What is a Reverse Osmosis Membrane
There are various different definitions that can be given to the word membrane, one definition is- “ An intervening phase separating two phases and/or acting as an active or passive barrier to the transport of matter between phases” (European `society of Membrane Science and Technology)
Another definition is “ an inter phase separating two homogenous phases and affecting the transport of different chemical components in a very specific way” (Prof Solt, School of Water Sciences, Canfield)
The final definition of a membrane is – a material that only allows some substances to pass through easily than others, this would be substance of a smaller size than the permeability of the membrane. This in turn is the basis of the separation process.
Membrane structure is an important aspect of the membrane; the main objective of the manufacturing of membranes is to create a product that can withstand a good proportion of mechanical strength. It is also important that the membrane can maintain a high throughput of a desired permeate with a high level of selectivity. These last two parameters are mutually counteractive. This is because a high level of selectivity can usually only be obtained by using a membrane with small pores and thus a high level of hydraulic resistance, or low permeability. The permeability of a material increases by increasing the level of pores within the material. This implies that a high level of material porosity is desirable. The overall membrane resistance is directly proportional to its thickness. Finally, selectivity will be compromised by a broad pore size distribution. Its sands to reason that the optimum physical structure for any membrane material is based upon, a thin layer of material and a narrow range of pore size and high porosity.