Superhydrophobic Polymeric Hollow Fiber Membrane Contactors For Co2 Absorption
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Date
2014-08
Authors
Mohammed, Harith Noori
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
In recent years the climate change became a global concern due to the increasing of the earth’s surface temperature. This phenomenon was exacerbated by the expansion of industrial activities due to the increasing emissions of the greenhouse gas (mainly CO2). Many efforts were conducted to capture CO2 from the industrial process streams. Membrane gas absorption system (MGAS) was proposed as an alternative technique to overcome disadvantages of the conventional CO2 absorption processes. However, there are still many challenges in order to commercialize MGAS such as membrane surface stability, absorbent liquid efficiency and compatibility between absorbent liquid and membrane material. In order to solve this problem, a porous superhydrophobic layer of low density polyethylene (LDPE) had been coated on the outer surface of the polypropylene (PP) and polyvinylidene fluoride (PVDF) hollow fiber membrane via solvent non-solvent coating method. Parameters to prepare superhydrophobic flat surface (non-solvent type, non-solvent content in coating solution and polymer concentration) had been studied and optimized. It was observed that non-solvent like ethanol did produce polymeric surface with higher water contact angle (WCA) compared to methyl ethyl ketone used as non-solvent additives. The increasing of ethanol content in the coating solution up to 50% (v/v) led to the increased of WCA from 110±2.8o to 160±1.4o. The hydrophobicity of the coated layers were analysed in terms of surface roughness, physical structure and water contact angle. It was found that the WCA of the coated PP and PVDF hollow fiber membranes surfaces prepared via direct dip coating were less than the flat surface. Indirect method was proposed and the maximum WCA of modified PP and PVDF membranes were 161±2.3o and 152±3.2o, respectively. A continuous MGAS inhouse-built was designed to evaluate the performance of modified membranes in term of CO2 removal from gas stream of 20% (v/v) CO2 balanced with N2. The operating parameters (liquid velocity, gas velocity and packing density of the membrane module) and other effects on the CO2 removal were studied. The CO2 absorption performance was investigated for different absorbent liquids namely piperazine (PZ), monoethanolamine (MEA), diethanolamine (DEA) and their blends. PZ exhibited higher absorption efficiency than other absorbents. In terms of the membrane’s compatibility with PZ, PVDF membrane was found to have high surface stability compared to the PP membrane. In addition, it was observed that the activated MEA had CO2 absorption efficiency higher than activated DEA at the same concentrations and operating conditions. The mass transfer resistance through the membrane module was determined via Wilson plot method. It was observed that the liquid mass transfer resistance was the controlling step in all amine solutions. Moreover, the overall mass transfer coefficient was increased with the increasing of the activator concentration in the amine blends.
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Keywords
Membrane gas absorption system