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1.
Teflon AF2400/Ultem composite hollow fiber membranes for alcohol dehydration by high‐temperature vapor permeation 下载免费PDF全文
Dan Hua Tai‐Shung Chung Gui Min Shi Chao Fang 《American Institute of Chemical Engineers》2016,62(5):1747-1757
High‐temperature vapor permeation has a stringent requirement of membrane stability under harsh feed environments. This work reports the design of Teflon AF2400/Ultem composite hollow fiber (HF) membranes for alcohol dehydration via vapor permeation. Fabrication parameters such as Teflon concentration and coating time were systematically investigated. Interestingly, the fabricated composite HF membranes possess an unusual surface with honeycomb‐like microstructure patterns. Owing to the Teflon protective layer, the newly developed composite HF shows a promising and stable separation performance with a flux of 4265 gm?2 h?1 and a separation factor of 383 for 95% isopropanol dehydration at 125°C. The composite HF also performs well under extreme vapor feed compositions from 87 to 99 wt % isopropanol. In addition, it exhibits impressive separation performance for the dehydration of ethanol and n‐butanol. This work may provide useful insights of designing thermal‐stable and high‐performance composite polymeric membranes for vapor permeation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1747–1757, 2016 相似文献
2.
Physical aging of both thick and thin films of “high free-volume” glassy perfluoropolymers was studied by monitoring changes in pure gas permeability of O2, N2 and CH4. All permeability measurements were done at a fixed temperature of 35 °C for more than 1000 h of aging. Two grades of perfluoropolymers, Teflon AF and Hyflon AD, having different comonomer structures but with similar comonomer ratios were studied to understand the effect of comonomer type and content on the aging behavior. The effect of casting process (solution vs. spin coating) and solvent type (vapor pressure and boiling point) had a significant effect on the absolute permeability of both thick and thin films; however, the aging rates were more affected by thickness and solvent type rather than the casting process for similar thicknesses. After 1000 h of aging, the relative permeability for thin films of Teflon AF 2400 was decreased by 27% compared to only 10% for thick films prepared from Novec 7500 solvent. Teflon AF, which has a higher fractional free volume (FFV) than Hyflon AD, is believed to undergo significant aging well before the initial permeability measurement could be made (after ∼ 1 h of aging) and, therefore, Teflon AF materials showed a lower decrease in relative permeability compared to Hyflon AD for the same aging time. The comonomer type and content has a significant effect on the permeability; the initial absolute oxygen permeability for AF 2400 was an order of magnitude higher compared to AD 60. The physical aging of thin films of the various glassy perfluoropolymers was also tracked by recording changes in the refractive index and thickness with time by ellipsometry. The ellipsometry data also confirmed higher aging rates in Hyflon AD compared to Teflon AF materials. The volumetric aging rate, obtained from the change in the refractive index using the Lorentz–Lorenz equation, and the permeability reduction rate from the (P1000h/P1h) ratio showed an excellent linear correlation. The (P1000h/P1h) ratio also showed a stronger correlation with (Tg−35) °C than with FFV. 相似文献
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Hydrophobic solid surfaces with controlled roughness were prepared by coating glass slides with an amorphous fluoropolymer (Teflon® AF1600, DuPont) containing varying amounts of silica spheres (diameter 48 μm). Quasi-static advancing, θA, and receding, θR, contact angles were measured with the Wilhelmy technique. The contact angle hysteresis was significant but could be eliminated by subjecting the system to acoustic vibrations. Surface roughness affects all contact angles, but only the vibrated ones, θV, agree with the Wenzel equation. The contact angle obtained by averaging the cosines of θA and θR is a good approximation for θV, provided that roughness is not too large or the angles too small. Zisman's approach was employed to obtain the critical surface tension of wetting (CST) of the solid surfaces. The CST increases with roughness in accordance with Wenzel equation. Advancing, receding, and vibrated angles yield different results. The θA is known to be characteristic of the main hydrophobic component (the fluoropolymer). The θV is a better representation of the average wettability of the surface (including the presence of defects). 相似文献
5.
