This work reports
the phase-equilibrium measurements and thermodynamic
modeling for the binary system CO2 + geraniol, and two
ternary systems comprising these components and ethyl acetate or acetic
acid, which are related to geraniol (trans)esterification using supercritical
CO2 as a solvent. Measurements at each composition were
carried out in a high-pressure variable-volume view cell at temperatures
ranging from 303.2 to 343.2 K. The CO2 molar fraction ranged
from 0.4120 to 0.9325 in the CO2 + geraniol system, from
0.5526 to 0.8000 in the CO2 + geraniol + acetic acid system,
and from 0.6011 to 0.8993 in the CO2 + geraniol + ethyl
acetate system. Under these conditions, vapor–liquid (VL),
liquid–liquid (LL), and vapor–liquid–liquid (VLL)
phase transitions were detected. The experimental data were modeled
with the Peng–Robinson cubic equation of state with the van
der Waals (vdW2) quadratic mixing rule.
This work provides a general insight on lipase-catalyzed synthesis of geranyl acetate through esterification of geraniol with acetic acid. Although this reaction is relatively well known, the replacement of organic solvents by supercritical fluids is fairly recent and the role of CO2 is still not completely understood. Therefore, reactions were performed with Lipozyme® RM IM and Novozym® 435 as biocatalysts, and hexane and CO2 as solvents. For similar reaction conditions, geraniol conversions obtained using hexane were much higher, rather than supercritical CO2 (scCO2, 82.9% versus 12.0% after 4 h). The results obtained indicated that CO2 might help the migration of water from the enzyme surface to reaction bulk and then to the vapor phase. Thus, by increasing the vapor phase extension, the geraniol conversion enhanced to 60.5% after 4 h. Such improvement represents one step forward to comprehend the influence of CO2, a safer and greener solvent as compared to hexane.
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