Membrane reactors

The main requirement for a membrane reactor (MR) is a semipermeable membrane which allows the free passage of the product molecules but contains the enzyme molecules. A cheap example of such a membrane is the dialysis membrane used for removing low molecular weight species from protein preparations. The usual choice for a membrane reactor is a hollow-fibre reactor consisting of a preformed module containing hundreds of thin tubular fibres each having a diameter of about 200 mm and a membrane thickness of about 50  mm. Membrane reactors may be used in either batch or continuous mode and allow the easy separation of the enzyme from the product. They are normally used with soluble enzymes, avoiding the costs and problems associated with other methods of immobilisation and some of the diffusion limitations of immobilised enzymes. If the substrate is able to diffuse through the membrane, it may be introduced to either side of the membrane with respect to the enzyme, otherwise it must be within the same compartment as the enzyme, a configuration that imposes a severe restriction on the flow rate through the reactor, if used in continuous mode. Due to the ease with which membrane reactor systems may be established, they are often used for production on a small scale (g to kg), especially where a multi-enzyme pathway or coenzyme regeneration is needed. They allow the easy replacement of the enzyme in processes involving particularly labile enzymes and can also be used for biphasic reactions (see Chapter 7). The major disadvantage of these reactors concerns the cost of the membranes and their need to be replaced at regular intervals.

The kinetics of membrane reactors are similar to those of the batch STR, in batch mode, or the CSTR, in continuous mode (see later). Deviations from these models occur primarily in configurations where the substrate stream is on the side of the membrane opposite to the enzyme and the reaction is severely limited by its diffusion through the membrane and the products' diffusion in the reverse direction. Under these circumstances the reaction may be even more severely affected by product inhibition or the limitations of reversibility than is indicated by these models.

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This page was established in 2004 and last updated by Martin Chaplin
on 6 August, 2014