THE EFFECT OF COSURFACTANT IN CO2 ABSORPTION IN WATER – IN – OIL EMULSION

Abstract

Carbon dioxide is one of the main concern in the environment when it comes to energy usage of fuel, even the fuel
is coming from natural gas sources. Apart from endangered the environment, carbon dioxide also affects the caloric
value of the natural gas itself. The presence of carbon dioxide as contaminants is a nuisance for oil and gas industry
as its capability of forming corrosion in pipeline, thus its removal is vital for this industry. The absorption of carbon
dioxide in emulsions would be an effective method to prevent corrosion. This study focused on the effects of
cosurfactant, complementing 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) with surfactant which is sorbitan
oleate (SPAN 80), on the stability of water-in-oil (W/O) emulsion. This study also investigates the use of blended
amines which are methyldiethanolamine (MDEA)/2-amino-2-methyl-1-propanol (AMP) and MDEA as aqueous
phase. A modified rotating disk contactor (RDC) was used in absorption process and gas chromatography (GC) was
used to determine the amount of the CO2 absorbed. Analysis of carbon dioxide absorption through emulsion
indicates that different cosurfactant may change the absorption mechanism.

Full text

Environment & Ecosystem Science (EES) 2(2) (2018) 42-46
Cite The Ar ticle: I. N. M . Dali, K . S. N. Kamarud in (20 18). The Effect Of Cosurfact ant In Co 2 Absorpti on In Wat er – In – Oil Em ulsion .
Envir onment & Ecosyste m Scienc e
, 2( 2) : 42-4 6.
ISSN: 2521-0882 (Print)
ISSN: 2521-0483 (Online)
CODEN: EESND2
ARTICLE DETAILS
Article History:
Received 10 May 2018
Accepted 6 Jun 2018
Available online 10 July 2018
ABSTRACT
Carbon dioxide is one of the main concern in the environment when it comes to energy usage of fuel, even the fuel
is coming from natural gas sources. Apart from endangered the environment, carbon dioxide also affects the caloric
value of the natural gas itself. The presence of carbon dioxide as contaminants is a nuisance for oil and gas industry
as its capability of forming corrosion in pipeline, thus its removal is vital for this industry. The absorption of carbon
dioxide in emulsions would be an effective method to prevent corrosion. This study focused on the effects of
cosurfactant, complementing 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) with surfactant which is sorbitan
oleate (SPAN 80), on the stability of water-in-oil (W/O) emulsion. This study also investigates the use of blended
amines which are methyldiethanolamine (MDEA)/2-amino-2-methyl-1-propanol (AMP) and MDEA as aqueous
phase. A modified rotating disk contactor (RDC) was used in absorption process and gas chromatography (GC) was
used to determine the amount of the CO2 absorbed. Analysis of carbon dioxide absorption through emulsion
indicates that different cosurfactant may change the absorption mechanism.
KEYWORDS
Cosurfactant, water-in-oil emulsions, stability of emulsions, absorption, carbon dioxide.
1. INTRODUCTION
The usage of fossil fuel as a source of energy for worldwide has made an
impact to environment. This is due to burning of fossil fuel and releasing a
large amounts of carbon dioxide produced annually in various industries.
Natural gas that contains carbon dioxide and hydrogen sulphide is called
“acid gas”. A process of removal of certain undesirable contaminants such
as sulphur containing compounds, carbon dioxide, mercury, from
processed hydrocarbon is known as gas sweetening. A number of methods
are available for removal of acid gases from product streams. Some of the
more commonly used method are physical absorption, chemical
absorption, adsorption and membrane separation, among them physical
and chemical absorption methods have more industrial importance [1].
There are several consecutive steps for chemical absorption of gas in a
liquid phase which contains: (1) penetration of gas in the gas towards the
gas-liquid interface, (2) physical dissolution of gas in the liquid phase, (3)
diffusion in the liquid bulk of dissolved gas, and (4) chemical reaction
between the dissolved gas and a reactant in the liquid phase [1-3]. It can
be said that the physical dissolution in the liquid phase may control the
gas absorption rate due to fast chemical reaction between gas and the
reactant in the liquid phase. The rate of absorption can also be improving
by increasing the contact surface area between the gas and liquid phases
using small drops of liquids in the approach of emulsion.
