New Development of Investigations on the Solubilities of Disperse Dyes in Supercritical Carbon Dioxide

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1 New Development of Investigations on the Solubilities of Disperse Dyes in Supercritical Carbon Dioxide HE Liang, ZHANG Shu-fen*, YANG Jin-zong, YU Li-qiu (State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian , P. R. China) Abstract: Supercritical dyeing in carbon dioxide is a new approach in textile industry in order to reduce or eliminate effluent wastewater. To development and design supercritical dyeing processes, dye solubility data are necessary. Disperse dye solubility in supercritical carbon dioxide are reviewed. Key words: Supercritical carbon dioxide; Disperse dyes; Solubilities 1 Introduction Conventional dyeing of synthetic materials uses large amounts of water and also discharges much wastewater. Recently the textile industry has put great efforts to reduce a large amount of wastewater discharged to the environment in its dyeing process. Because of this object, a new dyeing process has been development in which supercritical carbon dioxide is used as a solvent for the dyes [1]. The advantages of supercritical carbon dioxide are that it can be recycled; it is low in cost, essentially nontoxic; and it has easily accessible critical conditions. Moreover, the dyes can be more usefully utilized, because of the dye dissolved in the supercritical fluid can be recovered when the fluid is expanded. To development and design supercritical dyeing processes, dye solubility data are necessary. In recent years, many researchers have reported extensive investigations of the solubility of disperse dyes in supercritical carbon dioxide. Disperse dyes usually used for the dyeing of synthetic materials are divided into two main groups, i.e., anthraquinone dyes and azo-dyes. The investigations on the solubilities of the two kinds of disperse dyes in supercritical carbon dioxide are reviewed in this paper. 2 Experimental Apparatus The investigations on the solubilities of dyes are mostly carried out using a flow type cylindrical equilibrium cell, which can be seen elsewhere [2]. The apparatus consists of three main sections: a compression, an equilibrium and solvent-trapping section. The dye is loaded into the equilibrium cell and mixed with glass beads. The glass beads are employed to obtain a uniform flow-distribution of the supercritical fluid. The pressure in the equilibrium vessel is determined using a pressure gauge, and is regulated by a back-pressure regulator. A metering valve is used to keep the pressure at the flow rate of the fluid at the desired values. The expanded carbon dioxide flows through a trap that is filled with some solvent. The dye solvent content is analyzed by a spectrophotometer. The solubility of the dye in supercritical carbon dioxide is then calculated by using the calculated densities of the supercritical fluid in the pump and the volume of supercritical carbon dioxide used during each collection and displaced at the pump. 3 Investigation Results 3.1 Anthraquinone Dyes The effect of temperature, pressure and density of carbon dioxide on solubility of dyes had been firstly investigated. Many results are obtained. Normally, solubilities of the dye increase with rising temperature at a constant solvent density ( Table 1)and equally with rising 64

2 The Proceedings of the 3rd International Conference on Functional Molecules solvent density at a given temperature (Table 2) [3-6]. Experimental data also showed that the dye solubility increases with density of carbon dioxide are more pronounced at high temperatures [7]. But, the solubilities of some dyes, i.e., C. I. Disperse Blue 77, are higher at lower temperature [8]. For some dyes, intersection points (Figure 2) of the concentration versus pressure solubility isotherms were found and discussed as [4, a density effect 8-11]. In this case, the concentration versus pressure isotherms can be subdivided into two ranges. In principle, a temperature rise at constant pressure favors the solvent power, but at the same time the solvent density decreases. At low pressures, the second effect dominates and the overall solubility of the dyestuff decreases with increasing temperature, whereas at higher pressures the first effect overcompensates the second one resulting a solubility that increases with temperature. interact with each other and in effect behave as a large molecular, resulting in lower solubilities [7]. It was explained in Figure 3 intuitively. The isotherms of AC04 (Figure 1, A1 alkyl=c4, analogically), AC08, AC12, AC16, and AC18 are shifted to higher densities corresponding to a lower solvent power of C 2 Table1 Solubility of A3-A6 (Figure 1) in C 2 at the density of 814.2±11.8kg/m 3 [6] Dye Solubility /10 5 y /K A A A A y = mole fraction of dye NHalkyl NHalkyl A1(alkyl=C 1-5,8,12,16,18 ) A2 A3 C2H5 A4 A5 Figure 1 Molecular structures of A1-A5 Comparatively, it is more interesting that the solubility measurements show how the solubility changes with molecular structure. In order to study the effects, some homologous series of alkylamino substituted anthraquinone dyes had been investigated. It could be found that the shortening of the alkyl chains results in an increase in solubility because mixing of nonpolar molecular with more similar sizes favors the dissolution process [9]. Kautz also obtained the similar results [10]. The polar groups also affect the solubility of dye in nonpolar carbon dioxide [8]. The dyes contain H and groups, which enable hydrogen bonding between different moleculars. Thus moleculars associate and Figure 2 Solubility of C.I. Disperse Blue 134 in SC-C 2 as a function of pressure. [11] Experimental: ( ) K; ( ) K; ( ) K; ( )calculated by modified PRSV ES. Table 2 Relationship of solubility and solvent density [2, 6] under constant temperature Density Solubility / 10 5 y (kg/m 3 ) A2 A3 A4 A5 DR 60 DB a 0.13 b 874± ± c For A3 A6, temperature = 308 K; for C. I. Disperse Red 60 (DR 60) and C. I. Disperse Blue 60(DB 60), temperature = K. a density =828.5, b density =836, c density =

