Patent DE-10336386-A1 (DE)
Title: Absorptive separation of acrylic acid, useful for the production water absorbents and adhesives, comprises recycling organic raffinate from the acid water extraction to the absorption unit at least one theoretical stage below its head
Inventor: DIEHL VOLKER
IPC: C07C51/44
Filed: 2003-08-06
Abstract: Process for the absorptive separation of acrylic acid from a product gas mixture, resulting from a heterogeneously catalyzed gas phase oxidation of propene comprises cooling of the product mixture and feeding to an absorption unit with recycling of the organic raffinate from the acid water extraction to the absorption unit whereby the recycle is carried out at least one theoretical stage below the head of the absorption unit. Process for the absorptive separation of acrylic acid from a product gas mixture, resulting from a heterogeneously catalyzed gas phase oxidation of propene to acrylic acid and containing acrylic acid and water vapor as well as by-products comprising low boiling material, middle boiling material, high boiling material and material that is difficult to condense, comprises cooling of the product mixture; passage of the cooled product mixture by counter current flow into an absorption unit containing an ascending high boiling point liquid hydrophobic organic absorption agent with avoidance of the formation of a liquid aqueous phase; cooling of the non-absorbed residual product mixture in a condensation unit with condensation of the water vapor and low boiling point material as acid water; recycling of a partial quantity as a diluent gas to the gas phase oxidation of propene with a partial quantity used as a stripping gas after passage through a washing unit to remove acrylic acid and disposal of the remaining gas; passage of a small amount of the absorbed liquid containing acrylic acid to a distillation unit as a high boiling point outlet that is recycled, as a vapor phase by heating, back to the absorption unit and the remaining high boiling point material is disposed of; the liquid outlet from the absorption unit containing acrylic acid is fed to a desorption unit and low boiling point material removed by the stripping gas with recycle of the stripping gas containing low boiling point material to the absorption unit; passage of the absorption agent stream containing acrylic acid to a distillation column having a concentrating and a distillation compartment with condensation of the absorption agent and high boiling point material in the sump of the distillation column; separation of crude acrylic acid via a side take-off from the concentrating compartment of the distillation column; recycle of the low boiling point materials from the head of the column to the absorption unit; removal of the absorption agent from the sump of the distillation column with optional addition of fresh absorption agent as required and passage through the wash unit in counter-current flow to the recycle gas flow to remove acrylic acid; partition of the absorption agent leaving the wash unit into two portions having the same composition whereby the larger portion is recycled to the head of the absorption unit and the smaller portion is mixed with acid water in an extractive exchange in order to take up the acrylic acid contained in the acid water into the absorption agent and the polar middle boiling material contained in the absorption agent into the acid water; recycle of the organic raffinate from the acid water extraction to the absorption unit whereby the recycle is carried out at least one theoretical stage below the head of the absorption unit.