Indian Journal of Chemical Technology
Vol. 3, March 1996,pp.107-111
Synthesis of sodium petroleum sulphonates and their interfacial
activity against IndIan crude oil
A Borthakur, A Sarmah, M Rahman & B Subrahmanyam
Regional Research Laboratory, Jorhat 785 006, India
Received 29 March 1995; accepted 21 August 1995
Aromatic rich hydrocarbon phase is separated from lube base stock by using solvent extraction
method. Acetonitrile is used as solvent. Sodium petroleum sulphonates are prepared by sulphonation
with concentrated (98%) sulphuric acid followed by neutralization with alkali solution. The formation of high molecular weight oil soluble petroleum sulphonates, i.e., benzene soluble and chloroform
soluble sulphonates constitute only 45% of the total sulphonates produced. Low concentration surfactant slugs are prepared using isoamyl alcohol as cosurfactant and sodium chloride as brine, while
oil soluble suiphonates are surfactants. Both chloroform and benzene soluble sulphonates could produce low interfacial tension 11FT)in the order of 10-2 mN/m against Naharkatiya INHK) crude oil.
Chloroform soluble sulphonate produce ultra low 1FT against heptane, while higher molec":
ular weight benzene soluble sulphonate gives lowest 1FT against nonane. The interfacial activity of
chloroform soluble sulphonates indicate that heptane is the equivalent alkane carbon number
(EACN) of NHK crude oil.
Petroleum sulphonate in the form of sodium salt
is extensively used as surfactant in enhanced oil
recovery (EOR) by surfactant flooding. The purpos~ of this application is to reduce interfacial
tension between the crude oil and the aqueous
fluid to the order of 10-3 dynes/cm. It is well established 1 that petroleum suiphonates having
equivalent weight 375-475 are capable of producing ultra low interfacial tension (IFf) of this
range. Generally, the surfactant slug is formulated
with cosurfactant and brine to produce the desired Iff. This formuiation of micellar slug is the
predominant
factor for achieving ultra low
IFf2 -7. If a low tension is achieved with a given
oil-surfactant pair, it is quickly lost on changing
the salinity, and cosurfactant. Cash et a/.s observed that any surfactant slug is capable of producing ultra low IFf against a specific alkane.
'Based on the Iff data they assigned an equivalent alkane carbon number (EACN) to any hydrocarbon or mixtures .of hydrocarbon including
crude oil. If a crude oil has EACN 7, it means
that any surfactant slug which pr:oduces lowest
IFf against heptane (C7 alkane) will produce lowest IFf against that particular crude oil. Their
work showed that9 most of the crude oil appears
to have an EACN ranging from 6.2-8.6.
In the present communication, petroleum sulphonate in the form of sodium salt is prepared
from aromatic rich lube base stock. The aromatic
rich hydrocarbon fractions were separated from
refinery's lube base stock by solvent extraction
method using acetonitrile as solvent. Low conc.entration surfactant slug was prepared using surfactant, cosurfac;tant andbrine.9il
soluble petrol~um
sulphonates (both benzene and chloroform soluble)
were used· as surfactant, isoamy alcohol as cosurfactant and NaCl as brine. Inteffacial behaviour of
the surfactant slug was evaluated using Naharkatiya (NHK) crude oil and C6-C14 alkanes.
Experimental Procedure
Aromatic
rich petroleum
Table la-Physical
characteristics
hydrocarbons
were
of lube base stock
Physical properties:Lube stock before extraction
0.937
I Density:
15°C
2 Pour point:
3 Refractive index (25°C):
4. Column chromatography
Total aromatics (%) =
Total saturates (%)
=
1.5240
22
77.5
5 Distillation characteristics:
Boiling range
°C
LB.P.
280
50% (wt/wt)
EB.P.
385
330
108
INDIAN J. CHEM. TECHNOL.,
Table 1b- Physical characteristics
MARCH 1996
of extracted aromatic rich hydrocarbons
Acetonitrile extract of the lube base stock at S/F ratio
Physical properties
1:1
0.970
1.5890
72
74
2:1
0.975
4:1
1.5865
0.981
1.5920
1 Density
82 index (25°C)
2 .Refractive
3 Column chromatography
5:1
6:1
0.967
0.967
1.5820
1.5820
70
70
(wt/wt"!o)
(1) aromatics
28.5
(a} Mono and dinuclear (wtlwt)
50
(b) Naphthene aromatics (wt/wt)
21.4
(c) Polar aromatics (wt/wt)
17.5
(2) Saturates (wt/wt%)
25.8
27.8
29.5
4 Molecular weight
extracted from refinery's lube base stock by using
solvent extraction method. Acetonitrile was used
as solvent. The physical characteristics of the lube
base stock and extracted aromatic fractions are
presented in Tables 1a and lb.
