Modeling of supercritical fluid extraction by enhancement factor of cosolvent mixtures

ABSTRACT

In this study, Sovová mass transfer-based mathematical model for supercritical fluid extraction was modified by incorporating a cosolvent enhancement factor. Modeling of supercritical carbon dioxide with different cosolvent mixtures was successfully performed in the extraction of model plants (Phyllanthus niruri and Polygonum minus) with an average absolute relative deviation (AARD) of less than 7.90%. The existence of non-typical extraction curves in SCO₂ with alcohol–water cosolvent was also well fitted and predicted by the modified model. In the extraction of both plants, internal mass transfer was found to be the rate-limiting factor in the first phase of extraction, namely pre-extraction.

Abbreviations: A: surface area; ɛ: porosity; d_p: particle size or size distribution; D: vessel diameter; E_C: enhancement factor; E_C,V: enhancement factor in vapor phase; E_C,L: enhancement factor in liquid phase; f: total solvent flow rate; H: height; k_Xa: mass transfer coefficient in solid phase; k_Ya: mass transfer coefficient in fluid phase; m_t: mass of extract; M_CER: global extraction yield at constant extraction rate; N: mass of the inert solid; $n_i^0$: moles of solvent without cosolvent; $n_i^{cos}$: moles of solvent with cosolvent; $n_t^0$: total solvent moles without cosolvent; $n_t^{cos}$: total solvent moles with cosolvent; P: pressure; Q_f: solvent mass flow rate; S_ij: selectivity; t: extraction time; T: temperature; t_CER: the end of the first extraction period; t_FER: the end of the second extraction period; U: solvent superficial velocity; W: model parameter related to the diffusion in solid phase; x_i, x_j: solvent mole fraction in liquid phase; X_k: mass of hardly accessible solute; X_o: initial mass of extractable material; X_p: ratio of extractable material at particle surface in solid phase; y_i, y_j: solvent mole fraction in vapor phase; $y_i^0$: mole fraction of pure governing solvent; $y_i^{cos}$: mole fraction of the solvent in the cosolvent mixtures; Y*: solute solubility in the solvent; Y_CER: solubility at constant extraction rate; Z: model parameter related to convection in the fluid phase; z_w: parameter of the second extraction period; ρ_f: solvent density; ρ_s: sample density; μ: viscosity.

KEYWORDS:

• Supercritical fluid extraction
• cosolvent mixtures
• mass transfer modeling
• plant matrices
• rate-limiting factor

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

The research was funded by the Malaysian Ministry of Science, Technology and Innovation (MOSTI) under the Intensified Research in Priority Area (IRPA), grant no. [09-02-02-0091-EA234], and by the University of Malaya, under Vote F [0168/2003A].