Fluidos super criticos

J. Chem. Eng. Data 2002, 47, 149-154

149

Compressed Liquid Densities of Carbon Dioxide + Ethanol Mixtures at Four Compositions via a Vibrating Tube Densimeter up to 363 K and 25 MPa
Abel Zuniga-Moreno and Luis A. Galicia-Luna* ´˜
Instituto Politecnico Nacional, ESIQIE-Graduados- Lab. de Termodinamica, Edif. Z, Secc. 6, 1ER Piso, UPALM, C.P. 07738, Mexico, D.F. (Mexico) ´ ´

PvTproperties in a single phase were determined for carbon dioxide + ethanol mixtures at four compositions from 313 to 363 K and up to 25 MPa with an uncertainty less than ((0.04 kg‚m-3) using a vibrating tube densimeter. The classical calibration method of the vibrating tube densimeter was used with N2 and H2O as the reference fluids.

Introduction PvT properties and vapor-liquid, vapor-liquid-liquid, andliquid-liquid equilibria of pure compounds and mixtures at high pressures are required in the development of supercritical fluid extraction processes. For over 20 years the vibrating tube principle has been widely and successfully applied for the experimental study of PvT properties of various fluids. High precision and applicability of this method for liquid density measurements in a widetemperature/pressure range make it attractive for experimenters and even competitive compared with the classical PvT methods. This research focused on a systematic study to get experimental vapor-liquid equilibria1-4 and PvT data5-7 of CO2 + alcohol mixtures for knowledge, development, and application of techniques directed toward supercritical extraction processes. The main objective is to performsystematic studies of PvT and phase equilibria of CO2 + alcohol binary mixtures containing from ethanol to decanol in order to select the best supercritical operating conditions focused on industrial applications such as extraction of carotenes from the cempasuchil flower of Mexico (tagetes erecta) and from the Chile Poblano of Mexico (Capsicum annum). Galicia-Luna et al.1,2 reported vapor-liquidequilibrium data of the CO2 + ethanol system at temperatures from 313 to 373 K. Zuniga-Moreno and Galicia-Luna5,6 reported ´˜ PvT data for ethanol and CO2 from 313 to 363 K and for pressures up to 25 MPa. In this work are presented liquid densities of binary mixtures at four compositions from 313 to 363 K and at pressures up to 25 MPa. The excess volumes for these mixtures and their dependence oncomposition, temperature, and pressure are reported. The reliability of the measurements for pure compounds has been checked by comparing the data calculated through the BRWS EoS fitted on data reported by Zuniga-Moreno ´˜ and Galicia-Luna5,6 (ethanol,5 1-propanol,6 2-propanol,6 and 1-pentanol5) with the data reported by several authors. The experimental results are in good agreement.
* To whomcorrespondence should be addressed. Mailing address: Prof. Luis A. Galicia-Luna, IPN-ESIQIE- Lab. de Termodinamica, APDO. ´ Postal 75-099, Col. Lindavista, C. P. 07301, Mexico, D. F. (Mexico). ´ ´ E-mail: lagalicia@dsi.com.mx. Telephone: (52) 5729-6000, ext 55133. Fax: (52) 5586-2728.

Figure 1. Feed cell: B and C, caps in titanium; EC, equilibrium cell; FV, feeding valve; GC, gas compressor; MR,magnetic rod; PI, Isco pump; PT, pressure transducer; PTPi, platinum probe i; ST, sapphire tube; TD, temperature digital indicator F250; VSE, variable speed engine; VP, vacuum pump.

Experimental Section Apparatus and Procedure. The apparatus used in this work is that reported by Zuniga-Moreno and Galicia-Luna.6 ´˜ This apparatus is designed to determine simultaneous VLE and PvT properties of pureand binary mixtures containing CO2 and alcohols. The measuring cell consists of a vibrating tube (Hastelloy C-276 U-tube) containing 1 cm3 of sample. We use the same experimental procedure described by Galicia-Luna et al.8 and Zuniga-Moreno and Galicia-Luna.6 ´˜ The pressure measurements are made directly in the equilibrium cell (see Figure 1) by means of a 25 MPa Sedeme pressure transducer. The...