Biodiesel Production : Biodiesel Production Technologies Types of Biodiesel Production Processes : Types of Biodiesel Production Processes Definition and standards
Fatty acid chains
Process issues Definition of “Biodiesel” : Definition of “Biodiesel” Biodiesel – a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, designated
Biodiesel must meet the specifications of ASTM D 6751 ASTM D 6751-02 : ASTM D 6751-02 Transesterification : Transesterification Triglyceride Sources : Triglyceride Sources Rendered animal fats: beef tallow, lard
Vegetable oils: soybean, canola, palm, etc.
Rendered greases: yellow grease (multiple sources)
Recovered materials: brown grease, soapstock, etc. Standard Recipe : Standard Recipe 100 lb oil + 21.71 lb methanol
→ 100.45 lb biodiesel + 10.40 lb glycerol + 10.86 lb XS methanol
Plus 1 lb of NaOH catalyst Competing Reactions : Competing Reactions Free fatty acids are a potential contaminant of oils and fats. Slide 9: O
|| + KOH
HO - C - (CH2)7 CH=CH(CH2)7CH3
Oleic Acid Potassium Hydroxide
→ K+ -O - C - (CH2)7 CH=CH(CH2)7CH3 + H2O
Potassium oleate (soap) Water Fatty acids react with alkali catalyst to form soap. Water is also a problem : Water is also a problem Water hydrolyzes fats to form free fatty acids, which then form soap. Soap : Soap Soaps can gel at ambient temperature causing the the entire product mixture to form a semi-solid mass.
Soaps can cause problems with glycerol separation and washing. Process Issues : Process Issues Feedstock requirements
Continuous vs. batch processing
Processing low quality feedstocks
Developing process options Feedstocks Used in Biodiesel Production : Feedstocks Used in Biodiesel Production Triglygeride or fats and oils (e.g. 100 kg soybean oil) – vegetable oils, animal fats, greases, soapstock, etc.
Primary alcohol (e.g. 10 kg methanol) – methanol or ethanol (44% more ethanol is required for reaction)
Catalyst (e.g. 0.3–1.0 kg sodium hydroxide)
Neutralizer (e.g. 0.25 kg sulfuric or hydrochloric acid) Reaction time : Reaction time Transesterification reaction will proceed at ambient (70°F) temperatures but needs 4-8 hours to reach completion.
Reaction time can be shortened to 2-4 hours at 105°F and 1-2 hours at 140°F.
Higher temperatures will decrease reaction times but require pressure vessels because methanol boils at 148°F (65°C).
High shear mixing and use of cosolvents have been proposed to accelerate reaction. Batch vs Continuous Flow : Batch vs Continuous Flow Batch is better suited to smaller plants (<1 million gallons/yr).
Batch does not require 24/7 operation.
Batch provides greater flexibility to tune process to feedstock variations.
Continuous allows use of high-volume separation systems (centrifuges) which greatly increase throughput.
Hybrid systems are possible. Hybrid Batch/Continuous Base Catalyzed Process : Hybrid Batch/Continuous Base Catalyzed Process Processing Lower Quality Feedstocks : Processing Lower Quality Feedstocks Biodiesel feedstocks vary in the amount of free fatty acids they contain:
Refined vegetable oils < 0.05%
Crude soybean oil 0.3-0.7%
Restaurant waste grease 2-7%
Animal fat 5-30%
Trap grease 75-100%
Price decreases as FFAs increase but processing demands increase, also.
Not suitable for high FFA feeds because of soap formation. Preferred method for High FFA feeds: Acid catalysis followed by base catalysis : Preferred method for High FFA feeds: Acid catalysis followed by base catalysis Use acid catalysis for conversion of FFAs to methyl esters, until FFA < 0.5%.
Acid esterification of FFA is fast (1 hour) but acid-catalyzed transesterification is slow (2 days at 60°C).
Water formation by
FFA + methanol ==> methyl ester + water
can be a problem.
Then, add additional methanol and base catalyst to transesterify the triglycerides. Acid Catalyzed FFA Pretreat System : Acid Catalyzed FFA Pretreat System Hi-FFA TG Esters to
Acid base- process Alcohol Acid Reactor Neutralize
Separate Water Methanol recovery Product Quality : Product Quality Product quality is important – modern diesel engines are very sensitive to fuel.
It is not biodiesel until it meets ASTM D6751.
Critical properties are total glycerol (completeness of reaction) and acid value (fuel deterioration). Reaction must be >98% complete. Developing Process Options : Developing Process Options Schemes for accelerating the reaction
High shear mixing
Solid (heterogeneous) catalysts
Easier glycerol clean-up Summary : Summary Biodiesel is an alternative fuel for diesel engines that can be made from virtually any oil or fat feedstock.
The technology choice is a function of desired capacity, feedstock type and quality, alcohol recovery, and catalyst recovery.
Maintaining product quality is essential for the growth of the biodiesel industry.