odiesel production process can reduce the cost if using in situ (trans)esterification. In this process,
costs for solvent extraction and oil purification can be reduced. So, biodiesel production becomes simpler
[11]. In situ (Trans)esterification, is a method to produce biodiesel that raw material (seed) is directly
contacted with alcohol/methanol assisted with acid/alkaline catalyst. In the process either with an acid or
alkaline catalyst, molar ratio of methanol/oil is much higher than the value calculated based on the
stoichiometry, for instance, 532:1 [12], 300:1 [13] and 543:1 [14]. Excess methanol will play the role as
the solvent extraction [12].
In situ transesterification was introduced by Harrington & Evans [12]. They used sunflower seed as a
raw material. Marinkovic et.al. [13] did experiments from sunflower seed with the same process. Haas et
al., [14] did in situ process from soybeans. Ozgul and Selma [15, 16] did in situ esterification with rice
bran as raw material and ethanol and methanol as solvent and Ginting et.al., [17] also did in situ
transesterification from castor seed (Jatropha curcas). The objectives of this research are to produce
biodiesel from rubber seed with in situ method which has not been done by previous researchers and to
study the influences of reaction time, ratio methanol to rubber seed and concentration of acid catalyst.