Vol.9 No.3 2017

Research paper : Development of HASClay® as a high-performance adsorption material (M. Suzuki et al.)−158−Synthesiology - English edition Vol.9 No.3 (2017) not only the desiccant air conditioning and humidity controlling building materials that we had been studying, but also many domains that the authors never imagined, including compositing with bers, compositing with rubber, cell immobilizers, release control of aroma, and others (Fig. 5). Since imogolite is composed of nanotubes, we conducted joint research with Hokkaido University to evaluate safety in organisms.As a result of talking to and conducting joint research with various companies, the following points can be raised as important.• No matter how good the performance, if its synthesis remains at a laboratory level and there is no prospect for being handled by some company in the future, it is difcult for the company which will be using this material to evaluate in terms of sales and marketing.• No matter how well it can be synthesized at a laboratory level, unless the method can be used for synthesis at an industrial level, the manufacturers cannot engage in production in tons.• No matter how well the performance, the range of use will be narrowed if it is expensive, wide diffusion to society cannot be expected, and initial performance may not be attainable since it will be mixed with other substances to cut costs (the only eld where it can be used despite high costs is the medical eld).• As can be seen with the case of asbestos, there is concern for the safety of nanotubes, even if we explain the imogolite properties or its form after dehydration.Considering the above points, we reached the conclusion that it was meaningless if we were stuck at the research level at AIST, even though the materials had interesting performance and were worthy of obtaining national development grants. It was necessary to conduct materials development that led to future practical use and was cost effective. Therefore, we decided to terminate the research of imogolite except for the medical eld.3.2 Development of a new adsorbent by setting target conditionsLearning from the research on imogolite described above, we conducted investigation on the possibility of forming composites of a HO-Si(-OAl)3 structure, which is the basic structure of allophane and imogolite, and a single layer of layered clay. The schematic diagram of the structure of this new adsorbent is shown in Fig. 6. As the background of this idea, the HO-Si(-OAl)3 structure, which is the basic structure of allophane and imogolite, is formed when the silicate aqueous solution in which the Si/Al molar ratio is prepared to 0.5 is mixed with an aluminum aqueous solution.[12] We thought it was possible to form a 1:1 layer of layered clay where the molar ratio is 1.0 by increasing the Si/Al molar ratio, and to create a composite that contained the structures of the two substances.On the other hand, we set the target values for the yield that enabled reasonable cost and mass production. For sales price, we targeted the price somewhere between that of silica gel (about 100 yen/kg) and zeolite (1,000 yen/kg) that were being used widely as adsorbents. We set the minimum necessary conditions needed for the synthesis at the beginning, and then started the development. The conditions are shown below (Fig. 7).(1) From the perspective of synthesis cost, it should be synthesized using raw materials of liquid glass, aluminum sulfate, and sodium hydroxide, to enable synthesis using substances with low raw material cost.(2) To enable industrial synthesis in tons, it should be synthesized using the method for zeolite which is widely Fig. 5 Fields in which imogolite is usedFig. 6 Schematic diagram of the formation of new adsorbent structureAroma release controlCell immobilizerRubber compositeFiber compositeFormClay mineral (imogolite)Ion exchangeHigh specic surface areaAdsorbent functionFineporeAdsorbent for hazardous pollutantsArticial barrier (for industrial wastes)Filler, binderFuel storage mediumCondensation prevention agentAutonomous humidity controlling materialsHeat pump heat exchanging agentQuick-dry desiccant!HO-Si-(OAl)3"!##"Formation of compositeBasic structure of layered clay(1:1 layer structure)Basic structure of allophane and imogolite (HO-Si-(OAl)3 structure)

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