Journal of Power and Energy Engineering, 2013, 1, 90-94 Published Online October 2013 (
Copyright © 2013 SciRes. JPEE
Efficiency of Amphoteric Surfactants as Flow Improvers
and Pour Point Depressants
Noura El Mehbad
Faculty of Sci ence, Nagran University, Saudi Arabia of Kingdom.
Received October 2013
Some amphoteric surfactants (N-Decyl-N-benzyl-N-methylglycine(AB) and N-Dodecyl-N-benzyl-N-methylglycine(CD)
were prepared in the laboratory. The physicochemical chemical characteristics were investigated. The adsorption be ha-
vior of these surfactants at oil/air interface was investigated by measuring the surface tension and interfacial tens ion as
function of concentration. Surface propertie s , in particular the critical micelle concentration (CMC), the maximum sur-
face excess CMC) and the minimum su rface area (AMIN) were measured. It is found that the surface and thermodynamic
properties of the prepared surfactants depend on their hydrocarbon chain length. Also it is found that there is a good
relation between surface properties of the additive and their efficiency in depressing the pour point. The mechanism of
the depressants action has be en suggested according the adsorp tion of each additive. Adsorption of the additive on the
surface of the wax particles inhibits their growth and alters the crystal habits through micelle core. As the resu lts the
surface and thermodynamic parameters confirm the suggested mechanism and the decreasing of pour point. This is re-
sulted in a multilayer, more isotropic wax crystal, and thus only a fi xed amount of wax separates at any given tempera-
tures. The r esults were discussed in terms of adsorption isotherm.
Keywords: Wax; Additives; Pour Point; Amphotric Surfactants; Waxy Gas O il
1. Introduction
In our previous work the synthesis of new additives as
pour point and antioxidants was described [1-3]. Pour
point of petroleum products, basically heavy fuel and
lubricating oils, are defined as the lowest temperature at
which the petroleum product is observed to flow when
cooled and below this temperature the product is stopped
to flow. Polyalkylphenol formaldehyde sulphonate and
its ethoxylate were synthesized and evaluated as pour
point depressant, viscosity improver and antioxidant. The
efficiency of these additives depends on their chemical
structure and degree of mixing (mole fraction). Values of
surface tension of these additives w ere measured in oil
phase and consequently CMC was deter min ed for all
additives and their mixtures. A novel method of inhibit-
ing oxidation was proposed. The author suggests the
mechanism according to surface activity of additive in oil
phase. More con firmations for suggested mechanism were
investigated by measuring the area occupied per mole-
cule of additive at oil phase. The results indicate that the
compatibility of sulphonate with ethoxylate group and
forming stable micelle which act as wax dispersant and
improver viscosity [1]. Some anionic surf actants had
been applied as p our point depressant by Omar et al. [4].
It is found that, the surface parameters and free energies
of micellization and adsorption confirm the decreasing
and improving of pour point. Also it is found that there is
a good relation b etween surface properties especially
interfacial tension of the surfactants and their efficiency
in depressing the pour point. Cacium octadecyl benzene
sulphonate and octadecyl phenol ethoxylate with 6 units
of ethylene oxide were synthesized and evaluated as pour,
cloud points depressants and viscosity index improvers.
These additives were compared with imported natural
wax dispersing agent. It is found that increasing concen-
tration of these additives is accompanied by an increase
in the minimum area occupied per molecule and surface
excess concentration. T here is a good relationship be-
tween the structure of hydrophilic group of the additive
and its efficiency.
Mixing the binary additives enhances its efficiency [5].
On the other hand the physical properties of the mixed
system of cationic/nonionic surfactant and its efficiency
in pour point depression were studied elsewhere [6]. The
modification of the lyophobic and lyophilic groups, in
the structure of the surfactant, may become necessary to
maintain surface activity at a su itable level. Some ester is
widely us ed as lubricants and h igh performance industri-
Efficiency of Amphoteric Surfactants as Flow Improvers and Pour Point Depressants
Copyright © 2013 SciRes. JPEE
al fluids. They are characterized by good biodegradabili-
ty, low volatility, good lubr icity, good thermal stability
and low pour points. Action mechanism of sorbitan pal-
mitate as multifunction additive for pour, cloud points
depressant and viscosity improver with oxidation of oil.
