Heterogeneous catalysis for valorisation of vegetable oils via metathesis reactions: ethenolysis of methyl oleate

Abstract

The cross-metathesis of methyl oleate (MO) with ethylene was studied on a second-generation Hoveyda–Grubbs complex supported on silica (HG/SiO₂). The reaction was carried out in a batch slurry reactor at 313–353 K and 2.5–7.5 bar of C₂H₄(5%)/N₂, using cyclohexane as a solvent. The MO ethenolysis products were methyl 9-decenoate and 1-decene. The competitive MO self-metathesis reaction formed 9-octadecene and methyl 9-octadecen-1,18-dioate. The yield (Y_E) and selectivity (S_E) for ethenolysis products at P_C2H4 = 0.125 bar (total pressure = 2.5 bar) were 52% and 69%, respectively. Both parameters increased with P_C2H4, essentially because the reaction equilibrium was shifted to higher methyl oleate conversions. Thus, at P_C2H4 = 0.250 bar, the Y_E and S_E values were 63% and 77%, respectively. Nevertheless, catalyst deactivation was observed for ethylene pressures higher than 0.125 bar, thereby suggesting that the presence of ethylene may suppress the metathesis cycle on HG/SiO₂ catalysts. The ethenolysis product yield decreased when the temperature was increased, reflecting mainly the MO equilibrium conversion diminution.