Today, the main industrial processes employed in the hydroformylation of olefins use compounds as catalysts without phosphine or phosphite additives.

The individual steps of the industrial process will now be explained using a cobalt catalyst in the hydroformylation of the quantitatively most important olefin feedstock - . The process can be divided into three stages:
1. Hydroformylation (including catalyst preparation)
2. Catalyst separation (including workup)
3. Isolation of the reaction products

To 1st process step:

Cobalt, either as metallic powder, hydroxide or as a salt, is fed into the stainless steel high pressure reactor. It reacts with the oxo gas (H₂+CO) in the liquid phase (propene+'oxo' products) under hydroformylation conditions (250-300 bar, 140-180 °C) with sufficient speed to form cobalt hydrocarbonyl. Although the olefin reaction product generally serves as solvent, alkane mixtures can also be used for this purpose.

Propene is then converted with H₂ and CO into a mixture of butyraldehyde and isobutyraldehyde:



The heat of reaction, about 28-35 kcal(ll8- 147 kJ)/mol olefin, is removed by a tubular heat exchanger.

The condensable crude product consists of ca. 80 wt% butyraldehydes, 10-14% butanols and butyl formates and 6-10% various compounds such as high boiling products. The n:iso butyraldehyde ratio varies from about 75:25 to 80:20. Up to 90% of the CO/H₂ mixture is converted into isolable aldehydes and alcohols. The remainder is discharged with inerts and combusted.

The selectivity to C₄ products is 82-85% (C₃H₆). 15-17% of the converted propene is present in the higher boiling substances or as propane in the waste gas.

The conversion and selectivities depend in a complex manner on numerous process variables. A few simplified concentration effects based on a rate equation derived by G. Natta are presented here. An industrially desirable high rate of formation of aldehyde is dependent on a large value for the concentration or partial pressure quotient:

This can, in principle, be achieved in two ways:
1. by low CO partial pressure
2. by high olefin and cobalt concentrations and a high H₂ partial pressure

To 1:

A low CO partial pressure causes the rate of hydroformylation to increase. However, a minimum CO pressure depending on reaction temperature must be maintained to ensure stability and consequently activity of the HCo(CO)₄ catalyst.

To 2:

If, for example, the H₂ partial pressure in the 'oxo' gas or the catalyst concentration is increased, then the rate of formation (i.e., propene conversion to butyraldehydes) becomes greater.

However, the n-butyraldehyde selectivity is simultaneously lowered due to further hydrogenation to the alcohol, and propane formation increases. Therefore, in order to attain high selectivity, the propene conversion should be decreased. This precaution soon reaches its limit because of an uneconomical space-time yield. Optimization is further complicated by other process variables interacting with one another.

One unsolved problem in the hydroformylation of propene is the resulting isobutyraldehyde, which cannot always be used economically. Therefore process modifications of the hydroformylation, mainly involving other catalyst systems, were developed primarily to increase the n-butyraldehyde selectivity.

To 2nd process step:

Two basic procedures, with variations by each 'oxo' producer, have been developed for the separation of the cobalt hydrocarbonyl from the liquid reaction products. In one case, the reaction mixture is heated after reducing the pressure to about 20 bar. A cobalt sludge results which is separated, regenerated, and recycled to the reactor (e.g., in the Ruhrchemie process).

Another cobalt separation is used mainly with the lower aldehydes. The catalyst is treated with aqueous acid (e.g., CH₃COOH in the BASF process, long-chain carboxylic acids in the Mitsubishi process, and H₂SO₄/CH₃COOH in the UCC process) in the presence of air or O₂ and the cobalt recovered as an aqueous Co salt solution or precipitated with alkali hydroxide as Co(OH)₂. Alternatively, it is extracted with NaHCO₃ as a hydrocarbonyl (e.g., in the Kuhlmann process) and, after acidification and extraction with the olefin feedstock or auxiliary agents, recycled to the process.

To 3rd process step:

The Co-free reaction product is separated by distillation at normal pressure.

A mixture of n-butyraldehyde and isobutyraldehyde is isolated in the first column. Because of the small difference in boiling points (10 °C), this must be separated into its pure components on a second column. The residue from the aldehyde separation contains n-butanol and isobutanol from the hydrogenation of the aldehydes during the oxo reaction, as well as other byproducts such as formates, acetals, and the so-called heavy oils. The residual mixture is hydrogenated either directly or after pretreatment (e.g., hydrolysis), and worked up to butanols.

If olefins higher than propene are hydroformylated, aldehydes are not ordinarily isolated, but the crude produce hydrogenated to a mixture of n-alcohols and isoalcok immediately after removal of the cobalt catalyst.