Showing papers on "Cellulose published in 2012"

Ionic liquid processing of cellulose

Abstract: Utilization of natural polymers has attracted increasing attention because of the consumption and over-exploitation of non-renewable resources, such as coal and oil. The development of green processing of cellulose, the most abundant biorenewable material on Earth, is urgent from the viewpoints of both sustainability and environmental protection. The discovery of the dissolution of cellulose in ionic liquids (ILs, salts which melt below 100 °C) provides new opportunities for the processing of this biopolymer, however, many fundamental and practical questions need to be answered in order to determine if this will ultimately be a green or sustainable strategy. In this critical review, the open fundamental questions regarding the interactions of cellulose with both the IL cations and anions in the dissolution process are discussed. Investigations have shown that the interactions between the anion and cellulose play an important role in the solvation of cellulose, however, opinions on the role of the cation are conflicting. Some researchers have concluded that the cations are hydrogen bonding to this biopolymer, while others suggest they are not. Our review of the available data has led us to urge the use of more chemical units of solubility, such as ‘g cellulose per mole of IL’ or ‘mol IL per mol hydroxyl in cellulose’ to provide more consistency in data reporting and more insight into the dissolution mechanism. This review will also assess the greenness and sustainability of IL processing of biomass, where it would seem that the choices of cation and anion are critical not only to the science of the dissolution, but to the ultimate ‘greenness’ of any process (142 references).

Dietary fibre in foods: a review

Abstract: Dietary fibre is that part of plant material in the diet which is resistant to enzymatic digestion which includes cellulose, noncellulosic polysaccharides such as hemicellulose, pectic substances, gums, mucilages and a non-carbohydrate component lignin. The diets rich in fibre such as cereals, nuts, fruits and vegetables have a positive effect on health since their consumption has been related to decreased incidence of several diseases. Dietary fibre can be used in various functional foods like bakery, drinks, beverages and meat products. Influence of different processing treatments (like extrusion-cooking, canning, grinding, boiling, frying) alters the physico- chemical properties of dietary fibre and improves their functionality. Dietary fibre can be determined by different methods, mainly by: enzymic gravimetric and enzymic—chemical methods. This paper presents the recent developments in the extraction, applications and functions of dietary fibre in different food products.

Novel enzymes for the degradation of cellulose

Abstract: The bulk terrestrial biomass resource in a future bio-economy will be lignocellulosic biomass, which is recalcitrant and challenging to process. Enzymatic conversion of polysaccharides in the lignocellulosic biomass will be a key technology in future biorefineries and this technology is currently the subject of intensive research. We describe recent developments in enzyme technology for conversion of cellulose, the most abundant, homogeneous and recalcitrant polysaccharide in lignocellulosic biomass. In particular, we focus on a recently discovered new type of enzymes currently classified as CBM33 and GH61 that catalyze oxidative cleavage of polysaccharides. These enzymes promote the efficiency of classical hydrolytic enzymes (cellulases) by acting on the surfaces of the insoluble substrate, where they introduce chain breaks in the polysaccharide chains, without the need of first “extracting” these chains from their crystalline matrix.

Biomass recalcitrance. Part I: the chemical compositions and physical structures affecting the enzymatic hydrolysis of lignocellulose

Abstract: Lignocellulosic biomass is recalcitrant to biodegradation due to the rigid and compact structure of plant cell wall The recalcitrance of biomass is mainly constructed by its chemical compositions that build a spatial network as a protective bulwark Generally, the factors affecting the accessibility of biomass cellulose can be divided into direct and indirect factors The direct factors refer to the accessible surface area, and the indirect factors include biomass structure-relevant factors (pore size and volume, particle size, and specific surface area), chemical compositions (lignin, hemicelluloses, and acetyl group), and cellulose structure-relevant factors (cellulose crystallinity and degree of polymerization) Pre-treatment is actually the process to alter indirect factors and improve direct factors thus enhancing the accessibility of cellulose In this review, we summarize the effects of chemical compositions and physical structures on the enzymatic digestibility of lignocellulosic biomass We suggest that future work should be focused on but not limited to the molecular mechanisms of biomass recalcitrance by investigating the microscale and nanoscale features as well as hydrogen bonds network of lignocellulosic biomass © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

How Does Plant Cell Wall Nanoscale Architecture Correlate with Enzymatic Digestibility

Abstract: Greater understanding of the mechanisms contributing to chemical and enzymatic solubilization of plant cell walls is critical for enabling cost-effective industrial conversion of cellulosic biomass to biofuels. Here, we report the use of correlative imaging in real time to assess the impact of pretreatment, as well as the resulting nanometer-scale changes in cell wall structure, upon subsequent digestion by two commercially relevant cellulase systems. We demonstrate that the small, noncomplexed fungal cellulases deconstruct cell walls using mechanisms that differ considerably from those of the larger, multienzyme complexes (cellulosomes). Furthermore, high-resolution measurement of the microfibrillar architecture of cell walls suggests that digestion is primarily facilitated by enabling enzyme access to the hydrophobic cellulose face. The data support the conclusion that ideal pretreatments should maximize lignin removal and minimize polysaccharide modification, thereby retaining the essentially native microfibrillar structure.

