Membranes, as perm-selective barriers, is widely used to meet the requirements of industrial separation, water and wastewater treatment, food and beverage processes, pharmaceutical and medical applications, chemical processing, and other separation or purification applications. Due to unique advantages such as product quality, increased separation capacity, lower risk factor, smaller footprint and generally lower chemical usage, the attraction towards membrane technology gains more importance in the field of research and industry.
In the area of synthetic membranes, membranes can be grouped as isotropic, anisotropic, ceramic, metal and liquid membranes. Microporous, nonporous, dense, and electrically charged membranes are categorized under the isotropic membranes. From the engineering perspective, pressure-driven membrane separation technologies are commonly used in the field of microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). These processes are commercially available especially in the water treatment applications.
The selection of membrane is a critical step for user which is highly dependent on the operation. Consequently, main steps can be followed during membrane selection:
Pore size determination
Membrane material statement
The choose of operational parameters (flow rate, pressure, temperature etc.)
Fick's law of diffusion is the governing equation behind the membrane technology. By using the mass transfer principles state by Fick's law, the total permeate flow can be calculated from
The effect of temperature on flux can also be estimated as
JT=J298K × 1.03 (T-298K)
Flux can also be calculated from
The permeability is directly proportional to the flux. Therefore, membranes with high permeability is preferred for high flux in the permeate side.
Recently, we have designed and integrated an experimental set-up for running tests on permeability of various gas agents on permeable materials. The major components of this unit is as follows:
1. Gas preparation unit, for generating various gas mixtures from pressurized gas cylinders by accurate control by mass flow controllers,
2. Vapor generation unit, for controlling (based on Antoine Principle) relative humidity of the outlet stream of gas preparation unit,
3. Gas Conditioning unit, for adjustment of gas flow through the test bed,
4. Test bed, holding the permeable material for testing under controlled temperature
5. Analyzer for determination of both upstream and downstream gas compositions
6. Process Control and Monitoring Unit, for running a flexible operation with user friendly software
Block diagram of the system is given below.
User interface Partial view of P&ID
Asystem: the surface of the membrane system (m2)
k: membrane permeability (L m-2 h bar-1)
J: the flux (L m-2 h-1)
JT: the flux at temperature T (L m-2 h-1)
J_298: the flux at 298K (L m-2 h-1)
PTMP: the transmembrane pressure (bar)
Qp: the permeate flow (L/h)
T: Temperature in Kelvin