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 Soybeans18.3 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 )  Batch  Continuous Acid Catalyzed  FFA 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

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.