In Parts 1 and 2 of this series of papers, the importance of interfacial properties in determining the stability of water- in-Buchan crude oil emulsions has been ...
Colloids and Surfaces
A: Physicochemical
0927-7757/94/$07.00
0 1994 -
and Engineering
Aspects,
83 (1994)
261-271
261
Elsevier Science B.V. All rights reserved.
Dewatering of crude oil emulsions 3. Emulsion resolution by chemical means R.A. Mohammeda”,
A.I. Bailey”,*, P.F. Luckham”,
S.E. Taylorb
aDepartment of Chemical Engineering and Chemical Technology, Imperial College of Science, Technology and Medicine, Prince Consort Road, London SW7 2BY, UK bSurface and Colloid Science Group, BP Group Research and Engineering Centre, Chertsey Road, Sunbury-on- Thames, Middlesex, T WI 6 7LN, UK (Received
15 July 1993; accepted
5 November
1993)
Abstract In Parts 1 and 2 of this series of papers, the importance of interfacial properties in determining the stability of waterin-Buchan crude oil emulsions has been demonstrated. In this third part of the series, we report on the chemical demulsification of water-in-crude oil emulsions. Two classes of experiment were carried out; bottle tests in which emulsion resolution was followed by the appearance of a separated aqueous layer in the bottom of the tube, and microscopic examinations, where resolution was directly followed by observing coalescence of the droplets. Demulsification was achieved by adding one of the commercial demulsifiers Unideml20 and BJl8. Unideml20 is a blend of non-ionic and anionic surfactants, whereas BJ18 was specially developed for the demulsification of Buchan crude. Some of the pure constituents of these blended surfactants were also used for resolving water-in-Buchan crude oil emulsions. Two types of behaviour were observed: type I behaviour, showing constant water separation with increased demulsifier concentration, and type II, showing reduced water separation with increased demulsifier concentration. To a small extent, there exists a degree of functional specificity in the demulsifier molecules towards interaction with the constituents of the interfacial film, and to a larger extent good emulsion resolution is governed by the interfacial properties of the demulsifier blend. Key words: Chemical
demulsification;
Crude oil emulsion;
Dewatering;
Introduction The destabilisation of water-in-crude oil emulsions is an important process in the oil industry [l-3]. During production, it is essential to remove water from crude oil in order to reduce corrosion of pipelines and hence optimise their usage. In refinery operations, potentially corrosive salts are removed from the crude by deliberate emulsification of fresh (wash) water to produce 5-10% waterin-crude oil emulsions, which are subsequently *Corresponding author. address: Drilling Fluids Group, Production ‘Present Department, Intevep, S.A., Apdo. 76343, Caracas 1070-A, Venezuela. SSDI
0927-7757(93)02706-K
Emulsion
resolution
with added broken using electrical dehydrators [ 21. Various chemicals demulsifying chemicals have been used as demulsifiers, such as non-ionic surfactants based on ethylene and propylene oxides [ 2,4]. The investigation of the kinetics of the chemical demulsification process is complicated by the interaction of three main effects [2]. These are (1) the displacement of the asphaltic film from the water/oil interface by the demulsifier, (2) flocculation, and (3) coalescence of water drops. The predominant rate-determining step is decided by the nature of the emulsion, and the stage which breaking has reached at any moment. Lawrence and Killner [S] referred to the concen-
262
R.A. Mohammed et al./Colloids Surfaces A: Physicochem. Eng. Aspects 83 (1994)
tration levels of the added demulsifier and concluded that their values should not greatly exceed the critical micelle concentration (CMC), suggesting that demulsifier action may be in part due to solubilisation of the asphaltic material. Little [6] described successful demulsifiers to be very poor emulsifiers, and stated that chemical demulsification is dependent on the collision rate between droplet particles after the demulsifier has been thoroughly mixed. Graham et al. [7] referred to the importance of the type of solvent on the demulsification process. By using bottle tests, these investigators identified two different water separation profiles of water-inForties crude oil emulsions, an immediate emulsion resolution and an inductive resolution where water separation occurred after a period of time. The former occurred, for example, when the demulsifier was added to the emulsion without the solvent