Study On Preparation And Extractive Desulfurization Performance Of RTIL's

Ionic liquids (ILs) are defined as pure compounds consisting of cations and anions, which melt below 100℃and therefore are also called low temperature molten salts or room temperature ionic liquids (RTIL's). ILs have been widely used as green solvents, suitable for a range of organic and polymeric synthesis and separation processes. The research of ILs used in extractive desulfurization of fuels is attracting increasing attention recently.Firstly, five kinds of ILs, [bmim]TBP, [bmin]PF6, [bmim]BeS, [bmim]BF4, and [bmim]AlCl4 were synthesized and characterized by IR and NMR spectrums.Secondly,the desulfurization mechanism using ILs was described based on intermolecular force theory and valence bond theory. The extractive desulfurization process using ILs follows a pure physical mechanism. The anions in ILs possess significant impact on the extraction properties of the ILs. If the central atoms of the anions have empty 3d orbitals with the similar energy level to 2p orbitals in carbon atom, the anions could form feedbackπ-bond with the delocalizedπ-bond in the molecules of thiophenes. Hence the selectivity of the extractive desulfurization process using ILs could be enhanced and higher desulfurization efficiency could be achieved. The anions with P as the central atom having a coordination number less than 6 should be chosen for the ILs. From the extraction mechanism of ILs, it could be predicted that ILs have high selectivity to thiophenes. With ILs as the extractants, thiophenes in fuels could be well removed and deep desulfurization of fuels could be reached.Finally, the extractive desulfurization performance of the ILs was investigated experimentally. With benzothiophene (BT)/octane and dibenzothiophene (DBT)/ octane as the model systems, the extraction conditions and their effect on desulfurization efficiency and the selectivity were estimated. Experimental results confirmed that the extraction process equilibrated within 2 minutes and the thermal effect during the extraction process using [bmim]TBP IL was quite insignificant. So room temperature was chosen in the rest experiments. The distribution coefficients of BT and DBT between [bmim]TBP IL and octane were 2.0 and 1.7 respectively. The desulfurization ratio of single stage extraction with a solvent/oil ratio 1:1 was 67% and 62.9%. The desulfurization ratio of the five stage extraction with a solvent/oil ratio 1:1 could reach above 95%, and the sulfur content could be reduced to 50ppm.