ABSTRACT
Biodiesel is emerging as an alternative fuel for diesel engines, which refers to long-chain alkyl fatty acid esters. The increase in petroleum prices and the environmental benets have resulted in an increased production of biodiesel. Biodiesel occupies 10% of total biofuel production, and the production is about 6 billion L/year globally (Nogueira, 2011). The basic requirements for biodiesel production are feedstock (oil), an alcohol, and a catalyst (e.g., base, acid, or an enzyme). The reaction of biodiesel production occurs in the following steps: production of free fatty acids from triacylglycerols (TAGs) and transesterication of free fatty acids to methanol. This results in the formation of new chemical 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 used, and catalyst (Marchetti et al., 2007; Avhad and Marchetti, 2015). In the alkali-based process, generally sodium hydroxide (NaOH) or potassium hydroxide (KOH) is used as the catalyst. During the initial phase of the reaction, the catalyst reacts with the alcohol and forms alkoxy, and this 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 difcult (Gerpen, 2005; Meher et al., 2006). In the acid-based method, an acid with triacylglycerols and alcohol are used. Sulfuric acid is a preferable catalyst in this method (Tran et al., 2013). The acid catalyst gives a high yield of esters, but the reaction
4.1 Introduction 61 4.2 Selection of Suitable Extraction Solvents 63 4.3 Extraction of Lipids from Dry Biomass 63 4.4 Lipid Extraction from Wet Biomass 66 4.5 Microalgae Cell Disruption for Lipid Extraction 66 4.6 Effect of Cell Disruption Methods on Lipid Extraction 67 4.7 Perspectives 70 References 70
rate for conversion requires a long time (Su and Guo, 2014). Although the production cost of biodiesel from the conventional methods such as acid and alkali catalysis is cheap, but associated with some problems, that is, methyl esters yield is normal, recovery of glycerol is difcult and repeated washing is required to purify methyl esters (Gog et al., 2012).
