Ta doped alkali niobate, K(1-x)Na(x)Nb(1-y)TayO(3) (KNNT) nanoparticles (ca. 60-80 nm) were continuously synthesized from Nb/Ta-sol with polyacrylic acid as a dispersant and NaOH/KOH solutions using a super-critical water flow system. The syntheses were carried out at temperatures from 400 to 480 degrees C, at pressures from 25 to 30 MPa, and at reaction times from 0.5 to 8 s. Single phase KNNT was obtained at 480 degrees C and 25 MPa for which the Na/(Na + K) and Ta/(Ta + Nb) molar ratios of the products increased with an increase in the precursor molar ratios with slopes of 2.7 and 1.0 for Na/(Na+ K) and Ta/(Ta +Nb), respectively. Single phase K0.5Na0.5Nb0.7Ta0.3O3 was obtained from the precursor composition with initial Nal(Na + K) and Ta/(Ta + Nb) molar ratios of 0.19 and 0.3, respectively. Crystallinity increased with an increase in the reaction time and the particles formed at 0.5 s were spherical-shaped and they were cube-shaped at the longer reaction times. Single KNNT phase was predominantly produced at high temperatures (ca. 420-480 degrees C) and moderate pressures (ca. 25-30 MPa), and was formed at 420 degrees C, 25 MPa where the density of water was less than 150 kg m(-3). The ferroelectric property of KNNT particles sintered at 1085 degrees C was determined to be 96.0 pC/N. 2016 Elsevier B.V. All rights reserved.

Catalytic activity of TiO2, ZrO2 and ZrO2 solid solutions (with CaO or TiO2) for the isomerization of glucose into fructose under hydrothermal conditions (120-180 degrees C for 5-15 min reaction time) was evaluated by experimental kinetic studies and surface acidity-basicity measurements. Kinetic studies were conducted with batch reactors heated by microwave. Under hydrothermal conditions regardless of the temperature, fructose yield was always below 10% and fructose selectivity was rapidly decreased with increasing glucose conversion. By adding 10 mM NaOH, fructose yield reached 20% at 160 degrees C for 5 min. In the presence of TiO2, fructose yield and selectivity were similar (160 degrees C, 47% of glucose conversion and 14% fructose yield). ZrO2 showed higher catalytic activity (160 degrees C, 63% glucose conversion and 21% fructose yield) compared with TiO2. The catalytic activity of TiO2 doped ZrO2 was between TiO2 and ZrO2. To increase the basicity of ZrO2, CaO was doped into the ZrO2 matrix. For experiments with the 24 wt% CaO doped ZrO2, fructose selectivity was higher than 70% even at 30% glucose conversion at 160 degrees C for 15 min. For systematical understanding catalytic activity of the metal oxides used, acidity and basicity of the catalysts were measured by temperature programmed desorption (TPD) using either CO2 or NH3. It was found that basicity on the surface increased with increasing the amount of CaO in the ZrO2 solid solution while acidity increased with amounts of TiO2. For a simple network model of glucose reactions, rate constants were fitted to the data assuming a simple network model and they were completed with the acid-base properties of TiO2, ZrO2 and CaO doped and TiO2 doped ZrO2. As a result, the reactivity was found to be correlated with the ratio of the base to acid sites on the surface and fructose formation was linearly proportional to the base/acid mole ratio on the surface of the catalysts. (C) 2016 Elsevier B.V. All rights reserved.

A flow-type cell was developed for measuring Compton scattering spectra of heat-sensitive aqueous solution. Compton scattering spectra of water and ethanol were measured in the region from ambient conditions to 623 K and 20 MPa. Compton profiles derived from measurement with the flow-type cell were comparable with those in the literature. Results obtained from the flow-type cell showed that delocalization of electronic charge density of water and ethanol at high temperatures occurred. Delocalization of the electronic charge density of ethanol was greater than that of water at high temperature, which is consistent with the prior works that use proton NMR chemical shifts to describe hydrogen bonding. Published by AIP Publishing.

Winterization is a simple method to remove saturated fatty acid contents in biodiesel fuels for improving their cold flow properties. In-this work, biodiesel fuels with different initial long-chain (C16 and above) saturated fatty acid constituents (S-i) were prepared from blends of palm, canola, and corn oils. The prepared biodiesels were treated at various winterization temperatures (T-w) to investigate the effect of T-w, and S-i on the final saturated fatty acid constituents (S-w) of the winterized biodiesel fuel. Optical microscopy showed that ball-like crystals formed with fluid regions at moderate cooling rates (-6 degrees C/h) could allow solid-liquid separation by filtration. A saturated fatty acid reduction ratio, R-s, defined as (S-i - S-w)/S-i X 100, was used with the experimental results on large samples (ca. 600 mL) to develop a correlation for winterization temperature as T-w (degrees C) = 0.659 S-i (wt%) - 0.104 R-s (wt%) - 10.197. The correlation can provide estimation of the required winterization temperature for reducing a specified ratio of fatty acids in a biodiesel fuel that mainly contains long-chain fatty acids from the initial saturated fatty acid constituents. When used with literature relationships for cold filter plugging point (CFPP) and S-w, estimation of the CFPP of winterized biodiesel fuels is possible without requiring-actual winterization treatment.

Zerovalent copper nanoparticles (CuNPs) (diameter, 26.5 +/- 9 nm) capped with polyvinylpyrrolidone (PVP) were synthesized in supercritical water at 400 degrees C and 30 MPa with a continuous flow reactor. The PVP-capped CuNPs were dispersed in distilled water, methanol, ethanol, 1-propanol, 2-propanol, butanol, and their mixed solvents to study their long-term stability. Temporal variation of UV vis spectra and surface plasmon resonance were measured and showed that ethanol, the propanols, and butanol solvents provided varying degrees of oxidative protection for Cu-0. Fourier transform infrared spectroscopy showed that PVP adsorbed onto the surface of the CuNPs with a pyrrolidone ring of PVP even if the CuNPs were oxidized. Intrinsic viscosities of PVP were higher for solvents that provided antioxidation protection than those that give oxidized CuNPs. In solvents that provided Cu-0 with good oxidative protection (ethanol, the propanols, and butanol), PVP polymer chains formed large radii of gyration and coil-like conformations in the solvents so that they were arranged uniformly and orderly on the surface of the CuNPs and could provide protection of the Cu-0 surface against dissolved oxygen. In solvents that provided poor oxidative protection for Cu-0 (water, alcohol water mixed solvents with 30% water), PVP polymer chains had globular-like conformations due to their relatively high hydrogen-bonding interactions and sparse adsorption onto the CuNP surface. Antioxidative properties of PVP-capped CuNPs in a solvent can be ascribed to the conformation of PVP polymer chains on the Cu-0 particle surface that originates from the interaction between polymer chains and its interaction with the solvent.

Alkali niobate, K1-xNaxNbO3, nanoparticles (ca. 50-60 nm) were continuously synthesized from Nb-sol and NaOH/KOH solutions with a supercritical water flow system. The syntheses were carried out at temperatures from 400 to 480 degrees C, at pressures from 25 to 30 MPa, and at reaction times from 0.1 to 8.3s. X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS) techniques were used to characterize the samples. Single phase KNbO3 was obtained at 480 degrees C and 25 MPa at an initial K/Nb molar ratio of 15. The K/Nb molar ratio of the products increased with an increase in the reaction time. For NaNbO3, single phase product was formed under supercritical water conditions irrespective of the temperature and pressure. The K1-xNaxNbO3 nanoparticles were synthesized at 480 degrees C and 25 MPa for varying Na/K concentrations. Single phase K0.5Na0.5NbO3 was obtained at an initial Na/K molar ratio of 0.25. To form the perovskite structure, the rearrangement of NbO6 units with alkaline ions is required. The rearrangement proceeds more rapidly with Na+ ions than with K+ ions probably due to the smaller ionic radius of Na+. Therefore, formation of K0.5Na0.5NbO3 was achieved at the excess amount of K+ ions than Na+ ions. (C) 2015 Elsevier B.V. All rights reserved.

Black liquor is an alkaline liquid residue from paper industry, containing similar to 80 wt% of water and similar to 20 wt% of organics and minerals. Hydrothermal conversion of black liquor in a batch reactor is particularly interesting towards hydrogen production, as the carbon dioxide is highly solubilized in the basic aqueous media. Thus hydrogen with higher purity than other processes is obtained. Cerium oxide nanocatalyst (cubic CeO2) is used to improve the amount of hydrogen produced and to decrease the coke formation, based on the water splitting into active species. Experiments have been carried out at sub and supercritical conditions 350 degrees C or 450 degrees C, 25 MPa) in a batch reactor for 15 min or 60 min. CeO2 nanocatalyst improved the conversion of black liquor at sub and supercritical conditions as expected. The amount of carbonaceous solid recovered was decreased due to the catalytic effect. Recovered hydrogen was not significantly affected by the catalyst as it was involved in secondary reactions such as hydrogenation. Oxidations reactions, as well as O-2 production, were also improved using catalyst and supercritical media. Supercritical water media combined with catalyst clearly affects the fragmentation of dissolved lignin compared to subcritical conditions. Then it was assumed that water splitting occurs and produces active hydrogen and oxygen species. Thus these actives species produced using catalyst are able to improve hydrogenation and oxidation reactions, as well as recombination into H-2 and O-2. (C) 2015 Elsevier B.V. All rights reserved.

