Mixed methanol–ethanol technology to produce greener biodiesel from waste cooking oil: A breakthrough for SO42−/SnO2–SiO2 catalyst

World energy crisis has become the foremost crucial topic in this new era. Unstable price of petroleum fuel in the world market and recent environmental concerns on gas emission during combustion have led to intensive search for alternative energy sources that are not only renewable but sustainable. Without doubt, one of the most important evolutions in the renewable energy sector is the development of biodiesel. Currently commercial biodiesel production is using methanol (non-renewable) as the main reactant to produce biodiesel due to its wide availability and low cost. However, biodiesel produced using methanol are not completely renewable as methanol can only be derived from petroleum fuel. Unfortunately, not much attention has been given on this issue. On the other hand, ethanol may emerge as a good solution to this problem as ethanol can be derived from renewable sources through fermentation process. The only constraint on the use of ethanol is its slow reaction rate in transesterification reaction and therefore resulted to energy inefficient biodiesel production process. Such limitations worsen if solid acid catalyst is used in the reaction. Thus, the aim of this present work is to introduce a simple mixed methanol–ethanol method to overcome these limitations and to produce biodiesel in a greener and sustainable manner. The effect of methanol to ethanol to oil molar ratio, reaction temperature, catalyst loading and reaction time towards biodiesel yield are discussed in detail. From this study, it was found that an optimum biodiesel yield of 81.4% can be attained at a relatively short reaction time of 1 h.

Research highlights
► Currently commercial biodiesel production that are using methanol are not completely renewable as methanol can only be derived from petroleum fuel.
► Unfortunately, not much attention has been given on this issue.
► Ethanol may emerge as a good solution to this problem as ethanol can be derived from renewable sources, but it has slow reaction rate in transesterification reaction.
► Such limitations worsen if solid acid catalyst is used in the reaction.
► Thus, the aim of this present work is to introduce a simple mixed methanol–ethanol method to overcome these limitations and to produce biodiesel in a greener and sustainable manner.