carrier, whereas the latter occurred when the demulsifier was mixed with the carrier solvent before introduction into the emulsion. Aveyard et al. [S] studied the kinetics of demulsification by considering two types of “low molar mass” demulsifier, a non-ionic and an anionic surfactant, in order to study their effects on the rate of resolving water-in-Forties crude oil emulsions. The demulsification rate increased with surfactant concentration up to the onset of surfactant aggregation either in the bulk phases, or in a third surfactant-rich phase. However, higher surfactant concentrations produced either a lower demulsification rate, or a slight increase to a plateau. Sjoblom et al. [9] conducted a destabilisation study on water-in-Norwegian crude oil emulsions using medium chain alcohols and amines. They demonstrated that these chemicals speed up the separation of water from water-in-crude oil emulsions. These authors concluded that alcohols modify the rigidity of the interfacial film by a diffusion/partitioning process, while amines show a strong and specific interaction with the interfacial groups constituting the film formed between water and crude oil. These specific interactions render the interfacial film more hydrophilic. Among other methods of resolving emulsions of
261-271
the water-in-crude oil type is electrical dehydration which will be discussed in detail in the next part of this series. Centrifuging stable emulsions often results in the separation of a concentrated waterin-oil emulsion, which does not break the protective film surrounding the water drops. However, elevation of temperature has several useful effects. It reduces the viscosity of the external oil phase, increases the difference in density of the phases, increases the chances of droplet collision, and it usually weakens the stabilising film. To date, rigorous studies to examine demulsification rates of crude oil emulsions have been hindered by many factors, such as the opacity of the crude and the variation in composition. A method claimed to be promising is based on electroacoustics [ 10,111, since it is not affected by the opacity of the crude in order to obtain information on the demulsification rates. One would anticipate that the success of this method will depend on the type of emulsion being examined. The application of this method to monitor the coagulation of oilin-water emulsions would be expected to be successful since double layer effects exist. This method has been used by Isaacs and co-workers [ 10,111 to study the coagulation of water-in-crude oil emulsions following their treatment with chemical demulsifiers. In a previous publication in this series [ 121, we have reported on the effectiveness of two chemical demulsifiers in destabilising the asphaltene films formed at the oil/water interface by studying the rheological properties of the interfacial films. In this paper, we study the effect of these materials on the resolution of water-in-crude oil emulsions. Furthermore, since the commercial materials tend to be blends of surfactant designed to give optimum performance, we have also studied the resolving power of single surfactants in the blend. Experimental Materials The crude oil was from the Buchan oil field and was used as supplied. The demulsifiers applied to
R.A. Mohammed et al./Colloids
Surfaces A: Physicochem.
Eng. Aspects 83 (1994)
263
261-271
resolve Buchan crude emulsions were from Grace Dearborne plc. These surfactants are of the non-
in length and 2 in in diameter at room temperature. Water-in-Buchan crude oil emulsions (10%)
ionic type, Pluronic (PE) and Tetronic (T) series, containing different amounts of poly(ethylene
were prepared in a glass container which was inverted a number of times to ensure that the
oxide)
(PEO)
and
poly(propylene
oxide)
contents
(PPO)
were uniformly
distributed
before filling
groups (shown in Fig. 1). Table 1 presents the average molecular weights together with the number of PEO and PPO units in each demulsifier
up the tubes. The appropriate demulsifier was delivered using a microsyringe, followed by a careful inversion of the tubes in order to disperse
used and the calculated
the demulsifier.
The height of the separated
was
as a function
ance (HLB)
number.
hydrophile-lipophile The demulsifier
bal-
D112 is the
EOY
\
PO,-EOY
Ii
PO,-EOY
H
/ N -CH2-
CH2-N
/
of time,
water
until
no
further change occurred. Chemical demulsification was examined using a microscope stage cell based on a design by Taylor [ 33. This cell enabled chemical demulsification to be monitored using a video camera fitted to the microscope.
