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EFFECTS OF CONCENTRATION, TEMPERATURE, AND PH ON
ANIONIC SURFACTANT ADSORPTION ISOTHERM
Mohamed Ali Hamid, Mustafa Onur
Department of Petroleum Engineering, Universiti Teknologi PETRONAS
Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia
[email protected].
[email protected]
ABSTRACT
The adsorption of commercial anionic surfactant sodium dodecyl sulfate was studied by measuring the surfactant
concentrations before and after mixing with crushed samples from Berea cores. Langmuir-type isotherm at
equilibrium predicted successfully the equilibrium isotherms determined by static experiments. The main purpose of
the study is to determine the effect of concentration, temperature, and pH on adsorption isotherm coefficients (K and
Ym) in the Langmuir model. Cubic relationships between pH and K, and between pH and Ym were observed. Moreover,
it was found that the temperature is inversely proportional to the coefficients of the Langmuir isotherm model by a
quadratic relationship.
Keywords—adsorption, Langmuir, experiments, temperature, pH.
INTRODUCTION
Surfactants have been used for improving oil recovery
for a long time [1]. Surfactants are usually organic
compounds that are amphiphilic, meaning they
contain both hydrophobic groups (tails) and hydrophilic
groups (heads). Therefore, a surfactant contains both
a water insoluble (oil soluble) component and a water
soluble component. Surfactants will diffuse in water
and adsorb at interfaces between oil and water. The
insoluble hydrophobic group may extend out of the
bulk water phase, into the oil phase, while the water
soluble head group remains in the water phase [2].
The "tail" of most surfactants is fairly similar, consisting
of a hydrocarbon chain, which can be branch, linear,
or aromatic, Surfactants are classified according to
polar head group. The anionic surfactant carries a
net negative charge in the head group. This charge is
mainly responsible for the adsorption of surfactants
on solid surfaces. The adsorption of surfactants in the
reservoir rock may limit the effectiveness and increase
36
the cost of enhanced oil recovery (EOR) process. It
represents a loss of the surfactant from solution,
and consequently, a net reduction in the surfactant
slug. Therefore, the efficiency will be significantly
diminished not only in terms of technical aspects but
also in terms of economics.
The mechanism responsible for the surfactant
adsorption is mainly the electrostatic attraction
between the charged surface of the solid and the
charged head group of the surfactant molecule [3].
This is a process of transfer of surfactant molecules
from the bulk solution phase to the surface interface.
The conventional method of investigating surfactant
adsorption on sand is to measure the difference in
surfactant concentration before and after equilibrated
with sands in static experiments [4].
Many studies have been conducted on anionic
surfactants [5], [6], [7]. The adsorption of surfactants
from solution is affected by its physical-chemical
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properties such as pH [6], [8], temperature [9]. These
physical-chemical solution properties can also affect
the dissolution behavior of minerals so as to result
in significant changes in the precipitation behavior
of the surfactants [10]. Sodium dodecyl Sulfate (SDS)
surfactant is an anionic organic compound with the
formula CH3(CH2)11OSO3Na consisting of a 12-carbon
tail attached to a sulfate group. SDS has proved an
effective reduction in interfacial tension (IFT) between
oil and water which leads to better microscopic sweep
efficiency [11].
The objectives of this study are to (1) to determine
the effect of concentration, temperature, and pHon
anionic surfactant adsorption, (2) to predict the
relationships between adsorption coefficients (K
and Ym) in the Langmuir model that can account
for concentration, temperature and pH changes. To
achieve these objectives, an extensive experimental
work has been conducted in a wide range of
concentrations, temperatures, and pH.
MATERIALS, EQUIPMENTS, AND PROCEDURES
To conduct the experimental work, some materials
and equipments were prepared and used. These
are: surfactant, alkaline, core samples, and UV light
spectrophotometer. In the following, the properties
of the materials and description of the equipments
are given.
Materials
Anionic surfactant sodium dodecyl sulfate was
provided by SIGMA-ALDRICH, which has shown
reduce IFT (interfacial tension) effectively. The alkaline
additives used to adjust pH were sodium carbonate
and sodium metaborate from SIGMA-ALDRICH.
Berea sandstones were purchased from BEREA with
properties summarized in Table I.
