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.