Abstract
This paper aimes at obtaining a kinetic model for coking reactions of heavy oils, such as Arabian Medium, Minas, Dun, Iranian heavy vacuum residues, decant and hydrogenated coal oils. Experiments were carried out for the temperature range from 390°C to 470°C. Products were fractionated into Benzene solubles (BS; Resin), Benzene insolubles-Quinoline solubles (BI-QS; Semicoke), and Quinoline insolubles (QI; Cokes). Semilogarithmic plots of BS on feed against the nominal reaction time (Fig. 1), indicated that the Resin could be composed of two kinetically different species, i.e., Resin1 (R1) and Resin2 (R2). The rate constant, k1, for the former species was estimated from the slope of the straight line in Fig. 1, whereas k2 for the latter species from the slope of the line on the semi-logarithmic plot of the remaining Resin. To assess the reaction steps, five mathematical models were examined. The other parameters, k3, k4 and k5 were calculated by fitting the experimental data to nominal reaction times and Arrhenius plots (Fig. 4). Based on the result the following generalised reaction model of heavy oil coking is proposed.
Resin1 (R1)→k1Semicoke(S)→k3Coke (C)
Resin2 (R2)→Volatile (V)
The rate constants, activation energies, frequency factors obtained are listed in Table 3. In addition, the above model was extended to the coking reaction of coal liquefaction.
Further, it was discussed that two species R1 and R2, which are formed during the heating-up period, might roughly correspond respectively to the heavy asphltenes turned to cokes, and to the light asphltenes or maltenes turned to volatile matters.
