Inhibition of Asphaltene Precipitation by Ionic Liquid Polymers Containing Imidazole Pendants and Alkyl Branches

High polar asphaltenes are easy to precipitate and deposit in transportation pipelines and subsequent processing. Adding chemical polymer inhibitors is an effective method to inhibit asphaltene aggregation. In this work, ionic liquid polymers containing the imidazole cation and/or alkyl branches were synthesized by free radical polymerization, and anions such as the bis(trifluoromethane)sulfonimide ion (TFSI-) and [phosphoric acid bis(2-ethylhexyl)] anion (DEHP-) were introduced by substitution. The chemical structure of asphaltenes was analyzed by Fourier transform infrared spectroscopy, H-1 nuclear magnetic resonance, elemental analysis, and time-of-flight spectroscopy. It is found the asphaltene has short side chain, a low H/C, and a high polarity. The precipitation inhibition of asphaltenes and the rheological behaviors of crude oil in the presence of ionic liquid polymers were studied by measuring the initial precipitation point (IPP), turbidity, particle size distribution, and morphology of asphaltenes in model oil. In the presence of same anions (Br-, TFSI-, and DEHP-), with the increase of length of imidazole pendant branches, the IPPs increase. However, when the chain length is close to the poor solvent n-heptane, the IPP first rises, then descends. The copolymer bearing both imidazole pendants and alkyl branches can increase the IPPs. Alkyl branches can inhibit the aggregation of asphaltenes by forming layers surrounding the asphaltene aggregates. With the reduction of asphaltene agglomeration, the turbidity and particle size decrease. For polymers bearing both the imidazole pendants and alkyl branches, upon the increase of anionic electronegativity, the interactions between asphaltenes are destroyed because strong hydrogen bonding is generated between the asphaltene and the ionic liquid polymer. DEHP- has strong electronegativity and high hydrophobicity. The polymer with DEHP- and alkyl branches can increase the IPP by 30%, reduce the turbidity of model oil by 50%, reduce the size of asphaltene by 80%, and decrease the viscosity of crude oil by 36.8% at 50 degrees C.

Automated summary

In this work, ionic liquid polymers containing the imidazole cation and/or alkyl branches were synthesized to inhibit the precipitation and deposition of asphaltenes. The alkyl branches can inhibit the aggregation of asphaltenes by forming layers, and the ionic liquid polymers can reduce the precipitation of asphaltenes by destroying the interactions between them and reducing the particle size. Additionally, the polymer with DEHP- and alkyl branches is an effective asphaltene inhibitor.