Gas adsorption rates of H2, CO2, and H2-CO2 gas mixture (H2/CO2=3.4) with tetra-n-butyl ammonium salt (bromide, chloride, and fluoride) semi-clathrate hydrate particles were measured at 269 K to assess their properties for gas separation. Equilibrium gas occupancies in the S-cages of the particles were in order of (high to low) for hexagonal structure-I, tetragonal structure-I, and superlattice of cubic structure-I structures with the maximum fractional occupancy by CO2 being about 40%. The CO2 diffusion rate depended on the anion size of the salt, which is attributed to distortion of the S-cage that is close to the molecular size of CO2. Simulations of semi-clathrate hydrate particles with theory showed that H2/CO2 selectivities could be as high as 36 (3.0 mol% TBAF) and that selectivities for an ideal membrane (3.3 mol% TBAF) could be &gt 100 (269 K, 0.3-4.5 MPa). Semi-clathrate hydrates have wide application as separation media for gas mixtures.

Emission of Zn2SiO4:Mn2+ can be readily controlled to have continuously variable colors between green and yellow by adjusting the pH of the starting solutions in supercritical water syntheses. Mostly single phase beta-Zn2SiO4:Mn2+ exhibiting yellow emission was formed at a pH of 10.5. By changing pH of the starting solution from low values (ca. 2.8) to high values (ca. 12.5), emission color could be proportionally varied from green emission to yellow emission because the amount of each phase was found to change. The selectivity of alpha- and beta-Zn2SiO4 crystallization in supercritical water is strongly related to the solubility of dissolved species of the zinc ion source, Zn(OH)(2) in water. Photoluminescence results showed that the reaction atmosphere determines emission color over a wide range of dominant wavelengths, 534-571 nm, according to the crystalline phases formed. The use of pH with supercritical water allows a simple control strategy for emission color control of Zn2SiO4:Mn2+ phosphors. (C) 2015 Elsevier B.V. All rights reserved.

Few viscosity and density data have been reported for CO2-poly(ethylene glycol) solutions, even though many vapor-liquid equilibrium data exist in the literature. In this work, viscosity and density of pure poly(ethylene glycol) (PEG, M=3000, 8300, 20,000 g mol(-1)) at atmospheric pressure were measured. Viscosities of PEG 3000 and PEG 8300 solutions with CO2 were measured with a torsional vibrating viscometer at 353.2 K and 373.2 K over the range of CO2 pressures from 5 MPa to 15 MPa. The densities of CO2-PEG solutions were calculated with the perturbed-chain statistical associating fluid theory equation of state. From shear viscosity measurements, PEG 3000 and PEG 8300 were confirmed to be Newtonian and PEG 20000 was confirmed to be non-Newtonian. The viscosity reduction ratio for PEG solutions saturated with CO2 was found to be independent of the PEG molecular weight (400 <= M <= 8300 g mol(-1)). A simple equation is proposed that can correlate CO2-PEG solution viscosity reduction ratio to within 0.08 in absolute units. The CO2-PEG solution viscosities could be correlated with free volume models to within 14% using the fitted value of CO2 occupied volume. (C) 2014 Elsevier B.V. All rights reserved.

Chitin is high in crystallinity in its natural form and does not dissolve into high temperature water (HTW), which often leads to decomposition reactions such as hydrolysis, deacetylation and dehydration when hydrothermally processed. In this work, we investigated the reactions of mechanically milled chitin in HTW. Mechanical milling pretreatment combined with HTW treatment improved the liquefaction of chitin giving a maximum water soluble fraction of 80%, where the untreated chitin was 55%. The reaction mechanism of the milled and raw chitin in HTW was shown to be different. For milled chitin, the dissolution of chitin occurred during the heating period to supercritical water conditions (400 degrees C) at short reaction times (1 min). Extended reaction time (10 min) led to decomposition products and aromatic char formation. For raw chitin, the dissolution of chitin in HTW did not occur, due to its high crystallinity, so that liquefaction proceeded via decomposition reactions. (C) 2014 Elsevier Ltd. All rights reserved.

Adsorption rates are reported for H-2-tetrahydroluran (THE), H-2-THF (D2O), H-2-THF-d8, H-2-furan, H-2-cyclopentane (CP) and H-2-tetrahydrothiophene (THT) binary clathrate hydrates at temperatures of 265273 K and pressures of 4-10 MPa. Adsorption rates of H-2-furan and H-2-6.8 mol% THE binary clathrate hydrates were the fastest among these binary clathrate hydrates. The lattice constant of hydrates were determined to analyze the adsorption data with a newly proposed multiple adsorption resistance (MAR) model. The effect of the non-included additive guest molecule on hydrogen adsorption rate was important because they promoted formation of pores and grain boundaries when hydrate particles formed. Activation energies, Delta E-Da, for H-2 diffusion into clathrate hydrates calculated from the Arrhenius plots depended on the hydrate guest additive and were determined to be: 18.0 kJ/mol (6.2 mol% THF), 30.7 kJ/mol (5.6 mol% THF), and 100 kJ/mol (cyclopentane). Based on the Delta E-Da) values, H-2 diffusion pathway in hydrate particles depends on the clathrate hydrate formation process and the interactions between guest additive molecule and the host molecule. (C) 2014 Elsevier Ltd. All rights reserved,

Surface-modified zero-valent copper nanoparticles (CuNPs) are of interest as conductive inks for applications in printed electronics. In this work, we report on the synthesis, stability and characterization of CuNPs formed with a continuous supercritical hydrothermal synthesis method. The precursor, copper formate, was fed as an aqueous solution with polyvinylpyrrolidone (PVP) surface modifier and mixed with an aqueous water and formic acid stream to have reaction conditions of 400 degrees C, 30 MPa and 1.1 s mean residence time. The reaction pathway seemed to proceed step-wise as the hydrolysis of copper formate, followed by dehydration to oxide products and subsequent reduction by hydrogen derived from precursor and formic acid decomposition. The formed surface-modified zero-valent CuNPs had particle sizes of ca. 18 nm, were spherical in shape and contained no oxide contaminants. The formed CuNPs were found to exhibit long-term (>1 year) stability in ethanol as evaluated by shifts in the surface plasmon resonance band of product solutions. Conductive films (0.33 mu m thickness) prepared with the CuNPs had a resistivity of 16 mu Omega cm. The methods reported in this work show promise for producing conductive inks for use in practical printed electronics. (C) 2013 Elsevier B.V. All rights reserved.

Selective glucose production by cellulose hydrolysis with initial or sequential water addition in the presence of solid acid catalysts in 1-butyl-3-methyl-imidazolium chloride ([bmIm][Cl]) under microwave irradiation was investigated at 120 °C and 1.2 MPa of N2 atmosphere. For revealing the effect of water on cellulose hydrolysis in [bmIm][Cl], the phase behavior during the reaction was observed. Colored compounds formed at lower amounts of water, while some amounts of cellulose precipitated at higher amounts of water. Glucose yield was highest (65 mol%) at 25 wt% water in [bmIm][Cl] for the case of initial water addition. To improve the glucose yield, sequential water addition in which water was added in steps as the reaction proceeded was examined. Glucose yields in the presence of Amberlyst-15 in [bmIm][Cl] were 68.5 and 75.0 mol% by two-step and three-step water addition, respectively. Employing three-step water addition, Dowex 50wx8-100 (ion-exchange resin), hydrothermally synthesized carbon catalyst and three types of nano-zeolites were assessed. The carbon catalyst-modified fuming sulfuric acid and H-type zeolites (mordenite and faujasite) gave comparable glucose yields as Amberlyst-15. Sequential water addition is an effective technique for improving reaction efficiency in cellulose/solid acid catalyst/ionic liquid reaction systems.

In this work, gas adsorption equilibria for H2 and for CO2 with THF clathrate hydrate particles and with tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate particles (250-355μm) were measured. The structures of the TBAB semi-clathrate hydrates were confirmed with Raman spectroscopy and with differential scanning calorimetry. The THF clathrate hydrate particles had the largest adsorption (ca. 13.7mmol-H2/mol-host) at 269K among all of the hydrates studied. H2 adsorption at 269K for 2.6mol% TBAB semi-clathrate hydrate (type-B rich) was ca. 6.9mmol-H2/mol-host and that for 3.7mol% TBAB semi-clathrate hydrate (type-A rich) was ca. 3.4mmol-H2/mol-host. For CO2, THF clathrate hydrate had higher adsorption capacity (ca. 68.5 mmol-CO2/mol-host) than type-A (ca. 16.3 mmol-CO2/mol-host) or type-B (ca. 29.0 mmol-CO2/mol-host) semi-clathrate hydrate. Type-B TBAB semi-clathrate hydrate had a larger Langmuir constant ratio (CCO2/CH2) than that of THF hydrate. The selectivity of type-B TBAB semi-clathrate hydrate implied by the Langmuir constant ratio can be expected to be large, however the results need to be confirmed with gas mixtures and other conditions including effect of semi-clathrate hydrate particle size. © 2013 .