The efficiency of this additive depend s on its critical mi-
celle concentration. The micelle core act as trap for hy-
drocarbon oxide radicals and terminate chain of hydro-
carbon oxidation. The micellar inhibition depend on in-
corporation of hydroperox ide or other polar oxygen con-
taining molecules to the reversed micelle, as the results
increase oxidation stability of oil [3]. The author studies
new antioxidant for lube oil. This antioxidant dibenzyl
s-phenyl thio glyconitrile and other derivatives were pre-
par ed phase transfere catalysts. These compounds were
added to oil in different concentrations. The antioxidants
activities of different dosages were evaluated and sug-
gested mechanism according to micelle and their ther-
modynamic [1].
The purpose of the present work study of prepared
amphoteric surfactants calcium salt of N-Decyl-N-ben-
zyl-N-methylglycine (AB) and N-Dodecyl-N-benzyl-N-
methylglycine (CD) which differs in hydrocarbon chain
length and apply as pour point and anti oxidant for the
paraffinic gas oil.
2. Experimental
Preparation the additive by phase transfer catalysts by
two techniques:
N-D ec y l -N-benzyl-N-me t hylgl y cine(AB) and N-Do-
decyl-N-benzyl-N-methylglycine(CD) were synthesized
by Omar [7]. 3 mol N methyl b enzylamine and 1 mol
calcium chloroacetate to react overnight in pure ethanol
at 50 C0 in the presence of 0.1 mol of benzyl triethanol
ammonium chloride as phase transfere catalyst. The re-
sulting solution was treat ed with sodium carbonate and
recrystallized by alcohol. The resulting prolcoduct cal-
cium salt of N-Decyl-N-benzyl-N-methylglycine (AB) and
N-Dodecyl-N-benzyl-N-methylglycine (CD).
Surface tension of different concentrations for 107 to
0.1 mol/L of the synthesized additives were measured by
using Kruss Model 8451 in petroleum ether at 30˚C ac-
cording to omar et al. [8].
The oxidation test was carried out at 120˚C according
to ASTM D 943 standard methods. The base stock sam-
ple was subjected to oxidation with pure oxygen at a
flow rate of 0.1 L/hour for maximum 70 hours. The in-
vestigated amphoteric surfactant was added in different
concentrations. Pour point depressants and viscosity ac-
cording to ASTM-D 97 and IP 71/80 respectively.
3. Results and Discussions
Detailed physic-ch emical characteristics of the paraffinic
oil are reported in Table 1. The prep ared compounds
were confirmed their chemical structure by micro ele-
mental analysis and IR spectra. These compounds can
only exist in two forms, either amphoteric ions or catio-
nics ions. The IR spectra of the synthesized compound
showed the following bands: Absorption band at 1590 -
1330 cm1 characterized the carboxyla te group. The C-N
streching vibration band is at 1590 cm1, while strong
absorption bands at 1540, 1670 cm1 were found to strech-
ing vibrations of carbonylgroup (Figure 1). The variation
of surface tension with concentration is shown in Fig-
ures 2 and 3. It is clear that the surface tension decreases
more with increasing the compound concentrations. The
difference between them is attributed to f unctional group
of each molecule (hydrocarbon group). The action of addi-
tive of oil phase can be calculated using Gibbs adsorption
equation [7, 8]. Comparing the data in Table 2 shows that
the CMC value for the compound (CD) was lower than
that of the compound (AB), which indicates that the for-
mer CD favors micellization pr ocesses at a lower con-
centration than the latter compound. Studying the results
in Table 2, shows that the synth esized amphotric surfac-
tants CD have large values of surface excess and mini-
mum surface area, indicating the CD is the most efficient
and gives a greater lowering in surface tension of oil.
