醋酸纖維素管狀薄膜接觸器應用於聚乙二醇水溶液之脫水研究

Study on dehydration of PEG solution through cellulose acetate tubular membrane contactor

吳右瑜(Yu-Yu Wu)

指導教授 ： 李魁然 ； 蔡惠安

中原大學/工學院/化學工程研究所/碩士(2020年)

https://doi.org/10.6840/cycu202000469

摘要

本研究利用乾/濕相轉換法製備親水性多孔醋酸纖維素(Cellulose acetate, CA)管狀薄膜應用於管式薄膜接觸器，進行聚乙二醇(Polyethylene glycol , PEG)水溶液脫水。研究中利用調整製膜時捲收速率、CA高分子濃度、共溶劑種類與共溶劑比例條件製備CA管膜並探討對於透過量之影響。
於研究中使用冷場發掃描式電子顯微鏡(FE-SEM)觀察薄膜之結構形態，原子力顯微鏡(AFM)觀察薄膜表面之形貌與粗糙度，以光穿透率測試，得知鑄膜液浸入凝聚槽(水)後的相分離速率，並利用重量分析法與過濾實驗計算出薄膜的總孔隙率與平均孔半徑。
在管式薄膜接觸器研究中，使用空氣做為管側掃流氣體，殼側進料液為30 wt% PEG水溶液且進料溫度為50°C。經研究結果可得知，隨著製膜時捲收速率提升，薄膜皮層變厚，使透過量下降。在高分子濃度變化下，以15 wt% CA/NMP具有最佳脫水效能，純水透過量為10.38 ± 0.54 kgm-2h-1而PEG 水溶液之脫水通量為9.11 ± 0.47 kgm-2h-1。
使用四種溶劑，分別為Acetone、TEP、DMSO以及DMAc，均以80 wt%的比例與20 wt% NMP混溶，形成溶於CA高分子的共溶劑系統。由於Acetone/NMP與TEP/NMP系統與非溶劑之親和性較弱，相分離速率較慢，因此孔隙率較低，平均孔半徑較小；而DMSO/NMP與DMAc/NMP系統下，其與非溶劑之親和性較較強，因此相分離速率較快，薄膜產生較多巨型孔洞，且孔隙率高，具有較大的孔半徑，使質傳阻力降低，透過量有所提升。
在DMAc/NMP共溶劑系統下，隨著DMAc比例增加，CA高分子溶液黏度有降低的趨勢，因此相分離速率增加，薄膜產生具有巨型孔洞，使孔隙率與平均孔半徑隨之增加。其中以重量比80/20的DMAc/NMP系統下具有最佳效能，為10.00 ± 0.78 kgm-2h-1的PEG 水溶液之脫水通量。
隨著進料溫度的增加，由於分子動能增加，蒸氣壓升高，驅動力提升，使透過量提升。隨著膜管側氣體流量下降，進料的液體分子較易擾動，使透過量增加。經長時間測試下，對PEG 水溶液之脫水通量仍高於10 kgm-2h-1，因此本研究所製備的親水性多孔管狀薄膜是具有潛力的可應用於薄膜接觸器對PEG 水溶液之脫水。

關鍵字

醋酸纖維素；管式薄膜；薄膜接觸器；共溶劑；成膜速率；聚乙二醇

並列摘要

In this study, cellulose acetate (CA) tubular membrane is prepared through dry-wet phase separation as a membrane contactor for polyethylene glycol (PEG) dehydration. Four parameters are varied to prepare the tubular membranes: (1) take-up speed; (2) CA concentration; (3) type of cosolvent; and (4) ratio of cosolvents.
Morphology and surface roughness of the membranes are verified using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The demixing rate of dope solution into water as coagulation bath was evaluated using light transmission experiment. Porosity and mean pore radius are determined using gravimetric analysis and filtration velocity method, respectively.
In tubular membrane contactor experiment, air is used as sweep gas and PEG concentration in the feed is 30 wt% at 50°C. As a result, increasing the take-up speed, the skin layer become thick, resulting in low permeation flux during membrane contactor test. The optimum concentration of CA/NMP is 15 wt% CA with permeation flux of 10.38 ± 0.54 kgm-2h-1 or 9.11 ± 0.47 kgm-2h-1 when the feed is pure water or 30 wt% PEG solution, respectively.
The four kinds of solvent are acetone, triethyl phosphate (TEP), dimethyl sulfoxide (DMSO), N,N-Dimethylacetamide (DMAc) at 80wt% which blended with 20wt% NMP respectively. According to the solubility parameter, the water (non-solvent) has weak affinity with either acetone/NMP or TEP/NMP solution. When CA is dissolved in either acetone/NMP or TEP/NMP, the demixing rate is slow, resulting in low membrane porosity and small mean pore radius. On the other hand, DMSO/NMP or DMAc/NMP solution as solvent of CA has faster demixing rate than the other solution. This is because DMSO/NMP or DMAc/NMP solution has a strong affinity with water (non-solvent). SEM images shows that the CA membrane produce with faster demixing rate, macrovoids are formed with higher porosity and larger mean pore radius than the CA membranes produced at slower demixing rate. Consequently, high porosity and large mean pore radius of CA membrane has low mass transfer resistance, resulting in high permeation flux.
The ratio of DMAc to NMP is varied. As the amount of DMAc increases, the viscosity of the CA solution decreases. Low viscosity solutions has a faster demixing rate than high viscosity solution and will form macrovoids. The optimum concentration of the solvents in CA solution is 80 wt% DMAc and 20 wt% NMP.
Increasing the feed temperature, the mobility and vapor pressure of the feed increases, thus increasing the driving force into the membrane, the permeation flux increases. For varying the gas flow rate, decreasing the flow rate in the inner side of the tube lead to increase the flow rate in the feed, resulting in high permeation flux.
Furthermore, CA tubular membrane exhibited a stable performance for long operation. Therefore, hydrophilic and porous CA tubular membrane contactor has a great potential for dehydration of PEG solution.

並列關鍵字

hydrophilic；cellulose acetate；cosolvent；membrane contactor；polyethylene glycol；tubular membrane

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