Reaction Monitoring by Ultrasounds in a Pseudohomogeneous Medium: Triglyceride Ethanolysis for Biodiesel Production

Inés Reyero,Gurutze Arzamendi,Luis M Gandía

doi:10.3390/pr10010012

Abstract

The sound propagation speed measurement us is used for monitoring triglyceride ethanolysis in a broad range of reaction conditions (mainly, temperature: 23–50 °C; ethanol/oil: from 6 to 24 mol/mol). Experimentally, us slightly increased with the reaction time in all cases as a result of the contribution of its dynamic mixture components. Nomoto’s expression for homogeneous mixtures offered suitable us estimation but with values notably higher than the experimental ones due to the resistance to sound propagation offered by the ethanol/oil interphase (non-homogeneous medium). Our strategy was based on both the comparison of the experimental us values and the theoretical ones correlated by means of triglyceride conversion and on the estimation of the sound speed of oil/ethanol that could emulate the resistance offered by the interphase. The evolution of the reactions was predicted quite well for all the experiments carried out with very different reaction rates. Nevertheless, at the beginning of the reaction, the estimated conversion (outside of industrial interests) showed important deviations. The presence of the intermediate reaction products, diglycerides, and monoglycerides could be responsible for those deviations.

Highlights

Due to the non-destructive nature of sound waves, the measure of its propagation speed has numerous applications in different fields of science and environmental [1,2], biomedical [3,4], mechanical, thermodynamic [5], marine, and civil applications
Field sound speed measurements can be used for the estimation of mechanical properties like the elastic parameters, corrosion, or mechanical failures [6,7], as well as for determining the thermal properties, such as conductivity
The reaction progression implied a decrease in the oil concentration (us (20 ◦ C) = 1464.3 m/s) in favor of the production of biodiesel with a slightly lower speed value (us (20 ◦ C) = 1406 m/s)

Summary

Introduction

Due to the non-destructive nature of sound waves, the measure of its propagation speed has numerous applications in different fields of science and environmental [1,2], biomedical [3,4], mechanical, thermodynamic [5], marine, and civil applications. The used ranges of ultrasonic wave frequencies can vary. Field sound speed measurements can be used for the estimation of mechanical properties like the elastic parameters, corrosion, or mechanical failures [6,7], as well as for determining the thermal properties, such as conductivity. The correlation of the experimental sound speed values with the corresponding prediction by semiempirical formulas such as Nomoto’s or ideal mixing relations allows for studying the nature of molecular interactions. Positive deviations are attributed to the molecular association, whereas negative deviations or lower positive deviations would indicate molecular dissociation, such as by the addition of solvents or increases in temperature [11]

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