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no / Research and technology innovations in the 1970s led to the significant commercial practice of gas separation by membranes that exists today. These advances involved developing membrane structures that could produce high fluxes and modules for packing a large amount of membrane area per unit volume (Murphy et al., 2009). At present, the share of using a polymeric membrane in the capture of CO2 is increasing and gradually the membrane technology is considered as the promising method in separation units, although the number of commercial membranes is not high. CO2 capture from natural gas is one of the controversial topics that many researchers and engineers try to find the best method satisfying both high efficiency and low capital cost. In common, chemical physical absorption towers are applied to remove CO2 from natural gas in order to prevent pipeline corrosion, even though the other component such as H2S gives rise to operating problems. The obscure angle of a conventional unit is related to the high energy consumption while the absorbent needs to be purified by the regeneration units which implement the temperature as a unique manipulating parameter for separating amine groups. The great advantages of using the membrane in gas industry are the low capital cost, easy installation and maintenance so that for this simple reason, new membranes come to the market for different types of processes. Capture of CO2 from natural gas accounts for one of the major difficulties so that the engineers try to employ membrane modules as to alter the process efficiency. However, there are only a limited number of membranes that can be used in real industry and the research still continues over this interesting topic (Burggraaf and Cot, 1996).

Yes / CO2 capture from natural gas was experimentally and theoretically studied using a dead-end polymeric permeation cell. A numerical model was proposed for the separation of CO2/CH4 using Polytetrafluoroethylene (PTFE) in a flat sheet membrane module and developed based upon the continuity, momentum and mass transfer equations. The slip velocity condition was considered to show the reflection of gas flow in contact with the membrane surface. The solution method was based on the well-known SIMPLE algorithm and implemented using MATLAB to determine the velocity and concentration profiles. Due to change in velocity direction in the membrane module, the hybrid differencing scheme was used to solve the diffusion-convection equation. The results of the model were compared with the experimental data obtained as part of this work and good agreement was observed. The distribution of CO2 concentration inside the feed and permeate chambers was shown and the velocity profile at the membrane surface was also determined using reflection factor for polymericmembrane. The modelling result revealed that increasing the amount of CO2 in gas feed resulted in an increase in the CO2 in the permeate stream while the gas feed pressure increased. By changing the permeability, the model developed by use of the solution-diffusion concept could be used for all polymeric membranes with flat sheet modules.

The present work was undertaken to develop a composite osmotic distillation (OD) membrane consisting of a thin hydrogel coating on a microporous hydrophobic substrate for the concentration of aqueous feeds containing surface-active agents. The range of OD applications using the hydrophobic membrane alone have been severely limited by the propensity for membrane wet-out when contacted by amphiphilic agents such as oils, fats and detergents. Wet-out allows the feed solution to track freely through the membrane pores with a resulting loss of solutes and a decrease in selectivity. The rationale for the approach taken was based on the hypothesis that the high water selectivity of the hydrophilic coating would maintain good water mass transfer to the underlying hydrophobic substrate but exclude other components including surface-active agents. The first stage of this work involved the identification of potential coating materials and the fabrication and structural characterization of films of these materials to determine their suitability. The second stage involved the development of techniques to facilitate adhesion of the hydrophilic coatings to the hydrophobic substrate, and the testing of the resulting composite membranes for OD performance and resistance to wet-out by surface-active agents. Sodium alginate was selected as the major coating component on the basis of its non-toxicity and its potential for stable hydrogel formation. Structural characterization of noncrosslinked films and films crosslinked using a water-soluble carbodiimide (WSC) was carried out using differential scanning calorimetry (DSC), Fourier Transform infrared spectroscopy (FT-IR) and swelling measurements. Maximum crosslinking through esterification of hydroxyl and carboxylic acid groups on adjacent polymer strands using the film immersion method was achieved with a non-solvent (ethanol) concentration of 60 vol % and a WSC concentration of 100 mM at pH 4. These conditions resulted in a hydrogel with an equilibrium water content of 60 wt %. DSC measurements of noncrosslinked and crosslinked alginate films showed an increase in crystallinity and hence rigidity on crosslinking. Therefore, several coatings were prepared as blends of sodium alginate and amorphous highly flexible carrageenan gum in order to meet the flexibility requirements of a membrane subjected to varying operating pressures in an industrial OD plant. Structural characterization with respect to polymer blend ratio was carried out using scanning electron microscopy (SEM), DSC, X-ray diffraction (XRD). The optimisation for crosslinking conditions was undertaken as for sodium alginate alone. Optimum conditions for film preparation were 20 wt % carrageenan content and a crosslinking medium containing 60 vol % non-solvent (ethanol) and 120 mM WSC at pH 4. These conditions produced a hydrogel with an equilibrium water content of 85 wt %. Two different techniques were employed to anchor the coatings on substrate PTFE membranes. For membranes with a nominal diameter of 0.2 µm, the technique involved surface tension adjustment of the coating solution by ethanol addition in order to enhance penetration of the coating solution meniscus into the substrate pores. This was followed by polymer precipitation by the selective removal of water using OD to provide structural interlocking. T-peel strength measurements showed that this technique resulted in a ten-fold increase in adhesion strength when compared with a coating cast without surface tension adjustments. For membranes with a nominal diameter of 0.1µm, an interfacial bonding agent, myristyltrimethylammonium bromide (MTMA), was used. This technique gave a three-fold increase in adhesion strength relative to that of coating cast without the use of MTMA. The composite membranes were tested in extended OD trials using pure water and feeds containing limonene, the major surface-active components of orange oil. The sodium alginate-carrageenan blend membrane, which was the preferred membrane based on flexibility and water sorption considerations, was also tested against full-cream milk and an industrial detergent, sodium dodecylbenzene sulfonate (DBS). The results indicated that the coatings offered little resistance to water transport and were effective in providing protection against membrane wet-out. Durability trials showed that the composite membranes retained their integrity in water for a minimum of 30 days. Overall, this study has expanded the potential applications of OD to include many important industrial concentration steps that are currently being undertaken by conventional processes with unsatisfactory results. These include the concentration of citrus juices, full-cream milk and nuclear power plant liquid waste. These feeds contain limonene, fats and detergents respectively, all of which wet out unprotected hydrophobic membranes.