Ultrasound assisted oxidative desulfurization (UAOD) is a promising technology, which can result in ultra-low sulfur fuels in order to reduce the environmental crisis. Most of the UAOD studies have been executed in the batch-mode systems. Comparing to ultrasonic-assisted process in batch-mode, the ultrasonic-assisted process in continuous mode of operation seems to be more beneficial because of its several advantages. Moreover, development of the different ultrasonic reactors in continuous flow causes generation of the wide potential in the area of sonochemistry which can help to introduce into industry. Hence, cylindrical continuous-flow system was introduced. In this system injection below the horn tip was employed as an efficient strategy to intensify the reaction rate and minimization of the catalyst consumption. Indeed, one of the decisive factors for increasing the efficiency of reactions in two-phase systems is to increase the contact area between the phases to attain more efficient exposure of the reagents. Since the maximum energy dissipation rate takes place near the horn tip owing to the much fluctuating component of the velocity, this region can be considered as “active zoneâ€. In addition, detection of more hydroxyl radicals (.OH) generation near the radiating surface rather than other zones demonstrated that this region also could be chemically active zones, as well. As a result, this zone could be opted as the location of introducing the feed and/or oxidant/catalyst into the reactor in which the maximum energy is dissipated. Diesel fuel as the oil phase with sulfur content of 1550 ppmw and an appropriate mixture of hydrogen peroxide and formic acid as the aqueous phase were used. Significant improvement on the sulfur removal was observed specially in lower sonication time in the case of dispersion method in comparison with the conventional contact between two phases. Furthermore the effect of nozzle number was examined. Ultimately, the flow pattern induced by ultrasonic device, and also injection of the aqueous phase were analyzed quantitatively and qualitatively by capturing the sequential images. A hydrodynamic parameter is introduced to evaluate the relative strength of the ultrasonic jet versus aqueous jet in the injection strategy system.
Combination of experimental and simulation methods can be applied to understand a process. Besides, the elaboration of the ultrasound reactor characterizations can be identified by simulation outcomes. Numerical simulation could be used as an efficient tool to investigate the hydrodynamic behavior and other related phenomena. It can be beneficial to provide some insights regarding the complex fluid behavior in the sonoreactor, which might be difficult to obtain with the experimental methods.
In the present study, a computational fluid dynamic (CFD) model was developed to investigate the hydrodynamic behavior and flow characteristics in a sonoreactor. The CFD results indicate that the physical and chemical effects associated with the ultrasonic field can contribute to the enhancement of the reaction and sulfur removal rates. However, the physical effects are predominant as compared to the chemical effects. Indeed, homogenous mixing and fine micro-emulsification as a consequence of the physical effects lead to increase the interfacial area and mass transfer rate between the aqueous and oil phases.