Table I - The Chemical Composition
Of The Berea Sandstone
Component
Formula
Concentration, wt%
Silica
SiO2
93.13
Alumina
AI2O3
3.86
Ferric Oxide
Fe2O3
0.11
Ferrous Oxide
FeO
0.54
Magnesium Oxide
MgO
0.25
Calcium Oxide
CaO
0.10
Equipment
Spectrophotometer UV–Visible from SAFAS was used
to determine the UV adsorption of sodium dodecyl
sulfate (SDS). Calibrations of the absorbency values
versus concentrations of surfactant in the solvent of
interest were made and the unknown supernatant
concentrations interpolated by using Beer's law [7]. In
addition, a simple test tube was employed to perform
the static adsorption tests.
Description of test procedures
Static adsorption onto crushed sandstone was
determined in batch experiments. One gram of
crushed sandstone was mixed with 10 grams of the
surfactant solution of different concentrations and
varying temperatures and pH. The mixtures were
agitated for 24 h then left without shaking for another
day to achieve equilibrium, and then centrifuged
at 3000 rpm for 20 min. The supernatant liquid
was filtered and analyze. The amount of surfactant
adsorbed was determined by measuring different
concentrations in the solution before and after contact
with crushed rock [12]. The amount of adsorbed
surfactant (denoted by Ad in g surfactant/g rock) was
calculated from:
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RESULTS AND DISCUSSION
Adsorption isotherm
where V is the mass (g) of surfactant solution used,
m is the weight of the solid sample (g), and C0 and
Ce are the initial and equilibrium concentrations of
surfactant solution (wt%), respectively. The values of
Ad were then plotted against their corresponding Ce
values to construct the adsorption isotherms.
Quantitative analysis of SDS solution
For determination of concentration a colorimetric
method was used in this study. Beer-Lambert law,
which holds for many dilute solutions, states that
absorbance is linearly related to the concentration
was used (equation 2):
An adsorption isotherm is required to predict the
amount of adsorption at a certain concentration of the
component. The two adsorption isotherms that can
be used to describe the equilibrium adsorption are
the well-known monolayer Langmuir and empirical
Freundlich isotherms [14].
Isotherms are simply plots of the amount of surfactant
adsorbed per gram of solid or per surface area of
solid vs. the equilibrium surfactant concentration at a
constant temperature. It is a measure of the extent of
surface area of the adsorbent that is covered by the
adsorbent molecules at a given conditions. Results of
static experiments for the SDS are shown in Fig. 2.
where A is absorbance, ε is the molar absorptivity,
c is sample concentration, b is length of light path
through the sample (in cm). There is a UV adsorption
peak of sodium dodecyl sulfate at 210 nm, which was
selected as the detection wavelength for the maximal
UV adsorption occurs there. The concentration of
sodium dodecyl sulfate can be calculated using Beer's
law (see Fig. 1). The absorbance increases as the solute
concentration increases [13].
Fig. 2. SDS adsorption isotherm
Fig. 1. SDS concentration-light adsorption calibration
38
From Fig. 2, it can be seen that the Langmuir model
agrees better with the experimental data in the
whole range of test concentration. The Freundilch
model gives a good match of the test curve only
when concentration is low. The Langmuir adsorption
isotherm has been widely applied to many adsorption
processes. It has produced a good agreement with a
wide variety of experimental data for adsorption of a
solute from a liquid solution. A basic assumption of
the Langmuir theory is that the sorption takes place
at specific homogeneous sites in the adsorbent.
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Moreover, when a site is occupied by a solute, no
further adsorption can take place at that site [15].
in Fig. 3 indicate a reduction in adsorption with an
increase in temperatures.
The rate of adsorption to the surface should be
proportional to a driving force and area. The driving
force is the concentration difference, and the area is
the uncovered surface. The Langmuir equation relates
solid-phase adsorbate concentration, the uptake,
to the equilibrium liquid concentration at a fixed
temperature. The Langmuir equation is expressed as
[14]:
where Ad = amount adsorbed (g/g); Ym = maximum
amount adsorbed (g/g); K = Langmuir equilibrium
constant (dimensionless); Ce = equilibrium aqueous
concentration (wt %).
Equation [3] can be rewritten in the well-known
linearized expression of the Langmuir model as
follows:
Using equation [4] the maximum amount adsorbed
(Ym) and Langmuir equilibrium constant (K) were
calculated, and this procedure was employed to find
the effect of temperature and pH on Ym and K in a
wide range of surfactant concentrations (0.03-0.21
wt %) going beyond the critical micelle concentration
(CMC). Note that the value of CMC for sodium dodecyl
sulfate in water (no other additives or salts) at 25°C,
atmospheric pressure is 0.18 w t%.
