It is a fact that the world’s reservoirs of conventional oil are diminishing at a fast pace, forcing mankind to look for alternatives – possibly cleaner, sustainable and more environmentally friendly than fossil fuels.
While the technologies to exploit renewable sources of energy, like wind, tidal or solar power, mature to the point of replacing old-fashioned sources of energy, the use of sustainable fuels may bridge the gap between us and a greener future.
Biodiesel, a mixture of methyl esters of fatty acids, is an alternative to normal diesel that burns producing consistently less greenhouse gases and sulphurated compounds. Biodiesel can be produced via trans-esterification of vegetable or animal oils with methanol generally under acidic conditions; however, the process is as yet not cost-competitive with conventional diesel fuel.
A way to reduce costs is to use cheaper oils, containing free, unesterified fatty acids in the production process introducing an extra esterification step in the process.
Lingaiah et al., in a recently published paper, presented their work on a solid-phase catalyst for the acidic conversion of fatty acids into their correspondent methyl esters that simultaneously catalyses trans-esterification, avoiding the need for a separate reaction.
To provide the necessary acidity, the group employed 12-tungstophosphoric acid (TPA), a heteropolyacid, supported on tin oxide to increase its thermal stability and to reduce catalyst leakage in the reaction media. A full study of the effect of parameters like TPA loading, reaction temperature, stirring speed and catalyst concentration resulted in and optimised TPA loading of 15 wt% to provide ideal surface area and acidity.
The activity test were performed using palmitic acid as the model substrate at 65 °C with a total catalyst loading of 25%, in the presence of an excess of methanol (1:14) to improve conversion (since the esterification is a reversible reaction). After 4 hours, the palmitic acid conversion reached exceeded 70%, and tests showed the catalyst could be washed and reused 5 times without significant loss of activity.
To prove its industrial viability, simultaneous esterification/trans-esterfication in the presence of mixtures of triglycerides and free fatty acids was successfully performed.
Read the full paper here.
Efficient solid acid catalysts for esterification of free fatty acids with methanol for the production of biodiesel
K. Srilatha, Ch. Ramesh Kumar, B. L. A. Prabhavathi Devi, R. B. N. Prasad, P. S. Sai Prasad and N. Lingaiah
Catal. Sci. Technol., 2011, Advance Article
DOI: 10.1039/C1CY00085C, Paper
