Initial Cellulose Concentration Research Articles

Nanoprecipitation to produce hydrophobic cellulose nanospheres for water-in-oil Pickering emulsions

In recent years, there has been growing interest in replacing petroleum-based water-in-oil (W/O) emulsifiers with sustainable and less toxic natural materials. Pickering emulsifiers are considered well-suited candidates due to their high interfacial activity and the ability to form emulsions with long-term stability. However, only sporadic examples of natural materials have been considered as inverse Pickering emulsifiers. This study describes the synthesis of a series of hydrophobic cellulose nanospheres by bulk modification with acyl groups of different chain lengths followed by nanoprecipitation, and their application as inverse emulsifiers. Modification with acyl groups of longer chain length (C16, C18) afforded lower degrees of substitution, but resulted in greater thermal stability than groups with shorter acyl chains (C12, C14). Formation of nanospheres with low aspect ratios and narrow size distributions required low initial cellulose concentrations (< 1% w/v), high volumetric ratios of antisolvent to solvent (> 10:1), and slow addition rates (< 20 mL/h). The modified cellulose nanospheres were able to reduce the interfacial tension between water and hexane from 45.8 mN/m to 31.1 mN/m, with an effect that increased with the number of carbons in the added acyl chains. The stearate-modified nanospheres exhibited superhydrophobic behavior, showing a contact angle of 156° ± 4° with water, and demonstrated emulsification performance comparable to the commonly used molecular surfactant sorbitan stearate. Our findings suggest that hydrophobically modified cellulose nanospheres have the potential to be a bio-derived alternative to traditional molecular W/O emulsifiers.Graphical

Predicting Fine Root Decomposition from Functional Traits in 10 Temperate Tree Species

Decomposition of plant roots and their related fungal mutualists is a fundamental process of ecosystem material cycles. Despite the fact that fine roots are the dominant source of soil organic carbon (SOC) storage, our understanding of the functional traits controlling fine root decomposition is still far from clear. In the present study, the decomposition of fine roots among four arbuscular mycorrhizal (AM) and six ectomycorrhizal (EM) species was studied in a temperate forest after 570 days of exposure. Our results showed that fine roots among AM species decomposed faster than EM species. Our findings further suggested that initial aluminum (Al) and manganese (Mn) concentrations were the best predictors for decomposition of fine roots among the traits that we measured. Initial cellulose concentration, carbon:nitrogen ratio (C:N), and lignin:N ratio were closely related to decomposition among AM species. In contrast, among EM species, initial phosphorus (P), calcium (Ca), and non–structural carbohydrate (NSC) concentrations were the best predictors of fine root decomposition. The initial concentrations of Na, Fe, NSC, cellulose, and hemicellulose were useful predictors of fine root decomposition across the 10 studied tree species.

Cumulative cellulolytic enzyme activities and initial litter quality in prediction of cellulose degradation in an alpine meadow of the eastern Tibetan Plateau

