Continuous treatment of petroleum products in a tailor-made flow-through sonoreactor

Abstract

This research work focuses on treating typical petroleum products in terms of both desulfurization and cracking using ultrasonication. For desulfurization process, the ultrasound-assisted oxidative desulfurization (UAOD) method proves to be quite promising. Based on the optimal solution from a previous batch experimentation, a pilot flow-through sonoreactor was designed and built to investigate the effects of operating parameters such as input power, acid, type of feedstock and sonication time on sulfur removal efficiency in a system consisted of hydrogen peroxide as an oxidant, acetic acid as an oxidant promoter, tetraoctylammonium bromide as phase transfer agent (PTA) and Phosphotungstic acid as transition metal catalyst (TMC). Results showed the batch-phase removal efficiency of 61% at optimum conditions can increase to almost 80% in continuous-phase. Also, it was observed that increasing the power can improve the efficiency since it results in the increase in the concentration of free radicals entering the oxidation reaction. Continuous tests confirmed that elimination of acid can decrease the efficiency by an average of almost 26%, which affirmed the findings in literature and the fact that organic acid plays a dual role in the system., i.e., not only it reacts with oxidant to produce a powerful oxidizer known as peroxy acid, but also it helps sulfur removal through its extractive nature. Moreover, it was witnessed that increasing the sonication time up to 10 min, generally increases the sulfur removal; however, this behavior was somewhat different among different feedstocks. In this regard, the initial total sulfur content of the feed plays a key role. Results showed that feeds with higher sulfur content exhibit higher removal efficiencies under the same conditions. Also, it was concluded that sulfur removal from lighter fractions can be more efficient compared to heavier fractions under the same conditions. Also, the effect of UAOD on cracking of a commercial gas oil sample was studied. According to the results, the maximum reduction in kinematic viscosity due to UAOD process was 9.40% after 5 min of sonication and that its effect on viscosity was basically unpredictable for the gas oil. UAOD was not able to shift the distillation curve either. On the other hand, pure sonication of the gas oil sample reduced its kinematic viscosity by almost 13.5% after 5 min and was to some extent capable of cleaving the carbon-carbon bonds, thereby producing lighter products. However, results authenticated that far higher power should be supplied to experience tangible changes due to sonocracking.