delignification and inhibitory enzyme kinetics of alkaline peroxide pre-treated pine and deodar saw dust

Delignification of lignocellulosic biomass by alkaline peroxide pre-treatment is a preliminary important step for an overall biomass fractionation process. In the present work, saw dusts are pre-treated by aqueous alkaline peroxide solution under different temperatures over a predetermined time. It is seen that Combined Pre-treatment (CP) removes a substantially higher quantity of lignin from biomass under a particular temperature. At elevated temperatures, the extent of delignification is observed much better. The % removal is: [PR: 19.35%(30 °C):25.26%(50 °C):33.30%(100 °C)]; [CD:14.64%(30 °C):23.64%(50 °C): 28.83%(100 °C)]. Batch kinetics is investigated with certain models and corresponding parameters are estimated. As pre-treatment severity is strongly correlated to the pre-treatment temperature, increased value of “potential degree of delignification” is observed at escalated temperatures. Kinetics of enzymatic hydrolysis of delignified biomass shows decreased product inhibition with increased substrate concentration under a particular enzyme loading. Starting with a combination of 50 g/L substrate concentration with an enzyme loading of 13.23 g/L, an optimum concentration of 17.2 g/L and 21.19 g/L of glucose are produced from Pinus roxburghii and Cedrus deodara respectively. Experimental data fit quite well with the competitive inhibition kinetics based theoretical models with r2 ≥0.95. It is inferred that enzymes are competitively inhibited by glucose.

Intensification of delignification and subsequent hydrolysis for the fermentable sugar production from lignocellulosic biomass using ultrasonic irradiation

The present work deals with intensification of delignification and subsequent enzymatic hydrolysis of sustainable biomass such as groundnut shells, coconut coir and pistachio shells using ultrasound assisted approach so as to develop an economical approach for obtaining bioethanol. Process intensification, in the current context, is referred to as any improvements giving enhanced rates possibly with lower energy and chemical as well as enzyme requirement for delignification and hydrolysis respectively. Conventional processing for both delignification and enzymatic hydrolysis has also been investigated for establishing the degree of intensification. The obtained results for delignification of biomass established that for conventional alkaline treatment, the extent of delignification for the case of groundnut shells, coconut coir and pistachio shells were 41.8, 45.9 and 38% which increased to 71.1, 89.5 and 78.9% respectively giving almost 80–100% increase for the ultrasound assisted approach. Under optimized conditions, the conventional approach resulted in reducing sugar yields as 10.2, 12.1 and 8.1g/L for groundnut shells, coconut coir and pistachio shells respectively whereas for the case of ultrasound-assisted enzymatic hydrolysis, the obtained yields were 21.3, 23.9 and 18.4g/L in same order of biomass. The material samples were characterized by several characterization techniques for establishing the morphological changes obtained due to the use of ultrasound which were found to be favorable for enhanced delignification and hydrolysis for the ultrasound assisted approach. Overall, the results of this work establish the process intensification benefits due to the application of ultrasound for different sustainable biomass with mechanistic understanding based on the morphological analyses.

Modelling of pretreatment and saccharification with different feedstocks and kinetic modeling of sorghum saccharification

Experiments have been performed for pretreatment of sorghum, wheat straw and bamboo through high temperature alkali pretreatment with different alkaline loading and temperatures, and the data on extent of delignification in terms of the final compositions of cellulose, hemicellulose and lignin have been generated. Further, enzymatic saccharification has been carried out in all the cases to find the extent of conversion possible after 72h. The effect of different operating parameters on the extent of delignification and cellulose conversion are evaluated. This data is employed to develop a generalized multi-feedstock and individual feedstock based models which can be used to determine the extent of delignification and cellulose conversion for any and specific biomass respectively with alkaline pretreatment and similar enzyme conditions as considered in the present study. Also, a kinetic model is developed and validated for sorghum for cellulosic conversion.

Induction of wheat straw delignification by Trametes species.

