The effect of mixing on transesterification of beef tallow

Mixing is very important to the transesterification of beef tallow, because melted beef tallow and a sodium hydroxide–methanol solution (NaOH–MeOH) are immiscible. There was no reaction without mixing. When NaOH–MeOH was added to the melted beef tallow in the reactor while stirring, stirring speed was insignificant. Reaction time was the controlling factor in determining the yield of methyl esters. This suggested that the stirring speeds investigated exceeded the threshold requirement of mixing. When NaOH–MeOH was added to the melted beef tallow without stirring, higher stirring speeds or longer stirring times were needed to mix the two phases subsequently. In both cases, once the two phases were mixed and the reaction was started, stirring was no longer needed. Misekʹs equation was applicable to the former case. The droplet diameter was inversely proportional to the square of the rotation speed. But in the latter case, the droplet diameter was inversely proportional to n1.2. Smaller NaOH–MeOH droplets in melted beef tallow resulted in fast transesterification reaction and stable emulsion.