Selfmetathesis of ethyloleate – A process engineering approach

The metathesis reaction of unsaturated fatty acid derivates [1,2,3,4] is a promising approach leading to long-chained bifunctional compounds that can be used as monomers for polymer synthesis. However, the metathesis reaction is typically associated with a yield limitation caused by the reaction equilibrium. In the investigated metathesis reaction of ethyloleate, the equilibrium composition of the reaction mixture is 25 mol-% based on the target molecule octadec-9-ene-1,18-dicarboxylic acid ethyl ester.

For the future industrial scale application, the purification of the yielded reaction mixtures is a crucial step. Furthermore, removing the low-boiling side-product 9-octadecene should shift the position of the equilibrium towards the product side. A yield of 50 mol% is possible theoretically under ideal conditions, and if the side-product could be removed completely. Our aim was therefore to investigate whether the combination of reaction and separation in a reactive metathesis reaction is able to shift the equilibrium in the desired direction leading to an increase in the yield. We consequently simulated and evaluated the possibility of a reactive distillation process.

Short-path distillation is the method of choice for the separation of high-boiling and thermal instable compounds. Using this technique, it should be possible to remove the low-boiling side-product under gentle conditions without or at most with a barely increased deactivation of the used catalyst.

Therefore, the starting point of this work was to investigate the feasibility of the metathesis reaction under the required working conditions. Afterwards, a modified short-path apparatus was used to investigate the metathesis reaction under the conditions needed for the distillation process. Based on these experiments the requirements for the purification of metathesis product mixtures were determined and verified in initial basic experiments.

As a result of our work, we have been able to prove that although the separating capacity of the apparatus we used is not high enough to significantly increase the yield, that the reactive metathesis might still be an interesting approach to improve the performance of the reaction. Based on initial experimental results and process simulation an advanced apparatus consisting of several short-path evaporators and a rectification column to purify and recover the unconverted reactant was designed, and could lead to further improvements of the metathesis reaction.

References:
[1] R.H. Grubbs, Handbook of Metathesis, Vol. 1-3. 2003, Weinheim: Wiley-VCH
[2] T.A. Foglia, H.L. Ngo, and K. Jones, JAOCS , 2006. 83(7): p. 629-634.
[3] C. Boelhouwer and J.C. Mol, Prog Lipid Res , 1985. 24(3): p. 243-267.
[4] P.B. Van Dam, C. Boelhouwer, and M.C. Mittelmeijer, J. Chem. Soc., Chem. Commun., 1972(22): p. 1221-1222.