Thus the change in hydrocarbon group of (hydrophobic
part) affect of degree of micellization which will be re-
flected of efficiency of the additive of its activity in oil
phase. This concept is clearly observed in Figure 2. From
this figure, as concentration increases, the surface excess
concentration increase to reach a constant value at CMC,
while the additive CD has large value than AB as shown
in Table 2. These results c onfirm the compound CD
more solublize and more active in oil phase. These re-
sults are compatible by the author [1-3]. Thermodynamic
parameters of micellization (standard free energy, Gmic,
standard entropy change, Smic, and standard enthalpy
change, Hmic of the prepared surfactants were calculated
according Omar et al [7,8] as shown in Table 3. Gmic
Table 1. The physicochemical properties of the base oil.
Properties Base oil Test
Denisty (g/ml) at 15.5˚C 0.8958 D. 1298
Refactive index nD20 1.4955 D. 1218
ASTM colour 4.5 D. 1500
Kinematic viscoslty cSt
at 40˚C
at 100˚C
D. 445
D. 455
Pour point C 15 ASTM D 97
Molecular weight 520 GPC
Total paraffinic content, wr% 59.353 Urea adduction
Carbon residue contenty, wt% 1.9 ASTM D524
Ash content, wt% 0.0511 ASTM D482
Efficiency of Amphoteric Surfactants as Flow Improvers and Pour Point Depressants
Copyright © 2013 SciRes. JPEE
Figure 1. I.R spectra of CD additive.
Figure 2. Effec t of additive concentration on surface tension
reduction of oil at different temperature for the additive
values are negative indicating that the processes of mi-
cellization processes is a spontaneousity depend mainly
on the hydrocarbon chain length, while Smic are positive
reflect degree of random and increased upon transforma-
tion of one methylene group of the molecule of surfactant
from the interface to the bulk of micelles. The degree of
randomness is increased by increasing the temperatur e.
Figure 3. Effect of additive concentration on surface tension
reduction of oil at for the additive CB different tempera-
On the other hand Hmic values are positive due to the
endothermic process of amphoteric solvation upon mi-
Thermodynamic parameters of adsorption (standard free
energy, Gads, standard entropy change, Sads, and stan-
dard enthalpy change, Hads) for amphoteric surfactants
oil interface have more negative values than those cor-
Su rface ten sio n mNlm
-log C mol/L
Su rface ten sio n mNlm
-log C mol/L
Efficiency of Amphoteric Surfactants as Flow Improvers and Pour Point Depressants
Copyright © 2013 SciRes. JPEE
Table 2. Surface properties of additives at different temperatures.
Compound T, ˚C -log (CMC) Amin × 102 nm2 Γmax × 103 mol/cm2 Critical surface tension Mn/M2
AB 20
30 2.25
2.27 45.5
43.5 5.7
4.6 17
CB 20
30 3.01
2.29 95
160 2.5
0.86 14
Table 3. Thermodynamic parameters of additives at different temperatures.
Compound T, ˚C Gmic KJ/MOL Smic KJ/MOL Hmic KJ/MOL Gads KJ/MOL Sads KJ/MO L Hads KJ/MOL
AB 20
30 12.45
4.9 13.55
Table 4. Effect of different additives on pour point at different concentrations.
Kinematics viscosity, cSt at different temperatures Pour point, C Conc mollL Adittive
100 C 40 C
26.14 17
15 10 10 0.0000025
10 8 7 0.000003
5.1 7 5 0.0000035
5.5 7 4 0.000004
20 18 10 0.000002
17 13.7 7 0.0000025
7 12.5 4 0.000003
6 13 2 0.0000035
7 12.5 2.5 0.000004
responding to the micellization processes. This indicates
that the adsorption processes of surfactant molecules is
more energetically favored and these molecules act as
free before micellization. The results the activity of these
surfactants reach maximum at CMC and tend to steady
stable until limit value and scissors or decay. This value
has the critical surface tension and interfacial tension.
Furthermore, the higher positive values stan dard of free
standard entropy change, Smic, and standar d enthalpy
change, Hmic confirm the above mention and molecules
of surfactants prefer the adsorption at the interface rather
than formation micelle. At higher temperature, increase
the negativity of standar d free energy, Gmic and the po-
sitivity of standard entropy Smic, which confirmed the
adsorption preferability of the amphoteric surfactants at
oil interface at higher temperatures. So below CMC the
surface tension represents the critical value for adsorp-
tion and it’s activity of f ree molecules of surfactants
(Table 3).
