Hydrophobic Deep Eutectic Solvent and Glycolipid Biosurfactant as Green Asphaltene Inhibitors: Experimental and Theoretical Studies

Precipitation of asphaltenes in porous media undesirably influences oil recovery due to pore clogging and subsequent wettability alteration. This study reports, primarily, the potential application of two environmentally-friendly chemicals, a hydrophobic deep eutectic solvent (DES) and a glycolipid biosurfactant known as rhamnolipid (RL), as asphaltene precipitation inhibitors. While DES was prepared by mixing glycerol, as its hydrogen bond donor (HBD) component, with methyltrioctylammonium chloride, as its hydrogen bond acceptor (HBA) component, RL was extracted from the native strain of Pseudomonas aeruginosa. The inhibition potential of these green chemicals was then characterized from experimental and theoretical perspectives. In the experimental part, the inhibition efficacy of both chemicals was initially confirmed based on the precipitation experiments. Next, filtration and optical microscopy provided evidence of chemical interaction between inhibitors and asphaltenes. To further illustrate the structural alteration of asphaltenes recovered from the inhibitor-included solutions, Fourier transform infrared and elemental analyses were conducted. Results revealed that the dominant inhibition mechanism of DES was the cracking/dissolution of asphaltene particles compared to peptization in the case of RL. Increased oxygen content and H/C ratio plus the decreased aromaticity index of the asphaltenes recovered from the DEScontaining solution compared with those of the raw asphaltene were indications of the dissolution mechanism. In addition, comparing the performance of synthesized chemicals with a conventional inhibitor, dodecylbenzene sulfonic acid, revealed the preferable performance of the chemicals. In the theoretical part, the propensity of asphaltene precipitation was studied using the surface energy concept based on the extended DLVO theory. The results showed that acid-base interactions among different subcomponents of the surface energy played a key role in retarding asphaltene precipitation by decreasing the attraction force between similar asphaltene particles, further supported by the concepts of work of cohesion and adhesion.

Automated summary

This study demonstrates the potential of using environmentally-friendly chemicals, a hydrophobic deep eutectic solvent (DES) and a glycolipid biosurfactant known as rhamnolipid (RL), as asphaltene precipitation inhibitors. Experimental results confirm that these green chemicals interact with asphaltenes and alter their structure. Additionally, theoretical analysis based on the extended DLVO theory suggests that acid-base interactions play a key role in retarding asphaltene precipitation.