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Molten alkali (salt) decomposition of CFC-12 .

Author: ZouJinBao
Tutor: NingPing
School: Kunming University of Science and Technology
Course: Environmental Engineering
Keywords: CFCs molten alkali molten salt decomposition mechanism thermodynamics dynamics
CLC: O643.3
Type: Master's thesis
Year: 2009
Downloads: 8
Quote: 1
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Abstract

CFCs had bring with two global entironment problems:destroying ozonosphere and greenhouse effect. There were three approachs to solve CFCs problem. The first approach was that production and using of CFCs were forbided. The second approach was that substitutes for CFCs were exploited. The third approach was to treat existent CFCs. The first and second approachs had been practised. There were many problems for treating existent CFCs. In this paper,a new decomposing technology of CFCs was investigated. CFC-12 was decomposing by molten alkali and molten salt. Much experiment was investigated. Reaction dynamics' dissertation">thermodynamics, reaction dynamics, reaction mechanism were discussed.CFC-12 was decomposed by molten alkal. Alkali for experiment was NaOH. CFC-12 was decomposed to NaF, NaCl, Na2CO3, H2O,etal. By-products could react with molten NaOH. So secondary contamination was reduced. The results showed that: when reacting without H2O,exit concentration of CFC-12 reduced firstly,but it increased to inlet concentration after 60min. when reacting with H2O,exit concentration was very small,decomposition efficiency could reach 99%.Decomposition efficiency become higher with increasing quantity of H2O.NaOH was important to reaction. When quantity of NaOH was Og, exit concentration was equal to inlet concentration. When reacting with Na2CO3, effect was bad. Only when reacting with NaOH, effect was good.So effect of CFC-12 reacting with NaOH and CFC-12 reacting with H2O was bad,but effect of CFC-12 reacting with NaOH and H2O was good.When gas concentration was less than 81000mg/m3, decomposition efficiency was higher than 99%. Decomposition efficiency reduced with increasing gas concentration and increased with increasing reaction temperature.When quantity of NaOH was less than 75g, decomposition efficiency increased with quantity of NaOH,after continuing to increase quantity of NaOH,decomposition efficiency kept invariable.Decomposition efficiency reduced with increasing gas velocity.At the optimization condition, decomposition efficiency was higher than 99%. Gas concentration for 99% of decomposition efficiency was 2%,It was a simple and high efficiency technology for treating high concentration CFC-12. By-products could react with molten NaOH, so secondary contamination was reduced. Benefits of the technology were analysed.CFC-12 was decomposed by molten salt. Salt for experiment was CaCl2-NaCl salt. Catalyzers for experiment were Al2(SO4)3 and GuSO4. The results showed that:When reacting without catalyzer, decomposition efficiency of CaCl2-NaCl salt reacting with CFC-12 and H2O could reach 80%. Decomposition efficiency increased 20% when reacting with Al2(SO4)3 catalyzer. H2O was important to reaction, when reacting without H2O, exit concentration increased to inlet concentration quickly.When reacting with H2O,exit concentration was small and efficiency could reach 99%.Decomposition efficiency reduced with increasing gas concentration and gas velocity,but it increased with increasing reaction temperature.Catalyzing action of Al2(SO4)3 was more than CuSO4. CFC-12 was adsorped by 4#activated carbon, the biggest adsorption capability could reach 201mg/g at room temperature.It was a hydrolyzing reaction that CFC-12 was decomposed by molten alkali.H2O and NaOH were important to reaction, CFC-12 was hydrolyzed by OH-.It was a catalyzing-hydrolyzing reaction that CFC-12 was decomposed by molten salt. CaCl2-NaCl salt, CaCl2-NaCl and Al2(SO4)3, CaCl2-NaCl and CuSO4 were catalyzers.ΔrHmθ,ΔrSmθ,ΔrGmθof two reactions were calculated, bothΔrGmθwere negative and two reactions were spontaneous reaction, but reaction velocity was slow and it could been quickened by changing reaction conditions.The dynamics was also discussed.

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