The synthesis of alkane dinitrates and theirs efficiency for cetane improver

Article abstract of DOI:10.1134/S0965544109050181

Dinitrate compounds was prepared from alkane diols; 1,6-hexane diol, 1,8-octane diol, 1,10-decane diol, and 2-methyl-2,4-pentane diol using nitration reaction. These dinitrate compounds were used as cetane improver for diesel fuel. Results showed that the cetane number values has increased about 1 and 3 units for 0.05 and 0.10% by weight of dinitrate compounds, respectively, compared with base oil. Their efficiency is higher than commercial cetane improver, 2-ethylhexyl nitrate.

Full text of DOI:10.1134/S0965544109050181

ISSN 0965-5441, Petroleum Chemistry, 2009, Vol. 49, No. 5, pp. 432–435. © Pleiades Publishing, Ltd., 2009.
The Synthesis of Alkane Dinitrates and Theirs Efficiency
1
for Cetane Improver
a
b
b
b
Songsom Siraprapakit , Polkit Sangvanich , Preecha Lertpratchya , and Somchai Pengprecha
a
Program of Petrochemistry and Polymer Science, Faculty of Science, Chulalongkorn University Payatai,
Rd., Patumwan, Bangkok, 10330, Thailand
b
Research Centre for Bioorganic Chemistry, Department of Chemistry, Faculty of Science, Chulalongkorn University,
Payatai, Rd., Patumwan, Bangkok, 10330, Thailand
e-mail: polkit@gmail.ru
Abstract—Dinitrate compounds was prepared from alkane diols; 1,6-hexane diol, 1,8-octane diol, 1,10-decane
diol, and 2-methyl-2,4-pentane diol using nitration reaction. These dinitrate compounds were used as cetane
improver for diesel fuel. Results showed that the cetane number values has increased about 1 and 3 units for
0
.05 and 0.10% by weight of dinitrate compounds, respectively, compared with base oil. Their efficiency is
higher than commercial cetane improver, 2-ethylhexyl nitrate.
DOI: 10.1134/S0965544109050181
1
When a fine spray of fuel is injected into a combus- temperatures in the combustion chamber. The products
tion chamber of a diesel engine, ignition does not occur of decomposition help initiate fuel combustion and,
immediately. The heat produced by compression varies
thus, shorten the ignition delay period from that of the
fuel without additive.
from about 440.5°C at 10 : 1 compression ratio to about
5
65.5°C at 15 : 1 compression ratio, and is the sole
source of ignition. The interval between the beginning
of the fuel injection and ignition is called the ignition
delay period. If the delay is long, the engine may be
hard to start. When the accumulated fuel ignites, the
excessive energy released causes the engine to knock.
The shorter the delay, the easier the engine is to start
and the smoother it operates [1]. Ignition delay is mea-
sured by the Cetane Number (CN) test [2], which uses
a single-cylinder, variable compression ratio engine
An increase in cetane number from a given concen-
tration of EHN varies from one fuel to another. It is
greater for a fuel whose natural cetane number is
already relatively high. The incremental increase gets
smaller as more EHN is added, so there is little benefit
to exceeding a certain concentration. EHN typically is
used in the concentration range of 0.05 to 0.40%
wt./wt. and may yield a 3 to 8 cetane number benefit.
analogous to the Octane Number engine. In this case, Other alkyl nitrates, as well as ether nitrates and some
the ignition delay of the test fuel is measured at a fixed nitroso compounds, also have been found to be effec-
compression ratio. This result is compared with the
results from standard reference fuels consisting of
blends of n-cetane and methylnaphthalene. Normal cet-
ane has a short delay period and ignites readily. It has a
cetane number of 100. Heptamethylnonane has a long
delay period and does not ignite readily. It has a cetane
number of 0. The cetane number of a diesel fuel is the
percentage by the volume of normal cetane in a blend
tive cetane number improvers, but they are not cur-
rently used commercially. Di-tertiary butyl peroxide
has been recently introduced as a commercial cetane
number improver. One of the disadvantages of EHN is
that EHN decreases the thermal stability of some fuels
[6, 7]. The effect of the other cetane number improvers
on thermal stability is unknown, but it seems likely that
with methylnaphthalene that matches the ignition qual- they will be similarly disadvantaged. Consequently,
ity of a reference fuel with known cetane number.
new cetane improvers are required. The mechanism of
cetane improver involved the nitrate group so dinitrate
compound, which contain two group of nitrate, are con-
sider an effective cetane improver.
Cetane number improvers [3, 4] can reduce combus-
tion noise and smoke. The magnitude of the benefit var-
ies among engine designs and operating modes, rang-
ing from no effect to readily perceptible improvement.
In this work, alkyl dinitrates as cetane improvers
were synthesized by nitration of alkane diols using a
mixture of cone. H SO and cone. HNO . The proper-
2
-Ethylhexyl nitrate (EHN) or octyl nitrate is the most
widely used as cetane number improver [5]. EHN is
thermally unstable and decomposes rapidly at high
2
4
3
ties of the blend between diesel base oil and prepared
alkyl dinitrates have been investigated.
1
The article is published in the original.
4
32

