Solvent Crystallization of Palm-Based Dihydroxystearic Acid
Zainal Abidin @ Murad, Sumaiya (2006) Solvent Crystallization of Palm-Based Dihydroxystearic Acid. Masters thesis, Universiti Putra Malaysia.
Palm based 9,lO-threo dihydroxystearic acid (DHSA) was produced from epoxidation of oleic acid with performic acid, followed by hydrolysis of the epoxide. It is widely used as ingredient in cosmetic industries. However, it is a requirement for low purity crude DHSA to undergo a purification stage in order to fulfil the stringent quality requirement in this field. Solvent crystallization has been employed with detailed examination to produce good quality crystallized product. The objective of this research work is to carry out a preliminary and detailed study on the solvent crystallization of palm based DHSA. Preliminary study was done using two different solvents, ethanol and hexane, at several concentratipns and cooling conditions. The chemical and physical product properties of the crystallized product are evaluated using gas chromatography (GC), crystal size distribution (CSD) and scanning electron microscopy (SEM). The preliminary studies suggested that crystallization of DHSA using ethanol has been successfully achieved and natural cooling mode gives better performance compared to rapid cooling mode, almost in all aspects. However, crystallization of DHSA using hexane as solvent was unable to shape DHSA into crystal. It produced bulk solid DHSA with low purity percentage (79%). Based on preliminary studies, an investigation on controlled cooling crystallization using a fabricated crystallizer has been conducted. This study focuses on various operating conditions, namely temperature (24"C, 26"C, 28"C), time (1 - 12 hours), seeding process (2.5, 5, lograms) and cooling modes (natural and controlled crystallization). Effect of these parameters on crystal size distribution (CSD), purity and yield of crystallized product has been examined. Quality and quantity of crystals produced via the controlled cooling crystallizer are greatly influenced by the operating temperature. Higher working temperature produced crystals with higher purity and larger average crystal size. However, the yield is lower. Controlled crystallization process results in a better crystal properties compared to natural cooling crystallization, generally in almost all aspects. Furthermore, the addition of DHSA seed into the solution could reduce the purity of product and at the same time, as it could retard the crystal growth.
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