Propionic Acid Production from Ethylene

The process under analysis comprises four major sections: (1) ethylene hydroformylation; (2) propionaldehyde separation; (3) propionaldehyde oxidation; and (4) Propionic Acid separation.

* Ethylene hydroformylation. Syngas and ethylene are initially passed through a purification step to remove catalyst poisons. In the hydroformylation, ethylene reacts with carbon monoxide and hydrogen at mild temperatures and low pressures in the presence of a homogeneous rhodium based catalyst with an organophosphine ligand, yielding propionaldehyde. The reaction takes place in a jackted stirred-tank reactor.

* Propionaldehyde separation. The effluent from hydroformylation is passed through a condenser and a flash separator and subsequently fed to a stripping column for separation of aldehyde from unreacted raw materials. The aldehyde-rich stream is sent to a second column, where propionaldehyde is separated from heavy impurities.

* Propionaldehyde oxidation. The propionaldehyde generated upstream is fed to three tube and shell reactors operating in series, where it is oxidized to Propionic Acid under mild pressures in the liquid phase in the presence of air. Crude acid taken off at the bottom of the last reactor is routed to separation and purification steps downstream.

* Propionic Acid separation. The crude acid is fed to a decomposition column, where perpropionic acid contaminant is decomposed by heating under a positive nitrogen pressure. Then, unconverted propionaldehyde is recovered in a subsequent column and recycled to the oxidation reaction. The rich Propionic Acid stream is routed to a light-ends column for the removal of light impurities and high purity Propionic Acid (99.5 wt%) is finally obtained by azeotropic distillation using ethyl acetate as entrainer.