(156g) Synthesizing a Novel Aromatic Extraction Separation Using Ionic Liquid Solvents

The separation of aromatics from aliphatics in hydrocarbon mixtures using solvents is a practice common in industry. The liquid extraction separation that is best exemplified by the sulfolane process combines integrates three separation steps. A liquid extraction step is used to purify a hydrocarbon of aromatics and obtain an aromatic-rich extract, the aromatic extract is stripped of residual aliphatics in an extractive stripping column, and finally the aromatic and extract are separated in a solvent recovery column and the solvent is stripped of aromatics by a stripping agent. Ionic liquids (ILs) have been investigated as alternative solvents to sulfolane with a key feature being non-volatility. It is commonly claimed that IL non-volatility leads to a fundamentally simpler aromatic extraction process.

We investigate these claims by examining each separation step in the aromatic extraction process and find an IL solvent requires unrealistically high selectivity to eliminate an extractive stripping column or achieve stripping in a single flash stage. We also find the low concentration of aromatics required to make lean solvent necessitates the use of a stripping agent and a staged column for the aromatic-solvent separation. The only simplification enabled by non‑volatility of an IL solvent is the elimination of reflux and a rectifying section for the aromatic-solvent separation, which is not significant for the low volatility conventional solvents. We demonstrate the processing requirements of an IL aromatic extraction process are very similar to the sulfolane process.

Our analysis of the fundamental separation steps in the aromatic extraction process and how they are interrelated allow us to develop an energy-optimum process targeted towards the separation of low aromatic content hydrocarbons where the conventional sulfolane aromatic extraction process is not utilized. The modifications address issues related to the large solvent heat load and higher extractive stripping column temperatures. We solve these issues by improving the solvent heat integration and introducing a control scheme that allows independent control of extractive stripping column reboiler temperature.