Catalytic cracking of Canadian oil sand bitumen in supercritical water was performed to clarify the effect of CeO2 nanoparticles. The cracking was performed at 723 K to promote a redox reaction between the water, bitumen, and catalyst for the production of hydrogen and oxygen. As the catalyst, CeO2 with two different morphologies was employed because the redox reaction of CeO2 with water and organics is expected and its activity can be controlled by its structure. In this study, two roles of water were considered as well. Water is attractive as a high potential medium with low dielectric constant and density at near the critical point (374 degrees C, 22.1 MPa) that allows formation of highly crystalline smaller metal oxides particles. However, the chemical effects of water are investigated with heavy oil catalytic cracking. Transmission electron microscopy images indicated that CeO2 nanoparticles with cubic and octahedral shape were synthesized using a plug-flow reactor under hydrothermal conditions. The particles sizes were 8 and 50 nm for cubic and octahedral CeO2, respectively. At 773 K, it was found that the oxygen storage capacity (OSC) of the cerium oxide nanoparticles with cubic {100} facets was nearly 3.4 times higher than that of the cerium oxide nanoparticles with octahedral {111} facets. Heavy oil fractions of bitumen were cracked in a batch-type reactor at 723 K in order to produce as much light oil as possible, and the effect of the catalyst loading and reaction conditions on the conversion rate and coke formation were investigated. As a result, it was demonstrated that it is possible to obtain a high conversion rate by increasing the exposed surface area and reducing the particle size of the catalyst. The highest conversion was obtained in the presence of 20 mg loading of cubic CeO2 nanoparticles (8 nm) with reaction time of 1 h.

Viscosities of microcrystalline cellulose + 1-butyl-3-methylimidazolium acetate ([bmIm][Ac]) solutions (0.6-1.2 wt%) in contact with CO2 were measured at 312 K with a resonant vibrational viscometer. At 4 MPa and 312 K, the CO2 could reduce the viscosity of 1.2 wt% cellulose + [bmIm][Ac] solution by about 80 %, whereas N-2 at the same conditions gave less than a 10 % reduction in viscosity. The viscosity-averaged degree of polymerization and IR spectrum showed that cellulose did not decompose during experiments and that [bmIm][Ac] acted as a non-derivatizing solvent during the dissolution and viscosity reduction process. Further, although CO2 does react with [bmIm][Ac] to form 1-butyl-3-methylimidazolium-2-carboxylate, the reaction seems to be reversible and it does not affect the cellulose. Thus, [bmIm][Ac] with CO2 provides an effective solvent for cellulose and the solvent system can probably be recycled or reused.

The dissolution and recovery of microcrystalline cellulose from 1-butyl-3-methylimidazolium chloride, [bmIm][Cl], were studied. At 90 °C and 5 h dissolution time, the regenerated cellulose could be recovered above 80 wt% with a less than 10% decrease in the value of the viscosity-average degree of polymerization, DPv, regardless of water content. Recovery ratio and DPv of regenerated cellulose at 120 °C decreased with time regardless of water content. The regenerated cellulose after dissolution at 120 °C for 10 h regardless of water content had cellulose II structure. Regenerated cellulose at short dissolution times or low temperature had high amorphous content. Both [bmIm][Cl] and [bmIm][Cl] with water act as a non-derivatizing solvent for microcrystalline cellulose at 90 °C, and as a derivatizing solvent at 120 °C. The main effect of added water on the dissolution of cellulose at high temperature was the promotion of cello-oligosaccharide and levoglucosan formation. © 2012 Elsevier Ltd. All rights reserved.

Upgrading bitumen by converting asphaltene to maltene whilst suppressing coke formation is desirable though technically difficult. Mass transfer behavior under sub-and super critical water conditions was observed in an autoclave-type reactor revealing that the dissolution of asphaltene core attenuates coke formation and promotes the formation of upgraded products. On the basis of this new information, a continuous hydrothermal extraction method using near supercritical water in a column flow reactor was tested. The results at 300 degrees C, 3-6 MPa, and water flow of 3-10 g/min, showed higher degree of upgrading than in the autoclave reactor. Significant conversion of asphaltene to maltene with lighter maltene composition was obtained, while coke formation was completely suppressed. A continuous hydrothermal extraction method using a column flow reactor has thus been shown can solve the problem of incompatibility between enhancing the degree of upgrading of heavy oils and suppressing the formation of coke. In the proposed mechanism, low levels of asphaltene core extraction results in the formation of coke in the oil phase, whereas high levels of asphaltene core extraction results in the suppression of coke formation due to low concentrations of asphaltene core remaining in the oil phase, and the solvent properties that asphaltene core acquires at high concentrations in the water phase. (C) 2012 Elsevier Ltd. All rights reserved.

Model compounds (glucose and glycerol) and real biomass (sugarcane bagasse and Chlorococcum littorale) were partially oxidized to hydrogen in high temperature high pressure water (120-300 degrees C at saturated pressure of water). Biomass conversion into gas directly by partial oxidation in a one-pot process was considered by use of a catalyst in a batch type reactor. The total gas yield and hydrogen selectivity from all the reactants were low. To improve the gasification efficiency, a two-step process was proposed: partial oxidation of the organic compound into hydrogen precursor (here formic acid) followed by selective decomposition of the intermediate into hydrogen. To clarify the possibility of the process, model compounds (glycerol and glucose) were used. The effects of operation parameters for each step (temperature, water to organic ratio, oxygen to organic ratio, catalyst) were investigated using a batch reactor. For glycerol oxidation at lower temperature (120-160 degrees C), kinetic analysis was performed to clarify the reaction mechanism and formic acid formation. For formic acid decomposition into hydrogen, several metal oxides were carried out to accelerate the reaction rate, and ZnO was found to be effective at 300 degrees C. The yield of hydrogen from the combination of formic acid formation from glucose and hydrogen formation from the oxidized material including formic acid was investigated using a flow apparatus. However, the yield of hydrogen was lower than expected and further improvement of the two-step reaction process is required.

Infinite dilution partition coefficients of benzene and benzene derivative compounds (chlorobenzene, bromobenzene, toluene, ethylbenzene, benzaldehyde, benzyl alcohol and phenol) between supercritical carbon dioxide and ionic liquids (1-butyl-3-methylimidazolium chloride [bmim][Cl], 1-butyl-3-methylimidazolium acetate [bmim][Ac] and 1-butyl-3-methylimidazolium octylsulfate [bmim][OcSO(4)]) were measured with a packed-column chromatographic technique. The Sanchez-Lacombe equation of state was used to correlate the data and could describe the qualitative changes of the infinite dilution partition coefficients over a wide range of temperatures (313-352 K) and pressures (5-15 MPa). A linear solvation energy relationship (LSER) model, LSER-delta, was developed for compressible phases that uses solute, solvent and ionic liquid solubility parameters. Partition coefficients were generally in the order of solute volatility with the exception of hydrogen bonding solutes. LSER solute volume (McGowan's volume, V) and solute dipolarity/polarizability (S) greatly affected the partition coefficient values. It was found that the McGowan's volume can be considered as a function of the CO2 solubility parameter, which may be helpful in extending LSER theory to supercritical fluid systems. Both models could describe the partition coefficient well and were useful in understanding some of the interactions of the solute with the supercritical CO2 and ionic liquid phases. (c) 2011 Elsevier B.V. All rights reserved.

Hydrothermal treatment was conducted on alginate in the interest of obtaining organic acids. Formic acid, acetic acid, lactic acid, glycolic acid, 2-hydroxybutyric acid, succinic acid, malic acid, mannuronic acid and guluronic acid were obtained by the hydrothermal treatment of alginate. The total yield of the organic acids were 46% at maximum yield 350 degrees C, 40 MPa and 0.7 s reaction time. The formation of organic acids, suggest that the carboxyl group structure of the alginate was preserved during the hydrothermal decomposition of the alginate. The formation of dicarboxylic acids is evidence that oxidation reactions occur during the hydrothermal treatment, introducing carboxyl groups into the decomposition products. The product distribution indicates that both acid and base catalyzed reactions occurred during the hydrothermal treatment of alginate. Hydrothermal treatment of an uronic acid, glucuronic acid, gave the same organic acids as those obtained from hydrothermal treatment of alginate. The reaction from alginate to organic acids probably proceeds via the formation of hexuronic acid (mannuronic acid and guluronic acid) under hydrothermal conditions. (c) 2012 Elsevier B.V. All rights reserved.

As a key renewable chemical for plastics and fine chemicals, the preparation of 5-hydroxymethylfurfural (5-HMF) from biomass is an important research topic. Cellulose, although abundant in nature, is difficult to convert to 5-HMF in good yields due to its recalcitrant and heterogeneous nature. In this work, we show an efficient two-step process for converting microcrystalline cellulose into 5-HMF with ionic liquids under mild conditions. In the first step, high glucose yields of above 80% could be obtained from the cellulose hydrolysis by a strong acidic cation exchange resin in 1-ethyl-3-methyl imidazolium chloride ([EMIM][Cl]) with gradual addition of water. In the second step, the resin was separated from the reaction mixture and CrCl(3) was added which lead to a 5-HMF yield of 73% based on cellulose substrate. The strategy can allow practical conversion of biomass into bio-derived products.

