Reactive Extraction Technology - Process Intensification for Green Chemistry - page 279

reactive extraction, the filtrate was stirred with 100ml recycled n-hexane for 30 minutes
before being transferred to a separating funnel. The upper dark yellow-coloured layer
was decanted after 1 hour and excess n-hexanewasevaporatedtorecovertheFAME.The
separation procedure was repeated twice for the lower dark brown-coloured layer to
ensure complete separation of FAME from glycerol. The volume of the collected FAME
sample was then measured and recorded for calculation using Equation 10.1.

10.2.2.2 Result and Discussion

Figure 10.5 shows the variation of temperature and pressure towards FAME yield for
supercritical reactive extraction with different solid particle sizes. At lower temperatures
( 240 C), FAME yield was extremely low, as predicted, due to the poor miscibility of

methanol with the extracted oil without the addition of catalyst or supercritical
conditions (above 240 C and 8.1MPa) [18,19]. Oil conversion to FAME was found
to be directly proportional to the reaction temperature, particularly beyond the super-
critical condition, where the conversion rate was intensified. Smaller particle sizes,
which led to higher extraction efficiency, were favourable for higher FAME yields (with
the only exception at particle size 0.5mm; maximum 71.4%w/w at 300 C), since the
smaller particles, which are stickier, tend to agglomerate and thus limit FAME conver-
sion due to their lower surface area. It can therefore be concluded that the rate of oil
extraction is higher than the rate of transesterification at low temperature ranges due to
the significant extraction efficiency of n-hexane. The kinetics of the transesterification
process, which was low before attaining supercritical conditions, becomes the limiting
factor. However, at higher temperature and pressure ranges, supercritical conditions
enable the transesterification to proceed at a much higher pace than the extraction of oil
[18]. Thus, jatorpha oil will be converted to FAME as soon as it is extracted from the
seeds, and the kinetics of extraction becomes the limiting factor. The 103.5% FAME
yield, exceeding the theoretical 100.0% yield for particle size 1mmat 300 C, was

due to the higher pressure exerted under supercritical conditions, which was able to

120.0

Unsieved
2.0 mm
1.0 mm
0.5 mm

100.0

80.0

60.0

40.0

20.0

0.0

200ºC/40 Mpa 220ºC/60 Mpa 240ºC/90 Mpa 260ºC/140 Mpa 280ºC/180 Mpa 300ºC/240 Mpa

Temperature/Pressure (ºC/MPa)

Figure 10.5 Effect of varying temperatures and pressures to biodiesel (FAME) yield with
different particle size for SCF reactive extraction. Reprinted from Lim et al # 2010, with
permission from Elsevier.