Isopropyl Alcohol Production from RG Propylene

The process under analysis is comprised of three major sections: (1) Isopropanol synthesis; (2) propylene recovery; and (3) purification.

Isopropanol synthesis. Refinery grade (RG) propylene (70 wt%) is converted into Isopropanol through two consecutive reaction steps. First, gaseous propylene is contacted with weak sulfuric acid in a reactive absorber, forming isopropyl sulfates. Then, the sulfates are hydrolyzed by steam addition in a stripper reactor, generating isopropanol. The stripper gaseous product is absorbed in caustic solution for residual acid neutralization and sent to the purification section. The stripper liquid effluent, containing dilute sulfuric acid, is treated in an acid reconcentration unit for further reuse in the process.

Propylene recovery. The reactive absorber gaseous effluent is treated in a caustic scrubber for residual acid removal and fed to a column for recovery of unreacted propylene. Propane contained in the RG propylene is withdrawn from this column as oveheads product and purged from the process. Recovered propylene is recycled to the Isopropanol synthesis section.

Purification. The crude isopropanol from both the caustic scrubber and the stripper reactor are directed to an ether separation step, where diisopropyl ether (generated in side reactions) is separated and recycled to the absorber reactor to react with sulfuric acid, forming sulfate and isopropanol. The ether-free crude isopropanol is transferred to the alcohol column for removal of high boiling impurities. The overheads product from alcohol column comprises an azeotropic mixture of isopropanol and water. Finally, dry isopropanol is produced after dehydration by means of azeotropic distillation using diisopropyl ether as azeotroping agent.