AbstractAimsPlant litter decomposition is a key ecosystem process that determines carbon and nutrient cycling in terrestrial ecosystems. As a main component of litter, cellulose is a vital energy source for the microbes associated with litter decomposition. The important role of cellulolytic enzymes in litter cellulose degradation is well understood, but seasonal patterns of cellulose degradation and whether cumulative enzyme activities and litter quality forecast cellulose degradation in an alpine meadow remain elusive, which limits our understanding of cellulose degradation in herbaceous plant litter.MethodsA two-year field litterbag experiment involving three dominant species (Ajuga ovalifolia, Festuca wallichanica, and Pedicularis roylei) was conducted in an alpine meadow of the eastern Tibetan Plateau to explore the seasonal patterns of cellulose degradation and how cumulative cellulolytic enzyme activities and initial litter quality impact cellulose degradation.Important findingsOur study demonstrates that cellulose degraded rapidly and exceeded 50% during the first year, which mainly occurred in the first growing season (31.9%–43.3%). At two years of decomposition, cellulose degradation was driven by cumulative endoglucanase (R2 = 0.70), cumulative cellobiohydrolase (R2 = 0.59) and cumulative 1,4-β-glucosidase (R2 = 0.57). In addition, the concentrations of cellulose, dissolved organic carbon, total phenol, lignin and lignin/N accounted for 52%–78% of the variation in cellulose degradation during the two years of decomposition. The best model for predicting cellulose degradation was the initial cellulose concentration (R2 = 0.78). The enzymatic efficiencies and the allocation of cellulolytic enzyme activities were different among species. The cellulolytic enzyme efficiencies were higher in the litter of F. wallichanica with relatively lower quality. For the complete cellulose degradation of the leaf litter, A. ovalifolia and F. wallichanica required 4-fold and 6.7-fold more endoglucanase activity, 3-fold and 4.5-fold more cellobiohydrolase activity and 1.2-fold and 1.4-fold more 1,4-β-glucosidase activity, respectively, than those required by P. roylei. Our results demonstrated that although microbial activity and litter quality both have significant impacts on cellulose degradation in an alpine meadow, using cellulose concentration to predict cellulose degradation is a good way to simplify the model of cellulose degradation and C cycling during litter decomposition.

Fabrication of milled cellulose particles-stabilized Pickering emulsions

Pickering emulsions stabilized by milled cellulose particles of the sizes ranging from 38 nm to 671 nm, which were prepared from a simple organic solvent -free media-milling process using cellulose powders with original sizes of 10–90 μm, have been successfully fabricated. The milled cellulose particles maintained their original rod-like shapes after the milling process. However, a notable decrease in the crystallinity of milled cellulose particles with the increase of milling time was verified by using X-ray diffraction. The effects of milling time, initial cellulose concentrations and oil/water ratios on the droplet sizes and stability of cellulose particles-stabilized Pickering emulsions were investigated. The milled cellulose particles were irreversibly adsorbed at the oil/water interface and formed stable emulsions with droplet size between 40 and 60 μm, which exhibited good stability over one-month storage. Milled cellulose stabilized emulsions also exhibited good stability against a wide range of pH (3, 5, 7, 9) and salt conditions (0.1–100 mM) with slight change in the droplet sizes. The rheological tests indicated the formation of gel network in the emulsions, which further promoted the emulsion stability. As sustainable biomolecules without negative impact on environment, cellulose particles processed through media-milling open opportunities for developing environmentally friendly new materials for emulsion stabilization.

Branch Wood Decomposition of Tree Species in a Deciduous Temperate Forest in Korea

Woody debris, which is supplied by branch litter, is an important component of forest ecosystems as it contains large quantities of organic matter and nutrients. We evaluated changes in branch wood dry weight and nutrient content of six common species (Fraxinus rhynchophylla, Pinus densiflora, Prunus sargentii, Quercus mongolica, Acer pseudosieboldianum, and Symplocos chinensis for. pilosa) in a deciduous temperate forest in Korea for 40 months. Branch wood disk samples 1.4–1.6 cm thick were cut, and mass loss was measured over time using the litterbag method. No significant differences in mass loss were recorded among the six tree species. Further, mass loss was negatively correlated with initial lignin concentration and positively correlated with both initial cellulose concentration and wood density for each species. Species with high wood cellulose content had high wood density while the lignin content in wood was relatively low. Accordingly, cellulose contributed to wood density, creating a relatively lower lignin content, and the decreased lignin concentration increased the wood decomposition rate.

