Measurement and modeling of supercritical fluid extraction curves of Eichhornia crassipes for enhanced stigmasterol production: Mechanistic insights of the process

• SFE curves of bulk extract and stigmasterol, from stalks and leaves of Eichhornia crassipes.
• Experimental conditions tested: 200–300 bar, 0.0–5.0 wt.% ethanol, 5.0–10.0 g min−1.
• Experimental data evidence a selectivity advantage favorable to stigmasterol.
• Modeling disclosed that intraparticle diffusion is the governing resistance to mass transfer.
• Broken plus intact cells model evidence that selectivity to stigmasterol is driven by kinetics.

SFE curves of Eichhornia crassipes are measured for different pressure (200, 250, and 300 bar), ethanol content (0 and 5 wt.%), and CO2 flow rate (5.0, 7.5 and 10.0 g min−1) conditions, and studied in terms of total (ηtotal) and stigmasterol (ηstigm) extraction yields. Ethanol addition was able to increase total yield up to 60% within the 6 h of extraction, reaching up to ηtotal = 1.25 (wt.%). For stigmasterol uptake, two yield plateaus were observed within the six runs: one at ηstigm = 0.17 (wt.%) for 0.0 (wt.%) ethanol and the other at 0.23 (wt.%) for 5.0 (wt.%) ethanol, which suggests that the attainable practical amount of extractives depends on whether cosolvent is used or not. Simplified modeling disclosed that both intraparticle diffusion and film diffusion may be present in the SFE process. On the other hand, the broken plus intact cells (BIC) model of Sovová allowed to fit experimental data with deviations of 4.20% for ηtotal and 4.02% for ηstigm, and to get instructive insights on the process. In fact, BIC model evidenced the existence of a selectivity advantage favorable to stigmasterol that is driven by kinetics rather than by solubility, which is corroborated by the fact that shorter extraction periods were noticed in stigmasterol yield curves than in the global extract yield curves. In the whole, these results and insights support the realization of scale-up assays and provide a contribution for the valorization of water hyacinth through a green process devoted to the production of stigmasterol enriched extracts.

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