Scientists from Egyptian Petroleum Research Institute, Capital University (formerly Helwan University) and a few other Egyptian research centers have proposed a method for producing diesel fuel with very low sulfur content via ultrasound, hydrogen peroxide and special catalysts based on iron, cobalt and nickel oxides.
The problem with modern quality standards for diesel fuel is that they require almost complete sulfur removal, and the main industrial technology (hydrotreatment) struggles with that task. Hydrotreatment consists in treating the fuel with hydrogen at high temperatures and pressures. While this approach is effective at removing simple sulfur compounds, it can be less effective with more stable ones, such as dibenzothiophene. Plus, the process is energy-intensive and expensive. The new process requires much milder conditions, with reactions accelerated by ultrasound. It creates microbubbles that collapse in the liquid and generate localized intense heat and pressure, accelerating chemical processes.
The key element of this approach is the catalyst. In order to find the most effective option, the scientists synthesized several materials based on iron, cobalt and nickel oxides, after which they compared their performance. They found that the catalyst obtained with the shortest synthesis time yielded the best results. Since it has a larger surface area and smaller pores, it interacts better with sulfur compounds. However, if the catalyst takes longer to synthesize, the particles stick together, which means that the surface area decreases along with efficiency.
The scientists then moved on to selecting the process conditions. The optimal conditions turned out to be a temperature of about 60°C and a processing time of roughly 90 minutes, under which it was possible to remove approximately two-thirds of the sulfur. The researchers then added another stage – solvent extraction. Since sulfur compounds had already been oxidized at the previous stage, it became easier to extract them from the fuel, with overall purification efficiency rising to almost 90%.
At the next stage, the researchers intensified the effect by modifying the catalyst, coating it with a thin layer of polystyrene. This structure makes it possible to attract sulfur molecules, hold them in the pores and facilitate access for reactants at the same time. As a result, sulfur content was reduced from 21,700 parts per million to about 920 parts per million, a removal rate of over 95%.
In addition, the scientists demonstrated that the process takes place at a high rate with a relatively low energy barrier. Calculations showed an activation energy of about 13.7 kJ/mol, which was much lower compared to many conventional methods. This is linked to the fact that ultrasound and the catalyst accelerate the oxidation of sulfur compounds and their subsequent removal from the fuel.
Next, the Egyptian researchers plan to take steps to improve the practical applicability of their technology. This includes further optimization of the catalyst and process conditions to maintain high efficiency while reducing costs. Among other things, it is important to improve the catalyst structure and select reactants and operating modes that are better suited to industrial use.