The theory in the absorption of carbon dioxide in emulsion is that, since
the chemical reaction between the gas and the reactant in the liquid phase
is spontaneous (and may be fast depending on the reactant type), the other
following steps in the chemical absorption process is a diffusion of gas
through the gas and the liquid boundary layers, and gas diffusion in the
liquid phase control the absorption rate. Therefore, measures the gas
dissolving in the liquid, can enhance the rate and capacity of gas
absorption in the liquid phase. Thus, to increase the interfacial area in the
mass transfer path is by introducing tiny liquid droplets of reactive phase
into another liquid phase, i.e. applying an emulsion in contact with the gas
phase.
Emulsion may provide a large interfacial area between the continuous and
the dispersed liquid phases where the gas will dissolve physically from the
gas phase into continuous phase, and then transfer to the dispersed
reactive phase to react with the reactive component. On the other hand,
applying a W/O emulsion can provide a thin film on the absorption
equipment and may slacken the corrosion phenomenon where, often
observed when amine is used as solvent [1]. Emulsion stability is affected
mainly by surfactant, thus with correct formulation of surfactant, the rate
of gas absorption in liquid phase can be investigated. In this study, the
absorption of CO2 in W/O emulsion will focus on the effect of surfactant in
the stability of emulsion and the rate of removal of CO2.
CO2 removal is vital for natural gas before it is release as a product to sale
to customer. From previous studies it is shown that absorption of CO 2 in
emulsion is an effective method to prevent corrosion. However, it is
important to maintain the stability of the emulsion which depends on the
type and the quantity of surfactants. Unstable emulsion or
demulsifications reduces the absorption rates thus reduces its ability to
prevent corrosion because amines may directly in contact with the metal
surfaces.
Suitable formulation will produce stable emulsion with high efficiency of
the separation. It was reported that surfactant plays and important role
during the absorption because excessive stability of emulsion reduced the
efficiency of separation process [4]. Previous studies showed that the
problem arise as CH4 was also absorbed together with CO2 during the
absorption process. Therefore, a new formulation using different type of
surfactant need to be identified in order to produce stable emulsion with
high percentage of separation.
The selection of surfactant was based on the HLB number, which the value
is less than 5 and non-ionic surfactant such as Span 80 are able to stabilize
W/O emulsions [5,6]. The method of W/O emulsion preparation using
Environment & Ecosystem Science (EES)
DOI : http://doi.org/10.26480/ees.02.2018.42.46
THE EFFECT OF COSURFACTANT IN CO2 ABSORPTION IN WATER – IN – OIL
EMULSION
I. N. M. Dali*, K. S. N. Kamarudin
Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, Skudai, Johor Bahru.
*Corresponding author Email: inuralisa2@live.utm.my
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any
medium, provided the original work is properly cited

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Cite The Ar ticle: I. N. M . Dali, K . S. N. Kamarud in (2018) . The Effect Of Cos urfactant In Co2 Ab sorption In Wa ter – In – Oil Em ulsion .
Envir onment & Ecosyste m Scienc e
, 2( 2) : 42-4 6.
Span 80 has been widely used by previous studies [5]. Two different types
of aqueous phase were used, there were the combination of MDEA/AMP
and MDEA only. For MDEA/AMP, 8% v/v MDEA and 88% NaOH and 4%
v/v AMP and for MDEA, 8% v/v MDEA was the best for CO2 absorption [7].
Despite the appealing features of emulsion, this technique used in
absorption is not widespread used due to the instability of emulsion [8].
Thus, this study suggesting forming an adhesive emulsion that could
stabilize the emulsion based on experiment conducted by some
researchers [6]. A stable adhesive emulsion using DOPC as surfactant and
the cosurfactant the molecular structure complementary to DOPC was
Span 80 and DHA. This study applied the preparation technique to
produce a stable emulsion as a medium for separation of CO2 gas.
