Catalytic cracking of model molecules of fatty acids
Azevedo Júnior, A. F.1*, Félix, C. R. de O. 2,3, Pacheco, J. G.4 , Frety, R4 , Brandão, S. T.2
1
Universidade Federal do Recôncavo da Bahia - UFRB, Feira de Santana - BA, 44042-280, Brasil
Universidade Federal da Bahia - UFBA, Salvador - BA, 40210-730, Brasil
3
Instituto Federal de Educação, Ciência e Tecnologia da Bahia - IFBA, Simões Filho - BA, 43.700-000, Brasil
4
Universidade Federal de Pernambuco - UFPE, Recife - PE, 21941-594, Brasil
*[email protected]
2
Keywords: Fast pyrolysis, palmitic acid, oleic acid, stearic acid, SAPO-5, biofuels.
1. Introduction
The pyrolysis of fatty compounds can be slow and
fast, with fast pyrolysis leading to lighter
compounds. Pyrolysis can also be conducted either
with or without a catalyst, and at temperatures
ranging from 573 to 1073 K. A higher amount of
light products, including gases and compounds with
a high degree of deoxygenation, generally results
from pyrolysis at higher temperatures or in the
presence of catalysts [1].
The pyrolysis or thermal cracking is an alternative
method for the use of vegetable oils. Although
biodiesel is a renewable fuel, it is based on
monoalkyl esters of fatty acids which has some
disadvantages, such as higher viscosity and cloud
point than conventional diesel fuel, which limits its
application in several areas [2].
The pyrolysis reaction is a particularly promising
option in areas where the hydroprocessing industry
is well established because the technology is quite
similar to conventional petroleum refining [3; 4].
The nature of the fatty compounds also has a
significant influence on the composition of the
products. Thermal pyrolysis of crude triglycerides
and fatty residues at 673–773 ◦ C leads to rather
complex liquid products and only moderate yields of
deoxygenated compounds. Catalytic pyrolysis also
produces a complex liquid mixture, with the surface
properties of the catalyst affecting the mixture
composition. Acidic catalysts with strong Bronsted
sites favor the formation of aromatics and
polyaromatics, whereas catalysts with moderate or
no acidity are able to direct pyrolysis toward the
formation of linear saturated and unsaturated
hydrocarbons [1].
The present work aims to evaluate the performance
of SAPO-5 based catalysts in the rapid pyrolysis
reaction of fatty compounds and to identify the
differences between thermal and catalytic pyrolysis
in the decomposition of these compounds.
2. Experimental Part
The synthesis of silicoaluminumophosphate (SAPO5) was performed to obtain catalyst with Si / Al ratio
equal to 0.35 in the gel. The following molar
chemical composition was used: 0.35SiO2: P2O5:
Al2O3:
1.4 (C2H5)
3N:
0.072CTMABr:
4.4Hexanol: 40H2O. The calcination was carried out
at 823 K under a flow of 100 mL.min-1 of nitrogen
and air for 5 hours. The precursor solution of the
MoO3 metal oxide was ammonium heptamolybdate
of appropriate concentration to obtain the 10%
content. The impregnation was then carried out with
the nickel nitrate solution for the 5% nickel material.
Prior to the adsorption of the fatty compounds, the
catalysts (in powder form) were thermally treated at
423-473 K to remove the major part of the adsorbed
water. Micro quantities of the organic compounds,
about 10% by weight, were added to the catalyst.
The fatty compounds used in the present work
constitute a model system, since they are not
mixtures, to elucidate the rapid pyrolysis reaction of
vegetable oils. Palmitic acid, stearic acid and oleic
acid were used as fatty compounds. The catalytic
assay was performed on a Pyroprobe-5200 CDS
microtroller associated with a GC / MS analytical
system. The reaction temperature used was 923 K.
The samples were maintained at the reaction
temperature for 15 seconds.
3. Results and discussion
The thermal pyrolysis of oleic acid to 923 K resulted
in the formation of gaseous products, terminal
olefins, internal olefins, saturated hydrocarbons,
cyclic hydrocarbons, carboxylic acids, aldehydes,
esters, ketones and nitrogenates. In the pyrolysis of
the oleic acid adsorbed on the SAPO-5 catalysts,
aromatic compounds, branched hydrocarbons,
alkadienes, alkatrienes, alkynes and alcohols were
observed. All the obtained compounds are identified
in the global pyrogram with their respective
retention times (tR) observed in Figure 1.
