Oxidation of several liquid, long chain hydrocarbons (alkanes, alkenes, arenes, and a light gas oil, LCGO, product of a coking process) has been studied by using a low-pressure high-voltage oxygen plasma. Olefins were readily oxidized to epoxides and carbonyl compounds, O(3P) being the active species in the plasma. At long treatment times the saturated chains of the olefins also reacted to produce secondary alcohols and ketones. These compounds and tertiary alcohols, only when tertiary carbons were present, were obtained with alkanes. At 5 min 4-phenyl-1-butene showed reaction mostly on the olefinic CC, followed by oxidation of the aromatic ring. At 120 min the olefinic fraction of the compound was eliminated and the reaction of the saturated −CH2− groups represented only 0.6% of the total conversion. LCGO, with a composition of 65.1% alkanes, 34.8% aromatics, and 3.1% olefins, was treated under similar conditions used for the model compounds. At 120 min the olefinic fraction of the mixture was eliminated and the cetane number, a parameter indicating the quality of fuel oils, was improved by 66% without any additional treatment.

Oxidation of eight liquid cycloalkanes and two diesel fuels has been studied by using a low pressure high voltage oxygen plasma. Naphthenes were individually oxidized to alcohols and ketones, O( 3 P) being the active species in the plasma. Tertiary C-H bonds were the most reactive. At long treatment times the main products suffered successive oxidation to produce two oxygenated groups in the same molecule. cis-Decaline was four times more reactive than transdecaline. For this two isomers and bicyclohexyl the conversions were the lowest, the yield of the tertiary carbon being between 40 and 80% of the total. Methyl-, ethyl-, and n-propylcyclohexane gave similar results. The reactivity of the two tertiary carbons of iso-propylcyclohexane amounted to c.a. 80%. This compound was the most reactive. Due to steric effects of the alkyl group, tertbutylcyclohexane showed low reactivity. Addition of 4.7-7.0 wt % of oxygen to the diesel fuels has been achieved in one-step process with the plasma.

Characterization of a water plasma was carried out in a range of water vapor flow rate of 0.1 to 2.2 mmol/h in a radio frequency discharge, in order to study its properties as either an oxidizing or a reducing agent in heterogeneous reactions with different liquid hydrocarbons. The variation of relative population of the species in the plasma, namely ·H, O(3P), and ·OH, was studied by optical emission spectroscopy by varying the flow rate, at a fixed radio frequency power of 100 W. Reactions with liquid hydrocarbons, such as fuel residuals and organic compounds with similar functionalities, were performed. Hydrogenation products were the most abundant at low flow rates, whereas oxidation was the prevalent process at moderate-to-high flow rates, alcohols, carbonyl compounds, epoxides and phenols being the products, depending on the starting substances. The cetane number of a light gas oil, containing 89.75% of alkanes, 5.57% of aromatics, and 4.68% of olefins, was improved by 59% after 8 h treatment at 0.071 mmol of water per hour.