Cellulose In Supercritical Water Research Articles

ReaxFF molecular dynamics simulation of nickel catalysed gasification of cellulose in supercritical water

Reactive force field (ReaxFF) molecular dynamic simulation was performed to elucidate the mechanism of Ni-catalysed supercritical water gasification of cellulose considering the effects of temperature and cellulose to water ratio. Simulations showed that Ni could decrease the activation energy of C–C and C–O bond cleavage, promoting the depolymerisation and ring-opening process of cellulose. The yields of gaseous products increase with the increasing temperature. H2 yield mainly depends on H free radical number, which can be generated from cellulose dehydrogenation and water splitting reactions. These two reactions were promoted on Ni surface, leading to an increase in H2 yield. In the presence of Ni catalyst, water plays a limited role in providing H free radicals to produce H2, while the hydrogen atoms in cellulose are the primary source of H2 generation. Meanwhile, reducing the concentration of O•H could enhance H2 production as the combination of O•H and H• is a H radical consumption process. Small organic fragments would be absorbed on the Ni surface, where they undergo deoxygenation via the cleavage of C–O bonds, resulting in a decrease in CO and CO2 yields. The increase in water mass fraction would promote the H2 yield as more H radical would be produced due to water splitting reaction. Moreover, the addition of water would occupy the Ni active sites and prevent the adsorption of organic fragments. These dissociative fragments are prone to produce more CO. The carbon deposition on the Ni surface results in the deactivation of the catalyst. Simulation results suggested that carbon deposition and permeation increase with increasing temperature. In contrast, the increase in water mass fraction can favour carbon elimination from the catalyst surface.

Hydrolysis of Cellulose in Supercritical Water: Quantum Simulation

Hydrolysis of Cellulose in Supercritical Water: Quantum Simulation

Hydrolysis of cellulose in supercritical water: reagent concentration as a selectivity factor

In this work, the influence of reagent concentration on hydrolysis reactions of cellulose in supercritical water was analyzed. The hydrolysis was carried out at 400 °C and 25 MPa with reaction times between 0.07 and 1.57 s and feeding cellulose concentrations between 5 and 20 % w/w (1.5–6 % w/w at reactor inlet). Also, a flash separator was used to separate vapor in the product stream in order to increase the final concentration. The best result for sugar production (79 % w/w) was obtained working with a cellulose concentration of 5 % w/w and 0.07-s reaction time. For glycolaldehyde production, the best result (42 % w/w) was obtained with a concentration of 20 % w/w and 1.57 s. The employment of a flash separator allowed reducing the water content by 50 %. It was also observed that by increasing the cellulose concentration in the reactor up to 4 % w/w, the hydrolysis took place with a similar kinetic as that in the heterogeneous media, thus reducing the conversion rate of cellulose in supercritical water.

Solubility of cellulose in supercritical water studied by molecular dynamics simulations.

The insolubility of cellulose in ambient water and most aqueous systems presents a major scientific and practical challenge. Intriguingly though, the dissolution of cellulose has been reported to occur in supercritical water. In this study, cellulose solubility in ambient and supercritical water of varying density (0.2, 0.7, and 1.0 g cm(-3)) was studied by atomistic molecular dynamics simulations using the CHARMM36 force field and TIP3P water. The Gibbs energy of dissolution was determined between a nanocrystal (4 × 4 × 20 anhydroglucose residues) and a fully dissociated state using the two-phase thermodynamics model. The analysis of Gibbs energy suggested that cellulose is soluble in supercritical water at each of the studied densities and that cellulose dissolution is typically driven by the entropy gain upon the chain dissociation while simultaneously hindered by the loss of solvent entropy. Chain dissociation caused density augmentation around the cellulose chains, which improved water-water bonding in low density supercritical water whereas the opposite occurred in ambient and high density supercritical water.

Hydrolysis of Microcrystalline Cellulose for Fermentable Hexose in Supercritical Water

AbstractEthanol extracted from cellulose has attracted considerable attention and previous studies have shown that hydrolysis is a key process for extraction of hexose from cellulose. This study describes the effects of solid-liquid ratio of cellulose/water on production of fermentable hexose by hydrolyzing microcrystalline cellulose in supercritical water (400°C) at different reaction times (6, 7, and 8 min). Thermal property of microcrystalline cellulose was characterized by thermogravimetric (TG) analysis. The concentration of fermentable hexose (glucose and fructose) was determined by using high-performance liquid chromatography (HPLC). Scanning electron microscopy (SEM) was carried out to observe the morphology of the hydrolysis residues. The results demonstrate that the concentration of hexose produced increased with increasing the solid-liquid ratio of cellulose/water in the hydrolysis process. The maximum concentration of fermentable hexose (37.98 g/L), corresponding to a hexose yield of 11.39%, ...

