Lipase catalyzed green epoxidation of oleic acid using ultrasound as a process intensification method

“Epoxidized fatty acids are important green intermediates for chemical industry. This work was focused on the direct epoxidation of oleic acid (OA) using immobilized lipase Novozym® 435 as the catalyst and hydrogen peroxide (HP) as the epoxidation agent. The impacts of reactant molar ratio (HP:OA = 1...2), reaction temperature (30–60 ◦C), catalyst loading (7 wt-%) and stirring rate (500–1000 rpm) on the fatty acid conversion and epoxide selectivity were evaluated Acoustic irradiation and an advanced stirring system were implemented for reaction intensification and different ultrasound amplitudes (0–90%) were screened. Novozym® 435 revealed to be an efficient and durable catalyst for fatty acid epoxidation. The reaction was promoted by an excess of HP. The highest epoxide selectivity was about 80% at full conversion of oleic acid reached within 200 min. Ultrasound irradiation (90% amplitude) enhanced the initial reaction rate by a factor two compared to silent conditions and higher oleic acid conversions were reached compared to silent experiments. The catalyst preserved its activity and selectivity rather well, which was confirmed by catalyst recovery experiments conducted in the absence and presence acoustic irradiation. The main ring-opening agent is the fatty acid itself, which resulted in the formation of esters.”

Highlights:

• ”[...] contrary to the previous statements, a high stirring speed of 1000 rpm was appropriate for this system. A possible hypothesis is that the filter around the SpinChem ® device protects the immobilized lipase from being damaged by a grinding effect of the agitator.”
• The drawback of the lipase-catalyzed reaction is the cost of the immobilized lipase; it needs to be recycled to be competitive in cost. To address this, the authors used the immobilized lipase in a rotating bed reactor and recycled the enzyme.
• Using ultrasound offered advantages and disadvantages; the reaction rate was improved by the ultrasound but the cavitation from the ultrasound damaged the lipase beads.

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