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
Gaseous fueling of an adapted commercial automotive spark-ignition engine: simplified thermodynamic modeling and experimental study running on hydrogen, methane, carbon monoxide and their mixtures
(Elsevier, 2023) Urroz Unzueta, José Carlos; Diéguez Elizondo, Pedro; Arzamendi Manterola, Gurutze; Arana Burgui, Miguel; Gandía Pascual, Luis; Ingeniería; Ingeniaritza; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Zientziak; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In the present work, methane, carbon monoxide, hydrogen and the binary mixtures 20 % CH4–80 % H2, 80 % CH4–20 % H2, 25 % CO–75 % H2 (by volume) were considered as fuels of a naturally aspirated port-fuel injection four-cylinder Volkswagen 1.4 L spark-ignition (SI) engine. The interest in these fuels lies in the fact that they can be obtained from renewable resources such as the fermentation or gasification of residual biomasses as well as the electrolysis of water with electricity of renewable origin in the case of hydrogen. In addition, they can be used upon relatively easy modifications of the engines, including the retrofitting of existing internal combustion engines. It has been found that the engine gives similar performance regardless the gaseous fuel nature if the air–fuel equivalence ratio (λ) is the same. Maximum brake torque and mean effective pressure values within 45–89 N⋅m and 4.0–8.0 bar, respectively, have been obtained at values of λ between 1 and 2 at full load, engine speed of 2000 rpm and optimum spark-advance. In contrast, the nature of the gaseous fuel had great influence upon the range of λ values at which a fuel (either pure or blend) could be used. Methane and methane-rich mixtures with hydrogen or carbon monoxide allowed operating the engine at close to stoichiometric conditions (i.e. 1 < λ < 1.5) yielding the highest brake torque and mean effective pressure values. On the contrary, hydrogen and hydrogen-rich mixtures with methane or carbon monoxide could be employed only in the very fuel-lean region (i.e. 1.5 < λ < 2). The behavior of carbon monoxide was intermediate between that of methane and hydrogen. The present study extends and complements previous works in which the aforementioned fuels were compared only under stoichiometric conditions in air (λ = 1). In addition, a simple zero-dimensional thermodynamic combustion model has been developed that allows describing qualitatively the trends set by the several fuels. Although the model is useful to understand the influence of the fuels properties on the engine performance, its predictive capability is limited by the simplifications made.
Open Access
Conversion of a gasoline engine-generator set to a bi-fuel (hydrogen/gasoline) electronic fuel-injected power unit
(Elsevier, 2011) Sáinz Casas, David; Diéguez Elizondo, Pedro; Urroz Unzueta, José Carlos; Sopena Serna, Carlos; Guelbenzu, E.; Pérez Ezcurdia, Amaya; Benito Amurrio, Marta; Marcelino Sádaba, Sara; Arzamendi Manterola, Gurutze; Gandía Pascual, Luis; Ingeniería; Ingeniaritza
The modifications performed to convert a gasoline carbureted engine-generator set to a bi-fuel (hydrogen/gasoline) electronic fuel-injected power unit are described. Main changes affected the gasoline and gas injectors, the injector seats on the existing inlet manifold, camshaft and crankshaft wheels with their corresponding Hall sensors, throttle position and oil temperature sensors as well as the electronic management unit. When working on gasoline, the engine-generator set was able to provide up to 8 kW of continuous electric power (10 kW peak power), whereas working on hydrogen it provided up to 5 kW of electric power at an engine speed of 3000 rpm. The air-to-fuel equivalence ratio (λ) was adjusted to stoichiometric (λ = 1) for gasoline. In contrast, when using hydrogen the engine worked ultra-lean (λ = 3) in the absence of connected electric load and richer as the load increased. Comparisons of the fuel consumptions and pollutant emissions running on gasoline and hydrogen were performed at the same engine speed and electric loads between 1 and 5 kW. The specific fuel consumption was much lower with the engine running on hydrogen than on gasoline. At 5 kW of load up to 26% of thermal efficiency was reached with hydrogen whereas only 20% was achieved with the engine running on gasoline. Regarding the NOx emissions, they were low, of the order of 30 ppm for loads below 4 kW for the engine-generator set working on hydrogen. The bi-fuel engine is very reliable and the required modifications can be performed without excessive difficulties thus allowing taking advantage of the well-established existing fabrication processes of internal combustion engines looking to speed up the implementation of the energetic uses of hydrogen.
