Influence of hydrothermal treatment on filterability of fine solids in bitumen froth

Abstract Bitumen froth generated during the oil recovery operation from Athabasca oil sands needs to be cleaned to remove water and fine mineral solids for subsequent bitumen upgrading or pipeline transport. Two currently used bitumen froth cleaning methods, naphthenic froth treatment (NFT) and paraffinic froth treatment (PFT), either cannot generate market-spec bitumen froth (NFT) or causes losses of bitumen (PFT). In this study, a combination of hydrothermal treatment, venting and filtration was investigated to clean the bitumen froth. Laboratory hydrothermal treatment was conducted at 300–420 °C for 0–180 min. The filterability of fine solids was quantitatively characterized by room-temperature filtration or hot filtration at 200 °C. Mineralogical composition and particle size distribution of the untreated and treated fine solids were determined by quantitative X-ray diffraction using RockJock and focused beam reflectance measurement (FBRM) particle size analyzer. The microscopic observation of clay particle stacking behavior at the filter cake-filter medium interface was made by scanning electron microscope (SEM). The results show that hydrothermal treatment followed by venting and filtration is an effective way to remove water and fine solids from bitumen froth: the water content was reduced from 14 wt% to 0.03 wt%, and the fine solids content was reduced from 8 wt% to 0.08 wt% by hot filtration at 200 °C using a 0.5 μm pore size stainless steel filter medium. After hydrothermal treatment, no noticeable changes were observed to the clay mineralogy and fine solids particle size. However, the platy clay particles at the filter cake-filter medium interface turned from preferential orientation to random orientation due to the attachment of numerous ultrafine particles on the basal surface of the clay, increasing the porosity of the filter cake and facilitating the filtration. Such a change in the filter cake was hypothesized to be caused by the re-structuring of the organic-mineral aggregates into the ultrafine-particle-coated platy clays, releasing the organics and the ultrafine solids during the hydrothermal treatment. The released ultrafine solids then adsorbed onto the clay platelets. It was indeed observed that the total organic carbon content of the bulk fine solids decreased from 14.7 wt% to 10.3 wt%, but the carbon concentration on the fine solids surface increased from 35.6 at.% to 47.7 at.%.