Process for treating hydroformylation catalyst

In a process for producing an aldehyde by hydroformylation of allyl alcohol with carbon monoxide and hydrogen, in the presence of a rhodium-tertiary phosphine complex hydroformylation catalyst, which comprises, in a reaction zone, providing a liquid reaction medium which comprises a solution of said catalyst dissolved in an organic solvent, supplying carbon monoxide, hydrogen and allyl alcohol to said liquid reaction medium under conditions that effect hydroformylation of said allyl alcohol to convert same to the aldehyde, then extracting the aldehyde from the liquid reaction medium with water and separately recovering said solution of said catalyst dissolved in said organic solvent wherein the recovered solution of said catalyst is substantially free of said aldehyde, hydrogen and carbon monoxide and contains spent catalyst, the improvement which comprises:

• placing said recovered solution in a treatment zone separate from said reaction zone and, in said treatment zone, heating said recovered solution at a temperature of from 40.degree. to 100.degree. C., in contact with a gaseous mixture of carbon monoxide and hydrogen mixed at a volume ratio of from 1:99 to 80:20, to restore the activity of said spent catalyst whereby said solution containing the restored catalyst an be recycled to said reaction zone as said liquid reaction medium.