Membrane technology
Membranes are used to facilitate the transport or rejection of substances between mediums, and the mechanical separation of gas and liquid streams.
In the simplest case, filtration is achieved when the pores of the membrane are smaller than the diameter of the undesired substance, such as a harmful microorganism.
In recent years, different methods have been used to remove environmental pollutants, like adsorption, oxidation, and membrane separation.
[4] Researchers are trying to find a solution to synthesize an eco-friendly membrane which avoids environmental pollution.
The importance of membrane technology is growing in the field of environmental protection (Nano-Mem-Pro IPPC Database).
Even in modern energy recovery techniques, membranes are increasingly used, for example in fuel cells and in osmotic power plants.
The general approach of the solution-diffusion model is to assume that the chemical potential of the feed and permeate fluids are in equilibrium with the adjacent membrane surfaces such that appropriate expressions for the chemical potential in the fluid and membrane phases can be equated at the solution-membrane interface.
This principle is more important for dense membranes without natural pores such as those used for reverse osmosis and in fuel cells.
The effect is referred to as concentration polarization and, occurring during the filtration, leads to a reduced trans-membrane flow (flux).
Concentration polarization is, in principle, reversible by cleaning the membrane which results in the initial flux being almost totally restored.
The tangential flow on the front creates a shear stress that cracks the filter cake and reduces the fouling.
The dead-end membranes are relatively easy to fabricate which reduces the cost of the separation process.
The most commonly used synthetic membrane devices (modules) are flat sheets/plates, spiral wounds, and hollow fibers.
Flat membranes used in filtration and separation processes can be enhanced with surface patterning, where microscopic structures are introduced to improve performance.
These patterns increase surface area, optimize water flow, and reduce fouling, leading to higher permeability and longer membrane lifespan.
Research has shown that such modifications can significantly enhance efficiency in water purification, energy applications, and industrial separations.
[7] Several such pockets are then wound around a tube to create a tangential flow geometry and to reduce membrane fouling.
Membranes have to provide enough mass transfer area to process large amounts of feed stream.
The main modeling equation for the dead-end filtration at constant pressure drop is represented by Darcy's law:[7]
where Vp and Q are the volume of the permeate and its volumetric flow rate respectively (proportional to same characteristics of the feed flow), μ is dynamic viscosity of permeating fluid, A is membrane area, Rm and R are the respective resistances of membrane and growing deposit of the foulants.
This resistance is a membrane intrinsic property and is expected to be fairly constant and independent of the driving force, Δp.
R is related to the type of membrane foulant, its concentration in the filtering solution, and the nature of foulant-membrane interactions.
The solute sieving coefficient and hydraulic permeability allow the quick assessment of the synthetic membrane performance.
Microfiltration and ultrafiltration is widely used in food and beverage processing (beer microfiltration, apple juice ultrafiltration), biotechnological applications and pharmaceutical industry (antibiotic production, protein purification), water purification and wastewater treatment, the microelectronics industry, and others.
It describes the maximum pore size distribution[10] and gives only vague information about the retention capacity of a membrane.
Using track etched mica membranes[11] Beck and Schultz[12] demonstrated that hindered diffusion of molecules in pores can be described by the Rankin[13] equation.
One possibility is the filtration of macromolecules (often dextran, polyethylene glycol or albumin), another is measurement of the cut-off by gel permeation chromatography.
The selectivity is highly dependent on the separation process, the composition of the membrane and its electrochemical properties in addition to the pore size.
When choosing membranes selectivity has priority over a high permeability, as low flows can easily be offset by increasing the filter surface with a modular structure.
[15] Green membrane or Bio-membrane synthesis is the solution to protected environments which have largely comprehensive performance.
