Beveridge, Kirsten; (2003) Magnetically stabilised fluidised bed reactor for biotransformations. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A novel type of reactor, the magnetically stabilised fluidised bed reactor (MSFBR) aims to overcome the disadvantages of packed beds by increasing the bed voidage and linear velocity through the reactor. The fixation of enzymes to magnetic susceptible supports and placement in a magnetic field will introduce an extra degree of freedom in controlling the bioreactor. Applying a magnetic field increases the escape velocity of the particles allowing substantially higher flowrates through the reactor compared with a conventional fluidised bed. A cost efficient method of producing magnetic particles has been developed to manufacture the particles to test the feasibility of the MSFBR as a biocatalytic reactor under various process conditions. Two enzymes, penicillin acylase and α-chymotrypsin have been successfully immobilised to the magnetic particles. The specific activity and operational stability for both enzymes were comparable to the respective commercially available enzymes. A physical characterisation of both the magnetic particles and the MSFBR was undertaken. The horizontal magnetic field varied by 2% radially across the reactor. Bed expansion curves were completed to examine the effect of flowrate and magnetic field strength on the escape velocity of the particles and voidage of the bed. The ability of the reactor to allow pH control has been tested by a first model system using the penicillin acylase catalysed conversion of Penicillin G to 6 aminopenicillanic acid. The performance of the MSFBR was comparable to that achieved in identical packed bed reactor experiments. The ability to allow processing in the presence of solids has been tested by a second model system using an α-chymotrypsin catalysed reaction for the conversion of N-acetyl tyrosine ethyl ester to N-acetyl tyrosine. This model reaction also presented the problem of pH control. The MSFBR had shorter, 95% conversion times than identical runs in a conventional fluidised bed reactor. The reaction could not be operated in a packed bed reactor due to high pressure drops.

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