Kinetics of nopyl acetate synthesis by homogeneously catalyzed esterification of acetic acid with nopol

Abstract

The esterification of nopol with acetic acid to produce nopyl acetate using sulfuric acid as homogeneous catalyst was studied. The reactions were carried out in a batch reactor, at different temperatures (50, 60, 70 and 80°C), catalyst concentrations (0.0184, 0.0275, 0.0367 and 0.0480 molL −1 and molar ratio of acetic acid to nopol (1: 1, 1:2, 1:3 and 1: 4); the chemical equilibrium composition was measured at those reaction conditions. It was found that the equilibrium composition is a weak function of temperature, equilibrium conversion was 63, 68, 71 and 75% at 50, 60, 70 and 80°C, respectively. The reaction was described with a simple power-law model with a second-order kinetic model for both the forward and the backward reaction, using concentration and activities which were predicted by the Universal Functional group Contribution (UNIFAC) method for considering non-ideal behavior of the liquid phase. The forward reaction rate and the equilibrium constants increased with temperature; the relation of the pre-exponential factor with the catalyst amount was evaluated. The activation energy and pre-exponential factor estimated for the forward reaction using the kinetic model based on concentration, were respectively, 28.08 kJmol −1 and 11126 Lmol −1 h −1 with a concentration of catalyst of 0.0275 M. Using the kinetic model based on activities, the forward reaction rate constant was 28.56 kJmol −1 and the k f o,act was 33860 Lmol −1 h −1. The enthalpy (34.90 kJmol −1) and the entropy (0.12 kJmol −1 K −1) of reaction were determined using van't Hoff equation. RESUMEN: Se estudió la esterificación de nopol con ácido acético para producir acetato de nopilo utilizando ácido sulfúrico como catalizador homogéneo. Los experimentos se llevaron a cabo en un reactor por lotes variando la temperatura (50, 60, 70 y 80°C), la concentración del catalizador (0.0184, 0.0275, 0.0367 y 0.0480 molL −1) y la relación molar de ácido acético a nopol (1: 1, 1:2, 1:3 y 1: 4); la composición del equilibrio químico se midió a las condiciones de reacción. La conversión de equilibrio fue 63, 68, 71 y 75% a 50, 60, 70 y 80°C, respectivamente. La reacción se describió con un modelo de potencia simple con un modelo de segundo orden en ambas direcciones, usando concentraciones y actividades, las cuales se predijeron con el método de contribución de grupos UNIFAC. Se determinaron las constantes de velocidad de la reacción directa y la constante de equilibrio, las cuales aumentaron con la temperatura; se evaluó la relación del factor pre-exponencial con la cantidad de catalizador. La energía de activación y el factor pre-exponencial estimados para la reacción hacia adelante usando el modelo basado en concentración fueron respectivamente 18.08 kJmol −1 y 11126 Lmol −1 h −1 con una concentración de catalizador de 0.0275 M. Usando el modelo basado en actividades la constante de velocidad directa fue 28.56 kJmol −1 y el factor pre-exponencial 33860 Lmol −1 h −1. La entalpía (34.90 kJmol −1) y la entropía (0.12 kJmol −1 K −1) de reacción se determinar...

Considerations for Scaling Up the Synthesis of a Glycine‐Based Ionic Demulsifier

“…The entropy (0.078 kJ mol -1 K -1 ) makes a very small contribution, and it means that the reaction tends to be more disorderly as it progresses. Similar enthalpy values for esterification reactions are reported in the literature, e.g., for the esterification of acetic acid with methanol (29.99 kJ mol -1 ) [25], acid acetic with nopol (34.90 kJ mol -1 ) [26], acrylic acid with ethanol (71.94 kJ mol -1 ) [27], and acrylic acid with 2-ethylhexan-1-ol (25-46.1 kJ mol -1 ) [28]. The negative Gibbs free energies mean that, at the studied temperatures, the reaction is spontaneous, and increasing the temperature of the endothermic reaction favors the formation of products.…”

Esterification of rosin with methyl alcohol for fuel applications

“…The use of homogeneous catalysts has been reported for different esterification reactions leading to high ester yields (e.g., >90% of conversion of nopol into nopyl acetate has been reported with sulfuric acid as a catalyst [12]). This kind of catalyst is typically used in the esterification of rosin and resin acids with different alcohols, particularly, Lewis and Brønsted acids, such as acetic acid, sulfuric acid, and ptoluenesulfonic acid.…”