(449c) Solubility and Binary Phase Equilibria of Chlorosilanes in Supercritical Carbon Dioxide

Phase boundaries, dew points, bubble points, and critical points, for binary mixtures of four chlorosilanes and carbon dioxide are reported. Measurements were made in a 0.3-L, stainless-steel cell. A piston separated the cell into two variable-volume chambers: the constant-composition, equilibrium chamber (equipped with a sapphire window) and the pressure-control chamber. An ISCO syringe pump supplied carbon dioxide at high pressures to both chambers. The chlorosilane and the supercritical CO₂ were loaded into the equilibrium chamber with a known composition. The other chamber was filled with pure carbon dioxide. Before each run, the system was calibrated by measuring the critical properties of pure CO₂. The system was also validated by measuring a critical point to a binary mixture with a 0.0075 mole fraction of naphthalene in CO₂. Moreover, a test showed that the apparatus produced no hysteresis. Then, phase envelopes of binary systems of methyltrichlorosilane (MTCS), dimethyldichlorosilane (DMDCS), trimethylchlorosilane (TMCS), or diethyldichlorosilane (DEDCS) and CO₂ were measured at constant composition (concentration isopleths) for mole fractions ranging from 0 to ~0.14. A total of 33 concentration isopleths containing more than 240 data points are reported. The resulting pressures were between 6.6 MPa and 12.2 MPa and the temperatures were between 35°C and 74°C. The mixtures critical points shifted with respect to that of pure CO₂ to values up to 11.81 MPa and 74°C depending on the chlorosilane and its concentrations. According to the results obtained, the largest chlorosilane (DEDCS) produced the highest shift in critical pressure and the lowest shift in critical temperature with respect to pure CO₂.