No abstract

Bitumen recovery from oil sands was found to severely deteriorate at operating temperatures lower than a “critical” value, suggesting a substantial change in one or more key process variables. A sharp increase in bitumen viscosity at lower temperatures has been considered as the major contributor to such deterioration. On the basis of the fact that the addition of selected chemicals does improve bitumen recovery without affecting bitumen viscosity, there must be other physicochemical factors that affect bitumen recovery and undergo a sharp change with temperature. In the present study, the interaction and adhesion forces between bitumen and sand grains or clays in water were measured as a function of temperature using an atomic force microscope. The results show that the measured adhesion force between clay and bitumen decreases with increasing temperature until a critical value of about 32−35 °C, above which the adhesion force disappears. As the adhesion force between clay and bitumen controls clay slime coating on bitumen surface and subsequently bitumen aeration, increase in the adhesion force with decreasing processing temperature would lead to slime coating and lower bitumen recovery. The effect of a chemical additive, methylisobutyl carbinol (MIBC), on the colloidal forces was also studied. The results show that MIBC addition can reduce the adhesion force between clay and bitumen, thus facilitating bitumen aeration.

Atomic force microscopy (AFM) was used to measure the surface forces between a silicon nitride AFM tip and a deposited layer of Athabasca bitumen; the measurements were carried out in pure water (pH 6.0–6.5) and 1 mM KCl solution (pH 9). An AFM pyramidal‐shaped tip was moved stepwise using an operator‐controlled offset (10 nm per step) and the tip‐bitumen colloidal forces were measured at each location. Surface charge densities at the bitumen‐water interface were calculated from the measured colloidal forces using a theoretical model that combined both electrostatic and van der Waals forces for a conical tip‐flat substrate system. Fitted values of the bitumen surface charge density ranged from –0.002 to –0.004 C/m2 in water (pH 6.0–6.5), and –0.005 to –0.022 C/m2 in KCl solution (pH 9); the variation of local charge density along the bitumen surface appeared random. Bitumen surface potentials were also calculated from the surface charge densities using the Graham equation; the values ranged from –90 to –130 mV in water, and –45 to –110 mV in KCl solution. This study suggests the presence of bitumen surface domains of different surface charge densities/surface potentials. The domains are estimated to have characteristic sizes of 20 to 40 nm or less.

in Wiley InterScience (www.interscience.wiley.com).A temperature-sensitive polymer, poly(N-isopropylacrylamide) [poly(NIPAM)], was tested to flocculate kaolinite clay suspensions. Settling tests at both room temperature and 408C were carried out. The results show that settling at 408C resulted in significantly higher settling rates and smaller sediment volumes. This behavior indicates that the polymer molecules changed from a stretched structure to a coil-like conformation with increasing temperature. It is the change in conformation that induced more compacted flocs, thus resulting in faster settling. To understand the role of temperature in the flocculation, the long-range interaction and adhesion forces between kaolinite clay particles in the polymer solutions at both room temperature and 408C were measured using an atomic force microscope (AFM). The measured adhesion forces correlated well with the settling characteristics: a stronger adhesion led to a higher initial settling rate. The retraction force profiles obtained at different temperatures confirmed the conformational change of the polymer with temperature.