Oxidative Delignification Research Articles

Microfibrillated Cellulose with a Lower Degree of Polymerization; Synthesis via Sulfuric Acid Hydrolysis under Ultrasonic Treatment

A new approach is being considered for obtaining microfibrillated cellulose with a low degree of polymerization by sulfuric acid hydrolysis with simultaneous ultrasonic treatment under mild conditions (temperature 25 °C, 80% power control). Samples of initial cellulose, MCC, and MFC were characterized by FTIR, XRF, SEM, DLS, and TGA. It was found that a high yield of MFC (86.4 wt.%) and a low SP (94) are observed during hydrolysis with ultrasonic treatment for 90 min. It was shown that the resulting microfibrillated cellulose retains the structure of cellulose I and has an IC of 0.74. It was found that MFC particles are a network of fibrils with an average size of 91.2 nm. ζ-potential of an aqueous suspension of MFC equal to -23.3 mV indicates its high stability. It is noted that MFC has high thermal stability, the maximum decomposition temperature is 333.9 °C. Simultaneous hydrolysis process with ultrasonic treatment to isolate MFC from cellulose obtained by oxidative delignification of spruce wood allows to reduce the number of stages, reduce energy costs, and expand the scope.

Composition and Structure of Aspen (Pópulus trémula) Hemicelluloses Obtained by Oxidative Delignification.

In this study, hemicelluloses of aspen wood (Pópulus trémula) were obtained by oxidative delignification in an acetic acid-water-hydrogen peroxide medium at temperatures of 70-100 °C and a process time of 1-4 h. The maximum polysaccharide yield of up to 9.68 wt% was reported. The composition and structure of the hemicelluloses were studied using a complex of physicochemical methods: gas and gel permeation chromatography, Fourier-transform infrared spectroscopy, 2D nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. The xylose, mannose, galactose, and glucose monomer units were identified in the hemicelluloses by gas chromatography. The weight average molecular weight Mw of the products determined by gel permeation chromatography was found to range within 8932-33,142 g/mol. The reported Fourier-transform spectra of the hemicelluloses contain all the bands characteristic of heteropolysaccharides; a weak lignin absorption signal in the spectra at 1500-1510 cm-1 is attributed to a minor content of phenolic fragments in the structure of the obtained hemicelluloses. The use of thermogravimetric analysis established that the hemicelluloses isolated from aspen wood are resistant against heating to temperatures of up to 90-100 °C and, upon further heating up to 400 °C, start destructing at an increasing rate. The antioxidant activity of the hemicelluloses was examined using the compounds that mimic free radicals (1,1-diphenyl-2-picrylhydrazyl) and hydroxyl radicals (salicylic acid). It was found that the activity of all polysaccharides in neutralizing DPPH and hydroxyl radicals is lower than the absorption capacity of vitamin C at all the tested concentrations (0.5, 2, and 5 mg/mL) and attains 81.7 and 82.9%, respectively.

Oxidative delignification: The roles of lignin reactivity and accessibility

This study compared oxidative delignification of birch kraft pulp fibers to pulp fibers from acid hydrotropic fractionation (AHF) using p-toluenesulfonic acid (p-TsOH). Under oxygen delignification at 20% consistency, AHF pulps with lower hemicellulose content showed higher delignification than kraft pulps with similar lignin content despite its residual lignin (cellulosic enzymatic lignin, CEL) being less reactive with fewer β-O-4 ether aryl linkages based on 2D13C-1H nuclear magnetic resonance (NMR) spectroscopy. The water retention value (WRV) of AHF pulp fibers, a measure of fiber accessibility to water or oxidative chemicals, was substantially greater than that of kraft pulp fibers. Similar comparison of various AHF pulps further suggested that fibers with lower hemicellulose content were easier to delignify (bleach) despite having more lignin with lower reactivity (fewer β-O-4 linkages). Additionally, the present study also indicated that oxygen delignification was more effective at high fiber consistency, which can be attributed to thinner water films on the fiber surfaces at higher fiber loadings. These results indicated that mass transfer was the rate controlling process in oxidative delignification of wood fibers.

