Imidazolium-based ionic liquids for asphaltene dispersion; experimental and computational studies

Abstract

Heavy and bituminous crude oils containing asphaltene are expected to compensate for the decline of conventional oil production in the upcoming days. Asphaltene precipitation is detrimental to petroleum processing owing to blockage of the wellbores and formation of tough emulsions that diminishes the recovered oil amount. As a result, the petroleum industry resorts to asphaltene dispersants to overcome these challenges. In this regard, ionic liquids (ILs) can be utilized as a green chemistry alternative to the surfactants to prevent asphaltene aggregation in the petroleum feed stream. Ionic liquids are environmental, recyclable, and non-corrosive candidates, which destabilize or breakdown water in oil (W/O) or oil in water (O/W) emulsions through dispersing or replacing asphaltene molecules at the interface. Also, ionic liquids containing long alkyl chains can be effective asphaltene dispersants owing to the formation of hydrogen bonding and π-π∗ interactions with asphaltene aggregates. In this work, different ILs salts and their modified Lewis-acid structure were synthesized by mixing iron (III) chloride with different halogenated alkyl imidazolium salts with yield% of 73.56, 72.9, and 71.12% respectively. The thermogravimetric analysis indicates the thermal stability of the synthesized ILs to 463 °C. The critical micelle concentration (CMC) and interfacial tension (IFT) were investigated at simulated reservoir conditions of high-pressure high temperature (HPHT). ILs exhibited CMC values at 1000, 800, and 600 ppm, while IFT values lie in the range of 3–8 mN/m at 298 K. ILs efficiency as asphaltene dispersants were assessed experimentally through viscometric and spectroscopic methods using 1000 ppm of asphaltene extract. The viscometric method displays asphaltene onset precipitation at 65% n-heptane after the addition of [(-C4H9-IL) FeCl4−] dispersant, while spectroscopic method asphaltene onset precipitation at 55, 60 and 75% after the addition of [(-CH3-IL) FeCl4−], [(-C2H5-IL) FeCl4−] and [(-C4H9-IL) FeCl4−], respectively. Molecular dynamics (MD) simulation was carried out to investigate the compatibility of ionic liquids as a function of asphaltene and crude oil molecules. The asphaltene molecules modeled as a continental model involves a dominant polyaromatic nucleus linked to peripheral substituted side chains. The computational results are in great compliance with the experimental ones.