Prilezhaev epoxidation of oleic acid in the presence and absence of ultrasound irradiation

“BACKGROUND Epoxidation of double bonds in vegetable oils provide valuable green intermediates for the chemical industry. The epoxidation of oleic acid with hydrogen peroxide according to the Prilezhaev principle was studied experimentally in a multiphase laboratory-scale batch reactor operated isothermally at 50 °C and atmospheric pressure. A solid cation exchanger (Amberlite IR-120) was used as the solid catalyst to enhance the slow step in the Prilezhaev process: the in situ formation of the epoxidation agent, peracetic acid, from hydrogen peroxide and acetic acid. A rotating basket stirrer was used to suppress the external mass transfer limitations and to guarantee a turbulent random flow in the vicinity of the catalyst particles. Kinetic experiments demonstrated the catalytic effect of the cation exchanger. Several experiments were performed in the presence and absence of ultrasound irradiation at different amplitudes.

RESULTS The exposure of ultrasound irradiation on the multiphase reaction mixture impaired the conversion of the double bonds and the yield of the epoxide, compared to a reference experiment conducted under silent conditions. Catalyst characterization by scanning electron microscopy and the determination of the acid sites in recycled catalyst samples confirmed that the main reason for deactivation was leaching and/or neutralization of the sulfonic acid groups from the solid catalyst matrix.

CONCLUSIONS The application of ultrasound at different input powers resulted in lower reaction yields compared to the silent reference experiment. This observation was attributed to deactivation of the catalyst caused by leaching and/or neutralization of the sulfonic groups promoted by ultrasound exposure.”

Highlights:

• “A special mixing device (SpinChem RBR) was used, which consisted of a hollow rotating bed device that contained the immobilized catalyst particles inside and worked as the stirring element itself.”
• “All the experiments were performed under 1000 rpm stirring speed at 50 °C and a catalyst loading of 12% with respect to oil mass. The high stirring speed was used to remove the external mass transfer resistance around the catalyst particles and to maintain the oil–aqueous phase emulsion.”
• “Previously, our group studied fatty acid epoxidation under the influence of several process intensifiation techniques, such as microwave irradiation, heterogeneous catalysis and a rotating bed reactor. In most cases, the application of these process intensification techniques resulted in significantly higher reaction yields in shorter times and simplification of the experimental procedure, such as the elimination of previously necessary separation processes.”