Fine particles of KNbO3 can be synthesized on a time scale of seconds in supercritical water with a flow-type reactor. The restructuring of NbO6 octahedrons was found to be a primary factor in the mechanism of KNbO3 crystallization in high-temperature aqueous environments. Two different crystallization routes exist depending on the conditions of water. The ion product of water affects whether the restructuring of edge-sharing NbO6 octahedrons to corner-sharing NbO6 octahedrons proceeds directly or stepwise according to the degree of dehydration. The direct crystallization route provides polygonal-shaped KNbO3 particles via direct restructuring, namely, homogenous nucleation from supercritical water that is strongly correlated with a low ion product. The stepwise crystallization route provides irregularly shaped KNbO3 particles via restructuring in stages to produce an intermediate K4Nb6O17 phase that is correlated with a high ion product. As the ion product of water decreases in high-temperature water, the stability of crystalline phase is in order of KNbO3 > K4Nb6O17 > K4Nb6O17 center dot 3H(2)O > defect pyrochlore due to the suppression of dehydration. Water acts to not only dominate the restructuring mechanism of NbO6 octahedrons but also to provide efficient transport of K+ and OH- ions that allows rapid restructuring of NbO6 octahedrons during KNbO3 crystallization. (C) 2011 Elsevier B.V. All rights reserved.

Effects of oxygen and nitrate on fatty acid/lipid production from a highly CO(2)-tolerant microalgal species Chlorococcum littorale were examined under photoautotrophic conditions of 295 K, a light intensity of 170 mu mol-photon m(-2) s(-1), a bubbling CO(2) concentration of 5% (v/v) and bubbling oxygen concentrations to be volumetrically adjusted by mixing oxygen gas with inert nitrogen gas at concentrations ranging from 0% to 95% (v/v). The results showed that maximum fatty acid content reached ca. 34 wt.% under oxygen-freely bubbling conditions and this value decreased to be ca. 20 wt.% when air-like oxygen concentration of 20% was chosen. This means that degree of the accumulation strongly depended on the level of bubbling oxygen concentrations, which can be a crucial factor after nitrogen depletion in the photoautotrophic culture system. TLC-FID/FPD analyses showed that triglycerides were found to be a dominant lipid class for this accumulation. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.

Decomposition kinetics and recycle of hydrogen-tetrahydrofuran (H-2-THF) clathrate hydrates were investigated with a pressure decay method at temperatures from 265.1 to 273.2 K, at initial pressures from 3.1 to 8.0 MPa, and at stoichiometric THF hydrate concentrations for particle sizes between 250 and 1000 mu m. The decomposition was modeled as a two-step process consisting of H-2 diffusion in the hydrate phase and desorption from the hydrate cage. The adsorption process occurred at roughly two to three times faster than the desorption process, whereas the diffusion process during formation was slightly higher (ca. 20%) than that during decomposition. Successive formation and decomposition cycles showed that occupancy seemed to decrease only slightly with cycling and that there were no large changes in hydrate structure due to cycling. Results provide evidence that the formation and decomposition of H-2 clathrate hydrates occur reversibly and that H-2 clathrate hydrates can be recycled with pressure. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 265-272, 2011

Upgrading of bitumen was examined with formic acid in supercritical water (SCW) from 673 to 753 K and at a water/oil ratio from 0 to 3. Decomposition of bitumen in SCW + HCOOH gave higher conversions of asphaltene and lower coke yields than those of pyrolysis or with only SCW. Decomposition of bitumen was also conducted in SCW + H(2), SCW + CO, toluene and tetralin, which revealed that decomposition of asphaltene was promoted and coke formation was suppressed when using SCW + HCOOH. In SCW + HCOOH, an increase in the water/oil ratio promoted both decomposition of asphaltene and suppression of coke formation. Formic acid in SCW seemed to enhance the conversion of bitumen to lower molecular weight compounds because formic acid seems to produce active species in SCW. The low temperature region (ca. 723 K) was suitable for upgrading bitumen with formic acid in SCW since coke formation was strongly promoted at high temperature (>753 K). A reaction model was proposed and the model predicted that hydrogenation of the asphaltene core was important for the suppression of coke formation. (C) 2010 Elsevier B.V. All rights reserved.

Reactions of D-xylose were investigated with a flow apparatus in water at high temperatures (350 and 400 degrees C) and high pressures (40-100 MPa) to elucidate the reaction pathway and reaction kinetics. The products obtained from the reaction of D-xylose were furfural, D-xylulose, glyceraldehyde, glycolaldehyde, dihydroxyacetone, pyruvaldehyde, lactic acid and formaldehyde. Experimental results showed evidence of a dehydration reaction pathway, a retro-aldol reaction pathway and a Lobry de Bruyn-Alberta van Ekenstein (LBET) pathway from D-xylulose. The proposed reaction pathway and kinetic model were in accord with the experimental results. The kinetic constants showed dependence with water density (pressure). At 400 degrees C and water density of 0.52 g/cm(3) at 40 MPa, the reaction from D-xylose to D-xylulose occurred by the LBET pathway with the reverse reaction being negligible. At 400 degrees C, increasing the water density from 0.52 to 0.69 g/cm3 decreased the kinetic rate constant of the forward LBET pathway and increased that of the reverse LBET pathway. The kinetic rate constant of the dehydration of D-xylulose to furfural increased with increasing water density at constant temperature. The kinetic rate constant of the retro-aldol reaction of D-xylose increased, and the retro-aldol reaction of D-xylulose decreased with increasing water density at 400 degrees C. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

Phase equilibrium data for H-2 + tetrahydrofuran (THF) and H-2 + cyclopentane (CP) binary clathrate hydrate systems were determined from temperature and pressure measurements with a newly designed semimicro (approximate to 0.78 cm(3)) cell. The range of conditions studied for the two systems was at pressures from (2 to 14) MPa and at temperatures from (278 to 285) K. Inclusion characteristics of the hydrogen molecules for both systems were similar according to their Raman spectra. The measured data for the H2 THF binary clathrate hydrate system were in agreement with some of the data in the literature. New phase equilibrium data and Raman spectroscopy analyses for the H-2 + CP binary clathrate hydrate system are reported. The dissociation enthalpies determined from data in the pressure range from (8 to 14) MPa were (212 and 220) kJ.mol(-1) for the H-2 + THF and H-2 + CP binary clathrate hydrate systems, respectively.

Heavy oil (Canada oil sand bitumen) upgrading in high density water (100 and 200 kg/m(3)) at 723 K was performed by a batch reactor. Yields of asphaltene, maltene, and coke were evaluated. With increasing water density, the rate of coke formation was promoted. To get some hints of coke formation mechanism, the formed coke was observed by scanning electron microscope (SEM). The most part of the coke formed st neat pyrolysis (pyrolysis in the absence of high density water) was coalescent structure of some small coke particles, while that at pyrolysis in the presence of water (200 kg/m(3) of water density) was porous structure that indicated occurrence of phase inversion of coke precursors. Based on the results, the reaction mechanism of the heavy oil upgrading was considered: lighter oil was extracted in high density water and the concentration of light hydrocarbon decreased in a heavier oil phase, while the concentration of heavier oil in the oil phase increased. Thus, the lighter oil decomposed further in high density water phase and the heavier oil in the oil phase combined together to form coke due to its higher concentration. (C) 2009 Elsevier B.V. All rights reserved.

To convert cellulosic organics contained in industrial paper sludge into glucose, reaction of pseudo paper sludge composed of cellulose and inorganic compounds (calcium carbonate (CaCO3), talc (Mg-3(Si4O10)(OH)(2)), kaolin (Al-2(Si2O5)(OH)(4))) under hydrothermal conditions was studied. Significant amounts of glucose (ca. 23%) could be produced from cellulose in the absence of CaCO3 for reaction in water at 523 K and 12 min reaction time. On the other hand, in the presence of CaCO3, most glucose decomposed over all conditions, whereas the addition of talc and kaolin to the mixtures increased the glucose yield to about 30%. For the case of chemical recycle of paper sludge with hydrothermal treatment to obtain D-glucose, it can be concluded that it is preferable to separate the calcium carbonate from the paper sludge before hydrothermal treatment. (C) 2010 Elsevier Ltd. All rights reserved.

The depolymerization of sodium alginate with hydrothermal treatment (180-240 degrees C) was studied to understand the selectivity of monosaccharide generation. Alginate depolymerized to oligosaccharides, monosaccharides and decomposition products that included lactic acid and glycolic acid. Alginate depolymerization under hydrothermal conditions occurred in a manner that initially released mannuronic acid (M) and then was followed by the release of guluronic acid (G). Monosaccharides were generated through the hydrolysis of the glycosidic bonds between the unit monomer with different selectivities among M-M, M-G and G-G units rather than random sites within alginate. Hydrothermal treatments shows promise as a method to modify the structure of alginate polymers. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.

An efficient method for converting glucose into 5-hydroxymethylfurfural (5-HMF), in the presence of CrCl3 catalyst, is developed by using the ionic liquid 1-butyl-3-methyl imidazolium chloride as solvent. A 5-HMF yield of 71% is achieved in 30 s for 96% glucose conversion with microwave heating at 140 degrees C. The activation energy of glucose conversion is determined to be 114.6 kJ mol(-1), with a pre-exponential factor of 3.5 x 10(14) min(-1). Fructose, sucrose, cellobiose, and cellulose are studied and 5-HMF yields of 54% are obtained for cellulose conversion at 150 degrees C during 10 min of reaction time. Recycling of the ionic liquid and CrCl3 is demonstrated with six cycles of use.