It can be concluded that, the activity of the additive in
oil phase enhances by degree of temperature and the
values of CMC. This is due to the fact the moiety of mo-
lecules increases, as results increase their adsorption ra-
ther than giving stable micelle. These results are depicted
on Table 3.
The investigation of the ability of additives as pour
point depressant and viscosity improver are shown in
Tables 4. It is clear that the pour point and kinematic
viscosity are improved by increasing the additive con-
centration. The optimum value for reduction pour and
kinematic viscosity at its the critical micelle concentra-
tion. These results can be discussed according the surface
properties of the additive and its thermodynamic para-
meters (Tables 2 and 3). From the structure of additive,
it has lyophilic part like the paraffinic wax which com-
pletely miscible with wax molecule, while the lyopho bic
group (COO, or N+ group) adsorbs at interface. The
author suggests the conversion of the amphoteric species
to the protonated cationic form which is characterized by
less surface activity. i.e the free molecules can act as
cationic or ioic surfactants depend on the hydrogen pro-
ton in oil phase. As the results, disperse wax crystal lat-
tice to small sizes, consequently the pour point decreases
and viscosity improves. i.e these addictives have multi-
function pur pos e s .
The effect of these addictives on the oxidation stability
of oil is given in Figure 4. The data shows the additive
retards the oxidation of oil COO group and CN+ in each
additive, which act as trap for free radical of R-O. From
Figure 4, the total acid decrease by increasing the addi-
Efficiency of Amphoteric Surfactants as Flow Improvers and Pour Point Depressants
Copyright © 2013 SciRes. JPEE
Figure 4. Effect of different concentrations of the prepared additive son acid number.
tive concentrations and reach the optimum value at CMC
each additive as confirmed by the author early [1-3].
Further increase concentration of the additive, the oxida-
tion stability decreases due the increase in surface ten-
sion, which affects on interfacial tension and degree of
adsorption at interface. Comparing between two addi-
tives in increasing oil stability, the additive CD is the
slightly high of AB, due to it has the surface properties
slightly small difference. The COO group inhibits prop a-
gation of fr e e radicals and terminates reaction processes
of free radicals.
4. Conclusion
1) The oxidation stability of oil as measured by total
acid number indicates that, the oxidation inhibitor effi-
ciency follows the order.
CD > AB. These results depend on value of CMC and
area occupied per molecule at oil interface and thermo-
dynamic parameters of surfactants.
2) The synthesized additives have a multifunction for
pour point depressant, improving viscosity and enhance
oxidation stability of oil. These results depend on ad-
sorption of additives at oil ph a s e and critical s urface ten-
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by Phase Transfer Catalysts for Lubricati ng Oil,” Biotech
Conference, Expo, 12-16 May 2013.
[2] N. El Mehbad, “Developments of Multifunctional Addi-
tives for High Quality Lube Oil,” Journal of Power and
Energy Engineering, Sanya, 29 November - 1 December
[3] N. El Mehbad, “The Development and Application of
Ester for Lubricating Oil by Phase Transfer Catalysts,”
19th International Colloquium, 21-23 January 2013, Ger-
[4] T. T. Khidr, E. M. S. Azzam, S. Mutwaa and A. M. A.
Omar, “Study of Some Anionic Surfactants as Pour Point
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brication and Tribology, Vol. 59, No. 2, 2007, pp. 64-68.
[5] T. T. Khidr and A. M. A. Omar , “Anionic/Nonionic Mix-
ture of Surfactants for Pour Point Depression of Gas Oil
Egyptian,Journal of Petroleum, Vol. 12, 2003, pp. 21-
[6] T. T. Khidr, D. Ismail and A. M. A. Omar, “Improving
the Flow Properties of n-Paraffi n Gas Oi l by Cationic and
Non-Ionic Surfactants,” Journal of Faculty of Education,
Vol. 25, 2000, pp. 121-135.
[7] A. M. A. Omar, “Separation of Emulsifiable Oil from
Solution by Surface Tension Control,” Adsorption Science
and Technology, Vol. 19, No. 1, 2001, pp. 91-100.
[8] A. M. A. Omar, Journal of Petroleum Science and Tech-
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Acid number , mgl KOH lgm
Ti m e , hours