Both methanol and ethanol have stronger polarity in comparison with
n-butanol. Thus, the catalyst was soluble in the reaction mixture and
its recoverability is not as convenient as a solid catalyst. For the purpose
of more convenient isolation, the supported organic–inorganic POM–ILs
were used for biodiesel production [26]. However, the catalytic activity
decreased obviously during 2–7 cycles due to the loss of active sites in
the reaction processes.