Supercritical hydrolysis of cellulose for oligosaccharide production in combined technology

A combined supercritical/subcritical technology was used as a pre-treatment and hydrolysis method for ethanol production from cellulose/lignocelluloses. In a batch study for supercritical hydrolysis, which is the primary step of the combined technology, 60 mg of microcrystalline cellulose in 2.5 ml deionized water was loaded into each reactor and heated in a salt bath at a selected temperature for a specified reaction time. Cellulose was quickly hydrolyzed to oligosaccharides, hexoses and other small molecular products at temperatures above the critical point of water. Temperature and reaction time were the two key parameters that determined the products of cellulose hydrolysis. The highest yield of oligosaccharides (approximately 40%) was obtained at optimum conditions of 380 °C and a reaction time of 16 s. The corresponding yield of hexoses was 24%, giving a maximum yield of hydrolysis products of approximately 63%. A complete decomposition of hydrolysis products occurred at higher temperatures and/or longer reaction times. A kinetic analysis was performed to explain the reaction of cellulose in supercritical water. The results presented here provide a rigid framework for the use of combined supercritical/subcritical technology in subsequent research.

Hydrogen production by catalytic gasification of cellulose in supercritical water

Cellulose, one of the important components of biomass, was gasified in supercritical water to produce hydrogen-rich gas in an autoclave which was operated batch-wise under high-pressure. K2CO3 and Ca(OH)2 were selected as the catalysts (or promoters). The temperature was kept between 450°C and 500°C while pressure was maintained at 24–26 MPa. The reaction time was 20 min. Experimental results showed that the two catalysts had good catalytic effect and optimum amounts were observed for each catalyst. When 0.2 g K2CO3 was added, the hydrogen yield could reach 9.456 mol·kg−1 which was two times of the H2 amount produced without catalyst. When 1.6 g Ca(OH)2 was added, the H2 yield was 8.265 mol·kg−1 which is lower than that obtained using K2CO3 as catalyst but is still 1.7 times that achieved without catalyst. Comparing with the results obtained using K2CO3 or Ca(OH)2 alone, the use of a combination of K2CO3 and Ca(OH)2 could increase the H2 yield by up to 2.5 times that without catalyst and 25% and 45% more than that obtained using K2CO3 and Ca(OH)2 alone, respectively. It was found that methane was the dominant product at relatively low temperature. When the temperature was increased, the methane reacts with water and is converted to hydrogen and carbon dioxide.

Noncatalytic Gasification of Cellulose in Supercritical Water

We gasified cellulose in supercritical water, in the absence of heterogeneous catalytic effects, by using quartz reactors. We also report the first systematic study of the effects of temperature, cellulose loading, water density, and reaction time on the production of H2, CH4, CO, and CO2 from supercritical water gasification. The results show that the total gas yields and H2 mole fraction are lower in quartz reactors than in stainless steel reactors, suggesting that the gases from previous studies in metal reactors arise from both homogeneous and heterogeneous reactions, even in the absence of an added catalyst. The rate of formation for all gas species increases with temperature. Manipulating cellulose loading and water density provides an efficient means to control the product selectivity, since the relative amounts of H2 and CH4 were strongly influenced by these two process variables.

Hydrogen production from catalytic gasification of cellulose in supercritical water

Abstract Interests in large-scale use of biomass for energy and in hydrogen are motivated largely by global environmental issues. Cellulose and sawdust were gasified in supercritical water to produce hydrogen-rich gas in this paper, and Ru/C, Pd/C, CeO 2 paticles, nano-CeO 2 and nano-(CeZr) x O 2 were selected as catalysts. The experimental results showed that the catalytic activities were Ru/C > Pd/C > nano-(CeZr) x O 2 > nano-CeO 2 > CeO 2 particle in turn. Low-concentration sodium carboxymethylcellulose (CMC) (2–3 wt.%) was mixed with particulate biomass and water to form a uniform and stable viscous paste which can be efficiently gasified. The 10 wt.% cellulose or sawdust with CMC can be gasified near completely with Ru/C catalyst to produce 2–4 g hydrogen yield and 11–15 g potential hydrogen yield per 100 g feedstock at the condition of 500 °C, 27 MPa, 20 min residence time in supercritical water.

