Optimization of solvent free ohmic-assisted heating as a promising esterification tool for ethyl butyrate synthesis

Solvent free ohmic-assisted esterification (OAE) was investigated as a promising tool for ethyl butyrate (pineapple flavor) synthesis. To this end, Amberlyst 15 dry was used as an ion exchange catalyst to promote the esterification reaction between ethanol and butyric acid. Solubility, electrical conductivity, and heating rate of the reaction mixture as affected by different salt types and concentrations were studied. Then, the OAE operation parameters (i.e., electrical field, catalyst concentration, and mole ratio of ethanol:butyric acid) were optimized. The highest ethyl butyrate yield (63%) was achieved after 90 min in presence of 1% LiCl, 2% Amberlyst 15 dry using field strength of 25 V/cm and an ethanol:butyric acid mole ratio of 1:1. Optimum conditions of OAE were also compared with microwave- and magnetic stirrer-assisted esterification methods. OAE provided the highest yield (61.20%) at a shorter time with the lowest specific energy consumption (0.04 kWh/g ethyl butyrate) and specific CO2 emission (0.03 kg CO2/g ethyl butyrate). The micrographs of scanning electron microscopy showed less structural damages in the catalyst structure using OAE compared to other esterification methods. Therefore, OAE can be proposed as a cost-effective and environmentally friendly technology for the synthesis of flavor esters in the food industry.

Automated summary

The study successfully synthesized ethyl butyrate using solvent-free ohmic-assisted esterification (OAE) and found that this method outperformed microwave- and magnetic stirrer-assisted esterification in terms of yield, energy consumption, and CO2 emission.