Toward sustainable chemical synthesis: metathesis of sunflower- derived ethyl esters and evaluation of the surfactant potential of the product mixtures

Abstract

Metathesis of functionalized alkenes from sustainable biological feedstocks like plant oils is an important chemical reaction pathway, that could contribute toward improving the environmental sustainability of the chemical synthesis industry. In this study, the metathesis of unsaturated fatty acid ethyl esters derived from higher purity ethyl oleate (HPEO) and sunflower oil-based ethyl esters (SB) using the Grubbs second-generation catalyst was investigated, and the potential of the metathesis-enriched product mixture to act as a surfactant was evaluated. The product distribution of the metathesis reaction and the surfactant potential of the product mixtures were determined. Metathesis of the HPEO performed best at 50 °C and 0.2 mol % catalyst loading, resulting in 67.4% conversion of unsaturated fatty acid esters and a yield of 47.7% (based on the formation of 9-octadecene and diethyl 9-octadecene). For the SB feedstock, 87.8% feedstock conversion was achieved under optimum conditions (0.4 mol % catalyst loading at 50 °C) but at lower yields of ∼11.6%, due to the complexity of the feedstock and the multiple coproducts that can form. Surfactant studies showed that the surfactant potential of the reaction mixtures obtained from the feedstocks was upgraded through metathesis (C20 of 8305 mg/L for HPEO compared to C20 of 4995 mg/L for metathesized HPEO, and C20 of 8.90 mg/L for SB compared to C20 of 0.08 mg/L for metathesized SB). The C20 of some of the reaction product mixtures was in the same order as that of the industrial surfactant Flotanol (C20 of 7742 mg/L), although product mixtures lacked the foaming capacity of the industrial surfactant, making them suitable for specific applications where nonfoaming surfactants are desired, like paper making or textile dyeing industries. The study confirmed that the metathesis of unsaturated ethyl esters from sunflower oil generates a range of useful chemical products, which can make an important contribution toward the chemical synthesis industry moving away from fossil-based inputs.