Development of a membrane immobilised amidase bioreactor system
Thesis (MScEng (Process Engineering))--Stellenbosch University, 2008.
Nitriles are precursors of important amides and organic acids (e.g. acrylamide, nicotinamide, mandelic acid and acrylic acid) which are used, inter alia, as food additives, in plasticisers, detergents, make-up, medicine and as chemical intermediates in the production of various important polymers. Traditionally, chemical processes are used to convert nitriles to amides and organic acids but these processes are non-specific causing various by-products to form. Chemical processes are also environmentally unfriendly and require harsh conditions. Nitrile conversions through an enzymatic route, on the other hand, have the distinct advantages of excellent chemo-, regio- and stereo selectivities, mild process conditions and reduced downstream processing costs. The enzymatic process is mediated via an initial nitrilase catalysed conversion to amide, followed by an amidase catalysed conversion to acid. This research focused on the latter part of the enzymatic transformation of nitriles, which is the amidase catalysed biotransformation of an amide to an acid, specifically with respect to the development of a membrane immobilised amidase continuous process which has the major advantage of enzyme retention coupled with product separation. The research was conducted in three parts namely the characterisation of the free amidase, the development of the experimental bioreactor system and the quantification of the membrane immobilised amidase process.