| Budget Amount *help |
¥14,200,000 (Direct Cost: ¥14,200,000)
Fiscal Year 2005: ¥4,700,000 (Direct Cost: ¥4,700,000)
Fiscal Year 2004: ¥9,500,000 (Direct Cost: ¥9,500,000)
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| Research Abstract |
Disposal of waste polyvinyl chloride (PVC) is a serious problem for environmental safety because of the large quantity of CI ions included in the waste PVC. In order to overcome this problem, techniques to disperse the slurry containing Ca(OH)_2 or CaCO_3 into flue gases from inclnerators have been developed, where HCl involved in the flue gases was completely fixed in the calcium salts as CaCl_2. Waste solids thus yielded have been generally carefully grounded under the ground. However, this technique will not necessarily be an environmentally safe method, because CaCl_2sis well dissolved into the water under ground and widely spreads to cultivated fields for agriculture to react with other organic compounds for the production of undesired chlorinated organics.
Thus, the purpose of this research project is to recover Cl ions, as C_<12> gas, from waste CaCl_2 solids using a kind of DEACON reaction as follows ; CaCl_2+1/2O_2=CaO+Cl_2. Thermodynamically, this reaction is much endothermic,
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and even at 1173 K, where CaCl_2 is melted, ΔG is estimated to be +29 kcal/mol ; suggesting almost no reaction will occur. In order to accelerate the progress of reaction, a trace amount of Cl_2 gas and CaO yielded should be taken out of the reactor, which will thermodynamically push the reaction to proceed toward the right side. Then, we have tried to employ a large flowing rate of O_2 gas into the reactor, expecting flush up yielded Cl_2 gas out of the reactor. Another technique we applied is to mix SiO_2 or TiO_2 powders with CaCl_2 prior to the DEACON reaction, expecting the progress of the reaction between CaO yielded and SiO_2 or TiO_2. The reaction SiO_2 or TiO_2 with CaO means the production of SiCaO_3 or TiCaO_3, and thus the CaO yielded will be out of the reaction system. At the moment, optimum O_2 flow rate is 150 ml/min and optimum SiO2 addition is 3.0 g for the recovery of Cl_2 gas from 3.0 g of CaCl_2 at 1173 K. In these reaction conditions, more than 70 wt% of Cl ions in CaCl_2 was recovered as pure Cl_2 gas (not contaminated by HCl gas), which will be used again for the production of PVC. Less
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