隨著石油、天然氣等能源之蘊藏量日益枯竭，如何淨潔利用蘊藏量最豐富的煤炭能源，將是未來能源發展之重要課題。煤炭氣化複循環發電技術(IGCC)無論在技術成熟性、能源效率及環保性能與其他發電技術相較均佔優勢，因此將會是未來發電的主流技術，目前商業運轉之大型煤炭氣化複循環發電機組皆使用商業化之溼式除硫程序，然而溼式除硫必須用水來冷卻煤氣，使系統熱效率降低，為提高熱效率降低發電及環保成本，高溫除硫方法是目前較受重視的處理技術。
　　基於土壤低成本及蘊藏量豐富之特性，本研究以土壤為吸收劑在高溫下吸收煤炭氣化氣中之硫化氫。結果顯示每種土系對硫化氫皆有去除效果，其中以老埤土壤(紅壤)具有較高的脫硫容量。在去除土壤中的游離鐵後發現對硫化氫的去除能力明顯降低，顯示游離鐵在除硫方面扮演相當重要的角色，同時亦發現高游離鐵含量的土壤具有較佳的脫硫容量。此外，經由理論計算所得之脫硫容量與實驗所得之脫硫容量差異不大，顯示去除硫化氫之機制主要來自於鐵與硫的反應。綜合上述實驗結果，選擇老埤紅壤作為後續處理硫化氫的實驗主角。
　　觀察在不同操作條件下硫化氫去除的情形，發現提高反應溫度會降低硫化氫的去除能力，此與各種不同狀態的氧化鐵有著密切的關係。在還原狀態下，紅壤中的氧化鐵會因高溫過度還原而形成與硫化氫親和力較差的二價鐵 (FeO)，最佳反應溫度在773K。另外，隨一氧化碳濃度的增加，氫氣與二氧化碳濃度的減少，脫硫容量明顯的增加，此結果可以water-shift reaction來說明。空間流速在1,000-10,000 mlhr-1g-1之間脫硫容量受空間流速之影響並不顯著；硫化氫濃度對脫硫容量之影響亦不顯著。
　　經由FTIR的鑑定與解析，發現有CO2, SO2與 COS等中間產物的產生。其中CO2的生成與water-shift reaction有關；SO2的生成可能來自於紅壤中的有機質與H2S的反應。隨脫硫時間的增加，SO2與CO2的濃度明顯下降。在完成脫硫反應後，大量的COS產生。經由熱力學的計算得知COS的生成主要是進流氣中的CO與H2S反應所導致。於多次除硫/再生的實驗中發現老埤紅壤具有不錯的再生能力，在經過十次除硫/再生後的老埤紅壤仍具有80%的除硫能力。

　　XRPD的結果顯示在脫硫後老埤紅壤中氧化鐵的晶相消失，但並未觀察到有Fe-S晶相的產生，這可能是在反應後的Fe-S是以無定型(amorphous)之狀態存在於紅壤之中。由EDS的鑑定得知紅壤中的部分氧被硫所取代。經由XPS與TPO的進一步分析得知，鐵與硫的鑑結可能是以非化學計量比之關係存在於紅壤中，可能的化學式為Fe0.985S或Fe0.975S。EXAFS數據顯示，距中心鐵原子2.362Å有2.75個硫原子，該配位數明顯高於其理論值，此發現證明反應後老埤紅壤之產物主要是以非化學計量比之硫化鐵存在。
　　為了解造成紅壤脫硫效率衰退的原因，將十次脫硫/再生後的紅壤進行分析與鑑定。結果顯示仍有部分殘餘的硫吸附在再生後的紅壤中。由XPS的解析發現殘餘的硫主要是以硫酸根與元素硫以及部分金屬硫化物為主，這些硫化物可能是造成紅壤脫硫效率降低的主要原因之一。此外，由固態核磁共振的結果顯示五配位的鋁矽化合物存在於再生後的紅壤，該鋁矽化合物的生成可能與再生過程中過度的放熱反應有關，部分游離態的鋁與土壤中的矽鍵結生成。
　　由動力的研究發現，第一型衰退模式所求得之活化能為131.51 kJ/mol，碰撞因子為2.31*1017。第二型衰退模式所求得之活化能為34.02 kJ/mol，碰撞因子為2.49*107。以兩模式進行貫穿曲線之預測，結果亦顯示該兩模式皆可正確預估實驗之貫穿曲線。
　　另外，將紅壤與其他商用吸收劑以及自製吸收劑做一系列之比較後，結果顯示不論在脫硫能力、再生性能評估、再生後孔洞結構上，紅壤對吸收硫化氫之效果並不遜於商用吸收劑與自製吸收劑。

