Evaluation of the Effectiveness of Inhibitors for Middle Eastern Asphaltenes by Quartz Crystal Microbalance with Dissipation

In times of increasing crude oil demand, enhanced oil recovery methods, such as CO2 flooding, are gaining interest as alternative approaches to more efficient oil extraction. In conjunction with this technology, which inevitably affects the oil chemistry, stands the pressing issue of asphaltene precipitation, which results in significant increases in operating expenses for these operations. Here, we report details of an analytical protocol that uses quartz crystal microbalance with dissipation module (QCM-D) for testing the immediate- and long-term effects of chemically modified inhibitors against asphaltene deposit growth onto asphaltene-coated carbon steel, a situation that is often encountered in oil production equipment. The inhibitors were tested within a large concentration range on model solutions of different Middle Eastern asphaltene samples. Unlike the traditionally and commonly used precipitation test, QCM-D provides accurate and time-dependent information on physicochemical processes, such as adsorption, removal, and inhibition, onto/from a desired surface within a single experiment. The results indicate that the inhibitor chemistry and, particularly, the electronic properties of the functional groups in the inhibitor molecules are central to their performance. Specifically, while non-Bronsted-acid-type additives with electron-withdrawing functional groups are ineffective toward removal of previously adsorbed asphaltenes, complex Bronsted-acid-type molecular mixtures having electron-withdrawing functional groups remove deposits at very low concentrations. However, Bronsted-acid-type additives having electron-withdrawing functional groups can also aggravate deposition above a certain concentration threshold, which is not the case for the non-Bronsted-acid-type additives. Surprisingly, the addition of a second electron-withdrawing functional group to an already electron-poor Bronsted-acid-type inhibitor was found to have an adverse effect on the inhibitor's performance. It is also shown that single-component inhibitors can compete with multicomponent systems in removal; however, they are less effective in prevention of precipitation after the removal.