A homogeneous Ru-catalyst was investigated toward its potential recycling in methyl oleate epoxidation under mild conditions using hydrogen peroxide as a green oxidant. The literature-known catalyst complex, in situ formed from ruthenium acetylacetonate and dipicolinic acid, offers excellent selectivity toward epoxidation of technical grade (91.5%) methyl oleate. The resulting product methyl 9,10-epoxy stearate exhibits versatile applications. It is used industrially as a biobased epoxide for plasticizers and lubricants, or it can be further processed into polyurethanes. In this work, we first report a concept for homogeneous catalyst recycling, including extraction of the epoxide into an organic phase. Particular emphasis was on the effect of water, as it would accumulate due to recycling of the aqueous catalyst phase and replenishment of hydrogen peroxide prior to each recycling run. Consequently, mass transfer limitations needed to be addressed. By a combined extraction-distillation technique, we report the first sufficient homogeneous catalyst recycling strategy for Ru-catalyzed epoxidation of methyl oleate. Removal of water and separation of epoxide allowed for a ∑TON of 1243 after seven recycling runs with 97% selectivity toward epoxide and a TTON of 1384 after 13 runs, respectively, while catalyst leaching into the product phase was negligibly small. Moreover, pervaporation using a poly(vinyl alcohol) membrane was investigated as a promising technique for both removal of water and retention of the catalyst showing very promising results.