An efficient one pot, two-step process was developed for the preparation of 5-hydroxymethylfurfural (5-HMF) from inulin in ionic liquids under mild conditions. In the first step, the ionic liquid 1-butyl-3-methyl imidazolium hydrogen sulfate ([BMIM][HSO(4)]) was used as both solvent and catalyst for the rapid hydrolysis of inulin into fructose with 84% fructose yield in 5 min reaction time. In the second step, 1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]) and a strong acidic cation exchange resin were added to the mixture to selectively convert fructose into 5-HMF, giving a 5-HMF yield of 82% in 65 min at 80 degrees C, which is the highest 5-HMF yield reported by thus far for an inulin feedstock.

Polycarbonate (PC) could be completely decomposed into its monomer, bisphenol A (BPA) with high pressure (not atmospheric pressure) high temperature steam (573 K) in 5 min reaction time. The maximum yield of BPA was about 80 mol% based on the starting PC. PC decomposition at 573 K in liquid water phase near the saturated pressure for the comparison. For 30 min in reaction in liquid water at 573 K residual PC still remained and the BPA yield was about 50% as maximum. (C) 2009 Elsevier Ltd. All rights reserved.

Photoautotrophic fatty acid production of a highly CO2-tolerant green alga Chlorococcum littorale was investigated in the presence of inorganic carbon and nitrate at 295 K and a light intensity of 170 mu mol-photon m(-2) s(-1). CO2 concentration in the bubbling gas was adjusted by mixing pure gas components of CO2 and N-2 to avoid photorespiration and beta-oxidation of fatty acids under O-2 atmosphere conditions. Fatty acid content was almost constant for the CO2 concentrations ranging from 5% to 50% under nitrate-rich conditions corresponding to the logarithmic growth phase. After nitrate depletion, the content drastically increased with a decrease in CO2 concentration. HCO3-/CO2 ratio in the culture media was found to be a controlling factor for fatty acid production after the nitrate limitation phase. For a CO2 concentration of 5%, the fatty acid content was ca. 34 wt.% at maximum, which is comparable with other land plant seed oils. (C) 2009 Elsevier Ltd. All rights reserved.

Reaction of lactic acid was investigated with a flow apparatus in water at high temperatures (450 degrees C) and high pressures (40-100 MPa). The major products obtained from the reaction of lactic acid were acrylic acid, acetaldehyde, and the minor products were acetic acid and propionic acid. The maximum selectivity of acrylic acid was 44% at 23% lactic acid conversion that was obtained at 450 degrees C, 100 Mpa and a residence time of 0.8 s. The reaction kinetics could be modeled by considering two pathways defined as a dehydration pathway to acrylic acid and a combined reaction pathway that consisted of decarboxylation and decarbonylation to acetaldehyde. The data and the kinetic analysis consistently show that both dehydration and the combined decarboxylation and decarbonylation reactions continue to be promoted in supercritical water as pressure (water density) increases. However, high water densities increase the selectivity of the dehydration reaction. (C) 2009 Elsevier B.V. All rights reserved.

Shikimic acid can be rapidly separated (ca. 5 min) from Chinese star anise with hot water extraction at temperatures of 120 degrees C or higher to obtain recoveries of 100%. Extraction recoveries of shikimic acid close to 97% can be obtained with water at 70 degrees C using slightly longer extraction times (ca. 10 min) than those at 120 degrees C. A semi-batch flow apparatus was used to study the effect of temperature, average particle size, water flow rate, and extraction time on the experimental recoveries. For 0.5 g Chinese star anise raw material that contained ca. 8% shikimic acid, 100% recoveries of shikimic acid could be obtained with 60 g water at 150 degrees C at 15 MPa in 4 min for star anise material having a particle size range from 355 to 600 mu m. A one-site kinetic model was found to provide good correlation of the data and the kinetic parameters of the model could be written in terms of linearized contributions in temperature, average particle diameter and flow rate. (c) 2009 Elsevier B.V. All rights reserved.

Carotenoid production from highly CO., tolerant microalga Chlorococcum littorale in photoautotrophic cultures with downstream supercritical fluid processing was studied. Increasing temperature, increasing light intensity and decreasing CO(2) and O(2) gas concentrations, enhanced growth rate under nitrate-rich conditions. Carotenoid content was insensitive to nitrate concentration, temperature and gas composition, but was greatly promoted by light intensity. Growth rate and carotenoid content had an Optimum light intensity of ca. 120 mu mol-photon . m(-2)s(-1). Separation of two sample cultures was studied by applying supercritical fluid extraction with CO, and 10 mol% ethanol co-solvent. Extraction yield of carotenoids was 90% with 10 mol% ethanol at 333 K and 30 MPa. Selectivity of a sample with less lipid content (12.9 wt%) was five-fold higher than that with higher lipid content (29.4 w%).

Sulfated zirconia was prepared by impregnation with H(2)SO(4), and was characterized using BET Surface area, XRD, TG-DTA and FNR techniques. The sulfated zirconia was evaluated as a catalyst for the dehydration of fructose to 5-hydroxymethylfurfural (5-HMF) by microwave heating. With sulfated zirconia catalyst, high fructose conversion of 93.6% with 5-HMF yield of 72.8% could be attained at 180 degrees C for 20 min reaction time in acetone-dimethylsulfoxide (DMSO) mixtures. Sulfated zirconia is an effective catalyst for producing 5-HMF from fructose in non-aqueous solvent but shows low catalytic activity in water solvent. (C) 2009 Elsevier B.V. All rights reserved.

The growth rate of a highly CO2-tolerant green alga, Chlorococcum littorale, was investigated in semi-batch cultures at a temperature of 22°C, a light intensity of 170 μmol-photon m-2 s -1 and CO2 concentrations ranging from 1 to 50% (v/v) at atmospheric pressure. In the experiments, solutions were bubbled with CO 2 and N2 gas mixtures to adjust CO2 concentrations to minimize the influence of O2. Growth rate, which was defined in terms of a specific growth rate μ, decreased with increasing CO2 concentration at the conditions studied. The inhibition of growth by CO2 gas could be attributed to the concentration of inorganic carbon in the culture medium. A growth model is proposed where key assumptions are the formation of bicarbonate ion HCO3- as substrate for algal growth and equilibrium between CO2 inhibitor. The proposed growth model based on the Monod equation agreed with the experimental data to within 5% and provides better correlation than the conventional inhibition model, especially in the high CO2 concentration region. © 2009 American Institute of Chemical Engineers.

An efficient process for the dehydration of fructose into 5-hydroxymethylfurfural (5-HMF) in ionic liquid 1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]) by using a sulfonic ion-exchange resin as catalyst was developed. A fructose conversion of 98.6% with a 5-HMF yield of 83.3% was achieved in 10 min reaction time at 80 degrees C. When the reaction temperature was increased to 120 degrees C, a 5-HMF yield of 82.2% was obtained in only 1 min for essentially 100% fructose conversion. No large decrease in 5-HMF selectivity occurred for initial fructose concentrations of up to 20 wt.%. Water content of up to 5% in the [BMIM][Cl] had no effect on the fructose conversion rate and 5-HMF yield, but water content higher than 5 wt.% led to lower conversions and yields. The ionic liquid and sulfonic ion-exchange resin could be recycled and exhibited constant activity for 7 successive trials. The proposed process of using an ionic liquid with ion-exchange resin catalyst greatly reduces the reaction time required over previous works for converting fructose to 5-HMF.

Catalytic dehydration of D-fructose to 5-Hydroxymethylfurfural (5-HMF) in acetone/dimethyl sulfoxide solvent mixtures was studied in the presence of a strong acidic cation-exchange resin catalyst (DOWEX 50WX8-100) by microwave heating. The addition of acetone to the dimethyl sulfoxide (DMSO) solvent promoted the formation of 5-HMF from D-fructose. For a D-fructose conversion of 97.9%, the 5-HMF selectivity was 91.7% for a 20-min reaction time in 70:30 (w/w) acetone/DMSO solvent mixtures. Concentrations as high as 10 wt % D-fructose were studied, for which it was found that 5-HMF yields of 82.1% for a reaction time of 10 min could be obtained. The stability of the ion-exchange resin used as the catalyst was confirmed. Compared to pure DMSO solvent, the combination of low-boiling-point acetone with DMSO used as the reaction medium not only gives highly selective 5-HMF formation, but also improves the separation efficiency and reduces environmental risk.

Production of 5-hydroxymethylfurfural (5-HMF) from glucose and fructose catalyzed by TiO2 and ZrO2 under microwave irradiation was studied. For the case of TiO2 used in the fructose reaction, 5-HMF yield was 38.1% for a fructose conversion of 83.6% for 5 min reaction time. A 5-HMF yield of 30.5% for a fructose conversion of 65% was obtained for 5 min reaction time in the presence of ZrO2. The ZrO2 was found to promote isomerization of glucose to fructose, in which the selectivity of fructose from glucose became higher than 60% for about 50% glucose conversion for a reaction time of 1 min. Under the conditions (5 ml of 2 wt% fructose solution, 0.05 g of TiO2, 200 degrees C, and 3 min), fructose conversion and HMF yields by microwave heating (73% and 35%, respectively) were higher than those by sand bath heating (27% and 12%, respectively). (C) 2008 Elsevier B.V. All rights reserved.

