Influence of the Axial Dispersion on the Performance of Tubular Reactors during the Noncatalytic Supercritical Transesterification of Triglycerides

MARIANA M. BUSTO; SILVANA M. D'IPPOLITO; JUAN C. YORI; MARISA E. ITURRIA; CARLOS L. PIECK; JAVIER M. GRAU; CARLOS R. VERA

ENERGY & FUELS (PRINT)

American Chemical Society

Lugar: Columbus OH; Año: 2006 vol. 20 p. 2642 - 2647

0887-0624

Transesterification of fats and oils by methanol is known to proceed by a three-step consecutive reaction mechanism in which the formation of the diglyceride is the rate-limiting step. At low conversion values (<25-35%), the system has mass transfer limitations due to the immiscibility of the oil-methanol system. Noncatalytic transesterication in supercritical methanol overcomes this problem by forming a one-phase reacting system. The implementation of this reaction mode in the continuous tubular reactor is needed for the evaluation of the effect of the backmixing that appears when methanol acquires a gaslike mobility in the supercritical state. Such a study was performed here, and it was found that supercritical transesterification reactors must be operated at an axial Pe´clet number equal or higher than 1000 in order to limit backmixing effects to a minimum and achieve batchlike conversions at residence times of 1 h or less. High conversion values at low Peclet numbers can only be obtained by working at inconveniently high temperatures and high methanol-to-oil ratios.