Design of a permanent continuous esterification process without reverse reactions

Fatty acid esters are widely used as biofuels and chemical raw materials. Currently, they are industrially produced by transesterification of edible oils, but this process raises concerns about competition with food sources. An alternative method has been proposed for producing them by esterification of fatty acids, a byproduct of vegetable oil refining that is produced in large quantities but not effectively utilized. However, despite being proposed very long ago, this method has not yet been implemented in practical applications.

Our group has also proposed a production process using porous cation-exchange resin as a catalyst and reported that the esterification proceeds irreversibly without excessive methanol addition and the removal of byproduct water. However, in a continuous production system, it was found that a byproduct, water, accumulates within the resin. This accumulation leads to a decrease in the conversion. By supplying alcohol for removing water accumulated in the resin as regeneration step, the catalytic activity is completely recoverable. However, the periodic alcohol supply and the installation of its storage tanks presented a significant economic and environmental burden, becoming a bottleneck in the practical application of this process.

In this research, we designed a semi-permanent continuous esterification process without reverse reactions by controlling the accumulation of water in the resin through the optimization of the molar ratio of reactants to methanol. Under these conditions, an equal amount of water produced in the resin is dispersed into the bulk liquid phase, effectively preventing water accumulation within the resin. Consequently, we found that the continuous esterification could be sustained for about half a month without any decrease in catalytic activity, thus realizing a permanent production process.