A new method of measuring the complex dielectric constant of a thin sheet of polymer samples at microwave frequency is presented.
In order to obtain the complex dielectric constant in terms of reflection coefficient, a higher order power series solution
has been introduced. Application of lower order power series solution to the greater thickness of the sample requires a frequency
of less than 1.5 GHz. To overcome this constraint and to extend the range of working frequency, the higher order power series
solution is used to obtain the complex dielectric constant. This method is used to measure the complex dielectric constant
of poly(ethylene vinyl acetate), polyurethane, polyvinyl acetate, and polystyrene. The results obtained are in good agreement
with literature.
Electronic Publication 相似文献
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Nair RR Ren W Jalil R Riaz I Kravets VG Britnell L Blake P Schedin F Mayorov AS Yuan S Katsnelson MI Cheng HM Strupinski W Bulusheva LG Okotrub AV Grigorieva IV Grigorenko AN Novoselov KS Geim AK 《Small (Weinheim an der Bergstrasse, Germany)》2010,6(24):2877-2884
A stoichiometric derivative of graphene with a fluorine atom attached to each carbon is reported. Raman, optical, structural, micromechanical, and transport studies show that the material is qualitatively different from the known graphene-based nonstoichiometric derivatives. Fluorographene is a high-quality insulator (resistivity >10(12) Ω) with an optical gap of 3 eV. It inherits the mechanical strength of graphene, exhibiting a Young's modulus of 100 N m(-1) and sustaining strains of 15%. Fluorographene is inert and stable up to 400 °C even in air, similar to Teflon. 相似文献
8.
Rahul R. Nair Wencai Ren Rashid Jalil Ibtsam Riaz Vasyl G. Kravets Liam Britnell Peter Blake Fredrik Schedin Alexander S. Mayorov Shengjun Yuan Mikhail I. Katsnelson Hui‐Ming Cheng Wlodek Strupinski Lyubov G. Bulusheva Alexander V. Okotrub Irina V. Grigorieva Alexander N. Grigorenko Kostya S. Novoselov Andre K. Geim 《Small (Weinheim an der Bergstrasse, Germany)》2010,6(24):2773-2773
A stoichiometric derivative of graphene with a fluorine atom attached to each carbon is reported. Raman, optical, structural, micromechanical, and transport studies show that the material is qualitatively different from the known graphene‐based nonstoichiometric derivatives. Fluorographene is a high‐quality insulator (resistivity >1012 Ω) with an optical gap of 3 eV. It inherits the mechanical strength of graphene, exhibiting a Young’s modulus of 100 N m?1 and sustaining strains of 15%. Fluorographene is inert and stable up to 400 °C even in air, similar to Teflon. 相似文献
9.
Igor V. Elmanovich Mikhail S. Kondratenko Dmitry O. Kolomytkin Marat O. Gallyamov Alexei R. Khokhlov 《International Journal of Hydrogen Energy》2013
In the present work we suggest a new approach to the thin-film design of active layers for electrodes of fuel cells with phosphoric acid electrolyte in a polymer matrix. A fluoropolymer binder is introduced into common Pt@C active layer materials using supercritical (SC) CO2 as a solvent. Unique wetting properties of this non-hazardous and environmentally friendly solvent allow one to deposit highly uniform thin fluoropolymer films on dispersed carbon supports. As a result, well-percolated gas-permeable fluoropolymer phases are produced in active layers already at comparatively small polymer loadings. Teflon AF 2400 was chosen as a stable high-molecular-weight fluoropolymer soluble in SC CO2 with high oxygen permeability and high Tg value. Fluoropolymer-containing active layer materials prepared via the SC CO2 deposition routes were studied by means of cyclic voltammetry and were tested in operating fuel cells using steady state voltammetry and electrochemical impedance spectroscopy. Polarization curves of operating fuel cells indicate that the optimal content of deposited from SC CO2 fluoropolymer in active layer is about 3–5%. Results of impedance spectra fitting yield information used to explain the detected values of optimal loading. 相似文献
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