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Abstract: The aim of this work is the investigation of the solubility of three disperse dyes in a mixture of CO2 and ethanol. Experimental solubilities of disperse blue 79, disperse orange 3 and solvent brown 1 in a mixture containing 5.5mol% of ethanol in carbon dioxide have been measured using a dynamic apparatus and compared with those in pure carbon dioxide [A. Ferri, M. Banchero, L. Manna, S. Sicardi, J. Supercrit. Fluids 30 (2004) 41–49]. The effect of the co-solvent is so pronounced that solubilities similar to those measured in pure carbon dioxide have been achieved in the mixture at pressures 100bar lower. The experimental results have been correlated with three different approaches: the Peng–Robinson equation of state [D.Y. Peng, D.B. Robinson, Ind. Eng. Chem. Fundam. 15 (1976) 59–63], the semi-empirical Chrastil equation modified for ternary systems [J.C. Gonzales, M.R. Vieytes, A.M. Botana, J.M. Vieites, L.M. Botana, J. Chromatogr. A 910 (2001) 119–125] and, finally, a correlation recently proposed by our research group for binary systems [A. Ferri, M. Banchero, L. Manna, S. Sicardi, J. Supercrit. Fluids 32 (2004) 27–35] here applied for the first time to ternary systems. The results have pointed out that the third semi-empirical equation gives the best agreement between the experimental and calculated solubilities. [Copyright &y& Elsevier]

Abstract: The equilibrium uptake of three disperse azoic dyes in a commercial PET yarn in presence of supercritical carbon dioxide was measured. The dye uptake was found to be much more sensitive to temperature than to pressure in the tested operative conditions. The equilibrium partition coefficient between the fibre and the supercritical fluid was evaluated from previously measured solubility data [A. Ferri, M. Banchero, L. Manna, S. Sicardi, An experimental technique for measuring high solubilities of dyes in supercritical carbon dioxide, J. Supercrit. Fluids 30 (2004) 41; A. Ferri, M. Banchero, L. Manna, S. Sicardi, A new correlation of solubilities of azoic compounds and anthraquinone derivatives in supercritical carbon dioxide, J. Supercrit. Fluids 32 (2004) 27]. The high values of the partition coefficients demonstrated that the partition of the dye between the fluid and the polymer is an important parameter to evaluate the feasibility of the dyeing process in supercritical carbon dioxide. The partition coefficients were correlated with three equations: an equation proposed by Funazukuri et al. with four fitting parameters [Ind. Eng. Chem. Res. 41 (2002) 2812]; a semi-empirical equation, with five fitting parameters, that was developed assuming a Langmuir-type absorption of the dyes into the yarn; and an empirical equation, with three fitting parameters, developed from simple experimental data observation. The best agreement was obtained with the second, semi-empirical equation. Good results were also obtained with the third, empirical equation and the agreement with experimental data was better than that obtained with the equation proposed by Funazukuri et al. even though it makes use of one fitting parameter less. [Copyright &y& Elsevier]

Abstract: Supercritical dyeing has risen good expectation in the last few years due to the attractive perspective of complete elimination of water from dyeing processes. A lot of research activities have been developed in the last decade both to deepen the knowledge of the interaction mechanisms between CO2, dye and polymers and to solve the technological problems of the process set-up. Among the last ones that of a non-uniform dye distribution when a yarn package is subjected to dye impregnation is one of the most undesired. The same problem is usually faced in the industrial practice of traditional aqueous dyeing and has always been solved empirically. Aim of the present work is to propose a simple model that simulates the dyeing process of a spool of yarn both with the aqueous and supercritical techniques pointing out the main characteristic times and allowing calculation of dye concentration profiles both in the dyeing ‘bath’ and along the yarn spool. The analysis of the influence of characteristic times ratios gives some indications on the best operative conditions that should be attained to guarantee an uniform dye distribution along the package radius both for aqueous and supercritical dyeing; the two processes, in fact, mainly differ for the order of magnitude of the characteristic times. To support the discussion arisen from the different roles of characteristic times on the model, a practical example of supercritical dyeing simulation is also performed for a specific PET package with a disperse dye already used in the literature at well defined working conditions. [Copyright &y& Elsevier]

Solubilities of azoic compounds and anthraquinone derivatives in supercritical carbon dioxide were correlated with a new semiempirical equation and five equations taken from literature. All solutes are dyestuffs or compounds with a molecular structure similar to dyestuffs. The equations were applied to literature solubility data [J. Supercrit. Fluids 21 (2001) 1; J. Supercrit. Fluids 13 (1998) 37; Fluid Phase Equilib. 158–160 (1999) 707; J. Supercrit. Fluids 13 (1998) 43; Talanta 48 (1999) 951; Fluid Phase Equilib. 200 (2002) 31; Fluid Phase Equilib. 194–197 (2002) 895; J. Supercrit. Fluids, in press] and to a new data set of solvent brown 1, experimentally measured by us. Altogether, 16 compounds and over 400 solubility data were considered. In the development of the new correlation, which has three fitting parameters, a dimensionless group was defined: this group, which involves solute molar volume and fusion properties, is a function of solvent density over a significant range of pressures and temperatures. The proposed equation is able to correlate solubility data with good agreement. The mean average absolute percent deviation (AA%D) of the new equation was the lowest among the equations with the same number of fitting parameters. [Copyright &y& Elsevier]

The solubilities of colour index (C.I.) disperse orange 3, red 324, blue 79 and quinizarin were measured at the temperatures of 353.2, 373.2, 393.2 K between 18 and 30 MPa with a ‘flow method’ conceived for determination of high solubilities in order to avoid the flow instability problems connected with dye precipitation. The comparison of results with the literature underlines the advantage of this new technique: higher solubility values are obtained especially at the most severe operating conditions. Experimental data for disperse orange 3 were also compared with similar results obtained by the authors using a ‘batch method’ in a previous work. The comparison of the results shows how the ‘flow method’, even though adapted for high solubility measurements, reveals to be the simplest and more efficient technique to evaluate dye solubility in supercritical fluids. [Copyright &y& Elsevier]