Study on separation of long carbon chain aromatics/alkanes in diesel systems with DBU-based ionic liquids

Based on the structural designability of ionic liquids (ILs), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-based ILs ([Bz-DBU]NTF2) were designed and synthesized. Their physical properties were analyzed by FT-IR, 1H NMR, DSC and TGA. Highly selective separation between aromatic and alkane by [Bz-DBU]NTF2 was achieved. Under the optimal conditions, the distribution coefficient (D) and separation selectivity (S) of [Bz-DBU]NTF2 for tetraline were 0.833 and 54.2. The IL was regenerated six times without decrease in separation selectivity, demonstrating good stability. For the multi-component simulated diesel, nearly 100% of the bicyclic alkanes could be removed by five-stage cross-flow extraction processes. While the removal rate of total aromatics reached up to 84.39 and the contents of alkanes and total saturated alkanes reached 56.64% and 96.69%, respectively. For the real diesel, after two-stage cross-flow extraction experiments, the removal rates of monocyclic, bicyclic, tricyclic aromatic hydrocarbons reached 63.9%, 91.3% and 100%, respectively. The final product reached the standard of high quality ethylene cracking feedstock.