Tsutomu Sugeta

High pressure vapor-liquid and vapor-liquid-liquid equilibria for systems containing supercritical carbon dioxide, water and furfural

Abstract We measured vapor-liquid equilibrium for a binary system CO2furfural at temperatures of 303 and 323 K and vapor-liquid-liquid equilibrium for a ternary system CO2waterfurfural at temperatures of 303, 323 and 343 K and pressure of 5 MPa to obtain fundamental data for concentration of furfural by using three phase separation technique. Furthermore the experimental data were compared with results calculated by the Peng-Robinson equation of state combined with an asymmetric mixing rule. Results indicated that (1) the furfural-rich liquid phase contained more than 90wt% furfural on CO2-free basis and its concentration increased with decrease in temperature, and (2) the Peng-Robinson equation correlated the binary vapor-liquid equilibrium satisfactorily and estimated the ternary vapor-liquid-liquid equilibrium fairly well.

Solubility and adsorption of high pressure carbon dioxide to poly(styrene)

Abstract Solubility and adsorption of high pressure carbon dioxide (CO2) to poly(styrene) (PS) were measured at 313.2 K and pressures up to 17 MPa using a quartz crystal microbalance (QCM) as a detector. Two kinds of PS film, made by dip coating (d-PS) and plasma polymerization (p-PS), were used as samples. The amount of adsorption onto both films was almost the same within the experimental range. The solubility to both films increased almost linearly against activity of CO2 up to unity, and that to p-PS was slightly higher than that to d-PS. Above unity, the solubility to p-PS film increased with the increase in activity. In contrast, solubility to d-PS sharply decreased near the unity and became a constant value.

Hydrogen bonding in supercritical methanol studied by infrared spectroscopy

We report the first Fourier transform infrared spectroscopic studies of the hydrogen-bonding interactions in supercritical methanol and methanol/methanol-d1 mixtures. At 523 K and below ∼0.3 mol/l, methanol chiefly existed in a monomeric form. However, at 523 K and between ∼0.3 and 2 mol/l, in the regions of O–H, C–O, and C–H stretching vibrations, there were clear indications of methanol monomer–dimer equilibrium. The effect of temperature on the equilibrium constant was also investigated. As a result, the partial molar volume difference and enthalpy of the dimerization were estimated and correlated with the behavior of the methanol isothermal compressibility. It was also concluded that at 523 K and density higher than ∼15 mol/l, the hydrogen-bonding equilibrium started to shift toward larger aggregates.

Effects of supercritical impregnation conditions on the properties of silica–titania aerogels

Abstract The preparation of silica–titania aerogel by supercritical impregnation of titanium isopropoxide (TP) or modified with acetylacetone (TPAA) using flow type apparatus was performed. The influence of the physical state of TP/CO 2 TPAA/CO 2 mixture was investigated. Homogeneous and rapid impregnation on monolithic silica alcogel was achieved using supercritical TP/CO 2 or TPAA/CO 2 mixtures at the single phase condition (353 K, 20 MPa). Crystallization of impregnated titania using this system was attained by increasing temperature during the depressurization process after impregnation.

Microscopic solvent structure of subcritical and supercritical methanol from ultraviolet/visible absorption and fluorescence spectroscopies

Ultraviolet/visible absorption and fluorescence spectroscopies at different temperatures and pressures were applied to investigate the microscopic solvent structures of subcritical and supercritical methanol using 4-nitroanisole, ethyl-(4-dimethylamino)benzoate, Reichardt’s dye, and anthracene as the probe molecules. It was found that at temperatures higher than 150 °C the long winding chains of sequentially hydrogen-bonded methanol molecules were probably broken, but the small hydrogen-bonded aggregates possibly existed in methanol even at higher temperature. It was also found that the solvation process of the anthracene molecule in the S0-ground state obeyed the Langmuir adsorption model. However, in the case of fluorescence measurements in supercritical methanol, we detected deviations from the simple Langmuir adsorption model. These deviations were explained in terms of preferential solvation of the solvent molecules around photoexcited anthracene. Judging from the experimental results, it was conclud...

