Vol.3 No.2 2010

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Research paper : Establishment of compact processes (A. Suzuki et al.)−157−Synthesiology - English edition Vol.3 No.2 (2010) was comparable to the basic structure, and verified that the exchange amount of heat equivalent to the substance production of several hundred tons/year could be carried out rapidly and stably through the compact process that could be installed in about 1 m × 2 m space. Comparing the capacity of the high-pressure microheater by direct energization heating used here with the conventional electric furnace heating method, the heat efficiency is estimated to be about 2 times, and the overall heat-transfer coefficient is 100 times or more. Since the difference of heat efficiency is directly related to the energy requirement, the energy cost will be one-half. Moreover, the difference of heat-transfer coefficient is thought to be almost proportional to the required heat transfer area, or the total length of the heating tube, and the heating tube will be 1/100 or less in length. As mentioned above, with 100 kg/h production capacity, the high-pressure microheater must have the total length of heating tube of 4 m (200 mm × 5 tubes/module × 4 modules/device = 4,000 mm), but the electric furnace heating method will require 400 m or more and the facility will grow large.Figure 11 summarizes the processes of high-pressure microengineering including the items discussed above. Stage 0 (foundation) means the clarification of technical issues such as rapid heat exchange toward the integration of the microreactor technology and the supercritical fluid technology. To solve the issues, starting from the establishment of basic technologies such as micro structuring and micro bonding (Stage 1), moving on to configuration design and optimization of the high-pressure device such as mixers, and the various high-pressure equipments (Stage 2-3), we are working our way toward the developments for process applications.4 Establishment of the compact process through high-pressure microengineering 4.1 Organic synthesis process using supercritical waterThe organic synthetic process using supercritical water and high-pressure and high-temperature water overturned the common knowledge that the supercritical water was inappropriate media as a organic synthesis field, as in the Beckmann rearrangement explained earlier, by realizing the rapid heating and cooling in the order of millisecond to microsecond by microengineering technology[8]. As another example, we describe the nitration of the aromatic derivatives. The most frequently used nitration in industry is the method using nitric-sulfuric acid, or the so called mixed acid. However, this production method has been used from the early 20th century without any change in methodology. The serial problems of the disposal of sulfuric acid waste as well as safety still remain, and the development of a new nitration technology with decreased waste has been awaited. To overcome the problems, we developed the new nitration without mixed acid by using the high-pressure and high-temperature microengineering technology, to generate nitronium ion or radical from diluted nitric acid in the high-pressure and high-temperature water. Even though the strong acids including nitric acid in high-pressure and high-temperature water create very corrosive conditions, we newly developed some microdevices, such as microtubes and joints made of titanium-lined inconel 625 and succeeded to operate these strong acids in high-temperature and high-pressure conditions using these devices. Using the high-pressure and high-temperature resistant titanium-lined devices, we conducted the nitration of aromatics, such as naphthalene, with nitric acid. The conceptual diagram of the apparatus is shown in Fig. 12, and the results are shown in Fig. 13. The reaction condition was 40 MPa and 200~325 ºC. The nitration of naphthalene proceeded at 225 ºC or above, and 91 % of the maximum yield of nitronaphthalene (1-nitronaphthalene 85 % and 2-nitronaphthalene 6 %) was achieved at 250 ºC within only 1.3 sec reaction time. It was also found that hardly any highly explosive dinitronaphthalene and trinitronaphthalene were produced.Fig. 12 Outline of non-catalyzed nitration apparatus under high-temperature high-pressure waterInconel tubes and joints lined with titanium in the interior are used after introduction of nitric acid up to rapid cooling.Fig. 13 Result of nitration experiment of naphthaleneNitration progressed at 225 ºC or over, and maximum yield of 91 % was achieved at 250 ºC.Ø 1.6 mm Ø 0.5 5 mm Ø 0.7 mm Ø 1.6 mm Ø 0.5 5 mm Ø 0.7 mm Ø 1.6 mm Ø 0.5 5 mm Ø 0.7 mm 625 1.6mm0.55mm80µm 625 Inconel 625 (titanium-lined)T-shaped mixerInconel 625 (titanium-lined)Outside diameter1.6 mm, inside diameter 0.55 mm, thickness of titanium 80 µmØ 0.7 mmØ 0.55 mmØ 1.6 mmRapid cooling(micromixer)Rapid heating(micromixer)Nitrated product200~325 ℃40 MPa1 ~ 1.5 secCoolingwaterDilutednitric acidHigh-temperature and high-pressure waterAromaticcompoundNO2NO2NO2OORetention time (min)IntensityReaction temperature (ºC)2-Nitronaphthalene1-Nitronaphthalene1,4-NaphthoquinoneNitrobenzeneAcetone24681012140500100015002000pA325300275250225200NaphthaleneNaphthalene

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