In this study, adhesive emulsion was introduced in the separation process
where the particles of the adhesive components are equal in size with
emulsion components (the liquid vehicle for carrier throughout which the
adhesive components are dispersed). This feature will give the adhesive a
continuous surface and creates stronger initial and ultimate adhesion (as
there is a larger surface area over which the adhesive bond can form) [6].
Adhesive emulsion was considered in this study to evaluate the separation
process of CO2 from gas mixture. This adhesive emulsion was stabilized by
1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) which typically
unstable because of its molecular structure.
Previous study showed that with low stability of emulsion, it will affect the
separation process [9]. To achieve a stable adhesive water-in-oil
emulsion, a cosurfactant was added and identified as Span 80. With
addition of cosurfactant whose molecular shapes could be complementary
to that of DOPC thus far better stabilizes W/O emulsions and was applied
in CO2 separation. Thus, the focus is to formulate a stable emulsion using
DOPC with cosurfactant, Span 80 and to investigate the percentage of
absorption of CO2 gas using adhesive emulsion.
2. EXPERIMENTAL
2.1 Materials
Emulsion was formed by homogenizing the aqueous and organic phase.
For the aqueous phase, a combination of blended amines were used,
MDEA/AMP and MDEA. Sodium hydroxide (NaOH) pellets were dissolved
in water to form sodium hydroxide solution for the aqueous phase.
Organic phase consists of DOPC with SPAN 80 to form a cosurfactant, are
used in the formulation while the diluent used was kerosene.
2.2 Emulsion Preparation and Observation
To prepare the aqueous phase, MDEA and AMP was mixed in a beaker with
0.1 M NaOH solution. 4 g of NaOH pellet was dissolved in 1 L of water. From
the previous studies, combination of 8% of MDEA and 4% of AMP gave the
highest absorption rate which is 66.8%. The beaker was covered with
aluminum foil. Next, the mixture was stirred on a hot plate magnetic stirrer
at 30°C at the speed of 700 rpm for 15 minutes.
Prior to emulsification of MDEA/AMP, an organic phase of kerosene and
DOPC and SPAN 80 was prepared. DOPC was dissolve in ethanol, where
the solubility of DOPC is 25 mg/ml in ethanol. An organic phase was
prepared by following the respective formulation shown in Table 1. The
mixture was prepared in the same manner as aqueous phase was prepared
in this study.
The emulsion was prepared using the high-performance dispenser Ultra
Turrax® T25 with 18G mixing shaft. Water-in-oil emulsion was obtained
by homogenizing the aqueous and organic phase that has been produced
in the previous step. The kerosene solution of DOPC and SPAN80 was
mixed first, and this mixture was then emulsified with an aqueous phase.
The emulsification process started where organic phase was place on the
homogenizer and the homogenizer speed was set at 5000 rpm. Within 2
minutes, aqueous phase was slowly added into the organic phase ready in
the beaker. After that, the emulsion was homogenized again at 1000 rpm
for another 7 minutes until milky emulsion was formed
Table 1: Formulation and condition used during emulsion preparation for different concentration of cosurfactant.
Sample number
100 mL Organic Phase
100 mL Aqueous Phase
1
92% v/v Kerosene : 8% Span 80
8% v/v MDEA : 88% NaOH : 4% v/v AMP
2
8% v/v MDEA : 92% NaOH
3
92% v/v Kerosene : 8% DOPC
8% v/v MDEA : 88% NaOH : 4% v/v AMP
8% v/v MDEA : 88% NaOH : 4% v/v AMP
4
92% v/v Kerosene : 4% v/v DOPC : 4% v/v Span 80
5
8% v/v MDEA : 92% NaOH
2.3 Stability of Emulsion
Stability test was conducted by water break-up test, where the prepared
samples was filled in graduated test tubes and placed in a room at
temperature 25°C. After 24 hours, total volume of separated layers was
measured. The stability of the emulsion was evaluated by using the
equation below. The emulsion is considered stable if the separated layer
is less than 10%.