surfactant octylphenol-formaldehyde condensate with PO + EO. IL2 is dodecylbenzenesulphonic acid (DBS), a wetting agent. Unidem120 is a blend of T1301, IL2, D112, and DW12, and BJ18 is a complex EO/PO based on a polyfunctional amine. Bottle tests were conducted in glass tubes 3 in
H EOY40,
recorded
60 I x 0
H
EOY
H
EO
Y PO I x 0
PO I x 0
H
EO
Y 60 I x 0
H
\
H EOY-POX
(B) H EOyH
E”Y d
d 90 3H
,‘I 0
d12
C9H 19
H
25
m=S-8 w
(D)
Fig. 1. The structure of the demulsifiers used in this study: (A) the structure of the tetronics series; (B) the demulsifier DI12, octylphenol-formaldehyde condensate + PO + EO; (C) the demulsifier DW12, nonylphenol-formaldehyde condensate + PO + EO; (D) dodecylbenzenesulphonic acid.
R.A. Mohammed et al./Colloids Surfaces A: Physicochem. Eng. Aspects 83 ( 1994 ) 261-271
264
Table 1 The average molecular weight of the commercial different demulsifier components
demulsifier
components
together
with the number
of PEO and PPO
Surfactant
No. average mol. wt.
PPO mol. wt.
No. of PPO units (x)
PEO mol. wt.
No. of PEO units (y)
HLB,,,,
T701 T803 T1301 T1302 T1501 PE6200 PE6400 DIl2” DW12b
3700 5000 6900 7400 7900 2500 3000 4000 3000
3300 3500 6000 6000 7100 2000 1800 1740 None
15 15 25 25 30 34 31 7.5
370 1500 700 1400 800 500 1200 1400 1300
1.5 8.5 4.0 8.0 4.5 11 27 8.0 3.5
5.3 7.6 4.6 5.9 4.0 9.1 5.8
“Average bAverage
molecular molecular
weight of octylphenolLHCH0 weight of nonylphenolkHCH0,
units of the
resin, 500. 1700.
Results Bottle test Results from such tests indicate the suitability of using a particular surfactant as a demulsifier in terms of quality and quantity of water separation in the oilfield. The time taken for the first appearance of separated water was recorded. A profile of percentage volume of water separated at different concentration levels of added demulsifier was then constructed. Good resolution corresponds in general to a mirror-like sharp interface. Addition of Unideml20 The demulsifier blend
Unidem120,
when added
to the emulsion in the concentration range 1000-20 000 ppm at room temperature, produced murky water. The amount of water settled increases with demulsifier concentration until a plateau is reached (Fig. 2). This behaviour is designated type I as opposed to type II (see later). Earlier trials using a lower concentration range (lo-50 ppm) produced very little separation. In the oilfield, these demulsifiers are added at stream temperatures of about 40°C and at a very low concentration (l-5 ppm). Both heat and electrical
. Fig. 2. The resolution of 10% water-in-Buchan crude emulsion by Unideml20 in the concentration range 1000-20000 ppm at room temperature.
treatment will then help to resolve the emulsion. The interface shown in the figure appears to be sharp and well defined; large drops of water had completely coalesced and separated. Addition of components of Unideml20 When a component of Unidem120, T1301 was added, there was an increase in water separation with concentration. Initially at 50 ppm, 15% water separation was achieved. A maximum resolution of 38% water separation was achieved at an optimum concentration of 700 ppm, beyond which
R.A. Mohammed et al./ColEoids Surfaces A: Physicochem. Eng. Aspects 83 (1994 j 261-271
(above dropped
1000 ppm) the level of separated to a constant
water had
value of 21% as shown
in
265
be clean. Similar water appearances were observed when the components D112 and DW12 were
Fig. 3. This behaviour is designated as type II behaviour. In the concentration range within the overdosing region (i.e. above 1000 ppm) the water
applied.
appeared
Addition of BJ18 The demulsifier BJ18, when added to the emulsion, produced an interface which appeared to be
to be clean, and a phase rich in surfactant
was observed at the bottom of the tube. When IL2 was added at 70 ppm, 5% water separated. An increase to about 37% in water level was observed when the demulsifier concentration was increased to 800 ppm. Above this concentration, the water level had reached a plateau as shown in Fig. 4. The separated water appeared to
10
’
0
I
I
1000
I
I
2000 3000 4000 5000 ~1301concentration ppm
6000
7000
Fig. 3. Plot of percentage volume of water separated from 10% water-in-Buchan crude emulsion vs. T1301 concentration in ppm at room temperature. The continuous line connects the experimental data.
