Renewable plant-based soybean oil methyl esters as alternatives to organic solvents

Abstract

The physico-chemical properties of soybean oil methyl ester (SBME), better known as biodiesel, of importance to its use as a solvent in liquid–liquid separations have been examined. Partition coefficients of several organic species between SBME–water have been determined and compared to log P (1-octanol–water). The free energy of transfer of a methylene group has been obtained and the solvent properties of the SBME–water system determined from distribution data of a small solute set using Abraham's generalized solvation equation. Solute distribution behavior is similar to that found for conventional organic solvent–water systems, but is most similar to other vegetable oils such as olive oil. When ionizable solutes are partitioned in the SBME–water system at differing pH, the neutral species show the highest distribution. Partitioning is dependent on the solute's ability to form hydrogen bonds between water and its charged state. Metal ions (e.g., Fe³⁺, Co²⁺, and Ni²⁺) exhibit moderate partitioning to the SBME phase from water only in the presence of extractants. Actinides (UO₂²⁺, Am³⁺) exhibit significant partitioning to the SBME from aqueous solutions with the use of octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO). Soybean oil methyl ester may be a suitable “green” alternative for the replacement of volatile organic solvents in liquid–liquid extractions in selected applications.