Removal of Sulfur Compounds from Diesel/Crude Oil Using Extractive Liquid Membrane Contactor (ELMC) and Supported Ionic Liquid Membrane (SILM)

摘要

The feasibility of using an extractive liquid membrane contactor (ELMC) and supported ionic liquid membranes (SILMs) for the desulfurization of hydrocarbon streams, such as raw diesel and whole crude oil, was investigated in separate efforts. For each, the separation capability and mass transfer rate were studied using ionic liquid (IL) (n-butyl-3-methyl pyridinium methylsulfate) and other extractive organic solvents, such as furfural and light naphtha. The SILM study using n-butyl-3-methyl pyridinium methylsulfate to remove sulfurous species from hydrocarbons exhibited very low mass transfer coefficients (i.e., values of 8.75 x 10~(-7) to 2.1 x 10~(-4) kg/m~2.s were obtained for different membrane materials and pore sizes, and under different experimental conditions). This result is attributed to the diffusion of big molecules of sulfurous species, such as Dibenzothiophene (DBT), as indicated by the low value of the estimated diffusion coefficient of DBT in IL (on the order of 10~(-11) m~2.s) obtained. Consequently, the use of extractive liquids, such as furfural and naphtha, in the ELMC boosts the transfer rate of sulfurous species as compared to the use of IL, as indicated by the high value of the mass transfer coefficient (k) (i.e., values of 4.4 x 104 to 6.7 x 10~(-4) kg/m~2.s were obtained using different membrane materials and pore sizes, and under different experimental conditions). This is a result of the higher diffusion coefficient (on the order of 10~(-6) m~2.s) of sulfurous species in furfural and light naphtha when compared to that of ILs (on the order of 10~(-11) m~2.s). Furthermore, the mass transfer coefficient (k) showed significant dependence on the flow rate of both feedstock and extractive liquid streams, as the mass transfer coefficient of sulfurous compounds increased with the increase in the flow rate of either stream or both. The mass transfer resistance offered by the membrane is very significant, as clearly indicated by the increase in mass transfer coefficient with increasing membrane pore size. This suggests that the diffusion resistance is contributing significantly to the overall resistance of the transfer of the sulfur species from feedstock to extractive liquid streams. This therefore indicates that the membrane material is clearly not affecting the transfer rate of the sulfurous compounds. Furthermore, when furfural is used with crude oil as a feedstock, the fouling on the membrane surface from the crude oil side is significant, which limits the transfer rate. Light naphtha is more promising as an extractive liquid for the reason that it transfers under the osmotic pressure difference to the whole crude oil side, which prevents fouling and therefore promotes faster diffusion of sulfurous species.