Hydrogen production from biomass was attempted in high pressure high temperature water at 573 K by adopting partial oxidation to increase the yield of H-2 via CO production in the presence of ZnO. The results revealed that an addition of H2O2 as an oxidant to the reaction of glucose and sugarcane bagasse brought about the trend of increasing the yields of H-2, CO, and CO2. However, the sensitivity of H-2 yield on H2O2 amount was different from those of CO and CO2, namely the excess amount of H2O2 tends to decrease the H-2 yield with giving a maximum at a certain H2O2 amount. These indicated that the controllability of partial oxidation would be a key factor for maximizing the H-2 yield through biomass conversion by partial oxidative gasification in high pressure high temperature water

Catalytic dehydration of fructose into 5-hydroxymethylfurfural by microwave heating was studied in acetone-water mixtures in the presence of a cation exchange resin catalyst. The use of acetone-water reaction media resulted in yields of 5-HMF as high as 73.4% for 94% conversion at 150 degrees C. It was confirmed that there was no decrease of catalytic activity and selectivity for five reuses of the resin, which was in accordance with the elemental analysis results that showed that sulfonic acid groups attached on the resin were stable at the experimental conditions. A comparison between conventional sand bath heating and microwave heating revealed that the latter had a remarkable accelerating effect not only on fructose conversion, but also on 5-HMF yield. Under the conditions (5 ml of 2 wt% fructose solution, 0.1 g of resin, 150 degrees C and 10 min), fructose conversion and HMF yields by microwave heating (91.7% and 70.3%, respectively) were higher than those by sand bath heating (22.1% and 13.9% respectively). Therefore, the process that we developed in this study showed that high 5-HMF yields from fructose could be achieved under mild conditions.

A laser-Doppler vibrometer was used to measure the vibration of a vibrating tube densimeter for measuring P-V-T data at high temperatures and pressures. The apparatus developed allowed the control of the residence time of the sample so that decomposition at high temperatures could be minimized. A function generator and piezoelectric crystal was used to excite the U-shaped tube in one of its normal modes of vibration. Densities of methanol-water mixtures are reported for at 673 K and 40 MPa with an uncertainty of 0.009 g/cm(3). (c) 2007 American Institute of Physics.

CH4-CO2 replacement in CH4 hydrate with high pressure CO2 was studied with in-situ laser Raman spectroscopy at 273.2 K and at initial pressures of 3.2, 5.4, and 6.0 MPa. Replacement rates increased with increasing pressures up to 3.6 MPa and did not change at higher pressures (similar to 6.0 MPa). These results showed that the replacement rates were dependent on pressure and phase conditions with the driving force being strongly related to fugacity differences of the two guest components between fluid and hydrate phases. When CH4 hydrate was contacted with CO2 under flow conditions, in-situ Raman measurements of the hydrate phase showed differences of cage decomposition rates between the Medium-cage (M-cage) and the Small-cage (S-cage) in the CH4 hydrate with decomposition of the M-cage being faster than that of the S-cage. The van der Waals-Platteeuw model was applied to the measurements of the transient data and it is shown that the theory allows estimation of occupancies of each component during replacement. (c) 2007 American Institute of Chemical Engineers.

Interfacial tension of water-CO2 interface was measured by pendant drop method in the presence of a surfactant of various concentrations. The surfactants used were three surfynols which are non-ionic blanched hydrocarbon with different length of the alkyl side chain. Prior to the interfacial tension measurements, the solubility of the surfynols in CO2 were determined from cloud point method. The measured interfacial tensions indicated that an addition of small amount surfactant did reduce the interfacial tension. The interfacial activities of surfactants were evaluated from the slope of the interfacial tension reduction curve against the surfactant concentration and rationalized in terms of the molecular natures such as hydrophobic alkyl chain length. (c) 2007 Elsevier B.V. All rights reserved.

Glycerol conversion was conducted in hot-compressed water (HCW: 573-673 K, 25-34.5 MPa) using a batch and a flow apparatus and the influences of temperature, H2SO4, glycerol concentration, and pressure, were examined. The yield of acrolein was enhanced by higher glycerol and H2SO4 concentration, and higher pressure. Approximately 80% selectivity of acrolein was obtained at 90% of glycerol conversion with an acid catalyst in supercritical condition (673 K and 34.5 MPa). The rate constant of acrolein decomposition was always higher than that of acrolein formation in the absence of acid catalyst but the rate constant of acrolein formation could be overcome that of acrolein decomposition by addition acid in supercritical condition. (c) 2006 Elsevier Ltd. All rights reserved.

Reaction Of D-glucose in water to yield 5-hydroxyinethylfurfural (5-HMF), 1,2,4-benzenetriol (BTO) and furfural was studied at high temperatures (up to 400 degrees C) and high pressures (up to 80 MPa) using a continuous flow reactor. Maximum temperature and pressure conditions gave maximum furfural yield, Increasing pressure from 40 to 70 and 80 MPa enhanced dehydration reactions to 5-HMF, but also enhanced hydrolysis of 5-HMF leading to the production of BTO and thus lead to lower yields of 5-HMF (below 10%). Remarkably, the dehydration reaction to 5-HMF and the hydrolysis of 5-HMF were both enhanced by the increase in water density at 400 degrees C. (c) 2006 Elsevier B.V. All rights reserved.

Liquefaction of glucose in-to oil was examined in hot-compressed water at 300 degrees C and 30 or 60 min in a tumbling batch reactor. The effects of alkali (KHCO3), a hydrogenating agent (HCO2H), and a cobalt catalyst (Co3O4) were studied. Also the combinations of these additives were investigated. HCO2H and KHCO3 showed a positive effect on oil formation. Co3O4 was found to be an advantageous additive as well, increasing the oil formation from glucose, but the stability of this catalyst under reaction conditions was quite low. (c) 2006 Elsevier Ltd. All rights reserved.

Stearic acid (C17H35COOH: C-17-acid) was treated using a batch reactor with supercritical water (SCW) of 673 K and 0.17 g/cm(3\) for 30 min. In SCW, C-17-acid was stable (2% conversion) and the main products were CO2 and C-16 alkene. An addition of alkali hydroxide (NaOH and KOH) in the SCW reaction enhanced the decarboxylation of C-17-acid with the main products being CO2 and C-17 alkane. Metal oxides (CeO2, Y2O3 and ZrO2) enhanced the decarboxylation of C-17-acid and the main products were C02 and C16 alkene. Based on the results, the reaction mechanism was proposed. (c) 2006 Elsevier Ltd. All rights reserved.

The extraction of carotenoids from Japanese persimmon peels by supercritical fluid extraction (SFE), of which the solvent was CO2, was performed. In order to enhance the yield and selectivity of the extraction, some portion of ethanol (5 - 20 mol%) was added as an entrainer. The extraction temperature ranged from 313 to 353 K and the pressure was 30 MPa. The effect of temperature on the extraction yield of carotenoids was investigated at 10 mol% of the ethanol concentration in the extraction solvent, and a suitable temperature was found to be 333 K among the temperatures studied with respect to the carotenoid yield. With increasing the entrainer amount from 0 to 10 mol% at a constant temperature (333 K), the carotenoid yield in the extraction was improved, whereas the selectivity of the extracted carotenoids was drastically depressed. We also conducted qualitative and quantitative analyses for the carotenoid components in the extract by HPLC, and analyzed the extraction behavior of each individual carotenoid (alpha-carotene, beta-carotene, beta-cryptoxanthin, lycopene, lutein, and zeaxanthin). The selectivity of each carotenoid changed with the elapsed time and its time evolution was dependent on the carotenoid component, indicating that the location profile and the content can be important factors to understand the SFE behavior of each carotenoid in persimmon peels.

Gasification of lignin and 4-propylphenol, which is a model of low-molecular weight compounds from lignin, over supported metal catalysts in supercritical water was studied at 673 K. Supported ruthenium catalysts were active in supercritical water. The catalytic gasification rate was enhanced by the increase of water density. The gasification of lignin proceeded in supercritical water through two steps: (i) decomposition of lignin to low-molecular weight compounds and (ii) gasification of the low-molecular weight compounds over metal catalysts. The rate of 4-propylphenol gasification was not affected by the water density; this was different from lignin gasification. These results indicated that the first step ( decomposition to low-molecular weight compounds) in the lignin gasification was enhanced by increasing the water density.

Research in biomass gasification with subcritical and supercritical water is reviewed. Catalytic conversion of biomass in sub- and supercritical water is a low-temperature gasification technique that can be carried out from 473 to 973 K. Research is categorized according to temperature and water density, since reaction mechanisms greatly depend on these variables.

Hydrothermal synthesis of metal oxide (AlOOH/Al2O3, CuO, Fe2O3, NiO, ZrO2) nanoparticles from metal nitrate aqueous solution was carried out at 673 K and pressures ranging from 25 MPa to 37.5 MPa with a flow-through supercritical water method. Size, phase and crystallinity of the obtained particles were characterized by TEM, XRD and TG, respectively. Effect of the difference of the metals in starting materials, pressures and concentrations on particle size and crystallinity was analyzed on the basis of supersaturation, which was evaluated by estimated metal oxide solubility. The result suggests that supersaturation should be set to higher than around 10(4) in this method to obtain particles under 10 nm in diameter. Further, crystallinity of the obtained particles was evaluated as weight loss through TG analysis. It was found that higher supersaturation decreased the crystallinity. This result can be explained that high supersaturation led to the inclusion of water molecules during the formation of particles.

