48
J.-G. Na et al. / Catalysis Today 156 (2010) 44–48
Table 2
these conditions, cracking and decarboxylation occurred simulta-
neously. Heptadecene was formed by direct decarboxylation of
oleic acid. Decanoic acid, which is detected in the other cases, lost
their CO2 by MG63 and MG70 and then turned into nonane. Based
on these product analysis by GC–MS, decarboxylation by hydro-
talcites are active when the reaction temperature was the same or
higher than 673 K. It is closely related with adsorption–desorption
behavior of MgO, considering MgO–CO2 desorption temperature
around 623 K [15,16].
GC/MS percentage peak areas of major liquid products at 673 K.
Name of compound
Percentage peak area (%) (catalysts)a
Blank
MG30
MG63
MG70
Heptane
4.05
4.93
1.44
4.75
2.82
4.18
5.68
1.78
4.87
2.50
2.83
6.56
3.36
3.48
Octane
Octanoic acid
Nonane
6.98
6.00
Nonanoic acid
Nonadecanone
Decane
2.83
4.15
1.76
3.48
1.98
5.27
1.75
2.56
4.18
2.19
0.75
0.84
1.31
0.97
1.28
1.03
2.28
1.09
3.65
3.15
3.78
14.80
4. Conclusions
Decanoic acid
Undecane
4.01
1.70
3.36
1.09
Undecanone
Undecanoic acid
Dodecane
To obtain hydrocarbon fuels from vegetable oil, decarboxyl-
0.70
1.04
0.76
0.68
0.94
1.83
0.84
6.76
6.71
3.26
14.38
ation reaction with
a series of hydrotalcite catalysts was
2.22
1.65
1.23
1.98
4.91
2.17
9.76
6.93
6.42
1.89
1.43
1.17
1.80
3.02
2.56
9.69
6.50
4.91
investigated. It was found that MgO ratio in hydrotalcites and
reaction temperature played key roles in decarboxylation
reaction. At lower reaction temperature and low MgO concen-
tration in hydrotalcite, the conversion of oleic acid scarcely
occurred. On the other hand, oleic acid conversions were more
than 98% and the oxygen content in the reaction product was
less than 1 wt% in the case of decarboxylation with MG63 and
MG70 at 673 K. Also, reaction temperature must be higher than
623 K in order to inhibit saponification with MgO and fatty acid.
Previous studies on decarboxylation of fatty acids usually have
used high-pressure hydrogen for hydrodeoxygenation or pre-
cious metal catalyst system. In this study, hydrotalcites showed
the activity of decarboxylation without hydrogen and could
produce pure hydrocarbon streams. It was confirmed that most
of the oxygen in oleic acid were removed in the form of CO2 from
the elemental and FT-IR analysis of the liquid products.
Tridecane
Tetradecane
Pentadecane
Nonyl cyclohexene
Hexadecane
Heptadecene
Heptadecane
Undecyl cyclohexane
Oleic acid
a
Percentage peak area = individual peak area/total peak area.
Heating of biomass at high temperature without oxygen might
bring about pyrolysis and dehydration, which resulted in the
increase of olefin and aromatic contents in reaction product. These
types of reaction must be minimized because they degrade fuel
quality of resultant hydrocarbon products. Unstable olefin
compounds reduce long-term stability of fuel and aromatic
compounds produce pollutants during combustion. H/C ratio
slightly increased in these reaction conditions (reaction tempera-
ture of 673 K and MG63/MG70), implying that the generation of
olefin and aromatic compound was minimized and hydrotalcites
catalyzed decarboxylation reaction selectively. Thus, most of the
oxygen in oleic acid was removed in the form of CO2 by
decarboxylation reaction.
Components of reaction product were precisely analyzed and
identified by gas chromatography with mass spectrometer (GC–
MS). As the reaction temperature increased up to 623 K, the
intensity of oleic acid peak decreased regardless of catalysts. But,
any other peaks did not appear. On the other hand, various types of
reaction products appeared and the intensity of oleic acid
decreased when the reaction temperature went up to 673 K.
Fig. 6 shows the identified components of the liquid products at
673 K and Table 2 summarizes GC–MS percentage peak areas for
major products. In case of blank test and MG30 catalyst at 673 K,
not only a series of hydrocarbons, but also low molecular weight
fatty acids, such as decanoic acid was presented. Cracking the
double bond (9th carbon) in oleic acid explains the production of
octane and decanoic acid. It indicates that cracking, instead of
decarboxylation, seems to be the dominant reaction pathway in
this condition. However, pure hydrocarbons such as octane,
nonane and heptadecene were produced only when the reaction
temperature was 673 K and catalysts were MG67 and MG70. In
However, selectivity of heptadecene,
a product by direct
decarboxylation of oleic acid was not very high, implying that
the cracking and decarboxylation occurred simultaneously
during the reaction by hydrotalcites.
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