Date: 20 Nov 2010

Mass Transfer and Equilibrium Parameters on High-Pressure CO2 Extraction of Plant Essential Oils

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Abstract

Supercritical fluids (SCF) in general and supercritical carbon dioxide (CO2) in particular allow convenient and environmentally friendly extraction processes because of their liquid-like solvent properties and gas-like transport properties, that allow efficient and fast extraction processes, and complete elimination of solvent traces from extracts and treated substrates. High-pressure CO2 is an inexpensive gas that offers safe and selective supercritical fluids SCF extraction (SCFE) processes at near-environmental temperatures that can be use to recover high-value compounds in vegetable substrates.

This chapter reviews mass transfer and of phase equilibrium parameters that are required to design industrial SCFE processes for plant essential oils. Relevant mass transfer parameters include an external mass transfer coefficient and an effective diffusivity (D e), among others. Values of D e range from 102 to 105 times the binary diffusion of plant essential oils in CO2 which suggests pronounced limitations to mass transfer within the solid matrix during SCFE of plant essential oils. A relevant phase equilibrium parameter is the “operational” solubility of plant essential oils in high-pressure CO2, which depends markedly on system temperature and CO2 density, the amount of essential oils in the plant material, the interactions between the many constituents of the essential oils, and the interactions between the essential oil components and the solid matrix, all of which decrease solubility of the essential oil components as compared to their thermodynamic solubility in simple CO2-containing binary and ternary systems.

We would like to dedicate this chapter to the memory of our coauthors and friends Damian Cardarelli (1964–2007) and Miguel Mattea (1955–2007) who died tragically as a result of injuries sustained during a fire accident on December 5, 2007, in the pilot plant of the Facultad de Ingeniería in the Universidad Nacional de Rio Cuarto (Córdoba, Argentina). We met them either briefly (JMdV) or a long time ago (JdlF), but we were touched by their intellectual capacity, perseverance, camaraderie, and warmness.