FLAMMABILITY HAZARDS OF LOWER ALIPHATIC-ALDEHYDES AT ELEVATED PRESSURE AND TEMPERATURE

A large and potentially hazardous decrease in aldehyde autoignition te mperature (AIT) occurs with increased pressure. The AIT-pressure curve determined in a 5 L stainless steel sphere was similar for propionald ehyde and butyraldehyde in air, falling from about 185 degrees C at at mospheric pressure to 90 degrees C at 140 psia. Reduction of oxygen co ncentration had little effect on propionaldehyde AIT. At 100 degrees C and 140 psia, autoignitions accompanied by at least a doubling of pre ssure were observed above 4 % oxygen. In the presence of a few grams o f free liquid, propionaldehyde vapor ignited in air at initial conditi ons significantly below the ATT. The mechanism appears to involve rapi d Fe-catalyzed exothermic liquid-phase oxidation leading to autoigniti on of the adjacent heated gas layer. An acetaldehyde vapor-air mixture in the presence of free liquid and rust exploded at room temperature when air pressure was increased to 95 psia; this result is discussed w ith reference to a cylinder overpressurization that occurred while mak ing up an ostensibly sub-LFL calibration mixture with compressed air. Propionaldehyde's limiting oxygen concentration CLOG was investigated in the near-autoignition region using the same 5L apparatus; the findi ngs are discussed with reference to an overpressurization incident in an air-liquid partial oxidation reactor The general results are used t o illustrate the ap plication of LOC in partial oxidation processes su bject to autoignition and to discuss elements of the current ASTM draf t test method for LOG, which does not address test difficulties associ ated with condensable and/or reactive gas systems.