Potential applications of nanobiocatalysis for industrial biodiesel production

Biodiesel refers to long-chain alkyl fatty acid esters and is emerging as an alternative fuel for diesel engines (Byreddy et al., 2016). The increase in the petroleum prices and environmental benefits resulted in the increased production of biodiesel. Biodiesel occupies 10% of total biofuel production and the production is about 6 billion liters/year globally (Nogueira, 2011). The basic requirements for biodiesel production are feedstock (oil), an alcohol and catalyst (e.g. base, acid and enzyme). The reaction of biodiesel production occurs in the following steps: production of free fatty acids from triacylglycerols and transesterification of free fatty acids to methanol, resulting in the formation of new 350chemical compounds called methyl esters. The important process variables during the production of biodiesel are reaction temperature, ratio of alcohol to vegetable oil, amount of catalyst, mixing intensity (RPM), raw oils use and catalyst (Avhad and Marchetti, 2015; Marchetti et al., 2007). In the alkali-based production process generally sodium hydroxide (NaOH) or potassium hydroxide (KOH) are used as the catalyst. During the initial phase of the reaction, the catalyst reacts with the alcohol and forms an alkoxy moiety which reacts with the TAG to produce biodiesel and glycerol. Glycerol and biodiesel can be separated easily based on gravity. There may be a chance of soap formation by free acid or water contamination that makes the separation process difficult (Gerpen, 2005; Meher et al., 2006). In the acid- based method, sulfuric acid is the most preferable catalyst for converting triacylglycerol (Tran et al., 2013). The acid catalyst gives a high yield of esters, but the reaction for conversion requires a long time (Su and Guo, 2014). Although the production cost of biodiesel produced by the conventional methods such as acid and alkali catalysis is cheap, however there are challenges with respect to the recovery of glycerol and repeated washing requirement to purify methyl esters (Gog et al., 2012).