Optimization of dihydroxystearic acid synthesis from palm kernel oil based oleic acid using taguchi's method / Noorfazlida Mohamed

This study looks to establish the process factor that will contribute to the enhancement of the reaction rate and yield of dihydroxy stearic acid (DHSA) formation from palm kernel oil based crude oleic acid. Previous studies showed high quality of DHSA can be produced at satisfactory yield in batches. However, details on the influence of reaction parameters and reaction optimization that associate with the degradation of oxirane ring in water are lacking. For this purpose, the crude oleic acid was first epoxidized in a CSTR and optimized using the traditional one factor at a time (OFAT). The optimized conditions include reaction temperature (55-75 °C), agitation speed (200-300 rpm) and sulfuric acid catalyst loading (0.5-2.0g). It was found that the epoxidation yield resulted around 56% at agitation speed of 300 rpm, reaction temperature of 55°C and sulfuric acid catalyst loading of 2.0g. The FTIR analysis confirmed the formation of epoxy functional groups at 1210-1320 cm"1 absorption band region whereas the IV value recorded at 33.44 are comparable to previous epoxidation studies of vegetable oils. Subsequently, hydrolysis reaction on the pre prepared epoxidized oleic acid produces dihydrostearic acid (DHSA). The formation of hydroxyl compound which characterized the DHSA was confirmed by the FTIR spectrum which showed the absorption band of hydroxyl group at the region 3200- 3600cm"1 . In addition, the IV value of the DHSA was found to be at 10.4 which is within the range commonly reported value for DHSA. The application of Taguchi optimization method that supported by ANOVA statistical analysis allow for determination of optimum hydrolysis reaction conditions. It was found that all four reaction factors selected (reaction temperature, oil to solution ratio, catalyst type and agitation speed) were all significant in influencing the course of hydrolysis reaction. The optimum DHSA formation as indicated by the reduction in RCO(%) was achieved at the shortest reaction time of around 5 hours at reaction temperature of 80°C (level 3), oil to solution ratio of 0.75 (level 3), H2S04 catalyst (level 2) and agitation speed of 650 rpm (level 1). This study also highlighted the kinetics of the hydrolysis reaction that is fundamental in designing a commercial scale DHSA production facility. The oxirane ring cleavage (hydrolysis) reaction rate constant K, were examined at reaction temperature of 55°C, 70°C, 80°C and 90°C. The corresponding kinetics analysis showed a linear relationship with reaction time, suggesting a pseudo first order reaction with respect to oxirane concentration. On the other hand, the reaction order examined at three water concentrations of 13.86, 27.76 and 38.88 molL"1 revealed that the oxirane cleavage reaction was second order with respect to water concentration. It was determined that the DHSA synthesized through oxirane ring cleavage in water follows a kinetic model r=k[EP][H20]2 . Finally, the activation energy in the oxirane cleavage reaction was found to be 50.32 kJmol"1 . Overall, this work demonstrated that DHSA produced from palm kernel based oleic acid is commercially appealing not only because of the unique structure and properties that it possess but also because of other inherent advantages as they are derived from renewable and biodegradable source and hence reduces our dependency on petroleum and animal based oils.