Nanocellulose: From Nature to High Performance Tailored Materials

Abstract: This specialist monograph provides an overview of the recent research on the fundamental and applied properties of nanoparticles extracted from cellulose, the most abundant polymer on the planet and an essential renewable resource. The author pioneered the use of cellulose nanoparticles (cellulose nanocrystals or whiskers and cellulose microfibrils) in nanocomposite applications. The book combines a general introduction to cellulose and basic techniques with more advanced chapters on specific properties and applications of nanocellulose.

Characterization of Hydrochars Produced by Hydrothermal Carbonization of Lignin, Cellulose, d-Xylose, and Wood Meal

Abstract: Hydrothermal carbonization of cellulose, lignin, d-xylose (substitute for hemicellulose), and wood meal (WM) was experimentally conducted between 225 and 265 °C, and the chemical and structural properties of the hydrochars were investigated. The hydrochar yield is between 45 and 60%, and the yield trend of the feedstock is lignin > WM > cellulose > d-xylose. The hydrochars seem stable below 300 °C, and aromatic structure is formed in all of these hydrochars. The C content, C recovery, energy recovery, ratio of C/O, and ratio of C/H in all of these hydrochars are among 63–75%, 80–87%, 78–89%, 2.3–4.1, and 12–15, respectively. The higher heating value (HHV) of the hydrochars is among 24–30 MJ/kg, with an increase of 45–91% compared with the corresponding feedstock. The carbonization mechanism is proposed, and furfural is found to be an important intermediate product during d-xylose hydrochar production, while lignin hydrothermal carbonization products are made of polyaromatic hydrochar and phenolic hydrocha...

Rationalizing cellulose (in)solubility: reviewing basic physicochemical aspects and role of hydrophobic interactions

Abstract: Despite being the world’s most abundant natural polymer and one of the most studied, cellulose is still challenging researchers. Cellulose is known to be insoluble in water and in many organic solvents, but can be dissolved in a number of solvents of intermediate properties, like N-methylmorpholine N-oxide and ionic liquids which, apparently, are not related. It can also be dissolved in water at extreme pHs, in particular if a cosolute of intermediate polarity is added. The insolubility in water is often referred to strong intermolecular hydrogen bonding between cellulose molecules. Revisiting some fundamental polymer physicochemical aspects (i.e. intermolecular interactions) a different picture is now revealed: cellulose is significantly amphiphilic and hydrophobic interactions are important to understand its solubility pattern. In this paper we try to provide a basis for developing novel solvents for cellulose based on a critical analysis of the intermolecular interactions involved and mechanisms of dissolution.

Oxidative cleavage of cellulose by fungal copper-dependent polysaccharide monooxygenases.

Abstract: Fungal-derived, copper-dependent polysaccharide monooxygenases (PMOs), formerly known as GH61 proteins, have recently been shown to catalyze the O2-dependent oxidative cleavage of recalcitrant polysaccharides. Different PMOs isolated from Neurospora crassa were found to generate oxidized cellodextrins modified at the reducing or nonreducing ends upon incubation with cellulose and cellobiose dehydrogenase. Here we show that the nonreducing end product formed by an N. crassa PMO is a 4-ketoaldose. Together with isotope labeling experiments, further support is provided for a mechanism involving oxygen insertion and subsequent elimination to break glycosidic bonds in crystalline cellulose.

Drying cellulose nanofibrils: in search of a suitable method

Abstract: Increasing research activity on cellulose nanofibril-based materials provides great opportunities for novel, scalable manufacturing approaches. Cellulose nanofibrils (CNFs) are typically processed as aqueous suspensions because of their hydrophilic nature. One of the major manufacturing challenges is to obtain dry CNFs while maintaining their nano-scale dimensions. Four methods were examined to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercritical drying (SCD), and (4) spray-drying (SD). The particle size and morphology of the CNFs were determined via dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and morphological analysis. SCD preserved the nano-scale dimensions of the cellulose nanofibrils. FD formed ribbon-like structures of the CNFs with nano-scale thicknesses. Width and length were observed in tens to hundreds of microns. SD formed particles with a size distribution ranging from nanometer to several microns. Spray-drying is proposed as a technically suitable manufacturing process to dry CNF suspensions.

