Improvement of enzymatic oxidation in the continuous Scalable Agitated Baffle Reactor (SABRe) system

Enzymes are nature’s own working bees, and the sole reason chemical reactions can be carried out in the neutral environment within all cells.

Recently, chemists have tried to harness the great potential of enzymes in reactions, which are difficult to achieve by common chemical methods. One of the most attractive enzyme classes is oxidoreductases, more specifically oxidases, which use molecular oxygen either as an oxidant or as an electron acceptor for oxidation.

Oxidases – Advantages and Limitations

Compared to common chemical methods, enzymatic oxidation has many advantages, the main one being conversion at ambient temperatures and pressures. However, as enzymatic oxidation is done in aqueous media, the overall conversion is highly limited by solubility of oxygen in water, and by extension, the oxygen mass transfer rate through the gas-liquid interface.

In the model reaction, glucose was converted to glucono-1,5-lactone by means of glucose oxidase and molecular oxygen. The product was subsequently converted to gluconic acid by spontaneous hydrolysis. The reaction was repeated under the same conditions in both a common bench-scale batch reactor and in the SABRe.

Experimental Procedure

The experiments were run in 400mM phosphate buffer solution at pH 7 and 500 rpm with 100mM glucose and 0.27 mM oxygen as substrates and 2g/L glucose oxidase (Novozym^® 28166 from Aspergillus niger). Moreover, 0.1g/L catalase was used to convert the resulting hydrogen peroxide to water and oxygen to avoid product inhibition of the glucose oxidase. 

For the batch reaction, a 250mL reactor with 100mL working volume was used, corresponding to the 100mL reactor insert used in the SABRe. Samples were taken from the batch reaction from 10-150min reaction time, while the flow in the SABRe were varied to obtain similar results based on residence time in the reactor.