STABILIZATION OF ASPHALTENES IN ALIPHATIC SOLVENTS USING ALKYLBENZENE-DERIVED AMPHIPHILES .2. STUDY OF THE ASPHALTENE AMPHIPHILE INTERACTIONS AND STRUCTURES USING FOURIER-TRANSFORM INFRARED-SPECTROSCOPY AND SMALL-ANGLE X-RAY-SCATTERING TECHNIQUES

In the preceding paper in this issue, the influence of the chemical structure of a series of alkylbenzene-derived amphiphiles on the stabilization of asphaltenes was described. In this paper. we present the results of using Fourier transform infrared (FTIR) spectroscopy and small-angle X-ray scattering (SAXS) techniques to study the interaction between asphaltenes and two alkylbenzene-derived amphiphiles, p-alkylphenol and p-alkylbenzenesulfonic acid. FTIR spectroscopy was used to characterize and quantify the acid-base interactions between asphaltenes and amphiphiles. It was found that asphaltenes could hydrogen-bond to p-dodecylphenol amphiphiles. The hydrogen-bonding capacity of asphaltenes was estimated to be 1.6-2.0 mmol/g of asphaltene. On the other hand, the FTIR spectroscopic study indicated that asphaltenes had a complicated acid-base interaction with p-dodecylbenzenesulfonic acid (DBSA) amphiphiles with a stoichiometry of about 1.8 mmol of DBSA/g of asphaltene. The UV/vis spectroscopic study suggested that asphaltenes and DBSA could associate into large electronic conjugated complexes. Physical evidence of the association between asphaltenes and amphiphiles was obtained by SAXS measurements. It was found that asphaltenes in an alkane solution with p-nonylphenol (NP) amphiphiles could be dispersed as well as they were dispersed in toluene. Due to the weak X-ray scattering of NP and weak asphaltene-NP association, the measured radius of gyration of NP-asphaltene colloids was only slightly larger than that of asphaltenes. The significant change of the asphaltene's SAXS profile in the presence of DBSA clearly verified the association between asphaltenes and DBSA in apolar media. The finding that DBSA could associate itself into reverse micelles suggested asphaltenes might be surrounded and stabilized by multilayers of DBSA molecules in apolar media. However, under a higher weight ratio of asphaltene to DBSA, the shortage of DBSA to form a stable steric layer for asphaltenes could cause asphaltenes to aggregate into large colloids.