以觸媒焚化法去除揮發性有機物之模式適用性探討

Abstract

在揮發性有機物之控制技術中，以觸媒焚化法 (Catalytic Incineration) 處理對工廠所排放之揮發性有機物其去除效率可達90%以上，且具有將有機物完全氧化之優點。而針對不同的揮發性有機物或觸媒型態，其觸媒焚化器之設計考量亦有不同。本研究同時發展二維解析解模式及效率因子模式，並分析比較其適用性。此外並將其利用來設計處理有機物(苯、乙基苯、苯乙烯及甲苯)之觸媒反應器大小，以及孔隙內擴散及反應器外擴散對觸媒反應的影響探討。 研究結果顯示，二維解析解對於有機物之去除效率有較佳之預測效果，較適用於觸媒反應器之設計。本研究利用文獻中之觸媒基本條件進行觸媒反應器之設計，若欲控制上述四種有機物之去除效率於90%以上時，則在孔道寬度為0.3cm，觸媒溫度為575°K之條件下，空間速度需控制於23000hr-1以下。另外，藉由真實活化能及表觀活化能的計算，可推求出各有機物之化學吸附能，發現在Pt/Al2O3觸媒上，苯之吸附性是各物種中最小的。而若比較各有機物之擴散影響，低溫時苯的反應受孔隙內擴散影響較大，而在高溫時苯的反應受孔隙內擴散影響則最小，乙基苯則在高溫時受孔隙內擴散影響最大。就反應器外擴散限制而言，同樣會隨溫度升高而增加，在低溫時苯的反應受反應器外擴散的影響較其它物種大，而高溫時苯的反應所受之外擴散影響反而是最小。

Catalytic incineration is one of the VOCs control techniques that has the advantages of high efficiency and complete oxidation. There were two types of models currently used for the design and improvement of catalytic incineration process, the lumped parameter model and the mass transfer model. However, their applications and limitation have not been compared and studied. In this study, a two-dimensional mass transfer model and one-dimensional effectiveness factor model were developed and their applications were compared. They were then used to design the catalytic incineration reactor and to analyze the effects of pore diffusion and external diffusion. An analytical solution of the two-dimensional mass transfer model was derived so that both models are simple and can be applied easily. The results indicated that two-dimensional analytic solution model has a better prediction in the VOCs removal efficiency and then can be applied to design the catalytic incineration reactor. Using the catalyst data in the literature, the design results showed that when the channel pitch is 0.35cm and temperature is 575°K, the space velocity has to be controlled to below 23000hr-1 for ensure 90% removal efficiency. As a result of comparison of the four VOCs, benzene, ethylbenzene, styrene and toluene, it found that the adsorptive capacity of benzene among the four is the smallest compound. The influence of pore diffusion on benzene destruction is the largest at higher temperatures while it is the lowest at temperature higher than 460°K. On the other hand, benzene is suffered most from external diffusion at high temperature.