Open Access
Gold supported on CuOₓ/CeO₂ catalyst for the purification of hydrogen by the CO preferential oxidation reaction (PROX)
(Elsevier, 2014) Arzamendi Manterola, Gurutze; Gandía Pascual, Luis; Química Aplicada; Kimika Aplikatua
Hydrogen produced from the conversion of hydrocarbons or alcohols contains variable amounts of CO that should be removed for some applications such as feeding low-temperature polymer electrolyte membrane fuel cells (PEMFCs). The CO preferential oxidation reaction (PROX) is particularly well-suited for hydrogen purification for portable and on-board applications. In this work, the synthesis and characterization by XRF, BET, XRD, Raman spectroscopy and H2-TPR of a gold catalyst supported on a coppercerium mixed oxide (AuCeCu) for the PROX reaction are presented. The comparison of this catalyst with the copper–cerium mixed oxide (CeCu) revealed that the experimental procedure used for the deposition of gold gave rise to the loss of reducible material by copper lixiviation. However, the AuCeCu solid was more active for CO oxidation at low temperature. A kinetic study has been carried over the AuCeCu catalyst for the PROX reaction and compared with that of the CeCu catalyst. The main difference between the models affected the contribution of the CO adsorption term. This fact may be related to the surface electronic activity produced by the interaction of the cationic species in the AuCeCu solid, able to create more active sites for the CO adsorption and activation in the presence of gold.
Open Access
Outstanding performance of rehydrated Mg-Al hydrotalcites as heterogeneous methanolysis catalysts for the synthesis of biodiesel
(Elsevier, 2018) Navajas León, Alberto; Campo Aranguren, Idoia; Moral Larrasoaña, Ainara; Echave, Javier; Sanz, Oihane; Montes, Mario; Odriozola, José A.; Arzamendi Manterola, Gurutze; Gandía Pascual, Luis; Química Aplicada; Kimika Aplikatua; Institute for Advanced Materials and Mathematics - INAMAT2
There is still a need for active, selective and stable heterogeneous catalysts for the synthesis of biodiesel. In this work, magnesium-aluminium hydrotalcites with Mg/Al molar ratios within the 1.5–5 range were synthesized by coprecipitation and used as transesterification catalysts for the synthesis of biodiesel. The mixed oxides obtained after calcination recovered the hydrotalcite structure in the form of meixnerite after rehydration in boiling water. The solids were characterized by XRD, TGA, N2 adsorption-desorption, and SEM. Basic properties were assessed by means of Hammett indicators and CO2-TPD. Rehydrated materials with the highest Mg/Al ratios showed some distinctive features: low surface area, well defined flake-like crystals, high basicity and strong basic sites with H_ values above 11. They were also the most active catalysts allowing to achieve 51–75% sunflower oil methanolysis conversion after 8 h of reaction under mild conditions (60 °C, 1 atm), methanol/oil molar ratio of 12 using between 2 and 6 wt% of catalyst. The conversion increased up to 96% (92% fatty acid methyl esters yield) using 2 wt% catalyst and methanol/oil molar ratio of 48. Catalyst leaching was not a serious problem with these solids that could be reutilized maintaining very good activities. A general accordance between solids basic properties and their catalytic performance has been observed. These results are among the best reported in the literature for heterogeneous methanolysis catalysts and have been attributed to the high basicity of the rehydrated solids and the presence of strong and accessible basic sites probably consisting in interlayer hydroxide anions at the edges of the crystals.
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.