Molecular Characteristics and Antioxidant Activity of Spruce (Picea abies) Hemicelluloses Isolated by Catalytic Oxidative Delignification.

Spruce (Picea abies) wood hemicelluloses have been obtained by the noncatalytic and catalytic oxidative delignification in the acetic acid-water-hydrogen peroxide medium in a processing time of 3–4 h and temperatures of 90–100 °C. In the catalytic process, the H2SO4, MnSO4, TiO2, and (NH4)6Mo7O24 catalysts have been used. A polysaccharide yield of up to 11.7 wt% has been found. The hemicellulose composition and structure have been studied by a complex of physicochemical methods, including gas and gel permeation chromatography, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The galactose:mannose:glucose:arabinose:xylose monomeric units in a ratio of 5:3:2:1:1 have been identified in the hemicelluloses by gas chromatography. Using gel permeation chromatography, the weight average molar mass Mw of hemicelluloses has been found to attain 47,654 g/mol in noncatalytic delignification and up to 42,793 g/mol in catalytic delignification. Based on the same technique, a method for determining the α and k parameters of the Mark–Kuhn–Houwink equation for hemicelluloses has been developed; it has been established that these parameters change between 0.33–1.01 and 1.57–472.17, respectively, depending on the catalyst concentration and process temperature and time. Moreover, the FTIR spectra of the hemicellulose samples contain all the bands characteristic of heteropolysaccharides, specifically, 1069 cm−1 (C–O–C and C–O–H), 1738 cm−1 (ester C=O), 1375 cm−1 (–C–CH3), 1243 cm−1 (–C–O–), etc. It has been determined by the thermogravimetric analysis that the hemicelluloses isolated from spruce wood are resistant to heating to temperatures of up to ~100 °C and, upon further heating, start destructing at an increasing rate. The antioxidant activity of the hemicelluloses has been examined using the compounds simulating the 2,2-diphenyl-2-picrylhydrazyl free radicals.

Insight into the negative effects of lignin on enzymatic hydrolysis of cellulose for biofuel production via selective oxidative delignification and inhibitive actions of phenolic model compounds

Oxidative pretreatment of wheat straw with sodium chloride has been used for selective delignification to obtain ideal samples to understand the negative effects of lignin on cellulose accessibility of lignocellulosic biomass. Strong interactive effects has been found between hemicellulose and lignin. To achieve a high enzymatic glucan conversion (EGC) (>80% with 20 FPU/g solid) in the case of high xylan content (25–30%), a moderate degree of delignification (56.3%) with relatively low lignin content (11.9%) is necessary; while in the case of low xylan content (2.6–3.9%), slight removal of lignin by oxidative treatment can well increase cellulose digestibility with a final EGC reaching 90% even that the residual lignin content is as high as 30.9%. Delignification greatly modifies substrate surface morphology with deformation, fracture of cell wall layers and even disappearance of middle lamella. Oxidation also modifies the functional groups and surface properties of lignin, leading to reduction in the inhibitive effects. Phenolic hydroxyl group (Ph-OH) in p-hydroxyphenyl unit has been found to show the strongest inhibition to filter paper activity of cellulase cocktail. Ph-OH exerts stronger inhibition to β-glucosidase than to the endo- and exo-glucanases. Hydrogen bonding and electrostatic interaction are primarily responsible for the inhibitive action of Ph-OH.

Effect of Steam and Bleaching Treatment on the Characteristics of Pineapple Leaves Fibre Derived Cellulose

