Table of contents

In the report the results of investigations of the mechanism and kinetics of the formation of cobalt doped corundum in water vapor medium are represented. Moreover, it is given the study result of changing of lattice position of cobalt ions and their state during synthesis. Aluminium hydroxide was using as raw material. Doping agent was cobalt nitrate. The doping of synthesis products (boehmite and corundum) occurs during their formation in solvothermal conditions and then in supercritical water fluid. The additives with reducing or oxidizing properties were brought in reaction medium. The products of the synthesis doped with cobalt were explored by various physicochemical methods: the X-ray phase-analysis, DR-spectroscopy, the magnetometry and SEM. It was found that the processes of the lattice rearrangement and doping take place simultaneously. In solvothermal conditions, below water critical point cobalt ions are initially chaotically distributed in the interlaminar space of the boehmite structure. At supercritical conditions the doped boehmite transforms into cobalt doped corundum. Such crystals of corundum exhibit superparamagnetic properties. After heating in vacuum (1900°C) the corundum doped with higher concentrations of cobalt acquire the ferromagnetic properties. The authors guessed that cobalt ions aggregate into the nano-sized particles of cobalt in vacancies complexes of corundum structure.

The hydrolysis of glycylglycine was studied at the temperature range of 240 to 300°C and reaction time up to 200 s. The Experiments were conducted using a continuous-flow tubular reactor. An interesting reaction phenomenon relating to the production of amino acids from hydrolysis of proteins in subcritical water was observed. Other than hydrolysis of glycylglycine to produce glycine, cyclodehydration also took place producing cycloglycylglycine. The product of glycine from cycloglycylglycine was also verified. Under the temperature range in this study, it was observed that the temperature did not has any effect on the reaction selectivity of hydrolysis and cyclodehydration of glycylglycine.

Solvothermal processes are characterized by mild temperature conditions. The use of high pressure appears important for enhancing chemical reactivity. The roles of the solvent and the reagents in the mechanisms governing the formation of a specific material are underlined. Some new directions of research, at the interface with others scientific domains, are discussed.

Utilization of used polyethyleneterephthalate (PET) is now one of the most important ecological problems.

Its solution is related mainly with various difficulties. The solution of this problem seems to be in the creation of remunerative processes, for which post-consumer PET is used as a source material. Were developed several highly profitable processes of utilization of PET articles.

This study aimed to produce acetic acid from vegetable wastes by a new hydrothermal two-step process. A continuous flow reaction system with a maximum treatment capacity of 2 kg/h of dry biomass developed by us was used. Five kinds of vegetables of carrots, white radish, chinese cabbage, cabbage and potato were selected as the representation of vegetable wastes. First, batch experiments with the selected vegetables were performed under the condition of 300°C, 1 min for the first step, and 300°C, 1 min and 70% oxygen supply for the second step, which is the optimum condition for producing acetic acid in the case of using starch as test material. The highest yields of acetic acid from five vegetables were almost the same as those obtained from starch. Subsequently, similar the highest yield of acetic acid and experimental conditions from vegetables were also obtained successfully using the continuous flow reaction system. These results should be useful for developing an industrial scale process.

Solvothermal crystallization of the hydroxide gels obtained by hydrolysis of alkoxides (Zr, Ta, Nb, ln, Sn, Ti and Al) was examined. Nanocrystals having high surface areas (S_BET > 170 m² g^-1) were obtained except for the product derived from indium isopropoxide. The effect of water in organic solvent upon the crystallinity of the product was investigated. The increase in the activity of water by using high concentration of alkoxide or intentional addition of water to the solvothermal medium led to crystal growth of the products. In contrast, decrease in activity of water by adding ethylene glycol before solvothermal treatment caused a decrease in crystallinity of the product.

Gahnite with various particles size was synthesized from boehmite of different particles sizes via interaction with zinc oxide or zinc acetate. It was found that the decrease of the size of gahnite particles is accompanied by decrease of the crystallite size, change of the state of oxygen vacancies and optical properties. The UV light absorption decreases, the blue-shift of an absorption edge is observed, the luminescence of gahnite and Eu³⁺ ions in gahnite changes.

Hydrogen production from biomass was attempted in high pressure high temperature water at 573 K by adopting partial oxidation to increase the yield of H₂ 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 H₂, CO, and CO₂. However, the sensitivity of H₂ yield on H₂O₂ amount was different from those of CO and CO₂, namely the excess amount of H₂O₂ tends to decrease the H₂ 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 H₂ yield through biomass conversion by partial oxidative gasification in high pressure high temperature water

The generation of non-thermal plasmas was studied under supercritical conditions. This is interesting in view of both the basic phenomena involved and of potential industrial applications. When supercritical fluids are combined with discharge plasma they develop unique characteristics, including an enhanced chemical reactivity. This is the motivation for investigating the generation of discharge plasma in supercritical CO₂. In this study, breakdown voltages were measured in CO₂ in order to generate electric discharges in supercritical CO₂. The experimental data show that the breakdown voltage increased smoothly up to the intersection points, but beyond these points the rates of increase of the breakdown voltage are different. This phenomenon can be explained with the help of pressure-density curves of carbon dioxide at a constant temperature. In addition, the generated plasma in supercritical CO₂ was applied to several chemical reactions. The alpha conversion of tocopherols and transesterification of soybean oil with methanol were investigated. In addition, we explored the possibility of replacing catalysts with plasma in supercritical CO₂.

Recently, conversions of polysaccharides included in biomass resources have been studied in order to recover valuable chemicals. Degradation of polysaccharides has been attracted by many researchers, whereas by-products from secondary reactions of the materials have not been studied very well. For the purpose of understanding reaction behavior of various monosaccharides in high-temperature and high-pressure water regions, we investigated reaction pathway and kinetics through reaction experiments of degradation of saccharides in subcritical water. The experiment was conducted by using continuous flow-type micro-reactors. Glucose was used as the starting material. From the experimental results, the conversion of glucose increased with increasing the residence time. The yields of fructose and 1, 6-anhydro-β-D-glucose decreased with increasing the residence time. The yields of organic acids and some aldehydes increased with increasing the residence time.