Dissolution kinetics of Ca-maleate crystals: Evaluation for biotransformation reactor design
✍ Scribed by Marco J. F. Michielsen; Karin A. Reijenga; René H. Wijffels; Hans Tramper; Rik H. Beeftink
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1998
- Tongue
- English
- Weight
- 267 KB
- Volume
- 73
- Category
- Article
- ISSN
- 0268-2575
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✦ Synopsis
In order to develop a bioreactor for solid to solid conversions the biocatalytic conversion of solid Ca-maleate to solid Ca-D-malate is studied. The dissolution of Ca-maleate is the Ðrst step in this process and is described here. A kinetic model, based on the interfacial-barrier theory and the di †usion-layer theory, was developed which describes the increase in Ca-maleate concentration due to dissolution with the help of the time-dependent parameters. According to the model two processes contribute to the dissolution of crys-Ca-maleate É H 2 O tals : (1) the dissolution (and dissociation) reaction of Ca-maleate at the solidÈ liquid interface, characterized by a time-independent reaction rate coefficient, and (2) the transport of Ca2and maleate2~across a boundary liquid Ðlm, characterized by a time-dependent mass-transfer rate coefficient. In addition, the surface of a crystal and the driving force are time-dependent variables. Since crystals are not uniform, a crystal-size distribution was also Ca-maleate É H 2 O used in the model. The e †ects of stirring speed, temperature, pH, and initial Ca2c oncentration on the dissolution rate of crystals were deter-Ca-maleate É H 2 O mined experimentally in order to evaluate the model. The model Ðtted the data well (R2 [ 0É97). In order to determine whether the overall dissolution process was reaction or transport controlled, a method based on overall reaction and transport rates (per unit of driving force) was developed. This showed that the dissolution of Ca-maleate was reaction controlled. Temperature inÑuenced the reaction rate coefficient the most ; it ranged from 5É7 ] 10~6 m s~1 at 10¡C to 67 ] 10~6 m s~1 at 60¡C. The reaction rate coefficient was also inÑuenced by the pH and the initial Ca2concentration, but, as expected, hardly by the stirring speed. Simplifying the model by omitting the time-dependent mass-transfer rate coefficient and by assuming uniform crystals, resulted in only slightly worse Ðts of the data with R2 being at most 0É004 smaller.