Effect of pressure on the thermo-oxidative behavior of saturates, aromatics, and resins (S-Ar-R) mixtures

Abstract

To understand the effect of pressure on the interactions between saturates, aromatics, and resins (S-Ar-R) fractions during thermo-oxidation reactions, this study evaluates the oxidation behavior of saturates:resins (S:R), saturates:aromatics (S:Ar), and aromatics:resins (Ar:R) mixtures at 0.084, 3.0 and 6.0 MPa. Oxidation was analyzed by high-pressure thermogravimetric analysis in terms of mass change and rate for mass change. Kinetic analysis was done using a first-order kinetic model discretizing thermal profiles in four regions: oxygen chemisorption (OC), decomposition of chemisorbed oxygen-based compounds (DCO), first combustion (FC), and second combustion (SC). The results demonstrate the role of pressure on the simultaneous oxidation of S:Ar, S:R, and Ar:R mixtures. First, S:Ar thermo-oxidative profiles are described by FC and SC at 0.084 MPa, regardless of the S:Ar ratio. When the oxidation is evaluated at 3.0 and 6.0 MPa, OC and DCO zones are observed, and the amount of oxygen chemisorbed increased as pressure increased. The same trend was observed for S:R and Ar:R systems. Between the S:Ar mixtures, the oxygen chemisorption increased as the amount of aromatics increased too, at 3.0 and 6.0 MPa. The structures formatted at high pressure, present higher reactivity, and therefore, the total consumption of the samples end at lower temperatures. During S:R oxidation, the higher the content of resins, the higher the oxygen chemisorption and the lower the temperature required to decompose the samples. Finally, the mixture between aromatics and resins shows slower kinetic rates than for the other systems. The products from the oxidation of the resins' aliphatic structure react in FC with the aromatics, promoting combustion reactions at higher pressures. The kinetic parameters corroborated the results obtained. For the systems with higher chemisorption, the effective activation energy values were higher, therefore the DCO values. In comparison, the pre-exponential factor showed opposite results, given slower reaction kinetics in these stages.