Conversion of Arabian Light Crude Oil to Light Olefins via Catalytic and Thermal Cracking

The thermal and catalytic cracking of Arabian Light crude oil, which has a density of 34 degrees API, were evaluated in a fixed-bed microactivity test (MAT) unit between 550 and 650 degrees C. For the catalytic cracking, two catalysts were used, a steamed commercial MFI catalyst (M-cat) and an equilibrium FCC catalyst (E-cat). Thermal and catalytic cracking were compared at the same conversion, 34%, at 650 degrees C. For both, as the temperature increased, the yields of light olefins, LPG, dry gas, and coke increased, associated with a consistent decrease in heavy ends (LCO and HCO). The naphtha yield for catalytic cracking decreased as temperature increased; however, for thermal cracking, it was nearly constant. The superiority of catalytic cracking over thermal cracking for the propylene yield was interpreted in terms of mechanisms of free radicals and carbenium ions. Thermal cracking gave a higher yield of ethylene. At high temperature (650 degrees C) and catalyst to oil (C/O) ratio of 4, the olefins yield decreased in the order of M-cat (32.7 wt %) > E-cat (30.3 wt %) > thermal cracking (22.8 wt %). The highest yields of ethylene and propylene (10.9 and 15.7 wt %), achieved over M-cat at 650 degrees C, are attributed to shape selectivity and higher acidity. The naphtha yield for E-cat was much higher than for M-cat; for instance, at 550 degrees C it was 48.3 wt % for E-cat and 24.4 wt % for M-cat. This was attributed to diffusion limitations for M-cat. The effect of the C/O ratio on conversion and yields was also inspected, and the analysis showed that after a C/O ratio of 4, further increases had only a minor effect. Lastly, the effect of mixing E-cat and M-cat at different percentages was evaluated, and the investigation showed an optimum point at 58% M-cat, with the corresponding yields of ethylene and propylene at 10.7 and 19.2 wt %, respectively.