0
’
0
I
500
I
,
I
I
1000 1500 2000 2500 IL2 concentration ppm
I
3000
The separation
profiles
for these surfac-
tants were of type I.
blurred
as shown in Fig. 5. This was because
large
unresolved water drops in the bulk of the emulsion had rested on the interface. BJ18 has been formulated especially for resolving Buchan crude emulsions. Overdosing due to excessive levels of added BJ18 is apparent in the sharp decrease in the amount of water separated as shown in the figure. A plot of the percentage water separated vs. BJ18 concentration is presented in Fig. 6. A maximum level of water separation of about 46% was observed, this separation corresponding to a concentration of 1500 ppm. The separation decreases to zero at 6000 ppm, conforming to type II behaviour. Each test was repeated twice and the average value of the percentage of separated water was recorded. Addition of other single surfactants The surfactants T701 and T803, whose composition is presented in Table 1, were also tested as demulsifiers for water-in-Buchan crude oil emulsions. Emulsion overdosing by T701 resulted in a
I 3500
Fig. 4. Plot of percentage volume of water separated from 10% water-in-Buchan crude emulsion vs. IL2 concentration in ppm at room temperature. The continuous line connects the experimental data
Fig. 5. The resolution of 10% water-in-Buchan by BJ18 at room temperature.
crude emulsion
R.A. Mohammed et al./Colloids Surfaces A: Physicochem. Eng. Aspects 83 (1994)
266
261-271
type I behaviour, whereas T1501 exhibited type II behaviour. Surfactants from the Pluronic series, PE6200 and
PE6400,
were
also
examined
for emulsion
resolution. Both surfactants’ profiles followed type I behaviour. The separated water was coloured. Microscopic
examination
0 0
1000
2000
3000 BJ16
4000
5000
6000
7000
concentration ppm
Fig. 6. Plot of percentage water separated from 10% water-inBuchan crude emulsion vs. BJ18 concentration at room temperature. The continuous line connects the experimental data.
separation of clear water, and the profile corresponds to type I behaviour. The action of the surfactant T803 in the concentration range 50-200 ppm yielded a clean water and sharp interface. However, slightly yellowish water and a blurred interface were observed in the concentration region 600-1000 ppm. T803 produced an increased water resolution in the concentration range 1000-6000 ppm. The water appeared to be coloured and there was a sharp interface. This is shown in Fig. 7. Among this series of surfactants, T1302 and T1501 were tested for their ability to break waterin-Buchan crude oil emulsions. T1302 followed
A video recording was made for a sample of 2 ml of a centrifuged 10% water-in-Buchan crude oil emulsion being treated chemically by demulsifiers. The demulsifier blends BJ18 and Unidem120, together with its components, were tested. In addition, other surfactants from the Tetronics series, T701, T803, T1302, T1501, and those from the Pluronics series, PE6200 and PE6400 were studied. All these materials were added at the two concentrations 0.17% and 16.7% in xylene. 40 ~1 quantity of the demulsifier solution in xylene was equivalent to a concentration of 36 ppm and 3600 ppm, respectively, in total in the volume of emulsion, i.e. in solvent + crude. The reason for choosing these concentrations was to ensure that coalescence would be observed under conditions of low and excessive dosing respectively. Observations made from the video recording are presented in Table 2. Figures 8, 9 and 10 show video frames taken from the recording on the effects of Unidem120, BJ18 and PE6400 respectively. Coalescence was observed in all cases when the demulsifier was added. At low concentrations, emulsion drops started to coalesce, grew in size
Fig. 7. The resolution of 10% water-in-Buchan by T803 at room temperature.
crude emulsion
and then sedimented. Coalescence was initially fast (in less than 0.5 s). It then slowed down and eventually ceased. Further demulsifier additions did not cause any further coalescence. Each time a demulsifier drop was added, turbulence was created when the demulsifier solution diffused into the bulk of the emulsion. Such effects also appeared to induce flocculation between drops. When the demulsifier was added neat, without solvent, local coalescence occurred at the spot where the demulsifier drop was placed, but no such turbulence was
R.A. Mohammed
et al./Colloids
Surfaces A: Physicochem.
