de Maere d'Aertrycke, Jean-Baptiste
[UCL]
Calcium L-lactate is an organic salt of economic importance in many fields such as food, cosmetic or pharmaceutical industry. Indeed, this compound, generally recognized as safe, can intervene as a conservative to extend shelf life of freshly cut fruits and vegetables and is used as an excipient or to treat calcium deficiency. Since its discovery in 1780, calcium lactate has been produced by fermentation. Such process allows working in mild conditions and is economically interesting. However, at the end of the fermentation step, calcium lactate is contaminated by other metabolites of the fermentation broth and diluted in water. In this context, crystallization is the method of choice for its purification and recovery under solid form in a single step. Several attempts to crystallize calcium lactate in solution were already tried in the past and evidenced that calcium lactate crystallization kinetics are not optimal since it has a high tendency to form fines that are difficult to process afterwards. In addition, these studies are not directly applicable to the context of a crystallization in the fermentation broth at an industrial scale. In this work, we tried to develop a crystallization process for calcium lactate recovery under a pure solid form from its fermentation broth. As this was conducted in the scope of a future industrial application, the process was designed with the objective of being easy to implement at a reduced cost and with high robustness. Indeed, the fermentation step has a strong variability in term of final lactate concentration and impurity profile, which is inherent to any biological process. The crystallization process developed was hence designed to take this variation in consideration. For that matter, we first tried to raise a better understanding of calcium lactate thermodynamics. This aspect is crucial for the development of a crystallization process or down-line processing of the solid material to prevent uncontrolled crystallization or solid-solid transformation during storage. Up to now, the only solid forms of calcium lactate characterized were a crystalline pentahydrate and an amorphous anhydrate, while other forms were only mentioned. By combining various solid-state analysis techniques, we were able to confirm the existence of these two forms and were the first to characterize three new crystal forms of calcium lactate: an anhydrate, a monohydrate and a dihydrate. The pentahydrated form was found to be the most interesting form both for crystallization in water and for storage. We then studied its solubility and nucleation in water. As calcium lactate solubility has a strong dependence towards temperature, a cooling crystallization process appeared to be promising. Different operation modes were considered and revealed the importance to control seeding and solid/liquid ratio of the suspension to prevent caking of the reactor. A slurry crystallization process was then designed to address these specificities. Several variables were influencing the outcome of this process and interactions between them are suspected. Therefore, the process was optimized through a full factorial design of experiment. At the end of this work, a crystallization process, robust towards the composition of the fermentation broth and economically interesting, was fully developed at laboratory scale.
Bibliographic reference |
de Maere d'Aertrycke, Jean-Baptiste. Development of a crystallization process for calcium lactate recovery from a fermentation broth. Prom. : Leyssens, Tom |
Permanent URL |
http://hdl.handle.net/2078.1/237675 |