CaO is the best known solid base catalyst for transesterification
of low FFA content oils. It is relatively cheap and non-toxic. CaO has
been tested for transesterification of many vegetable oils [12].
However, like most alkaline catalysts, soap formation is the main
problem consuming and deactivating the catalyst for transesterification
of high FFA content vegetable oils.
The morphology of CaO catalyst from CaCO3 greatly depends on
the treatment temperature and time. Granados et al. [29] treated
pulverized CaCO3 at 800 C for 1 h and found a BET-surface area of
43 m2
/g, pore diameter of 24 nm and a pore volume of 0.3 cm3
/g.
The catalyst was used for transesterification of sunflower oil and
a FAME yield of 90% was obtained for 14:1 methanol to oil ratio, 5 h
of reaction time and at 60 C. Kouzu et al. [30] treated CaCO3 at
900 C for 1.5 h and a surface area of 13 m2
/g was measured. The
catalyst was used in transesterification of soybean oil (SBO) with
more than 12:1 methanol to oil ratio and at 65 C. Nearly complete
conversion was obtained after 2 h of reaction time. Higher calcination
temperature and longer time of treatment reduce the
surface area and increases the pore diameter in bulk CaO catalyst
preparation. Fortunately, increasing the calcination temperature
(up to decomposition temperature of CaCO3) for CaO increases the
basicity of the catalyst which is an important property for the
catalyst activity in transesterification [31]. In this study, high
treatment temperature and longer time of treatment reduced the
surface area to 2 m2
/g as shown in Table 2. The catalyst is expected
to have high surface basicity due to increased treatment temperature
and time.
The CaO with such surface properties was tested for its activity
in transesterification of JCO and only 18% FAME yield was obtained
and much soap was formed as shown in Fig. 2. Although CaO is very
active catalyst for transesterification of low FFA oils, the activity of
the catalyst is highly affected by the presence of FFA and favors
unwanted side reactions. The same catalyst was also tested for its
activity for commercial RSO under the same reaction conditions.
A complete conversion was obtained after 3 h of reaction time as
shown in Fig. 3c.
T