Abstract
Novel selective ceramic-supported thin polyimide films produced in a single dip coating step are proposed for membrane applications at elevated temperatures. Layers of the polyimides P84®, Matrimid 5218®, and 6FDA-6FpDA were successfully deposited onto porous alumina supports. In order to tackle the poor compatibility between ceramic support and polymer, and to get defect-free thin films, the effect of the viscosity of the polymer solution was studied, giving the entanglement concentration (C*) for each polymer. The C* values were 3.09 wt. % for the 6FDA-6FpDA, 3.52 wt. % for Matrimid®, and 4.30 wt. % for P84®. A minimum polymer solution concentration necessary for defect-free film formation was found for each polymer, with the inverse order to the intrinsic viscosities (P84® ≥ Matrimid® >> 6FDA-6FpDA). The effect of the temperature on the permeance of prepared membranes was studied for H2, CH4, N2, O2, and CO2. As expected, activation energy of permeance for hydrogen was higher than for CO2, resulting in H2/CO2 selectivity increase with temperature. More densely packed polymers lead to materials that are more selective at elevated temperatures.
Highlights
The existing socioeconomic situation creates an increase of the energy demand in both industrialized and developing nations, expected to be doubled by 2050 [1]
Hydrogen production is the largest use of syngas, with steam methane reforming (SMR) being the predominant technology, which is a well-established process with two main reactions, reforming and water gas shift reaction [3,4]
Field-emission scanning electron microscope (FE-SEM) (Zeiss Ultra 55), equipped with EDX for elemental analysis was used for measuring the thickness of the samples and studying the contact quality of organic/inorganic materials, as well as the correct and the continuous formation of thin film layers
Summary
The existing socioeconomic situation creates an increase of the energy demand in both industrialized and developing nations, expected to be doubled by 2050 [1]. Different types of membranes for hydrogen separation have been developed, and they can be classified according to the selective layer material as polymeric, metallic, ceramic, and carbon membranes [5]. As in the case of several industrial processes, the solubility factor is even more reduced, and the diffusivity factor is more dominant compared to ambient temperatures Under those conditions, the permeability selectivity will be mainly influenced by the differences in the diffusion coefficients of gases dissolved in the polymer. The polymer membranes have to be processed as thin film composite membranes (TFCMs), where the supporting structures of the selective layer should possess high thermal and chemical stability whilst being highly permeable at the same time. The gas transport properties of the obtained membranes were studied with a variety of gases as a function of temperature
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