(67d) The Case of the Missing Asphaltenes from the Naphthenic Froth Treatment Process

Asphaltenes are a complex polydisperse system, and the molecular structure, kinetic and thermodynamic properties vary within a crude oil sample. The effects of this polydispersity can be manifested in various ways. For example, the sizes of asphaltene clusters follow a power-law distribution, where larger asphaltenes exist in decreasing likelihood¹ and the largest are nearest their phase transition². Further, the double bonds equivalent of asphaltene molecules is inversely correlated to asphaltenes solubility³, and surface-active asphaltenes can be separated by adsorption onto inorganic or water interfaces⁴. Therefore, the isolation and investigation of the most impactful asphaltenes are pivotal for understanding the influence of asphaltenes on different phenomena. In this presentation, we will present evidence that a fraction of asphaltenes is lost during the naphthenic froth treatment process used in the oil sands industry. We used toluene to dilute two bitumen samples, one extracted by toluene and the other one extracted by naphtha, then titrated heptane into diluted bitumen solution to destabilize asphaltenes. The naphtha extracted bitumen needs higher heptane concentration to destabilize asphaltenes, which implies the poorly soluble asphaltenes are lost in the naphthenic froth treatment process. These “missing asphaltenes” are hypothesized to migrate to water-in-oil and inorganic clay interfaces, and are thus removed from the bitumen product. The effect of these processes on stabilizing water-in-oil emulsions is of critical concern to improve product quality and reduce corrosion concerns. Evidence for this hypothesis comes from observations on asphaltenes and solids co-aggregation, where co-aggregation clusters were cut by Focused Ion Beam and imaged by SEM. Nano-scale (20~200 nm) clay particles were found to be distributed in the precipitated asphaltene particles. Based on these findings, our objective is to isolate and investigate the missing asphaltenes, which may be the “tail end” of the size distribution or the poorly soluble asphaltenes. Based on our preliminary results, approximately less than 1% of the asphaltenes (equivalent approx. 0.1% of bitumen mass) are lost in the naphthenic bitumen extraction. To extract and characterize this “missing” fraction, we assembled a nano-filtration system to isolate the most unstable asphaltenes and the nano-scale inorganic solids these asphaltenes may associate with. The filtration process was operated under process conditions with a bitumen (B) to diluent (D, naphtha) ratio of D:B = 0.7 at 80 ËšC.

Reference

[1] Fenistein, D., and L. Barre. Fuel 80.2 (2001): 283-287.

[2] Zhao, Bei, and John M. Shaw. Energy & Fuels 21.5 (2007): 2795-2804.

[3] Clingenpeel, Amy C., et al. Energy & Fuels 31.6 (2017): 5933-5939.

[4] Jarvis, Jacqueline M., et al. Energy & Fuels 29.11 (2015): 7058-7064.