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) ar e immiscible. There was no reaction without mixing. When NaOH-MeOH was adde d to the melted beef tallow in the reactor while stirring, stirring speed w as insignificant. Reaction time was the controlling factor in determining t he yield of methyl esters. This suggested that the stirring speed:; investi gated exceeded the threshold requirement of mixing. When NaOH-MeOH was adde d to the melted beef tallow without stirring, higher stirring speeds or lon ger stirring times were needed to mix the two phases subsequently. In both cases, once the two phases were mixed and the reaction was started, stirrin g was no longer needed. Misek's equation was applicable to the former case. The droplet diameter was inversely proportional to the square of the rotat ion speed. But in the latter case, the droplet diameter was inversely propo rtional to n(1.2). Smaller NaOH-MeOH droplets in melted beef tallow resulte d in fast transesterification reaction and stable emulsion. (C) 1999 Elsevi er Science Ltd. All rights reserved.