Abstract
BackgroundAt present, the conversion of oils to biodiesel is predominantly carried out using chemical catalysts. However, the corresponding lipase-catalysed process has important advantages, which include mild reaction conditions and the possibility of using cheap, low quality feedstocks with a high free fatty acid content. Further increases in the efficiency of the enzymatic process are desired to make it even more attractive and suitable for large-scale applications.ResultsHerein, we present a simple and efficient two-phase lipase-catalysed system for the preparation of biodiesel in which different parameters (biocatalyst composition, ethanol concentration and the presence of additives) were optimised in order to obtain the maximum productivity starting from triolein with a high free oleic acid content. In the two-phase system, the enzyme tolerated high-ethanol concentrations, which made it possible to reach high conversions. The addition of silica particles increased the reaction rate substantially. It was suggested that such particles can catalyse acyl migration as a step to the full conversion to glycerol and biodiesel. However, in the system studied here, the effect of the particles was shown to be due to the formation of smaller and more uniform emulsion droplets leading to better mass transfer between the two phases. Particles of widely different size had positive effects, and the highest rate was obtained with silica particles derivatised with phenyl groups. The optimal conditions were applied to the solvent-free ethanolysis of rapeseed oil, and a yield of 96% was reached in 5 h. Under the mild conditions used, chemical catalysts were inefficient.ConclusionsTriacylglycerol oils with a high free fatty acid content can be efficiently converted to ethyl esters using Thermomyces lanuginosus lipase as the catalyst in an aqueous/organic two-phase system. Fast mass transfer can be achieved using silica particles, which helped to decrease the size of the emulsion droplets and thus led to a more efficient process. The high-ethanol concentration tolerated by the lipase in this system made it possible to reach almost quantitative yields.
Highlights
At present, the conversion of oils to biodiesel is predominantly carried out using chemical catalysts
T. lanuginosus lipase was efficient in converting all the acylglycerols and was found to be the most suitable biocatalyst for biodiesel preparation
We have developed a very effective method for the enzymatic preparation of biodiesel, which is useful for oils with a high free fatty acid content
Summary
The conversion of oils to biodiesel is predominantly carried out using chemical catalysts. These processes present several drawbacks such as the need to remove inorganic salt in the downstream process, the high temperature required and undesirable side reactions These systems have been found to be inefficient when a high free fatty acid (FFA) content is present in the starting material [12], Mangas-Sánchez and Adlercreutz Biotechnology for Biofuels (2015) 8:58 which restricts the use of conventional chemical pathways to a highly pure feedstock. The catalyst has to be reused many times in order to be economically feasible [18] For these reasons, the use of liquid lipase preparations has attracted interest, but the optimisation of these processes is needed in order to establish them as a realistic industrial alternative
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