THE SYNTHESIS OF ALKANE DINITRATES
433
1
2
3
4
5
6
1
2
3
4
5
6
7
8
O NO–CH –CH –CH –CH –CH –CH –ONO O NO–CH –CH –CH –CH –CH –CH –CH –CH –ONO
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
,6–hexane dinitrate
1,8–octane dinitrate
2
CH
3
1
2
3
4
5
6
7
8
9
10
1
|
4
5
6
3
O NO–CH –CH –CH –CH –CH –CH –CH –CH –CH –CH –ONO
CH –CH–CH –CH –CH
2
2
2
2
2
2
2
2
2
2
2
2
3
2
2
3
|
|
ONO2
ONO2
1
,10–decane dinitrate
2
–methyl–2,4–pentane dinitrate
Schematic of alkane dinitrates.
EXPERIMENTAL
pentane dinitrate (MPDN); yellow liquid, were 80, 86.9
8.5 and 53.2%, respectively. Most of products were
very high yield about 95%, except, 2-methyl-2,4-pen-
tane dinitrate that might be due to its sensitivity to auto-
oxidation. Additionally, 2-methyl-2,4-pentane dinitrate
was hygroscopic and sensitive to air.
8
Preparations of Alkyl Dinitrates from Alkane Diols
All four alkyl dinitrates were prepared from alkyl
diol; 1,6-hexane diol, 1,8-octane diol, 1,10-decane diol,
and 2-methyl-2,4-pentane diol, using the same protocol
as described below. A mixture of 65% HNO 7 ml,
6% H SO 12 ml and water 7 ml was placed in a round
3
9
2 4
bottom flask, then well stirred, and maintained at the
temperature of 23°C. Urea 1.36 g was added to the mix-
ture, and the solution was stirred for a half an hour.
Structure Elucidation of Alkane Dinitrate
The IR spectrum of 1,6-hexanediol and 1,6-hexane
dinitrate were compared. No sign of absorption bands
Then, a solution of alkyl diol 2.5 g and CHCl 30 ml
–1
3
of OH stretching group of 1,6-hexanediol (3500 cm )
was slowly added to a reactor while maintained the
temperature of 23°C for an hour. The mixture was then
allowed to warm at room temperature and then organic
phase was separated. The organic phase was washed with
in IR spectrum of 1,6-hexane dinitrate. Additionally,
there were the absorption bands of NO stretching
2
(
asymmetric and symmetric) and NO stretching at
–1
1
630, 1287, and 871 cm , respectively. Moreover, the
4
× 30 ml of an aqueous saturated sodium chloride solu-
tion and then dried over anhydrous sodium sulphate.
structure of 1,6-hexane dinitrate was confirmed using
1
13
1
H-NMR and C-NMR spectra. The H-NMR spec-
Characterization and detennination of the products trum showed a 4 protons (δ 4.36 (t)) which concerns
were carried on the Nicolet Fourier-Transform Infrared with I3C-NMR absorption at 5 73.36 (C-1 and C-6).
Spectroscopy model Impact 410 and Brucker Nuclear- Other 4 proton (δ 1.65 (q)) which located on C-3 and
Magnetic Resonance Spectroscopy model AC-F 200 C-4 (8 26.38) were also recorded. Finally, the last 4 pro-
(
200 MHz).
tons of 1,6-hexane dinitrate were recorded at δ 1.36 (t)
Determination of properties and Cetane Number of and these proton belong to C-2 and C-5 (δ 25.08).
1
13
blended base diesel fuel containing dinitrate com-
H and C-NMR spectra together with IR spectrum
pounds Blended base diesel fuels containing 0.05, 0.10, allowed the complete structure of 1,6-hexane dinitrate
0
.15, and 0.20% by weight of dinitrate compounds to be established (Fig. 1).
were prepared and their properties were determined
The product of nitration of others alkane diols were
using the following protocols. The values of Cetane studies using the same techniques. All results suggested
Number were measured using ASTM D613 [8] using that all alkane diols were converted to dinitrate com-
PetroSpec model Cetane 2000.
RESULTS AND DISCUSSION
pounds (see spectroscopic data in Tables 1 and 2).
Properties Determination of Blended Base Diesel Fuel
Oil Containing Dinitrate Compounds
Synthesis of Dinitrate Compounds
The dinitrate compounds were blended with base oil
fuels. Each of 0.05 and 0.10% by weight of HDN,
ODN, DDN, and MPDN, respectively, were used and
their properties were determined and compared with
EHN. The results were shown in Table 3.
Dinitrated compounds were synthesized by nitration
reaction using cone, nitric acid and cone, sulphuric
acid. In this study, all four alkyl dinitrates; 1,6-hex-
anediol,
1,8-octanediol,
-methyl-2,4-pentanediol, were prepared. The yield of
,6-hexane dinitrate (HDN); colourless liquid, 1,8-
1,10-decanediol,
and
2
1
From the results suggested that the physical proper-
octane dinitrate (ODN); colourless liquid, 1,10-decane ties of blended base diesel fuels with alkane dinitrate
dinitrate (DDN); colourless liquid, and 2-methyl-2,4- did not change compared with base diesel fuel.
PETROLEUM CHEMISTRY Vol. 49 No. 5 2009

