CRYSTAL-GROWTH KINETICS OF PENTAERYTHRITOL

The growth kinetics of pentaerythritol (PE) in aqueous solutions were determined from batch and continuous experiments; growth rate values about two orders of magnitude lower were obtained operating in batch mode. This behaviour, which agrees with previous results reported by various authors, validates the hypothesis that some impurity adsorbed on the crystal surface is capable of strongly depressing the growth kinetics. This influence is also confirmed by the remarkable decrease in PE growth rate observed on adding selected impurities (1% formaldehyde or 2% formic acid) to the solution. The inhibiting effect of the impurity on the growth process is substantially reduced when a threshold supersaturation value equal to about 0.06 g(PE) per g(solution) is exceeded. The growth process can also be improved by increasing the temperature, which reduces the adsorption rate of the impurity, or by washing the crystal seeds, i.e. partially removing the impurity adsorbed over the crystal surface.