Continuous-flow ultrasound assisted oxidative desulfurization (UAOD) process: An efficient diesel treatment by injection of the aqueous phase

Sono-oxidative desulfurization of fuels using heterogeneous and homogeneous catalysts: A comprehensive review

Recently, environmental pollution has increased significantly due to petroleum-based fuels widely used in vehicles. This environmental pollution is mainly due to the acidic SO₂ gas generated by the combustion of fuels and emitted into the atmosphere. SO₂ gas causes not only acid rain but also corrosion of metal parts of engines in vehicles. In addition, it functions as a catalyst poison in catalytic converters in exhaust system. Due to these damages, strict regulations have been introduced to reduce the amount of sulfur in fuels. As of 2005, the permissible amount of sulfur in diesel fuels in Europe and America has been limited to 10 and 15 ppm by weight, respectively. Due to the decreasing oil reserves in the world, high viscosity petroleums containing high sulfur and heavier fractions (i.e., low-quality oils) are increasing, thus making desulfurization difficult and leading to high costly process. Since time and economic loss are very important today, these two terms have to be reduced to a minimum. Recently, ultrasound wave in ODS shown as an alternative to HDS is utilized to further increase desulfurization in shorter times. Ultrasound wave locally creates high temperatures and high pressures (hot-spot theory) in liquid, causing the desulfurization reaction to accelerate further. In this review, the advantages and difficulties of oxidative desulfurization, the economics of ultrasound-assisted oxidative desulfurization are summarized and recommendations for improving the process are presented.

Insights to the oxidative desulfurization process of fossil fuels over organic and inorganic heterogeneous catalysts: advantages and issues

Strict environmental laws have been put in place around the world to reduce the amount of sulfur in the fuel to reduce the emissions of harmful gases from fuel combustion and improve air quality. Therefore, extensive researches have been undertaken to devise effective processes or to improve the desulfurization processes. Among the desulfurization processes, the oxidative desulfurization (ODS) process is a promising method to achieve very low and near-zero sulfur content of the fuel. In this process, sulfur compounds are converted to the corresponding sulfone by a catalyst and in the presence of an oxidant. The obtained compounds by polar solvents or adsorbents are removed from the fuel. In recent decades, extensive studies have been carried out on the catalysts used in the oxidative desulfurization process. In this review, a comprehensive survey has been performed on heterogeneous catalysts used in the oxidative desulfurization process. According to the reported researches, the heterogeneous catalysts used can be divided into five groups: ionic liquids, carbon materials, polyoxometalates, transition metal oxides stabilized on porous solid substrates, and metal-organic frameworks. The proposed mechanisms with different catalysts have also been studied in this work.

Study on ultrasound-assisted oxidative desulfurization for crude oil

The existence of sulfur compounds in crude oil will bring many problems such as corrosion, catalyst poisoning and pollution to the petroleum processing process. Therefore, how to reduce the sulfur content as much as possible in the process of crude oil processing has become an important research topic in the petroleum processing industry. In this paper, ultrasonic-oxidative desulfurization is studied. The effects of reaction temperature, reaction time, amount of oxidant and demulsifier on desulfurization rate are investigated. And the effect of oxidative desulfurization and single oxidative desulfurization under ultrasonic treatment are compared. It is found that the addition of ultrasonic treatment can enhance the desulfurization effect of desulfurizer, the desulfurization efficiency can be increased by about 10% under ultrasonic treatment (100 W, 70 kHz); ultrasonic wave plays an auxiliary role in the system, it can promote heterogeneous reactions, improve the activity of oxidants, and promote the degradation of macromolecular compounds. Finally, physical desulfurization, chemical desulfurization and biological desulfurization technologies are compared.

Ultrasound assisted oxidative deep-desulfurization of dimethyl disulphide from turpentine

A promising approach of ultrasound assisted oxidative desulfurization (UAOD) was studied for deep desulfurization of simulated sulphated turpentine containing dimethyl disulphide (DMDS) as model pollutant. The effect of ultrasound parameters such as power (80-120 W) and duty cycle (50-80%) as well as operating conditions as initial concentration (50-100 ppm), volume (100-300 ml) and temperature (28 °C as ambient condition, 50-70 °C) on the extent of desulfurization have been studied. The effect of addition of various oxidizing agents such as hydrogen peroxide over the range of 3-18 g/L, Fenton reagent by varying FeSO₄ loading from 0.75 g/L to 1.75 g/L at constant H₂O₂ loading and titanium dioxide (loading over the range 1-4 g/L) in the presence of ultrasonic horn have also been investigated at laboratory scale. The addition of oxidizing agents in presence of ultrasound enhanced the extent of DMDS removal. The extent of desulfurization was found to be remarkably low for individual approaches as compared to combination approaches of US/oxidizing agents. The kinetic analysis revealed that oxidation follows first order kinetics. A significant increase in cavitational yield was observed for combination approach of US/H₂O₂/TiO₂ (5.78 × 10^-9 g/L) compared to individual ultrasound approach (2.04 × 10^-9 g/L). Under best conditions of 120 W power, 70% duty cycle, 50 ppm initial concentration, 15 g/L H₂O₂ loading and 4 g/L TiO₂ loading, 100% desulfurization was obtained at 23.19 Rs/L as the treatment cost. Based on the obtained results it can be concluded that US/H₂O₂/TiO₂ approach is highly efficient desulfurization technique for deep desulfurization of simulated sulphated turpentine.

