CO2/CH4 gas separation is a very important applicatable process in upgrading the natural gas and landfil gas recovery. In this work, to investigate the membrane separation process performance, the gas permeation results and CO2/CH4 separation characteristics of different prepared membranes (via blending different molecular weights of polyethylene glycol (PEG) as a modifier with acrylonitrile- butadiene-styrene (ABS) as a backbone structure) have been studied. Furthermore, SEM analysis was carried out for morphological investigations. The effect of PEG content on gas transport properties on the selected sample was also studied. The effect of pressure on CO2 permeation was examined and showed that at the pressure beyond 4 bar, permeability is not affected by pressure. The results showed that more or less in all cases, incorporation of PEG molecules without any significant increase in CH4 permeability increases the CO2/CH4 selectivity. From the view point of gas separation applications the resultant data are within commercial attractive range.

Membrane processes are among the common methods for water sweetening and desalination, however, due to the cost and energy consumption, membrane processes are more suitable and have more practical applications. Designing of membranes in different shapes and dimensions, performing of separation process at room temperature, minimum consumption of chemical materials including solvents, and other additives are among the advantages of membrane process in respect to classical and common separation processes. Different membrane processes are used for water sweetening including reverse osmosis, electrodialysis, microfiltration, ultrafiltration, and nanofiltration membrane processes in which the reverse osmosis and electrodialysis methods are more important. Polymers are commonly used as membranes for the water sweetening industry, and due to their versatile structures and properties have a specific position in such a way that their applications are growing steadily. The most suitable and efficient polymeric membranes applied in the country are cellulose acetate, polyamide composite membranes, polysulfone, polyethylene, polypropylene, polycarbonate, polytetrafluoroethylene, polyvinylidene fluoride, and polydimethylsiloxane. There are different methods for improving the efficiency of polymeric membranes in the water desalination process in which preparation of copolymers and polymer blends, chemical modifications on the polymeric structure or their chemical functionalization, preparation of composites, and physical or chemical modifications on the surface of some polymers are more important that should be resulted in a suitable collection of physical, hydrophobic, chemical, thermal, and hydrolytic stability of the polymer and also led to remarkable flux and salt rejection. In this article, different membrane processes, and polymers that are applying in this industry is briefly introduced.

In order to enhance the water flux and rejection of polyethersulfone (PES) membranes for membrane distillation process (MDP), we have developed a new PES membrane using a oleic acid as a hydrophobic agent. The synthesis membranes are fabricated via the phase inversion procedure and we examined the effects of oleic acid on hydrophobicity, porosity, surface roughness, morphology and MDP performance. For the membrane characterization, the produced membranes were characterized by contact angle, FTIR spectroscopy, field emission scanning electron microscopy, atomic force microscopy and porosity measurements. The outcomes demonstrated that the presence of the small amount of oleic acid in the membrane has led to an increment in the membrane hydrophobicity and porosity, and also improves the water flux and rejection of the MDP. The increment amount of oleic acid not only have no positive efficacy on the membrane performance, but can also reduce the MDP efficiency. In some areas, the excess concentration of oleic acid prevents the crossing of vapors evaporation through the cavities, so it will diminish the MDP flux.

In this study, the combination of chemical, biological and membrane processes was investigated for landfill leachate treatment. In order to reduce the contamination level, the chemical coagulation process was used by coagulants such as aluminum sulfate and poly aluminum chloride. Also, the optimum pH range and concentration of the coagulant were determine following by the biological process of activated sludge. Finally, the leachate separation of the aerobic bioreactor was carried out by FO-MBR membrane process and the effect of powder activated carbon adsorbent was studied on this process. The results showed that the amount of COD in leachate decreased by 48% after pretreatment using coagulants (optimum concentration of 1 g/l and pH = 8). Then, the COD removal rate reached to 24% by using the aerobic activated sludge process under optimum aeration conditions, F/M = 0. 312 COD/MLSS. d ratio and 24h hydraulic retention time. In the last section, the usage of synthesized cellulose membrane in form of the frame and plate modules immersed in the aerobic bioreactor of the FO-MBR process, was examined. Furthermore, 2 g/l powder activated carbon adsorbent was used to improve the performance of this process and the reduction of membrane fouling, which improved the performance of the landfill leachate wastewater treatment system by increasing the COD removal rate from 74% to 92% as well as the changes in MLSS concentration during the 4-day FO-MBR process increased by 24% compared to the absence of adsorbent.

Attentions to use of ultrasound for cleaning of polymeric membranes are less than one decade. In this experiment, the cleaning efficiencies of various frequencies of ultrasound in different membrane modules and the barrier effect of structural design and membrane module during cleaning process using ultrasound were evaluated. Three membranes, hollow fiber without module, flat sheet membrane including stainless steel and acrylic module and spiral wound with polyethylene modules applied during forward flushing cleaning process by ultra pure distilled water for 30 minutes after fouling by skimmed milk 1% using ultrasonic irradiation of 28, 45 and 100 kHz frequencies in constant intensity of 300W. The permeate flux and hydrodynamic resistance of new, fouled and cleaned membranes during sonication using various frequencies of ultrasound were determined separately. In this manner the cleaning efficiency of each treated membranes were calculated. The data statistically analyzed using ANOVA table. The results showed that the most cleaning effects obtained in all tested membranes by various frequencies of ultrasound at first 5 minutes of cleaning process. The highest amounts of cleaning effect achieved in hollow fiber membrane using all tested frequencies especially in 28 kHz. The maximum cleaning efficiency achieved more than 95 percent for the first 5 minutes and may be due to lack of barrier such as holder or membrane support in the design of this membrane module. However, we observed the cleaning efficiency of 92 percent after 30 minutes in flat sheet membrane module using ultrasound in28 kHz and the amounts of cleaning efficiencies in same conditions were lower than hollow fiber module. The other tested frequencies were not significant cleaning effects and stainless steel and acrylic holders in design of membrane module prevented to reach of sonic power to surfaces and pores of flat sheet membrane. The minimum ultrasound cleaning efficiency achieved in spiral wound membrane modules only 21 percent after 30 minutes ultrasonication using 28 kHz during forward flushing and it seems that only outside of membrane surfaces are affected. This is may be due to special design of membrane module and barrier effects of configuration and membrane holders.

A 2D mathematical model with two approaches for unsteady CO2 permeation through a flat sheet polymeric gas separation membrane was developed. This model considered axial and radial transport in the membrane.Modeling results for CO2 transport, were compared with experimental data measured for the acrylonitrile butadiene styrene/poly vinyl acetate blend membrane. Gas permeability in various polymeric compositions and the effect of pressure on permeability are the main objectives of the comparisons. The model predictions were in excellent agreement with the experimental data.