Performance Improvement of Zeolite Concentrator for VOCs Removal - Adsorbent Modification and Combining with Condenser
|關鍵字:||中孔洞材料;氣膠促進自我聚集程序;吸附/脫附;高沸點揮發性有機物;疏水性;半導體及光電產業;mesostructured materials;aerosol assisted self-assembly process;adsorption/regeneration;volatile organic compounds of high boiling point;hydrophobicity;semiconductor and optoelectronic industry|
|摘要:||沸石轉輪系統是相當適合處理大風量、低濃度之揮發性有機(volatile organic compounds, VOCs)廢氣污染物，自商業化以來，該系統不論是學術研究或在實廠運作經驗中，對於VOCs之去除效率均可達到90%以上，不過該系統仍存有部分尚待研究解決之項目，例如所處理VOCs廢氣中，若含有比例較大之高沸點物質(沸點大於140℃)則會導致處理效能下降，以及沸石經過反覆吸脫附後，處理效率呈現衰退等現象。
在沸石轉輪結合冷凝器之實廠VOCs處理效能提升方面，本研究有別傳統需降至氣體露點溫度以下之方式，以冷凝溫度操作於10℃即可將所處理廢氣濕度與高沸點VOCs形成液膜，並以該液膜之吸收機制，應用在處理半導體廠去光阻製程所排放含高沸點物質、具多重成分及低濃度VOCs廢氣。結果顯示將去光阻製程所排放之含多量高沸點物質之 VOCs廢氣預先分流至冷凝器處理，其中所含有之二甲基亞□(dimethyl sulfoxide, DMSO)及N-甲基砒喀烷酮(1-methyl-2-pyrrolidinone, NMP)等高沸點VOCs去除效率均可大於80%以上。雖然廢氣中其他VOCs如異丙醇(isopropyl alcohol, IPA)與丙酮(acetone)等中、低沸點物質去除效能不甚理想，不過將其導入末端之沸石吸附焚化系統處理後，此結合系統對於整廠VOCs處理效率可長時間(連續九個月月平均記錄值)保持於95%以上，優於原先單由沸石轉輪系統處理之效能，並能延長轉輪之使用壽命，而此結合系統所需之成本經評估後亦較單獨沸石轉輪運轉處理更具經濟可行性。
在探討沸石轉輪吸附材改良方面，本研究以氣膠程序所合成之六角晶型奈米結構沸石微粒(hexagonal nanostructured zeolite particles, HNZP)進行半導體晶圓廠VOCs總排放量佔最大比例之丙酮吸附特性研究，並與現行商用ZSM-5型沸石相互比較其效能。研究結果顯示在全新吸附劑之吸附效能測試中，所合成之HNZP具備大比表面積，且可視需要調整平均孔徑，其具備之特性可使得吸附效能呈現優於目前商用沸石之趨勢。在反覆再生後再次測試吸附效能方面，HNZP較ZSM-5型沸石更不易劣化，且HNZP再生後之吸附效能與全新樣本相比起來差距甚小。經分析ZSM-5型沸石反覆再生後所造成劣化之原因，在於所含之鋁成份使其具有觸媒催化作用，故於進行200℃熱脫附時會將丙酮催化形成積碳鍵結物質，阻塞有效吸附位置、降低了吸附效能；在環境存在濕度進行吸附測試顯示，純矽之HNZP具有良好疏水性、吸附效能較不受濕度影響，反觀ZSM-5型之組成具有鋁成份，所以使得其具有親水性、影響了吸附丙酮之效能。由於HNZP具備反覆再生後不易劣化之吸附效能及良好疏水特性，加上可在製備過程中調整操作參數控制所需之比表面積與孔徑等特點，使得其具有取代商用ZSM-5型沸石成為新世代吸附劑之可行性。
One of the most commonly used volatile organic compounds (VOCs) abatement devices by the semiconductor and optoelectronic manufacturers is zeolite concentrator. The excellent efficiency of zeolite concentrator for VOCs removal has been proved to be over 90%. However, the the adsorption capacity of zeolite is reduced due to the repeatedly adsorption/desorption process and the removal efficiency can be lowered when zeolite concentrator deals with high boiling point VOCs. This study aimed at improving the performance of zeolite concentrator for VOCs removal. They were achieved by both field on application of combining condenser pre-treatment devices and the development of new adsorbent that could tolerate repeated adsorption/desorption process. The condenser pretreatment devices after the stripping process was for the purpose of pretreating the high boiling point VOCs. This could help to prevent the follow up zeolite concentrator from damage. The performance of the integrated system of condenser/zeolite concentrator could therefore remain highly efficient for a longer operation time. Its annual cost would also be lower than installing the zeolite concentrator only. The zeolite concentrator combining condenser for VOCs removal was examined in the semiconductor field test. The reaction temperature of the condensers was controlled at around 10oC, it was relatively higher than the traditional condenser reaction temperature. Both VOCs and water vapors were condensed and formed liquid films. This results in an enhancement of the VOCs removals, especially for VOCs of high boiling points or solubility. This study synthesized a new adsorbent, hexagonal nanostructured zeolite particles (HNZP) synthesized by aero-spray method, for adsorbent modification of zeolite concentrator and examined the performance of HNZP for acetone adsorption. It also compared the results with that of commercial mobil synthetic zeolite-5 (ZSM-5) type zeolite. The HNZP was a pure siliceous adsorbent with different values of pore diameter and surface area being adjustable by the manufacturing condition. The results indicated that a slight increase in the average pore diameter (d) of HNZP from 2.0 to 2.5 nm led to an increase in the acetone adsorption capacity even though its surface area was decreased, in which case (d=2.5 nm) the adsorption capacity of fresh HNZP was better than that of ZSM-5 zeolite. Even for the fresh HNZP (d=2.0 nm) whose adsorption capacity was less than that of the ZSM-5 zeolite at relative humidity (RH) of 0%, its adsorption capacity was not deteriorated after repeated regeneration, but the adsorption capacity of regenerated ZSM-5 zeolite decayed markedly. Thus after only one regeneration, the adsorption capacity of HNZP (d=2.0 nm) became better than that of the ZSM-5 zeolite. The decrease in the adsorption capacity of regenerated ZSM-5 zeolite might be due to its aluminum content that catalyzed the acetone into coke and thus blocked the adsorption sites. Furthermore, result on the moisture effect showed that because the pure siliceous HNZP was more hydrophobic than the ZSM-5 zeolite, the acetone adsorption efficiency of fresh HNZP (d=2.0 nm) was better than that of ZSM-5 zeolite at RH=50%. This study also verified that the reaction temperature was an important reaction parameter on the surface area, distribution of pores and particles of the HNZP. The appropriate reaction temperatures not only led the precursor solvents to be fully evaporated, but also promoted the micelles crystallization of surfactant organizing. As comparing the materials synthesized by aerosol spray method with the materials made by the conventional hydrothermal method, it was concluded that both the time and the amount of surfactant required for the aerosol process were much less than those for the hydrothermal method in synthesizing mesoporous materials of the same surface area and pore size.
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