Eng. Aspects 83 (1994)
Table 2 Microscopic observations of the effect of different demulsifiers on the coalescence of water drops in water-in-Buchan crude oil emulsion Demulsifier Dilute T701 Concentrated T803 Dilute T1301 Concentrated T1301 Dilute T1302 Concentrated T1302 Dilute T1501 Concentrated
T1501
Dilute PE6200 Concentrated PE6200 Dilute PE6400 Concentrated PE6400 Concentrated Concentrated
Unidem120 BJ18
Observations Fast coalescence Drop dissolution Fast coalescence Initially fast coalescence Fast coalescence Drop dissolution Fast coalescence, terminated shortly Fast coalescence, terminated shortly Fast coalescence Drop dissolution Fast coalescence Drop dissolution, gel-like patches Fast coalescence Fast growth, coalescence terminated formation of floes
observed. However, when the emulsion was overdosed, those demulsifiers which produced type I behaviour (constant level of separated water produced by excessive additions of the demulsifier within the overdosing region) appeared to solubilise water drops, whereas those that produced type II behaviour (decreased levels of separated water produced by excessive additions of the demulsifier within the overdosing region) caused water drops to grow in size by coalescing with each other. Coalescence eventually ceased, leaving larger drops. The component IL2 of the Unidem120
blend
showed
a prolonged
demulsifi-
cation action. The blend Unidem120 (Fig. 8) produced fast coalescence. The initial action of the demulsifier BJ18 on the drops was to promote coalescence when added in excessive amounts. The formation of large noncoalescing floes from droplets was observed. This caused coalescence to cease (Fig. 9). Patches which appeared to have a gel-like structure from their flow behaviour were observed. This resulted from the turbulence created by the addition of the demulsifier PE6400 as shown in Fig. 10. This was confirmed in the bottle test by the separa-
261-271
tion of a cloudy
261
water phase. The separated
water
was slightly more viscous than that separated from emulsions treated with demulsifier at low concentrations. Discussion The addition concentrations stabilisation
of various produced
demulsifiers
at different
several effects on the de-
of water-in-Buchan
crude
oil emul-
sions. Microscopic observation revealed that coalescence promoted by the addition of the appropriate demulsifier is very fast but eventually slows down. The efficiency of a surfactant to act as a demulsifier depends on many factors related to the structure of the surfactant, namely, the distribution of the demulsifier molecules throughout the bulk volume of the emulsion, the partition of demulsifier between the phases, as well as on the temperature, pH and salt content of the aqueous phase. Also important are the mode of injection of the demulsifier, the concentration of demulsifier, type of the solvent carrier, amount of water in the emulsion, emulsion age, and type of crude oil. It is possible to explain the behaviour of those surfactants that produced coloured water in the bottle test by considering the ratio of ethylene oxide to propylene oxide, EO/PO. The surfactant T701, for instance, contains a small number of EO groups, and the EO/PO ratio of 0.1 is among the smallest in the surfactant groups investigated. As a result, T701 has a low solubility in water, and would therefore partition strongly to the oil phase. When its concentration exceeds a critical value (referred to as the “critical aggregation concentration” (CAC) by Aveyard et al. [S]), surfactant aggregates begin to form in the oil phase, giving clear water. T1301 and T1501 have EO/PO ratios of 0.15 and 0.16 respectively, and would therefore produce clear water when added to the emulsion. The EO/PO ratio for the surfactant T803 is about 0.57, which is significantly higher than that for T701. T803 partitions strongly to the aqueous phase and would therefore form surfactant aggregates above its CAC value, giving rise to the
268
R.A. Mohammed et al./Colloids
Surfaces A: Physicochem.
