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.

Automated summary

DBU-based ILs ([Bz-DBU]NTF2) were designed and synthesized based on the structural designability of ionic liquids (ILs). Their physical properties were analyzed and they showed highly selective separation between aromatic and alkane compounds. The IL demonstrated good stability and could effectively remove bicyclic alkanes and aromatics from simulated diesel and real diesel, meeting the quality standards for high-quality ethylene cracking feedstock.