In this thesis, a kinetic model is described for the conversion of solid Ca-maleate to solid Ca-D-malate. The reaction is catalysed by maleate hydratase in permeabilized Pseudomonas pseudoalcaligenes and is executed in a batch reactor seeded with Ca-D-malate (product) crystals. To this end, separate kinetic models were first developed for each of the constituent steps, i.e. substrate crystal dissolution, bioconversion (with biocatalyst inactivation superimposed), and product crystal growth.According to both the crystal dissolution and the crystal growth model, the rate is controlled by the rate of crystal surface processes, by the rate of solute transport from or to the crystal surface (in case of dissolution or growth, respectively), or by both. Tools are developed to determine the rate-controlling process(es). Dissolution of Ca-maleate crystals and growth of Ca-D-malate crystals were both found to be surface-controlled, obeying linear and exponential rate laws, respectively. The kinetic parameters were determined by fitting data sets of concentration versus time.The biokinetic model featured substrate inhibition, competitive product inhibition, and simultaneous first-order biocatalyst inactivation. The kinetic parameters were determined by fitting the complete kinetic model simultaneously through three data sets of maleate (substrate) concentration versus time. Furthermore, the biokinetic model was used to determine under which conditions the total costs of substrate and biocatalyst were minimal in a continuous system with biocatalyst replenishment and recycling.The individual kinetic models of the constituent processes were then integrated into one overall process model. The model gave a very good quantitative prediction of the solid-to-solid bioconversion in a batch reactor seeded with Ca-D-malate crystals.Finally, two potentially attractive modes for operation of a reactor for solid-to-solid bioconversions, batch operation at very high concentrations of undissolved substrate and continuous operation, are evaluated with respect to their feasibility and overall costs per kg of product.