Takeshi Sako

Micronization and Polymorphic Conversion of Tolbutamide and Barbital by Rapid Expansion of Supercritical Solutions

ABSTRACT Rapid expansion of supercritical solutions (RESS) was applied to tolbutamide and barbital. The solubility in supercritical CO2 was determined to estimate the extraction efficiency roughly by a simple method and accurately by a direct spectrophotometric technique. The latter revealed that the solubility of tolbutamide was a function of applied pressure and temperature and was proportional to the pressure. No significant difference in solubility between polymorphic Forms I and II of tolbutamide was detected. Tolbutamide and barbital particles produced by the RESS were characterized by size distribution measurement, polymorph identification and morphological evaluation. Significant size reduction to micron or sub-micron level with narrow size distribution was achieved, while conventional mechanical grinding had only slight effect. The particle size was greatly affected by both extraction and expansion conditions. The lower the extraction temperature was, the smaller was the mean particle size. Higher extraction pressure resulted in smaller mean particle size when compared at the same extraction temperature. The mean particle size was reduced by lowering the spray nozzle temperature, by lowering the expansion chamber temperature, by increasing the CO2 amount per spray, and by increasing the exhaust gas flow rate. The RESS processing realized the polymorphic conversion as well. As for tolbutamide, three polymorphs (Forms I, II, and IV) out of four could be produced by changing the extraction conditions, and in the case of barbital, one polymorph (Form II) out of three was produced consistently.

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.

Energy conversion of biomass with supercritical and subcritical water using large-scale plants

Exploiting unused or waste biomass as an alternative fuel is currently receiving much attention because of the potential reductions in CO2 emissions and the lower cost in comparison to expensive fossil fuels. If we are to use biomass domestically or industrially, we must be able to convert biomass to high-quality and easy-to-use liquid, gas, or solid fuels that have high-calorific values, low moisture and ash contents, uniform composition, and suitable for stored over long periods. In biomass treatment, hot and high-pressure water including supercritical and subcritical water is an excellent solvent, as it is clean and safe and its action on biomass can be optimized by varying the temperature and pressure. In this article, the conversion of waste biomass to fuel using hot and high-pressure water is reviewed, and the following examples are presented: the production of large amounts of hydrogen from waste biomass, the production of cheap bioethanol from non-food raw materials, and the production of composite powder fuel from refractory waste biomass in the rubble from the Great East Japan Earthquake. Several promising techniques for the conversion of biomass have been demonstrated in large-scale plants and commercial deployment is expected in the near future.

Novel strategic lipase-catalyzed asymmetrization of 1,3-propanediacetate in supercritical carbon dioxide

Abstract In lipase-catalyzed asymmetrization of 1,3-propanediacetate no enantioselectivity was observed in conventional organic solvents, whereas in supercritical carbon dioxide (scCO2) enantioselectivities were observed up to 50% ee, which probably arose from a conformational changing of lipase at the active site due to a transformation of the amino group of lysine into carbamic acid.

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.

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.

A proposal of a new technique for the density measurement of solids

Abstract A new experimental technique for the measurement of unstable solid density that uses an oscillating U-tube was proposed. The technique was based on the simultaneous lever rules for the mass and the volume of two phase, solid+liquid (molten solid), in the U-tube. By means of this technique, the solid density can be easily determined from the overall density of solid+liquid with the combination of the literature phase diagram. To ensure the reliability, density of an amphiphilic congruent melting compound, tetrahydrofuran clathrate (THF·17H 2 O), was measured at 276.37 K under the atmospheric pressure. The density of the hydrate was estimated to be 998.40 kg/m 3 . The value was very close to the theoretical one, 999.14 kg/m 3 This technique needs a phase diagram of clathrate though it is very useful because of its simplicity and easiness to expand to a wide range of temperatures and pressures.

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.