4
34
SONGSOM SIRAPRAPAKIT et al.
Table 1. The IR spectrum data of alkane dinitrates
Determination of Cetane Number (CN) of Blended
Base Diesel Fuel Containing Dinitrate Compounds
Wave number, cm–1
Assignment
The Cetane Number each blended base diesel fuels
was determined according to ASTM D613 [3]. All
alkane dinitrates gave a higher improvement compared
with EHN (commercial additive). It might be due to
these compound contain 2 nitrate group which more
enhance the ignited-oxidation. The chain length of
hydrocarbon did not have an effect on the increasing of
cetane number value since HDN, ODN, and DDN show
a similar results. Moreover, the increasing of concentra-
tion of alkane dinitrate did not show any effect on the
improving of cetane number value.
HDN
ODN
DDN
MPDN
C–H stretching,
aliphatic
2941,
2878
2931,
2859
2936,
2863
2991,
2935
NO asymmetric 1630
1625
1630
1634
2
stretching
C–H bending,
aliphatic
1471,
1393
1471,
1383
1471,
1388
1460,
1393
CONCLUSIONS
The alkane dinitrate compound could be easily pre-
pared by direct nitration using alkane diols and conc.
NO symmetric
1287
1282
1287
1280
2
stretching
HNO and conc. HCl. The blended diesel fuel with con-
3
taining alkane dinitrate at 0.05 and 0.10% by weight
did not change any specification of physical properties.
Calculated cetane index values of blended diesel fuels
were determined and found to be higher than base die-
sel fuel alone; about 4 units. Moreover, alkane dini-
trates show the similar CN value than 2-ethylhexyl
nitrate (common commercial cetane improver). Then
these alkane dinitrate compounds had a potential to be
use for improving of cetane number in base oil fuel.
C–O stretching
N–O stretching
967
871
982
861
982
861
1280
871
Note: HDN = 1,6-hexane dinitrate, ODN = 1,8-octane dinitrate,
DDN = 1,10-decane dinitrate, and MPDN = 2-methyl-2,4-
pentane dinitrate.
Table 2. The H-NMR and 13C-NMR spectrum data of alkane dinitrates
1
Chemical shift (δ, ppm)
1H-NMR
13C-NMR
Position
HDN
ODN
DDN
MPDN
HDN
ODN
DDN
MPDN
1
2
3
4
5
6
7
8
9
4.36(t)
1.65(q)
1.36(t)
1.36(t)
1.65(q)
4.36(t)
4.36(t)
1.65(q)
4.36(t)
1.64(q)
1.47(m)
1.47(m)
73.36
26.38
25.08
25.08
26.38
73.36
73.40
28.72
26.48
25.35
25.35
26.48
28.72
73.40
73.44
29.14
26.26
25.52
25.52
25.52
25.52
26.26
29.14
73.44
31.12
27.40
48.96
65.00
23.93
70.95
1.25–1.40(m) 1.25–1.37(m) 2.14(d)
1.25–1.40(m) 1.25–1.37(m)
1.25–1.40(m) 1.25–1.37(m)
1.25–1.40(m) 1.25–1.37(m)
1.65(q)
4.36(t)
1.25–1.37(m)
1.25–1.37(m)
1.64(q)
1
0
4.36(t)
Note: 1. m = multiplet, q = Quintet, and t = triplet.
. Chemical shifts are relative to solvent signal (CDCl3).
2
PETROLEUM CHEMISTRY Vol. 49 No. 5 2009

