酸催化合成生物柴油

b) NaOH + CH3OH
CH3O- + Na+ CH3O- + H2O + Na+
Strong nucleophile
Figure 2. Formation of the active species in transesterification reactions using a base catalyst.
group of the alcohol.
Kiss A A, et al. Adv. Synth. Catal. 2006, 348, 75-81.
8
1.4. Limitations of alkaline catalysis
Strict feedstock specifications, FFA content must not
CHOH +
CH2OOCR3
Monoglyceride
CH2OH
Glycerol
R3COOCH3
Overall reaction:
CH2OOCR1
CH2OH
R1COOCH3
Catalyst
CHOOCR2 + 3 CH3OH
CHOH
+ R2COOCH3
CH2OOCR3
CH2OH
R3COOCH3
Triglyceride
O
O (3) R2 O
OR O-
O R1
O
R3
O R2 O
O-
+ R1COOR
O
R3
O
O
O (4) R2 O
O-
O
R3 + BH+
O R2 O
OH
+B
O
R3
O
O
B: base catalyst; R1, R2, R3: carbon chain of the fatty acids; R: alkyl
Zhao H.; et al. Science, 2007, 315, 804-807.
4
Lotero E, et al. Ind. Eng. Chem. Res., 2005, 44, 5353-5363. 5
CH2OOCR1
CH2OH
Catalyst
CHOOCR2 + CH3OH
CHOOCR2 + R1COOCH3
Biodiesel: CH3(CH2)nCO2R
Nonpetroleum-based fuel derived from either the transesterification of triglycerides (TGs) or the esterification of free fatty acids (FFAs) with low molecular weight alcohols.
R OMe
Base cat.
O
+ R OH
MeOH
Figure 3. (a) Base catalyst reaction with FFAs to produce soap and water, both undesirable byproducts. (b) Water promotes the formation of FFAs. These, then, can deactivate the catalyst and produce soap, as in (a).
3
1.1. Biodiesel: properties & advantages
➢ The flow and Combustion properties are similar to th e the common diesel oil; ➢ Releases about 90% of the energy that normal diesel d does; ➢ Renewable resource; ➢ No need for changing engine. ➢ Sulfur low-content and nontoxic.
Synthesis of Biodiesel via Acid Catalysis
1
报告内容
1. Background 2. Methodologies based on acid-
catalyzed reactions 3. Summary and prospect
2
1. Background
CH2OOCR3
Triglyceride
CH2OH
CH2OH
CHOOCR2
Catalyst
+ CH3OH
CHOH
+ R2COOCH3
CH2OOCR3
Diglyceride
CH2OOCR3
Monoglyceride
CH2OH CHOH
CH2OH
Catalyst
+ CH3OH
exceed 0.5 wt %; anhydrous (total water content must
be 0.1-0.3 wt % or less) and corrosive.
O a) R OH + NaOH (or MeONa)
O R O-Na+ + H2O (or MeOH)
O
b)
+ H2O
Glycerol
Methyl esters (Biodoesel)
Figure1. Transesterification of triglycerides 6
1.2. Alkaline catalysis
Catalysts: NaOH, KOH, CH3ONa, CH3OK, etc.
a)
CH3O-Na+
Kiss A A, et al. Adv. Synth. Catal. 2006, 348, 75-81.
7
1.3. Alkaline catalysis mechanism
(1) ROH + B
RO- + BH+
O (2) R2 O
O
O R1 + RO-
O
R3
O
O R2 O
OR O-
O R1
O
R3
Kulkarni M G.; et al. Green Chem., 2006, 8, 1056–1062.
9
2. Methodologies based on acidcatalyzed reactions
2.1. The Feedstock Issue
➢Vegetable oils: major feedstock; ➢Animal fats: low cost; ➢Waste greases: low cost, recycle waste oils, lowquality feedstocks in terms of FFA and water content; ➢Microbial oils: potential sustainable sources!