Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2007
Publication Date: 8/3/2007
Citation: Doll, K.M., Moser, B.R., Erhan, S.Z. 2007. Surface tension studies of alkyl esters and epoxidized alkyl esters relevant to oleochemically based fuel additives. Energy and Fuels. 21:3044-3048. Interpretive Summary: The surface tension of a liquid is a very important factor in liquid atomization (breaking up of a liquid into very small droplets). Because atomization is the first step in fuel combustion, the injector must be able to properly atomize the fuel for efficient use. The surface tension of a fuel additive must be known for this reason. In earlier work we have made several different compounds from soybean oil and tested them for other fuel enhancing properties. Now we have examined the surface tension properties of these additives and will be able to use our knowledge to determine maximum amounts of these compounds that can be added to a fuel mixture. This research benefits the biodiesel industry by helping us to determine proper use of our fuel additive materials. It also benefits the vegetable oil industry by helping to open markets for vegetable oil derived fatty materials.
Technical Abstract: We report the surface tension of several epoxidized oleochemicals and their comparable fatty esters at temperatures between 25 and 60 deg C. Surface tensions of the olefins measured at 40 deg C range from 25.9 mN m-1, for isobutyl oleate, to 28.4 mN m-1 for methyl linoleate. The epoxy versions of the same compounds displayed higher surface tensions of 28.1 mN m-1 and 32.1 mN m-1, respectively. Branched ester compounds also had surface tensions between 27.4 and 30.2 mN m-1. Several trends and observations were elucidated. More epoxidation or unsaturation leads to higher surface tension. Epoxidation has a larger effect on surface tension than unsaturation. Linear alkyl head groups on fatty esters have similar surface tensions, but branched headgroups gave slightly lower surface tensions. Soy methyl esters, or epoxy soy methyl esters, give surface tensions which are between that of their two main components. Overall, the results show that there is not enough of a surface tension increase in any of these compounds to prevent their use as a biofuel additive.