Separation of Archipelago- and Continent-Type Asphaltenes on Ultrafiltration Membranes

Asphaltenes, which are macromolecular compounds contained in heavy oils, tend to aggregate and precipitate, thereby causing a number of problems during oil transportation and refining. The tendency toward aggregation is primarily manifested by molecules with the continental architecture, while asphaltenes with the archipelago molecular structure, on the contrary, contribute to the stability of the petroleum fluid. Selective removal of the continental asphaltene fraction from the oil reduces deposit formation and viscosity, thereby mitigating the problems in oil transportation, storage, and processing. In this study, the possibility of using polyacrylonitrile membranes for the selective separation of continent type asphaltenes prone to aggregation from their archipelago molecules has been explored. For this purpose, the filtration separation of solutions of asphaltenes and fuel oil in toluene has been studied using membranes with a pore size larger than the size of asphaltene molecules. It has been shown that during filtration through such membranes, agglomerates of molecules rather than individual species are retained. With a relatively low total membrane rejection of 35–67%, this makes it possible to effectively separate continental asphaltenes prone to agglomeration, for which the rejection reached 90%, from the archipelago-type molecules. The maximum difference between the membrane rejections of the continent and archipelago molecules has been observed at low concentrations of asphaltenes, so that the most efficient separation of the components can be achieved. At the same time, significant membrane fouling has been observed in the case of filtration of solutions of M-100 fuel oil in toluene with a concentration of 2–10 g/L. This effect depends on the concentration of dissolved substances, and the decline in membrane permeability is significantly slowed down by decreasing the fuel oil content. At low concentrations, the decrease in flux through the membranes during filtration did not exceed 18%, providing permeate fluxes of more than 286 L/(m2 h).