Second generation biofuels from microbial oil

Biodiesel can be produced from different oleaginous sources. Currently, the most extended biodiesel originates from vegetable oils, due to their availability and similar properties to diesel fuel. However, the use of vegetable oil as feedstock to produce biodiesel is controversial due to biodiesel low sustainability, potential conflict with food and the use of arable land for energy purposes. In this context, this thesis reviews novel alternatives to the traditional raw materials used to produce biodiesel. Moreover, for sustainability reasons, the use of agricultural practices in oilseed crops, focused on fertilizers, should be reduced. In the present thesis, no influence over the quality of biodiesel has been found, thus environment benefits are achieved. The study of microbial oil produced from oleaginous yeasts in tandem with reutilization of agro-industrial waste is another key point of this thesis. Oleaginous yeast accumulates intracellular lipids through the fermentation of various agro-industrial wastes. These microorganisms accumulate different amounts of lipid with variable fatty acid composition, according to the substrate used or the growth conditions. Thus, it appears that glycerol, a by-product from the biodiesel industry, in combination or not with hydrolysates from oilseed meal, is suitable as a carbon source for many oleaginous yeasts for the production of lipids. Finally, it may be concluded that the optimization of the culture conditions (culture mode, temperature, etc.) for each oleaginous yeasts can improve the intracellular lipid accumulation.El biodiésel se puede producir a partir de diferentes fuentes oleaginosas, siendo las más utilizadas los aceites vegetales, debido a su disponibilidad y a aportar un biocombustible con propiedades similares al gasóleo. Sin embargo, el uso de aceite vegetal genera controversia debido a su baja sostenibilidad, el conflicto potencial con el sector alimenticio y la utilización de tierra cultivable para uso energético. Por ello, en esta tesis se hace una revisión sobre alternativas novedosas a las materias primas tradicionales para producir biodiésel. Por motivos de sostenibilidad, el uso de prácticas agrícolas en los cultivos oleaginosos, principalmente fertilizantes, debe reducirse al mínimo. En esta tesis se ha apreciado que no afecta a la calidad del biodiésel producido, lo cual redunda en un beneficio para el medio ambiente. Otro pilar en que se sustenta esta tesis trata sobre el biodiésel obtenido a partir de aceite microbiano producido por levaduras oleaginosas, junto a la reutilización de residuos agroindustriales. Estos microorganismos pueden acumular diferentes cantidades de lípidos con perfil de ácidos grasos variable, según el sustrato utilizado o las condiciones de crecimiento. Así, se aprecia que la glicerina, subproducto de la producción de biodiésel, combinado o no con hidrolizado de torta de prensado de semillas oleaginosas, es una fuente de carbono adecuada para muchas levaduras oleaginosas en la producción de aceite. Finalmente, se concluye que una optimización de las condiciones de cultivo (modo de cultivo, temperatura, etc.) para cada una de las levaduras puede mejorar la acumulación de lípidos intracelulares

Optimization of the Transesterification of Waste Cooking Oil with Mg-Al Hydrotalcite Using Response Surface Methodology

Nowadays, biodiesel has become a very promising alternative to fossil diesel fuel, regarding environmental concerns and fuel resource depletion. Biodiesel is usually produced through homogeneous or heterogeneous transesterification of different fatty raw materials. Although main research has been carried out with homogenous catalysts, heterogeneous catalysts may be of interest due to ease of recovery and recycling, as well as readiness for continuous processing. In this work, calcined Mg-Al hydrotalcite (HT) was used for the heterogeneous transesterification of waste cooking oil. Three reaction parameters, namely, reaction time, amount of catalyst, and methanol-to-oil molar ratio, were optimized by means of Response Surface Methodology (RSM) at constant temperature (65 C), using a Box-Behnken design. Optimal fatty acid methyl ester (FAME) content (86.23% w/w FAME/sample) was predicted by the model with an R-squared value of 98.45%, using 3.39 g of HT (8.5% w/w oil) and an 8:1 methanol-oil molar ratio, for a duration of 3.12 h. It was observed that calcination of HT, while avoiding the previous washing step, allowed the presence of chemical species that enhanced the effect of the catalyst. It can be concluded from this field trial that calcined and nonwashed Mg-Al hydrotalcite may be considered an effective basic catalyst for the production of biodiesel from waste cooking oil. Also, RSM proved to be a useful tool for predicting biodiesel yield

Influence of Short Carbon-Chain Alcohol (Ethanol and 1-Propanol)/Diesel Fuel Blends over Diesel Engine Emissions

Oxygenated fuels, in this case short carbon-chain alcohols, have been investigated as alternative fuels to power compression ignition engines. A major advantage of short-chain alcohols is that they can be produced from renewable resources, i.e., cultivated commodities or biomass-based biorefineries. However, before entering the market, the effects of short-chain alcohols on engine performance, exhaust emissions, noise and sound quality need to be understood. This work sheds light on the relationship between the physicochemical properties of the alcohol/diesel fuel blends (ethanol and 1-propanol) on engine performance, exhaust emissions and, for the first time, on noise and sound quality. It has been demonstrated that when the content of alcohol in blends increased, soot and soluble organic material emissions drastically decreased, mainly due to the increase of oxygen content in the fuel. Reduction in soot emissions combined with higher thermodynamic efficiency of alcohol fuels, with respect to diesel fuel, enable their utilization on compression ignition engines. There is also an improvement in the soot-NOx trade off, leading to large reductions on soot with a small effect on NOx emissions. The oxygen content within the fuel reduces CO and THC emissions at extra-urban driving operation conditions. However, hydrocarbons and CO emissions increased at urban driving conditions, due to the high heat of vaporization of the alcohol fuels which reduces cylinder temperature worsening fuel atomization, vaporization and mixing with air being more significant at lower cylinder temperature conditions (low engine loads and speeds). Similarly, the higher the presence of alcohol in the blend, the higher the noise emitted by the engine due to their low tendency to auto-ignition. The optimization of alcohol quantity and the calibration of engine control parameters (e.g., injection settings) which is out of the scope of this work, will be required to overcome noise emission penalty. Furthermore, under similar alcohol content in the blend (10% v/v), the use of propanol is preferred over ethanol, as it exhibits lower exhaust emissions and better sound quality than ethanol