Membranes downstream processing methods

The growing interest in various )5-lactam antibiotics, especially the cephalosporins, over the last decade has called upon improvement in their production methods via modification of either the basic process and the microbial strain or the downstream processing techniques. The product recovery may involve various methods of extraction and purification which play an important role in the overall process economics [12]. During recent years much attention has been given to the development of liquid membrane (LM) processes which usually exhibit high extraction rates and selectivity as compared to those achievable in conventional solvent extraction and adsorption processes. 

The separation schemes vary with the state of the products. For example, intracellular products must first be released by disrupting the cells, while those products bound to cell membranes must be solubilized. As the concentrations of products secreted into the fermentation media are generally very low, the recovery and concentration of such products from dilute media represent the most important steps in downstream processing. In this chapter, several cell-liquid separation methods and cell disruption techniques are discussed. 

For industrial biotransformations, catalyst recovery and reuse are major issues. This may be desirable either for reasons of downstream processing or for repeated use in order to reduce the specific catalyst costs per kg of product produced. A very simple method is the use of membrane filtration. Because of the increasing number of membranes from different materials (polymers, metal or ceramics) this is an attractive alternative. Whereas for whole cells microfiltration or centrifugation can be applied, for the recovery of soluble enzymes ultrafiltration membranes have to be used120-221. Often immobilization on a support is chosen to increase the catalyst s stability as well as to facilitate its recovery. The main advantages of immobilization are ... 

Unsurprisingly, properly accounting for the driving forces in OSN involves calculating the activity coefficients of the organic species present in the fluid streams upstream and downstream of the membrane. This is analogous to the thermodynamic calculations one must undertake for other separation processes, such as distillation, and techniques and methods (such as UNIFAC) can be employed. 

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