1. 0.31
0.37
1.04
0
10
20
30
40
50
60
70
80
90
100
0
2
4
6
8
10
12
14
16
1
2
3
%Yield
TotalAcidNumber,TAN
(mgKOH/g-sample)
Sample Number
Star1ng
TAN
Post-­‐Dry
End
TAN
%Yield
Caustic Washing for Acid Reduction in Biodiesel Production
Drexel University, Chemical & Biological Engineering
Edwin Guillermo, Dr. Richard A. Cairncross
Introduction
Biodiesel is a drop-in fuel that can be produced from refined
vegetable oils and waste greases. Waste greases contain impurities
that must be removed to produce fuel grade biodiesel.
• Greases are made up of mostly lipids
Ø Lipids are organic fatty acids and their derivatives.
• Free fatty acids (FFA) are converted to biodiesel through
esterification. Forms fatty acid methyl esters (FAME)
Ø Incomplete reaction leads to unreacted FFA and acidic
biodiesel (high total acid number)
• The total acid number (TAN) is a representation of acidic content
and must be below a certain standard to meet specifications
Ø TAN can be lowered through saponification
Base solution
added until FAME
obtains pink tint
Water added for
phase separation
Washing continues
until neutral water
obtained
Conclusions
TAN Reduction
• Higher wash water temperature:
Ø Reduces water consumption but can also result
in higher TANs
Ø Possibly promotes a reverse reaction
• Lower yields found when washing high FFA
biodiesel
Ø High FFA à more saponification à greater
emulsification à lower yield
Recommended Wash Steps
• After titration is complete, agitate the solution
Ø Alternate between shaking and settling every
30 seconds for 5 minutes
• Add room temperature water
Ø Agitate gently on first wash (slowly invert)
Ø Increase intensity of second and third washes.
Ø Shake well for fourth wash.
• Decant Water and FAME. Dry FAME overnight.
Heat/Shake &
Centrifuge
Esterification
(FFA to FAME)
Wash
Process for Producing Biodiesel from Waste Greases
• Waste greases collected from
restaurants/water treatment
facilities
• Acidulated to increase FFA yield
• Heated and shaken to liquefy
• Lipid layer forms followed
by waste layers (floating
solids, water, sediments)
• Lipid layer is decanted and
esterified (TAN on avg. 175)
• Methanol is bubbled into the lipids to create
FAME (Fatty Acid Methyl Ester) (TAN on
avg. of 1-3)
R-COOH + CH3OH -----> R-COOCH3 + H2O
(FFA) (Methanol) (FAME)
• Excess acid catalyst
washed out with water
• Washing repeated until
neutral
Definitions
Greases are composed of mostly lipids. Lipids are
organic fatty acids and their derivatives
• Free Fatty Acids (FFA) are long carbon chain
carboxylic acids
• Esterification: Acid reacted with an alcohol to form
an ester
Esterification
• Total acid number (TAN) is measured in mg-KOH/
g-sample. Determines how much base is needed
to neutralize the acids. Calculated through
titration. Maximum TAN allowed = 0.50 mg-KOH/
g-sample
• Saponification: Base solution added to convert
unreacted FFA to soap
Project Objectives
Develop a robust caustic washing procedure to reduce FFA content
of biodiesel to meet ASTM specifications:
• Determine optimal amount of base to add for saponification
• Determine optimal temperature for washing for minimal emulsion
• Minimize water usage and maximize yield of process
Caustic Washing Procedure
Total
Washes
Total
Water
Added
(mL)
Post-­‐Dry
End
TAN
%Yield
%TAN
Reduc1on
Soaps
(PPM)
1
5
320
0.31
84
98
1508
2
4
130
0.37
67
97
1512
3
3
110
1.04
83
93
108
• FAME samples with various
TANs prepared
• Studied variability of yield and
TAN reduction based on initial
TAN
• FAME + base solution allowed to
sit for various times
• Studied TAN reduction based on
sitting time. (5,10,15 minutes)
• Water added to cause phase separation
between FAME and water
Ø Soap solubility varies with temperature
Ø Parametric study performed on effect of
washing temperature
• Decanted water is
acidulated and disposed
• Dried at 50-60˚C
overnight
Heated Wash Water Room Temperature Wash Water
R
E
S
U
L
T
S
TAN Reduction of High FFA Biodiesel TAN Reduction of Low FFA Biodiesel
Greater yield for high FFA
biodiesel washed with
heated water
33% of heated samples met
specification
100% of room temperature
samples met specification
Base Titration
Acidic
samples
prepared
with a pH
indicator
Base
added
slowly to
sample
Base
titration
complete
when
sample
stays pink
Base
Water
FFA
Soap Molecule
+ K-O-H
+ H-O-H
KO
Temperature of wash water does
not appear to affect the final
soap concentration
Acid
Catalyst
Acid Alcohol Ester Water
R’
R’
R-O-H H-O-H
Total
Washes
Total
Water
Added
(mL)
Pre-­‐Dry
End
TAN
Post-­‐Dry
End
TAN
%Yield
%TAN
Reduc1on
Soaps
(PPM)
8
3
120
0.63
0.86
93
43
1670
9
3
120
0.60
0.77
92
49
1896
10
3
120
0.31
0.46
95
70
1410
11
4
180
0.21
0.23
95
85
1670
12
4
180
0.26
0.26
94
83
1719
13
4
180
0.23
0.24
93
84
1750
0
10
20
30
40
50
60
70
80
90
100
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
8
9
10
11
12
13
14
%Yield
TotalAcidNumber,TAN
(mgKOH/g-sample)
Sample Number
Star1ng
TAN
Pre-­‐Dry
End
TAN
Post-­‐Dry
End
TAN
%Yield
Dried in oven
• Soap molecules
contain hydrophilic
& hydrophobic ends
• Enables soap to
behave as an
emulsifier between
water & oil:
Ø Hydrophilic end
attracts water
Ø Hydrophobic end
attracts oils
Specified TAN
(0.50 mg KOH/g-sample)
Pre-dry TAN
consistently lower
than post-dry TAN
Acknowledgements
Dr. Peter Wade, Chemistry Department
Megan Hums, Ph.D Candidate
Zachary Gibbins, Undergraduate Student
Adam Moody, Undergraduate Student
References
1. "Spring Of Chemistry." Spring Of Chemistry. N.p., n.d. Web. 25 Aug. 2015.
2. ASTM D6751-15a, Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle
Distillate Fuels, ASTM International, West Conshohocken, PA, 2015, www.astm.org
3. "Soap - How Does It Get Things Clean?" Soap - How Does It Get Things Clean? N.p., n.d. Web.
25 Aug. 2015.
[1]
[2]
[3]
Emulsification
Saponification