Possibilities of using waste plum stones in biodiesel production were
investigated. The plum kernels were used as a source to obtain oil by the
Soxhlet extraction method, while the whole plum stones, the plum stone shells
that remained after the crashing, and the plum kernel cake that remained
after the oil extraction, were burned off to obtain ashes. The collected
ashes were characterized by elemental composition, porosity, and base
strength and tested for catalytic activity in transesterification of
esterified plum kernel oil. Dominant elements were potassium, calcium, and
magnesium at different contents in the three obtained ashes. The most active
catalyst was the plum stone shell ash, so the effect of temperature (40, 50,
and 60?C) on the reaction rate was investigated. The reaction rate constant
increased with the reaction temperature with the activation energy value of
58.8 kJ mol-1. In addition, the plum stone shell ash can be reused as a
catalyst after recalcination.