About 100 mL of lube base stock was taken in
a separating flask equipped with a mechanical
stirrer and a jacketed wall to control the temperature of extraction. Acetonitrile in varying proportions were added and stirred the liquid vigorously
for half an hour at a temperature of 15°C. It was
then allowed to settle for an hour. Two immiscible layers were formed. One is the acetonitrile
layer containing the aromatic phase and other the
saturates. The, acetonitrile layer was separated out
and treated with excess volume of water. The aromatic hydrocarbon phase present in this layer was
further extracted with toluene. Toluene was distilled off to get the aromatic rich hydrocarbon
from lube base stock.
Aromatic rich hydrocarbon feedstock obtained
by extraction with acetonitrile using 5:1 solvent
to feed ratio was taken as feedstock f{)r sulphonation. About 100 mL of the aromatic feedstock
obtained as above in equal volume of hexane was
taken in a three necked flask fitted with a reflux
condenser and a mechanical stirrer. The assembly
was mounted on a thermostatic bath. The temperature was maintained at 50°C. The parameters for
the synthesis of petroleum sulphonates are presented in Table 2. Concentrated sulphuric acid
(AR 98%) was added dropwise from the top of
the reaction vessel by a separating funnel at the
rate of 10 mUh. After addition the reaction was
continued for 1.1/2 h. The unreacted oil phase
was separated out. It was neutralized with saturated solution of sodium bicarbonate. The reaction
mixture was washed several times with n-hexane
till the colour of the hexane layer disappeared.
The crude product was then extracted with iso-
I
I
!
11
29.8
289
!
,
~ II'
II!
II
II..
'1"'111111
M~I "I
I'" II
I
Table 2-Synthesis
Aromatic
feedstock
mL
100
Cone.
of sodium petroleum sulphonates
Yield of total sulphonates
H2S04
mL
Bzsol
CHC13 sol
Water sol
("!o)
("!o)
("!o)
100
5
10
85
50
7
19
74
35
10
23
66
18
i8.6
26.4
55
15
15
25
60
propyl alcohol,distilled off the solvent to get semi
solid solution. It was repeatedly extracted with
benzene, followed by chloroform to get the benzene soluble petroleum sulphonate (PSI) and
chloroform soluble petroleum sulphonate (PSII).
The remaining part in the raffinate was water soluble sulphonate (PSill). The solvents from all the
fractions were distilled off. The traces of unreacted oil present in the product were separated by
silica gel column chromatography using hexane as
eluent. The product was isolated by distilling the
solvent and drying in vacuum oven.
Molecular weight of the petroleum sulphonates,
PSI and PSII were determined by two phasetitrat:\on method 10. The known amount of dried and
oil free sulphonate was dissolved in chloroform
and titrated with a quarternary ammonium salt
(Hyamine 1622) in the presence of dilute sulphutic acid. A mixture of dimidium bromide and disulphine blue was used as the indicator. At the endpoint the colour of the chloroform layer changed
from red to blue .. Quarternary ammonium salt,
Hyamine 1622 was standardized using standard
solution of sodium lauryl sulphate.
Degree of sulphonation was determined by thin
layer chromatography (tlc) technique adopted by
Sandvik et at.]] Silica gel tIc plates were pretreated by spraying with an aqueous 2% ammonium
II
BORTHAKUR
et al.: SYNTHESIS OF SODIUM PETROLEUM
SULPHONATES
109
The acetonitrile extract aromatic phase was fursulphate solution. It was then dried for 3 h at
60°C. Developing solvent was a 70:30:6 mixture ther evaluated by IH NMR spectroscopy. The relof chloroform, methanol and 0.1 N sulphuric acid.
ative abundance of IH in various positions of
IH NMR spectra were measured on a Varian NMR spectra is presented in Table 3. From this
EM-360, 60 MHz spectrometer and TMS as in- table, it appears that the relative abundance of
ternal standard using CCl4 solvent except for pet- aromatic proton (6.5-7.5 d) and the l'HmflH.,
roleum sulphonates where tetra tluoro acetic acid reaches the optimum value at SIF ratio 4:1. At
was taken as solvent. Sample concentrations SIF ratio 1:1 the relative abundance of aromatic
were in the range of 8-10 wt%.
