UV/ozone degradation of gaseous hexamethyldisilazane (HMDS)

As a carcinogen, hexamethyldisilazane (HMDS) is extensively adopted in life science microscopy, materials science and nanotechnology. However, no appropriate technology has been devised for treating HMDS in gas streams. This investigation evaluated the feasibility and effectiveness of the UV (185 + 254 nm) and UV (254 nm)/O3 processes for degradation of gaseous HMDS. Tests were performed in two batch reactors with initial HMDS concentrations of 32–41 mg m−3 under various initial ozone dosages (O3 (mg)/HMDS (mg) = 1–5), atmospheres (N2, O2, and air), temperatures (28, 46, 65 and 80 °C), relative humilities (20%, 50%, 65%, 99%) and volumetric UV power inputs (0.87, 1.74, 4.07 and 8.16 W l−1) to assess their effects on the HMDS degradation rate. Results indicate that for all conditions, the decomposition rates for the UV (185 + 254 nm) irradiation exceeded those for the UV (254 nm)/O3 process. UV (185 + 254 nm) decompositions of HMDS displayed an apparent first-order kinetics. A process with irradiation of UV (185 + 254 nm) to HMDS in air saturated with water at temperatures of 46–80 °C favors the HMDS degradation. With the condition as above and a P/V of around 8 W l−1, k was approximately 0.20 s−1 and a reaction time of just 12 s was required to degrade over 90% of the initial HMDS. The main mechanisms for the HMDS in wet air streams irradiated with UV (185 + 254 nm) were found to be caused by OH free-radical oxidation produced from photolysis of water or O(1D) produced from photolysis of oxygen. The economic evaluation factors of UV (185 + 254 nm) and UV (254 nm)/O3 processes at different UV power inputs were also estimated.