Continuous production of biodiesel by the CaO-catalyzed transesterification operated with continuously stirred tank reactor

Abstract

A major problem for continuous production of biodiesel by the heterogeneously-catalyzed transesterification is a serious limitation of the mass transfer under the reacting condition. For resolving the problem mentioned above, the rapeseed oil transesterification catalyzed by powdery CaO was operated with continuously stirred tank reactor (CSTR), which is characterized by the perfectly mixed flow. To the best of our knowledge, the present work is the first trial for CSTR operation of the heterogeneously-catalyzed transesterification. The tracer test elucidated that the powdery CaO was catalyzed the transesterification in the perfectly mixing flow. As a result, the CSTR operation of the CaO-catalyzed transesterification could reach the steady state. But, the wide residence time distribution resulting from the perfectly mixing flow seemed to limit the FAME yield to some 90%. The limitation of the FAME yield will probably be relieved by multiplying the tank reactors in series, on the basis of the kinetic data obtained under steady state. Another novelty of the present work is to recycle the used CaO catalyst into calcium glycero-phosphate, which functions as a pharmaceutical materials or a high-priced food additive. The experimental product from the used CaO catalyst consisted of the finer crystallites than the commercial product from calcium hydroxide.