Stability of emulsion (%);
= 𝑉𝑇− 𝑉𝑆
𝑉𝑇
𝑋 100 (1)
Where VT = Total volume (mL), VS = Separated volume (mL)
2.4 Carbon Dioxide Absorption
Rotating disc contactor (RDC) column system was used in the study of CO2
gas absorption. RDC will increase the contact time between the gas of CO2
and emulsion. Firstly, in the determination of CO2 gas absorbed, the pure
CO2 gas was injected into the gas chromatography (GC) to determine the
quantity of CO2 before absorption. The emulsion was then poured into the
RDC. The gas flowed into RDC at the flowrate of 20 L/min for 1 minute and
CO2 was allowed to absorb for 10 minutes. The pressure in RDC was 20
kPa and the stirring speed was set at 450-500 rpm. In the RDC, the gas
mixture flows upward in the circular motion. The amount of CO2 gas
leaving the RDC was measured by GC. The result was compared with result
obtained when the gas mixture was injected into the GC without passing
through the emulsion. The result was used to analyze the percentage of
CO2 removal from the injected pure gas of CO2.
3. RESULTS AND DISCUSSION
In this study, there are several variables that affect and influence the
absorption of CO2 through the emulsion. The emulsion was prepared by
different aqueous phase which are MDEA/AMP and MDEA and different
organic phase which are SPAN 80, DOPC and DOPC/Span 80. The stability
and the viscosity of the emulsion measured. The performance of the
emulsion was evaluated based on CO2 absorption.
The emulsion was prepared by homogenizing aqueous phase and organic
phase using homogenizer until milky emulsion was formed. The aqueous
phase used was MDEA/AMP and MDEA in NaOH solution and surfactants,
Span 80 and DOPC was mixed with kerosene. The emulsion formulation
shown in Table 2 was prepared to formed water-in-oil emulsion and to
study the absorption of CO2 through an emulsion.
Table 2: Formulation and condition used during emulsion preparation.
Sample
number
100 mL Organic Phase
100 mL Aqueous Phase
1
92% v/v Kerosene : 8%
Span 80
8% v/v MDEA : 88%
NaOH : 4% v/v AMP
2
8% v/v MDEA : 92%
NaOH
3
92% v/v Kerosene : 8%
DOPC
8% v/v MDEA : 88%
NaOH : 4% v/v AMP
8% v/v MDEA : 88%
NaOH : 4% v/v AMP
4
92% v/v Kerosene : 4%
v/v DOPC : 4% v/v Span
80
5
8% v/v MDEA : 92%
NaOH
Emulsification
speed
10,000 rpm
Emulsification
time
5 minutes
Agitation
speed
500 rpm
Absorption
time
10 inutes

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Envir onment & Ecosyste m Scienc e
, 2( 2) : 42-4 6.
3.1 Stability of Emulsion
The stability of the emulsion was measured after 24 hours from emulsion
preparation. The stability of emulsion was evaluated by using equation
(1). The result from calculation of the sample was presented in Figure 1
and was discussed in this study.
Figure 1: The stability of emulsion using different formulation
Based on Figure 1, Sample 1 shows a reading of 94% in terms of stability
when the emulsion contained Span 80 and MDEA/AMP as surfactant and
extractant respectively. The formulation is referred to Table 2, the stability
of Sample 2 (96%) which is slightly higher than stability of Sample 1
(94%). This is due to the different amine formulation, but both sample
used Span 80 as a surfactant.
DOPC was introduced to form an adhesive emulsion due to its ability as
phospholipids to form bilayers from two monolayers of each droplet
surface. Based on Figure 1, the stability of emulsion was at lowest which
at 9.6% when DOPC acted as the only surfactant for sample 3. This finding
agreed with paper published by Kim et al., where the researcher reported
that DOPC is typically unstable because of its molecular structure whose
HLB value is moderate(7), therefore resulting in the poor stability of W/O
emulsion [6].
As DOPC was proved to formed unstable emulsion, to form a stable
adhesive emulsion, another formulation was prepared by adding Span 80
to DOPC to increase the stability. This is because the molecular shape of
Span 80 becomes a complimentary to that of DOPC thus able to stabilize
the emulsion [6]. Figure 1 shows that the stability of emulsion for Sample
4 was recorded at 96% using MDEA/AMP as extractant in emulsion
formulation. Meanwhile, MDEA as aqueous phase also shows the same
patterns as Sample 5 stability of emulsion was measured at 98% compared
to Sample 4 at 96%. Thus, this finding proved that by adding DOPC/Span
80 in organic phase, a stable adhesive emulsion was formed.
