Process intensification : a study of calcium carbonate precipitation methods on a spinning disc reactor
Over recent years, the spinning disc reactor (SDR) has been developed as a chemical processing device whereby rapid mass and heat transfer rates can be obtained from the thin film of liquid produced by the act of rotation. In exploiting these characteristics, the SDR is considered a tool of process intensification; compact, flexible, intrinsically safe, continuous and capable of delivering better product quality. An SDR and spinning cone reactor were previously investigated in the precipitation of barium sulphate crystals. It was seen that incredibly rapid mixing coupled with high levels of supersaturation lead to very small crystals with a tighter size distribution being produced. This was seen to produce better quality than conventional process techniques. The present study investigates the potential of the spinning disc as a reactor for the precipitation of calcium carbonate. Three different process routes were identified for the study. The first route is the carbonation of calcium hydroxide solution; the second is the carbonation of calcium hydroxide slurry. The third was the precipitation from mixing sodium carbonate and calcium chloride solutions. For each study, the process parameters and crystal size distributions of the product are evaluated for the spinning disc and complimentary batch reactions. As calcium carbonate is capable of forming three polymorphs, the size, size distribution and shape of the crystals are studied using particle size analysis and electron microscopy. The gas-liquid reaction study showed the SDR to have a higher mass transfer rate than a 1-litre batch with a smaller crystal size distribution. The calcium hydroxide slurry carbonation showed that the SDR could process the slurry faster than the batch with comparable size distribution. Mixing two solutions together yielded different sizes and shapes at different supersaturations but by adding glutamic acid to the process, some degree of shape control was achieved.