Though a considerable number of publications about biodiesel can be found in literature, several problems remain unsolved, encompassing economical, social, and technical issues. Thus, the biodiesel industry has come under attack by some environmental associations, and subsidies for biofuel production have been condemned by some governments. Yet, biodiesel may represent a truly competitive alternative to diesel fuel, for which fuel tax exemption and subsidies to energetic crops are needed. Biodiesel must increase its popularity among social movements and governments to constitute a valid alternative of energy source. In this sense, the use of nonedible oils to produce biodiesel is proposed in the present review. Moreover, the compromise of noninterference between land for energetic and food purposes must be addressed. Concerning technical issues, it is important to consider a transesterification optimization, which is missing or incomplete for too many vegetable oils already tested. In most cases, a common recipe to produce biodiesel from any raw material has been adopted, which may not represent the best approach. Such strategy may fit multifeedstock biodiesel plant needs but cannot be accepted for oils converted individually into biodiesel, because biodiesel yield will most likely fail, increasing costs. Transesterification optimization results depend on the chemical composition of vegetable oils and fats. Considering "sustainable" vegetable oils, biodiesel from Calophyllum inophyllum, Azadirachta indica, Terminalia catappa, Madhuca indica, Pongamia pinnata, and Jatropha curcas oils fits both current biodiesel standards: European EN 14214 and US ASTM D 6751 02. However, none of them can be considered to be the "ideal" alternative that matches all the main important fuel properties that ensure the best diesel engine behavior. In search of the ideal biodiesel composition, high presence of monounsaturated fatty acids (as oleic and palmitoleic acids), reduced presence of polyunsaturated acids, and controlled saturated acids content are recommended. In this sense, C18:1 and C16:1 are the best-fitting acids in terms of oxidative stability and cold weather behavior, among many other properties. Furthermore, genetic engineering is an invaluable tool to design oils presenting the most suitable fatty acid profile to provide high quality biodiesel. Finally, most published research related to engine performance and emissions fails in using a standard methodology, which should be implemented to allow the comparison between tests and biofuels from different origin. In conclusion, a compromise between social, economical, and technical agents must be reached.

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Alcohols have an interesting potential as blending components for diesel fuels because of their capacity to reduce soot formation. Because they have increasing routes for their production from renewable sources, they could contribute toward increasing the renewable fraction of these fuels and, therefore, toward reducing the impact of diesel transportation on the global warming effect. To increase the knowledge about the implications of the use of short- and long-chain alcohols/diesel fuel blends in diesel engines, the stability, lubricity, viscosity, and cold filter plugging point (CFPP) have been tested. Blends of methanol, ethanol, propanol, butanol, and pentanol with diesel fuel have been analyzed at 1, 2.5, 7.7, 17, 50, 75, and 90% in volume [including 95% (v/v) in the case of CFPP]. Results have shown that short-chain alcohols depict poor blending stability and low viscosity (mainly for concentrations of ethanol and propanol in diesel fuel blends beyond 22 and 45%, respectively). A synergistic effect was observed in viscosity when moderate concentrations of butanol and pentanol were mixed with diesel fuel. The lubricity of the blends decreases with the alcohol content, but this effect is partially compensated by the alcohol volatility. The blends with the highest restriction of use are those containing pentanol, which should be limited to concentrations below 10% (v/v), because its volatility does not compensate for its lubricating capacity. The use of alcohol/winter diesel fuel blends provides a substantial benefit only when high alcohol concentrations are used. It can be concluded that alcohols can be blended with diesel fuel under low and high concentrations, although to improve the blending stability of short-chain alcohols in medium concentrations, the use of additives or fatty acid esters would be necessary.

No abstract

Environmental concerns are driving industry to develop viable alternative fuels from renewable resources. On the other hand, to reduce food surplus, the Agricultural Policy of the European Union (EU) obliges the European farmers to leave a percentage of the arable land as set-aside, where can be grown, as an exception, vegetables for nonfood purposes, i.e., energetic ones. Currently, fossil fuels are used in diesel engines and are essential in industrialized places. In addition, petroleum-based diesel increases environmental pollution. To solve these problems, transesterified vegetable oil that has been grown in set-aside lands can be considered to be a renewable energy resource. In this sense, this work describes the optimization of the parameters involved in the transesterification process of Brassica carinata oil. Gas chromatography was used to determine the fatty acid composition of Brassica carinata oil and its esters. Results revealed that the free fatty acid content is a notorious parameter to determine the viability of the vegetable oil transesterification process. In this sense, it was not possible to perform a basic transesterification using Brassica carinata oil with a high erucic acid content. The transesterification process of Brassica carinata without erucic acid required 1.4% KOH and 16% methanol, in the range of 20-45°C, after 30 min of stirring. Our results suggest that the greater the presence of KOH, the lesser the methanol requirements. However, this is valid only under certain limits. Also, if the presence of KOH or methanol is lower or higher than the optimal values, the reaction either does not fully occur or leads to soap production, respectively. Based on this field trial, biodiesel from Brassica carinata oil could be recommended as a diesel fuel candidate if long-term engine performance tests provide satisfactory results.