Hilmi Mukhtar

Natural Gas Purification Technologies - Major Advances for CO2 Separation and Future Directions

In an effort to satisfy the rising global demand for energy and at the same time to combat the environmental impacts such as global greenhouse gas (GHG) emissions, it’s worth searching for potential energy alternatives. As a base line for most approaches, the issues of producing sufficient quantity of energy with high quality, economical viability and environmental sustainability are the concern of the present. One of such vital components of the worlds supply of energy that has fulfilled the aforementioned requirement is natural gas.

Latest Development on Membrane Fabrication for Natural Gas Purification: A Review

In the last few decades, membrane technology has been a great attention for gas separation technology especially for natural gas sweetening. The intrinsic character of membranes makes them fit for process escalation, and this versatility could be the significant factor to induce membrane technology in most gas separation areas. Membranes were synthesized with various materials which depended on the applications. The fabrication of polymeric membrane was one of the fastest growing fields of membrane technology. However, polymeric membranes could not meet the separation performances required especially in high operating pressure due to deficiencies problem. The chemistry and structure of support materials like inorganic membranes were also one of the focus areas when inorganic membranes showed some positive results towards gas separation. However, the materials are somewhat lacking to meet the separation performance requirement. Mixed matrix membrane (MMM) which is comprising polymeric and inorganic membranes presents an interesting approach for enhancing the separation performance. Nevertheless, MMM is yet to be commercialized as the material combinations are still in the research stage. This paper highlights the potential promising areas of research in gas separation by taking into account the material selections and the addition of a third component for conventional MMM.

Effect of fixed carbon molecular sieve (CMS) loading and various di-ethanolamine (DEA) concentrations on the performance of a mixed matrix membrane for CO2/CH4 separation

Polyethersulfone (PES) as a polymer along with carbon molecular sieves (CMS) as an inorganic filler and di-ethanolamine (DEA) as the third component were used to fabricate amine mixed matrix membranes (A3Ms). The CMS and the developed membranes were characterized by variable pressure field emission scanning electron microscopy (VPFESEM) and thermal gravimetric analysis (TGA). FESEM micrographs showed that with the addition of DEA, uniform distribution of CMS particles in the PES matrix was achieved with good polymer-filler contact. The combined effect of DEA concentration (5–15 wt%), feed pressure (2–10 bar) and CMS loading on the CO2/CH4 transport properties of the PES–CMS–DEA membranes were studied. The results revealed that the PES–CMS–DEA (15 wt% DEA) membrane showed a CO2 permeance of 123.49 GPU at 2 bar, which is more than a threefold increment with respect to the native PES membrane. The corresponding CO2/CH4 ideal selectivity was increased from 5.40 for PES to 51.39 for PES–CMS–DEA (15 wt% DEA). The CO2 permeance of the PES–CMS–DEA (A3Ms) membranes was higher than PES membranes over the operating pressure range.

Mixed Matrix Membranes for Water Purification Applications

Membrane technology has been utilized for water purification application for a long time. Both polymeric and ceramic membranes have been center of interest for their tremendous contribution in this area. Despite their advantages, these synthetic membranes have limitations in terms of performance and durability. To meet the new demands and standards, mixed matrix membranes (MMM) have gained serious importance due to their ability to combine the features of the aforementioned membrane materials, offering better solutions in terms of performance, fouling, permeate quality and longevity. Besides such attractive features, MMMs have not yet reached sufficient maturity to challenge conventional membranes commercially. This review categorizes MMMs on its filler basis into four types; (i) inorganic filler-based MMMs, (ii) organic filler-based MMMs, (iii) biofillers-based MMMd, and (iv) hybrid filler-based MMMs. A discussion is extended to modules and cost of these membranes along with the specific applications of each type of fillers. It also identifies the issues and challenges in the MMM area and highlights the domains that remain to be investigated.

Surface modification in inorganic filler of mixed matrix membrane for enhancing the gas separation performance

Abstract The development of mixed matrix membrane (MMM) in gas separation process has drawn great attention due to its promising properties. MMM consists of a polymer as the matrix phase, whereas the inorganic filler serves as the dispersed phase. However, poor contact between these two phases often results in unselective gas flow and becomes one of the major issues in the MMM development. Currently, various modification techniques of the inorganic filler to improve the compatibility between the polymers and the particles have been reported. Because of this modification, the CO2 separation from natural gas is expected to enhance. This review provides a better understanding about the modification of inorganic filler. Mechanisms and factors affecting the modification of filler such as the effect of solvent polarity, the effect of water content in solvent, and the effect of drying condition are discussed. The details of the current progress in the MMM involving the silane-modified fillers are also summarized.