Simultaneous saccharification and fermentation of cactus pear biomass—evaluation of using different pretreatments

Lignocellulosic biomasses of two species of cactus pear (Opuntia ficus indica and Nopalea cochenillifera) were tested for the production of ethanol. Their ability to grow in water-stressed regions makes them eligible for reducing the production cost of biofuels in drought regions. The biomass was pretreated using three different strategies: alkaline hydrogen peroxide, alkaline using NaOH, and acid using H2SO4 followed by alkaline delignification with NaOH. Analyses of the composition, crystallinity, and enzymatic hydrolysis were performed on the material before and after pretreatment. An experimental design was used to evaluate the influence of temperature and initial cellulose concentration on the process of simultaneous saccharification and fermentation (SSF) using the pretreated material, which showed the best performance in previous tests, and two strains of Saccharomyces cerevisiae (PE-2 and LNF CA-11). Biomass characterization showed a content of 31.55% cellulose, 17.12% hemicelluloses, and 10.25% lignins for N. cochenillifera and 34.86% cellulose, 19.97% hemicelluloses, and 15.72% lignins for O. ficus indica. The alkaline pretreatment provided the best enzymatic saccharification yields. The SSF experiments resulted in the greatest cellulose-to-ethanol yields using strain PE-2 with the pretreated N. cochenillifera (93.81%) at 40°C and an initial cellulose concentration of 4%. N. cochenillifera showed better yields than O. ficus indica, and the PE-2 strain performed better than CA-11. These results suggest a good potential for cactus pear cladodes in the production of cellulosic ethanol.

Effects of cellulose concentrations on the syntrophic interactions between Clostridium cellulovorans 743B and Rhodopseudomonas palustris CGA009 in coculture fermentation for biohydrogen production

The integration of dark and photo fermentation is a promising strategy to enhance biohydrogen productivity and substrate utilization, and therefore can be adopted to advance the development of industrial biohydrogen production. However, the mutualistic interactions between dark fermentative and purple non-sulfur photosynthetic microorganisms remain poorly understood due to the challenges of incorporating two physiologically different bacteria in one integrated fermentation system. In this work, an experimentally and genetically tractable model combining the cellulose-degrading bacterium Clostridium cellulovorans 743B and photosynthetic bacterium Rhodopseudomonas palustris CGA009 was successfully established. The responses of this coculture system to different cellulose concentrations were characterized. At all four levels of initial cellulose concentrations (2, 3, 4 or 5 g/L), the hydrogen productivity and cellulose degradation of cocultures were all significantly enhanced to varying extents in comparison to monocultures. The mechanism of the beneficial interaction was due to consumption of volatile fatty acids by R. palustris, which in turn balanced the pH to increase cellulose consumption by C. cellulovorans. Overall, the results demonstrated that the mutualism between C. cellulovorans and R. palustris could lead to a more efficient biohydrogen production process, thus making the pairing of these two strains a suitable model for further study on syntrophic interactions.

Cellulose Hydrolysis in Acidified LiBr Molten Salt Hydrate Media

We screened nine acidified molten salt hydrates (solutions with water to salt molar ratio equal or less than the coordination number of the cation) as reaction media for cellulose hydrolysis, and we found that cellulose can be efficiently hydrolyzed in LiBr acidified MSH under mild conditions (>90% yield to water-soluble products in 0.05 M H2SO4 at 85 °C for 30 min). The effect of various factors (temperature as well as acid and initial cellulose concentrations) on the kinetics of hydrolysis reaction was also investigated. At the lowest temperatures examined (70 and 85 °C) low amounts of degradation products have been observed, and glucose appears to be in equilibrium with its dimers and possibly other oligomers. Higher temperatures (100–115 °C) enhanced the formation of degradation products (organic acids and humins). Analysis of the kinetic data indicate that hydrolysis rates are first order in cellulose and in H2SO4 concentration, and the initial hydrolysis rates have an apparent activation energy ∼123...

Kinetics of Formic Acid-catalyzed Cellulose Hydrolysis

Hydrolysis is a reaction to produce sugars from lignocellulosic raw materials for biochemical production. The present study elucidates the hydrolysis of cellulose and formation of glucose decomposition products catalyzed by 5% to 20% (w/w) formic acid at 180 to 220 °C with an initial cellulose concentration of 10 to 100 g/L. Microcrystalline cellulose was used as a model compound. The experimental findings indicated that cellulose hydrolysis follows first-order kinetics in formic acid. A side reaction from cellulose to non-glucose products was required to explain the experimental results. A kinetic model was developed for the hydrolysis of microcrystalline cellulose in formic acid, based on a rate constant expression in accordance with the specific acid catalysis. The model showed good agreement with the experimental data. This study demonstrates how kinetic parameters can be fitted in a case-specific manner for the hydrolysis part of the kinetic model, while the well-established glucose decomposition model is utilized directly from literature.

