Immobilisation Techniques and On-Line Production

The characteristics of a support material are of great importance to the measured enzyme activity [79, 101]. Hydrophobic carriers have a low ability to attract water, thus leaving more available for the enzyme, hence Wehtje et al. [102, 103] have shown that celite is a suitable carrier for the PaHnl to yield an immobilized form of the enzyme. In contrast, controlled pore glass (CPG) and Sephadex G25 were found to be less well suited to enzyme support as, using these systems, cyanohydrin synthesis was significantly reduced (over 30%). Sephadex also promoted the spontaneous addition of HCN to benzaldehyde [102]. A series of batch experiments showed that if the solvent (diisopropyl ether) surrounding the immobilised PaHnl contained insufficient water (i. e. less than 2 %), it would be extracted from the enzyme preparation and consequently enzyme activity was lost [102]. These results were the basis for the production 

An excellent production figure for (R)-mandelonitrile (2400 g/1 per day) was achieved by Kragl et al. [105] using a continuously stirred tank reactor in which an ultrafiltration membrane enables continuous homogenous catalysis to occur from an enzyme (PaHnl) which is retained within the reaction vessel. In order to quench the reaction the outlet of this vessel was fed into a vessel containing a mixture of chloroform and hydrochloric acid, which allowed for accurate product analysis. 

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