Supported ionic liquid membrane and liquid–liquid extraction using membrane for removal of sulfur compounds from diesel/crude oil

The feasibility of using liquid–liquid extraction with membrane (LLEM) and supported ionic liquid membranes (SILMs) for the desulfurization of hydrocarbon streams, such as raw diesel and whole crude oil, was investigated separately and for each, separation capability and mass transfer rate were studied. The SILM study using ionic liquid (IL) to remove sulfurous species from hydrocarbons exhibits very low mass transfer coefficients. However, the use of extractive liquids, such as furfural and naphtha, in LLEM boosts the transfer rate of sulfurous species as compared to IL as indicated in the high value of mass transfer coefficient (k). Furthermore, the mass transfer coefficient (k) shows significant dependence on the flow rate of both feed stock and extractive liquid streams, as the mass transfer coefficient of sulfurous compounds increased with increase in the flow rate of either stream or both. The mass transfer resistance offered by the membrane is also significant as clearly indicated by increase in mass transfer coefficient with increasing membrane pore size. In addition, when furfural is used with crude oil as feed, the fouling on the membrane surface from the crude oil side is significant, which limits the transfer rate. However, light naphtha is more promising to act as an extractive liquid as it transfers under the osmotic pressure difference to the whole crude oil side, which prevents fouling and thus promotes faster diffusion of sulfurous species.