n-Valeric acid: Expansion of the two phase hydroformylation to butenes

n-valeric acid (n-pentanoic acid) is the basis of new ester-type lubricants for CFC-substitutes in refrigeration systems which are made from the carboxylic acid with trimethylolpropane, pentaerythritol or dipentaerythritol. Together with UCC, Hoechst is one of the largest producers of n-valeric acid for this field of application. Valeric acid is prepared from butene cuts through hydroformylation to valeraldehyde with subsequent oxidation. The RCH-RP process of low-pressure hydroformylation [1] used at the Ruhrchemie side of Hoechst, involving an aqueous rhodium-TPPTS catalyst system (TPPTS = triphenylphosphane trisulfonate, sodium salt), has been used since 1984 to produce roughly 300,000 ton of n-butyraldehyde from propylene per year. A further development of this successful technology has been achieved using the available feedstock base of isomeric butenes (raffinate II) for the preparation of n-C-5 products (n-valeraldehyde, n/iso-amyl alcohol and n-valeric acid) [2]. The process developed permits high selectivity of the n/iso ratio to the desired n-aldehyde and it is environmentally benign as waste water contamination has been substantially reduced. In December 1995 production of n-valeraldehyde was started up in a new plant. Oxidation to produce the acid using the Hoechst/Ruhrchemie process is carried out with proven technology.