Microwave-assisted Petroporphyrin Release from Asphaltene Aggregates in Polar Solvents

Abstract

This work presents an efficient approach for the primary separation of the petroporphyrin component from asphaltene aggregates. The n-pentane asphaltenes separated from the vacuum residue of Canadian oil sands bitumen were used as the feedstock. The release behavior of petroporphyrins from feed asphaltenes in polar solvents with the assistance of microwave irradiation was investigated. UV–vis spectroscopy was utilized to calculate the petroporphyrin release efficiency (PRE). The effects of asphaltene concentrations and solvent properties on the PRE were discussed. Results show that, under the microwave irradiation, asphaltenes could be rapidly separated into soluble and insoluble fractions. The solubles are enriched with vanadyl porphyrins, while the insolubles present only weak absorption of nickel porphyrins at proper asphaltene concentrations. The dispersion force (fd) of solvents has a strong correlation with the PRE. Under the optimized conditions of the methanol/toluene volume ratio of 2:1, the microwave time of 10 min, and the asphaltene concentration of 0.08 g/L, the PRE can reach up to 45%. Compared with the traditional solvent extraction method, the PRE of this new method is improved prominently. The possible mechanism of selective activation of petroporphyrin motivated by the microwave irradiation and the formation of asphaltene vesicles is proposed. This work could provide a more efficient technique to purify petroporphyrins from asphaltenes and could give insight into the interactions between petroporphyrins and asphaltene aggregates.