polymeerikalvot

Polymeerikalvot, or polymer membranes, are thin, semi-permeable barriers made from polymers that separate mixtures by selective transport of components. They are used in gas separation, water purification, and energy conversion to generate streams with different compositions. Separation is driven by pressure, concentration, or temperature differences across the membrane; performance is described by permeability (rate) and selectivity (ratio of permeabilities).

Membranes are broadly classified as nonporous (dense) or porous. Dense membranes rely on solution-diffusion, where solubility and diffusivity govern transport through a polymer film. Porous membranes use defined pore sizes and selective transport in a porous framework. Real-world devices often employ asymmetric or composite structures, including thin selective skins on porous supports or hollow-fiber modules.

Common polymer materials include polyimides, polysulfones, cellulose esters, polyethersulfones, and fluorinated polymers such as Nafion for proton-exchange membranes. Fabrication methods include solution casting, phase inversion to create porous supports, interfacial polymerization for thin-film composites, and electrospinning for nanofiber mats. Mixed-matrix approaches add fillers to improve performance.

Applications span seawater desalination and wastewater treatment (reverse osmosis and nanofiltration), natural gas sweetening and CO2 capture in gas separations, and fuel cells using proton-exchange membranes. Key performance metrics include permeability, selectivity, fouling resistance, chemical and thermal stability, and long-term durability. The Robeson plot illustrates trade-offs between permeability and selectivity.

Ongoing research seeks to surpass current trade-offs with advanced architectures, new polymers with higher free volume, crosslinking strategies, and mixed-matrix membranes. Challenges include chemical aging, chlorine sensitivity in some polyamides, fouling, and scale-up for large modules. Economic and environmental factors drive the adoption of energy-efficient, durable polymer membranes.