In this article, we have dealt not only with the organic synthetic reactions using supercritical water in the absence of acid or base catalysts, but also with the chemical fixation of carbon dioxide to carbonates under supercritical conditions. In the former case, the Beckmann rearrangement to ε-caprolactam and the disproportionation of benzaldehyde to benzylalcohol proceed even without acid and base, respectively. In the latter the yield of carbonates can be enhanced just by pressure and temperature manipulation, giving a maximum yield of 85% in the synthesis of styrene carbonate in the absence of any additional catalysts.

View full abstract

The effects of temperature and concentration of dissolved CO₂ on the death kinetics of Saccharomyces cerevisiae were demonstrated. Several combinations of pressures (4, 6, 8, 10 MPa) and temperatures (30, 34, 36, 38°C) were used. The D-values obtained were 0.14 min at 8 MPa and 38°C, and 0.15 min at 10 MPa and 36°C. The log D-values were related linearly to the treatment temperature and to the dissolved CO₂ concentration. The thermal resistance constant was 9.5°C, and the CO₂ resistance constant was 7.2 γ. This work enables the estimation of the D-values at any temperature and any CO₂ concentration. Non-thermal inactivation of microorganisms would be realized by the present technique.

View full abstract

We have been developing a process that uses supercritical CO₂ to detoxify environmentally hazardous waste, namely chromated copper arsenic- (CCA-) treated wood. We measured the solubility of CuHAsO₄, which is believed to exist in wood, and found it to be of the order of 10^-9 to 10^-8. We were able to correlate the experimental data by using a solution model. We then undertook experiments designed to extract metals from CCA-treated wood by using supercritical CO₂ and a chelating agent. The addition of acetylacetone as a chelating agent markedly enhanced the extraction yield. We found that the continuous addition of acetylacetone raised the extraction ratio to about 90%.

View full abstract

Though PCB disposal lagged for fear of generating dioxin's by incineration since 1974, it has been permitted by means of chemical treatment with revision of the law in June 1998. By introducing technology from SRI of the US, we developed hydrothermal decomposition method for PCB so that it will be decomposed in hydrothermal water containing sodium carbonate. The result of fundamental test and pilot test demonstrated that PCB can be treated regardless of its concentration. We also demonstrated that paper, wood and organic solvent can be decomposed, and easily established the treatment system to make harmless perfectly the polluted vessels like a transformer or a capacitor.

View full abstract

A new recycling process for wastes using supercritical water has been developed. The monomers obtained from supercritical water hydrolysis are the raw material of condensation polymers such as poly(ethylene telephthalate), polyurethane and so on. This process was applied to TDI (Tolylene Diisocyanate) distillation residue. By the process with super- or sub-critical water, TDA can be obtained from the residue comprising TDI oligomers. The plant for the commercial use of the chemical recycling process for TDI residue using supercritical water was constructed at the end of 1997, and is now functioning as an environmentally friendly plant.

View full abstract

The internal pressure (∂E/∂V)_T has a range of 0.2-2 GPa for pure liquids. Its effect on the rate and equilibrium constants of chemical reactions can be gauged approximately if the reaction can also be studied in the gas phase at the same temperature. The influence of internal pressure is not different from that of external pressure. A few examples are mentioned. The effect is unfortunately usually overshadowed by other solvent properties such as its ability to engage in hydrogen bonding and solvation of ions and dipoles.

View full abstract

It is found that the experimental absorption coefficient of β-FeSi₂ in the range of photon energy of about 0.3 eV beyond the band gap is a few orders of magnitude larger than the first-principles calculated absorption coefficient. No critical points with negative hydrostatic pressure coefficients such as those of Si and GaAs are observed in β-FeSi₂ near the band gap. The pressure coefficient for the direct band gap of β-FeSi₂ is determined to be 15.9 meV/GPa. This small coefficient is due to the negative deformation potential of the valence-band maximum and the large bulk modulus of β-FeSi₂.

View full abstract

High pressure generation tests were performed in order to clarify the effect of surface roughness on the efficiency of pressure generation in a multi-anvil apparatus. The efficiency of three kinds of sintered diamond (SD) anvil sets, which have differing surface roughness was compared. The following results were obtained. (1) The smaller the surface roughness of the SD anvil was, the better the efficiency of pressure generation was. (2) This effect was large at low pressures but was decreased at high pressures. The reason why these results were obtained is discussed.

View full abstract