2-Ethylhexanoic Acid Production from Butyraldehyde

The process under analysis comprises the following major sections: (1) aldol condensation; (2) hydrogenation, (3) oxidation and (4) purification.

* Aldol Condensation. The n?butyraldehyde is fed to a stirred tank along with a caustic soda solution, used as catalyst. An aldolization reaction occurs under thorough mixing, yielding butyraldol, which is immediately dehydrated to 2-ethyl-2-hexenal. The effluent from the condensation reactor is directed to a reactive distillation step, to strip off light ends and unreacted butyraldehyde from the condensation reactor effluent. The unreacted n-butyraldehyde is recycled to the reactor, while the liquid stream withdrawn from column’s bottom is fed to a caustic removal step. After the caustic removal, a stream composed primarily of 2-ethyl-2-hexenal is then routed to the hydrogenation area, downstream.

* Hydrogenation. In this section, the 2-ethyl-2-hexenal stream is combined with hydrogen and fed to a fixed-bed reactor filled with a Palladium catalyst on carbon support, where hydrogenation reaction takes place. The 2-ethyl-2-hexenal selectively reacts with hydrogen, yielding 2-ethylhexanal.

* Oxidation. The 2-ethylhexanal stream is mixed with a potassium salt of 2-ethylhexanoic acid (used as additive to enhance the selectivity of the oxidation reaction) and fed along with compressed air, to a shell and tube reactor with forced circulation, where an oxidation reaction takes place in the liquid phase. Crude acid taken off at the bottom of the oxidation reactor is routed to the purification section downstream, while the reactor off-gas, mainly containing inert nitrogen contained in the air feed, is discharged as waste.

* Purification. The purification is composed of two distillation columns operating under vacuum. The first column, the heavies column, separates a mixture of 2-Ethylhexanoic Acid and potassium salt of 2-ethylhexanoic acid by column’s bottom, which is then recycled to the oxidation reactor after a small purge to avoid the buildup of heavy impurities. The second column, the lights column, removes the light impurities from the 2-Ethylhexanoic Acid product.