Wheat straw is the major crop residue in European countries which makes it the most promising material for bioconversion into biofuels. However, cellulose and hemicellulose are protected with lignin, so delignification is an inevitable phase in lignocellulose processing. The organisms predominantly responsible for its degradation are white-rot fungi and among them Trametes species represent promising degraders due to a well-developed ligninolytic enzyme system. Although numerous studies have confirmed that low molecular weight compounds can induce the production and activity of ligninolytic enzymes it is not clear how this reflects on the extent of delignification. The aim of the study was to assess the capacity of p-anisidine and veratryl alcohol to induce the production and activity of Mn-oxidizing peroxidases and laccases, and wheat straw delignification by six Trametes species. Significant inter- and intraspecific variations in activity and features of these enzymes were found, as well as differences in the potential of lignocellulose degradation in the presence or absence of inducers. Differences in the catalytic properties of synthesized enzyme isoforms strongly affected lignin degradation. Apart from enhanced lignin degradation, the addition of p-anisidine could significantly improve the selectivity of wheat straw ligninolysis, which was especially evident for T. hirsuta strains.

Supercritical carbon dioxide combined with 1-butyl-3-methylimidazolium acetate and ethanol for the pretreatment and enzymatic hydrolysis of sugarcane bagasse

The use of green solvents for the partial delignification of milled sugarcane bagasse (1mm particle size) and for the enhancement of its susceptibility to enzymatic hydrolysis was demonstrated. The experiments were carried out for 2h using 40g of supercritical carbon dioxide combined with 1-butyl-3-methylimidazolium acetate and 15.8g of ethanol. The effects of temperature (110–180°C), pressure (195–250bar) and IL-to-bagasse mass ratio (0:1–1:1) were investigated through a factorial design in which the response variables were the extent of delignification and both anhydroglucose and anhydroxylose contents in the pretreated materials. The highest delignification degree (41%) led to the best substrate for hydrolysis, giving a 70.7wt% glucose yield after 12h using 5wt% and Cellic CTec2® (Novozymes) at 10mgg−1 total solids. Hence, excellent substrates for hydrolysis were produced with a minimal IL requirement, which could be recovered by ethanol washing for its downstream processing and reuse.

Streptomyces griseorubens mediated delignification of paddy straw for improved enzymatic saccharification yields

Biological pretreatment of paddy straw was carried out using an actinomycete isolate, identified as Streptomyces griseorubens ssr38, for delignification under solid state fermentation and enhanced sugar recovery by enzymatic saccharification. After 10days incubation, the inoculated paddy straw was extracted with mild alkali and high absorbance at 205nm was shown by the extracts indicating the ability of S. griseorubens ssr38 to depolymerize/solubilize lignin to a high extent. Also, almost 25% of depolymerized lignin could be recovered as value-added acid-precipitable polymeric lignin (APPL) as compared to controls. Enrichment in carbohydrate content of inoculated paddy straw following delignification led to a high saccharification efficiency of 97.8% upon enzymatic hydrolysis with Accelerase®1500. The study, therefore, proves the potential of actinomycetes, besides the conventionally used white-rot fungi, for biological pretreatment, in the biomass to bioethanol process, with respect to the high extent of delignification, lignin recovery, cellulose enrichment and very high saccharification efficiency.

Structural changes in switchgrass lignin and hemicelluloses during pretreatments by NMR analysis

Switchgrass is currently being developed as a sustainable bio-energy crop due to its broad adaptability, high mass yield and low agricultural input. Its current conversion to biofuels is detrimentally impacted by its native recalcitrance which is typically addressed using chemical and/or biological pretreatments. In this study, extractives free switchgrass was pretreated with steam, dilute H 2SO 4 and lime at 160 °C for 1 h. The degradation and impact of pretreatment was estimated semi-quantitatively by 13C– 1H HSQC (heteronuclear single quantum coherence) NMR analysis of ball milled untreated and pretreated switchgrass samples in perdeuterated pyridinium chloride–DMSO-d 6 solvent system. As a result of steam pretreatment the resulting switchgrass was depleted of xylan and a slight degradation of lignin were observed. This was confirmed by the relative decrease of cross peak intensity for β-aryl ether, phenylcoumaran, resinol and dibenzodioxocin units. Significant structural changes observed due to the lime pretreatment of switchgrass was deacetylation/dissolution of hemicellulose and the extent of delignification was less however, a preferential removal p-hydroxy of benzoyl ester, ferulate and coumarate type linkages were notified from the HSQC studies. Finally the most significant degradation resulted in acid pretreatment involving ∼90% loss of hemicellulose and a substantial degradation of various lignin sub-units. These results are further supported by the composition analysis of the respective switchgrass samples.

