Synthesis Of Switchable-hydrophilicity Solvent And Its Application In Oil Sands Separation

With the increasing energy demand in society development and the reduction of conventional petroleum resources,many countries have begun to pay more attention to unconventional oil resources such as heavy oil,oil sands,oil shale,etc.Using solvent extraction for oil sands separation possess many advantages,such as universal applicability,low operating temperature,high extraction rate and easy recovery of solvent.The addition of additives,such as water and ionic liquids,in solvent extraction can further enhance extraction effect.However,this technology still has some problems which limit its further commercial application.For example,solvents usually have high volatility,solvent recovery need huge energy consumption and solvent or fine sand may leave in products.Therefore,the design and development of novel green solvents and additives for clean separation is an important research direction in oil sands separation.Switchable-Hydrophilic Solvents?SHSs?are a type of organic solvents with high-boiling point,low-volatility and switchable properties between hydrophilicity and hydrophobicity.Therefore,SHSs have attracted much attention in extraction fields.SHSs,being as solvents or additives,prove excellent separation ability in oil sands extraction.However,there is no process that could combine dual effects of SHSs?i.e.,solvent effect and additive effect?in one extraction process.In this paper,a new type of SHSs called N,N,N',N'-tetraethyl-1,3-propanediamine?TEPDA?is synthesized and TEPDA-water hybrid extraction process is developed in order to achieve the dual role of SHS in oil sands separation.The structure and switchable properties of the synthesized TEPDA are characterized,which prove that TEPDA is a novel diamine-structured SHS.Based on theoretical calculations,it is found that TEPDA has three state transitions in water.Simulation software predicts the toxicological properties of TEPDA,which is advantageous than traditional SHSs.Based on the above studies,TEPDA-water hybrid extraction process is developed to extract bitumen from oil sands.The addition of different water volume and different solvent volume is considered in affecting bitumen extraction rate.It is found that the one-staged bitumen recovery rate can reach 90%and the two-staged recovery rate can reach 96%,when the ratio of oil sands to TEPDA to water is 1:2:0.6?g/mL/mL?at 25°C for 30min.By bubbling CO₂ and N₂ assisted with heating,TEPDA can be separated and recovered easily.The recovered TEPDA can be used for further cycles without affecting extraction rate.Additionally,this hybrid process can improve the quality of the extracted products,with less fine sands entrained in bitumen and less solvent left in residual sands.In order to further explore its mechanism,the interactions between TEPDA and solid,TEPDA and bitumen,are studied through characterizations such as Zeta potential,water droplet penetration test,QCM-D and interfacial tension measurement.TEPDA shows dual role of both solvent and additive in extraction process.Most of the TEPDA acts as a solvent in its non-ionic state to soften and dissolve bitumen,reducing the viscosity of bitumen.Additionally,a small amount of TEPDA is ionized in water,which acts like a surfactant in enhancing separation.When the aqueous solution is in contact with the diluted oil,the TEPDA ions accumulate at the oil–water interface,which reduce the interfacial tension,make the solid surface more hydrophilic and thereby enhance oil sands separation.Therefore,in this paper,TEPDA-water hybrid extraction process can be used to separate bitumen from oil sands,which provides a new guidance for unconventional oil exploitation.