Supercritical fluid extraction of lipids from spent coffee grounds was studied in this work Extraction experiments were carried out with supercritical carbon dioxide at different pressure and temperature conditions to study the influence of those process parameters on the extraction rate and oil composition Supercritical carbon dioxide extracted up to 85% of the total amount of oil of spent coffee grounds after 3 h of extraction (corresponding to a maximum yield of 154 g oil /100 g dry spent coffee ) The fatty acid composition of the extracted oil showed the presence of fatty acids of C14, C16, C18, and C20 carbon chains Palmitic (C16:0) and linoleic (C18:2) acids were the major fatty acids and comprise about 35% each of the total fatty acid content of the oil A soxhlet extraction with n -hexane was done for comparison resulting in a maximum yield of oil of 183 g oil /100 g dry spent coffee  Finally, a diffusional model that takes into account the properties of the substrate, the solute partition between the solid and the supercritical phase, and the mass transfer coefficient and axial dispersion in the fluid phase was applied to this system and a good agreement with experimental results was obtained

Supercritical fluid extraction of lipids from spent coffee grounds

The supercritical fluid extraction (SFE) of liquids and solid materials is gaining increasing interest and commercial application in last decades, most particularly under the recent concept of green chemistry and biorefinery. Hence, it is fundamental to provide adequate modeling of the SFE, in order to optimize operating conditions and simulate the global process. This work intends to review the most significant and physically sound models published in the literature for countercurrent liquid-supercritical fluid extraction and SFE of solid matrices, such as the linear driving force, shrinking core, broken and intact cells, and the combination of BIC and shrinking core models. The main assumptions and mass transfer expressions are presented and discussed.

Review of kinetic models for supercritical fluid extraction

Mass transfer models on supercritical carbon dioxide (SC-CO 2 ) extraction of vegetable oils are reviewed, that may facilitate the scale-up of laboratory data for industrial design purposes. Reviewed mechanisms of oil transport within the solid matrix include the desorption from the solid, the formation of a shrinking core of condensed oil in a non-adsorbing porous matrix, and diffusion in a homogenous medium. Analyzed simplificat ions of a general mass transfer model include external control of mass transfer rates, internal control of mass transfer rates, consideration of a linear driving force, and steady state approximations, among others. More complex two-stage models, and critical comparisons of some of the proposed models are also included. Trends for the external mass transfer coefficient and effective diffusivity in the solid matrix from studies on SC-CO 2 extraction of oil from vegetable substrates are thoroughly discussed and contrasted with those obtained using simpler model systems. The possib...

Supercritical CO2 extraction of oilseeds: review of kinetic and equilibrium models.

The effect of the main process variables affecting the supercritical CO 2 extraction of oil from seeds (namely grape seeds) was investigated, both experimentally and through modeling. The dependency of the extraction kinetics on the variables more tested in the literature (pressure, temperature, particle size and solvent flow rate) was confirmed, and original trends were obtained for the less investigated variables, such as the bed porosity ɛ and the extractor diameter to length ratio ( D / L ). The extraction kinetics did not depend on ɛ for 0.23 ≤  ɛ  ≤ 0.41, while a further decrease in ɛ lowered the extraction rate, likely due to the occurrence of channeling. The effect of a variable D / L ratio was studied letting constant the ratio of substrate mass to CO 2 mass flow rate: the lower was D / L , the lower the specific CO 2 consumption. Through modeling, the values of internal and external mass transfer parameters were calculated and critically discussed on the basis of well-known literature correlations.

Supercritical CO2 extraction of grape seed oil: Effect of process parameters on the extraction kinetics

This paper focuses on supercritical CO 2 extraction of grape seed oil which has been analyzed both experimentally and theoretically. Extractions on crushed seeds at pressures varying in the range 280–550 bar and at a fixed temperature of 313 K were performed. From the initial linear portion of the experimental curves oil solubility data in the supercritical solvent have been obtained. By modeling the complete curves, the transport parameters regulating the oil mass transfer inside the seed particles have been calculated: the internal transport coefficient and the effective diffusivity. Three different extraction baskets (0.1, 0.2 and 0.5 l) have been utilized: the differences in the extraction curves have been modeled and explained in terms of the different void volume of the apparatus for the various baskets. A procedure to obtain consistent solubility data when dealing with extractor vessel with non-negligible void volume has been described.

Jordi Puiggené

Papers

Free liquid-to-supercritical fluid mass transfer in packed beds