Dimensionless Parameter Approach for Oxygen Delignification Kinetics

In this study, the kinetic analysis of oxygen delignification of Turkish southern hardwood Kraft pulp was carried out. The kinetic rate data were collected in a high pressure batch reactor at industrially significant conditions of temperature, alkali charge, and oxygen partial pressure. The mass transfer effects were examined for the system studied. After eliminating the mass transfer resistances in the delignification system, the kinetics of oxygen delignification was studied and the governing rate equations were derived. The kinetics of the carbohydrate degradation was analyzed to determine the extent of delignification without the reduction in the pulp strength below the acceptable level; which is usually taken as the removal of no more than half of the lignin in the pulp entering the oxygen stage. The kappa number, intrinsic viscosity, and reaction time were expressed in dimensionless forms to generalize the results and to make them independent of the initial values, experimental conditions, and pulping conditions prior to oxygen delignification. These dimensionless parameters were fitted to nonlinear equations. These equations can also be used for the control of the oxygen delignification towers. The same approach was also used for the reported studies in the literature which allowed the comparison with the results of this study.

The Influence of Operating Parameters on the Biodelignification of Eucalyptus globulus Kraft Pulps in a Laccase–Violuric Acid System

The potential of a laccase mediator system on the delignification of Eucalyptus globulus kraft pulp was investigated under diverse operating conditions. A series of enzymatic treatments were performed to determine how biodelignification is influenced by pulp consistency, oxygen pressure, reaction time, dose of laccase, and dose of mediator. The mediator used was violuric acid. The results revealed that the extent of biodelignification remains practically constant between 1% and 2.5% of pulp consistency then decreases. However, its effect is less pronounced than the mediator or laccase charge. In fact, an increase in the mediator charge from 1% to 4% leads to an increase in the extent of delignification (fixed laccase charge = 20 IU/g and reaction time 120 min) from 28.4% to 52.2%. On the other hand, at a mediator charge of 4%, the increase of laccase charge from 10 to 40 IU/g has a similar impact on delignification. As for oxygen pressure, the extent of delignification increases with oxygen pressure, from 38.9% to 48.6%, when air and pure oxygen at 4 bar gauge are used. From the standpoint of reaction time, delignification is characterized by a very fast phase followed by a much slower one, leading to a plateau.

Measuring Flow Velocity and Uniformity in a Model Batch Digester Using Electrical Resistance Tomography

AbstractThe literature shows that the extent of delignification in batch digesters varies as a function of chip location in the vessel. This non‐uniformity may be exacerbated by a number of factors but is commonly attributed to poor and/or non‐uniform liquor flow through the reactor (which causes poor chemical and heat distribution to the chip mass during the cook). Electrical resistance tomography (ERT) was used to evaluate the uniformity of liquor flow in a laboratory model digester under scaled industrial conditions (a 1:15 geometrically scaled vessel, a vessel to particle diameter ratio of 93:1 to minimize wall effects, and close approximation of liquor superficial velocity and pore Reynolds number). Local interstitial flow velocities were measured using pixel‐pixel cross correlation techniques. It was possible to create uniform zones in the digester, but a stagnation point was observed in the centre of the vessel at the screen level. This point coincides with the location of highest kappa numbers (lowest degree of cooking) reported in industrial tests.

