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Internal Combustion Engines

Oxidative Stability of Algae Derived Methyl Esters

[+] Author and Article Information
Harrison Bucy

Department of Mechanical Engineering,  Colorado State University, Fort Collins, CO 80523-1374

Anthony J. Marchese

Department of Mechanical Engineering,  Colorado State University, Fort Collins, CO 80523-1374marchese@colostate.edu

J. Eng. Gas Turbines Power 134(9), 092805 (Jul 23, 2012) (13 pages) doi:10.1115/1.4006712 History: Received November 22, 2011; Revised January 13, 2012; Published July 23, 2012; Online July 23, 2012

Microalgae are currently receiving strong consideration as a potential biofuel feedstock to help meet the advanced biofuels mandate of the 2007 Energy Independence and Security Act because of its theoretically high yield (gal/acre/year) in comparison to current terrestrial feedstocks. For algal methyl ester biodiesel, fuel properties will be directly related to the fatty acid composition of the lipids produced by the given microalgae strain. Several microalgae species under consideration for wide scale cultivation, such as Nannochloropsis, produce lipids with fatty acid compositions containing substantially higher quantities of long chain-polyunsaturated fatty acids (LC-PUFA) in comparison to terrestrial feedstocks. It is expected that increased levels of LC-PUFA will be problematic in terms of meeting all of the current ASTM specifications for biodiesel. Moreover, these same LC-PUFA fatty acids, such as eicosapentaenoic acid (EPA: C20:5) and docosahexaenoic acid (DHA: C22:6) are known to have high nutritional value, thereby making separation of these compounds economically attractive. Given the uncertainty in the future value of these LC-PUFA compounds and the economic viability of the separation process, the goal of this study was to examine the oxidative stability of algal methyl esters with varying levels of EPA and DHA. Tests were conducted using a Metrohm 743 Rancimat with automatic induction period determination following ASTM D6751 and EN 14214 standards, which call for induction periods of at least 3 and 6 h, respectively. Tests were conducted at a temperature of 110 °C and airflow of 10 l/h with model algal methyl ester compounds synthesized from various sources to match the fatty acid compositions of several algae strains subjected to varying removal amounts of roughly 0% to 100% LC-PUFA. In addition, tests were also conducted with real algal methyl esters produced from multiple sources. The bis-allylic position equivalent (BAPE) was calculated for each fuel sample to quantify the level of unsaturation. The induction period was then plotted as a function of BAPE, which showed that the oxidative stability varied exponentially with the amount of LC-PUFA. The results suggest that removal of 45% to 65% of the LC-PUFA from Nannochloropsis-based algal methyl esters would be sufficient for meeting existing ASTM specifications for oxidative stability.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of BAPE and APE sites

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Figure 2

Nannochloropsis oculata—formulation and actual BAPE, APE, and BAPE + APE comparison

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Figure 3

Nannochloropsis sp—formulation and actual BAPE, APE, and BAPE + APE comparison

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Figure 4

Isochrysis galbana—formulation and actual BAPE, APE, and BAPE + APE comparison

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Figure 5

Induction period as a function of BAPE for all tested methyl esters

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Figure 6

Induction period as a function of BAPE + APE for all tested methyl esters

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Figure 7

Induction period as a function of BAPE for the Nannochloropsis oculata growth formulations

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Figure 8

Induction period as a function of modeled percent EPA and DHA removed for the Nanno oculata growth formulations

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Figure 9

Induction period as a function of BAPE for Nannochloropsis sp formulations

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Figure 10

Induction period as a function of modeled percent EPA and DHA removed for Nannochloropsis sp formulations

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Figure 11

Induction period as a function of BAPE for Isochrysis galbana formulations

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Figure 12

Induction period as a function of modeled percent EPA and DHA removed for Isochrysis galbana formulations

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Figure 13

Induction period as a function of BAPE for Nannochloropsis sp formulations with TBHQ additive

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Figure 14

Induction period as a function of modeled percent EPA and DHA removed for Nannochloropsis sp formulations with TBHQ additive

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