Biodiesel Production – Part 1:Feedstocks and ProductionRenewable Products Development Laboratories
Portland, Oregon, USA
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.
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
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
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 ???
Quality Requirements for “Standard” Biodiesel Production
• Free Fatty Acid (FFA) Content
< 2.0 %
• Moisture Content
< 0.1 % desired
< 0.5 % permitted
• Phosphorus and Sulfur Content
< 15 ppm
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.
Categories of Biodiesel Processes
• Base Catalyzed – (Transesterification) BatchContinuous
• Acid CatalyzedFFA Pretreatment (Direct Esterification)
• Non-catalytic Co-solvent processes Supercritical
• Heterogeneous (Solid) Catalyst
Key Process Variables
• Temperature
• Pressure
• Oil : Alcohol Ratio
• Reaction Time
• Mixing
• Batch or Continuous Processing
Base Catalyzed Batch System
E-1
E-2
E-3
E-4
P-1
P-2
P-3
P-4
P-5
P-6
P-7
P-8
Batch Reactor
Ester – GlycerolDecanter
AlcoholEvaporator
Esters to Refining
AlcoholEvaporator
Crude Glycerol
Continuous CSTR System
E-1
E-2
E-3
E-4
P-1
P-2
P-3
P-4
P-5
P-6
P-7
P-8
Ester – GlycerolDecanter
AlcoholEvaporator
Esters to Refining
AlcoholEvaporator
Crude Glycerol
E-5
P-9
CSTR Reactors
Base Catalyzed PFR System
E-1
E-2
E-3
P-1 P-2
P-3
P-4
P-5
P-6
PFR Reactor
Flash
Alcohol
Esters
Glycerol
Decanter
Heterogeneous Catalyst System
E-2
E-3
P-1
P-2
P-3
P-4
P-5
P-6
Fixed Bed Reactor
Flash
Alcohol
Esters
Glycerol
DecanterE-4
Process Conditions
• Alcohol:TG Ratio
- Base Catalyzed: 6:1 to 10:1 typical
- Acid Catalyzed: 9:1 to 40:1
• Residence Time
- Base Catalyzed: 5 min to 4 hr
- Acid Catalyzed: 15 min to 8 hr
Biodiesel Production Chemistry
• Esterification is a three step reaction:
- Solubility limited
- Rate limited
- Product inhibition (glycerol) limited
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
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
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.