Membranes are a promising technology for bulk CO2 separation from natural gas mixtures due to their numerous advantages. Despite the numerous fundamental studies on creating better quality membrane efficiency, scaling up the research work for field testing requires huge efforts. The challenge is to ensure the stability of the membrane throughout the operation while maintaining its high performance. This review addresses the key challenges in the application of polymeric technology for CO2 separation, focusing on plasticization and aging. A brief introduction to the properties and limitations of the current commercial polymeric membrane is first deliberated. The effect of each plasticizer component in natural gas towards membrane performance and the relationship between operating conditions and the membrane efficiency are discussed in this review. The recent technological advancements and techniques to overcome the plasticization and aging issues covering polymer modification, high free-volume polymers, polymer blending and facilitated transport membranes (FTMs) have been highlighted. We also give our perspectives on a few main features of research related to polymeric membranes and the way forwards. Upcoming research must emphasize mixed gas with CO2 including minor condensable contaminants as per real natural gas, to determine the competitive sorption effect on CO2 permeability and membrane selectivity. The effects of pore blocking, plasticization and aging should be given particular attention to cater for large-scale applications.

PETRONAS embarks on breakthrough technology for natural gas sweetening in high CO2 gas fields. Membrane technology is found to be one with high potential and a promising technology for bulk CO2 removal from natural gas. It can be suited to wide operating conditions to process varied natural gas composition, pressure and temperature. This paper focuses on the extensive development of PETRONAS in-house membrane and its evaluation for gas separation performance for high CO2 feed gas at different operating conditions; eg. feed gas flowrate, temperature, pressure, CO2 concentration in mixed gas system, and permeate pressure. For all the cases in this study, samples were tested at optimum gas flowrate of 1000 standard cm3/min (sccm) to obtain representative membrane performance. Feed gas pressure and CO2 concentration have shown significantly affect membrane permeation properties; whereas feed gas temperature and permeate pressure showed negligible impact. There is a trade-off between permeance and selectivity when CO2 concentration is increased from 40% to 70%; where the CO2 permeance increased by 12% which consequently reduces CO2/CH4 selectivity by 15%. In summary, the membrane developed in this study demonstrates high pressure durability up to 50 bar and temperature up to 55oC with satisfactory gas separation performance in the presence of high CO2 concentration in feed gas (up to 70% CO2). This work is breakthrough in establishing the operational boundary of PETRONAS Membrane for technology development and deployment in monetizing high CO2 gas field.

Development of new technology in the area of separation process is essential in order to deal with with product quality, environmental issues, energy efficiency, cost reduction and increasing safety. In membrane separation processes, membrane contactor has attained considerable attention due to the wide range of its applications. Since most of chemical separation processes are related to the contact of two different phases (liquid-liquid or gas/vapor-liquid), the operations such as gas absorption and stripping, liquid-liquid extraction, distillation, heterogeneous reactions, emulsification, demulsification, humidification and dehumidification can be conducted through a membrane contactor system (Drioli et al. 2005). Development of membrane contactor for acid gas removal is an emerging technology recently especially to overcme the disadvantages of commercial packed towers and bubble columns. Physical solvents such as DEPG (Selexol™ or Coastal AGR®), NMP or N-Methyl-2-Pyrrolidone (Purisol®), Methanol (Rectisol®), and Propylene Carbonate (Fluor Solvent™) are well known as commercial gas treating solvents, especially for acid gas removal. Physical solvents tend to be favored over chemical solvents when the concentration of acid gases or other impurities is very high (Burr and Lyddon 2008). Among the physical solvents, Selexol shows the highest H2S solubility. However, due to Selexol solvent is less hazard as compared to NMP, this compatibility study was conducted using Selexol as the solvent for H2S removal with various types of polymeric membrane material. The main objective of the study was to test the stability of potential porous membrane material with the selected physical absorbent for H2S removal. From the physical characterization consist of physical abservation, Fe-SEM, FTIR and contact angle that have been conducted on the membranes that have been immersed in the physical absorbent for 1 month, it is found that 3 membrane materials are most stable and compatible with the selected physical absorbent. The 3 shortlisted membrane material are PTFE, PP and PEEK membrane that could be further developed for H2S removal using membrane contactor technology.

Membranes with a stable performance during the natural gas sweetening process application are highly demanded. This subject has been immensely explored due to several challenges faced by conventionally used polymeric membranes, especially the high tendency of plasticization and physical aging. In this study, polysulfone (PSf) hollow-fiber membrane was formulated and tested for its application in natural gas sweetening based on several compositions of CO2/CH4 mixed gas. The effects of operating conditions such as pressure, temperature and CO2 feed composition on separation performance were analyzed. The findings showed that the formulated membrane exhibited decreasing CO2 permeation trend with the increase in pressure. Conversely, the increase in operating temperature boosted the CO2 permeation. High productivity can be attained at higher operating temperatures with a reduction in product purity. Interestingly, since PSf has higher plasticization pressure, it was not affected by the change in CO2 percentage up to 70% CO2. The experimental study showed that the membrane material formulated in this study can be potentially evaluated at the field stage. Longer testing duration is needed with the real feed gas, appropriate pre-treatment based on the material limitations, and optimum operating conditions at the site to further confirm the membrane’s long-term lifetime, resistance, and stability.