Sulfur Extraction from Oil Using Ionic Liquids

Organosulfur compounds are amongst the most problematic components present in crude oil which has a direct influence on the performance of the refinery processes as well as during storage, transportation and separation. The presence of sulfur species in fuels are clearly a major issue in air pollution, airborne particulate emissions and endangering health public. The sulfur content of crude oil is an important characteristic which effects the oil price. Catalytic approaches for sulfur removal, such as hydrodesulfurisation (HDS), are the most commonly applied techniques. Aromatic S-compounds in diesel oil are however, difficult to remove completely by HDS. Therefore, alternative methods to HDS have been studied including oxidation, precipitation, extraction, adsorption, distillation and alkylation. In the current study, ionic liquids (ILs) have been used for the removal of thiophene (Th), benzothiophene (BT) and dibenzothiophene (DBT) by liquid-liquid extraction and polymerisation. The first stage of the study involved the investigation of the thermodynamics of thiophenic species partitioning into Deep Eutectic Solvents (DESs). It was shown that the extraction process depends on the size of S-compounds and the energy required to make holes in the networks of DESs molecules of suitable dimensions to fit the S-containing molecules. The second stage of the study used a 1:1 mixture of 1-butyl-3-methylimidazolium chloride (Bmim)Cl and FeCl3 for the extractive electropolymerisation of Th and BT from alkane layers. While the process could be carried out, the kinetics of polymer formation were too slow to make this a viable process. The final part of the work used a different composition (Bmim)Cl: 2FeCl3 to chemically remove sulfur containing compounds from alkane based liquids. It was shown that the rate of the chemical polymerisation reaction of Th is around 1000 times faster than electrochemical polymerisation. The technical aspects of the scale up were investigated and it was shown that recycling the catalyst was possible but not simple.