Fig. 3. Effect of temperature on SDS adsorption
As can be seen from Fig. 3, an increase in the
temperature leads to a considerable decrease in the
adsorption of surfactants of high concentration. The
lower the temperature, higher the amount adsorbed.
These results are in agreement with literature
observations [16]. Adsorption means the movement of
molecules from solution to solid surface, furthermore
at high temperature surfactant solubility is improved
[9]. This improvement in surfactant solubility will
result in decreasing adsorption at high temperatures,
because at high temperature molecules of surfactant
prefer to stay in the solution rather than going onto
solid surface. To study the effect of temperature on
Langmuir coefficients values, plots of Ym and K vs.
temperatures were produced (see Figs. 4 and 5).
Temperature effects
To determine the temperature effect on the
surfactant adsorption, static tests were conducted
in temperature range between (25-85°C). High
surfactant concentrations were used to improve the
accuracy of adsorption estimations. Results shown
Fig. 4.
Effect of temperature on Ym
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Fig. 5.
Fig. 6.
Effect of temperature on K
From Figs. 4 and 5, an increase in temperature will lead
to a decrease in the values of adsorption coefficients.
Although not shown here, different mathematical
relationships were tested, among them a quadratic
type of relationship was best fitted the changes in Ym
and K as shown in Figs. 4 and 5, respectively.
Effect of pH
A more detailed investigation of the effect of
surface charge (pH) on adsorption was carried out
by observing the changes in values of adsorption
coefficients (K and Ym) while changing the medium
pH. Without addition of alkali pH of surfactant solution
was 7.8. When the value of pH was increased we
observed a decrease in values of Ym and K as shown in
Figs. 7 and 8, respectively.
In chemistry, pH is a measure of the activity of the
hydrogen ion. p[H+], which measures the hydrogen
ion concentration. If pH is less than seven means the
medium is acidic and if greater than seven the medium
is basic. The more the pH is raised, the less positive
the surface becomes. The pH effect depends upon
the type of the surfactant and its net head charge,
anionic SDS surfactant adsorption tend to decrease
with an increase in pH [17]. Alkali can decrease the
positive charge on the surface of the rock in terms
of increasing solution pH, as a result adsorption
of the negative charged surfactant (anionic) will
be decreased. In this study, the effect of pH was in
agreement with the literature investigations. Four
different initial surfactant concentrations were used.
In all cases adsorption was reduced by increasing pH,
but the reduction was more at high concentration as
shown in Fig. 6.
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Effect of pH on SDS adsorption
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Fig. 7.
Effect of pH on Ym
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Universiti Teknologi PETRONAS.
REFERENCES
Fig. 8.
[1]
J. D. Shosa, “Surfactants: Fundamentals and
Applications in the Petroleum Industry,” Palaios, vol.
16, no. 6, pp. 615–615, Dec. 2001.
[2]
N. D. Denkov and S. Tcholakova, “Surfactants
– classification , Surfactants features and and
applications applications features,” 2010.
[3]
H. Liu, X. Cai, Y. Wang, and J. Chen, “Adsorption
mechanism-based screening of cyclodextrin
polymers for adsorption and separation of pesticides
from water.,” Water research, vol. 45, no. 11, May 2011.
[4]
F. J. Trogus, T. Sophany, R. S. Schechter, and W. H.
Wade, “Static and Dynamic Adsorption of Anionic
and Nonionic Surfactants ac,” Society of Petroleum
Engineers Journal, vol. 2, 1977.
[5]
S. Paria and K. C. Khilar, “A review on experimental
studies of surfactant adsorption at the hydrophilic
solid-water interface,” Advances in colloid and
interface science, vol. 110, no. 3, pp. 75–95, Aug. 2004.
[6]
A. C. Hari, R. a Paruchuri, D. a Sabatini, and T. C. G.
Kibbey, “Effects of pH and cationic and nonionic
surfactants on the adsorption of pharmaceuticals to
a natural aquifer material.,” Environmental science &
technology, 2005.
[7]
M. J. McGuire, J. Addai-Mensah, and K. E. Bremmell,
“Spectroscopic investigation of the adsorption
mechanisms of polyacrylamide polymers onto iron
oxide particles.,” Journal of colloid and interface
science, Jul. 2006.
[8]
Q. Liu, M. Dong, X. Yue, and J. Hou, “Synergy of alkali
and surfactant in emulsification of heavy oil in
brine,” Colloids and Surfaces A: Physicochemical and
Engineering Aspects, vol. 273, no. 1–3, pp. 219–228,
Feb. 2006.
