Disadvantages of membrane separation process
Disadvantages of membrane separation process:
1. Membrane processes seldom produce 2 pure products, that is, one of the 2 streams is almost always contaminated with a minor amount of a second component. In some cases, a product can only be concentrated as a retentate because of osmotic pressure problems. In other cases the permeate stream can contain significant amount of materials which one is trying to concentrate in the retentate because the membrane selectivity is not infinite.
2. Membrane processes cannot be easily staged compared to processes such as distillation, and most often membrane processes have only one or sometimes two or three stages. This means that the membrane being used for a given separation must have much higher selectivities than would be necessary for relative volatilities in distillation. Thus the trade-off is often high selectivity/few stages for membrane processes versus low selectivity/many stages for other processes.
3. Membranes can have chemical incompatibilities with process solutions. This is especially the case in typical chemical industry solutions which can contain high concentrations of various organic compounds. Against such solutions, many polymer-based membranes (which comprise the majority of membrane materials used today), can dissolve, or swell, or weaken to the extent that their lifetimes become unacceptably short or their selectivities become unacceptably low.
4. Membrane modules often cannot operate at much above room temperature. This is again related to the fact that most membranes are polymer-based, and that a large fraction of these polymers do not maintain their physical integrity at much above 100 oC. This temperature limitation means that membrane processes in a number of cases cannot be made compatible with chemical processes conditions very easily.
5. Membrane processes often do not scale up very well to accept massive stream sizes. Membrane processes typically consist of a number of membrane modules in parallel, which must be replicated over and over to scale to larger feed rates.
6. Membrane processes can be saddled with major problems of fouling of the membranes while processing some type of feed streams. This fouling, especially if it is difficult to remove, can greatly restrict the permeation rate through the membranes and make them essentially unsuitable for such applications.
7. Membrane processes are limited to their upper solid limit.
8. Membrane processes are expensive compared to other processes.