| Summary: | 博士 === 國立中央大學 === 化學工程與材料工程研究所 === 96 === The evolution of semiconductor industries promotes the economic development of Taiwan, but it also results in environmental pollution problems. The employment of a variety of chemicals during the semiconductor manufacturing process is very complicate due to the numerous types of process facilities. Till now, the Environmental Protection Administration has carried out the rule of“Regulation Governing the Air Pollution of Semiconductor Manufacturing Industries”, in order to restrain stringently the emission of related semiconductor manufacturers. Moreover, the Kyoto Protocol has been signed on December 11, 1997, and entered into force on 16 February 2005. Countries that ratify this protocol commit to reduce their emissions of carbon dioxide and five other greenhouse gases. Therefore, it is a very important issue that how to develop an effective method to abate the waste gases from semiconductor process in the future.
Perfluoro compounds(PFCs) are greenhouse gases which is very chemical stable and difficult to remove by decomposition. Nowadays, the PFCs destruction of semiconductor manufacturer by present treatment methods are not effective. Chapter 3 of the thesis shows the test results for the direct destruction and removal of PFCs by thermal plasma method. According to the test results, the destruction efficiency of PFCs under 12kW of plasma torch power could achieve 94% when the concentrations of C2F6 and CF4 are 20,000ppm and 10,000ppm and the flow rates are 200L/min and 50L/min, respectively. The main products are CO2 and HF, and the HF acidic waste gas could be absorbed completely by wet scrubber and then treats as waste water to avoid the effluence of HF(g). The lifespan of plasma torch has been promoted from 215 hr. to above 800 hr. after improvement.
Volatile organic compounds(VOCs) are other important harmful gases which also emitted from semiconductor industry. Chapter 4 and 5 of the thesis report the complete oxidation of 2-propanol and benzene over gold based catalyst respectively. Concerning the complete 2-propanol oxidation, the catalyst of gold deposited on CeO2 support shows more active than on other supports(eg.Fe2O3、γ-Al2O3 and TiO2). The factors which affect the activities of complete oxidation of 2-propanol over Au/CeO2 including the calcination temperature、the gold particle size、the amount of gold loading and the moisture content in feed. Concerning the gold loading on catalyst, too much amount of gold (eg.2.1%Au) will result in aggregation of gold particles which would cause lower activity. According to the activity test, the 1.6Au/CeO2 catalyst shows lower light off temperature, and the nano gold particles(≦5nm) were highly dispersed on the CeO2 support. Moreover, the Au/CeO2 catalyst which calcined at 300℃ is more active than catalysts calcined at other temperations, and this result could be related to the presence of high oxidation state of gold(Au+n). On the other hand, the more moisture content in feed, the more active on complete 2-propanol oxidation over 1.6%Au/CeO2 catalyst.
Concerning the complete benzene oxidation, Au/CeO2 and Au/V2O5/CeO2 are studied. The factors affect the activities of complete benzene oxidation are calcination temperature and gold loading. The results indicate that the Au/CeO2(b) catalyst(c300) could oxidize benzene completely at 200℃. After the addition of 2%V2O5 to Au/CeO2(b)(c300), the activity just shows slight enhancement. Moreover, the Au/2%V2O5/CeO2 catalyst(c400) are obviously more active than Au/CeO2(c400). However, the activities are almost the same for Au/CeO2(b)(c300) and Au/2%V2O5/CeO2(b)(c400). The XPS results shows these two catalysts all contained Au+n which indicated that the presence of high oxidation state of Au(Au+n) could enhance the activity of complete benzene oxidation. The high oxidation state of Au(Au+n) could be obtained by lowering the calcination temperature of Au/CeO2 or the addition of V2O5 to Au/CeO2. On the other hand, the durability test shows that the Au/CeO2 could maintain 100% conversion, and the Au/V2O5/CeO2 shows slight activity decrease after 120hr.
Comparing the activity of supported Au and Pt catalysts, the Au catalyst is more active than Pt catalyst for complete benzene oxidation. Moreover, The price of Au is cheaper than Pt and Au catalysts do not need to be reduced by hydrogen before use. These could be the advantages for practical application.
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