Abstract
With rising prices for imported fossil fuel and growing concerns about global warming, the developing countries of Sub-Saharan Africa may no longer be able to depend upon fossil diesel as a reliable source of energy in the future. Fortunately, the availability of local resources such as ethanol (EtOH), bio-oils, and hydrated lime makes it feasible to introduce renewable sources of power such as biodiesel via ethanolysis. A previous paper from our group reported concentration changes of triglycerides (TG), diglycerides (DG), monoglycerides (MG), and the added glycerol (GL) in the pretreatment with glycerol, and identified the glycerolysis of TG as the mechanism behind the reaction rate enhancement of the following transesterification. It will also be important, for actual application to biodiesel production, to determine the reaction rates and equilibrium constants. In the present study we determined the thermal pretreatment kinetics of a groundnut (Arachis hypogaea) oil feedstock premixed with glycerol and calcium hydroxide (Ca(OH)2) at 100 °C over reaction times from 1 to 3 h, while measuring the concentration changes of TG, DG, MG, and GL over time to determine the rate constants. Next, we used the data obtained to calculate the equilibrium constants. Through this approach, we successfully determined the reaction rate of the catalytic TG glycerolysis, the process that yielded DG and MG as reactive intermediates for the ethanolysis reaction. A GL/TG molar ratio of 2.35 is recommended for optimal performance of TG glycerolysis.