Intensification of diesel oxidative desulfurization via hydrodynamic cavitation

A Hydrodynamic Cavitation Assisted Oxidative Desulfurization (HCAOD) process was applied for treatment of diesel fuel feedstock using hydrogen peroxide and formic acid as the oxidant and catalyst, respectively. Investigation on the effect of main process variables including pressure drop (3-6 bar), time of treatment (10-30 min) and formic acid to oxidant molar ratio (n_A/n_O) (1-5), was performed through applying Response Surface Methodology (RSM) based on Box-Behnken design. Single and interactive effects of the parameters were recognized. A remarkable 95% extent of desulfurization at optimum conditions with HC pressure drop of 4.2 bar, acid to oxidant ratio (n_A/n_O) of 3.2 at 29 min was achieved. The results were also compared to an oxidation system without the aid of hydrodynamic cavitation. Accordingly, HCAOD can be considered as a promising treatment scheme for intensification of diesel oxidative desulfurization.

A novel multi-probe continuous flow ultrasound assisted oxidative desulfurization reactor; experimental investigation and simulation

In this work, a cylindrical multi-probe continuous flow system with different injection strategies was exploited to study ultrasound assisted oxidative desulfurization process. The effects of nozzle number, nozzle diameter, ultrasonic power and volumetric flow rate (residence time) on the desulfurization efficiency of the diesel fuel were investigated. It was found that the sulfur removal increases by increasing the nozzle diameter when the flow rate is fixed. Sulfur removal was increased by increasing the residence time, for all types of the nozzles. Injection of the aqueous phase below the horn tip in the active zone provides the conditions by which the higher interfacial area between the phases and thus greater conversion rate can be obtained. The results indicated that over 97% sulfur removal was achieved using the double-nozzle injection with nozzle diameter of 1.5 mm, residence time of 15 min, electrical power of 277.2 W and volumetric flow rates of the aqueous and oil phases 48.89 and 244.44 mL/min, respectively. The simulation results showed that choosing a proper injection strategy has an impact on the hydrodynamic and flow pattern induced by ultrasonic field and in turn could effectively influence the mixing of the two-immiscible phases. A more uniform distribution of the aqueous-phase volume fraction was observed in the system with double-nozzle injection in comparison with the single nozzle injection.

Investigations in enhancement biodesulfurization of model compounds by ultrasound pre-oxidation

In this study, complicated model sulfur compounds in crude oil were biodesulfurized in a batch process by microbial consortium enriched from oil contaminated soil. Dibenzothiophene (DBT) was selected as model sulfur compounds. Ultrasonic radiation was used to pre-oxidize the model sulfur compounds before the biodesulfurization (BDS) process. The enhancement mechanism of ultrasound pre-oxidation (UPO) on the biodesulfurization of DBT was investigated. The effects of initial conditions on the biodesulfurization of DBT in UPO/BDS system such as solution initial pH, DBT initial concentration, sulfur source, biocatalyst initial concentration, and incubation temperature were discussed. The results show that the application of UPO before BDS procedure significantly improved the efficiency of the biodesulfurization and allowed sulfur removal in shorter time through oxidizing DBT to DBT sulfone, resulting in shortening the "4S" pathway for biodesulfurization from 4 steps to 2 steps, enhancement in reaction velocity and enzyme-substrate affinity as well as reduction in substrate inhibition. The concentration of 2-HBP increased fast with the use of ultrasound pre-oxidation, which was dependent on solution initial pH, DBT initial concentration, sulfur source, biocatalyst initial concentration, and incubation temperature.

Hydrodynamic and mass transfer investigation of oxidative desulfurization of a model fuel using an ultrasound horn reactor

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 researches have been conducted with the experimental approaches. In the present study, a computational fluid dynamic (CFD) model has been developed to investigate the hydrodynamics as well as the reactions involved in a sonoreactor. The 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 caused by the physical effects lead to increase the interfacial area and mass transfer rate between the immiscible aqueous and oil phases. The dibenzothiophene concentration predicted by the simulation was in a reasonably good agreement with the corresponding experimental data. Another key hydrodynamic parameter induced by ultrasonic field was turbulent kinetic energy, which can play an important role in the sulfur removal rate. The results indicate the higher desulfurization efficiency has been attained at the regions with the higher velocity fluctuations.

Current knowledge and potential applications of cavitation technologies for the petroleum industry

Technologies based on cavitation, produced by either ultrasound or hydrodynamic means, are part of growing literature for individual refinery unit processes. In this review, we have explained the mechanism through which these cavitation technologies intensify individual unit processes such as enhanced oil recovery, demulsification of water in oil emulsions during desalting stage, crude oil viscosity reduction, oxidative desulphurisation/demetallization, and crude oil upgrading. Apart from these refinery processes, applications of this technology are also mentioned for other potential crude oil sources such as oil shale and oil sand extraction. The relative advantages and current situation of each application/process at commercial scale is explained.

Ultrasound-assisted oxidative desulfurization and denitrogenation of liquid hydrocarbon fuels: A critical review

Nowadays, a continuously worldwide concern for development of process to produce ultra-low sulfur and nitrogen fuels have been emerged. Typical hydrodesulfurization and hydrodenitrogenation technology deals with important difficulties such as high pressure and temperature operating condition, failure to treat some recalcitrant compounds and limitations to meet the stringent environmental regulations. In contrary an advanced oxidation process that is ultrasound assisted oxidative desulfurization and denitrogenation satisfies latest environmental regulations in much milder conditions with more efficiency. The present work deals with a comprehensive review on findings and development in the ultrasound assisted oxidative desulfurization and denitrogenation (UAOD) during the last decades. The role of individual parameters namely temperature, residence time, ultrasound power and frequency, pH, initial concentration and types of sulfur and nitrogen compounds on the efficiency are described. What's more another treatment properties that is role of phase transfer agent (PTA) and solvents of extraction step, reaction kinetics, mechanism of the ultrasound, fuel properties and recovery in UAOD are reviewed. Finally, the required future works to mature this technology are suggested.