Design of supercritical fluid extractor using dry ice as a supercritical solvent

Abstract

The supercritical fluid extraction is the most effective and efficient way to extract valuable constituent in botanicals but the apparatus is usually very complex, complicated and expensive. Carbon dioxide gas needs to be pumped and pressed to reach its supercritical pressure. In this research, the supercritical CO2 condition was achieved by sublimation of a certain amount of dry ice (CO2 solid). The achieved pressure depends on the mass of dry ice. By developing supercritical extraction technology using this dry ice, the apparatus becomes simpler so the price becomes less expensive. Since this method is also able to be operated in a batch operation, the equilibrium data could be obtained. The objective of this research was to design of supercritical fluid extraction apparatus using dry ice as a supercritical solvent. The designed apparatus consisted of 2 main vessels. The first one was a high-pressure extractor for extracting process using supercritical CO2 solvent. The second one was a separator vessel for separating solvent and extract. During the experiment, the gas leakage of the high-pressure apparatus often occurred. To avoid the leakage, the valves and pipes used the standard brands of Swagelok and Sanvik. Similarly, the design of extractor cover used o ring with silicone rubber material. The leakage that occurred during high-pressure operations was very dangerous. To ensure safety, installation of series of apparatus was covered by perforated iron with 2 pieces of windows made of an acrylic material to facilitate in monitoring the process. In this research, the correlation of the dry ice mass and the achieved pressure at a temperature of 40 °C was also studied. The Equation of State (EOS), such as Ideal Gas, van der Waals, Redlich Kwong, Soave-Redlich Kwong, and Peng Robinson were explored to predict the operating condition (supercritical pressure and temperature). By comparing the calculated pressure at various Equation of State and the experimental data, the Peng Robinson was the most appropriate Equation of State.