Synthesis, isolation and characterization of methyl levulinate from cellulose catalyzed by extremely low concentration acid

A direct synthesis of methyl levulinate from cellulose alcoholysis in methanol medium under mild condition (180–210 °C) catalyzed by extremely low concentration sulfuric acid (≤0.01 mol/L) and the product isolation were developed in this study. Effects of different process variables towards the catalytic performance were performed as a function of reaction time. The results indicated that sulfuric acid concentration, temperature and initial cellulose concentration had significant effects on the synthesis of methyl levulinate. An optimized yield of around 50% was achieved at 210 °C for 120 min with sulfuric acid concentration of 0.01 mol/L and initial cellulose concentration below 100 g/L. The resulting product mixture was isolated by a distillation technique that combines an atmospheric distillation with a vacuum distillation where n-dodecane was added to help distill the heavy fraction. The light fraction including mainly methanol could be reused as the reaction medium without any substantial change in the yield of methyl levulinate. The chemical composition and structural of lower heavy fraction were characterized by GC/MS, FTIR, 1H-NMR and 13C-NMR techniques. Methyl levulinate was found to be a major ingredient of lower heavy fraction with the content over 96%. This pathway is efficient, environmentally benign and economical for the production of pure levulinate esters from cellulose.

Continuous Cellulosic Bioethanol Fermentation by Cyclic Fed-Batch Cocultivation

Cocultivation of cellulolytic and saccharolytic microbial populations is a promising strategy to improve bioethanol production from the fermentation of recalcitrant cellulosic materials. Earlier studies have demonstrated the effectiveness of cocultivation in enhancing ethanolic fermentation of cellulose in batch fermentation. To further enhance process efficiency, a semicontinuous cyclic fed-batch fermentor configuration was evaluated for its potential in enhancing the efficiency of cellulose fermentation using cocultivation. Cocultures of cellulolytic Clostridium thermocellum LQRI and saccharolytic Thermoanaerobacter pseudethanolicus strain X514 were tested in the semicontinuous fermentor as a model system. Initial cellulose concentration and pH were identified as the key process parameters controlling cellulose fermentation performance in the fixed-volume cyclic fed-batch coculture system. At an initial cellulose concentration of 40 g liter(-1), the concentration of ethanol produced with pH control was 4.5-fold higher than that without pH control. It was also found that efficient cellulosic bioethanol production by cocultivation was sustained in the semicontinuous configuration, with bioethanol production reaching 474 mM in 96 h with an initial cellulose concentration of 80 g liter(-1) and pH controlled at 6.5 to 6.8. These results suggested the advantages of the cyclic fed-batch process for cellulosic bioethanol fermentation by the cocultures.

Power generation from cellulose using mixed and pure cultures of cellulose-degrading bacteria in a microbial fuel cell

Microbial fuel cells (MFCs) have been used to generate electricity from various organic compounds such as acetate, glucose, and lactate. We demonstrate here that electricity can be produced in an MFC using cellulose as the electron donor source. Tests were conducted using two-chambered MFCs, the anode medium was inoculated with mixed or pure culture of cellulose-degrading bacteria Nocardiopsis sp. KNU (S strain) or Streptomyces enissocaesilis KNU (K strain), and the catholyte in the cathode compartment was 50mM ferricyanide as catholyte. The power density for the mixed culture was 0.188mW (188mW/m2) at a current of 0.5mA when 1g/L cellulose was used. However, the power density decreased as the cellulose concentration in the anode compartment decreased. The columbic efficiencies (CEs) ranged from 41.5 to 33.4%, corresponding to an initial cellulose concentration of 0.1–1.0g/L. For the pure culture, cellobioase enzyme was added to increase the conversion of cellulose to simple sugars, since electricity production is very low. The power densities for S and K strain pure cultures with cellobioase were 162mW/m2 and 145mW/m2, respectively. Cyclic voltammetry (CV) experiments showed the presence of peaks at 380, 500, and 720mV vs. Ag/AgCl for the mixed bacterial culture, indicating its electrochemical activity without an external mediator. Furthermore, this MFC system employs a unique microbial ecology in which both the electron donor (cellulose) and the electron acceptor (carbon paper) are insoluble.

