Effect of amphiphilic molecules on asphaltene precipitation

Abstract

The ability of amphiphilic molecules to stabilize crude oil by adsorption with asphaltenes is an active area of research. Based on the structure of amphiphilic molecules, one would expect these molecules to stabilize asphaltenes by creating physical dispersion and hindering the particles from aggregating. The purpose of this study is to investigate the relationship between degree of stabilization and pKa which provides important information on how acid-base reactions with alkylbenzenes stabilize asphaltenes at low alkylbenzene concentrations. In order to study how the strength of alkylbenzene basicity affects asphaltenes, several basic alkylbenzenes were used: nonylacetophenone (NNPN), octyloxybenzonitrile (OOBN), nonylphenol (NP), nonylaniline (NNAL), and dodecyloxybenzaldehyde (DDBD). The stability of asphaltenes in the presence of alkylbenzenes was measured in microscopy experiments. The pKa measurements of alkylbenzenes were performed in tetrahydrofuran using potentiometric titration. The results from microscopy experiments have demonstrated that the presence of amphiphilic molecules destabilizes crude oil because chemical adsorption is dominant at low alkylbenzene concentrations. The degree of destabilization was found to be in the order: DDBD > NNAL > NP > OOBN > NNPN. The pKa values of DDBD, NNAL, NP, OOBN, and NNPN are 8.06, 7.76, 6.47, 4.97, and 4.78, respectively. These findings suggest that there is a correlation between the pKa and the degree of destabilization; the weakest bases were the most destabilizing and the strongest bases were the least destabilizing.