Biodiesel: synthesis, life cycle assessment, and performance in a diesel engine

Abstract

Reductions in greenhouse gas emissions and the depletion of fossil fuels are among the main reasons for the development of new biofuel technologies. In this sense, biodiesel represents a suitable alternative to fossil fuels, as it is renewable, biodegradable, non-toxic and reduces emissions of hydrocarbons, sulfur, carbon monoxide and polyaromatic hydrocarbons. The main biodiesel production route is the methyl transesterification of triglycerides using a homogeneous basic catalyst, such as potassium hydroxide. However, these catalysts produce soap, and they are not recovered and reused, therefore the biodiesel purification process generates a large amount of wastewater. In such a context, studies have been developed to enable the use of heterogeneous catalysts, since they produce less waste and can be recovered and reused. Among the most used catalysts, calcium oxide (CaO) can be mentioned. Therefore, the present work uses calcined chicken eggshells as a catalyst for the methyl transesterification reaction of soybean oil, and nonylphenol ethoxylated surfactants as interfacial tension reducing agents, improving the contact between the phases. To assess the environmental impacts caused by the production of biodiesel, a life cycle assessment (LCA) of the biodiesel synthesis method proposed in this work was carried out, using the surfactant and encompassing the catalyst synthesis step. In addition, a comparative study of the environmental impacts generated with the usual biodiesel manufacturing process using potassium hydroxide as a homogeneous catalyst was also carried out. Another aspect evaluated in this work was the distillation of biodiesel, where two fractions were obtained, one with a higher concentration of light esters and another fraction with a higher concentration of heavy esters. The fractions obtained were added to commercial diesel and the new fuels were tested in a diesel engine, in order to evaluate the effect of these fractions on combustion and engine performance. The results showed that the use of surfactants reduces the methanol/oil molar ratio and the reaction time. With the addition of 1.5% of surfactant, using an oil alcohol molar ratio of 1:4 and 2% of catalyst, it was possible to obtain a conversion greater than 90% for a reaction time of 1.5h. The LCA showed that the production of biodiesel using the surfactant is 77% more eco-efficient and has less environmental impacts than the usual process using KOH. The addition of distillate biodiesel and its fractions to diesel promoted a lower specific consumption, as well as an increase in thermal efficiency. With regard to the analysis of emissions, there was a reduction of up to 35% in carbon monoxide emissions with the addition of biodiesel.