Quality Characteristics of Brassicabased Biodiesel

1
Quality Characteristics of Brassica-based
Biodiesel

• Jon Van Gerpen
• Department of Biological and Agricultural
  Engineering
• University of Idaho

U.S. Canola Research Conference November 14, 2006
2
Biodiesel Fuel Quality

• Currently the two greatest obstacles for the
  development of the biodiesel industry are
• Cost
• Quality
• Customers have very low tolerance for operational
  problems caused by low quality.
• Low quality fuel caused serious problems last
  winter in Minnesota.

3
Quality

• There are two categories of quality concerns
• Production concerns fuel does not meet the
  specification.
• Feedstock concerns biodiesel from different
  feedstocks has different properties. Biodiesel
  produced from some feedstocks may not be fit for
  use in some situations.

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Transesterification
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Completeness of Reaction

• ? Triglyceride ? Diglyceride ? Monoglyceride ?
  Glycerol
• Methyl ester Methyl ester Methyl
  ester
• ? Incomplete reaction mixtures contain tri-, di-
  and monoglycerides

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Unreacted products

• ? The glycerol portion of the tri-, di-, and
  monoacylglycerols is called the bound glycerol.
• ? Total glycerol bound glycerol free
  glycerol.
• ? Total glycerol lt 0.24

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Monoglycerides, not soap
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Another production problem is soap formation.
Soap usually appears as a gel or slime
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ASTM D 6751 Biodiesel Specifications
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Quality problems

• Productions problems tend to be common for all
  feedstocks.
• Feedstock choice can influence the cetane number,
  viscosity, cold flow properties, and oxidative
  stability of the final product.

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Cetane Number The primary ignition quality
parameter for diesel fuel.

• Ester A c i
  d
• C160 C180 C181 C182
• Methyl 85.9 101.0 59.3 38.2
• Ethyl 93.1 97.7 67.8 39.6
• Propyl 85.0 90.0 58.8 44.0
• iso-Propyl 82.6 96.5 86.6
• 2-Butyl 84.8 97.5 71.9
• G. Knothe, A.C. Matheaus, T.W. Ryan, Fuel
  82971-975 (2003).

Longer chain length gives higher cetane
number. More unsaturation gives lower cetane
number.
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Biodiesel from a saturated feedstock
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Cold flow properties

Pour point (add 3 degrees)
Cloud point
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Oxidative Stability

• Structural reason for the auto-oxidation of
  fatty compounds
• Allylic CH2 positions
• ? ?
• H3CO2C-(CH2)x-CH2-CHCH-CH2-CHCH-CH2-(CH2)y-CH3
  
• ?
• especially bisallylic CH2 positions
  

Two conjugated double bonds gives a large
increase in the tendency of the fuel to oxidize.
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Potential Feedstocks
Most important for cold flow and cetane
Should be low for best oxidative stability
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Characteristics of Biodiesels from Brassicas
Exceeds the European viscosity limit of 5.0 cSt
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Summary

• Feedstock choice can influence the quality of
  biodiesel.
• Brassica crops tend to be low in saturated fatty
  acids which give superior cold flow properties.
• Canola is high in monounsaturated fatty acid
  (oleic), which is the best compromise between
  cetane , oxidative stability, and cold flow.