Prediction of gas transport across amine mixed matrix membranes with ideal morphologies based on the Maxwell model

The incorporation of highly selective molecular sieve such as carbon molecular sieve (CMS) and highly affinitive solvent such as diethanolamine (DEA) into polyethersulfone (PES) have been implemented to synthesize amine mixed matrix membranes (MMMs) with an enhanced gas performance. Synergetic effect of CMS and DEA has caused the improvement of carbon dioxide (CO2) permeability and ideal CO2/CH4 selectivity. While existing theoretical models define the relative permeability well for binary mixed matrix membranes they fail to predict the relative permeability of amine mixed matrix membranes. In fact, the degree of deviation from the simple model predictions provides understanding into the detailed properties of the third component, which has been neglected in previous analyses of these models. Modification of an existing model, namely the Maxwell model, provides an outline to analyze the gas permeation properties of model systems with CMS and DEA in glassy polymer phase. The new model is developed by modifying the basic Maxwell MMMs model. The modification also includes the optimization of λdm, which is defined as the ratio of dispersed phase permeability to matrix permeability, and the determination of permeability of the dispersed phase. Furthermore, this Maxwell model has been extended to model the performance of amine mixed matrix membranes by incorporation of combined volume fraction of filler and amine φ*ad. The proposed approach can predict the permeability of CO2 through amine MMMs and also lowers the AARE % value.

Polyethersulfone (PES) Membranes for CO2/CH4 Separation: Effect of Polymer Blending

Effect of polymer blending on physico-chemical and gas permeation properties of polyethersulfone (PES) membrane was studied. PES was chosen as base polymer and polysulfone (PSF) and polyvinyl acetate (PVAc) were added as glassy and rubbery polymer additives respectively. The morphology, thermal stability and miscibility of PES membranes were characterized by FESEM, TGA and DSC respectively to observe the effect of polymer blending. The prepared membranes were tested for permeation of CO2 and CH4 at a feed pressure of 2 to 10 bar. PES-PSF membrane exhibits the separation properties identical to PES membrane. PES-PVAc blend membrane was found to be immiscible and high permeability was achieved while the selectivity was lost.

An investigation of blended polymeric membranes and their gas separation performance

This research work was carried out to investigate the influence of blending polymer membranes on the performance of CO2/CH4 separation. This was obtained via blending glassy and rubbery polymers at different concentrations, using solution casting and a solvent evaporation method. All fabricated membranes were characterized by field emission scanning electron microscopy (FESEM), thermo gravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). The membranes were observed to have a dense structure as depicted by FESEM, low residue solvent by TGA and a miscible homogeneous blend structure by DSC. The performance of CO2/CH4 separation of the new blend membranes was compared against that of pure PES membrane at pressures varying from 2 to 10 bar. The experimental results showed that the incorporation of rubbery polymer, polyvinyl acetate (PVAc), into pure polyethersulfone (PES), which is a glassy polymer, resulted in membranes having more efficient CO2 separation. However, by increasing the pressure, the permeability dropped because of the glassy behavior of the membranes. The significant improvement of CO2/CH4 selectivity by adding PVAc in comparison to pure PES membrane indicates that the rubbery polymer (PVAc) can be used to enhance CO2 separation from CO2/CH4 mixtures.

Preparation and Characterization of Newly Developed Polysulfone/Polyethersulfone Blend Membrane for CO2 Separation

Polymeric membranes suffer from so called upper bound tradeoff between permeability and selectivity as described by Robeson. Polymer blending is a valuable technique to tune the properties of polymeric membranes by physical mixing of different polymers in a single mixture. In this study, preparation and characterization of newly developed polysulfone/polyethersulfone (PSF/PES) blend flat sheet dense membranes is described for CO2/CH4 separation. Blend membranes with different blending ratios were prepared and the developed membranes were characterized by FESEM, FTIR and TGA to see the effect of blend ratio on morphology, bonding and thermal stability respectively. Permeability of CO2 and CH4 gases in pressure range of 2-10 bar is recorded to find out the ideal selectivity of prepared membranes. The results are discussed and compared with individual polymer membranes.

A Review on Glassy Polymeric Membranes for Gas Separation

Polymeric membranes are widely used for gas separation purposes but their performance is restricted by the upper bound trade-off discovered by Robeson in 1991. The polymeric membrane can be glassy, rubbery or a blend of these two polymers. This review paper discusses the properties of glassy polymer membranes and their performance in gas separation. The area of improvement for glassy membrane with development of mixed matrix membrane is also highlighted.