Crystallization of vitamin C in a continuous DT MSMPR crystallizer - Size independent growth kinetic model approach

The experimental results concerning continuous mass crystallization process in L(+)-ascorbic acid - water system are presented and discussed. Influence of L(+)-ascorbic acid concentration in a feeding solution and mean residence time of suspension in laboratory DT MSMPR crystallizer on product crystal size distribution as well as nucleation and growth kinetics were determined. Kinetic parameter values were evaluated on the basis of size-independent growth (SIG) kinetic model (McCabe's ΔL law). It was observed, that within the examined range of crystallizer productivity (120-1600 kg LAA crystals m ^-3h^-1) crystal product population of mean size _Lm from 0.2 to 0.3 mm and CV from 66.6 to 49 % is withdrawn. Linear growth rate values present decreasing trend (from ca. 7 · 10^-8 to ca. 6 · 10^-8 m s^-1) with the productivity increase (assuming constant mean residence time of suspension τ = 900 s). Occurrence of secondary nucleation within the circulated and mixed suspension, resulting from crystal attrition and breakage, was observed. The parameter values in design equation connecting linear growth rate and suspension density with nucleation rate were determined.