Pineapple leaf fibres (PALF) is one of the abundant residues generated from pineapple plantation. The residues are left on the plantation for nutrient cycling or burning, and this circumstance leads to environmental issues. PALF has high cellulose content among other natural fibres. Cellulose is a reinforcing element that exists as whisker-like microfibrils and has a long-chain structure. In this study, cellulose produced from PALF was treated by steam and chemical treatment. The fibre was treated with steam at 121°C, a pressure of 21 psi for 30 or 60 min. Next, the steam-treated fibre was treated with 5 wt% sodium chlorite (NaClO2) solution with pH adjusted between 4 and 5 for 90 min. The condition was varied with three different temperatures, which were room temperature, 50, and 70°C. Then, the bleached fibre was treated with 5 wt% sodium hydroxide (NaOH) at room temperature for 3 h. After the treatments, the fibre was analysed for its thermal stability, morphology, and chemical composition. Cellulose obtained from the treatment condition of steam for 60 min, bleaching at 70°C, and alkali treatment at room temperature expressed the highest degradation temperature of 276°C at 20% weight loss, percentage of cellulose of 86% and lowest moisture content (8%) compared to others sample. It also had an excellent surface morphology with finest fibril disintegration. It showed longer steam treatment (60 min) degrading more hemicellulose; and bleaching treatment at high temperature (70°C), increasing the rate of oxidative delignification. In conclusion, the suggested treatment provides a simple but efficient method to isolate cellulose that can be used for various types of applications.

Deep Delignification of Woody Biomass by Repeated Mild Alkaline Treatments with Pressurized O2.

Delignification is essential in effective utilization of carbohydrates of lignocellulosic biomass. Characteristics of the delignification are important for the yield and property of the resulting carbohydrates. Oxidation with O2 of biomass in alkaline water can potentially produce high-purity cellulose at high yield. The present authors chose a Japanese cedar and investigated its oxidative delignification at 90 °C. The delignification selectivity was determined mainly by the chemical structures of lignin and cellulose. Treatment conditions, except for temperature, hardly changed the relationship between delignification rate and cellulose retention. During the treatment, dissolved lignin underwent chemical condensation in the aqueous phase. This “unfavorable” condensation consumed O2-derived active species, slowing down further delignification. Repeated short-time oxidation with renewal of alkaline water suppressed the condensation, enhancing the delignification. Repetition of 2-h treatments four times achieved 96% delignification, which was 8% higher than a single 8-h treatment at 130 °C.

Oil palm empty fruit bunch (OPEFB) (Elaeis guineensis Jacq.) cellulose conversion into levulinic acid using hierarchical Mn/ZSM-5 heterogeneous catalyst

Oil palm empty fruit bunch (OPEFB) is one of the potential biomasses containing cellulose that can be used as a source for renewable energy. However, the cellulose is tightly connected with lignin in lignocellulose system, which needs to be separated, so called delignification, before being used. To investigate the effect of delignification on conversion reaction, the pretreated cellulose was treated with different delignification processes, i.e. alkali delignification using 10 % NaOH (w/v) and oxidative delignification using 2 % NaOCl (v/v). Furthermore, cellulose conversion from OPEFB into levulinic acid was performed using hierarchical Mn/ZSM-5 (Mn/Hi_ZSM-5) heterogeneous catalyst with various reaction times and concentration of H3PO4. The cellulose conversion into levulinic acid in the absence of catalyst was also conducted to study the effect of catalyst. High Performance Liquid Chromatography (HPLC) analysis showed the highest cellulose conversion into levulinic acid was achieved using cellulose from alkali delignification (28.08 % yield) in optimum reaction condition of 40 % H3PO4 (v/v), 30 % H2O2 (v/v), and 0.1 g of Mn/Hi_ZSM-5 at 100 °C for 10 h. Mn/Hi_ZSM-5 revealed good selectivity for levulinic acid with the absence of 5-HMF as an intermediate compound in conversion reaction.

Enhancing saccharification of Agave tequilana bagasse by oxidative delignification and enzymatic synergism for the production of hydrogen and methane

Agave tequilana bagasse is a suitable lignocellulosic residue for energy production. However, the presence of lignin and the heterogeneous structure of hemicellulose may hinder the availability of polysaccharides. In this work, the pretreatment of A. tequilana bagasse with alkaline hydrogen peroxide (AHP) followed by enzymatic saccharification with hemicellulases and cellulases was assessed for the removal of lignin and extraction of fermentable sugars, respectively. Results of the AHP pretreatment indicated that it is possible to attain up to 97% delignification and recover 88% of cellulose and hemicellulose after only 1.5 h of treatment. Regarding the saccharification process, the total sugar yield and productivity were both increased by 2-fold using an enzymatic mixture (cellulases + hemicellulases) compared to single enzyme hydrolysis (cellulases), evidencing synergism. Further evaluation of the hydrolyzates as substrate for hydrogen and methane production, resulted in yields 1.5 and 3.6-times (215.14 ± 13 L H2 and 393.4 ± 13 L CH4 per kg bagasse, respectively) superior to those obtained with hydrolyzates of non-pretreated bagasse processed with a single enzyme. Overall, using AHP pretreatment and subsequent hydrolysis with enzymatic mixtures improves the saccharification of A. tequilana bagasse enhancing the production of hydrogen and methane.

