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C3 Integrated product isolation in a multiphase-bed reactor with selective adsorption

(Bohnet/Buchholz/Jördening)

The division C3 of the SFB enzymatically synthesizes isomaltose by transfer of a glycosyl residue mediated by the enzyme dextransucrase, which obtains its glucose by sucrose hydrolyzation. The enzyme dextransucrase is entrapped within insoluable alginate gel beads. The beads have been hydrodynamically adapted to the application in a multiphase fluidized bed reactor. The immediate, selective removal of the product isomaltose from the reaction mixture is crucial as isomaltose itself can serve as an acceptor for further glycosylation reactions. Dealuminized beta-zeolithes can perform the selective adsorption of isomaltose from the reaction system.

Further goal of this project is the advancement and verification of the exisiting reaction and rector model by extended data sets, so the present model can be optimized in more detail. For this the influence of substrate/acceptor ratio should be researched, so the reaction kinetics can systematically be investigated. Using other acceptors like fructose (leucrose formation) both concepts could be validated. Moreover recombinant dextransucrase produced from division A and B can come into operation. The properties changed within these new dextransucrases effect the reaction system, because of differing activities, substrate specifities and immobilization needs. This comes along with new requirements for the selective adsorption of the product, so that the division C2 (Seidel-Morgenstern) connects to our division.

A novel perspective for the optimization of the product recovery exhibits the co-immobilization of dextranase with dextransucrase. Dextranase breaks dextran down to isomaltose. Thus, the molar yield of isomaltose will be increased by conversion of the by-products of dextransucrase into isomaltose by action of dextranase. Further, the reaction boundaries can be extended as very high acceptor concentrations are no more compulsory. At first, dextranase should be adsorbed onto bentonite and lateron be co-immobilized with dextransucrase into alginate or other polymers. A double shell distribution with dextransucrase in the centre and dextranase on the outer surface should be carried out. For a detailed model of this novel system not only the kinetic properties of both enzymes must be taken into account, but also their distribution and concentration.

The zeolith suspension loaded with product should be processed either by a continuous centrifuge or filtration system. Discontinuous filtration has not resulted in satisfactory outcomes yet. As for the desorption and further downstreaming initial experiments have been started.

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