Study on the Aggregation Behaviors of Asphaltene Derived from Low Temperature Coal Tar in Organic Solvents by Absorbance and Fluorescence Spectroscopy

The aggregation behaviors of asphaltene derived from low temperature coal tar (CTA) in tetrahydrofuran (THF) and carbon tetrachloride (CCl4) solvents have been investigated by employing FTIR, absorption and fluorescence spectroscopy (excitation, emission and synchronous spectroscopy). The results indicate that CTA molecule mainly consists of 2-4 rings fused aromatic nucleus and contains multiple chromophores and fluorophores. It presents strong propensity to aggregate. CTA presents similar aggregation behaviors in the two used organic solvents. The concentration of CTA solutions has great influence on its aggregation performance. CTA exists as monomer species in very dilute solution with the concentration lower than similar to 10 mg/L. The consistent result has been inferred from the analysis of excitation, emission and synchronous spectra that the onset aggregation of CTA occurs at concentration of similar to 25 mg/L. With the increasing of concentration, CTA aggregates gradually and the smaller aggregates form into larger aggregates at higher concentration. CTA exist as variously aggregated species in THF and CCl4 solutions at higher concentrations. In addition, the larger CTA aggregates show strong fluorescence quenching effect.