Continuous Saponification of Methyl Laurate Using Long Narrow Tubes as a Reactor

Abstract

Saponification of methyl laurate with an aqueous solution of sodium hydroxide was carried out in long narrow tubes made of silicone rubber. The saponification rate obeyed the Nernst diffusion equation. The apparent diffusion constant in the tubular reactor with a tube of 1.7 mm inner diameter and 8 m length was about 300 times larger than that in a beaker at 333 K. The apparent activation energies of diffusion were determined to be 14 and 12 kJ mol-1 for tubular reactors with tubes of 8 m length and 0.8 and 1.7 mm inner diameter, respectively. These values are in good agreement with those of some reagents, 12−21 kJ mol-1, in a liquid phase. The results indicated that the rate-controlling step of the saponification is diffusion of sodium ions and/or hydroxide ions into methyl laurate. In addition, the apparent diffusion constant depended on the length and inner diameter, and it increased with an increase in surface area of the inner wall of the tubular reactor. It is concluded that a tubular reactor with a long tube and a large surface area of the inner wall is applicable to saponification without a promoter and stirring.