An optimization of microwave hydrodistillation extraction of vetiver oil using a face-centered central composite design

Several methods of vetiver oil extraction are developed. One of these refers to microwave hydrodystillation. The parameters of each of these methods have a major impact on the extract results. Parameter optimisation is usually applied by classical techniques where one variable changes at a time while another variable remains constant but they do not provide adequate information on the interaction between the experimental variables tested. Besides, they require a huge amount of time and materials. The face-centered central composite design (FCCD) technique of the response surface methodology (RSM) is efficient in comparing the individual effects and the interactions between the variables. Therefore FCCCD technique is used in this study to optimize, model and analyze the effects of each variable and their interactions in the course of microwave hydrodistillation applied to extract vetiver oil from dried vetiver (Vetiveria zizanioides). The variables used as parameters refer to the microwave power (300 W, 450 W, 600 W), the feed to solvent (F/S) ratio (0.3 g/mL, 0.4 g/mL, 0.5 g/mL) and the extraction time (60 min, 120 min, 180 min). The experimental design indicates that a maximum yield of 0.828 % is obtained in case of a microwave power of 600 W, a F/S ratio of 0.358 g/mL and extraction time of 180 min. Based on the design R² value of 0.7955, it can be concluded that the model obtained can be used to describe the experimental results and determine the yield of vetiver oil. Furthermore, the results of variance (ANOVA) analysis show that the essential factors which determine the oil yield refer to the microwave power, the F/S ratio and the extraction time.