Propylene Production from Propane (Oxydehydrogenation)

The process under analysis comprises four major sections: (1) Reaction; (2) CO2 Separation; (3) Gas Separation; and (4) Fractionation.

Reaction. Propane is fed into a depropanizer column to heavy impurities removal. The depropanizer distillate is vaporized, mixed with steam, and pre-heated before entering the reformer, where most of the propane conversion takes place. Next, the effluent is fed to the oxyreactor, where hydrogen is selectively combusted by oxygen. The process gas is cooled in a series of heat exchanges to recover heat to be utilized in the process and is compressed.

CO2 separation. The compressed gas is fed to an absorption column, where CO2 is removed in the bottoms by washing with an aqueous piperazine activated methyldiethanolamine (MDEA) solution. This stream is depressurized, liberating gases that are recycled to the absorption column. The CO2-rich liquid solution from the flash vessel is fed to the solvent regeneration column, which separates CO2 in the overheads and the MDEA solution in the bottoms, which is recycled to the absorption column.

Gas separation. The overhead stream of the absorption column is dried in a molecular sieve and fed to a low-temperature separation system (cold box) for the removal of lights. In this system, a hydrogen-rich stream is also obtained, which is purified in a pressure swing adsorber (PSA) unit to obtain high purity hydrogen byproduct.

Fractionation. The liquid fraction from the cold box is sent to the fractionation area, which consists of a deethanizer column for removal of lights and a P-P splitter, where polymer grade propylene is obtained. Unconverted propane from the P-P splitter bottoms is recycled to the reaction area.