Formation of Liquid Inclusions in Adipic Acid Crystals during Recrystallization from Aqueous Solutions

Liquid inclusions consist of pockets of saturated solution entrapped in host crystals during crystallization from solution. Inclusions are contaminants that exert deleterious effects on the properties of the host crystals. When adipic acid was crystallized from aqueous solutions by cooling, the amount of included water was found to be less at a higher initial temperature or after slower cooling. Changes in the degree of agitation in the practical range (150−350 rpm) did not influence the amount of included water. Addition of increasing concentration of seeds or sodium dodecylbenzenesulfonate to the crystallizing solution progressively decreased the amount of included water. Addition of trimethyldodecylammonium chloride to the crystallization solution exerted a complex effect, generally increasing the amount of included water. The inclusion of water in adipic acid crystals can be explained by the relatively high growth rates of the hydrophobic faces (010 and 110), and the relatively low growth rate of the hydrophilic face (001) of individual crystals, to extents that are determined by the experimental conditions.