沼氣中二氧化碳與甲烷氣體之最佳分離吸附劑探討

Abstract

甲烷(CH4)與二氧化碳(CO2)均為溫室效應氣體，而沼氣中同時含有此兩種溫室氣體，以往沼氣因為缺乏經濟效益而任意排放至空氣中，造成溫室氣體濃度增加。而隨著國際間對溫室效應與新能源開發之日益重視，如果能發展出從沼氣中將CH4與CO2分離之技術，可以將沼氣濃縮純化，成為具高能源價值之甲烷燃料，並同時減少二氧化碳溫室氣體之排放，可謂一舉兩得。 研究篩選各種沸石，以進行從模擬沼氣中吸附CO2，而可使CH4氣體純化。本研究結果顯示適當的前處理可以有效提昇沸石之吸附容量，沸石的矽鋁比越低、比表面積越大及表面官能基含胺或鈉等，其對CO2之吸附量會較其它類沸石為佳，如在CO2吸附效率達80%時， CBV300、NaY及13X之吸附容量分別為73 mg/g、69 mg/g及44 mg/g。在成本考量下，因CBV300之售價過高，因此對較具成本效益與吸附量高的NaY及13X工業用沸石進行後續實驗測試探討。研究成果顯示，NaY及13X沸石會隨著溫度及溼度上升，而使其對CO2吸附量呈現下降的趨勢，另外隨著CO2濃度的上升，吸附量會成正比。以NaY與13X進行重複吸脫附測試，皆可穩定維持99%以上之吸附容量。由此可知，NaY及13X，在吸附CO2以分離出CH4上，應具有相當的開發潛力。

Biogas contains methane (CH4) and carbon dioxide (CO2) which belonged to greenhouse gas. In past, biogas which was less economic was arbitrarily discharged into the atmosphere, resulting in the increased concentration of the greenhouse gas. With the increasing attention on the greenhouse effect and development of novel energy, it is required to develop the new technologies separating the CO2 and CH4 from the biogas and the concentrated CH4 gas could be high-valuable fuels. Meanwhile, the reduction of CO2 emission could be achieved as well. In this study, three different types of zeolites are utilized for the separation of CO2 and CH4. The results showed that appropriate temperature of the pretreatment process can significantly enhance the adsorption performance of the zeolites. In addition, the adsorptive performance can be also greatly enhanced of the zeolites with lower Si/Al ratios, higher specific surface area as well as the surface modification with amino functional groups. Adsorbents of CBV300, NaY and 13X could achieve 73mg/g, 69mg/g and 44mg/g of adsorption capacity, respectively, as the removal efficiency of CO2 was 80%. In the view of economic aspect, NaY zeolite with high adsorption capacity and low cost was extensively studied as an adsorbent for separating CO2 and CH4 instead of CBV300 zeolite which is more costly. The CO2 breakthrough tests showed that the adsorption capacity decreased with the increase of operational temperature and humidity. Besides, the adsorption capacity increases linearly with respect to the inlet concentration of CO2. Cyclic adsorption-desorption tests implied that NaY and 13X zeolites could be completely regenerated. As a result, NaY and 13X zeolites could be promising adsorbents for the separation of CH4 and CO2.