Influence of Sulfur Impregnation on the Carbonaceous and Non-carbonaceous Adsorbents for Mercury Removal from Caol Combustion Flue Gase

[[abstract]]本研究利用椰殼活性碳、活性碳纖維及沸石分子篩配合不同溫度(300 C 650 C)之氣相硫含浸程序進行吸附劑表面改質，應用於燃煤煙道氣中汞蒸氣之去除。硫含浸造成各吸附劑之物理性質影響不盡相同，經硫含浸改質活性碳，在含浸溫度為中(400 C)、低溫(300 C)時，硫分子進入吸附劑孔洞，導致吸附劑之表面積大幅下降，在高溫含浸時，除了可造成硫分子含浸於活性碳表面外，也具備了擴孔之功能，可擴大原本之微孔結構成為中大孔結構。然而氣相硫含浸程序無法有效的將硫粉置入沸石分子篩孔徑結構中，因此經含浸之沸石分子篩其表面積無明顯的改變。 研究結果顯示，未改質之吸附劑Hg0蒸氣吸附能力依序為椰殼活性碳>活性碳纖維氈>沸石分子篩，經中、低溫含浸改質之碳基吸附劑，能有效的提昇汞蒸氣之吸附能力，改質吸附劑之硫含量隨含浸溫度下降而增加，大致上各吸附劑之吸附效能隨其硫含量增加而提昇，但其吸附能力仍仰賴吸附劑起始原料之物化特性。而非碳基之吸附劑經含浸前後，對於汞的去除效率較差。當吸附劑於無煙氣環境下，易於短時間內達吸附貫穿且Hg0蒸氣的吸附能力較煙氣環境下低，煙氣組成中的酸性及氧化性氣體有助於吸附劑對於Hg0蒸氣的吸附能力。擬二階吸附動力模式可得較佳的模擬結果，暗示Hg0吸附傾向於雙分子反應(bimolecular reaction)，也就是說，吸附一個Hg0分子需要兩個活化位址。此外本研究中所有具有高飽和吸附量之硫含浸活性碳，其反應動力均不佳，顯示硫含浸活性碳之吸附平衡與吸附動力呈現相反的趨勢。[[abstract]]Carbonaceous (i e coconut-shell activated carbon and carbon fiber) and noncarbonaceous adsorbents (i e zeolite molecular sieve) were impregnated with sulfur at 300650 C The influence of gaseous sulfur impregnation on the surface physical/chemical properties and the effectiveness of sulfur impregnation on removal of the trace amount of mercury (Hg) from coal combustion flue gas were further investigated Sulfur impregnation significantly altered the surface properties of adsorbents at the low (i e 300 C) and moderate (i e 400 C) temperature range The sulfur contents of carbonaceous adsorbents increased as the sulfur impregnation temperature decreased Sulfur molecules appeared to access into the porous structure and markedly decreased the specific surface area of adsorbents At the high temperature range (i e 650 C) sulfur molecules played a role to open and /or broaden porous structures and introduce the sulfur onto the surface Sulfur molecules were not successfully introduced into the porous structure of zeolite molecular sieve via the gaseous sulfur impregnation process As a result a significant change on the surface area of zeolite molecular sieve after sulfur impregnation was not observed The Hg adsorption capacities for untreated adsorbents in a declining order were CS>ACM>zeolite The Hg adsorption capacities were significantly increased for carbonaceous adsorbents treated at low and moderate temperature ranges Results also indicated that the Hg adsorption capacity increased as an increase in sulfur contents and greatly depended on the inherent physical and chemical properties of raw samples The tested noncarbonaceous adsorbent had a small Hg adsorption capacity even when the sample was impregnated with sulfur Acid and oxidizing components in flue gases strongly increased the Hg adsorption capacities of raw and sulfur-treated samples The modeling results also showed that a pseudo-second-order equation can better describe the adsorption behaviors of all tested adsorbents indicating that Hg adsorbed on the adsorbent surface was in a bimolecular reaction form Samples with greater adsorption capacities typically had poor adsorption kinetics indicating that the mercury adsorption equilibrium and kinetics for the tested adsorbents were reversely correlate