A MATHEMATICAL-MODEL FOR LACTOSE DISSOLUTION

Many users of lactose crystals have to dissolve the sugar before they can use it in processing. To date, the design of the vessels used to perform this operation has been carried out either on an ad hoc basis or based on past experience. There is therefore a need to define the system in terms of its rate-limiting steps so that appropriate design decisions can be made. Here the relevant literature on lactose dissolution is reviewed and the first-order reaction kinetics for the mutarotation of alpha-lactose to beta-lactose are combined with the appropriate mass transfer equations to model the dissolution process. The resultant predictions are compared with experimental data. Three main mechanistic regions are identified: the first is when saturated solutions of lactose are required, the second is when lactose concentrations between the alpha-lactose solubility limit and saturated solutions are targeted and the third is when solutions below the alpha-lactose solubility limit are desired. The model, when modified to allow for the variation in alpha-lactose solubility with beta-lactose concentration, has modelled successfully the first two regions, but fitted only poorly the region below the alpha-lactose solubility limit.