Figure 2 shows the emulsion physical appearance on stability test after 24
hours of emulsion formation. Based on Figure 2(a) an adhesive emulsion
shows a highly stable emulsion after 24 hours. Figure 2(b) clearly shows
that the emulsion was separated into 3 layers (oil, emulsion and aqueous)
that shows the emulsion undergoes demulsification process [10,11]. A
stable emulsion is important in CO2 absorption process. Figure 2(b) shows
the emulsion after 24 hours, when DOPC was used as surfactant. DOPC
covered emulsion droplets could not act as stabilizer themselves, the
molecular shape need to be complemented with Span 80. Result from Span
80 as cosurfactant for DOPC in DOPC/Span 80 surfactant system giving a
physical appearance of emulsion after stability test shown in Figure 2(a).
Figure 2: (a) Sample 5 (DOPC/SPAN 80-surfactant) and (b) Sample 3
(DOPC-surfactant)
3.2 Viscosity of Emulsion
The study of viscosity in this experiment will help further understand the
mass transfer process that occur in the absorption. In this study the
viscosity of emulsion was measured using Brookfield Viscometer Model
DV-I Prime. The viscosity has great influence in providing information for
emulsification and stability of emulsion [10]. If the solution is highly
viscous, it resulted in stable emulsion, but too high viscosity may reduce
the dispersion of droplets in the organic phase [12]. Figure 3 shows the
recorded data for viscosity based on different formulation.
Figure 3: Viscosity of the emulsion based on formulation
Figure 3 shows the viscosity value of Sample 1 (318.9 cP), which is lower
than Sample 2 (670.9 cP). Both samples used Span 80 as surfactant but
different amine formulation. The viscosity value of sample containing
DOPC as surfactant (Sample 3), where it is the lowest (263.9 cP). It shows
that as the viscosity of emulsion is lower the stability also decreases. This
is due to that DOPC molecular structure, cannot retained the shape of
globules, thus poor in stabilized a W/O emulsion. Adding Span 80 as
cosurfactant to DOPC resulting in higher viscosity value that shown in
Figure 3. Viscosities of Sample 4 and Sample 5 is 399.9 cP and 884.8 cP
respectively. This is because, Span 80 contain a relatively small
hydrophilic head groups, compared to long hydrophobic carbon chain,
thus resulting it’s to have low HLB number where it able to stabilize W/O
emulsion. In addition, a cone shape molecular geometry possibly induced
a better packed interface with phospholipids, preventing coalescence
between dispersed droplets in the emulsion [6]. Increasing viscosity is one
of methods to increase the stability of emulsion globules [7]. Viscosity of
emulsion increase as SPAN 80 used as cosurfactant complementary to
DOPC, however increase in viscosity may inhibit the absorption process as
it can reduce the solubility of CO2 [13]. High stability emulsion is necessary
to maintain the emulsion formed in the absorption process, but it should
allow CO2 to diffuse through it. The relationship between viscosity and
stability was shown in Figure 4.
Figure 4: Relationship between viscosity and stability of an emulsion
Figure 4 shows the viscosity of emulsion is proportional to the stability of
emulsion. The value in Figure 4 shows a relationship between viscosity
and stability which higher value of viscosity the stable emulsion [9]. As
reported by Sreedhar et. at., highly viscous may inhibit the absorption
produce as it reduces the solubility of CO2 [13]. A summary from Figure 4,
the stable the emulsion indicates the higher number of viscosity value.
3.3 Carbon Dioxide Removal
In this study, the most important aspect is to investigate the percentage of
CO2 when emulsion was applied in the separation process. By introducing
adhesive emulsion, the stability increased that resulting a stable medium
for absorption of CO2 gas. In this study, the performance of emulsion was
determined by CO2 gas removal. CO2 gas was used as feed gas, passing
through the RDC column that contained emulsion. The amount of CO2 gas

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Envir onment & Ecosyste m Scienc e
, 2( 2) : 42-4 6.
absorbed was calculated and the effect of different surfactant on the
absorption was analyzed. Figure 5 shows the amount of carbon dioxide
absorbed for different emulsion formulation.