Glucose reactions were conducted in hot compressed water (473-773 K, 4-40 MPa) by means of a batch-type reactor. The reactions in the heating period (about for 60 s) were observed. More than 80% of the glucose was consumed in the heating period above 573 K. Gasification of glucose was promoted with increasing temperature. The effect of heating rate (from 4.2 to 15.8 K/s) on glucose conversion was also examined, and gasification of glucose was enhanced with increasing the heating rate. (c) 2005 Elsevier Ltd. All rights reserved.

The effects of the homogeneous catalysts (H2SO4 and NaOH) and heterogeneous catalysts (TiO2 and ZrO2) on glucose reactions were examined in hot compressed water (473 K) by a batch-type reactor. From the homogeneous catalyst studies, we confirmed that the acid catalyst promoted dehydration, while isomerization of glucose to fructose was catalyzed by alkali. Anatase TiO2 was found to act as an acid catalyst to promote formation of 5-hydroxymethylfuraldehyde (HMF). Zirconia (ZrO2) was a base catalyst to promote the isomerization of glucose. The effects of the additives were also confirmed through fructose reactions. (c) 2005 Elsevier Ltd. All rights reserved.

The dynamics of CH4 replacement in the CH4 hydrate with saturated liquid CO2 at 273.2 K was measured with a high pressure optical cell. The results showed that CH4 in the hydrate gradually moved to the liquid CO2 phase while CO2 in the liquid phase penetrated into the hydrate from the quantitative analysis. The decomposing process of the CH4 hydrate during the replacement was analyzed with in situ Raman spectroscopy, which allowed us to distinguish the cage structure of the CH4 hydrate and discuss the microscopic view of the replacement in the hydrate. It was found that the decomposition of the medium cage (M-cage) in the CH4 hydrate proceeded faster than that of the small cage (S-cage). The observed rate difference could be related to the stability of the S-cage in the CH4 hydrate or the re-formation tendency of CH4 and water molecules in the S-cage after decomposing the hydrate structure, whereas the guest molecule exchange of CH4 with CO2 could occur in the M-cage. Based on the experimental data, we developed a kinetic model for calculation of the CH4 remaining in the hydrate considering the decomposition rate difference between the M-cage and S-cage in the CH4 hydrate. The results indicate that the driving force could be the fugacity difference between the fluid phase and the hydrate phase for the replacement process. (c) 2004 Elsevier Ltd. All rights reserved.

The dynamics of CH4 replacement in CH4 hydrate with high-pressure CO2 was observed with in situ laser Raman spectroscopy at temperatures ranging from 271.2 to 275.2 K and at an initial pressure of 3.25 MPa. The amount of CH4 hydrate decomposition was found to be almost proportional to that Of CO2 hydrate formation for a series of 150 h experiments at fixed temperatures. This confirmed that the CH4-CO2 replacement mainly occurred in the hydrate phase. Based on the rate data, a kinetic model was developed for CH4 hydrate decomposition and CO2 hydrate formation. Under CH4-CO2 replacement in the hydrate, the activation energies were determined to be 14.5 kJ/mol for CH4 hydrate decomposition and 73.3 kJ/moI for CO2 hydrate formation after a given initial period (ca. 10 h). It was found that CH4 hydrate decomposition was probably dominated by re-arrangement of water molecules in the hydrate whereas CO2 hydrate formation seemed to be dominated by diffusion in the hydrate phase. (c) 2004 Elsevier B.V. All rights reserved.

The water density dependence of formaldehyde (HCHO) reaction in supercritical water (SCW) was studied with batch experiments. Major products from the reaction were methanol (CH3OH), formic acid (HCOOH), hydrogen (H-2), carbon monoxide (CO) and carbon dioxide (CO2). It was found that the Cannizzaro reaction mechanism was the preferred reaction pathway for HCHO reaction in SCW. At higher water densities, CH3OH yields increased confirming the predominance of the Cannizzaro reaction mechanism. At low water densities, CO yields increased and CH3OH yields decreased, which indicated that monomolecular decomposition became the main reaction pathway. Addition of base to the reacting mixtures was found to promote the Cannizzaro reaction path whereas addition of acid promoted monomolecular decomposition. (C) 2003 Elsevier B.V. All rights reserved.

Lignin and cellulose were gasified at 400 °C with gas yields of 30% and 70%, respectively, in supercritical water with a ruthenium catalyst. In both cases, the main gas product was CH4 and no solid product was formed. Without water or catalyst, lignin and cellulose were gasified slightly and a brown solid product was formed. The decomposition of formaldehyde was also demonstrated in supercritical water. Formaldehyde was rapidly decomposed to gases such as CH4, CO2, and H2 with ruthenium, whereas formaldehyde was converted into methanol and CO2 without catalyst. The catalytic conversion of biomass with ruthenium in supercritical water is an efficient method for biomass gasification at temperatures of ∼400 °C.

Partial oxidation of methane was conducted in supercritical water at O-2/CH4 ratios of 0.03 at 673 K with a flow-type reactor. The main products were CO, methanol, formaldehyde and a small amount of CO2 and H-2. With increasing water density, methane conversion increased due to the formation of formaldehyde. A free radical reaction model was applied to this reaction and it was confirmed that the dependence of selectivities for CO and CO2 on pressure could be well described. The experimental results and model prediction shows that an increase of water density shifted product distribution to partial oxidation products and formaldehyde was found to play an important role in the product selectivity and the partial oxidation chemistry. (C) 2003 Elsevier B.V. All rights reserved.

Gasification of alkylphenols as lignin model compounds was examined in the presence of supported noble metal catalysts in supercritical water without hydrogen donor at 673 K. The activity of the catalyst was in the order of Ru/gamma-alumina > Ru/carbon, Rh/carbon > Pt/gamma-alumina, Pd/carbon, and Pd/gamma-alumina. The effect of water density with the Ru/gamma-alumina catalyst was examined in detail. The main gas products were methane, carbon dioxide, and hydrogen. The yield of gases and the ratio of methane increased with increasing water density. The gasification of the isomers of propylphenols was also examined with the Ru/gamma-alumina catalyst. The reactivities of o- and p-propylphenols were relatively higher than those of m-propylphenols.

The decomposition of lignin was examined in supercritical water with and without phenol at 673 K. In the absence of phenol, the yield of tetrahydrofuran (THF)-insoluble (TIS) products decreased and the molecular weight distribution of THF-soluble (TS) products shifted toward lower molecular weights as the water density increased. The increase in water density enhanced the lignin conversion. In the presence of phenol, the yield of TIS products was lower and the molecular weight distribution of TS products shifted toward lower molecular weights than those in the absence of phenol. Some alkylphenols were obtained only in the presence of phenols, because of the reaction of phenol with the decomposition products. These results show that the reaction of phenol with reactive sites occurred in supercritical water and suppressed cross-linking reactions among reactive sites of large fragments. This promoted the decomposition of lignin to lower-molecular-weight compounds.

Formaldehyde (HCHO) reactions in supercritical water (673K and 25-40MPa) with and without acid and base catalysts (homogeneous: H2SO4 and NaOH, and heterogeneous: CeO2, MoO3, TiO2, and ZrO2) were conducted by use of batch reactors. Cannizzaro reaction (2HCHO+H2O → CH3OH+HCOOH) and self-decomposition of HCHO (HCHO → CO+H2) were found to be primary reactions for all the cases and the contribution of each reaction depended on the condition. In the case of the homogeneous systems, Cannizzaro reaction became dominant with increasing bulk hydroxyl ion (OH-). The simple network model can well express the experimental results in the homogeneous conditions. We correlated the ratio of the yield of CH3OH to that of CO (at 15min) against bulk OH- in the homogeneous system. For elucidating acidity and basicity of metal oxide catalysts on HCHO reaction in supercritical water, OH- concentration on the metal oxide surface was calculated by use of the above correlation and the following order was found: CeO2 &gt ZrO2 &gt MoO3 &gt TiO2 (rutile) &gt TiO2 (anatase). At the reaction condition, CeO2 and ZrO2 were base catalysts, and MoO3 and TiO2 were acid catalysts. The experimental results with the metal oxides can be expressed by the model that was developed under homogeneous systems, with the values of the OH- concentrations that were calculated from the correlation about the CH3OH/CO ratio at 15min of reaction time. © 2003 Elsevier Science B.V. All rights reserved.

UV-visible spectra of quinoline was measured in sub- and supercritical water (25 degreesC<T<430 degreesC and 0.1 MPa<P<40 MPa), and the degree of hydrogen bonding between quinoline and water was estimated from solvatochromic shifts in the pi-pi(*) absorbance band. Hydrogen bonding decreased with increasing temperature from 25 to 360 degreesC. At supercritical conditions (380 degreesC<T<400 degreesC), hydrogen bonding abruptly decreased where the isothermal compressibility of water was large (0.5<rho(r)<1.5). In this condition, local density around quinoline was lower than bulk density, namely negative solvation, and it led to the cleavage of hydrogen bonding between quinoline and water. (C) 2003 American Institute of Physics.