Decomposition behavior of cellulose in supercritical water, subcritical water, and their combined treatments

A comparative study on decomposition of cellulose between supercritical water (400°C, 40 MPa) and subcritical water (280°C, 40 MPa) treatments was made to elucidate the difference in their decomposition behavior. Consequently, the supercritical water treatment was found to be more suitable for obtaining high yields of hydrolyzed products. However, cellulose was found to be more liable to fragment under supercritical water treatment, resulting in a decrease in the yield of hydrolyzed products. On the contrary, cellulose was found to be liable to more dehydration in the subcritical water treatment. Based on these results, we have proposed the combined process of short supercritical water treatment followed by subcritical water treatment so as to inhibit fragmentation. Consequently, this combined treatment was able to effectively control the reaction condition, and to increase the yield of hydrolyzed products.

00/02390 Co-liquefaction of coal and cellulose in supercritical water

The economic transition in developing countries is not always the result of the change from a centrally-planned to a free-market economy, but may be found within an already existing free-market economy as a result of profound political change, as in South Africa. The release of Nelson Mandela in February 1990 heralded an end both to the political system of apartheid and to the concomitant social, political, and economic disenfranchisement of 30 million non-White people in South Africa. The first freely elected non-White government came to power in 1994 and initiated a number of social and economic reforms aimed at alleviating the worst consequences of apartheid. This paper examines the effect of post-apartheid economic and social transition on the growth and development of urban children.Over 4000 children born in Soweto and Johannesburg were enrolled in the Birth to Ten (BTT) birth-cohort study in 1990. Whilst these children were born with lower birth weights than in developed countries, they did grow strongly in infancy, particularly in weight, to reflect normal reference values for body mass index (BMI) by 1 year of age. While post-apartheid social and economic changes were expected to take some time to affect child growth and development, the rate of change has been slower than expected. Data from the BTT study demonstrate that the growth of White children continues to be superior to that of their non-White peers and differences that existed at birth and during infancy have not diminished during childhood and early adolescence. Whatever factors are changed at the national or community levels during economic (and social) transition in South Africa appear not yet to have resulted in improved child physical growth.

6-8.超臨界水中におけるセルロースの部分酸化反応を用いた水素化反応に関する研究(Session 2.5.6 バイオマス・新エネルギー・リサイクル)

6-8.超臨界水中におけるセルロースの部分酸化反応を用いた水素化反応に関する研究(Session 2.5.6 バイオマス・新エネルギー・リサイクル)

99/03604 Co-liquefaction of coal and cellulose in supercritical water: Matsumura, Y. et al. Fuel, 1999, 78, (9), 1049–1056

99/03604 Co-liquefaction of coal and cellulose in supercritical water: Matsumura, Y. et al. Fuel, 1999, 78, (9), 1049–1056

Co-liquefaction of coal and cellulose in supercritical water

Co-liquefaction of biomass and coal in supercritical water is proposed with the intention that hydrogen matching between biomass and coal takes place, resulting in enhanced coal liquefaction and preferable liquefaction products. A semi-batch packed-bed reactor is employed to co-liquefy cellulose utilized for a model compound of biomass and Ishikari coal in supercritical water at 673K and 25MPa. No interaction between coal and cellulose is observed for the production of residue and water-insoluble product, judging from the yield and its composition. On the contrary, the yield of the water-soluble product increased for the case of co-liquefaction. Both hydrogen to carbon ratio and oxygen to carbon ratio of the water-soluble product increased by co-liquefaction. The mechanism for this interaction is proposed based on the addition reaction of compounds derived from cellulose with coal-derived compounds to increase the recoverable yield of the water-soluble product.

Conversion of polymers and biomass to chemical intermediates with supercritical water

AbstractRecent results are described on conversion of polymers and biomass to chemical intermediates and monomers by using subcritical and supercritical water as the reaction solvent. Reactions of cellulose in supercritical water are rapid (<50 ms) and proceed to 100% conversion with no char formation. They show a remarkable increase in hydrolysis products and lower pyrolysis products when compared with reactions in subcritical water. Further, there is a jump in the reaction rate of cellulose at the critical temperature of water. If the methods used for cellulose are applied to synthetic polymers, such as PET, nylon or others, high liquid yields can be achieved although the reactions require about 10 min for complete conversion. The reason is the heterogeneous nature of the reaction system. For polyethylene, higher yields of short‐chain hydrocarbons, higher alkene/alkane ratios and higher conversions were obtained in supercritical water than those obtained by pyrolysis.