Optical flow cell and apparatus for solubility, salt deposition and Raman spectroscopic studies in aqueous solutions near the water critical point

A flow cell fitted with large diameter optical ports suitable for visual observation and Raman spectroscopic studies of aqueous solutions to temperatures of 500 °C and pressures to 25 MPa is described. The cell uses commercially available compression fittings that have proven to be reliable and robust to cycles of assembly, temperature exposure, and disassembly. A unique design is given for construction of the optical ports. The design of a heated cylindrical insert for salt solubility, salt deposition and salt nucleation studies in near-critical aqueous solutions is described. A method for in situ detection of the crystalline phase of salt deposited from aqueous solution at near-critical conditions and then surrounded by pure supercritical water is demonstrated for Na2SO4, using Raman spectroscopic observation.