Dielectric Behavior of Reaction Mixture during Acid-Catalyzed Transesterification Reactions in Biodiesel Production

Abstract

Information on the behavior of the dielectric properties of electrolytic solutions, such as reaction mixtures, during acid-catalyzed transesterification reactions in biodiesel production is essential in the design of processes involving microwave-heating technology. The influence of the acid catalyst on the dielectric parameters during the methanolysis and ethanolysis of crude Brazil nut oil was investigated employing H 2 SO 4 , H 3 PO 4 , ClSO 3 H and CH 3 SO 3 H as the catalysts. Refined Soybean, refined babassu and waste Brazil nut oils were used to study the dielectric behavior during the transesterification reaction catalyzed by H 2 SO 4 . Measurements were taken using a vector network analyzer with an open-ended coaxial probe (300 MHz -13 GHz). The dielectric properties of the reaction mixtures during the transesterification reaction were frequency-dependent and varied markedly with the conversion to biodiesel. The catalyst used significantly affected the dielectric properties, contributing to the high values (0.14-0.40) for the loss tangent of the reaction mixtures. The high content of free fatty acids and water in the oils also contributed considerably to the dielectric behavior during the transesterification reaction.

Quantum Tunneling Contribution for the Activation Energy in Microwave-Induced Reactions

“…As shown in Figure a–c, the behavior of the ε rms / f ratio closely resembles the measured ,− behavior of the loss factor and, as a rule, the maximum value attained by the field does not occur exactly at the relaxation frequencies (where the loss factor is at its maxima). Instead, it occurs at successively increasing frequencies as the temperature increases.…”

“…Reaction mixtures have dielectric properties that can differ considerably from those of pure liquids. Table exemplifies this fact with data for the acid and alkaline methanolysis and ethanolysis of vegetable oils. − For the acid route, an alcohol to oil molar ratio of 6:1 was used with 3% H 2 SO 4 V / V T . , For the alkaline route, in ethanolysis an ethanol/oil molar ratio of 9:1 was used while in methanolysis a methanol/oil molar ratio of 5:1 was employed. In both cases, the catalyst concentration was NaOH 0.18% by weight of oil .…”

“…As preliminary results the rms value was calculated for the field/frequency ratio ε rms / f ) in the pure liquids ethanol, methanol and glycerin, selected because their dielectric properties are widely available in the literature. ,− The strong dependence of the dielectric properties on the field frequency and temperature should be reflected in ε rms / f , as expected from eq . Figure shows the behavior of the rms value for the field/frequency ratio based on measured values for the complex permittivity (in the frequency range 0.3–13 GHz) at various temperatures for the pure liquids ethanol, methanol, glycerin and sulfuric acid, considering that the samples absorb an average power of 1 kW.…”

“…For the alkaline route, data were only collected at the beginning of the reaction. Data concerning the dielectric properties during the reactions were obtained with the reaction performed under conventional heating. − In Table , the field and effective activation energies were calculated assuming that the reactions are performed under 1 kW of microwave power, with a constant reaction temperature (maintained by simultaneous cooling, for example), applying the same value used for conventional heating. In alkaline route it is the oxygen atom that can tunnel and the barrier width is reduced , to a ≅ 0.4 Å.…”

Dynamics and Aggregate Structuring of Water Molecules in Edible Oil Analyzed by Dielectric Spectroscopy

“…It is well known that oil changes its chemical structure by an aging effect like oxidation [1], and these changes necessarily induce further changes in physical structures and properties such as fluidity and cohesion. Though dynamic behaviors of oil molecules have been investigated so far [2], reports on the molecular mechanism of aging about physical structures and properties are still few.…”