Papers by Mercedes Martínez
Background: In Spain, few studies have evaluated prenatal exposure to heavy metals. The objective... more Background: In Spain, few studies have evaluated prenatal exposure to heavy metals. The objective of this study was to describe lead, mercury and cadmium concentrations in blood from a sample of newborn–mother-father trios, as well as to investigate the association between metals in cord blood and parental variables. We also explored the relationship between cord blood metal concentrations and child characteristics at birth.
Energy & Fuels, 2006
In recent years, the acceptance of fatty acid methyl esters (biodiesel) as an alternative fuel ha... more In recent years, the acceptance of fatty acid methyl esters (biodiesel) as an alternative fuel has rapidly grown in Spain. The raw materials to produce biodiesel in this country include traditional seed oils (sunflower and rapeseed), alternative seed oils (Brassica carinata), genetically modified vegetable oils (high oleic sunflower), and used frying oils. In this study, the above vegetable oils with free fatty acid content from 0.02 to 6.47% were transesterified with methanol using potassium hydroxide as a catalyst in a batch-stirred reactor. Biodiesel yield and ester content were independent of the type of vegetable oil, but both decreased when the vegetable oil acid value increased due to the neutralization of the free fatty acid content in the oil. Yield losses were also due to triglyceride saponification and methyl ester dissolution in glycerol, according to the material balance of the process. On the other hand, the stoichometric potassium hydroxide to neutralize the free fatty acids was added to the amount of potassium hydroxide used as a catalyst for the vegetable oils with the highest proportion of free fatty acid. In every case, biodiesel met the glyceride concentration specifications, but the process gave much lower yields. The viscosity, peroxide value, and acid value were within EU specifications for the methyl ester evaluated. The iodine value was above the EU specification for the methyl esters from sunflower oil and low erucic B. carinata oil.
Energy & Fuels, 2006
A study was made of the kinetics of Brassica carinata oil methanolysis. This reaction yields fatt... more A study was made of the kinetics of Brassica carinata oil methanolysis. This reaction yields fatty acid methyl esters and glycerol and consists of three consecutive reversible reactions. Diglycerides and monoglycerides are intermediate products. The mechanism of B. carinata oil methanolysis involves an initial stage of mass-transfer control, followed by a second region of kinetic control. However, the initial mass transfercontrolled step is negligible using an impeller speed of at least 600 rpm. The experiments were performed in a batch reactor stirred at 600 rpm over 2 h using potassium hydroxide as the catalyst at atmospheric pressure with a 6/1 molar ratio of methanol to B. carinata oil. The resultant mixture was analyzed by gas chromatography. The effects of temperature and catalyst concentration on the reaction rates were analyzed, determining the reaction rate constants and the activation energies. The B. carinata oil methanolysis can be described as a pseudo-homogeneous catalyzed reaction system, following a second-order mechanism for the forward and reverse reactions. Higher temperatures and catalyst concentrations increased the reaction rates. The proposed mathematical model matched the experiment results.
Bioresource Technology, 2007
A study was made of the material balance for the fatty acid methyl ester (biodiesel) synthesis fr... more A study was made of the material balance for the fatty acid methyl ester (biodiesel) synthesis from sunflower oil using potassium hydroxide as the catalyst. A factorial design of experiments and a central composite design have been used to evaluate the influence of operating conditions on the process material balance. The responses chosen were the biodiesel yield and the yield losses due to triglyceride saponification and methyl ester dissolution in glycerol, while the variables studied were temperature, initial catalyst concentration and the methanol:vegetable oil molar ratio. The biodiesel yield increased and therefore the yield losses decreased by decreasing catalyst concentration and temperature. However, the methanol:sunflower oil molar ratio did not affect the material balance variables significantly. Second-order models were obtained to predict the biodiesel yield and both yield losses. Within the experimental range studied, these models largely matched the results from the experiments.
Bioresource Technology, 2007
A study was made of the material balance for the fatty acid methyl ester (biodiesel) synthesis fr... more A study was made of the material balance for the fatty acid methyl ester (biodiesel) synthesis from sunflower oil using potassium hydroxide as the catalyst. A factorial design of experiments and a central composite design have been used to evaluate the influence of operating conditions on the process material balance. The responses chosen were the biodiesel yield and the yield losses due to triglyceride saponification and methyl ester dissolution in glycerol, while the variables studied were temperature, initial catalyst concentration and the methanol:vegetable oil molar ratio. The biodiesel yield increased and therefore the yield losses decreased by decreasing catalyst concentration and temperature. However, the methanol:sunflower oil molar ratio did not affect the material balance variables significantly. Second-order models were obtained to predict the biodiesel yield and both yield losses. Within the experimental range studied, these models largely matched the results from the experiments.
Industrial & Engineering Chemistry Research, 2005
A study was made of the kinetics of sunflower oil methanolysis. This reaction yields methyl ester... more A study was made of the kinetics of sunflower oil methanolysis. This reaction yields methyl esters (biodiesel) and glycerol and consists of three consecutive reversible reactions. Diglycerides and monoglycerides are intermediate products. A reaction mechanism was proposed involving an initial region of mass transfer control followed by a second region of kinetical control. An analysis was also made of the effects of impeller speed, temperature, and catalyst concentration on the reaction rates, determining the reaction rate constants and the activation energies. The reactions were performed in a batch stirrer reactor, and the reaction mixture was analyzed by gas chromatography. The initial mass transfer-controlled region was not significant using 600 rpm. The kinetically controlled section followed a second-order mechanism for the forward and reverse reactions, where the reaction system could be described as a pseudo-homogeneous catalyzed reaction. The temperature and catalyst concentration increased the reaction rates. The proposed mathematical model fitted the experimental results well.
Journal of The American Oil Chemists Society, 2005
Synthesis of FAME from Brassica carinata oil to produce biodiesel was accomplished using potassiu... more Synthesis of FAME from Brassica carinata oil to produce biodiesel was accomplished using potassium hydroxide as the catalyst. A factorial design of experiments and a central composite design were used. The variables chosen were: type of Brassica carinata oil, initial catalyst concentration, and temperature; and the responses were FAME purity and yield. The type of B. carinata oil included high-erucic B. carinata (HEBC) and lowerucic B. carinata (LEBC) varieties. The results show that the type of B. carinata oil does not affect the purity and yield of FAME. However, HEBC oil is more suitable for biodiesel production because its iodine value is lower and within the European Union specifications. The initial catalyst concentration is the most important factor, having a positive influence on FAME purity but a negative effect on FAME yield. The temperature has a significant positive effect on FAME purity and a significant negative influence on FAME yield. Second-order models were obtained to predict FAME purity and yield as a function of catalyst concentration and temperature for HEBC oil methanolysis. The best conditions for this process are 25°C, and 1.2–1.5 wt% for the catalyst concentration.
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Papers by Mercedes Martínez