Location: Bio-oils Research Unit
Title: Fatty acid alkyl esters as solvents: An evaluation of the kauri-butanol value. Comparison to hydrocarbons, dimethyl diesters and other oxygenates Authors
Submitted to: Industrial and Engineering Chemistry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 2011
Publication Date: February 28, 2011
Citation: Knothe, G.H., Steidley, K.R. 2011. Fatty acid alkyl esters as solvents: An evaluation of the kauri-butanol value. Comparison to hydrocarbons, dimethyl diesters and other oxygenates. Industrial and Engineering Chemistry Research. 50(7):4177-4182. Interpretive Summary: Biodiesel is an alternative diesel fuel derived from vegetable oils such as soybean oil, or other sources such as animal fats and waste frying oils. It is largely a mixture of compounds called fatty acid methyl esters (FAME). Biodiesel is also known to possess good properties as a solvent. In this work, the solvent properties of the FAME in biodiesel were investigated by determining the so-called kauri-butanol (KB) value. The KB value is a common test for assessing solvent power. Biodiesel components perform well in this test. Such results are important as they provide the basis for other applications of biodiesel. In turn, additional markets for biodiesel help provide economic stability to this product in light of the volatility of fuel markets, potentially giving biodiesel producers an additional revenue stream.
Technical Abstract: Esters, most commonly methyl esters, of vegetable oils or animal fats or other lipid feedstocks have found increasing use as an alternative diesel fuel known as biodiesel. However, biodiesel also has good solvent properties, a feature rendered additionally attractive by its biodegradability, low toxicity, and low content of volatile organic compounds. The kauri-butanol (KB) value is a parameter used for describing the solvent strength of a liquid. In this work, the KB values of individual fatty acid alkyl esters were determined. The KB values of fatty esters depend on chain length, including the alcohol moiety, and unsaturation, a phenomenon observed similarly in hydrocarbons. The KB values of fatty acid methyl esters range from well over 100 for short-chain esters to the 40-60 range for C18 esters, with a maximum being attained for methyl esters of C4-C5 acids. For comparison, the KB values of dimethyl diesters and hydrocarbons (alkanes) were also determined as well as those of some standard solvents. Compounds with eight carbons were selected to compare the influence of various functional groups on solvent strength as documented by the KB value. The relation to solubility parameters is briefly discussed. It was also shown that KB values can be determined with good accuracy by reducing the amount of KB solution from 20g to 5g, thus using correspondingly less solvent sample.