Electrochemical Oxidation/Modification of Lignin Mediated By Aminoxyl Radicals

Lignin is an abundant biopolymer with an aromatic backbone and offers a bio-based source of aromatic commodity chemicals upon depolymerization.[i] Oxidation methods are widely used for the deconstruction of lignin; successful examples include oxidative delignification in the pulp and paper industry and breakdown of lignin by oxidative fungal enzymes. The hydroxyl functional groups of lignin are particularly susceptible to oxidation. Building on these concepts, our group recently began exploring the controlled oxidation of lignin hydroxyl groups as a means to facilitate lignin depolymerization.[ii] We previously reported an aerobic oxidation method that employs aminoxyl radicals, such as TEMPO, as the catalyst. Acid treatment of the resulting oxidized lignin lead to depolymerization, affording up to 60 wt% yield of low-molecular-weight aromatic compounds.[iii]Aminoxyl radicals undergo facile electron transfer at the electrode surface to generate an oxoammonium species that is reactive towards hydroxyl oxidation (Figure 1a). This facile electron transfer provides a foundation for selective oxidation of hydroxyl groups under electrochemical conditions.[iv] This talk will highlight some of our advances in the use of aminoxyl radicals as mediators for chemoselective oxidation of hydroxyl groups in the structure of lignin. The beta-O-4 linkage (Figure 1b) is the most prevalent linkage in the structure of lignin that includes hydroxyl functional groups and was used as the model for this study. Nitroxyl-mediated electrochemical oxidation methods enable selective and quantitative conversion of the primary hydroxyl group of lignin and beta-O-4 model compounds to the corresponding carboxylate under mildly basic conditions. The modified lignin has a high loading of carboxylic acids, which enhance its water solubility relative to native lignin. The sodium salt of the modified lignin behaves as a polyacid polyelectrolyte in aqueous solution. Acid treatment of the oxidized lignin model affords approximately 30 wt% of monomeric aromatic compounds. [i]. Upton, B. M.; Kasko, A. M. Chem. Rev., 2016, 116, 2275. [ii]. Rahimi, A.; Azarpira, A.; Kim, H.; Ralph, J.; Stahl, S. S. J. Am. Chem. Soc. 2013, 135, 6415. [iii]. Rahimi, A.; Ulbrich, A.; Coon, J. J.; Stahl S. S. Nature 2014, 515, 249. [iv]. Rafiee, M; Miles, K. C.; Stahl, S. S. J. Am. Chem. Soc. 2015, 137, 14751. Figure 1

Evaluation, applicability and optimization of advanced oxidation process for pretreatment of rice straw and its effect on cellulose digestibility

Abstract Rice straw, a renewable feedstock, is recalcitrant and its degree of polymerization makes pretreatment obligatory for subsequent bioconversion. The present study explores an advanced oxidation process i.e. Alkaline Wet Air Oxidation (AWAO) as a pretreatment for rice straw and scrutinizes the effect of operation parameters on cellulose recovery, hemicellulose solubilization and lignin removal through Response Surface Methodology (RSM). AWAO resulted in 68–90% cellulose recovery, 67–87% hemicellulose solubilization and 32–66% lignin removal while generating limited inhibitors. AWAO caused oxidative delignification, hemicellulose deacetylation and cleavage of carbohydrate-lignin linkages as revealed by FT-IR, thereby improving cellulose accessibility indicated by 42–89% enzymatic cellulose convertibility (%ECC) or % cellulose conversion. The findings of the present study indicate minimization of chemical input and absence of potent inhibitors in the liquor which collectively implies reduction in freshwater requirements, minimization of waste generation and its treatment cost.

