2.1 Membrane technology

Membrane processing is a technique which permits concentration and separation of compounds without use of heat. Particles are separated on the basis of their molecular size, shape and charge with use of a driving force [A] (i.e. pressure, concentration, electric potential…).

Membrane processes involve molecular interactions between membrane and fluid. Because of the differences in their degree of affinity, the rejection of the compounds with the membrane is expected to be different for each component. Thus separation becomes possible,[Hwang and Kammemeyer, 1982].
There are many advantages for using membranes in industrial processes:
• no phase changes or chemical additives (except in case of cleaning) ;
• simple in concept and operation;
• modular and easy to scale up ;
• good removal efficiency and good potential for recycling of by-products
All of these advantages translate into cost savings and more environmentally sustainable processes, [B].
2.1.1 Membrane Process

Membranes can be considered as perm-selective barriers between two phases. Transport of components through the membrane is possible when a driving force is applied to the components in the feed. There are several types of driving forces, such as pressure, concentration, temperature and electrical potential difference, but the most widely used driving forces are pressure difference and concentration difference.

Table 1: classification of membrane processes according to their driving forces
In the following table, there is the classification of the membranes according to their driving forces [Mulder, 1996, a]:
Pressure difference Concentration difference Temperature difference Electrical potential difference
- Microfiltration
- Ultrafiltration
- Nanofiltration
- Reverse osmosis
- Piezo-dialysis - Pervaporation
- Gas separation
- Vapor permeation
- Dialysis
- Forward osmosis
- Diffusion dialysis
- Carrier dialysis
- Carrier-mediated
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