Ž .Fluid Phase Equilibria 158–160 1999 707–712

Investigations on the solubility of anthraquinone dyes in supercriticalcarbon dioxide by a flow method

Bjorn Wagner, Cornelia B. Kautz, Gerhard M. Schneider )¨Lehrstuhl fur Physikalische Chemie II, Fakultat fur Chemie, Ruhr-UniÕersitat Bochum, D-44780 Bochum, Germany¨ ¨ ¨ ¨

Received 2 April 1998; accepted 11 September 1998

Abstract

Ž .The solubility of 1,4-bis- n-propylamino -9,10-anthraquinone in supercritical CO was measured spectro-2

scopically by a flow method. Isotherms were recorded for temperatures and pressures from 305 to 340 K andfrom 7.5 to 20 MPa, respectively. Within the range of the experiments, the equilibrium concentrations becomehigher with increasing pressures and densities at constant temperature. In the concentration vs. pressure plot theisotherms show intersection points, which can be explained by a density effect. q 1999 Elsevier Science B.V.All rights reserved.

Keywords: Flow method; Supercritical solvent; Solid–fluid equilibria; Spectroscopy; Anthraquinone dyes

1. Introduction

Dyeing synthetic materials with disperse dyes from supercritical CO is a promising alternative to2

conventional aqueous dyeing techniques. This method allows an easy recovering of the remainingdyestuff from the solvent and a reduction of auxiliary agents, thus avoiding waste-water problems.Moreover, a drying process is not necessary. Solubility data of disperse dyes in CO are of interest for2

w xthe optimization of this particular dyeing technique 1–3 .

2. Experimental

2.1. Apparatus

The apparatus consists of SFC-equipment that has been modified for solubility measurementsw x Ž .4–7 . The dyestuff under test see Fig. 1 is finely pulverized and packed into an extraction column

) Corresponding author. Tel.: q49-234-700-4250; fax: q49-234-709-4293; e-mail:gerhard.schneider@ruhr-uni-bochum.de

0378-3812r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0378-3812 99 00077-1

( )B. Wagner et al.rFluid Phase Equilibria 158–160 1999 707–712708

Ž . Ž .Fig. 1. 1,4-bis- n-propylamino -9,10-anthraquinone AC03 .

Ž .length 10 cm, inner diameter 2 mm , which is placed in an air thermostat. CO is pumped through2

the extraction column with a low flow rate by a syringe pump. The dissolved dye is spectroscopically

Fig. 2. Equilibrium concentration of AC03 in CO in mole per volume of solution as a function of pressure.2

Fig. 3. Equilibrium concentration of AC03 in CO in mole per volume of solution as a function of density of pure CO .2 2

( )B. Wagner et al.rFluid Phase Equilibria 158–160 1999 707–712 709

Table 1Solubility data of AC03 in CO : concentration, c, of AC03 in mole per volume of solution at different temperatures, T , as a2

Ž .function of pressure, p, and density, r, of pure CO at T and p given2

y3 y6 y3Ž . Ž . Ž .p MPa r g cm c 10 mol dm

T s 305.0 K7.9 0.641 319.0 0.720 69

10.1 0.753 9811.0 0.775 12312.4 0.801 15814.0 0.824 19215.4 0.840 22417.0 0.856 25618.8 0.872 289

T s 310.0 K8.4 0.483 98.9 0.610 379.6 0.662 59

10.0 0.686 8311.5 0.737 13912.3 0.751 17413.0 0.770 19214.1 0.792 22715.1 0.803 24716.1 0.817 28917.0 0.828 30618.1 0.839 32819.0 0.847 346

T s 315.0 K9.2 0.465 69.5 0.508 139.7 0.550 21

10.3 0.610 4311.0 0.655 7012.0 0.696 10813.0 0.725 14814.0 0.747 18315.0 0.766 22115.9 0.782 25716.9 0.796 28918.0 0.808 31918.9 0.819 344

T s 320.0 K10.2 0.472 1110.5 0.523 2211.1 0.576 4211.6 0.608 6312.1 0.636 87

( )B. Wagner et al.rFluid Phase Equilibria 158–160 1999 707–712710

Ž .Table 1 continuedy3 y6 y3Ž . Ž . Ž .p MPa r g cm c 10 mol dm

T s 320.0 K13.1 0.677 13114.0 0.705 17615.1 0.729 22416.1 0.750 26917.1 0.764 31017.9 0.777 34118.3 0.782 351