Acetone hydration in supercritical water: 13C-NMR spectroscopy and Monte Carlo simulation

The (13)C-NMR chemical shift of acetone delta((13)C[Double Bond]O) was measured in aqueous solution at high temperatures up to 400 degrees C and water densities of 0.10-0.60 g/cm(3) for the study of hydration structure in the supercritical conditions. The average number N(HB) of hydrogen bonds (HBs) between an acetone and solvent waters and the energy change DeltaE upon the HB formation were evaluated from the delta and its temperature dependence, respectively. At 400 degrees C, N(HB) is an increasing function of the water density, the increase being slower at higher water densities. The acetone-water HB formation is exothermic in supercritical water with larger negative DeltaE at lower water densities (-3.3 kcal/mol at 0.10 g/cm(3) and -0.3 kcal/mol at 0.60 g/cm(3)), in contrast to the positive DeltaE in ambient water (+0.078 kcal/mol at 4 degrees C). The corresponding Monte Carlo simulations were performed to calculate the radial and orientational distribution functions of waters around the acetone molecule. The density dependence of N(HB) calculated at 400 degrees C is in a qualitative agreement with the experimental results. In the supercritical conditions, the HB angle in a neighboring acetone-water pair is weakly influenced by the water density, because of the absence of collective HB structure. This is in sharp contrast to the hydration structure in ambient water, where the acetone-water HB formation is orientationally disturbed by the tetrahedral HB network formation among the surrounding waters.

Preparation of SiO2-TiO2 Aerogels Using Supercritical Impregnation

The preparation of SiO2-TiO2 aerogels by supercritical impregnation of titanium alkoxides into silica alcogels was investigated. A mixture of CO2 and 2-propanol with dissolved titanium tetraisopropoxide modified with acetylacetone was used as the impregnation medium. Prior to the experiments, the supercritical behaviour of the impregnation solution was investigated. The microstructure and properties of aerogels prepared by the supercritical impregnation method were almost identical to those generated by the liquid impregnation. However, the time for impregnation was substantially decreased and the homogeneity of the impregnated titanium distribution on the aerogel increased.

Microscopic solvent structure of supercritical carbon dioxide and its mixtures with methanol in the cybotactic region of the solute molecule

UV/VIS absorption spectroscopy was used to estimate the microscopic solvent polarities of supercritical carbon dioxide alone and its mixtures with methanol. It was found that the local composition of methanol in the cybotactic region of 4-nitroanisole was larger than the corresponding bulk concentration. With increasing pressure the methanol molecules were pressed out of the solvation shell of 4-nitroanisole by the carbon dioxide molecules. From the solubility measurements the solvation numbers of the carbon dioxide molecules around 4-nitroanisole were calculated as a function of fluid density.

Frequency change of a quartz crystal microbalance at the supercritical condition of carbon dioxide

Abstract The frequency change of a quartz crystal microbalance was examined at 40 °C and pressures up to 15 MPa with He, N2, and C02 as a pressurizing medium. The frequency largely decreased near the critical point of the C02. The change was caused by the rapid increase of the weight of C02 physically adsorbed on the evaporated silver electrodes surface.

Ene reaction of allylbenzene and N-methylmaleimide in subcritical water and ethanol

Ene reaction of allylbenzene and N-methylmaleimide was studied in water and ethanol solvents at subcritical temperatures (220–310 °C). Subcritical water was inappropriate for this reaction, because it rapidly hydrolyzed N-methylmaleimide. Subcritical ethanol was found to be a very promising solvent. The highest ene product yield in ethanol reached 40% in 480 min, and the highest trans-selectivity was 92%. The yields in pure ethanol were comparable to those in 1,2,4-trichlorobenzene with 10% hydroquinone added as a polymerization inhibitor. Addition of hydroquinone had a negligible effect on the yield in ethanol, suggesting that the solvent ethanol itself acts as an inhibitor of the side reactions. It is also expected that the polar environment and the high vapor pressure of ethanol favored pericyclic association between the apolar starting compounds.