Bias and Imprecision in the Determination of Free Glycerin in Biodiesel: The Unexpected Role of Limitations in Solubility

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• 作者：Richard W. Heiden ; Sigurd Schober…
• 关键词：Biodiesel ; Glycerin ; Bias ; Solubility
• 刊名：Journal of the American Oil Chemists' Society
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：94
• 期：2
• 页码：285-299
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Industrial Chemistry/Chemical Engineering; Biomaterials; Agriculture; Food Science; Biotechnology;
• 出版者：Springer Berlin Heidelberg
• ISSN：1558-9331
• 卷排序：94

文摘

Residual free glycerin (FG) is a critical marker of fatty acid methyl ester (biodiesel) fuel quality. Yet, routine determinations by standard methods display excessive imprecision, and the uncertainties undermine confidence in the data. Various degrees of agitation are used here to evaluate the possibility of heterophase formation as a contributor to imprecision and potential bias. Statistical markers from the analysis of 13 biodiesel samples reveal that seven contain unexpected heterophases, which, due to settling, cause underestimates of 15–68%. Agitation alone re-suspends heterophases for brief periods, easing potential biases, but also increases imprecision. A promising new sample pretreatment is presented, which reduces the deleterious effects of heterophases. Solubility limitations are explored as possible contributing factors, and measurements made at 23 °C in purified soy FAME reveal an equilibrium solubility which is more than 80% below previously published estimates. Strong interactions of liquid FG with small amounts of moisture reduce solubility to below international quality limits, while interactions of initially dissolved forms of moisture and FG produce bias-inducing heterophases at 0.02% FG. The unexpected low solubility of FG, exacerbated by interactions with impurities, is seen as an important contributor to underestimates and imprecision, and a strong influencing factor on the fate of residual FG in commercial biodiesel fuels.