Metal porphyrin occlusion: Adsorption during asphaltene aggregation

Abstract

ABSTRACTMetal compounds such as vanadyl and nickel porphyrins present in crude oils are associated to the most polar fraction defined as asphaltenes. The amount and kind of these compounds in the crude oil depend of the variations in origin, maturity, pressure, and temperature. During the asphaltene colloid formation the metal porphyrins could be trapped, occluded, or adsorbed, protecting these compounds from oxidation or chemical degradation. In this work the authors induce the aggregation of asphaltenes by changing the solubility parameter of the media in presence of metal porphyrins. UV-vis absorbance is used to monitored asphaltene aggregation at 350 nm to follow the variations in asphaltene aggregation and 405 nm to follow the porphyrin Soret band. The results showed that more than 50% of the porphyrins were trapped inside the asphaltene aggregate and posterior re-dissolution of the aggregates in toluene showed very low release of the porphyrins, demonstrating the strong interaction between the porphyrin and asphaltenes during the aggregation.