利用雙界面活性劑合成中孔洞材料應用於二氧化碳捕獲

Abstract

中孔洞矽材SBA-15可藉由製備條件之不同改變其孔洞結構，且同時具有微孔及中孔結構、管壁較MS41家族厚，因此有較高之水熱穩定性，是具備開發潛力之材料。本研究以SBA-15為基礎，利用雙界面活性劑作為模板，以P123為主，並分別搭配F68、F127、PEG200、PEG600及CTAB等合成中孔洞材料，經由組成種類與比例調整原有SBA-15比表面積、孔徑尺寸及孔洞體積等結構，將其應用於二氧化碳吸附上，探討結構改變對吸附能力之影響。 研究結果顯示P123搭配F68所合成之中孔洞材料可提升對二氧化碳之吸附能力，尤其以P123:F68=1:3時擁有最佳吸附量(41 mg/g)，優於以單一P123界面活性劑所製備者(30mg/g)，除此之外，也發現在P123與F68組合當中，F68添加比例增加有利於微孔結構之提升；並將材料孔洞結構與二氧化碳吸附量做關連性分析，發現當中孔與微孔結構同時存在時，微孔比表面積及微孔體積是影響二氧化碳吸附之關鍵因子，微孔結構之提昇有助於吸附能力。而以鹼性金屬鹽類溶液進行材料表面改質，由實驗結果顯示，以0.1 M之碳酸氫鈉溶液改質，可提升材料對二氧化碳之吸附(45 mg/g)，由於碳酸氫納為弱鹼，因此對材料結構之破壞較小且能提供適當鹼度。在針對煙道氣CO2/N2分離之CO2吸附捕獲測試溫度之效應結果發現，所合成與改質之最適中孔洞材料於較高溫度吸附二氧化碳時，將抑制原有吸附效能；而將材料應用於CO2/CH4沼氣分離模擬之結果顯示，當CO2/CH4比例減少時，由於二氧化碳濃度降低飽和吸附量隨之下降，將會降低對二氧化碳之選擇性。

SBA-15 possesses unique micro/mesoporous structure, thicker wall and higher hydrothermal stability. It has been reported in previous studies that pore structure plays a crucial role in the adsorbent performance. This work intends to utilize dual-surfactants for synthesizing SBA-15 materials with optimized structures in order to enhancing CO2 capture. The studying surfactants include P123, F68, F127, PEG200, PEG600 and CTAB. The pore structures such as surface area、pore size and pore volume of materials could be adjusted via different dual-surfactants combinations and ratios. These materials are applied on CO2 adsorption and the impact of structural changes are investigated. The results show that SBA-15 prepared with the dual templates of P123 and F68 exhibited better adsorption capacities. Especially for the one prepared with P123:F68=1:3, the adsorption capacity is 41 mg/g, which is superior to synthesized with single surfactant of P123(30 mg/g). In the combination of P123 and F68, the microporous structures increases as the amount of F68 increases. From the correlation of pore structures and CO2 adsorption capacity, the microporous surface area and micropore volume are the key factors for CO2 adsorption. The microporous structures can enhance adsorption capacity. Furthermore, the materials are modified via alkaline solution to increase CO2 adsorption capacity. According to the result, the materials modified by 0.1 M NaHCO3 can enhance the CO2 adsorption capacity (45 mg/g) but pore structure is effected by NaHCO3. The results on the temperature effect show that CO2 adsorption is decreased when temperature is increased. For the CO2/CH4 separation test, the selectivity of CO2 is slight declined when the CO2/CH4 ratio is decreased.