Formation of Alcohols and Carbonyl Compounds From Hexane and Cyclohexane With Water in a Liquid Film Plasma Reactor

In this paper, vaporized n-hexane in a flowing argon carrier gas was mixed with deionized liquid water and injected into a tubular plasma reactor. A liquid water film forms on the wall of the tubular reactor and plasma channels propagate along the gas-liquid interface. Gas-chromatography mass spectrometry and nuclear magnetic resonance spectroscopic analysis of the major products and their relative ratios collected in the effluent of the reactor confirm the formation of 3-hexanol (26%), 2-hexanol (21%), 3-hexanone (17%), 2-hexanone (17%), 1-hexanol (11%), and hexanal (8%). The functionalization is likely due to oxidation of the organic stating material by OH radicals formed from the dissociation of water by the plasma. The functionalization of cyclohexane was achieved in the same manner where analysis showed the formation of cyclohexanone (47%), cyclohexene (20%), cyclohexanol (19%), hexanal (11%), and 2-cyclohexenone (2%). Hydrogen peroxide was also produced in the presence of either organic compound and the amount formed decreased as the amount of organic flowing into the reactor was increased. It is likely that the hydrogen peroxide is formed in the gas phase close to the gas-liquid interface by OH radical recombination. This paper demonstrates the activation of the C-H bond using low temperature plasma by combining two common chemical feedstocks (hydrocarbon and water) and transforming them into the higher value functionalized organic products via a sequence of reactions where all necessary intermediate reactants are formed in situ by the electric discharge.