In situ Raman spectroscopy investigation of the solubility and dissolution mechanism of 1,2-dichlorobenzene in hot compressed water in a fused silica capillary reactor.

Hot compressed water (HCW), with its unique properties, is regarded as a promising solvent for industrial applications. A number of methods to measure the solubility of hydrophobic organic compounds (HOCs) in HCW have been reported. However, these methods were conducted in large-scale stainless-steel reactors, and few included an in situ study regarding the dissolution mechanism of HOCs in HCW during the solubility determination process. In this study, a fused silica capillary reactor in combination with Raman spectroscopy was applied to investigate phase changes, determine the solubility, and study the dissolution mechanism of 1,2-dichlorobenzene in HCW. The total dissolution process of 1,2-dichlorobenzene in HCW was observed under a microscope, and the images were recorded continuously using a digital camera. Raman spectroscopy was used to confirm the homogeneity of the 1,2-dichlorobenzene solution during dissolution. The solubility of 1,2-dichlorobenzene increased from 35.9 to 85.7 mg g⁻¹ in water with increasing temperature from 256.7 to 294.1 °C. Furthermore, the dissolution mechanism of 1,2-dichlorobenzene in HCW is proposed based on the Raman spectra of 1,2-dichlorobenzene and water during the dissolution process in the fused silica capillary reactor. The breakage of the fully hydrogen-bonded (tetrahedral) configuration and the consequent change in the static dielectric constant of water are deemed to be compelling reasons for the high solubility of 1,2-dichlorobenzene in HCW. Our experimental method exhibits great potential for determining the solubility of HOCs in HCW and for investigating their dissolution behavior and dissolution mechanism at elevated pressure and temperature conditions. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]