Removal of diisopropyl methyl phosphonate (DIMP) from heated metal oxide surfaces

Diisopropyl methyl phosphonate (DIMP) is an organophosphorus compound used as a surrogate of sarin, a chemical weapon agent. Thermal decomposition of DIMP and similar liquids may be affected by added inorganic solids. Understanding such effects is needed to guide decontamination and environmental mitigation work. Here, liquid DIMP mixed with powders of γ-Al₂O₃ or SiO₂, was heated to 350 °C in a thermogravimetric analyzer while observing effluent gas using a mass spectrometer. For both powders, evaporation of DIMP occurred between 50 and 200 °C, followed by a second mass loss step up to 350 °C. The amount of DIMP evaporated in the first step varied; however, the size of the second, mass loss step was consistent between experiments for each solid used. For γ-alumina, 2-propanol and propene were released below the DIMP boiling point and mostly propene at higher temperatures. Calcining alumina prior to exposure to DIMP reduced the release of 2-propanol. For silica, the second mass loss step was smaller and only propene was released. Powders exposed to DIMP and recovered at different temperatures showed FTIR peaks corresponding to the individual bond vibrations of DIMP. At higher temperatures, only the P-CH ₃ stretching vibration was observed.