　It is well known that hydrogen sulfide (H2S) is a toxic gas that presents widely in manufacture plants such as wastewater treatment plants, petroleum plants and coal gasification plants. H2S present in coal gasification syngas involved other inorganic reduction gases, carbon monoxide (CO) and hydrogen (H2), at high temperature (higher than 673K) make coal gasification plants different from others.
　Due to low cost and abundance, various soils series were chosen and assessed with their sorption performance of H2S at high temperatures. In addition, several spectroscopic techniques such as X-ray powder diffraction (XRPD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Solid-state nuclear magnetic resonance (SSNMR), Energy dispersive X-ray spectroscopy (EDS) and X-ray absorption spectroscopy (XAS) were used to characterize the soils’ structure before and after sorption and regeneration processes.
　Results show that all the tested soils have certain sorption efficiency for hydrogen sulfide under high temperatures. Free iron oxides play an important role for the sorption of hydrogen sulfide. Red soils have the best sulfur sorption capacity compared to other soils. The reaction temperature higher than certain level has a negative effect on the sorption of hydrogen sulfide as a result of unfavorable thermodynamic property of iron oxides with hydrogen sulfide in the reductive atmosphere. The reaction temperature of 773K is the optimal choice for the sorption of hydrogen sulfide by red soils.
　On the concentrations of CO and H2, the sorption efficiency of H2S by red soils increases with CO but decreases with H2. This can be explained via the water shift reaction theory. The effect of CO2 was also performed and appeared to be the negative effect, confirming that the water-shift reaction plays an important role in this process.
　Appreciable amounts of by-products, CO2, SO2 and COS were detected through the on-line FTIR spectroscopy during the initial and later stages of the sorption process. The formation of CO2 is related to the water-shift reaction, and SO2 is probably attributed to the reaction of organic matters in red soils with H2S. The concentration of COS after breakthrough was quantified by GC/FPD and found to be about 380 ppm, which is close to the equilibrium concentration of the reaction of inlet CO and H2S at a temperature of 773K.
　In the regeneration tests, the LP soils can be regenerated and thus reused after oxidation process. No significant degradation occurs on the LP soils after five sorption/regeneration cycles. The sulfur sorption capacity of the tenth regenerated sorbent still remains at least 80% compared to the fresh one.
　XRPD results indicate that iron oxide species disappear from the reacted soils. EDS analyses show that a significant amount of sulfur is present in the reacted LP soils, which is in agreement with the results of the elemental analysis and the calculated value based on breakthrough curves. XPS regression fitting results further indicate that sulfur retention may be associated with the iron oxides. S2p XPS fittings and temperature-programmed oxidation (TPO) point out that the major sulfur species present in the reacted soils are attributed to polysulfides. On the basis of the EXAFS analysis, the bond distance for Fe-S is 2.362Å with coordination number of 2.75. Higher coordination number indicates that the crystalline structural for Fe-S may be present in nonstoichiometric form.
　After regeneration, the residual sulfur species including sulfide, sulfate and elemental sulfur are observed in the soils by FTIR and XPS, which is the major reason to cause deactivation of soils.
　Additionally, significant changes in 27Al and 29Si were identified through the SSNMR analysis. A pentacoordinated structure is formed after regeneration, suggesting the formation of aluminosilicate. The losses of surface area may be associated with the structure changes in aluminum and silica.
　In the operating range of this study, the activation energy, Ea, is 136.35 kJ/mol and the frequency factor, A, is 6.25*1017 for type I model. The activation energy, Ea, is 34.02 kJ/mol and the frequency factor, A, is 2.49*107 for type II model. The predicted breakthrough behaviors derived from the fitting of the deactivation type I and II kinetic models agree well with the results of the experiments.
　Comparison with the commercial and lab-made sorbents, the sulfur sorption capacity, regenerability and structure stability for LP red soil have no significant loss. Meanwhile, red soil also has the lower preparation cost among all metal oxide sorebnts. Combined with these advantages, red soil can be taken into account as a potential sorbent for high temperature desulfurization.

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