T s 330.0 K11.3 0.427 811.8 0.461 1512.4 0.504 3012.9 0.541 5013.1 0.553 6113.5 0.575 7614.1 0.602 10815.0 0.636 15616.0 0.667 21717.0 0.691 27818.0 0.711 33118.5 0.720 355

T s 340.0 K11.9 0.362 412.4 0.392 912.9 0.426 1613.9 0.483 4214.8 0.524 7615.0 0.537 8916.1 0.578 14717.0 0.609 21218.1 0.638 29219.0 0.658 352

detected in a flow through cell, which is coupled to a diode array spectrometer by fiber optics.Concentrations are calculated from the integral absorbance, i.e., the area below the spectrum.Solubility isotherms have been measured in the temperature and pressure ranges from 305 to 340 Kand 7.5 to 20 MPa, respectively.

The experimental uncertainties of pressure and temperature are "0.05 MPa and "0.2 K,respectively, resulting in an experimental error for the solubility data of less than 5%.

2.2. Materials

Ž . Ž .CO 99.995 vol.% was purchased from Messer Griesheim. 1,4-bis- n-propylamino -9,10-anthra-2Ž .quinone AC03; see Fig. 1 was synthesized according to a procedure that has been described in the

Ž . w xliterature for 1,4-bis- n-octadecylamino -9,10-anthraquinone 8 .

( )B. Wagner et al.rFluid Phase Equilibria 158–160 1999 707–712 711

3. Results and discussion

Static measurements on disperse dyes have shown that the spectroscopic determination of concen-trations is affected by even small concentrations of more soluble impurities absorbing in the same

w xrange of the spectrum as the dyestuff itself 9–11 . The flow method often allows an easy extractionof such impurities; the continuous purification can be observed as a characteristic change in the shapeof the spectrum. The solubilities obtained by this dynamic method are in good agreement withmeasurements up to higher pressures determined by a static method, deviations are within the

w xexperimental error bound of 5% 12,13 .In Figs. 2 and 3 some concentration vs. pressure and concentration vs. density isotherms are plotted

Ž .for 1,4-bis- n-propylamino -9,10-anthraquinone in CO . The solubility is given in mole per volume of2w xsolution. Density values were calculated for pure CO from the EOS given by Span and Wagner 14 .2

The solubility data are given in Table 1. The concentration vs. pressure isotherms exhibit intersectionpoints. This can be explained by two competing effects. In principle, increasing temperature favorssolubility, but at the same time the solvent density decreases. At low constant pressures the decreaseof solvent density dominates, and the overall solubility of the dyestuff decreases with increasingtemperature. At higher pressures the solubilities increase with rising temperatures, because thedensities in this range only slightly depend on the temperature, and the normal temperaturedependence of solubility dominates. This explanation is supported by the concentration vs. densityplot where intersection points are no longer found.

Ž . ŽThe solubilities of homologous 1,4-bis- alkylamino -9,10-anthraquinones with alkylsmethylŽ . Ž . Ž . Ž . Ž ..AC01 , ethyl AC02 , n-butyl AC04 , n-pentyl AC05 and n-octyl AC08 have already been

w xmeasured by the flow method 15 . The solubility of AC03 is greater than that of AC01 or AC02 by afactor of about 10 and comparable to the solubility of AC04 or AC05.

4. Conclusions

Ž .The solubility of 1,4-bis- n-propylamino -9,10-anthraquinone in CO has been measured at various2

pressures and temperatures. The concentration vs. pressure isotherms show intersection points, whichcan be explained by a density effect, whereas for the concentration vs. density isotherms nointersection points are found any longer.

Acknowledgements

Financial support of the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Indus-trie is gratefully acknowledged.

References

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w x Ž .2 G.M. Schneider, in: E. Kiran, J.M.H. Levelt Sengers Eds. , Supercritical Fluids: Fundamentals for Applications,Kluwer, Dordrecht, 1994, pp. 739–754.

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