Optimization and correlation of piper betle leaves extraction using supercritical carbon dioxide

Abstract

Piper betle leaves, which contains a high level of eugenol, is abundantly grown and distributed in many Asian countries. Eugenol is an important principal phytochemical found in betel leaves. Interestingly, structure of eugenol consists of polar bond and non-polar bond which indicates that eugenol is a slightly polar compound. However, because the extraction solvent, carbon dioxide (CO2), is non-polar in nature, making it superior in extracting non-polar compounds, a modification to the supercritical fluid extraction (SFE) processing parameter is required to make it universal to the extraction of mild to highly polar compounds. An experimental investigation was conducted to explore the oil extracted and concentration of Eugenol by manipulating the supercritical carbon dioxide (SC-CO2) process parameters which were pressure of 10 MPa to 30 MPa, temperature of 40 oC to 70 oC and flow rate of 4 mL/min to 8 mL/min, at constant mean particle size of 302.5 µm with extraction time of 210 minutes. The optimum condition and the most influential SC-CO2 process conditions were investigated using the response surface methodology. Two established solubility models, including the Chrastil and the Del Valle and Aguilera were applied to describe the solubility behaviour. Furthermore, the mathematical model formulation and validation were employed for describing the mass transfer phenomena of Piper betle leaves oil. However, a reliable model that involves quantitative analysis of fluid flow phenomena is needed to explore the relationship between flow rate, temperature and pressure concurrently. Two models, namely Hot ball model and Lee BC model were used to obtaine diffusion coefficient and overall mass transfer coefficient data. Mass transfer correlation of Piper Betle leaves oil was also established to describe the behaviour of mass transfer of solute in SC-CO2 process condition with relation to the fluid flow. The maximum extraction yield (361 mg) and eugenol concentration (102.5 mg/g extract) were obtained at 10.16 MPa, 40.12°C and 8 mL/min, respectively. It was proven that interaction term between flow rate and pressure was the significant factors required to achieve high yield extract, whereas the interaction term between flow rate and temperature gave the significant impact to obtain high eugenol. In solubility study, the Chrastil model offered the best fitting to correlate the solubility data of Piper betle leaves extract with the lowest percentage of average absolute relative deviation (%AARD) of 5.72% at the highest CO2 flow rate. The coefficient values of k at flow rate of 4, 6 and 8 mL/min were 0.17, 0.26 and 0.75, respectively. It is hence believed that the solvation power of SC-CO2 was higher at high flow rate to increase the solubility of Piper betle extract. Furthermore, the diffusivity was obtained in the range of 0.3101 × 10-13 to 1.1240 × 10-13 m2/s. The overall mass transfer coefficient obtained was from 5.3535 × 10-8 to 23.5560 × 10-8 m/min. The mass transfer correlation model based on the dimensionless number of Reynolds, Sherwood and Schmidt was successfully established with the correlation of determination (r2) of 0.9987. The model equation established was Sh =0.0051ReSc1/3. The overall mass transfer coefficient was found to be strongly correlated between the observed and predicted data with r2 of more than 0.9 at the significant level of 0.05. The results of this study revealed that that the flow rate plays an important role along with pressure and temperature in supercritical fluid extraction process.