Lower saturated hydrocarbons have been used in large quantities as propellants in aerosol cans. In particular, isobutane, n-butane and propane have been used either alone or in +with halogenated hydrocarbons and especially fluorocarbons or chlorofluorocarbons.
Unexplainably, certain sources of hydrocarbon, and especially isobutane, have proved satisfactory for aerosol use and have been designated aerosol grade hydrocarbons. Most sources of hydrocarbons, and especially isobutane, have not been successfully used in aerosol containers without unacceptable levels of corrosion and odor.
Limited sources of hydrocarbons, and particularly isobutane, have been found to be satisfactory for use as propellants in aerosols. In particular, most sources of "technical" grade isobutane cause unsatifactory levels of corrosion and odor when placed in aerosol cans and allowed to remain there for several weeks or months. Examination of "technical grade" isobutane by conventional techniques has not determined the nature of the contaminant that causes such corrosion and odor. In particular, molecular sieves through which "technical grade" isobutane is passed do not indicate an impurity in "technical grade" isobutane not found in "aerosol grade" isobutane. Similarly, tests for sulfur compounds by mass spectroscopy revealed no evidence of sulfur compounds at the 50 part per billion level. Furthermore, no resolution between isobutane and isobutene was possible using mass spectroscopy.
Fractionation in a Podbelniak type column did not raise the impurities to a level in which the impurity could be detected. The only detected impurity, 2-ethylhexene-1, was found in trace amounts.
USPTO Backgrounds
USPTO Backgrounds