CATALYTIC OZONATION OF HARDWOOD PULP

First influence of variable valence metal ions on the ozonation process of hardwood pulp was investigated. The oxidative delignification and destruction process of hardwood pulp by ozone treatment of water suspension and ozone treatment in gas phase in the presence of ions Mn2+, Cr3+ и Fe2 by UV-spectrophotometry, IR-spectroscopy and viscosimetry methods was studied. It was showed, that addition of variable valence metal ions into the reaction mixture increased delignification depth in 1,1–1,6 times (Fe2+– Cr3+) under intensive pulp suspension mixing, and in 2,3 times (Mn2+) at insufficient mixing conditions (ozone-air mixture bubbling). The higher value of delignification depth was reached in the presence of variable valence metal ions – 39,8%. It was obtained that delignification depth was higher under the gas phase ozonation, than under the pulp suspension ozone treatment: till 62,1% without catalyst and till 67,5% in the presence of Mn2+ ions. Cellulose degradation increased with ions Mn2+, Cr3+ and Fe2+ concentration rising in the reaction mixture. Degree of polymerization varied from 1050 to 650, 720 and 800, respectively. IR-spectres of ozonated pulp are studied.

Kinetic studies and optimization of abies wood fractionation by hydrogen peroxide under mild conditions with TiO2 catalyst

The kinetic study of abies wood delignification by H2O2 in the medium acetic acid–water was first carried out in the presence of TiO2 catalyst under mild conditions: temperatures 70–100 °C, atmospheric pressure. The oxidative delignification process is described satisfactory by the first order equation in all temperature range. The rate constants varied between 0.80 and 12.3 × 10−3 min−1 and the activation energy was near 81 ± 0.21 kJ mol−1. The optimal parameters of the delignification process, providing the effective fractionation of abies wood on microcrystalline cellulose and soluble lignin, were established by experimental and numerical methods.

Effective alkaline metal-catalyzed oxidative delignification of hybrid poplar.

BackgroundStrategies to improve copper-catalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment of hybrid poplar were investigated. These improvements included a combination of increasing hydrolysis yields, while simultaneously decreasing process inputs through (i) more efficient utilization of H2O2 and (ii) the addition of an alkaline extraction step prior to the metal-catalyzed AHP pretreatment. We hypothesized that utilizing this improved process could substantially lower the chemical inputs needed during pretreatment.ResultsHybrid poplar was pretreated utilizing a modified process in which an alkaline extraction step was incorporated prior to the Cu-AHP treatment step and H2O2 was added batch-wise over the course of 10 h. Our results revealed that the alkaline pre-extraction step improved both lignin and xylan solubilization, which ultimately led to improved glucose (86 %) and xylose (95 %) yields following enzymatic hydrolysis. An increase in the lignin solubilization was also observed with fed-batch H2O2 addition relative to batch-only addition, which again resulted in increased glucose and xylose yields (77 and 93 % versus 63 and 74 %, respectively). Importantly, combining these strategies led to significantly improved sugar yields (96 % glucose and 94 % xylose) following enzymatic hydrolysis. In addition, we found that we could substantially lower the chemical inputs (enzyme, H2O2, and catalyst), while still maintaining high product yields utilizing the improved Cu-AHP process. This pretreatment also provided a relatively pure lignin stream consisting of ≥90 % Klason lignin and only 3 % xylan and 2 % ash following precipitation. Two-dimensional heteronuclear single-quantum coherence (2D HSQC) NMR and size-exclusion chromatography demonstrated that the solubilized lignin was high molecular weight (Mw ≈ 22,000 Da) and only slightly oxidized relative to lignin from untreated poplar.ConclusionsThis study demonstrated that the fed-batch, two-stage Cu-AHP pretreatment process was effective in pretreating hybrid poplar for its conversion into fermentable sugars. Results showed sugar yields near the theoretical maximum were achieved from enzymatically hydrolyzed hybrid poplar by incorporating an alkaline extraction step prior to pretreatment and by efficiently utilizing H2O2 during the Cu-AHP process. Significantly, this study reports high sugar yields from woody biomass treated with an AHP pretreatment under mild reaction conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0442-0) contains supplementary material, which is available to authorized users.

