This study investigates the recycling of used lubricating oil (ULO) by solvent extraction using a ternary solvent consisting of 2-propanol, 1-butanol and methyl ethyl ketone (MEK) followed by a vacuum distillation unit. In order to select the best combination of solvents for the liquid–liquid extraction process, many parameters were first evaluated on a laboratory scale such as the effect of the solvent composition, the solvent-to-oil ratio and the temperature. The oil recovery efficiency and the physicochemical properties of the oil obtained from the extraction process were measured, and the results showed that a ternary system consisting of 50% 1-butanol/25% isopropanol/25% MEK is the best mixture for effectively reducing the contaminants in ULO with a good sludge separation prior to the fractionation. Also, a solvent-to-oil ratio of 3:1 and a temperature of 25 °C are the optimal parameters for the extraction when the aforementioned solvent mixture is used. The whole re-refining process including the vacuum distillation unit was then simulated for a plant capacity of 2125 kg/h using Aspen Plus™. Four pseudo-components (saturate, monoaromatic, diaromatic and polyaromatic) together with the nonrandom two-liquid (NRTL) and universal quasichemical activity coefficient (UNIQUAC) were used to describe the liquid–liquid equilibrium (LLE) in the system solvent/lubricating oils during the extraction phase. The calculated yields on the extraction unit performed for different solvent composition, solvent-to-oil ratio and temperature showed a good agreement with the experimental data performed at the laboratory scale which verifies the right choice of the solvent mixture. The investigation of the amount and composition of oil loss inside the sludge obtained from the simulation showed that the contaminant reduction and the oil recovery depend on the percentage of 1-butanol in the solvent mixture. Also, the results confirmed that the amount of MEK and 2-propanol in the solvent mixture should not exceed 25% and the best results were obtained when 1-butanol was used as a base solvent with an amount of 50%. Finally, to check the feasibility of the process, the investment payback time and the return on investment of the re-refining process were evaluated. Based on the economic study results, the production process was found to be highly profitable with a return on investment equal to 55% and a payout period of 1.9 years in the worst-case scenario where the price of lubricating oil is 2.5 $/L.

Graphic abstract

中文翻译：

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通过溶剂萃取回收废润滑油：实验结果，Aspen Plus模拟和可行性研究

这项研究调查了通过使用由2-丙醇，1-丁醇和甲基乙基酮（MEK）组成的三元溶剂，然后进行真空蒸馏装置进行溶剂萃取来回收使用过的润滑油（ULO）的方法。为了为液-液萃取过程选择最佳的溶剂组合，首先在实验室规模上评估了许多参数，例如溶剂组成的影响，溶剂与油的比例和温度。测量了从萃取过程中获得的油的采油效率和理化性质，结果表明，由50％1-丁醇/ 25％异丙醇/ 25％MEK组成的三元体系是有效降低油的最佳混合物。在分馏之前，ULO中的污染物具有良好的污泥分离能力。另外，溶剂与油的比例为3：当使用上述溶剂混合物时，最佳萃取参数为1和25°C。然后，使用Aspen Plus™对包括真空蒸馏装置在内的整个再精炼过程进行模拟，得出装置产能为2125 kg / h。四种假组分（饱和，单芳族，二芳族和多芳族）与非随机二液（NRTL）和通用拟化学活度系数（UNIQUAC）一起用于描述系统中溶剂/润滑油的液-液平衡（LLE）在提取阶段。对于不同的溶剂组成，溶剂与油比和温度，在萃取装置上计算出的产率与实验室规模的实验数据吻合良好，这证明了溶剂混合物的正确选择。对通过模拟获得的污泥内部的油损失量和组成的研究表明，污染物的减少和油的回收率取决于溶剂混合物中1-丁醇的百分比。而且，结果证实了在溶剂混合物中MEK和2-丙醇的含量不应超过25％，并且当使用1-丁醇作为50％的量的基础溶剂时，可获得最佳结果。最后，为了检查该过程的可行性，评估了精炼过程的投资回收期和投资回报率。根据经济研究结果，发现生产过程是高利润的，在最坏的情况下（润滑油价格为2.5美元/升），投资回报率为55％，投资回收期为1.9年。

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