Biodiesel Production – Part 1: Feedstocks and Production

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Biodiesel Production Part 1Feedstocks and
Production

• Renewable Products Development Laboratories
• Portland, Oregon, USA

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What Is Biodiesel?

• Definition Biodiesel consists of the alkyl
  monoesters of fatty acids derived from vegetable
  oils and animal fats that meet the requirements
  of ASTM 6751.

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What Is NOT Biodiesel?

• Blends of biodiesel and petroleum diesel
• Unprocessed (un-reacted) fats and oils
• Mixtures or emulsions of alcohol and fats or oils
• Bio-derived fuels such as F-T diesel

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Biodiesel Reaction

• Chemical reaction between a primary alcohol (e.g.
  methanol, ethanol) and an oil or fat
• Basic Chemistry
• 100 lb Oil 10 lb Methanol ?
• 100 lb Biodiesel
• 10 lb Glycerol
• Requires a catalyst

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US Sources of Oils and Fats

• Soybeans 18.3 B lb/yr
• Corn 2.4 B lb/yr
• Other Seed Oils 2.9 B lb/yr
• Tallows 5.5 B lb/yr
• Lard Grease 1.3 B lb/yr
• Poultry Fat 2.2 B lb/yr
• Yellow Grease 2.6 B lb/yr
• Algae, other ???

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Quality Requirements for Standard Biodiesel
Production

• Free Fatty Acid (FFA) Content
• lt 2.0
• Moisture Content
• lt 0.1 desired
• lt 0.5 permitted
• Phosphorus and Sulfur Content
• lt 15 ppm

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Free Fatty Acids (FFA)

• FFA are weak organic acids with carbon numbers
  ranging from 8 to 22 or more.
• FFA are naturally occurring or products of
  partial decomposition of fats and oils.
• FFA are easily neutralized using alkali
  hydroxides making soap.
• FFA can be converted to biodiesel, typically
  using a mineral acid catalyst.

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Categories of Biodiesel Processes

• Base Catalyzed (Transesterification)
• Batch
• Continuous
• Acid Catalyzed
• FFA Pretreatment (Direct Esterification)
• Non-catalytic
• Co-solvent processes
• Supercritical
• Heterogeneous (Solid) Catalyst

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Key Process Variables

• Temperature
• Pressure
• Oil Alcohol Ratio
• Reaction Time
• Mixing
• Batch or Continuous Processing

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Base Catalyzed Batch System
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Continuous CSTR System
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Base Catalyzed PFR System
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Heterogeneous Catalyst System
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Process Conditions

• AlcoholTG Ratio
• - Base Catalyzed 61 to 101 typical
• - Acid Catalyzed 91 to 401
• Residence Time
• - Base Catalyzed 5 min to 4 hr
• - Acid Catalyzed 15 min to 8 hr

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Biodiesel Production Chemistry

• Esterification is a three step reaction
• - Solubility limited
• - Rate limited
• - Product inhibition (glycerol) limited

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Process Conditions

• Temperature
• - Solubility Limited Increasing T
  increases solubility
• - Rate Limited Reaction rate doubles
  with a 10 C increase in T
• - Product Inhibition Limited
• GL ? MG rate near MG ? DG rate
• Pressure Operate 10 to 15 psig above alcohol
  vapor pressure

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Batch or Continuous?

• Batch
• - indicated for small capacity or long
  residence times
• Continuous
• - indicated for large capacity systems
• - longer residence times can be accommodated
  using sequential CSTRs or PFRs
• - Residence time can be optimized using
  multiple parameters

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Summary

• Production of fatty acid esters is easy
  production of biodiesel is a deceptively
  difficult process.
• There are multiple ways to make biodiesel to meet
  multiple business models.
• There are multiple sources of fats and oils for
  biodiesel that can be adapted to local realities.