Microstructure And Solvent Extraction Process Of Indonesian Asphalt Rocks

Indonesian asphalt rock is one of the unconventional oil ores with high bitumen content and abundant reserves,showing broad prospects.However,its related studies started late,and theoretical knowledge and process development are both in their infancy.Currently no commercial process has been applied to recover the asphalt from Indonesian asphalt rocks.Considering the problems mentioned above,the microstructure and physicchemical properties of Indonesian asphalt rock have been investigated,and the results give guidance to the development of asphalt recovery process.The specific results are as follows:Scanning electron microscope and X-ray computed tomography were used to analyze the microstructure of Indonesian asphalt rocks.The results showed that the basic structure of Indonesia asphalt particle is asphalt-coated mineral particle,and the mineral particle is a multi-chamber shell structure.The results showed that the asphalt covered the outer surface of the asphalt rock particles and penetrated into the chamber inner through the pores but did not fill in the chamber inner.The thickness of the asphalt layer in the inner surface is about 2～3μm.After analysis and identification,it was found that the mineral particles of Indonesian asphalt rocks are foraminifera fossils,and the main mineral composition is calcite（Ca CO₃）.Combined with the geological history of Buton Island,it is inferred that oil penetrates into the chamber inner of the foraminifer fossil through the pores,and the mixture transformed into the Indonesian asphalt rocks after weathering and microbial oxidation decomposition.Based on the physicochemical properties and microstructure of Indonesian asphalt rocks,the solvent extraction process was selected to recover asphalt from Indonesian asphalt rocks in this paper.The results showed that the single extraction of Indonesian asphalt rocks by toluene can get a recovery over 75%,and up to 98%of the asphalt can be recovered after three times of extraction.The multi-chamber shell structure causes the entrainment or encapsulation of solvents and asphalt fractions in the chamber.After single extraction,the amount of the residual solvent in the residual sands is determined to be 0.53 g/g for the solvent involved.The water flooding method effectively recovered the residual solvent in the residual sands,and 88.3%～93.0%of the solvent can be recovered after three times of water flooding.The water flooding method also benefit to the recover of residual asphalt in the residual sands,and the wettability of the residual sand is significantly improved after water flooding.Although most of the particles can be effectively removed by sedimentation,there are still a large amount of suspended nanoparticles in the solution.Water-assisted flocculation method was used to remove the suspended nanoparticles in the solution.90μL high-purity water is added during the polymer flocculation,the addition of of the high-purity water（less than 1500 ppm）significantly improved the removal efficiency of nanoparticles.More than 90%of the nanoparticles have been removed by water-assisted flocculation method.Polyethylene oxide absorbs on the surface of nanoparticles through polymer bridging and effectively reduces the interfacial tension between toluene and water.Then the larger flocculated aggregates are formed and effectively settle down with the assistance of water droplets.To enhance the solvent extraction process,ionic liquid was used to assist the solvent to recovery the asphalt in Indonesian asphalt rocks,and its mechanism in the extraction process was investigated.Results show that the ionic liquid（[Emim⁺][BF₄]）promotes the solvent extraction and reduces the entrainment of nanoparticles.Compared with the single extraction by toluene,the asphalt recovery increased by 4.1%,and the nanoparticles in the bitumen solution is reduced by 52.86%.The force measurement by atomic force microscopy demonstrates that the addition of ionic liquid reduces the long-distance adhesion between asphalt and silica,and promotes the separation of asphalt from the surface of silica.Through sum frequency generation vibrational spectroscopy,it was found that the ionic liquid cations（[Emim⁺]）in the aqueous solution were adsorbed and accumulated on the surface of silica and asphalt,forming a positively charged Helmholtz-like layer.This study could provide theoretical and experimental guidance for the understanding,exploration and the processes technology development of the unconventional oil resources.