Pascale Subra

Supercritical antisolvent micronization of some biopolymers

Abstract We processed various biopolymers by semi-continuous supercritical antisolvent precipitation (SAS) to evaluate the possibility of producing nano and micro-particles of controlled size and distribution. First, some liquid expansion curves were experimentally produced to study the general behavior of the ternary systems antisolvent-solvent-biopolymer. A condition that guarantees a successful SAS micronization is that solute does not modify the expansion curves of the solvent-antisolvent binary system. SAS experiments were performed by varying the process parameters; we mainly studied the influence of pressure, temperature and liquid solution concentrations. SEM images of the processed material were used to study morphologies, mean particle size and particle size distribution. We successfully processed by SAS dextran, poly- l -lactide (PLLA) and poly-(hydroxypropylmethacrylamide) (HPMA), using dimethylsulfoxide (DMSO) and dichloromethane (DCM) as liquid solvents.

Contribution to the determination of the solubility of β-carotene in supercritical carbon dioxide and nitrous oxide: experimental data and modeling

Abstract The solubilities of β-carotene in supercritical carbon dioxide and nitrous oxide have been measured using a dynamic multi-pass flow system. Quantitation was performed by direct injection of an aliquot of the saturated supercritical solution into a high performance liquid chromatograph. Solubility was studied at temperatures of 310, 320, 330 and 340 K and pressures from 9 to 28 MPa. The mole fractions of β-carotene were in the ranges 10−8–10−6 mol mol−1 in carbon dioxide and 10−7–10−5 mol mol−1 in nitrous oxide. The results were compared with data from the literature. The discrepancies observed within the various studies are discussed regarding the method used for dissolution and for quantitation. The solubility data were correlated by a density-based equation as proposed by Chrastil, and modeled by using the Peng-Robinson equation of state. Because of the inaccuracy of the model when the critical parameters of the solute were estimated from group contributions, the data were regressed considering the interaction coefficient kij, the critical pressure and the sublimation pressure of β-carotene as adjustable parameters.

Extraction of β-carotene with supercritical fluids: Experiments and modelling

Abstract This work investigates extraction of β-carotene by supercritical carbon dioxide and nitrous oxide from impregnated beds and from freeze-dried carrots. Extraction rate was measured as a function of temperature, flow rate and particle size. Based on results from spiked beds, mathematical models were proposed to analyze the dynamic behavior of extraction from carrots. The validity of a diffusion model or a mass balance model was discussed through results on particle size. Although the diffusion model and the experimental results were in good agreement, provided that two stages of diffusion were considered for larger particle size, we further analyzed all data regarding a differential mass balance model. This model, accounting for external mass transfer, diffusion within the matrix and dissolution at the solid/fluid interface, described the time-dependent process satisfactorily despite assumptions on the matrix description. Results showed that both external mass transfer and desorption of solute from the matrix were the limiting steps.

Breakthrough curves and adsorption isotherms of terpene mixtures in supercritical carbon dioxide

The adsorption of a mixture of thirteen terpenes from supercritical carbon dioxide on silanized silica was studied with the aim of simulating essential-oil fractionation. Adsorption isotherms were obtained at temperatures of 310 and 320 K for isochoric conditions of a carbon dioxide density of 750 kg m−3. The equilibrium loadings, measured at individual solute concentration from 0.9 to 8 mg of solute per g of solvent were of the same order of magnitude for hydrocarbon and oxygenated terpenes. Temperature had only a minor influence. The adsorbed quantities were low, in the range of 10 mg of solute per g of sorbent. An explanation is offered by considering the adsorption of the supercritical solvent. Measurements of carbon dioxide adsorptive capacities for several mixtures showed that the solvent did indeed compete for adsorption. Due to their complex behaviour, the capacity data of the solutes were regressed according to an empirical Langmuir-like equation instead of a Langmuir model. The influence of temperature and density on the equilibrium loadings and on the breakthrough volumes are also discussed.

Anti-solvent and co-solvent effect of CO2 on the solubility of griseofulvin in acetone and ethanol solutions

Abstract A synthetic method was used for measuring the solubility of griseofulvin in acetone–CO 2 and ethanol–CO 2 mixtures. In this method, CO 2 is added gradually to a liquid solution previously introduced in a sapphire cell of variable volume. Resulting mixtures may have compositions richer in organic solvents than in CO 2 , close to compositions found in the batch anti-solvent process. Measurements with the griseofulvin–CO 2 –acetone system were made at 312.15 K at 60 and 100 bar, and at 326.15 K and 100 bar. Concerning the griseofulvin–CO 2 –ethanol system, investigations were carried out at 100 bar at temperatures of 312.15 and 326.15 K. The solubility of griseofulvin in acetone decreases at all investigated conditions when the CO 2 is added. In this case, CO 2 is acting as an anti-solvent. In contrast to this, griseofulvin solubility in ethanol–CO 2 mixtures is higher than the solubility in either pure solvents within a certain range of CO 2 molar fractions. In this case, CO 2 is acting as a co-solvent and promotes the solubility of griseofulvin.

Retention of some components in supercritical fluid chromatography and application to bergamot peel oil fractionation

Supercritical fluid chromatography was used in order to investigate the possibility of detoxification of an essential oil. Bergamot peel oil contains phototoxic compounds, the psoralens, which must be removed prior to its use. The retention of the major constituents of the oil was determined under various levels of pressure (from 75 to 160 bar) and temperature (37 to 57°C) of pure carbon dioxide. The highest selectivity against psoralens, and specifically, against bergapten was obtained at low pressure and high temperature. Bergapten elimination was then successfully achieved by adsorption from a supercritical feed.