الملخص الإنجليزي
One of the long-standing problems facing the petroleum refining industries is the presence of sulfur compounds in fuel oils. Sulfur causes many technical problems during refining and commercial use of fuel oil. Several novel deep desulfurization techniques have been utilized to achieve ultra-deep desulfurization. Among all the developed desulfurization technologies, extractive desulfurization (EDS) has shown promising results toward the removal of sulfur compounds from liquid fuels. The key to effective EDS processes is to find a relevant solvent with high affinity to sulfuric compounds. To minimize the economic and environmental effects of convectional solvents, recent studies have aimed to the development of sustainable alternative solvents. In this work, the extractive desulfurization of dibenzothiophene (DBT) and thiophene were investigated using a new tetrabutyl ammonium bromide (TBAB): Polyethylene glycol (PEG) deep eutectic solvents. The quaternary ammonium salt tetrabutyl ammonium bromide (TBAB) was used as the organic salt and Polyethylene glycol having average molecular weights of 200 and 600 (PEG200 and PEG 600) as hydrogen bond donors (HBD). The Central Composite Design (CCD) statistical approach was employed to analyze the experimental results and optimize the operating conditions. The solvents showed high sulfur removal efficiency of DBT and thiophene in simulated fuel. Using a solvent to fuel volume ratio of 1:1 (Vdes/V Fuel = 1:1), the extraction efficiency reached 82.40 % and 62.16% for DBT and thiophene respectively within the first extraction stage and at room conditions. Effect of solvent to volume ratio, time, temperature, initial concentration and speed of mixing on extraction efficiency were investigated. By increasing the solvent volume ratio (Vpes/V Fuel = 2:1) the extraction efficiency can reach up to 91.17 %and 77.83% for DBT and thiophene respectively. The results showed that increasing the speed of mixing has a great influence on the extraction efficiency.
The deep desulfurization of the simulated fuel was also carried out in multiple extraction stages. Performed experiments showed that 100% (DBT) and 95.15% (Thiophene) extraction efficiencies were achieved after three extraction stages only using a volumetric ratio of Vdes/V Fuel = 1:1. Optimal performance was achieved using two extraction stages with a volumetric ratio of Vpes/V Fuel = 3:1. Efficiencies of 100% and 97.79 % were achieved using these conditions. These represent the minimum number of extraction cycles so far reported using quaternary ammonium based eutectic solvents for the EDS process. Moreover, the desulfurization of real commercial diesel was studied and 46.75 % total sulfur removal from the diesel was achieved. Up to our knowledge, very little work has been reported on the effect of emulsification in the fuel-DES mixtures in the presence of an emulsifier. For this reason, the extractive desulfurization of dibenzothiophene (DBT) and thiophene was investigated in such systems. Furthermore, the effect of different process parameters such as temperature, speed of mixing, extraction time, and surfactants concentration on the emulsification extraction process were investigated. Surfactants addition to these systems showed noticeable enchantment on the extraction efficiency. Adding 10% of SDS to the (DES 1/fuel) mixture led to 2% increase on extraction efficiency of DBT and 8% increase on the extraction efficiency of thiophene. Additionally, the addition of different types of glycols was also investigated. These glycols were introduced to the mixture in different proportions and the performance of the extraction process follow the order: PEG 400 > PEG 200 > Dipropylene glycol > Triethylene glycol > Diethylene glycol. Finally, DESs were successfully regenerated and reused five times without significant loss of solvent activity. This is a very valuable and desirable result from an industrial point of view.