3 Figure 3 Comparison between the concentration-density isotherms of the selected dyes determined in C 2 at 330 K [9] Experimental showed that presence halogens in and Z5 (Figure 4 ) (Table 3). Intersection points in the concentration-pressure isotherms also can be seen [15]. But, some other results are obtained.dye molecular could enhance dye solubility (Table 6) [8, 13]. The only difference between C. I. Disperse Red 1 and C. I. Disperse Red 13, C. I. Disperse Red 30 and C. I. Disperse Brown 22, is the additional Cl group, results an order of increase in solubility. Also it was observed that the for these dyes with AC04 being the best soluble. But, the solubilities of AC01 and C. I. Disperse 11 (DR11) are lower than those of AC04 and AC08 because of their higher polarity. H N N Z1 N N Z2 3.2 Azo-dyes For azo-dyes, some results are similar to those of anthraquinone dyes. The solubility in Z3 Z4 C general increases with the temperature (Table 3) 2 H 5 2 N N N N C 2 H 5 and the density or pressure (Table 4) of carbon dioxide [5, 7, 12, 13, 14]. Also the low molecular H Z5 Z6 weight dyes showed higher solubility of that of the larger ones [5, 15, 16]. This seemed to be the case for Z2 and Z3 (Figure 4) (Table 5), not for Z4 Figure 4 Molecular structures of Z1-Z 6 [12, 14] Table 3 Solubility of some selected azo-dyes at the constant density of C 2 N N N 2 N N N N Parameters Solubility Parameters Solubility Parameters Solubility Density T Z4 Z5 Density T Z6 Density T DR324 DB79 (kg/m 3 ) (K) 10 6 y 10 5 y (kg/m 3 ) (K) 10 6 y (kg/m 3 ) (K) 10 6 y 10 6 y 850.8± ± ± a 49.9 a a density =592, DR324 =C. I. Disperse Red 324, DB79 = C. I. Disperse Blue 79 N N N 2 [13, 14, 17, 18] Table 4 Relationship of solubility and pressure of C 2 at K Solubility (MPa) D25 DR1 DR13 DB79 DR153 DY y 10 7 y 10 7 y 10 6 y 10 6 y 10 6 y D25 = C. I. Disperse range 25, DR1 = C. I. Disperse Red 1, DR13 = C. I. Disperse Red 13, DR153 = C. I. Disperse Red 153, DY119 = C. I. Disperse Yellow

4 The Proceedings of the 3rd International Conference on Functional Molecules solubilities parallel the order of the relative melting points (Table 3); the higher the melting points, the lower the solubility [13]. The solubilities of Z4, Z5and Z6 decrease in the order Z5>Z4>Z6, while their melting points increase in the same Table 5 Solubility of Z2 and Z3 at K [15] solubility (MPa) Z2 (10 3 y) Z3 (10 4 y) order Z5 (418~419 K) <Z4 (488~489 K) <Z6 (529~530 K). In concentration (density) isotherms of C. I. Disperse range 13, there are two intersections points [19]. The results show: (1) at pressures below the first intersection point, the temperature dependence of solubility is mainly determined by the vapor pressure of the dyestuff; (2) at the pressures between both intersection points, effect of a decrease of density and solvent power dominates with rising temperature; (3) at pressures above the second intersection point, the normal temperature dependence of solubility is found. [8, 13] Table 6 Solubility of some azo-dyes at K Solubility (10 7 y) Solubility (10 5 y ) (MPa) (MPa) DR1 DR13 DR30 DB DR30 = C. I. Disperse Red 30, DB22 =C. I. Disperse Brown 22 ther than the binary system of a single dye and carbon dioxide, the ternary system of two dyes and carbon dioxide was also investigated. Dyes mixture solubility of C. I. Disperse Blue 134 and C. I. Disperse Yellow 16 are also measured [11]. Comparing the binary and the ternary experimental results at K, the solubility of C. I. Disperse Blue 134 in the ternary system is close to the solubility in the binary system. However, the solubility of C. I. Disperse Yellow 16 in the ternary system is lower (average 10.4%) than the solubility in the binary system. Some results showed that the solubility changes with molecular structure, but different information was given by Özcan in his study [20]. Although there is a weak trend for lower solubilities with higher molar mass, there is not a strong correlation. ne would also expect dyes with polar groups like aromatic, -H, and groups to be less soluble, but this does not appear to the case for Z1 (Figure 4) and C. I. Disperse Red 60. It was also indicated that it was difficult to predict dye solubilities from structure, as so man unquantifiable effects seemed to be included. With the exception of anthraquinone dyes and azo-dyes, other disperse dyes, i.e., C. I. Disperse Yellow 82 and C. I. Disperse Blue 354, were also investigated [17, 20]. 4 Summary Supercritical dyeing in carbon dioxide is a promising dyeing process in order to eliminate wastewater. The solubility data of many disperse dyes are determined in supercritical carbon dioxide. Many useful results are obtained in the study. But the trends of solubility with molecular properties need to be further investigated. Acknowledgements The authors are grateful for financial support to the Trans-century Training Program Foundation for the Talents by the State Education Commission of China. Reference [1] Sous W., Knittel D., Schollmeyer E. Dyeing of textiles in supercritical carbon dioxide [J]. Textile Res. J. 1993, 63: [2] Sung H. D., Shim J. J. Solubility of C. I. Disperse 67

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