A Study of the Reinforcement Effect of MWCNTs onto Polyimide Flat Sheet Membranes

Polyimides rank among the most heat-resistant polymers and find application in a variety of fields, including transportation, electronics, and membrane technology. The aim of this work is to study the structural, thermal, mechanical, and gas permeation properties of polyimide based nanocomposite membranes in flat sheet configuration. For this purpose, numerous advanced techniques such as atomic force microscopy (AFM), SEM, TEM, TGA, FT-IR, tensile strength, elongation test, and gas permeability measurements were carried out. In particular, BTDA–TDI/MDI (P84) co-polyimide was used as the matrix of the studied membranes, whereas multi-wall carbon nanotubes were employed as filler material at concentrations of up to 5 wt.% All studied films were prepared by the dry-cast process resulting in non-porous films of about 30–50 μm of thickness. An optimum filler concentration of 2 wt.% was estimated. At this concentration, both thermal and mechanical properties of the prepared membranes were improved, and the highest gas permeability values were also obtained. Finally, gas permeability experiments were carried out at 25, 50, and 100 ◦C with seven different pure gases. The results revealed that the uniform carbon nanotubes dispersion lead to enhanced gas permeation properties

Cellulose-based carbon hollow fiber membranes for high-pressure mixed gas separations of CO2/CH4 and CO2/N2

Carbonized cellulose -based hollow fiber membranes were prepared by dry-wet spinning phase inversion method, followed by carbonization and evaluated in terms of gas separation performance for CO2/N2 and CO2/CH4 mixtures, under flow conditions. Permeability and real selectivity were measured for both mentioned mixtures, in a temperature range of 25 °C to 60 °C, a differential pressure range of 8 bar(a) to 20 bar(a) and a CO2 concentration range from 5% v/v to 15% v/v. The highest yielding mixture selectivity values were 42 for CO2/N2 at 10% v/v CO2, 25 °C & 8 bar(a) and around 150 for CO2/CH4 at the same conditions, whereas the respective CO2 permeabilities were 110 and 45 Barrer. Additionally, experiments of varying head pressure, while maintaining differential pressure, transmembrane pressure, at 8 bar(a), have revealed that CO2/N2 separation factor can be further enhanced with real selectivity being raised to 55 and permeability to 180 at 20 bar head pressure. The same approach had negligible effect on CO2/CH4 separation. This is an important finding by taking into consideration that natural gas treatment, i.e. sweetening and purification processes, is energetically and economically convenient if it takes place under the conditions, where the NG stream is extracted from the wells, or after a decompression. Moreover, Process simulation indicates that a two-stage system using the developed carbon membranes is technologically feasible to produce 96% methane with a low methane loss of <4%. Further improving membrane gas permeance can significantly reduce the specific natural gas processing cost which is dominated by the membrane-related capital cost.publishedVersionDOI:10.1016/j.seppur.2020.117473. Available online 31 July 2020 1383-5866/ © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/)

Well-Established Carbon Nanomaterials: Modification, Characterization and Dispersion in Different Solvents

Three different types of carbon nanomaterials, SWCNTs, MWCNTs and GNPs were prepared, modified, characterized, and their dispersibility behavior in three different solvents was evaluated. The carbon nanotubes were synthesized by using the well-known chemical vapor deposition method and the graphene nanoplatelets by wet physicochemical treatment techniques. Their characterization was accomplished by using various advanced techniques, such as powder X-ray diffraction and Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and N2 adsorption at 77 K. Furthermore, the carbon nanostructures were modified via plasma treatment and wet chemical surface modification in order to enhance their dispersion characteristics, for achieving more homogenous suspensions and therefore to be remained dispersed over a reasonable period of time without any sedimentation. The effect of treatment parameters and the use of different solvents were thoroughly studied mainly by optical methods, but also by using the DIN/EN classified ISO method of oil absorption and UV–Vis spectroscopy. The enhanced dispersion rate is observed in both CNTs and GNPs materials following their surface treatment, especially when using the solvent n-methyl-2-pyrrolidone. The aforementioned studied nanomaterials are perfect candidate fillers for preparing polymeric mixed matrix membranes

Comparison of flat and hollow-fiber mixed-matrix composite membranes for CO2 separation with temperature

Zeolite A/poly (1-trimethylsilyl-1-propyne) (zeoliteA/PTMSP) and [emim][Ac]/chitosan (IL/CS) are mixed-matrix membrane (MMM) materials with enhanced CO2/N2 permselectivity even at higher temperature. The scalability to asymmetric flat and hollow-fiber geometry by a simple dip-coating method was analyzed. The CO2/N2 separation performance was evaluated at different temperatures. The resulting composite membranes exhibit a significantly enhanced CO2permeation flux because the MMM layer thickness is reduced by 97?% from flat to hollow-fiber geometries in IL-CS composite membranes, while the selectivity is maintained similar to the self-standing membranes, thus proving that compatibility between the membrane component materials leads to a defect-free composite membrane, regardless the geometry and temperature.Financial support from the Spanish Ministry of Economyand Competitiveness (MINECO) under project CTQ2012-31229 at the Universidad de Cantabria is gratefully acknowl-edged. A.F.B. and C.C.C. also thank the MINECO for theEarly Stage Researcher (BES2013-064266) and ‘‘Ramón yCajal’’ (RYC2011-0855) contracts, respectively. The authorsthank F. Noboru Ramirez-Matsumoto for his contribution inthe synthesis and permeation experiments of the CS andIL-CS composite flat membranes by the modified IP method

Fabrication and characterization of PEI/PVP-based carbon hollow fiber membranes for Co2/Ch4 and Co2/N2 separation

Carbon hollow fiber membranes derived from polymer blend of polyetherimide and polyvinylpyrrolidone (PVP) were extensively prepared through stabilization under air atmosphere followed by carbonization under N2 atmosphere. The effects of the PVP compositions on the thermal behavior, structure, and gas permeation properties were investigated thoroughly by means of differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, and pure gas permeation apparatus. The experimental results indicate that the transport mechanism of small gas molecules of N2, CO2, and CH4 is dominated by the molecular sieving effect. The gas permeation properties of the prepared carbon membranes have a strong dependency on PVP composition. The carbon membranes prepared from polymer blends with 6 wt % PVP demonstrated the highest CO2/CH4 and CO2/N2 selectivities of 55.33 and 41.50, respectively