Alsaffar, Layth; (1995) A process design study of ammonium sulphate fractional protein precipitation. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The development of a process engineering framework for assessing ammonium sulphate fractional protein precipitation has been studied in this thesis. Existing theories of precipitation are reviewed. The use of fractionation diagrams to characterise the performance of a two precipitation process is discussed. A unified isotherm approach for modelling the fractionation is proposed and verified by comparison with experimental data. Comparison with polynomial fits, the usual method for modelling fractional precipitation, shows the isotherm method is superior in terms of its generic nature. Using the isotherm approach the effect of operating pH and of solids carry-over due to inefficient clarification at large-scale operation on the resultant fractionation have been examined. A series of design scenarios are presented for the case of the purification of alcohol dehydrogenase from Sacharomyces cerevisiae which illustrate how the position of precipitation cuts have to be altered in order to accommodate changes in pH and solids loading. The isotherm has been extended to the purification of an intracellular protein product of a recombinant E.coli strain in order to establish the generic nature of the approach. Issues of process scale-up and associated deviations from levels of performance achieved at laboratory scale are noted. The ability to use ammonium sulphate fractionation for crude enzyme purification prior to high resolution separation by hydrophobic interaction chromatography is discussed.

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