One-pot preparation of methyl levulinate from catalytic alcoholysis of cellulose in near-critical methanol

One-pot preparation of methyl levulinate (MLA) from cellulose in near-critical methanol was studied. Acids containing SO3H group were proven to be effective catalysts for the production of MLA from cellulose’s catalytic alcoholysis. The effects of different reaction conditions, such as an initial cellulose concentration of 10–30g/L, a temperature range from 170 to 190°C, and a sulfuric acid concentration of 0.01–0.03mol/L, on the production of MLA were investigated. The results showed the reaction temperature and acid concentration significantly affected the process of cellulose alcoholysis and the yield of MLA. A high yield of up to 55% MLA was achieved at 190°C for 5h, using 0.02mol/L H2SO4 as a catalyst.

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

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.

Cellulose aerogels prepared from cellulose/AmimCl solutions

Cellulose aerogel materials were prepared by combining dissolving cellulose in an ionic liquid, 1-allyl-3- methylimidazolium chloride (AmimCl), and drying in supercritical CO2. The rheological properties of the cellulose solutions of different concentrations and their gels regenerated in different coagulation baths were studied. The porous structure and morphology of cellulose aerogels were found to be affected by cellulose concentration and nature of the coagulation bath. With increasing initial cellulose concentration, the porous structure of cellulose aerogels became more dense and uniform, leading to the gradual decrease of the specific surface area. Further, it was also observed that, both viscosity and the polarity of coagulation bath affected the structure of cellulose aerogels. High specific surface area cellulose aerogel materials could be prepared by controlling the experimental conditions. The obtained cellulose aerogels had relatively high char yield at elevated temperature, which makes them potential precursors for fabrication of novel mesoporous carbon materials.

Enhancement of solubilization rate of cellulose in anaerobic digestion and its drawbacks

Hydrolysis is widely acknowledged as the rate-limiting step in anaerobic digestion of solid cellulose to biogas (methane), and pretreatment is generally considered to facilitate the process. However, few studies have investigated how such pretreatment may affect the rest of this complex process. The present study compared the solubilization rate in anaerobic digestion of cotton linter (high crystalline cellulose), with that of regenerated cellulose (amorphous cellulose), using pretreatment with NMMO. Batch digestions were performed, with the initial cellulose concentrations ranging between 5 and 40 g/l, and during 30 days of incubation, biogas and VFAs production as well as pH and COD changes were measured. The lag time before digestion started was longer for the high crystalline cellulose than for the amorphous one. The maximum solubilization rates of treated cellulose were 842 and 517 mg sCOD/g cCOD/day at the initial cellulose concentration of 5 and 30 g/l, respectively, while the solubilization rate of untreated cellulose never exceeded 417 mg sCOD/g cCOD/day. The difference between the two cellulose types was a direct result of the high rate of hydrolysis inhibiting the acetogenesis/methanogenesis microorganisms, a drawback to the rest of the process.