Reactions of formaldehyde (HCHO), acetic acid (CH3COOH), 2-propanol (2-PrOH), and glucose with some metal oxides (CeO2, MoO3, TiO2, and ZrO2) were conducted in supercritical water at 673 K and 25-35 MPa, using batch reactors. For the reactions of HCHO, CeO2 and ZrO2 showed basicity, on the other hand, MoO3 and TiO2 were acid catalysts. ZrO2 catalyst promoted bimolecular decarboxylation of CH3COOH to form acetone, which indicates that both acid and base sites exist on.-the surface-of ZrO2 in supercritical water. Dehydration of 2-PrOH with formation of propylene was promoted by acid catalyst (H2SO4), while its dehydrogenation with formation of acetone was catalyzed by alkali (NaOH). All the metal oxides that were used in this study promoted dehydration of 2-PrOH; namely there are mainly acidic sites for 2-PrOH reactions on the surface of all the metal oxides under the conditions used. Among the metal oxides, ZrO2 and TiO2 (rutile) enhanced the formation of acetone in the case of 2-PrOH reaction. This means there are also basic sites for 2-PrOH on the ZrO2 and TiO2 (rutile). In supercritical water at 673 K and 15 min, H-2 yield from glucose in the acidic atmosphere (namely in the presence of H2SO4) is lower than that in the absence of additive whereas, on the other hand, the H-2 yield in the presence of NaOH is twice as much as that in the absence of the additive. With CeO2 and ZrO2, the H-2 yield from glucose was almost twice as high as that without catalyst. By adding MoO3 and TiO2, the amount of H-2 formation was suppressed. Through this study, we can show the generality of acidity and basicity of the metal oxides for organic reactions in SCW.

The decomposition of 2-isopropylphenol at temperatures of 613-713 K and water densities of 0-0.6 g/cm(3) yielded phenol, propene, and 2-propylphenol. The decomposition was determined to occur via two reaction pathways: (1) dealkylation of 2-isopropylphenol to produce phenol and propene and (2) rearrangement of the propyl functional group from 2-isopropylphenol to 2-propylphenol. The rate constant for dealkylation increased proportionally with increasing water density. The reaction rate for rearrangement was invariant with the water density. The rate constants for dealkylation and rearrangement could be correlated as a function of temperature and water density with a global reaction model.

We conducted the batch experiments for hydrogen production from biomass (glucose and cellulose) with ZrO2 catalyst in supercritical water (673-713 K and 30-35 MPa). For comparison, we also conducted the experiments with alkali and without catalyst at the same conditions. The yield of hydrogen with zirconia was almost twice as much as that without catalyst for all the starting materials (glucose and Cellulose). (C) 2002 Elsevier Science Ltd. All rights reserved.

Reactions of acetic acid were conducted with alkali (KOH) and zirconia (ZrO2) catalysts in supercritical water (SCW) (673K and 25MPa-40MPa). For comparison, we also conducted the experiments without catalyst and/or water at the same reaction conditions. Decarboxylation of acetic acid with zirconia in supercritical water formed acetone, CO2, and water without forming any other compound. On the other hand, decomposition of acetic acid with alkali produced methane (CH4) and CO2 with acetone. Without water and/or catalyst, the main products were also CO2 and CH4 (without catalyst) or acetone (with ZrO2) however, by-products, such as a water-insoluble compound were formed. The structure of zirconia was changed during reaction in supercritical water. The rate of decarboxylation of acetic acid exerted an effect on the particle size of zirconia. © 2001 Elsevier Science B.V. All rights reserved.

In supercritical water the rate of methanol oxidation was controlled by ionic behavior as follows: the oxidation rate of methanol decreased with increasing proton and hydroxide ion concentration, possibly due to stabilization of the reactant, while that of CO was suppressed by added protons and enhanced by added hydroxide ions.

We propose a new process for the hydrotreatment of heavy oils in supercritical water (SCW). The discussion in this paper is composed of three parts: (1) hydrogenation through water-gas shift reaction in supercritical water, (2) selective formation of carbon monoxide by partial oxidation in supercritical water and through combinations of these two, and (3) hydrogenation of hydrocarbons through their partial oxidation in supercritical water. In the experiments involving hydrogenation of dibenzothiophene, carbazole, and naphthalene, faster hydrogenation rates could be obtained in a CO-SCW atmosphere than in a H-2-SCW atmosphere. Even in the case of a H-2-CO2-SCW atmosphere, similarly faster reaction rates were obtained, which suggests that an intermediate species of the water-gas shift, reaction is the actual reason for the high hydrogenation rates. Partial oxidation experiments were conducted for hexylbenzene and n-hexadecane. The selectivity of CO increased with increasing density of water, while CO2 was the main product of the gas-phase reaction. Partial oxidation of dibenzothiophene (with a sulfur-treated NiMO/Al2O3 catalyst) and n-hexadecane (without catalysts) were also examined. Hydrodesulfurization of dibenzothiophene proceeds effectively in water. For n-hexadecane oxidation, the alkane/alkene ratio increased with increasing water density. The observed product distribution is probably due to the production of carbon monoxide, which is followed by the formation of active hydrogenating species via the water-gas shift reaction. This work demonstrates that hydrogenation reactions can be greatly accelerated in supercritical water through the use of either direct introduction of carbon monoxide or in situ formation of carbon monoxide through the partial oxidation of hydrocarbons.

Pyrolysis experiments on n-hexadecane (n-C-16) were conducted at 673-723 K and n-C-16 concentrations of 0.07-1.47 mol/L by using batch type reactors. The main products of n-C-16 pyrolysis were n-alkanes and 1-alkenes at all the reaction conditions. The 1-alkene/n-alkane ratio decreased with increasing n-C-16 concentration at all the reaction temperatures. The rate of n-C-16 pyrolysis increased to a maximum and then decreased with increasing n-C-16 concentration. The activation energy of the overall rate constant of n-C-16 pyrolysis was 196 kJ/mol at 0.07 mol/L of n-C-16 concentration and 263 kJ/mol at 0.22 mol/L. To describe these phenomena, a mathematical model for the pyrolysis that expresses the radical network reaction, including initiation, isomerization, beta-scission, H abstraction, and termination, was developed. The effect of radical size-on the rates of bimolecular reactions (H abstraction and termination) was important for a correct quantitative description. Comparison between the experimental data and the model showed that the rates of bimolecular reactions were inversely proportional to the carbon number i of radical R-i. The model can predict product distribution and n-C-16 pyrolysis rate in a wide range of temperatures (603-893 K) and n-C-16 concentrations (6.86 x 10(-3) 2.48 mol/L). Furthermore, the model can describe the pyrolysis kinetics of n-C-10 - n-C-25 by considering the carbon number of the hydrocarbon.

We conducted a series of experiment for direct in situ observation of coal conversion in supercritical water (SCW) and in HCOOH-SCW at 380 degrees C and 85 MPa using a diamond anvil cell. The effective liquefaction of coal took place in HCOOH-SCW. We conducted another series of coal extraction experiments with supercritical water (SCW) and formic acid (HCOOH) - SCW co-solvent at 380 degrees C and 35MPa using a semi-batch type apparatus. The results clearly indicate that coal conversion (80 wt% daf) and the liquid yield (72 wt% daf) in HCOOH-SCW were higher than those in SCW.

We conducted a comparative study of catalytic hydrodesulfurization of dibenzothiophene (DBT) with NiMo/Al2O3 at 673 K and 30 MPa, in various atmospheres (H-2-SCW, CO-SCW, CO2-H-2-SCW, and HCOOH-SCW), using a tube bomb reactor. Higher conversion of DBT was obtained in CO-SCW, CO2-H-2-SCW, and HCOOH-SCW than in H-2-SCW. These results clearly indicate that a water-gas shift reaction in supercritical water (SCW) produces species which can hydrogenate DBT more effectively than H-2 gas. We also conducted another experiment for the partial oxidation of a DBT-hexylbenzene mixture in SCW. Even in the presence of oxygen, effective hydrogenation of DBT took place. This result is probably because CO forms through the partial oxidation of hexylbenzene and converts to the hydrogenating species through a water-gas shift reaction. We think the catalytic desulfurization of heavy oils in SCW will be a promising new technology, since even by introducing oxygen or air instead of hydrogen, an excellent hydrogenating atmosphere can be supplied.

This paper describes pyrolysis of polyethylene (PE) and n-hexadecane (nC16) in supercritical water (SCW). Batch reactions were conducted at temperatures ranging from 673 to 723 K, at a reaction time of 30 min, and water density between 0 and 0.42 g/cm3. The pyrolysis rate of nC16 in SCW was almost the same as that in 0.1 MPa argon (Ar) atmosphere. Product distribution was also more or less the same for both cases. PE pyrolysis results were clearly different from pyrolysis results in Ar. In SCW, higher yields of shorter chain hydrocarbons, higher 1-alkene/n-alkane ratio, and higher conversion were obtained. This difference of PE pyrolysis in SCW and in Ar could be explained by considering the difference in the reaction phase. © 1998 Elsevier Science B.V. All rights reserved.