Solvent-involved Processes For Bitumenrecovery From Oil Sands

During the past decades, the sharp declining reserves of conventional oil have resulted in an increasing activity to develop abundant unconventional oil reserves(~70% of total world oil reserves), such as oil/tar sands, heavy oil, shale oil etc. Characterized by extremely high viscosity and density, the conventional technologies vanish in extracting the unconventional oil economically. Fortunately, solvent has been found as a process aid to be able to reduce the operational expenditure and improve unconventional oil production. Therefore, developing novel processes with solvent, as well as the mechanisms, is essential and urgent for unconventional oil production to meet the current global oil needs. In this thesis, two types of extraction processes have been investigated for bitumen recovery from oil sands: solvent extraction and hybrid aqueous-nonaqueous process.Solvent extraction is a common method to extract valuable products from ores. Here, to understand the solvent role in the bitumen recovery from oil sands, the first thing is to reveal the composition of the surface materials on the sand grains, which plays an important role in the diffusion of solvent into bitumen. Additionally, the bitumen physical properties, especially the surface properties, such as the interfacial tensions etc. are much dependent on the surface materials composition, referring to the distribution of bitumen fractions in the bituminous layer. In this thesis, firstly, a conceptual model was proposed to illustrate the composition and distribution of SARA(saturate, aromatic, resin and asphaltenes) fractions in the bituminous layer on the surface of Athabasca oil sands, which was verified by elemental analysis, X-ray photoelectron spectroscopy, field emission scanning electron microscopy with energy dispersive spectrometer, and Fourier-transformed infrared spectrometer. The contents of S, N, and the ratios of C/S and C/N were characterized as potential indicators for evaluating the distribution of SARA fractions in the bituminous layer. The results indicated that the light fractions such as saturates tend to deposit at the outer bituminous layer, while the asphaltenes and resins were inclined to distribute at the inner layer. It is also suggested that the distribution of SARA fractions was thermodynamic dependent and was susceptible to thermal treatment. These findings came to support the simulation results with molecular dynamic(MD) simulation. This work provides experimental evidences and simulation supports for validating the distribution patterns of SARA fractions on the surface of Athabasca oil sands.Then, non-aqueous solvent extraction has been applied for bitumen recovery from oil sands. Influences of solvent type, temperature, contact time, stirring rate and solvent to oil sands ratio(V/M) on bitumen recovery were investigated. Results showed that solvent with solubility parameters of dispersion interaction: =15.0 ~18.4 MPa0.5; polar interaction: = 0~2.6 MPa0.5; and hydrogen bonding interaction: = 0~2 MPa0.5, would be good for the bitumen recovery(bitumen recovery>70%).Under the orthogonal(L9(34)) experiment conditions, the overall impacts of factors were ranked: V/M > stirring rate > contact time > temperature. Profiles of bitumen SARA fractions in the dissolved bitumen, suspended particles and residual bitumen were investigated in single factor experiments. Asphaltenes have higher temperature sensitivity than other fractions. About 3 ~ 7 wt% bitumen particles coexisted with clay minerals(50 ~ 70 wt% of the suspended particles) suspended in the solution, most of which were composed with asphaltenes. Approximately 75 ~ 90 wt% of SAR fractions(saturates, aromatics and resins) were dissolved in the composite solvent(Vheptane : Vtoluene = 3:1) under the experimental conditions. The amount of residual fractions varied with conditions and multi-stage extraction enhanced the bitumen recovery by up to 99%. The evaluation method for bitumen recovery based on dissolved fraction outperformed the methods based on the sum of dissolved and suspended particles.The hybrid aqueous-non-aqueous process has been studied here by Denver Cell floatation. The floatation tests under room temperature show that the addition of solvents(i.e., naphtha, toluene) and demulsifiers into the oil sands ores before slurry conditioning improves the bitumen recovery significantly according to two poor ores tests. To find out the mechanisms of solvent-enhanced bitumen recovery, sub-processes, such as bitumen liberation, bitumen aeration, are investigated systematically.Novel methods(modified empirical method, gridding method, and edge-covering method) were proposed to calculate the degree of bitumen liberation in this project, with which the bitumen liberation from real ores was investigated. Results from in-situ bitumen liberation visualization measurement indicate that soaking two poor-processing ores by solvents at 10-30 wt% of bitumen could significantly enhance not only the overall degree of bitumen liberation(ODBL) but also the rate of bitumen liberation(RBL) in the process water at ambient conditions. Although ore type- and solvent type-dependent, both ODBL and RBL increased sharply at 10-20 wt% solvent dosage. A further increase in solvent dosage showed a diminished increase in ODBL. To understand the observed improvement, viscosities of bitumen directly extracted from the ores and its mixture with solvents were measured, so was diluted bitumen-water interfacial tensions. Results showed that adding solvent into the bitumen reduced bitumen-water interfacial tension and more so for the reduction in its viscosity. Interestingly, the viscosity and interfacial tension were found to be dependent on the source of ores and the type of solvents. The ODBL was found to be inversely correlated with the interfacial tension and bitumen viscosity, while the RBL correlated almost linearly with the interfacial tension/viscosity ratio which acted as the balance of driving force/adhesion drag force. These correlations were less dependent on the types of ores and solvents. In-situ flow-cell liberation test and contact angle measurements showed that the demulsifiers addition is also beneficial to the bitumen liberation. The hydrodynamic model was applied successfully to fit the contact angle data. In addition, the addition of demulsifiers, such as EC, PEO/PPO, into the oil sands ore for conditioning was proved to be beneficial for the bitumen recovery and liberation under ambient conditions, suggesting that there would be a potential for the application of demulsifiers in oil sands extractions.Another key sub-step in bitumen recovery, air-bubble and diluted-bitumen attachment and coalescence have also been studied subsequently in process water by the Induction Timer, Total Organic Carbon(TOC) Analyzer, Zeta-phoremeter, AAS(Atomic Absorption Spectroscopy). Results showed that the induction time of air bubble-bitumen attachment decreased with the increasing of the solvent dosage from 0 to 10 wt%(based on bitumen) followed by an increase when solvent dosage increased from 10 wt% to 30 wt% of the bitumen. Additionally, the induction time of toluene-diluted bitumen-bubble attachment was observed to be shorter than that of naphtha-diluted bitumen-bubble attachment. Mechanistic study by bubble coalescence and TOC measurements suggested that the addition of solvent into bitumen exerted slight influence on the bubble properties but facilitated the adsorption of natural surfactants at the water-oil interface. The amount of absorbed surfactants by toluene-diluted bitumen was evidenced to be more than that on the naphtha-diluted bitumen surface. The zeta potential of diluted bitumen reached the maximum(less negative) when solvent dosage was at about 10 wt% of the bitumen for both of toluene and naphtha, and the toluene-diluted bitumen possessed a more negative zeta potential than that of naphtha-diluted bitumen. The solvent addition into the bitumen was also found to facilitate the adsorption of ions(Ca2+, Mg2+, Na+, K+) on the bitumen surface. Based on above results, an ion and natural surfactants adsorption mechanism has been finally proposed.Results above come to show us the solvent plays a vital role in reducing the bitumen viscosity, water-bitumen interfacial tension, air-bitumen induction time, which are beneficial for the bitumen recovery, GHG emission cutting and energy saving.