Hydrochloric acid‐catalyzed levulinic acid formation from cellulose: data and kinetic model to maximize yields

AbstractIn this study, the kinetics of the acid catalyzed hydrolysis of microcrystalline cellulose (Avicel PH101) to levulinic (LA) and formic (FA) acids was investigated in a batch reactor over the following range of conditions: 160–200°C, hydrochloric acid concentrations of 0.309–0.927 M (11.3–33.8 g/l), cellulose concentrations of 49.8–149 mM (8.06–24.1 g/l), and residence times of 0–50 min. The maximum LA yield of around 60% of theoretical was achieved for an initial cellulose concentration of 99.6 mM, acid concentration 0.927 M, and 180–200°C. A mathematical model and its analytical solution were developed to predict conversion of cellulose to LA and FA through glucose and hydroxymethyl‐2‐furfural based on an irreversible pseudo‐first order reaction. Rate analysis of each reaction indicated that the rate‐controlling step shifted from LA formation initially to HMF formation later. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Aerocellulose based on all‐cellulose composites

AbstractNovel aerogels (or aerocellulose) based on all‐cellulose composites were prepared by partially dissolving microcrystalline cellulose (MCC) in an 8 wt % LiCl/DMAc solution. During this process, large MCC crystals and fiber fragments were progressively split into thinner crystals and cellulose fibrils. The extent of the transformation was controlled by using cellulose concentrations ranging from 5 to 20 wt % in the LiCl/DMAc solution. Cellulose gels were precipitated and then processed by freeze‐drying to maintain the openness of the structure. The density of aerocellulose increased with the initial cellulose concentration and ranged from 116 up to 350 kg m−3. Aerocellulose with relatively high mechanical properties were successfully produced. The flexural strength of the materials reached 8.1 MPa and their stiffness was as high as 280 MPa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Structure–property relationship of all-cellulose composites

Novel all-cellulose composite films were prepared by partly dissolving microcrystalline cellulose (MCC) powder in an 8% LiCl/DMAc solution. Cellulose solutions were precipitated and the resulting gels dried in a vacuum bag to produce films approximately 0.2–0.3 mm thick. X-ray diffraction (XRD) was used to characterise lateral crystal size and transmission electron microscopy (TEM) was employed to assess the morphology of the composites. During dissolution, the fibrous fragments of MCC were split into thinner cellulose fibrils and crystals were progressively broken down into thinner crystals. The composites were tested in tension and fracture surfaces were inspected by scanning electron microscopy (SEM). It was found that the mechanical properties and final morphology of all-cellulose composites was controlled by the rate of precipitation, initial cellulose concentration and dissolution time. The precipitation conditions were found to play a large role in the optimisation of the mechanical properties by limiting the amount of defects that were induced by differential shrinkage. All-cellulose composites were produced with a tensile strength up to 106 MPa and a tensile modulus up to 7.6 GPa.

Influence of initial cellulose concentration on the carbon flow distribution during batch fermentation by Clostridium thermocellum ATCC 27405

The objective of this research was to understand how carbon loading influences hydrogen (H(2)) synthesis and metabolic flow patterns in the thermophilic, cellulolytic bacterium, Clostridium thermocellum. C. thermocellum was cultivated in batch cultures with high (5 g L(-1)) and low (1 g L(-1)) initial concentrations of alpha-cellulose at 60 degrees C. The growth rate of C. thermocellum was 22% lower (0.15 h(-1)) in cultures with low-cellulose concentration compared with cultures with high-cellulose concentrations. Although substrate depletion coincided with the end of log-growth in low-cellulose cultures, the prime reason for growth arrest in high-cellulose cultures was not identified. Ethanol, acetate, and formate were the major soluble end-products with concomitant release of H(2) and CO(2) under both conditions. Lactate appeared during the late log phase in high-carbon cultures when pH dropped below 6.4 and became the major end-product in stationary phase. During the exponential phase of cell growth, significantly higher yields for H(2) and acetate (1.90 +/- 0.14 and 1.11 +/- 0.04 mol/mol glucose equivalent, respectively) were obtained from low-cellulose cultures compared to those from high-cellulose cultures. The maximum specific rate of H(2) production, 6.41 +/- 0.13 mmol H(2)/g dry cell/h, obtained during the exponential phase from low-carbon cultures was about 37% higher than that obtained from high-carbon cultures.