Free Radical and Cationic Addition due to Clay Minerals Found in Bitumen Froth at 250 °C Probed with Use of α-Methylstyrene and 1-Octene

Abstract

Following previous evidence that hydrothermal treatment of bitumen froth does not lead to bitumen upgrading at 250 °C and promotes viscosity increase, the current study explores the free radical and cationic reactivity of clay minerals found in bitumen froth in promoting heavier material formation through addition reactions. The current investigation employed α-methylstyrene (AMS) and 1-octene as probe molecules instead of bitumen froth, and their conversion at 250 °C in the presence of clay minerals kaolinite and illite was studied in batch reactors. Thermal conversion of AMS and 1-octene at 250 °C in the absence of minerals was observed to be low. In the presence of clay minerals, not only the conversion of AMS and 1-octene was increased but also reactions such as dimerization of AMS and alkylation of 1-octene and toluene (used as solvents) were mainly promoted, leading to heavier product formation. Double-bond isomerization of 1-octene and cumene formation from AMS was side reactions that were also promoted by the clay minerals. Suppression of mineral-related conversion by pyridine and selectivity to different reaction products that enabled differentiation between free radical and cationic reaction pathways indicated that the mineral-related conversion was predominantly cationic in nature. Using the reactions in the presence of minerals and pyridine as surrogates for alkaline bitumen froth, it was concluded that even under alkaline conditions, minerals could promote heavier material formation through cationic addition.

Visbreaking of Bitumen Froth: Influence of Minerals, Water, and Solvent on the Physicochemical Changes in the Bitumen Phase

“…Subsequently, it was confirmed that cationic conversion due to clays, despite the slightly alkaline conditions, was definitely a contributing factor. 21 As anticipated, visbreaking is very effective at reducing viscosity but does not have a big impact on density changes. The density reduction after visbreaking (Table 13) reached low levels of 1.3%−3.5% at 25 °C, compared to the density of the untreated bitumen.…”

“…Some potential explanations for the effects of water and/or solids on the viscosity increase included the dissolution of lighter polar compounds into water, the formation of carboxylate ions, free radical polymerization, and acid-catalyzed addition reactions. Subsequently, it was confirmed that cationic conversion due to clays, despite the slightly alkaline conditions, was definitely a contributing factor …”

“…Polymerization addition reactions are reportedly enhanced in the presence of both Lewis and Brønsted–Lowry acids, which are found in clay structures such as kaolinite, which was found to be abundant in the froth used in this study . It has been reported that heavier materials can be formed during thermal treatment in the presence of clays via acid-catalyzed addition reactions, including dimerization of alphamethylstyrene and 1-octene . These reactions were found, despite the slight alkaline nature of the froth.…”

“…61 It has been reported that heavier materials can be formed during thermal treatment in the presence of clays via acid-catalyzed addition reactions, including dimerization of alphamethylstyrene and 1octene. 21 These reactions were found, despite the slight alkaline nature of the froth. In this regard, acid-catalyzed addition over clays during bitumen visbreaking in the presence of mineral solids, followed by the migration of the formed heavier compounds into the bitumen phase, could be a possible explanation for the increased viscosity and density observed for the systems containing solids.…”

“…More recently, it was reported that kaolinite and illite, two clay minerals in bitumen froth, caused predominantly cationic conversion at 250 °C. 21 The present study aimed to investigate the role of water, minerals, and solvent dilution on the physicochemical changes in the bitumen phase during froth visbreaking. The main objectives of this study were (1) to identify whether minerals and water can improve bitumen quality during upgrading by lowering its viscosity and density and (2) to study the effect of froth dilution with a paraffinic and a naphthenic solvent on the changes in bitumen properties during visbreaking.…”