Solubility estimations for Disperse Blue 14 in supercritical carbon dioxide M.D. Gordillo * , C. Pereyra, E.J. Martı´nez de la Ossa Department of Chemical Engineering, Food Technology and Environmental Technologies, Faculty of Sciences, University of Ca ´diz, 11510 Puerto Real (Ca ´diz), Spain Received 22 July 2004; received in revised form 14 November 2004; accepted 5 December 2004 Available online 19 February 2005 Abstract Supercritical carbon dioxide is an alternative solvent that is considered for dry dyeing processes in the textile industry. The application of this process requires a study to determine the dye solubility in supercritical carbon dioxide. The solubility in supercritical carbon dioxide of a disperse dye at temperatures of 40, 60 and 80  C and pressures from 100 to 350 bar was evaluated in a previous study. In the work described here, these solubility values have been correlated with fairly good accuracy using a model based on thermodynamic aspects and the use of equations of state. Physical properties and critical parameters of the solid have been estimated using different group contribution methods. The thermodynamic model has been developed by means of a program based on fitting the solid sublimation pressure and binary interaction parameter. The results obtained in the solubility correlation show that the choice of group contribution method is more important than the choice of equation of state. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Equation of state; Group contribution method; Critical properties; Fluidesolid equilibrium; Estimation; Disperse dye 1. Introduction The textile industry uses large amounts of water in its dyeing processes. Due to environmental problems such as the emission of organic materials in wastewater, a new dyeing process has been developed in which supercritical carbon dioxide is used as the solvent for dyes. The advantages of supercritical carbon dioxide are that it can be recycled, is low in cost, non-toxic and non- flammable. Moreover, the dyes can be more efficiently utilized because all the dyes dissolved in the supercritical fluid can be recovered when the fluid is expanded. Last year, many authors have investigated supercritical dyeing technology [1e13]. However, a crucial property for the design of several processes with supercritical solvents is the solubility of the substances treated in a supercritical fluid. The solubilities of many dyes have been measured by different investigators [14e28]. In addition, the design and de- velopment of processes with supercritical fluids depend on the ease of modelling and predicting the phase equilibrium as exactly as possible e in this case, the supercritical fluidesolid equilibrium. Fluidesolid thermo- dynamic modelling presents difficult mathematical chal- lenges, even when it is possible to obtain the experimental solubility data of the solute in the supercritical fluid. In most cases, it is necessary to introduce additional adjustment parameters. Furthermore, given the lack of thermodynamic data for the substances involved, it would also be necessary to estimate parameters that cannot be determined empirically. Very few studies have been published on the correlation of equilibrium data for this type of system. * Corresponding author. Tel.: C34 956 016 458; fax: C34 956 016 411. E-mail address: dolores.gordillo@uca.es (M.D. Gordillo). 0143-7208/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2004.12.013 Dyes and Pigments 67 (2005) 167e173 www.elsevier.com/locate/dyepig