Kinetics of Catalytic Oxidation of Benzene,n-Hexane, and Emission Gas from a Refinery Oil/Water Separator over a Chromium Oxide Catalyst

Abstract

With the advances made in the past decade, catalytic incineration of volatile organic compounds (VOCs) has become the technology of choice in a wide range of pollution abatement strategies. In this study, a test was undertaken for the catalytic incineration, over a chromium oxide (Cr 2 O 3 ) catalyst, of n-hexane, benzene, and an emission air/vapor mixture collected from an oil/water separator of a refinery. Reactions were carried out by controlling the feed stream to constant VOC concentrations and temperatures, in the ranges of 1300-14,700 mg/m 3 and 240-400 °C, respectively. The destruction efficiency for each of the three VOCs as a function of influent gas temperature and empty bed gas residence time was obtained.Results indicate that n-hexane and the oil vapor with a composition of straight-and branch-chain aliphatic hydrocarbons exhibited similar catalytic incineration effects, while benzene required a higher incineration temperature or longer gas retention time to achieve comparable results. IMPLICATIONSEmissions from oil/water separators in petroleum refineries generally contain thousands of mg/m 3 of light aliphatic and aromatic hydrocarbons. Complete catalytic oxidation has been identified as one of the most economical and efficient techniques for the abatement of these volatile compounds. There are few reports concerning the kinetic study of the complete catalytic oxidation of these compounds over metal oxide catalysts, especially Cr 2 O 3 . This paper assists in understanding the kinetics of deep catalytic oxidation of benzene, n-hexane, and a waste oil vapor from a refinery oil/water separator. The present work also provides data on the appropriate oxidation temperatures and gas residence times for catalytic incineration of the three VOCs over a bed of commercial Cr 2 O 3 catalysts.In the range of the VOC concentrations studied, at a given gas residence time, increasing the operating temperature of the catalyst bed increased the destruction efficiency. However, the much higher temperatures required for a destruction efficiency of over 99% may be not cost-effective and are not suggested. A first-order kinetics with respect to VOC concentration and an Arrhenius temperature dependence of the kinetic constant appeared to be an adequate representation for the catalytic oxidation of these volatile organics. Activation energy and kinetic constants were estimated for each of the VOCs. Low-temperature destruction of the target volatile organics could be achieved by using the Cr 2 O 3 catalyst.

Catalytic combustion kinetics of acetone and toluene over Cu0.13Ce0.87Oy catalyst

“…However, in some cases, the power-law model was found to be enough to represent catalytic combustion of VOCs. Wang and Chou demonstrated that a first-order equation with respect to VOC concentration and an Arrhenius temperature dependence of the kinetic constant were adequate to describe catalytic combustion of benzene and hexane in air over Cr 2 O 3 catalyst [32]. Miranda et al reported that power-law expression provided fairy good fits for oxidation of trichloroethene over metal oxide catalysts [33].…”

Influence of the Heat Transfer on Deactivation Processes in a Square Network

“…The range of the reaction activation energies has been taken from the literature. Supposing that the main reaction is a catalytic oxidation or a combustion of paraffin, the activation energy varies between 50 and 120 kJ/mol, corresponding to γ 1 ranging from 10 to 20. − The values of γ 2 and γ 3 can be estimated from 10 to 30 for a catalytic combustion, for catalytic dehydrogenations, , and for catalytic hydrogenations . The simulations led in the framework of this paper concern two values of the Thiele criteria: φ NW = 10 is typical for a reaction conducted under strong diffusional limitations.…”