.proton is highest but the corresponding yield of
Low concentrated surfactant slug was prepared this phase is poor. The aliphatic - CH3 proton
using 0.1% petroleum sulphonate, isoamyl alcohol (lRy) increases as the SIF ratio increased and
and sodium chloride. The surfactant slug was reaches the optimum value. Hp and Ha also
equilibrated by taking two thirds of aqueous reaches the optimum value at SIF ratio 4:1. The
phase and the one third of oil phase following the 1H NMR spectra of raffinate portion 00 not
method described by Chan and Shah7• The equili- show any significant aromatic proton abundance
brated oil and aqueous phases were separated out at and above SIF- ratio 4:1. In the present comafter clear separation of the two phases and inter- munication, acetonitrile extract phase obtained
facial tension (IFf) .was determined by using with 5:1 S/F ratio is taken for sulphonation.
spinning drop tensiometer (SITE 04. KRUSS
T~ble 2 indicates that large amount of sulphuric
GmbH, Germany). NHK crude oil and C6-C14 al- acid can produce predominantly water soluble sulkanes were used as triI phase. Isoamyl alcohol as phonates only. The yield of oil soluble sulphocosurfactant (CoS) and 0.1% surfactant (PSIIPSll) nates (benzene and chloroform soluble) increases
was. used in all the cases. ASTM:standard proce- with the decrease of sulphuric acid concentration.
dures were followed to investigate the physical The optimum concehtration of sulphuric acid
characteristics of the crude oil and its fractions.
which produces maximum yield of oil soluble sulphonates is 18 mL. At this concentration 45% of
Results and Discussion
the total sulphonates produced belong to oil solAcetonitrile is a powerful solvent for extraction uble sulphonates only. The physical characteristics
of aromatic· hydrocarbons from middle distillate of petroleum sulphonates used in this communicaof crude oill2• The physical characteristics of pet- tion are presented in Table 4. As reported elseroleum feedstock before and after extraction of where sulphonation of aromatic hydrocarbon mixaromatic hydrocarbon with acetonitrile is preseq,t- tures with concentrated sulphuric acid can proed in Tables la and lb. It indicates that at low sol- duce undesirably large. percentage of low equivavent to feed ratio acetonitrile extract contains lent weight, mono-, di- and poly sulphonated prohigher purity of aromatic hydrocarbons, although ducts. Thin layer chromatography technique
the total yield of this phase is negligible.The yield showed that both .PSI and PSll are monosulpho·
of the extract phase is found to be optimum at nates in nature whereas water soluble petroleum
and above solvent to feed ratio 4:1. Same is true sulphoJ)ates (PSill) contain. mono, di- and poly
for purity of the aromatic hydrocarbon mixtures. sulphonated compounds J.HNMR studies showed
At .solvent to feed ratio 5:1 the yield of aromatic that the ratio of 1HaV1Haris more for PSI than
rich phase is 30% of the total phase volume. It PSll. This indicates that the C-chain attached to
the aromatic ring is larger for PSI than that for
contains about70% aromatic hydrocarbons.
-
mono,di-,
3.85
mono
24.7
24.4
2.0-3.5
2.3
6.5-8.0
3.02
3.09
29
16
15.1
27.3
1.0-2.0
450
535acetonitrile
24
30
3.1
2.7
30.3
33
24.8
H
27.7
31.3
31.9
16.2
12.7
16.5
28.4
28
Ratio
ofpoly
Ratio
Degree
Relative
(PSIII)
of studies
abundance
Physical
ofproperties
1H in
c5ppm
Table 3-IH27
NMR
of
extract of petroleumsulph.
Water
soluble
(PSTI)
Chloroform
IH.l'H,.r(c5)
Eq.wt
Table5.75
4-Physical
(PSI) soluble
Petroleum sulphonates:
characteristics
of petroleum sulphonates
110
INDIAN
1.
CHEM. TECHNOL.,
PSII. PSI possesses highest molecular weight
(535), highly soluble in benzene and highly sensitive to brine. PSII having moderate molecular
weight (450) shows better salt tolerance than PSI.
In principle PSII should be able to produce ultra
low 1FT.