[9]
V. M. Z. and L. Handy, “Effect of temperature on
surfactant adsorption,” SPE, 1981.
Effect of pH on K
Figs. 7 and 8 also show that adsorption coefficients Ym
and K are related to pH by cubic relationships.
SUMMARY & CONCLUSIONS
In this paper, an extensive experimental work was
conducted to study the effects of concentration,
temperature, and pH on adsorption. The coefficients
in the Langmuir model were adjusted to account for
the effects of these parameters for SDS surfactant
and sandstone system. The major conclusions can be
summarized as follows:
•
It was shown that the Langmuir model gives the
most appropriate match of the experimental
results compare to Freundlich model in the whole
range of test parameters for SDS adsorption onto
sandstone surface.
•
The adsorption of SDS surfactant tends to
decrease by increasing the temperature and pH
of the medium.
•
It was found that the Langmuir adsorption
coefficients are related to temperature by a
quadratic relationship and to pH by a cubic
relationship.
ACKNOWLEDGEMENT
The authors acknowledge the support of this research
from the Enhanced Oil Recovery Center (EORC) at
[10] C. T. Q. Dang, Z. Chen, N. T. B. Nguyen, W. Bae, and
T. H. Phung, “Development of Isotherm Polymer/
Surfactant Adsorption Models in Chemical Flooding,”
SPE 147872, 2011.
[11] A. Dhabi and B. H. Oct, “SHELL REGIONAL
TECHNOLOGY FORUM Interfacial Phenomena and
Flow in Carbonates - With Focus on Field Applications,”
October, p. 2004, 2004.
VOLUME NINE NUMBER ONE JANUARY - JUNE 2013 PLATFORM
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[12] W. Lv, B. Bazin, D. Ma, Q. Liu, D. Han, and K. Wu, “Static
and dynamic adsorption of anionic and amphoteric
surfactants with and without the presence of alkali,”
Journal of Petroleum Science and Engineering, vol.
77, no. 2, May 2011.
[13] A. Kasal, M. Budesinsky, and W. J. Griffiths,
“Spectroscopic Methods of Steroid Analysis,” 2010.
[14] K. M. Khoda, “Adsorption Isotherms,” Langmuir, no.
April, 2009.
[15] M. Ahmed and M. Corresponding, “Equilibrium
Adsorption Isotherms of Anionic , Nonionic
Surfactants and Their Mixtures to Shale and
Sandstone,” Modern Applied Science, vol. 3, 2009.
[16] N. P. and O. G¨UVEN, “Solvent , Temperature and
Concentration Effects on the Adsorption of Poly (
n-Butyl Methacrylate ) on Alumina from Solutions,”
Turk J Chem, 2002.
[17] L. W. L. Gary A. Pope, Debojit Bhuyan, “Mathematical
Modeling of High-pH Chemical Flooding,” SPE 17398,
1990.
Mustafa Onur is currently holding
the Schlumberger Professorial Chair
at the Department of Petroleum
Engineering at Universiti Teknologi
PETRONAS (UTP), and Professor of
Department of Petroleum and Natural
Gas Engineering at Istanbul Technical
University, Turkey. Previously, he was the Head of the EOR
Centre at UTP. His expertise and research interests include
well testing, pressure-transient analysis, formation testing,
reservoir engineering, enhanced oil recovery methods,
nonlinear parameter estimation, and geothermal reservoir
engineering. He holds a BS degree from the Middle East
Technical U. in Turkey and MS and PhD degrees from the
U. of Tulsa, all in petroleum engineering. He has served
on the editorial committees of SPE Reservoir Evaluation
& Engineering and SPE Journal. He is the recipient of the
2010 SPE Formation Evaluation Award. Onur is currently the
Executive Editor of the SPE Journal.
AUTHORS' INFORMATION
Mohamed Ali Hamid was born in
Sudan in 1984. He received the B.Sc.
degree in chemical engineering from
University of Khartoum, Khartoum,
Sudan, in 2006. He joined Universiti
Teknologi
PETRONAS,
Tronoh,
Malaysia, in 2008 as a researcher
where he received the M.Sc. in Petroleum Engineering in
2010. His main areas of research interest are adsorption,
characterization, and mathematical modeling of chemicals
during EOR process. Mr. Mohamed is a member of the
Sudanese Engineering Council, Sudan; the Society of
Petroleum Engineers (SPE), and the Chemical Engineering
Society at University Of Khartoum, Sudan.
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