method for separating isoprene by two-stage extraktiver distillation

摘要

Isoprene is recovered in high purity from a cyclopentadiene-containing C5 fraction in a two-stage extractive distillation in the presence of a selective polar solvent. Substantially all of the cyclopentadiene is removed in the first or heavy ends extractive distillation zone wherein the concentration of the extractive distillation solvent is maintained at from 5 to 40 mole percent to thereby recover substantially all of the isoprene and more volatile hydrocarbons as overhead products from the zone. Isoprene is then separated from this overhead C5 fraction in a second or light ends extractive distillation zone and is recovered in the fat solvent from which it is recovered in an isoprene stripping zone. A high solvent concentration is maintained in the upper section of the isoprene stripping zone and cyclopentadiene is recovered from a lower section of the zone via a side draw. The dimer content of the solvent circulating in the light ends extractive distillation zone and isoprene stripping zone is controlled by recycling a portion of the stripped solvent from the bottom of the isoprene stripping zone to the heavy ends extractive distillation zone wherein the recovered dimer is rejected in the bottoms product. Solvent is recovered from that bottoms product in a heavy ends stripping zone as a vapor side draw.