CRYSTAL-GROWTH KINETICS OF PENTAERYTHRITOL

The growth kinetics of pentaerythritol (PE) in aqueous solutions were determined from batch and continuous experiments; growth rate values a bout two orders of magnitude lower were obtained operating in batch mo de. This behaviour, which agrees with previous results reported by var ious authors, validates the hypothesis that some impurity adsorbed on the crystal surface is capable of strongly depressing the growth kinet ics. This influence is also confirmed by the remarkable decrease in PE growth rate observed on adding selected impurities (1% formaldehyde o r 2% formic acid) to the solution. The inhibiting effect of the impuri ty on the growth process is substantially reduced when a threshold sup ersaturation value equal to about 0.06 g(PE) per g(solution) is exceed ed. The growth process can also be improved by increasing the temperat ure, 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.