利用廢輪胎熱解碳黑製成高比表面積硫化活性碳及其除汞應用技術之研究

High-Surface-Area Sulfurized Activated Carbon Using Carbon Black from Waste Tire Pyrolysis Process and Its Application on Mercury Removal

王照燕(Chao-Yen Wang)

指導教授 ： 林錕松

元智大學/工程學院/化學工程與材料科學學系/碩士(2013年)

https://doi.org/10.6838/YZU.2013.00307

摘要

近年來汞污染源主要來自工業生產中排出的含汞廢水、燃煤火力發電廠所排放之含汞廢氣及廢水，尤其燃煤或廢棄物之低沸點重金屬汞大部分以元素汞存在，且易隨著燃燒尾氣釋放至大氣環境中，造成生態和人體傷害，故研發有效控制Hg排放於水體及空氣技術是刻不容緩的課題。臺灣廢輪胎數量每年高達約120萬噸，其成分複雜且再生困難，亦不適合衛生掩埋，一直是環保爭議之問題。因廢輪胎約含有70-75 wt%碳及10-15 wt%硫份，可進一步經過碳化/化學活化法，轉化成具有高附加價值、高比表面積及高孔洞硫化活性碳吸附材料。因此，本論文之主要目的是以熱解及氣化程序來處理廢輪胎，除了可回收燃料油、可燃氣、合成氣(氫氣及一氧化碳)及熱能外，更可生成具有附加價值碳黑，並進一步利用化學活化法(添加KOH及ZnCl2)，將碳黑轉化成高比表面積及高孔洞活性碳吸附材料。
由實驗中可知碳黑熱解後經由FE-SEM分析可知，經過吸附汞處理後之碳黑的顆粒較大，外觀為圓球狀之顆粒結構、粒子間相互聚集非常明顯。經由BET分析碳黑的比表面積為108.38 m2/g，大孔洞、中孔洞及微孔洞之體積及比例分別為0.5 (8%)、0.13 (70%)及0.08 cm3/g (22%)。將碳黑在不同溫度下熱解後用XRD分析可知隨著熱解時的反應溫度上升，其強度會有逐漸增加的趨勢，是因為熱解溫度越高，零價硫的增加使得吸附氧化還原反應增加，吸附較多的Hg形成HgS。FTIR分析發現反應時所提供之含氧量不同會使燃燒的產物改變，因氧氣不足時反應不容易燃燒完全而產生一氧化碳，相對提供較多的氧氣時，一氧化碳的量會明顯減少，但因為溫度持續上升，故容易將二氧化碳還原成一氧化碳。隨著溫度上升，提供大量的反應能量，促使吸附在輪胎上的零價硫能進行氧化還原反應成為二價硫。ESCA分析得知熱解溫度增加能提升碳黑吸附氧化還原零價汞之能力，另外隨著溫度上升而零價硫的增加，有助於將零價汞還原成硫化汞，增加吸附零價汞之能力。
模擬含汞燃煤煙道氣為具昇華特性之HgCl2，因HgCl2為吸附劑去除機制可能為化學吸附；元素汞主要為物理吸附，吸附力較弱，相對不易被去除。此外，由XANES及EXAFS分析可說明汞之氧化價數主要為二價，可能是因在高溫之下一價Hg較不易形成，其中HgO、HgCl2及HgS之配位數分別為2、4和4，鍵距分別為2.09、2.32及2.43 #westeur006#，顯示Hg在高溫之下，可能與空氣中之氧或尾氣之氯形成HgO或HgCl2化合物，但更容易與吸附劑表面之硫元素，形成HgS鍵結。另外，廢輪胎氣化處理後能產生合成氣，可連結氣體燃料發電機直接發電；或經分離程序生成高純度氫氣，再供給燃料電池做為發電原料，深具發展再生能源之潛力。

關鍵字

廢輪胎 ； 碳黑 ； 熱解 ； 氣化 ； 化學活化法 ； 硫化活性碳 ； 除汞

並列摘要

The extreme toxicity of mercury poses a serious threat to the environment. Discharge of Hg from industries and thereby the contamination of waters has brought global concerns to environmental authorities. Recently, attention has been focused on the fate of Hg from emission from coal-fired utility plants, including Hg-containing flue gas scrubber waters. Combustion of coal power plant is usually the primary source of anthropogenic Hg emissions in countries with high levels of coal consumption. The high volatility and chemical inertness of Hg(0)(g) is the reason that practically all air pollution abatement technologies are not capable of controlling mercury emissions. In addition, over 1,200,000 TPY (tons per year) of waste tires (WTs) are generated and disposed in Taiwan recently. These WTs of complicated composition give rise to serious environmental problems including a difficult recycling with an intricate sorting, contamination of environment, no suitability of landfill, and low usage of WTs recovery. Therefore, the main objectives of the proposed study were to recycle and converted waste tires with 70-75 wt% carbon and 10-15 wt% sulfur to high-surface-area/porous carbon black (CA) or activated carbons (ACs). The surface modification was conducted by chemical activation method of KOH/ZnCl2 addition using pyrolysis/gasification processes with syngas, heat, and pyrolysis oil or gas recycling.
Experimentally, by using FE-SEM analyses, the aggregation of ball-like CBs particles was notable and enlarged after the adsorption of mercury. The surface area of CBs is 108.4 m2/g. The volumes and ratios of marco-, meso-, and micro-pore for CBs are 0.5 (8%)、0.13 (70%), and 0.08 cm3/g (22%), respectively. Higher Pyrolysis temperature, the carbon black of the peak strength is growing by XRD. Since the increasing of pyrolysis temperature, the intensity of XRD peaks of CBs pyrolyzed at different temperatures were increased. It may be resulted by the more adsorption of Hg and Hg-S was found. FTIR and ESCA spectra showed the CO and Hg adsorption capacity were increased with increasing temperatures.
The postulated mechanisms of the adsorption of HgCl2 and Hg(0) might be chemically and physically adsorbed on the surface of pore channels, respectively. The XANES and EXAFS data showed the most adsorbents possessed Hg(II) species in such a high temperature environment. The main species in adsorbents were HgO, HgCl2, and HgS having the bond distances of 2.09 #westeur006#, 2.32, and 2.43 #westeur006# with the coordination numbers of 2, 4, and 4, respectively. In addition, the gasification of WTs to syngas, production of high purity hydrogen, and final processing to make it suitable for an integrated fuel cell power generation system that would utilize a renewable energy resource from waste tires potentially.

並列關鍵字

Waste tire ； Carbon black ； Pyrolysis ； Gasification ； Chemical activation ； Pre-sulfurised activated Carbon ； Mercury Removal

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