Abstract:

Objective In order to promote the commercial application of supercritical fluid of carbon dioxide (SCF-CO₂) coloration technology, the study of the solubility of various dyes in SCF-CO₂ plays an important role in the effective selection of dyes, the design of processes, and the improvement of process efficiency, particularly for a good color matching and hue control. Therefore, the purpose of this work is to investigate the solubility and its dissolving behaviors of a new Reactive Disperse Red SCFX-AYRL dye in SCF-CO₂, which could provide a basis for the applications of the special dye and the SCF-CO₂ technology in practice.

Method In order to investigate the solubility and the dissolving behavior of the special dye in SCF-CO₂, a self-developed solubility testing device involving a sampling unit was used. Moreover, a calibration curve between the dye concentrations and its corresponding absorbance was constructed by a standard addition method in acetone solution. Thus, different solubilities and its dissolving behavior of the dye at different conditions were determined via a sampling method from the testing device system after a dissolving equilibrium. Then the results were fitted by an empirical Chrastil equation, and the dissolution behavior was also predicted by this model.

Result The effects of treatment duration, temperature, pressure, and cosolvent system on the solubility of the dye in SCF-CO₂ were investigated. A series of visible absorption spectra and a calibration curve for the special dye in acetone solution were developed for the determination of the dye solubility in subsequent experiments. At a system pressure of 20 MPa and various temperature conditions, the solubility of the dye in SCF-CO₂ first increased and then approached equilibrium as the dissolution duration extended from 10 min to 60 min. A significantly shortened dissolution equilibrium time was also observed as the temperature increased from 80 ℃ to 130 ℃. When the system pressure was raised from 6 MPa to 24 MPa under a same dissolution temperature condition along with dissolution duration of 60 min, the solubility of the special dye in SCF-CO₂ demonstrated a rapid increase first, and then its increasing became slower. These results showed that the increases in dissolving duration, temperature, and pressure in an appropriate range helped to improve the dissolving behavior of the dye under those conditions in pure SCF-CO₂fluid. As the cosolvents, octadecylamine and methyl salicylate were added, the solubility of the SCFX-AYRL dye in SCF-CO₂ was rapidly enhanced firstly as the dissolving duration prolonged from 10 min to 60 min, and then it approached equilibrium or saturated state. When the system pressure was increased from 6 MPa to 24 MPa under the conditions containing cosolvents and the same temperature, the solubility of the SCFX-AYRL dye was seen to increase first and then also tended towards equilibrium. It was made clear that selecting appropriate cosolvents would significantly improve the solubility of the dye in supercritical carbon dioxide. For the SCFX-AYRL dye, the solubility data obtained under different temperatures, pressures, and cosolvent conditions were well fitted and correlated by the Chrastil empirical model. Moreover, these results further indicated that the Chrastil empirical model were effectively correlate and predict the solubility data of the SCFX-AYRL dye in pure SCF-CO₂ and SCF-CO₂/cosolvent system, and the correlation between experimental data and the Chrastil empirical model could be effectively improved by the addition of cosolvents.

Conclusion In pure SCF-CO₂ system, the dissolving of the special dye in SCF-CO₂ could reach an equilibrium within 30-60 min under the conditions of 20 MPa and system temperatures over 80-130 ℃, and the solubility of the special dye could be improved by increasing the fluid temperature and system pressure in an appropriate range, respectively. The addition of cosolvents could improve the dissolving behavior of the special dye and significantly improve their solubility and dissolving rate, as well as decrease the influences from the system temperature and pressure. In addition, the dissolving behaviors of the special dye in SCF-CO₂ and SCF-CO₂/cosolvents were well correlated and predicted by the Chrastil empirical model.

Key words: supercritical carbon dioxide fluid(SCF-CO₂), reactive disperse dye, solubility, cosolvent, solubility correlation