Open Access
Reaction monitoring by ultrasounds in a pseudohomogeneous medium: triglyceride ethanolysis for biodiesel production
(MDPI, 2022) Reyero Zaragoza, Inés; Gandía Pascual, Luis; Arzamendi Manterola, Gurutze; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The sound propagation speed measurement us is used for monitoring triglyceride ethanol-ysis 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. Nev-ertheless, 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.
Open Access
Pseudo-homogeneous and heterogeneous kinetic models of the NaOH-catalyzed methanolysis reaction for biodiesel production
(MDPI, 2021) Zabala, Silvia; Reyero Zaragoza, Inés; Campo Aranguren, Idoia; Arzamendi Manterola, Gurutze; Gandía Pascual, Luis; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Methanolysis of vegetable oils in the presence of homogeneous catalysts remains the most important process for producing biodiesel. However, there is still a lack of accurate description of the reaction kinetics. This is in part due to the complexity of the reacting system in which a large number of interconnected reactions take place simultaneously. In this work, attention is focused on the biphasic character of the reaction medium, formed by two immiscible liquid phases. The behavior of the phases is investigated regarding their physicochemical properties, mainly density and mutual solubility of the components, as well as composition. In addition, two kinetic models with different level of complexity regarding the biphasic character of the reaction medium have been developed. It has been found that a heterogeneous model considering the presence of the two phases and the distribution of the several compounds between them is indispensable to get a good description of the process in terms of oil conversion and products yields. The model captures the effects of the main variables of an isothermal batch methanolysis process: methanol/oil molar ratio, reaction time and catalyst concentration. Nevertheless, some adjustment is still required as concerns modelling of the saponification reactions and catalyst deactivation.
Open Access
Acid-catalyzed etherification of glycerol with tert-butanol: reaction monitoring through a complete identification of the produced alkyl ethers
(MDPI, 2023) Cornejo Ibergallartu, Alfonso; Reyero Zaragoza, Inés; Campo Aranguren, Idoia; Arzamendi Manterola, Gurutze; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Higher tert-Butyl glycerol ethers (tBGEs) are interesting glycerol derivatives that can be produced from tert-butyl alcohol (TBA) and glycerol using an acid catalyst. Glycerol tert-butylation is a complex reaction that leads to the formation of five tBGEs (two monoethers, two diethers, and one triether). In order to gain insight into the reaction progress, the present work reports on the monitoring of glycerol etherification with TBA and p-toluensulfonic acid (PTSA) as homogeneous catalysts. Two analytical techniques were used: gas chromatography (GC), which constitutes the benchmark method, and( 1)H nuclear magnetic resonance (H-1 NMR), whose use for this purpose has not been reported to date. A method for the quantitative analysis of tBGEs and glycerol based on H-1 NMR is presented that greatly reduced the analysis time and relative error compared with GC-based methods. The combined use of both techniques allowed for a complete quantitative and qualitative description of the glycerol tert-butylation progress. The set of experimental results collected showed the influence of the catalyst concentration and TBA/glycerol ratio on the etherification reaction and evidenced the intrinsic difficulties of this process to achieve high selectivities and yields to the triether.

Arzamendi Manterola, Gurutze

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