Pretreatment and Lignocellulosic Chemistry

Abstract: Lignocellulosic materials such as wood, grass, and agricultural and forest residues are promising alternative energy resources that can be utilized to produce ethanol. The yield of ethanol production from native lignocellulosic material is relatively low due to its native recalcitrance, which is attributed to, in part, lignin content/structure, hemicelluloses, cellulose crystallinity, and other factors. Pretreatment of lignocellulosic materials is required to overcome this recalcitrance. The goal of pretreatment is to alter the physical features and chemical composition/structure of lignocellulosic materials, thus making cellulose more accessible to enzymatic hydrolysis for sugar conversion. Various pretreatment technologies to reduce recalcitrance and to increase sugar yield have been developed during the past two decades. This review examines the changes in lignocellulosic structure primarily in cellulose and hemicellulose during the most commonly applied pretreatment technologies including dilute acid pretreatment, hydrothermal pretreatment, and alkaline pretreatment.

Cellulose–Silica Nanocomposite Aerogels by In Situ Formation of Silica in Cellulose Gel

Abstract: Aerogels with their low density (0.004–0.500 gcm ), large internal surface area, and large open pores are promising candidates for various advanced applications. The utilization of inorganic aerogels, however, has been hampered by their poor mechanical properties. A prominent example is silica aerogel, which is prepared by an organic sol–gel process, and has unique features, such as ultralow density (the lightest silica aerogel has a density that is similar to the density of air, which is 0.00129 gcm ), near transparency, and low thermal conductivity. However, the extreme fragility of this aerogel necessitates its reinforcement for practical uses. A typical method is hybridization with organic polymers, such as polyurea, polyurethane, poly(methyl methacrylate), polyacrylonitrile, and polystyrene. Other candidates for the reinforcement of inorganic aerogels are insoluble polysaccharides, which are abundantly available and show wide varieties in structure and properties. The useful features of these compounds are hydrophilicity, biocompatibility, hydroxy reactivity, and reasonable thermal and mechanical stabilities. For example, nanofibrillar bacterial cellulose and microfibrillated cellulose gel have been proposed as templates for cobalt ferrite nanoparticles and titanium dioxide. While in the above-mentioned work native cellulose with cellulose I crystallinity was used, cellulose can be prepared as a hydrogel with cellulose II crystallinity through dissolution and coagulation. Some of the resulting aerogels have remarkable mechanical strength and light transmittance. They have high porosity with open structures and thus provide an effective substrate for the synthesis of metallic nanoparticles. To further utilize the regenerated cellulose gel, we herein attempted in situ synthesis of silica in cellulose gels. While a similar attempt has been reported, in which the cellulose gel was obtained from solution in N-methylmorpholine-N-oxide monohydrate, the development of the nanostructure (nitrogen BET surface area of 220–290 mg ) and the level of silica loading (less than 13% w/w) were rather limited. By using the aqueous alkali-based solvent, we obtained the cellulose aerogel with a surface area of 356 mg , and a silica loading of more than 60% w/w resulted in surface areas that exceeded 600 mg . We used the sol–gel synthesis method toward nanostructured silica, which typically starts from tetraethyl orthosilicate (TEOS). The resulting composite gels were dried with supercritical CO2 to give cellulose–silica aerogels with low density, moderate light transmittance, a large surface area, high mechanical integrity, and excellent heat insulation. This method can also lead to fabrication of silica-only aerogels through the removal of cellulose by calcination, that is, the use of cellulose aerogel as sacrificial template. Figure 1 shows the preparation of the aerogel. The cellulose hydrogel is a transparent material that has a water content of 92% and a porosity of 95%. The sol–gel process catalyzed by ammonia converts TEOS to SiO2, which is deposited on the cellulose network (Figure 1b). The composite is converted to an aerogel by drying with supercritical CO2 to maintain the porous structure (Figure 1c), thus resulting in a flexible and translucent cellulose–silica aerogel. Subsequent calcination removes the cellulose matrix to give a silica-only aerogel (Figure 1d and g). The cellulose aerogel is composed of regenerated cellulose fibrils, which are typically less than 10 nm wide (Figure 2a). The BET surface area of 356 mg 1 (determined by

Isolation of Cellulose-Degrading Bacteria and Determination of Their Cellulolytic Potential

