Bioenergy Opportunities for Northwest Wisconsin Understanding the Chemical and Physical Reactions In

1
Bioenergy Opportunities for Northwest
WisconsinUnderstanding the Chemical and
Physical Reactions In Production of Biodiesel

• Jun Yoshitani, P.E.
• Bioenergy Environment, Inc.

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Presentation Contents

• Definition of biodiesel
• Chemical reactions
• Effect of variables
• Feedstock, alcohol and catalyst
• Quality standards and cold flow properties

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Definition of Biodiesel

• A fuel comprised of mono-alkyl esters of long
  chain acids derived from vegetable oils or animal
  fats, designated B100.
• Biodiesel must meet the latest specifications of
  ASTM D 6751

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Standard Recipe

• Add 100 lb of triglyceride oil 21.71 lb
  methanol (61 molar ratio)
• Plus 0.35 to 1.0 lb of NaOH or KOH catalysts (or
  0.5 lb NaOCH3)
• To make 100.45 lb biodiesel 10.4 lb glycerol
  10.86 lb of excess methanol

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Basic Chemistry
O
O II
II CH2
O -- C R1 CH3 O - C
R1 I I
O
O CH2 - OH I
II
II I CH O C R2 3
CH3OH CH3 O C R2 CH - OH I

I
I O
O CH2 - OH I
II
II CH2 O C R3
CH3 - O - C R3 Triglyceride
Methanol Mixture of Fatty
Glycerin
Esters
Catalyst
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Initial Reaction Conditions

• Methanol distributed in oil as small droplets.
• Catalyst attracted to methanol, which is polar.
• Agitation required to keep methanol distributed
  as small droplets.

Oil
Methanol Catalyst
Oil
Oil
Oil
Oil
Methanol Catalyst
Methanol Catalyst
Oil
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Later Stages of the Reaction

• Glycerol has low solubility in oil and methyl
  esters.
• As more glycerol is produced, it attracts the
  catalyst and forms small droplets. Glycerol is
  polar.

Methyl esters
Glycerol Catalyst
Methyl esters
Methyl esters
Glycerol Catalyst
Glycerol Catalyst
Glycerol Catalyst
Methyl esters
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Mass Transfer Limited Reaction

• Reaction is limited by the rate at which oil can
  get to the methanol/catalyst droplets and the
  rate at which the methyl esters can get away.

Oil
Methyl ester
Methanol Catalyst
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Effect of Stoichiometry for Base
Transesterification
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Effect of Mixing
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Effect of Temperature
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Triglyceride Sources

• Vegetable oils soybean, rapeseed, cotton seed,
  palm, coconut, sunflower
• Inedible oils jatropha
• Rendered animal fats
• Yellow grease, brown grease
• Trap grease, float grease, soapstock

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Typical Soybean Oil Quality
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Feedstock Implications

• Differences in quality of feedstock relates to
  conversion.
• Free fatty acids level affects formation of soap
  lowers conversion rate.
• Water level affects formation of free fatty
  acids.
• Saturation level affects cold flow properties.
• Phosphatide level affects process efficiency.

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Alcohols

• Methanol and ethanol
• Biodiesel using ethanol requires 44 more pounds
  of ethanol
• Use of ethanol provides an all bio-based product
• Ethanol recovery is more difficult than methanol
• Ethanol costs more than methanol

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Catalyst Options

• Base catalysts NaOH, KOH, NaOCH3
• Sodium methoxide as a 25 or 30 concentrate in
  methanol is preferred catalyst
• Acid catalyst H2SO4, H3PO4
• Acid catalysts are usually used for conversion of
  free fatty acids to esters

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Biodiesel Quality Standards

• Flash point must be less than 130 deg C
• Water and sediment concentration must be less
  than 500 ppm
• Kinematic viscosity should be in range of 1.9 to
  6.0 cSt.
• Sulfated ash must not exceed 0.02
• Sulfur concentration must be less than15 ppm.
• Maximum copper corrosion is 3.
• Minimum cetane number is 47.
• Cloud point, Report
• Carbon residue must not exceed 0.05
• Acid value should be less than 0.8 mg KOH/g
• Max free glycerin must not exceed 0.02
• Max total glycerin must not exceed 0.24
• Maximum phosphorus content is 0.001

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Definition of Cold Flow Properties

• Cloud point (CP) T at which haziness is
  observed
• Pour point (PP) lowest T at which movement can
  be detected
• Cold filter plugging point (CFPP) lowest T at
  which 20 mL sample passes 45 um mesh at 0.0194
  atm vacuum in 60 sec.
• Low temperature filter test (LTFT) lowest T at
  which 180 mL sample passes 17 um mesh at 0.197
  atm vacuum in 60 sec.

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Cold Flow Properties (Co)
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Biodiesel/Glycerin Separation

• Gravity decanting
• Requires hours
• Sp. Gr. Of biodiesel 0.88
• Sp. Gr. Of glycerin 1.05 (mixed with methanol)
• Centrifuge
• High volume throughput
• Requires minutes
• Higher capital and operating cost
• Both decanter and centrifuge have difficulty with
  emulsions resulting from excess soap.

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Acidulation/Neutralization

• Residual catalyst can be neutralized by acid
  addition.
• NaOCH3 HCl gtgt CH3OH NaCl
• Soaps can be split into free fatty acids and salt
  by acidulation (requires pH of 4.5 to 5.0)
• Soap HCl gtgt Free fatty acids NaCl
• Eliminating soap will reduce formation of
  emulsion during washing.

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Methanol Removal

• Flash vaporization, falling film evaporators or
  wiped film evaporators.
• Removal before or after separation of biodiesel
  from glycerin has pro and con
• Pro separation of biodiesel and glycerin is
  sharper when methanol is present
• Con reverse transesterification can occur

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Methanol Recovery

• Excess methanol needs to be recovered.
• Distillation column is most often used for
  methanol recovery.
• Distillation also separates water from methanol.
• Spent washwater can also be passed through
  distillation column and reused.

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Water Washing to Remove Glycerin

• Use softened hot water (both biodiesel and water
  at 60 o C).
• Softened water minimizes the potential for
  mineral transfer (calcium, magnesium and iron) to
  the biodiesel.
• Want to encourage contact between the biodiesel
  and water with gentle agitation.
• Counter flow wash column (packed bed and rotating
  disc)

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Flash Drying

• Biodiesel should be dried to eliminate suspended
  droplets of water.
• Water and sediment requirement in ASTM D6751
• Biodiesel can absorb about 1500 ppm of water (2
  diesel absorbs 50 ppm)
• Water contributes to fuel instability in
  long-term storage.

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Understanding the Chemical and Physical
Reactions In Production of BiodieselThank you

• Jun Yoshitani, P.E.
• Bioenergy Environment, Inc.
• bioandenv_at_sbcglobal.net
• 630-231-2072