Experimental Optimization of the Alkaline Catalyzed Transesterification Process for Biodiesel Production from Pre-treated Rubber Seed Oil

Biodiesel is a very promising alternative fuel to the existing petroleum diesel due
to its renewability and environmental friendliness. Currently, biodiesel is mostly
produced from vegetable oils using alcohol and alkaline catalyst. However, most of the
vegetable oils have very high content of free fatty acid (FF A) especially rubber seed oil
(RSO) which requires the two-step transesterification process involving acid-catalyzed
esterification process (Step 1) followed by alkaline-catalyzed transesterification process
(Step 2). The acid esterification process is to reduce the FF A content to an acceptable
range ( < 1%) and it is usually followed by the alkaline transesterification process which
is to convert the oil to methyl esters (biodiesel). In this work, the crude rubber seed oil,
which is used as the feedstock, is first characterized and then the FF A content of the oil
is reduced to less than I% through the acid esterification process. The pre-treated rubber
seed oil is then used for the second step of alkaline transesterification process to produce
biodiesel using methanol and potassium hydroxide (KOH) as the catalyst. Experiment
runs are designed and conducted to optimize the alkaline transesterification process by
varying important factors such as alcohol to oil molar ratio, amount of catalyst, reaction
temperature, and time. Highest yield ofbiodiesel (75.51 wt%) is obtained at methanol to
oil ratio of 6: 1, temperature of 65°C, and catalyst amount of 0.5 wt% (oil basis). It is
found that the biodiesel yield is strongly affected by the catalyst amount, followed by the
temperature and the alcohol to oil ratio in descending order. The effect of reaction time
is also studied and the optimum reaction time is found to be at 2 hours which produces
biodiesel with highest yield and FAME concentration of 96.6 wt%. The properties of the
biodiesel produced at the optimal conditions and 2 hours of reaction time is found to
adhere to the international standards for biodiesel (ASTM and EN).