Surface modifications of agrowaste biomass for Hg(II) and MeHg(II) removal from aqueous solution, oilfield produced water and natural gas condensate

The removal process of Hg(II) and MeHg(II) from aqueous solution by surface modified agrowaste biomass (AWB) was studied. The surface modifications were carried out by methods of mercerization, oxidative delignification, acid treatment, and biological treatment using laccase. The modifications promoted disruption of AWB structural surfaces and thus changed their physical and chemical properties as well as Hg(II) and MeHg(II) adsorption performances. The adsorption efficiency of Hg(II) was higher than MeHg(II) for all AWB adsorbents. The adsorption capacity of Hg(II) and MeHg(II) for AWB-Pure was 0.97 and 0.17 mmol/g, respectively. The highest adsorption capacity of Hg(II) and MeHg(II) was respectively observed for the AWB-Laccase (0.98 ± 0.04 mmol/g) and AWB-NaOCl/NaOH (0.40 ± 0.07 mmol/g). The adsorption selectivity of modified AWB adsorbents towards Hg(II) and MeHg(II) studied using oilfield produced water and natural gas condensate samples was found to be lower as compared to AWB-Pure, but higher selectivity was observed for other metals. The renewability studies show that the pure and modified AWB adsorbents had similar adsorption performance characteristics. The high Hg(II) adsorption efficiency (η > 90 %) was observed up to the third adsorption cycle, while for the MeHg(II), it decreased after each adsorption–desorption cycle.

Cell wall-associated transition metals improve alkaline-oxidative pretreatment in diverse hardwoods

Cell wall-associated, redox-active transition metals play a critical role in the efficacy of oxidative delignification.

Pretreatment combining ultrasound and sodium percarbonate under mild conditions for efficient degradation of corn stover

Ultrasound (US) can be used to disrupt microcrystalline cellulose to give nanofibers via ultrasonic cavitation. Sodium percarbonate (SP), consisting of sodium carbonate and hydrogen peroxide, generates highly reactive radicals, which cause oxidative delignification. Here, we describe a novel pretreatment technique using a combination of US and SP (US–SP) for the efficient saccharification of cellulose and hemicellulose in lignocellulosic corn stover. Although US–SP pretreatment was conducted under mild condition (i.e., at room temperature and atmospheric pressure), the pretreatment greatly increased lignin removal and cellulose digestibility. We also determined the optimum US–SP treatment conditions, such as ultrasonic power output, pretreatment time, pretreatment temperature, and SP concentration for an efficient cellulose saccharification. Moreover, xylose could be effectively recovered from US–SP pretreated biomass without the formation of microbial inhibitor furfural.

Optimized methods for obtaining cellulose and cellulose sulfates from birch wood

The methods of obtaining cellulose and cellulose sulfates from birch wood based on the use of one-step catalytic delignification of wood by hydrogen peroxide in acetic acid–water medium were studied. The conditions of birch wood oxidative delignification by acetic acid/hydrogen peroxide mixtures in the presence of sulfuric acid catalyst were optimized in order to obtain an acceptable yield of cellulose product with low content of residual lignin. Cellulose extracted from birch wood by green method was used for preparation of cellulose sulfates in dioxane solution. The homogeneous sulfation of obtained cellulose by chlorosulfonic acid in dioxane allows to reduce the fragmentation of polymer and to synthesize cellulose sulfates with a finer and more homogeneous structure as compared to cellulose sulfates prepared by heterogeneous sulfation in harmful pyridine. Obtained samples of cellulose and cellulose sulfates were characterized by XRD, SEM, AFM, NMR, FTIR, Raman, XPS and chemical methods.

Использование растворимых продуктов окислительной каталитической делигнификации древесины в качестве связующих для получения топливных брикетов

Использование растворимых продуктов окислительной каталитической делигнификации древесины в качестве связующих для получения топливных брикетов

ChemInform Abstract: New Methods of Heterogeneous Catalysis for Lignocellulosic Biomass Conversion to Chemicals

AbstractReview: 54 refs.