(636a) Limitations on the Residual Solvent Recovery Imposed By the Gangue Characteristics

Non-aqueous solvent extraction (NAE) of bitumen from oil sands has the potential to replace the existing hot-water extraction process. One of the challenges of NAE is to minimize the residual non-aqueous volatile solvent in the resultant gangue after extraction. The gangue typically contains a mixture of solids with a wide range of sizes, connate water, residual solvent, and residual bitumen. It has been shown that solvent (cyclohexane in this study) evaporation mainly occurs in the initial steady state of drying in which there is a liquid film connectivity from the inside to the surface of the gangue sample. In this work, the initial evaporation rate of cyclohexane from gangue samples with different compositions was studied. Gangue samples with 12% cyclohexane, based on dry solids, and different water, fines, and bitumen contents were prepared. Mass loss of samples was measured at room temperature and ambient pressure and was used to signify the cyclohexane initial evaporation rate. There existed an optimum cyclohexane evaporation rate over a fines content range of 0 – 20%. In particular, it increased from 45.9 g/min.m² in the sample with no fines to 53.9 g/min.m² in the sample with 10% fines. However, it dropped to 39.8 g/min.m² in the sample with 20% fines. There also existed an optimum water concentration (3.7%) at which the cyclohexane evaporation rate was the highest. Residual bitumen content showed the most drastic impact compared to other components with a 30% reduction in the cyclohexane evaporation rate when only 1% bitumen is present in the gangue mixture. It is proposed that the initial flux of evaporation is controlled by the sorptivity of the sample at low contents of fines, water, and bitumen. The presence of an optimum amount of fines and water seems to increase the intrinsic sorptivity of the sample by decreasing the average pore size of the sample. On the other hand, bitumen reduces the sorptivity by drastically increasing solvent’s viscosity. Higher amounts of fines and water leads to the blocking of the pores, thereby entrapping cyclohexane, and consequently reducing its evaporation rate significantly.