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In view of developing new drug-delivery systems, microparticles of biocompatible polymer loaded with protein were produced using a supercritical antisolvent technique. As the polymer, poly(lactic acid) (PLA) of about 100 000 Da was used, whereas insulin was chosen as the protein model. To achieve microencapsulation, we started from a homogeneous solution of protein and polymer, to which the supercritical antisolvent is added; mixtures of dichloromethane and dimethyl sulfoxide were used to ensure the solubility of both the polymer and the protein. All experiments were performed in semicontinuous mode. A preliminary study with PLA alone was done in order to select the best operative condition and to control the particle dimension and their diameter distribution range, especially with mixtures of the two solvents. Then, the microspheres of PLA charged with insulin were produced; the average diameters ranged from 0.5 to 2 μm. The composition of these particles was determined analytically, and the protein bioa...

A method for calculating the vapor−liquid equilibria of mixtures between hydrofluorocarbons and lubricant oils is presented. A cubic equation of state is used (Sako, T.; et al. J. Appl. Polym. Sci. 1989, 38, 1839), containing three parameters: the attractive one, a, the volume parameter, b, and the number of external degrees of freedom per molecule, c. To allow calculation of the parameters of the high molecular weight components, whose critical constants and vapor pressure are unknown, a group-contribution approach is developed for a, b, and c. The extension to mixtures is achieved by applying Huron−Vidal mixing rules. A modified Uniquac model is used to evaluate infinite-pressure activity coefficients. With the proposed method, the density of pure heavy components (such as n-hexadecane and pentaerythritol esters) is predicted as a function of temperature. Vapor−liquid equilibria calculations are presented for binary mixtures between several hydrofluorocarbons and pentaerythritol esters or hexadecane; a...

Catalytic hydrogenation in supercritical carbon dioxide has been studied. Experimental results and theoretical calculations are presented, attempting to elucidate the effects of temperature, pressure, and CO{sub 2} concentration on the rate of reaction. An effort has been made to develop a procedure to test catalytic reactions in supercritical fluids in view of future industrial applications. Hydrogenation rates of the two double bonds of an unsaturated ketone on a commercial alumina-supported palladium catalyst were measured in a continuous gradientless internal-recycle reactor at different temperatures, pressures, and CO{sub 2}-to-feed ratios. A Berty-type reactor has been suitably modified for use with supercritical solvents. The accurate control of the organic, carbon dioxide, and hydrogen feed flow rates and of the temperature and pressure inside the reactor provided reproducible values of the product stream compositions, which were measured on-line after separation of the gaseous components. In order to develop a kinetic model, vapor-liquid equilibrium calculations were carried out through a Peng-Robinson equation of state, tuned on binary high-pressure-vapor-liquid equilibrium data. Compositions in the liquid phase inside the reactor were predicted, starting from the on-line analysis after depressurization. A simplified power law kinetic equation is shown to provide a good description of the experimental data.

This paper considers the calculation of homogeneous chemical equilibria in high-pressure gaseous systems. A modified Redlich-Kwong-Soave equation of state, which represents satisfactorily single-phase fugacity coefficients of pure fluids, is extended to mixtures. Mixture parameters are derived from the corresponding pure-component ones by means of the classical mixing rules. Equilibrium compositions are predicted for the ammonia synthesis, the water-gas shift reaction, and the methanol synthesis. In the case of ammonia, extensive experimental data between 10 and 80 MPa are reproduced with good accuracy ; when the model is extrapolated up to 350 MPa, still satisfactory results can be calculated. For the water-gas shift reaction, acceptable results are obtained with limited experimental data sets. As to methanol synthesis, an interesting behavior is evidenced when operating near methanol's critical temperature. The proposed model is shown to be superior to both the Lewis-Randall approach and the original Redlich-Kwong-Soave equation of state and can be used to predict equilibrium conversion of gas-phase reactions under high pressures.

We investigate the use of infinite-dilution activity coefficients to define the interaction parameters of the Redlich-Kwong equation of state (SRK-EOS), with the Huron-Vidal mixing rules. The group-contributions of a UNIFAC-type model were regressed from experimental infinite-dilution activity coefficients of a number of significant systems, including strongly polar components. Such parameters were then used to predict vapor-liquid equilibria (VLE) over the whole composition range, at pressures up to 6 MPa, with generally good results