Solvent crystallization of palm based dihydroxystearic acid (DHSA)-effects on crystal morphology and particle size distribution

摘要

In recent years, oleo based chemicals have made its presence felt among the ever blooming personal care segment, slowly but gradually chipping into the industry once dominated by petrol based chemicals. In particular, the industry has shown considerable interests in hydroxyl fatty acids due to their different behavior compared with ordinary fatty acids. Hydroxyl fatty acids and their derivatives are multipurpose intermediates in the synthesis of fine chemical products and one of the possible derivatives is known as dihydroxystearic acid (DHSA). In Malaysia, palm based DHSA is produced from epoxidation of oleic acid with formic acid, followed by hydrolysis of the epoxide. The crude waxy DHSA is purified by employing solvent crystallization. This study focuses on the use of ethanol and ethanol/water mixture as solvents. The crystallization process was carried out employing two different cooling conditions, i.e. rapid cooling (rapid crystallization) and natural cooling (slow crystallization). The chemical and physical properties of the DHSA crystals produced were evaluated in terms of crystal size distribution (CSD) and scanning electron microscopy (SEM). The results revealed that purification of DHSA through crystallization using ethanol and ethanol/water mixture as solvents was successfully achieved. The crystallization process when carried out with natural cooling mode performed better than that when carried out with rapid cooling mode and the best DHSA to ethanol ratio was of 1.0:1.0 as the combination produced the narrowest CSD curve with largest average crystal particle size.