THE SYNTHESIS OF ALKANE DINITRATES
435
Table 3. Cetane number of base oil and blended base oil
Additive
0.15
46.5 1.4 48.3 3.2 49.3 4.2 50.6 5.5
REFERENCES
%
1. D. S. Moulton and N. R. Sefer, Diesel Fuel Quality and
Effects of Fuel Additives (Transportation Research
Board, National Research Council, Washington, 1984).
0
.05
∆
0.10
∆
∆
0.20
∆
EHN
2. Standard Test Method for Cetane Number of Diesel Fuel
Oil [ASTM D613-01] (Annual Book of ASTM Stan-
dards, 2001).
HDN 47.4 2.3 49.2 4.1 51.0 5.9 52.8 7.7
ODN 47.4 2.3 49.4 4.3 50.9 5.8 52.6 7.5
DDN 47.6 2.5 49.4 4.3 50.1 5.0 52.8 7.7
MPDN 46.0 1.1 46.9 1.8 48.2 3.1 49.7 4.6
Note: 1. Cetane number of base oil = 45.1.
3
4
5
6
. M.-A. Poirier, D. E. Steere, and J. A. Krogh, US Patent
No. 348,528 (1995).
. R. F. Purcell and L. L. Hallock, US Patent No. 563,124
(1985).
2
. All cetane number is measured using ASTM613.
. G. J. Suppes,Y. Rui, A. C. Rome, and Z. Chen, Ind. Eng.
Chem. Res. 36, 4397 (1997).
3
. A is the in creasing values of cetane number from base oil.
. H. Bornemann, F. Scheidt, and W. Sander, Int. J. Chem.
Kinet. 34, 34 (2002).
ACKNOWLEDGMENTS
The authors express their gratitude to Graduated
School, Chulalongkorn University for partial financial
support. Moreover, we would like express gratitude tp
Petroleum Equipments (Thailand) Co., Ltd. for letting
us using Cetane Analyser.
7. J. C. Oxley, J. L. Smith, and E. Rogers, Energy Fuels 15,
194 (2001).
1
8
. Standard Test Method for Cetane Number of Diesel Fuel
Oil [D613-03b] (Annual Book of ASTM Standards,
2003).
PETROLEUM CHEMISTRY Vol. 49 No. 5 2009