Rhodium recovery from hydroformylation reaction product

Claim 1

In a process for catalytically hydroformylating propylene by the following steps: (a) reacting said propylene with carbon monoxide and hydrogen in the presence of a liquid reaction medium containing as the hydroformylation catalyst a complex of rhodium with a triorganophosphine to produce a liquid reaction mixture comprising triorganophosphine, butyraldehyde, and reaction by-products; (b) stripping said liquid reaction mixture by gas stripping, distillation, or evaporation during the course of said hydroformylation reaction to remove a vapor stream comprising said butyraldehyde and said hydroformylation catalyst overhead from said reaction mixture; (c) condensing said vapor stream and recovering a crude product condensate comprising said butyraldehyde; (d) distilling said condensate to form a distillate comprising the bulk of said butyraldehyde from said condensate and a residue comprising a crude reaction heavy ends mixture containing a minor amount of said butyraldehyde; and (e) distilling said crude reaction heavy ends mixture into (1) an overhead stream comprising those components of the crude reaction heavy ends mixture which are more volatile than said triorganophosphine and (2) a residue stream comprising those components of the crude reaction heavy ends mixture which are equal to or lower than said triorganophosphine in volatility and including any rhodium moiety initially contained in said vapor stream, the improvement which comprises: prior to step (e), stripping said residue containing said crude reaction heavy ends mixture obtained from step (d) with nitrogen gas to remove therefrom said minor amount of butyraldehyde.