Knowledge-based design of phyto-extraction

Equipment for solids extraction or leaching is usually designed based on some few beaker experiments and a lot of experience. In order to develop a systematic design procedure a standardized lab-scale mass-transfer cell has been realized, which allows quantification of mass-transfer kinetics for percolation and immersion, which are the mostly applied process options. Here this setup is applied to plant-based material, to recover specific plant components like pharmaceutically active components or spices. The evaluation is realized applying model-based experimental analysis (MEXA). In developing the basis for MEXA, it is originally assumed that the parameters of the model are actually the desired quantities. Thus, the accuracy of determining these parameters is taken as measure in judging the uncertainty obtained with the experiments.

This view unfortunately neglects that the model parameters are rarely the final result to be obtained. Instead, the models with their parameters are means to optimize performance of processes with respect to the final product costs. This of course has to be accounted for in optimal experimental design. It can be shown that accounting for the accuracy of the cost optimum leads to different optimal experimental conditions as compared to those, which optimize model-parameter accuracy. One of the major challenges of this approach is to differentiate clearly between the parameters of the lab-scale experiments performed in the standardized setup and those parameters found in the process of cost optimization of the technical process. For example the ratio between extractant and plant material is relevant in the lab-scale experiments but of course also in the optimized technical process. The optimum for the industrial-scale process generally will differ from that obtained for the optimal lab-scale experiments. Finally, also selectivity has been included into these considerations, allowing to account for the details of the extraction process, i.e. differentiating between equilibrium-based and kinetic selectivity.

Publications:

• J.B. Bol, A. Pfennig: Wissensbasierte Designmethode zur Auslegung von maßgeschneiderten Feststoffextraktoren auf der Basis von Laborversuchen. AiF final report on project 16146N, 2012. 
• J.B. Bol, A. Pfennig: Optimizing plant-material extraction processes. ISEC 2014, International Solvent Extraction Conference, Würzburg, 2014. 
• J.B. Bol: Optimale Versuchsplanung unter Berücksichtigung der Prozesskosten am Beispiel der Phytoextraktion. Ph.D. thesis, TU Graz, Austria.