Lignin degradation by white rot fungi on spruce wood shavings during short-time solid-state fermentations monitored by near infrared spectroscopy

Due to their outstanding capability of degrading the recalcitrant biomacromolecule lignin, white rot fungi have been attracting interest for several technological applications in mechanical pulping and wood surface modification. However, little is known about the time course of delignification in early stages of colonisation of wood by these fungi. Using a Fourier transform near infrared (FT-NIR) spectroscopic technique, lignin loss of sterilised spruce wood shavings (0.4–2.0 mm particle size) that had been degraded by various species of white rot fungi could be monitored already during the first 2 weeks. The delignification kinetics of Dichomitus squalens, three Phlebia species ( Phlebia brevispora, Phlebia radiata and Phlebia tremellosa), three strains of Ceriporiopsis subvermispora as well as the white rot ascomycete Hypoxylon fragiforme and the basidiomycete Oxyporus latemarginatus were determined. Each of the fungi tested was able to reduce the lignin content of spruce wood significantly during the first week. The amount of delignification achieved by the selected white rot fungi after 2 weeks ranged from 7.2% for C. subvermispora (FPL 105.752) to 2.5% for P. radiata. Delignification was significant ( P = 95%) already after 3 days treatment with C. subvermispora and P. tremellosa. Activities of extracellular ligninolytic enzymes (laccase, manganese peroxidase and/or lignin peroxidase), expressed by each of the tested fungi, were determined. Lignin was degraded when peroxidase activity was detected in the fungal cultures, but only a low level of correlation between enzyme activities and the extent of delignification was found.

A KINETIC MATHEMATICAL MODEL OF KRAFT PULPING PROCESS FOR CONTROL AND OPTIMIZATION APPLICATIONS

Kraft wood pulping is the predominant process used in the pulp and paper industry for its versatility and insensitivity to variations of wood supply. In this work, a deterministic model has been developed for a Kraft Pulping Process of Eucalyptus by combining intrinsic kinetic equations (Lignin, Carbohydrates) and it is used to investigate the effects of process conditions on the extent of delignification. The aim of this work is to develop a mathematical model which at some time is able to represent the main phenomena taking place in the process and suitable to be used in control and optimization applications.

The Effect of Particle Size Distribution on Pressure Drop through Packed Beds of Cooked Wood Chips

AbstractThe pressure drop of process liquors through columns of wood chips determines the operability, efficiency and control of both batch and continuous pulp digesters and the quality of the pulp produced from them. Pressure drop was measured through columns of industrial white spruce chips (produced with a chipping head‐rig) as a function of the chip size distribution and the extent of delignification. Flow resistance depended on the porosity of the chip bed which was affected by the kappa number of the chips (which affected their flexibility) and chip size distribution, the compaction forces applied to the column, and the liquid superficial velocity. The chip beds were compressible and inelastic. Previous work from the literature using the Ergun equation to characterize pressure losses through chip beds is examined and compared with results of this work.

Extraction of lignin from sugar cane bagasse and Pinus taeda wood chips using ethanol–water mixtures and carbon dioxide at high pressures

The utilization of carbon dioxide under supercritical conditions in the delignification of wood has already been reported in the literature for several species of tree. In these studies organic solvents (acetic acid, ethanol, methanol, dioxane, etc.) were used as co-solvent and very high pressures (15–25 MPa) were employed. Organosolv treatments of various woods have also been reported and have shown good results with ethanol–water mixtures, normally at volume ratios close to unit. This article describes a study of the pulping of Pinus taeda wood chips and sugar cane bagasse, combining the use of ethanol–water mixtures and carbon dioxide at high pressures. Ethanol–water mixture was varied from 50 to 100% ethanol for sugar cane bagasse and from 30 to 100% ethanol for P. taeda wood chips, and the reaction times from 30 to 120 min and from 30 to 150 min for sugar cane bagasse and P. taeda wood chips, respectively. The effect of pressure and temperature on the yield and extent of delignification was studied, using a factorial experimental design, over the ranges 14.7–23.2 MPa and 142–198 °C, respectively. The obtained results indicate important differences from the organosolv process, which may be due to the presence of carbon dioxide and/or the high pressure employed in this work. The pulp yields and extent of delignification showed, as expected, a much greater influence of temperature than of pressure. The best results were obtained at 16.0 MPa and 190 °C. Under these conditions the pulping yield and the residual Klason lignin content from P. taeda wood chips were 43.7 and 4.9%, respectively, and from sugar cane bagasse 32.7 and 8.7%, respectively. These data correspond to a delignification extent in the order of 93.1% for P. taeda wood chips and 88.4% for sugar cane bagasse. Higher pressures lead to similar pulp yields but higher residual lignin contents.