Abstract: Eight isolates of cellulose-degrading bacteria (CDB) were isolated from four different invertebrates (termite, snail, caterpillar, and bookworm) by enriching the basal culture medium with filter paper as substrate for cellulose degradation. To indicate the cellulase activity of the organisms, diameter of clear zone around the colony and hydrolytic value on cellulose Congo Red agar media were measured. CDB 8 and CDB 10 exhibited the maximum zone of clearance around the colony with diameter of 45 and 50 mm and with the hydrolytic value of 9 and 9.8, respectively. The enzyme assays for two enzymes, filter paper cellulase (FPC), and cellulase (endoglucanase), were examined by methods recommended by the International Union of Pure and Applied Chemistry (IUPAC). The extracellular cellulase activities ranged from 0.012 to 0.196 IU/mL for FPC and 0.162 to 0.400 IU/mL for endoglucanase assay. All the cultures were also further tested for their capacity to degrade filter paper by gravimetric method. The maximum filter paper degradation percentage was estimated to be 65.7 for CDB 8. Selected bacterial isolates CDB 2, 7, 8, and 10 were co-cultured with Saccharomyces cerevisiae for simultaneous saccharification and fermentation. Ethanol production was positively tested after five days of incubation with acidified potassium dichromate.

One-pot catalytic hydrocracking of raw woody biomass into chemicals over supported carbide catalysts: simultaneous conversion of cellulose, hemicellulose and lignin

Abstract: Using raw lignocellulosic biomass as feedstock for sustainable production of chemicals is of great significance. Herein, we report the direct catalytic conversion of raw woody biomass into two groups of chemicals over a carbon supported Ni-W2C catalyst. The carbohydrate fraction in the woody biomass, i.e., cellulose and hemicellulose, were converted to ethylene glycol and other diols with a total yield of up to 75.6% (based on the amount of cellulose & hemicellulose), while the lignin component was converted selectively into monophenols with a yield of 46.5% (based on lignin). It was found that the chemical compositions and structures of different sources of lignocellulose exerted notable influence on the catalytic activity. The employment of small molecule alcohol as a solvent could increase the yields of phenols due to the high solubilities of lignin and hydrogen. Remarkably, synergistic effect in Ni-W2C/AC existed not only in the conversion of carbohydrate fractions, but also in lignin component degradation. For this reason, the cheap Ni-W2C/AC exhibited competitive activity in comparison with noble metal catalysts for the degradation of the wood lignin. Furthermore, the catalyst could be reused at least three times without the loss of activity. The direct conversion of the untreated lignocellulose drives our technology nearer to large-scale application for cost-efficient production of chemicals from biomass.

Production of levulinic acid from cellulose by hydrothermal decomposition combined with aqueous phase dehydration with a solid acid catalyst

Abstract: In this paper we introduce a process to produce levulinic acid from cellulose without the use of a homogeneous acid catalyst. The process consists of 2 reaction steps: (1) non-catalytic hydrothermal decomposition of cellulose at moderate temperatures (190–270 °C) to produce organic water-soluble compounds including glucose and HMF; (2) water-soluble compounds are further reacted with a solid acid catalyst at relatively low temperatures (160 °C) to produce levulinic acid and formic acid. Unreacted cellulose can be recycled back to the first reactor for further decomposition. The cellulose hydrothermally decomposes at high initial cellulose concentrations of 29 wt% while maintaining high selectivity towards water-soluble compounds, which are levulinic acid precursors. The maximum amounts of usable water soluble organics are produced at relatively higher temperatures and shorter residence times (220 °C and 30 min). Amberlyst 70 was used as a solid acid catalyst for conversion of the water soluble organics into HMF, levulinic acid and formic acid. Amberlyst 70 has comparable activity to HCl, with a slightly lower selectivity towards levulinic acid. The maximum obtainable yield of levulinic acid we obtained was 28% of the theoretical. This study lays the grounds for further optimization to produce levulinic acid from cellulose without using homogeneous acid catalysts.

Production of levulinic acid and gamma-valerolactone (GVL) from cellulose using GVL as a solvent in biphasic systems

Abstract: Cellulose deconstruction at 428 K was studied in biphasic reaction systems consisting of GVL and aqueous solutions containing HCl (0.1–1.25 M) and a solute, such as salt or sugar. This biphasic system achieves high yields of levulinic and formic acids (e.g., 70%), and leads to complete solubilization of cellulose. The GVL solvent extracts the majority of the levulinic acid (e.g., greater than 75%), which can subsequently be converted to GVL over a carbon-supported Ru–Sn catalyst. This approach for cellulose conversion eliminates the need to separate the final product from the solvent, because the GVL product is the solvent. In addition, this approach eliminates the deposition of solid humin species in the cellulose deconstruction reactor, allowing these species to be collected and used for other processing options.