Membran asimetrik disediakan terlebih dahulu daripada pembentukan berstruktur tiub-nano karbon dinding berlapis kertas-bucky (TNKDB-KB) sebagai lapisan pra-memilih dan kemudiannya struktur tersebut disalut dengan selapis polivinil alkohol (PVA) yang nipis. Membran asimetrik tersebut digunakan dalam proses penyejattelapan untuk penyahidratan campuran berbilang komponen yang diperolehi daripada tindak balas eterifikasi. Keputusan penyejattelapan menunjukkan bahawa membran asimetrik mempamerkan masing-masing dua dan empat kali ganda peningkatan bagi fluks telapan air dan faktor pemisahan. Kesan ini adalah disebabkan kumpulan hidrofilik pada MWCNTs yang telah ditulenkan dan saluran-nano pada lapisan pra-memilih, yang memihak kepada penyerapan molekul air. Model larutan-resapan bagi Rautenbach adalah memadai bagi menerangkan proses penyejattelapan. Dalam kajian proses tindak balas eterifikasi, pemangkin MWCNTs yang telah disulfonasikan mempunyai tapak asid Lewis telah disediakan melalui proses pensulfuran dengan asid sulfurik. Prestasi bermangkin oleh pemangkin pensulfuran MWCNTs telah dikaji dalam proses tindak balas eterifikasi bagi tert-butil alkohol (TBA) dan etanol. Kesan pembolehubah proses (suhu tindak balas, masa tindak balas, nisbah molar etanol kepada TBA, bebanan pemangkin) terhadap penukaran TBA, kememilihan etil tert-butil eter (ETBE) and hasil ETBE telah dikaji melalui dua pendekatan berbeza: pendekatan konvensional dan pendekatan metodologi permukaan sambutan (RSM). Bagi pendekatan konvensional, keadaan tindak balas optimum terdiri daripada masa tindak balas selama 4 j pada suhu 140 oC, nisbah molar etanol kepada TBA 2:1 dan 3 % berat bebanan pemangkin. Optimum penukaran TBA, kememilihan ETBE dan hasil ETBE masing-masing ialah 64 %, 68 % dan 44 %. Sebaliknya, keputusan yang diperolehi daripada pendekatan RSM menunjukkan bahawa pembolehubah-pembolehubah individu dan interaksi-interaksi mereka memberikan kesan ketara kepada tindak balas eterifikasi. Tindak balas selama 4 j pada 146 °C, nisbah molar bagi etanol kepada TBA 2.17:1 dan 3.26 % berat bebanan pemangkin memberikan penukaran TBA yang optimum sebanyak 72 %. Tambahan pula, optimum kememilihan dan hasil ETBE masing-masing ialah 60 % and 43 %. Kedua-dua pendekatan mempunyai pembolehubah-pembolehubah proses optimum yang seakan-akan sama. Walau bagaimanapun, pendekatan RSM dapat memberi pembolehubah-pembolehubah proses optimum yang lebih tepat dan khusus kerana nilai-nilainya dianggarkan daripada persamaan-persamaan model. Satu mekanisma eterifikasi telah dicadangkan bagi menerangkan tindak balas eterifikasi. Pemangkin pensulfuran MWCNTs menunjukkan penurunan prestasi bermangkin yang tidak ketara selepas empat eksperimen yang dilakukan secara berturut-turut dan mudah dipulihkan selepas penjanaan semula. Selepas itu, campuran tindak balas optimum digunakan sebagai larutan suapan bagi penyahhidratan air menggunakan membran asimetrik baru. Jumlah fluks penyerapan lebih kurang 7 g/m2∙j dan faktor pemisahan lebih kurang 400 telah diperolehi.
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Asymmetric membranes were prepared by first forming multi-walled carbon nanotube-buckypaper (MWCNT-BP) structures as the pre-selective layer followed by coating the structures with a thin layer of polyvinyl alcohol (PVA) to form novel MWCNT-BP/PVA asymmetric membranes. The resultant asymmetric membranes were applied in the pervaporation process for dehydration of multi-component mixture obtained from an etherification reaction process. The pervaporation results revealed that the asymmetric membranes exhibited two- and four-fold enhancements of the water permeation flux and separation factor, respectively, compared to the pure PVA membrane. This effect was observed due to the hydrophilic group on the purified MWCNTs and the nanochannels of the pre-selective layer, which favour the permeation of water molecules. A solution-diffusion model of Rautenbach was adequately in describing the pervaporation process. In the etherification reaction process study, sulfonated MWCNTs catalyst containing Lewis acid sites was prepared via sulfonation process with sulfuric acid. The catalytic performances of sulfonated MWCNTs catalyst were investigated in the etherification reaction process of tert-butyl alcohol (TBA) with ethanol. The effect of process variables (reaction temperature, reaction time, molar ratio of ethanol to TBA, catalyst loading) on the conversion of TBA, selectivity of ethyl tert-butyl ether (ETBE) and yield of ETBE were investigated using two different approaches: conventional approach and response surface methodology (RSM) approach. In the conventional approach, the optimum reaction conditions consisted of 4 h of reaction time at 140 °C, a molar ratio of ethanol to TBA of 2:1 and a catalyst loading of 3 wt%. The optimum TBA conversion, ETBE selectivity and ETBE yield were 64 %, 68 % and 44 % respectively. On the other hand, the results obtained from RSM approach revealed that individual variables and their interactions affect the etherification reaction significantly. The 4 h reaction at 146 °C, molar ratio of ethanol to TBA of 2.17:1 and 3.26 wt% catalyst loading gave an optimum conversion of TBA of 72 %. Furthermore, the optimum selectivity and yield of ETBE were 60 % and 43 %, respectively. It was interesting to note that similar optimum process variables were obtained from both approaches. Nevertheless, RSM approach provides a better and specific optimum process variables since the values were predicted from model equations. An etherification mechanism was proposed to describe the etherification reaction. The sulfonated MWCNTs catalysts exhibited an insignificant dropped of the catalytic performance after four consecutive experimental runs and it was easily regained after regeneration. Subsequently, the optimized reaction mixture was applied as the feed solution for dehydration of water using the novel asymmetric membrane. The total permeation flux of approximately 7 g/m2∙h, and separation factor of approximately 400 were obtained.
Multi-walled carbon nanotubes as pervaporation buckypaper membranes and catalysts for etherification reaction_Yee Kian Fei _K4_2016_MYMY