Selective Homogeneous Oxidation System for Producing Hydroperoxides Concentrate: Kinetics of Catalytic Oxidation of Gas Oils

Abstract

A selective and mild (55 °C and 50 psig) homogeneous oxidation system has been described to produce hydroperoxides from a narrow cut made from typical gas oil. During this process oil, dissolved in wet acetic acid, is treated with air in the presence of the redox couple Co(III)/Co(II) (partially oxidized catalyst, POC). A straightforward route to POC consists of oxidizing Co(II) in wet acetic acid with calculated aqueous potassium chlorate. Initiation is the manifestation of the potent oxidizing ability of Co(III) toward generating alkyl radicals from hydrocarbons in the oil. Classical propagation then leads to assorted hydroperoxides, simultaneously decomposed by POC. Kinetics of the simultaneous formation and decomposition of hydroperoxides, under varying sets of process and composition variables, was studied in an isothermal, mechanically agitated, semibatch reactor, operating in the pure kinetic regime. A unique kinetic model, based on a rare irreversible consecutive reaction network (pseudo-first-order formation of hydroperoxides followed by their second-order decomposition), has been found to reasonably describe the kinetic data (R 2 = 0.9214). This kinetic model allowed the evaluation of the formation and decomposition rate constants that permitted the estimation of conversion of oil and selectivity to hydroperoxides. On average 15.12 ± 3.23% conversion was achieved in 9.3 ± 4.0 min with 99.86 ± 0.23, 92.88 ± 7.95, and 28.77 ± 11.67% selectivities for 0.10, 1.00, and 10.0% conversions, respectively.

Liquid-Phase Homogeneous Catalytic Oxidation of Gas Oil: Elucidation of Complex Chemical Transformation Network

“…Apart from this catalytic effect another notable function of Co(III) is the instantaneous initiation, even in the absolute absence of hydroperoxides. This is a manifestation of the powerful oxidizing ability of Co(III) that can abstract hydrogen from C H bonds through direct electron transfer [17,19,[30][31][32]. Based on these properties the following mechanism had earlier been proposed for liquid-phase air oxidation of hydrocarbon mixtures in the presence of the redox couple Co(III)/Co(II) and at sufficiently high dissolved oxygen concentration [17,19]:…”

“…Net effect of the branching reactions (A) and (B), responsible for the catalytic effect of the redox couple Co(III)/Co(II), can be expressed by a bimolecular process that does not involve metal ions [17,19]:…”

“…The path to carbonyls consists of C C bond cleavages in some of these free radicals that can easily be oxidized further to acids [21,22]. A rare irreversible consecutive reaction network had previously been proposed, to describe the observed kinetics of such a complex oxidation system, involving hundreds of elementary reactions, consisting of the following two simple steps [17,19]:…”

“…In addition to that there are numerous examples of processes where complex hydrocarbon mixtures are used as substrates. For example coal [2][3][4][5], bitumen/asphalt/tar [6][7][8][9][10], wax [11], and middle distillates [12][13][14][15][16][17][18][19] have been shown to be catalytically processed either to upgrade or to desulfurize these complex mixtures.…”

“…One novel preparation of the redox couple Co(III)/Co(II), had earlier been indicated as a potential homogeneous catalyst for a route from hydrocarbons (a narrow saturate cut of gas oil) to hydroperoxides that *Address correspondence to this author at the Department of Applied Chemistry & Chemical Technology, University of Karachi, Karachi, Pakistan; E-mail: ashrafkamal@uok.edu.pk are important constituents for polymerization and oxidation processes [17,19]. The present work was focused to establish the approximate product distribution during the homogeneous liquid phase reaction, between oxygen and a narrow saturate cut of gas oil the presence of the redox couple Co(III)/Co(II) in a medium comprising of wet acetic acid, as described earlier [17,19]. FTIR analyses of substrate and products were used to detect the chemical changes in the time domain.…”