The physical characteristics of NHK crude are
presented in Table 5. The effect of NaCI concentration on 1FT between surfactant slug (PSI and
PSII) and NHK crude oil is presented in Figs 1
and 2. In agreement with the observations made
by other workers, the results indicate that 1FT decTable 5-Physical
characteristics
of NHK crude oil
Pour point (0C):
30
2 API gravity:
29.4
3 Sp. gravity (60/60°F):
0.882
4 Wax content (wt/wt%):
10
< 0.1
5 As phaltenc content IIwt/wt%):
6 Resin content (wt/wt%):
7 AS1M distillation:
8.5
°C
92
IBP:
13
Distilled up to I5aoC:
·200°C:
250°C:
27
300°C:
42
18
MARCH 1996
reased as NaCl concentration increased up toa
point beyond which 1FT increased on further addition of NaCl. This minimum in 1FT is corresponding to the optimum concentration of NaCI
for the particular systeml,13.l4. For PSII the optimum concentration of NaCl is 1.0% as shown in
Fig .. 2. The surfactant slug consisting of 0.1%
PSII, 1.0% NaCland
2% isoamyl alcohol produces minirtlUm 1FT (0.011 mN/m) against NHK
crude oil. Isoamyl alcohol concentration is also
varied to get lower 1FT than that obtained. As
shown in Fig. 3, 2% isoamyl alcohol is found to
be optimum concentration for producing ultra low
1FT against NHK crude oil.
In order to evaluate the equivalent alkane carbon number (EACN) of NHK crtlde oil, 1FT was
determined with the same surfactant slug which
produces lowest 1FT against NHK crude oil. So
the crude oil is replaced by n-alkanes (C6-C12).As
presented in Fig. 4, PSII surfactant slug produces
minimum 1FT (0.008 mN/m) against n-heptane.
This indicates that heptane is the Nmin. for PSII
sulphonate.
Since this surfactant slug produces
lowest 1FT against NHK crude oil, the EACN of
this crude is 7. The effect of NaCI concentration
on 1FT against heptane is also studied using the
surfactant slug and presented in Fig. 2. As stated
earlier the optimum concentration of NaCI is
1.0%.
1
PSIL1~+CoSII~
PS"IO.l~ CoS~
•
+
•...
NIf< crude oil
..•.
NHK crude oil
n-heptane
-+
n-nonane
E
~
z~0.1
'jji
E
'u
~c~001
~
Ci .
+
0.1
I
0.001
0.001
1.5
0.5
a
Concentration
I' I
f
~
II'
~~ I
f
III" " II t, I illl tillI III:II .I
0.2
0.4
Concentration
of Nacl, ",
Fig. I-Effect
of NaCI concentration on interfacial tension
against NHK crude oil and against nonane using PSI surfactant slug.
!
o
2
0.6
0.8
of Nacl • '"
Fig. 2-Effect
of NaCI concentration on interfacia.1 tension
against NHK crude oil and against heptane using PSII surfactant slug
I,
BORTHAKUR
et al.: SYNTHESIS OF SODIUM PETROLEUM
PSlIIO.l%I+
'u
:2
0.1
0.1
0.01
NaCIIl%1
+-
I
E
0.001
111
SULPHONATES
-
tlPSll+.4lNaCl+~
--
I»lSI +1»4aC1+2ICoS
z"
.0c
..0
E
~
'jjj
c.E
..•.•....
0.001
o
0.5
1
1.5
2
Concentl'Cltion of isoamyl alcohol,
2.5
3
o
.,.
Fig. 3-Effect of isoamylalcohol concentration on interfacial
tension against NHK crude oil using PSII slug
A,S presented in Fig. 1, PSI surfactant slug consisting of 0.1% PSI, 0.4% NaCI and 0.2% isoamyl
alcohol produces lowest 1FT (0.Q07 mN/m)
against n-nonane. But it is not producing ultra
low Iff against NHK crude oil. The minimum
Iff is not obtained. Instead at a broad 1ange of
NaCl concentration, PSI surfactant slug produces
similar Iff. As stated above NHK crude has
EACN 7 and PSI slug has 1lu.in 9. So this slug will
produce ultra low Iff agianst a crude oil whqse
EACN is 9. This also indicates that higher molecular weight petroleum sulphonates are not suitable for producing ultra low IFf against crude oil.
Conclusion
Aromatic rich hydrocarbon fractions are separated from lube base stock by solvent extraction
using acetonitrile as solvent. Sulphonation with
concentrated sulphuric acid could produce petroleum sulphonates suitable for EOR. But the yield
of oil soluble petroleum sulphonates is only 45%
of the total sulphonates produced. Chloroform
soluble petroleum sulphonates give ultra low interfacial tension against heptane while benzene
soluble petroleum sulphonates produced ultra low
interfacial tension against nonane. Heptane is
found to be the Equivalent Alkane Carbon Number of NHK crude oil.
Fig. 4-Effect
2
4
6
B
Alkane carbon number
W
~
of alkane C-no. on interfacial
PSI and PSII surfactant slugs
~
ffi
tension using
Acknowledgement
The authors acknowledge Dr Anil C Ghosh,
Director, Regional Research Laboratory for providing facilities for this study.
References
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°