- 學位論文
平板式氟碳薄膜親疏水性對二氧化碳回收效能影響之研究
Study on the influence of hydrophobicity in plate fluorocarbon membrane on carbon dioxide recovery efficiency
摘要
本研究旨在探討不同親疏水性之氟碳薄膜對二氧化碳回收效能之影響，研究方法乃利用四氟化碳(CF4)氣體進行薄膜表面電漿改質以製備超疏水微孔洞聚二氟乙烯薄膜(Polyvinylidenefluoride, PVDF)，而後將製備出超疏水薄膜用於薄膜接觸器中進行二氧化碳的回收試驗。改變不同電漿參數、薄膜材料、吸收劑、氣體流量及與液體流量進行實驗與理論研究。 研究發現以CF4氣體進行薄膜表面電漿改質並搭配電漿操作參數於100瓦處理5分鐘可將PVDF薄膜超疏水化，薄膜表面含氟原子數及表面粗糙度皆增加使其接觸角可超過155o。將製備出PVDF薄膜與未改質前商業化PVDF薄膜以及商業化PTFE來進行二氧化碳回收效能的測試，經計算發現二氧化碳於三種薄膜的通量皆會隨著氣體流速的上升而增加而不隨液體流速改變有明顯變化；改變吸收劑發現，以PZ活化後的AMP吸收劑由於與二氧化碳反應極快使得二氧化碳通量較未活化吸收劑AMP來的大；而三級醇胺在系統中，由於反應速率慢使得二氧化碳通量最低。 電漿改質之PVDF疏水性及耐久性皆提升，因此可避免孔洞潤濕所造成的質傳阻力上升。而其於不同反應速率吸收劑下二氧化碳回收率皆比未改質PVDF及PTFE高約3%到8%。進一步計算於不同吸收劑下二氧化碳於三種相同厚度薄膜的質傳係數發現在AMP吸收劑的操作下仍以電漿改質後超疏水PVDF薄膜效果最佳，低流速下薄膜質傳係數可由未改質前的1.29×10-4 m/s提升至1.68×10-4 m/s，最高提升約30%的質傳係數；另一方面以PZ活化後的AMP混合醇胺吸收劑進行操作發現也有同樣的結果，二氧化碳於未改質PVDF薄膜之質傳係數為1.99×10-4 m/s，而於電漿改質後的PVDF薄膜其薄膜質傳係數可提升達2.42×10-4 m/s，提升約22%之薄膜質傳效能。
並列摘要
The aim of this study is to find out the relationship between membrane’s wettability and the carbon dioxide recovery efficiency in the membrane contactor system for carbon dioxide absorption. We prepare the super hydrophobic microporous Polyvinylidenefluoride (PVDF) membrane by surface modification using tetrafluoromethane (CF4) plasma, and then use the plasma-treated membrane in the absorption system. In this experiment, We changed the plasma modification parameter , membrane material, gas flow rate and liquid flow rate in carbon dioxide absorption system to do research. Firstly, the result of contact angle measurement of membrane surface modification shows that the PVDF membrane can become more hydrophobic, even super hydrophobic than original one at 100 watt plasma treatment for 5 minutes, it’s because the fluorine atom number and surface roughness on the membrane surface increase and the contact angle can reach 155o. And then compare the carbon dioxide recovery efficiency in the following three membranes, plasma-treated PVDF membrane, commercial PVDF and PTFE membrane, we can find that the flux of carbon dioxide in these three membranes will increase with gas flow rate but not appreciably change with liquid flow rate, then change the absorbent in this system and find that AMP absorbent, which activated by PZ, can have much higher carbon dioxide flux than original one because higher reaction rate with carbon dioxide, the third order alkanolamie, MDEA, has lower reaction rate with carbon dioxide so the carbon dioxide flux is small. The plasma-treated PVDF membrane has good hydrophobic characteristic and chemical resistance, it can avoid the absorbent penetrate into the pores of membrane causing the mass transfer resistance increase so the carbon dioxide recovery efficiency of plasma-treated PVDF membrane increases 3% and 8% more than commercial PVDF and PTFE membranes in different absorbents. Further, we calculate the carbon dioxide mass transfer coefficient in these three different membranes at the same thickness in different absorbent and compare PVDF membrane with plasma-treated PVDF membrane, we find the mass transfer coefficient in the plasma-treated PVDF membrane increases from 1.29×10-4 m/s to 1.68×10-4 m/s at low gas velocity, it’s about 30% higher than PVDF membrane. On the other hand, we use the blended alkanolamine, AMP/PZ, to operate the carbon dioxide absorption system and find the mass transfer coefficient in plasma-treated PVDF membrane is 2.42×10-4 m/s, about 22% higher than PVDF membrane (1.99×10-4 m/s) at low gas velocity.