Partial Oxidation of Light Hydrocarbons. 1. Major Differences Noted in Various Tubular Reactors

Abstract

Although the material of construction of the reactor used for the partial oxidation of light paraffins has a major effect on both the composition of the product obtained and on the kinetics of oxidation, the present investigation is the first one to investigate several reactors systematically over a wide range of operating conditions. Glass, aluminum, steel, and copper reactors were employed in the present investigation for partial oxidation of both methane and propane. Postulates proposed earlier to explain the role of the surface do not explain all results. The reactor surfaces were found in many cases to catalyze surface reactions.Numerous previous investigators have presented experimental information that indicates partial oxidation results often vary significantly in reactors with different materials of construction or with different pretreatments of the inner surfaces. Several postulates have been proposed Reid, 1954, 1961;Semenov, 1958;Knox, 1968; Baldwin et al., 1970;Euker and Leinroth, 1970) that explain relatively well certain results obtained over rather limited experimental conditions, but no postulate proposed to date explains results obtained over wide ranges of conditions. A proposed mechanism should explain both the kinetics'and composition of products obtained.In a steel reactor operated at atmospheric pressure, a relatively constant rate of oxidation of propane occurred over the entire range of oxygen conversion from essentially 0 to 100%

Partial Oxidation of Light Hydrocarbons. 3. Mechanism Incorporating Key Surface Reactions with Gas-Phase Steps

“…The levels of surface reactions (reactions F, G, and H) were demonstrated by Mahajan et al (1977b) to be as follows: copper > steel > aluminum > glass. Partial oxidation results in tubular reactors of the above materials of construction (Mahajan et al, 1977a) are consistent with the above ordering of the materials of construction. Partial oxidation reactions with type II kinetics and with high degrees of combustion occurred when steel and especially copper reactors were operated at atmospheric pressure.…”

“…(d) Increased operating pressures for partial oxidation experiments reduce the ratio of surface area to mass of reactants; the result is a net decrease in the importance of surface reactions. The results of Mahajan et al (1977a) and of Kao (1969) show the expected changes of both the kinetics of oxidation and the type of product in the pressure range of 1-4 atm. Using either a steel or copper reactor at 1 atm.…”

“…The surface reactions described in Tables I and II occur at similar operating conditions including temperature regardless of the paraffin being oxidized. Yet gas-phase reactions for the paraffins may require quite different operating conditions, as previously noted (Mahajan et al, 1977a).…”

“…The chain-branching sequences also result in increased amounts of oxygenated products. When, however, reactions F are important, fewer oxygenated products will be formed and the degree of combustion (Mahajan et al, 1977a) will be higher (i.e., more carbon dioxide and water). Propane is shown in reaction 3 as the hydrocarbon that supplied the hydrogen atom that was transferred.…”

Partial Oxidation of Methane in Glass and Metal Tubular Reactors

“…The experimental procedures employed were similar to those reported earlier by Holtzmeier and Albright (1969) and Mahajan et al (1977a). In general, the tubular flow reactors employed were 0.40 and 0.62 cm i.d.…”