Biphasic Catalysis on a Miniplant Scale

In this section one example of catalysis on a miniplant scale is described. Although the reaction itself is homogeneous, the catalyst separation is done by extraction, making the whole system biphasic. The reaction carried out is the palladium-catalyzed telomerization of 1,3-butadiene and CO2 to a 5-lactone [Eq. (6)] described by Behr et al. [29, 30). A possible side product in this reaction is the y-lactone. 

The reaction is homogeneously catalyzed by a system formed in situ from Pd(acac)2 and tricyclohexylphosphine in acetonitrile. During a batch experiment at 90 °C and 4 MPa, 48% conversion of butadiene could be reached with 95% selectivity to the lactone. The reaction mixture was separated by flash evaporation into a vapor phase consisting only of CO2, 1,3-butadiene plus acetonitrile and a liquid phase consisting of more than 95% 5-lactone (and side products). The vapor phase, after condensation, was recycled to the reactor, which allowed a closed loop for solvent and nonconverted feedstocks. 

The liquid phase was separated by extraction with 1,2,4-butanetriol into a rafEnate phase containing the catalyst and an extract phase containing the 8-lactone. The raffinate stream was recycled to the reactor. The extract phase was separated by distillation into a 8-lactone stream and a 1,2,4-butanetriol stream. The bottom stream consisted of 95 wt.% 8-lactone and 5 wt.% 1,2,4-butanetriol. The top stream consisted of 98 wt.% 1,2,4-butanetriol and 2 wt.% 5-lactone (and some catalyst), and was recycled to the extraction unit 

This process was realized in a continuous miniplant for 24 h of operation. The acetonitrile and the unreacted substrates were recycled from the flash evaporator to the reactor. No accumulation of side products was observed their amount after the continuous experiment was as high as after the batch experiment. Raising the temperature from 100 °C to 160 °C resulted in the isomerization of the 5-lactone to y-lactones and in the oxidation of the hgand. Therefore it was concluded that the several separation steps should be performed below 100 °C to avoid isomerization and catalyst deactivation. In further investigations, efforts shotdd be made to close the remaining recycle lops. 

The new recycling concept has been applied to the following model reactions  

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