Biodiesel Production Part 1 Feedstocks and Production Renewable
Biodiesel Production – Part 1: Feedstocks and Production Renewable 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 • Corn • Other Seed Oils 18. 3 B lb/yr 2. 4 B lb/yr 2. 9 B lb/yr • Tallows • Lard & Grease • Poultry Fat 5. 5 B lb/yr 1. 3 B lb/yr 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) Ø Batch ØContinuous • Acid Catalyzed ØFFA Pretreatment (Direct Esterification) • Non-catalytic Ø Co-solvent processes Ø Supercritical • Heterogeneous (Solid) Catalyst
Key Process Variables • • • Temperature Pressure Oil : Alcohol Ratio Reaction Time Mixing Batch or Continuous Processing
Base Catalyzed Batch System
Continuous CSTR System
Base Catalyzed PFR System
Heterogeneous Catalyst System
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.
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