Übertragung der Produktion hydrophober Substanzen mit immobilisierten Biokatalysatoren in den technischen Labormaßstab
- Implementation of the production of hydrophobic compounds by immobilized biocatalysts to technical laboratory-scale
Eberhard, Werner; Büchs, Jochen (Thesis advisor)
Aachen : Publikationsserver der RWTH Aachen University (2012)
Dissertation / PhD Thesis
Aachen, Techn. Hochsch., Diss., 2012
Biocatalysts play an essential role as reaction catalyst for synthesizing organic compounds due to their substrate-, stereo- and regiospecificity. While their natural environment is predominately the aqueous phase, many economically interesting reactants are poorly soluble in water. However, the product yield of such hydrophobic compounds can be increased by immobilizing the biocatalysts in a hydrogel matrix and then suspending them in an organic solvent. Here, the organic solvent acts as a reservoir for the educts and extracts simultaneously the hydrophobic products out of the hydrogel matrix. At the same time, the biocatalysts enclosed in the hydrogel matrix are protected against the organic solvent. As an example, in this work the enzyme carbonyl reductase from Candida parapsilosis (CPCR) was chosen to convert stereospecifically Acetophenone to (S)-1-Phenylethanol while oxidizing the cofactor NADH+H+. The spent cofactor was reduced again in an enzymatic regeneration process by the formate dehydrogenase (FDH) oxidizing simultaneously the co-substrate formic acid to CO2. This choosen biocatalytic process was scaled and implemented into a technical laboratory-scale while considering and viewing more in detail on system-specific and process relevant questions. In the first part of the work, a laboratory stirring reactor was build up and characterized with regard to average and maximum energy dissipation rate, complete suspension of the immobilized enzymes and the mixing time. To determine the complete suspension in an objective way, in this work a novel non-invasive method based on photometry and automatic analysis of images was developed and with it six different reactor configurations were compared. In the second part of the work, a mathematical process model was developed, parameterized and implemented into a software environment to better understand the reaction process. With this process model, a co-substrate feeding strategy was developed. By measuring the CO2 in the gas phase, released from the regeneration reaction, it was concluded on the reaction progress in the aqueous phase and so the aqueous-organic reaction system could be conducted as a CO2-controlled fed-batch process by controlled feeding of formic acid. In the third part of this work, the laboratory reactor was equipped with process analyzing and control technique plus a metering system for the co-substrate was provided. In reaction experiments with the selected two-phase enzymatic reaction system, the feasibility of the developed CO2-controlled fed-batch process was proofed successfully.