Patent ID: 8663461

Claim:
A method for recovering a polar hydrocarbon (HC) selective solvent substantially free of hydrocarbon (HC) impurities from a solvent-rich stream containing the selective solvent, measurable amounts of heavy HCs, and polymeric materials (PMs) generated from reactions among thermally decomposed or oxidized solvent, heavy HCs, and additives, which method comprises the steps of: (a) introducing a feed containing polar and less polar HCs into a middle portion of an extractive distillation column (EDC) and introducing a solvent-rich stream into an upper portion of the EDC as a selective solvent feed; (b) recovering a water-containing, less polar HC-rich stream from a top of the EDC and withdrawing a first solvent-rich stream containing solvent and polar HCs from a bottom of the EDC; (c) introducing the first solvent-rich stream into a middle portion of a solvent recovery column (SRC), recovering a polar HC-rich stream, that is substantially free of solvent and less polar HCs, from a top of the SRC, and removing a second solvent-rich stream from a bottom of the SRC; (d) introducing a first portion of the second solvent-rich stream into the upper portion of the EDC in step (a) as the selective solvent feed; (e) cooling a second portion of the second solvent-rich stream in step (c), mixing the cooled solvent-rich stream with a portion of water phase from step (h), and introducing the mixture into an upper portion of a solvent clean-up zone to form a solvent phase; (f) introducing a light HC-rich stream into a lower portion of the solvent clean-up zone, as a heavy HC displacement agent, to squeeze out heavy HCs and PMs from the solvent phase into a HC phase; (g) withdrawing an accumulated HC phase containing heavy HCs, PMs and minor amounts of solvent from an upper portion of the solvent clean-up zone, and recovering a solvent phase containing solvent and light HCs, which serves as heavy HC displacement agents, and has substantially reduced levels of heavy HCs and PMs, from a lower portion of the solvent clean-up zone; (h) introducing the HC phase from the solvent clean-up zone in step (g) into a water wash zone to remove the minor amounts of solvent from the HC phase into the water phase; and (i) introducing the solvent phase from the solvent clean-up zone in step (g) into a lower portion of the EDC in step (a) as part of a selective solvent feed to recycle purified solvent into a solvent loop.