(x100,000)
ketones. The compounds identified in the pyrogram
are shown in Figure 2.
AO/SAPO-5 (0,35)
7.0
AO/MoSAPO-5 (0,35)
6.0
5.0
(x1,000,000)
AO/NiMoSAPO-5 (0,25)
4.5
4.0
4.0
3.0
3.5
3.0
2.0
2.5
2.0
1.0
1.5
0.0
1.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0
21.0
22.0
23.0
24.0
25.0
26.0
27.0
28.0
29.0
30.0
0.5
0.0
Figure 1. Fragment of the global flash pyrolysis program
of oleic acid adsorbed on the catalysts.
The amount of detected products and the area of the
peak is more evident for the NiMo / SAPO-5
catalyst than in the case of SAPO-5. These results
suggest that NiMo / SAPO-5 is more active than
SAPO-5, and is responsible for a more complex
reaction scheme during pyrolysis of oleic acid.
When the fatty compound studied was palmitic
(saturated C16) acid, higher deoxygenation was
observed when compared to oleic acid. The results
are shown in Table 1.
Table 1. Compounds identified in the rapid pyrolysis of
palmitic acid adsorbed on catalysts.
a
Compounds
Formula
Propene
C3H6
2-Butene
C4H8
1-Pentene
C5H10
2-methyl-1C5H10
butene
1cyclopenten
C5H8
e
Acetic Acid
C2H4O2
1-Hexene
C6H12
3-methyl-1C6H12
Pentene
Benzene
C6H6
1-Heptene
C7H14
3-methyl-3C7H14
Hexene (Z)
Toluene
C6H7
1-Octene
C8H16
p-Xilene
C8H10
1-Nonene
C9H18
1-Decene
C10H20
1-Undecene
C11H22
2-Undecene
C11H22
1-Dodecene
C11H22
C13H28
1-Tridecene
C13H26
n-Tridecane
C14H28
1Tetradecene
a
SAPO-5 (0,35)
b
Mo SAPO-5 (0,35)
c
NiMo SAPO-5 (0,35)
tR
b
c
Percentage in area (%)
1,720
1,757
1,878
1,978
1,74
0,37
0,62
2,19
0,56
0,65
0,37
0,34
0,19
0,26
2,104
0,19
0,11
-
2,173
2,277
2,398
0,31
0,39
0,16
0,64
0,43
0,06
0,23
0,16
2,894
3,214
3,424
0,22
0,16
0,14
0,22
0,33
-
0,08
0,12
-
4,820
5,542
8,569
9,510
13,976
18,307
18,341
22,378
26,213
26,518
29,748
0,31
0,13
0,12
0,14
0,17
0,16
0,16
0,14
0,14
0,48
0,28
0,29
0,04
0,32
0,34
0,34
0,36
0,28
0,08
0,72
0,8
0,11
0,14
0,12
0,13
0,13
0,28
The presence of aromatic compounds only in the
catalytic pyrolysis of palmitic acid suggests a
hydrogen transfer ability attributed to the acid sites
of the catalysts.
Thermal pyrolysis of stearic acid at 923 K resulted
in the formation of terminal olefins, internal olefins,
saturated, cyclic, branched and polyunsaturated
hydrocarbons, carboxylic acids, aldehydes and
-0.5
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
22.5
25.0
27.5
30.0
32.5
35.0
37.5
Figure 2. Fragment of the pyrogram of the flash stearic
acid pyrolysis.
The deoxygenation was almost complete for the
thermal pyrolysis of palmitic and stearic and
catalytic acids of palmitic acid, being more effective
when compared to the pyrolysis of oleic acid. This
fact highlights the importance of this process for the
production of green fuels, which can be added to
fossil fuels, both in the gasoline and diesel fractions.
4. Conclusions
The mechanism of decomposition observed for the
fatty compounds studied in this work does not
always present as a first step the deoxygenation as
reported in the literature. Cracking within the chain,
close to the C = C double bond for the unsaturated
compounds, and at the β position of the carbonyl
group for the saturated compounds, may occur prior
to deoxygenation. The methodology of rapid
pyrolysis of fatty compounds adsorbed on catalysts
allows: to generate information about the
mechanisms of degradation of the compounds;
Characterize some properties of the catalyst, such as
the existence of specific catalytic sites; Generate
intermediate
products,
allowing
a
better
understanding of the mechanisms of reaction.
Acknowledgments
To the Federal University of Bahia and the Federal University of
Pernambuco.
References
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