Study of Membrane Filtration


Study of Membrane Filtration

29 May 2018

Study of “Membrane Filtration”

Membrane Filtration Study  in Vadodara, Gujarat , India. Membrane technology covers all engineering approaches for the transport of substances between two fractions with the help of permeable membranes. In general, mechanical separation processes for separating gaseous or liquid streams use membrane technology.

Membrane separation processes operate without heating and therefore use less energy than conventional thermal separation processes such as distillation, sublimation nor crystallization. The separation process is purely physical and both fractions can be used. Cold separation using membrane technology is widely used in the food technology, biotechnology, and pharmaceutical industries. Furthermore, using membranes enables separations to take place that would be impossible using thermal separation methods. For example, it is impossible to separate the constituents of azeotropic liquids or solutes which from isomorphic crystals by distillation or recrystallization but such separations can be achieved using membrane technology. Depending on the type of membrane, the selective separation of certain individual substances or substance mixtures is possible. Important technical applications include the production of drinking water by reverse osmosis, filtrations in the food industry, the recovery of organic vapors such as petrochemical vapor recovery and the electrolysis for chlorine production.

In wastewater treatment, membrane technology is becoming increasingly important. With the help of ultra microfiltration, it is possible to remove particles, colloids, and macromolecules so that waste-water can be disinfected in this way. This is needed if waste-water is discharged into sensitive waters especially those designated for contact water-sports and recreation.

About half of the market is in medical applications such as use in artificial kidneys to remove toxic substances by hemodialysis and as an artificial lung for the bubble-free supply of oxygen in the blood.

The importance of membrane technology is growing in the field of environmental protection. Even in modern energy recovery techniques membranes are increasingly used, for example in fuel cells and in osmotic power plants.

Mass transfer

Two basic models can be distinguished for mass transfer through the membrane:

  • The Solution-diffusion Model
  • The Hydrodynamic Model.

In real membranes, these two transport mechanisms certainly occur side by side, especially during ultra-filtration.

Solution-diffusion model

In the solution-diffusion model, transport occurs only by diffusion. The component that needs to be transported must first be dissolved in the membrane. 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 phase 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. During the filtration process, a boundary layer forms on the membrane. This concentration gradient is created by molecules which cannot pass through the membrane. The effect is referred as concentration polarization and, occurring during the filtration, leads to a reduced trans-membrane flow. Concentration polarization is the principle, reversible by cleaning the membrane which results in the initial flux being almost totally restored. Using a tangential flow to the membrane can also minimize concentration polarization.

Hydrodynamic model

Transport through pores-in the simplest case – is done convectively. This requires the size of the two separate components. Membranes which function according to this principle are used mainly in micro-and ultrafiltration. They are used to separate macromolecules from solutions, colloids from a dispersion or remove bacteria. During this process the retained particles or molecules from a pulpy.

Mass on the membrane and this blockage of the membrane hampers the filtration. This blockage can be reduced by the use of the cross-flow method. Here, the liquid to be filtered flows along the front of the membrane and is separated by the pressure difference between the front and back of the membrane into retentate on the front and permeate on the back. The tangential flow on the front creates a shear stress that cracks the filter cake and reduces the fouling.

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