Esterification of free fatty acids (FFAs) with short-chain alcohols
is one of the most important organic reactions due to the use of
fatty acid methyl esters (FAME) as “biodiesel” [10–14]. Many researchers believe that the Keggin-type POMs are able to be active
catalysts for biodiesel production because of their inherent advantages including ease of handling compared to mineral acids, fewer
side reactions, strong Brönsted acidity, high proton mobility, stability
and environmentally benign nature [15–25]. Some drawbacks including
low surface area, low porosity and difficult catalyst recovery prompted
further research toward biodiesel production using heterogeneous
POMs. Recently, the organic–inorganic POM–IL hybrids were used in
esterification of various acids with n-butanol [9]. The liquid–liquid biphasic heterogeneous reaction systems were observed and the catalyst
could be reused several times. However, it might bring some trouble in
separation of catalysts if they are directly used in biodiesel production