Membrane technology in gas separation and purification has grown exponentially since they were first introduced about 30 years ago. Compared to other conventional gas separation processes such as cryogenic distillation and absorption, membrane technology provides advantages like the simplicity of operation, ease of scale-up, smaller footprints and, low operating and capital cost. In membrane gas separation, a gas mixture that is fed to the unit gets split into two streams: permeate and retentate which either can be the product depending on the application. Some of the main applications of membrane technology are:
N2/O2 separation in Nitrogen/Oxygen generation
H2 removal from purge gas in Ammonia production
H2/CO2 separation in SMR (Steam Methane Reformers)
H2/H2S separation in Hydrotreatment
H2/light hydrocarbons in Hydrocrackers
Recovery of helium from rejected gas streams in Natural gas processing [1, 2, 3].
Membranes used in gas separation can be divided into two major groups: inorganic (metals, ceramics, …) and organic (polymers). Although inorganic membrane can be more selective than polymers, it is difficult to produce defect-free thin films, which makes them more expensive to make [4]. Some of the polymers that are used in membrane technologies are: polyimide (PI), cellulose acetate (CA), polyetherimide (PEI), and Polyethersulfone (PES) [2].
The separation in polymeric membranes is usually explained by the solution-diffusion model. According to this model, the gas molecules are first adsorbed on the polymer surface, diffuse through the polymer and desorb on the other side. The membrane unit usually works between two pressures: feed pressure and permeate. Permeate pressure is always lower than the feed pressure. [1, 2, 4]. Permeability and selectivity are two major factors that should be considered when choosing a membrane for a specific gas separation/purification purpose.
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References:
- Paola Bernardo, Gabriele Clarizia, 30 Years of Membrane Technology for Gas Separation, Chemical Engineering Transactions, 2013, 32, 1999-2004
- Xiao Yuan Chen, Serge Kaliaguine and Denis Rodrigue, A Comparison between Several Commercial Polymer Hollow Fiber Membranes for Gas Separation, Journal of Membrane and Separation Technology, 2017, 6, 1-15
- Sridhar, Sharifah Bee and Suresh K. Bhargava, Membrane-based Gas Separation: Principle, Applications and Future Potential, 2014, (https://www.researchgate.net/publication/265295121)
- Yousef Alqaheem, Abdulaziz Alomair,Mari Vinoba, and Andrés Pérez, Polymeric Gas-Separation Membranes for Petroleum Refining, International Journal of Polymer Science, 2017, Article ID 4250927