Vol.3 No.2 2010

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Research paper : Establishment of compact processes (A. Suzuki et al.)−158−Synthesiology - English edition Vol.3 No.2 (2010) We further developed a process for conducting safer nitration using highly active acetyl nitrate as a nitration agent under the high-pressure conditions in microreactor for the precise reaction control of reaction time, reaction temperature and reaction point. In this method, the acetyl nitrate was generated instantly in the micromixer by exothermic reaction with acetic anhydride and nitric acid, while the mixing temperature was maintained at desired temperature of 40 ºC ± 0.2 ºC. The nitration of phenol was achieved of the yield of 96 % with the selectivity of almost 100 % at reaction temperature of 40 ºC and the reaction time of 1.8 sec. Since the reaction was conducted at low temperature of 40 ºC, corrosion of reaction system hardly occurred and as the unreacted acetyl nitrate in reaction residue easily hydrolyzed in water after the reaction, we can safely and easily handle these reactions outside of the system. This reaction system can realize efficient low temperature nitration in high-pressure condition, and can be applied to the various aromatic compounds having substituent groups, particularly for the nitration using medical and agrochemical intermediates. We also realized ultrafast and highly efficient organic reaction in water for piancol rearrangement, Claisen rearrangement, and estirification by our reaction methodology with precise control by rapid heating, and rapid cooling in high-pressure and high-temperature micromixer[13]-[15]. At present, we further achieved the high yield, high selectivity synthesis of useful compounds from sugars derived from biomass, such as 5-hydroxymethylfurfural for which physiological activity such as blood pressure decrease has been reported[16].4.2 Metal oxide fine particle synthesis process using supercritical waterThe supercritical hydrothermal synthesis is a method for obtaining fine nano-level particles by reducing the solubility of the metal oxides produced in the hydrolysis and dehydration reactions by heating the metal salt water solution rapidly to a supercritical state[17][18]. In the subcritical condition (200~300 ºC), the reaction rate of the hydrothermal synthesis is low, the dielectric constant of water is high at about 30, and the produced crystals tend to grow large. On the other hand, in the supercritical condition (representative condition is 400 ºC, 30 MPa), the reaction rate increases, the dielectric constant falls to a single digit, and the produced crystals do not grow. Therefore, the point of this method is how to increase the temperature rapidly to supercritical condition, and this rapid heating can be realized by the direct mixing of the metal salt water solution and the supercritical water. Figure 14 shows the particle size distribution of the product obtained by using different mixers for the synthesis of boehmite by supercritical hydrothermal synthesis using aluminum nitrate as raw material. The mixers used were 1/16 inch STD TEE described above, swirl mixer, and central collision mixer (adjustable needle of fluid channel space is applied). The reaction condition was 400 ºC, 30 MPa, and 2 sec. From the figure, both the swirl mixer and the central collision mixer produced microscopic particles and showed narrow distribution compared to the standard T-shaped mixer (STD TEE: flow channel diameter 1.3 mm). In the central collision mixer, the fluid mixing performance is higher when the needle position is L = 1 mm (see Fig. 6) with narrower flow channel clearance, and as a result, fine particles were synthesized by rapid mixing. The efficacy of this technology was shown in the synthesis of compound oxides as well as single oxides, and is expected to be applied in various usages such as fluorescent substances, ferromagnetic substances, transparent electrodes, cell electrode materials, and catalysts.4.3 Innovative painting process by supercritical carbon dioxideThe total amount of volatile organic compounds (VOC) emitted from all industries in Japan is about 1.5 million tons (FY 2000), of which 33 % or 500,000 tons is the emission from the paint industry. The paint industry is the largest VOC emitter among all industries. The VOC is a cause substance of photochemical oxidants and suspended particulate matter, and their reduction is demanded immediately. We aimed to develop a painting method to significantly reduce the VOC emission by changing the thinner solvent (major VOC material) used abundantly in spray coating of conventional organic solvent paints, with extremely small amount of carbon dioxide, while maintaining the finish quality equivalent to the one achieved by organic solvent paints. The basic principle of this technology was developed as a new painting process[19] principally by the Union Carbide Corporation of the U.S.A., but in this process conventional static mixer was mainly used for mixing paint and carbon dioxide based on the fluid multi-stage segmentation theory, and quick mixing was difficult. For this reason, the paint Fig. 14 Particle size distribution of the fine particles from Beohmite synthesis by the micromixerLarge difference in the particle size distribution can be seen depending on the type of the high-pressure micromixer (difference in quick mixing property).400 ℃・30 MPaSupercritical hydrothermal synthesis was conducted using different types of rapid heating mixers.Reaction time 2 secCoolingwaterSupercriticalwaterMetal nitratesalt10100100005102025303515Particle diameter (nm)Frequency (%)Central collision type(needle position L = 1 mm)Central collision type(needle position L = 0 mm)Swirl mixerSTD T-shaped mixer

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