Cobalt recovery, hydroformylation

Several explanations may be taken into account for only a small decrease in importance an existing high-pressure infrastructure which is also used for the hydroformylation of olefins higher than propene, where cobalt-based processes are advantageous a combined cobalt recovery and recycle system for the hydroformylation of different olefins and the use of tail gases from low-pressure hydroformylation units. 

An aspect of the hydroformylation reaction which is of particular importance in continuous commercial operation is the separation of the catalyst from product aldehyde and/or alcohol, together with its recovery and recycle into the reactant stream. This feature is of considerable economic and process importance for cobalt reactions and of extreme economic importance for rhodium reactions. 

Unligated rhodium has the ability to hydroformylate a wide range of different olefins, both branched internal forms as well as linear. Virtually no water is used or created in the process (unlike a cobalt-catalysed system which needs water for catalyst recovery). Other key advantages of a rhodium (I) system are ... 

Phosphines. Polymeric phosphines exhibit strong metal-binding properties. Nonpolymeric phosphines, in particular triphenylphosphine, are employed as ligands for cobalt and rhodium in hydroformylation catalysts used in plasticizer manufacture. Extensive efforts have been made to attach phosphine-metal complexes to polymers in order to facilitate catalyst recovery and enhance selectivity... 

In catalyst recovery, only marginal improvements to the previous state of the art are described in the patents published by ExxonMobil. Some general aspects are presented here to illustrate this quite complicated part of the commercial hydroformylation process with cobalt. The catalyst, which is either already in the olefin feed to the reactor or is fed to the reactor as fresh catalyst, for example, in the form of dicobalt octacarbonyl Co2(CO)g or cobalt salt, or many other compounds, has to be removed from the reaction mass after the reaction. One... 

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