Modellbasierte Untersuchung der Prozessführung von pH-shift Kristallisationen von Itaconsäure

  • Model-based investigation of the process control in pH-shift crystallizations of itaconic acid

Holtz, Arne Matthias; Jupke, Andreas (Thesis advisor); Leonhard, Kai (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023


Carboxylic acids can be produced sustainably by biomass fractionation and subsequent fermentation and then used in a variety of ways. However, existing biotechnological processes are usually operated at elevated pH values in order to increase productivity. At the end of the processes the produced carboxylic acids are present in the fermentation broth in their dissociated form. To obtain the target product, the acid must be protonated before it can be crystallized in this form due to its significantly lower solubility. The pH-shift crystallization allows the protonation and crystallization of the carboxylic acid in one apparatus. The large number of components involved and phenomena taking place complicates the development of pH-shift crystallization processes. There are only few publications on this topic. Important aspects, such as the influence of the electrolytes - accumulating in the solution during the process - on the solubility and dissociation of the target component as well as on the crystallization kinetics, were given little consideration in previous studies. Compared to evaporation and cooling crystallizations, the process control of pH-shift crystallizations is poorly understood in general and in particular with respect to the continuous mode of operation. In this work, the pH-shift crystallization of itaconic acid from aqueous sodium itaconate solutions using hydrochloric acid is studied. Relevant physical properties, such as the pH dependent solubilities and the dissociation equilibria and crystallization kinetics of itaconic acid, are measured experimentally. This data is then integrated into a new computational model for pH-shift crystallizations, which can be used to compare different processes in terms of space-time yield and product crystal size distribution. Finally, a model-based optimization of the process control with respect to the space-time yield is performed. The development of an apparatus for the automated measurement of solubilities allows the determination of itaconic acid solubilities as a function of the relevant process parameters. It also enables the development of a mathematical function to describe this solubility behavior. The shift in dissociation equilibria due to sodium chloride is well represented by the ePC-SAFT model. The crystal growth kinetics indicate an increase in the growth rate of itaconic acid with increasing sodium chloride concentration. After successful validation of the computational model, the model is used to compare single-stage discontinuous as well as multistage continuous processes. The potential benefits of multistage continuous processes for optimized space-time yield are demonstrated.


  • Chair of Fluid Process Engineering [416310]