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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.

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Acid gas removal mainly CO2 and H2S from natural gas is an essential treatment process in the oil and gas industry to increase the heating value of sales gas, prevent corrosion of pipeline and process equipment’s and avoid crystallization during the liquefaction process (Ahmad et al., 2010). Among the popular acid gas removal technologies, the amine-based acid gas absorption process that relies on chemical absorption of acid gas into aqueous amine solution followed by thermal regeneration is one of the technologies that is widely used in the oil and gas industry for acid gas treatment (Brau et al., 2017; Yu et al., 2012; Tay et al., 2017). For amine-based acid gas removal technology, contactors play an important role to ensure efficient and economical separation processes. Membrane contactor technology is one of the promising alternatives to existing conventional contactors that provides a large surface area per unit volume, independent gas and liquid flow rate and ease of scale-up for the acid gas absorption process. In this study, the feasibility of using membrane contactor technology for CO2 and H2S co-removal at high pressure was investigated. The effect of operating parameters such as gas flow rate, liquid flow rate and amine concentration on CO2 and H2S removal performance using activated MDEA as liquid absorbent was conducted using the design of experiment approach. Results from experimental runs have shown that the H2S target outlet which is ≤50 ppm was achieved at all operating conditions but not for CO2 outlet. The target CO2 outlet which is 6.5 mol% was only achieved at experimental runs where the condition of gas flowrate is the lowest, liquid flowrate is the highest and amine concentration is the lowest. The results achieved have proven that there is a high potential to use membrane contactor technology for co-removal of CO2 and H2S from natural gas.

Regeneration of rich amine using membrane contactor (MBC) is studied with observation on factors of operating temperature, flowrate and pressure. The desorption of CO2 and H2S were analyzed, and as a result operating pressure and liquid temperature were identified as the most significant parameters affecting desorption. Higher acid gas flux was observed at higher temperature and higher flowrate. Desorption of CO2 at higher flowrate is limited by the membrane contact area; whilst H2S was more readily desorbed. The higher operating transmembrane pressure of 0.3 barg is preferred as it provided good control during regeneration operation. The optimized parameter for rich amine regeneration was determined through ANOVA analysis using DesignExpert software. The optimum condition was found to be at 90 °C and 0.3 barg; these parameters were then used for the integrated operation of the absorption and regeneration membrane contactor. Continuous integrated testing was carried out and successfully met the specification for both sections. The absorption membrane contactor was able to remove CO2 from 25% down to 6.5% and H2S from 500ppm to below 20ppm. The regeneration section maintained good desorption of H2S where the recycled amine had less than 200ppm and for CO2 desorption 0.2 mol CO2/mol amine loading was removed.