Figure 5: Percentage of CO2 absorption using different emulsion
formulation
Based on Figure 5, using MDEA/AMP as extractant (Sample 1), the
emulsion absorbed 281.26 mmol CO2, while emulsion containing MDEA as
extractant (Sample 2) absorbed 296.71 mmol CO2. This is due to different
formulation of aqueous phase used in the emulsion. The absorption of CO2
using DOPC as surfactant shows no CO2 removal because demulsification
has occurred. DOPC itself cannot retained the emulsion, thus leads to
breakdowns of emulsion. Due to this breakdown, the separation process
cannot take place as no medium for diffusion of CO2 to occur in the solution
[5]. A cosurfactant that was introduced in this study formed an adhesive
emulsion which lead highly stable emulsion. As shown in Figure 5, CO2
absorption for Sample 4 was only at 151.14 mmol of CO2 which is slightly
lower than Sample 5. (152.48 mmol of CO2) The differences of absorption
capacity are influenced by stability and viscosity of the emulsion.
CO2 removal was less in DOPC/Span 80 system as compared to Span 80 as
surfactant. This result shows that, even though the emulsion stable, it does
not have the ability to increase the absorption of CO2 gas. Figure 6 shows
a correlation between stability and the amount of CO2 absorbed. The
stability is linked with viscosity (Figure 4), where high viscosity, may
inhibit the absorption of CO2 [5]. lower CO2 absorption may also due to the
concentration of surfactant employed. Increase the surfactant
concentrations leads to a higher viscosity of the W/O emulsion and does
not favor the extraction kinetics [4]. Thus, it may create a resistance for
CO2 to diffuse through the emulsion. It was also reported that surfactant
plays an important role during the absorption because excessive stability
of emulsion may reduce the efficiency of separation process [4].
Figure 6: Relationship between amount of CO2 absorbed and stability of
an emulsion
It is also suggested that the use of cosurfactant DOPC/Span 80 has
produced a stable emulsion, but it does not facilitate CO2 absorption due
to its molecular structure as shown in Figure 7. As it forms an adhesive
emulsion and it also create a resistance for CO2 to pass through and diffuse
through the interface layer.
Figure 7: The structure of emulsion formed as DOPC/Span 80 act as surfactant [6]
Therefore, it is proved that mass transfer of CO2 in an adhesive emulsion
is having high CO2 resistance. This study shows that the stability of
emulsion does not assured high CO2 absorption. In summary, a selection
of surfactant as an emulsifier is vital for diffusion to occur, even if it does
produce a great stability of an emulsion but does not provide a good
medium for absorption process to occur thus it is not a suitable surfactant
to be used in a formulation.
4. CONCLUSION
An experimental research was carried out to study the role of cosurfactant
in stabilizing the emulsion in order to achieve a higher efficiency of
absorption. The result drawn from this study, provides a better
understanding on the relationship between the surfactant and the rate of
absorption. The result shows that even the emulsion is stable, it does not
facilitate the absorption process. This is due to the molecular structure of
the surfactant that surround the emulsion droplet may create a resistance
for CO2 gas to diffuse. The stable the emulsion, the higher the value of
viscosity value and thus becomes a resistance for CO2 to diffuse. In
conclusion, it is very vital decision in selecting a suitable surfactant as an
emulsifier for CO2 removal in the absorption process. This study
suggesting, by reducing the resistance in the emulsion may increase the
rate of absorption to occur in the emulsion thus increasing the efficiency
of separating the CO2 gas through an emulsion.
ACKNOWLEDGEMENT
I am grateful to Universiti Teknologi Malaysia (UTM) for the support in
this research. I am thankful to Assoc. Prof. Dr. Khairul Sozana Nor
Kamarudin, who has guided me. Besides, I am very thankful to Mrs. Siti
Balqis Mohd Najib, postgraduate student of Universiti Teknologi Malaysia
(UTM) for guiding me in understanding this research.
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