Eng. Aspects 83 ( 1994) 261-271
Fig. 8. Photomicrograph of a sample of 10% water-in-Buchan crude emulsion, taken from a video recording, showing the effect of the demulsifier Unidem120 (36 ppm) on the coalescence of water droplets: upper left, before the addition; upper right, after 2 s; lower right, after 10 s, lower left, after 15 s.
yellowish colour. The same explanation would apply to T1302 whose EO/PO ratio is 0.3. The demulsifier blend Unidem120 gave clear separated water in the concentration range lOOOG2000 ppm, and a coloured water phase in a high concentration range (greater than 4000 ppm) as a result of surfactant aggregation in water. The role played by two of the constituents of the demulsifier blend, IL2 and T1301, in the process of demulsification is considered below. The wetting agent IL2, dodecylbenzenesulphonic acid, showed a prolonged coalescence. The addition of IL2 neutralises basic groups present in the interfacial film and wets solids present such as waxes, etc. Hence it is possible to increase the hydrophilicity of asphaltenes constituting the film, and this will alter the stabilising effect on the interfacial film. IL2 alone produced good emulsion
resolution (see Fig. 4). Despite the fact that the surfactant T1301 produced good emulsion resolution with clear water at low concentrations, in the overdosing region, however, a surfactant-rich aqueous phase was observed. The possible mode of action of this surfactant is that it displaces the asphaltene from the oil/water interface. The coalescence of water drops is accompanied by a reduction in the interfacial area of the dispersed phase, and as a result the surface concentration of the demulsifier increases. For some surfactants, a change in phase may occur, leading to the formation of a liquid crystalline phase [ 131. This is believed to be the case with the surfactants PE6200 and PE6400. The microscopic examination of these surfactants for their action on water-inBuchan crude oil emulsions at low concentrations showed fast demulsification. Presumably, the sur-
R.A. Mohammed et al./Colloids Surfaces A: Physicochem. Eng. Aspects 83 { 1994) 261-271
269
Fig. 9. Photomicrograph of a sample of 10% water-in-Buchan crude emulsion, taken from a video recording, showing the effect of the demulsifier BJ18 on the coalescence of water droplets: upper left, before the addition; upper right, after less than 0.5 s; lower right, drop coalescence; lower left, formation of large non-coalescing floes.
factant molecules had replaced the asphaltic layer around the drop by a weak layer before the drops flocculated and coalesced. However, at higher surfactant concentrations, these demulsifiers solubihsed the water drops as shown in Fig. 10. The colour of the separated aqueous phase in the bottle test was yellowish. A possible mode of action of all the surfactants employed except IL2 is to cause the displacement of the asphaltic layer around water drops suspended in the emulsion by a weak layer of the surfactant molecules. However, as coalescence proceeds, the interfacial concentration increases due to the reduction in the surface area. At an interfacial concentration above the so-called CAC, these surfactants would either solubilise the water drops as in the case of type I behaviour or adsorb at the oil/water interface and hence increase the film strength, resulting in type II behaviour.
Coalescence may cease, resulting in reduced demulsifier efficiency. In the case of BJ18 (Fig. 5) the interface between the bulk of the emulsion and the aqueous phase appears to be blurred. This is due to the accumuiation of large water drops at the interface between the oil and the separated phase. The coalescence had advanced among these drops and stopped at an early stage. One possible explanation is that the interfacial concentration of the demulsifier molecules on the drops is increasing as a result of the reduction in the interfacial area. Another possible explanation may lie in the composition of the demulsifier blend lacking enough wetting agent to pull the asphaltic film into the oil. Further experimentation is needed to elucidate these points. Overdosing emulsions by the demulsifier BJlS shows effects different from those mentioned above.
270
R.A. Mohammed et al.lColloids
Surfaces A: Physicochem.
Eng. Aspects 83 ( 1994) 261-271
Fig. 10. Photomicrograph of a sample of 10% water-in-Buchan crude emulsion, taken from a video recording, showing the effect of surfactant PE6400 on the coalescence of water droplets: Upper left, before the addition; upper right, after less than 1 s; lower right, more demulsifier added; lower left, the formation of gel-like patches.
There was no water separation, but instead, a large number of floes were formed which were sterically stabilised against coalescence by a thick film around them after these drops have undergone a rapid initial coalescence. In the first paper of this series [ 121, experimental work on the rheology of the water/Buchan crude oil interface in the presence of the demulsifiers Unidem120 and BJ18 revealed that Unidem120 changes the solid viscoelastic character of a film aged for 8 h into a liquidlike viscoelastic film. This demulsifier successfully resolved the 8 h aged emulsion. However, the addition of the demulsifier BJ18 before creating the water/oil interface prevented the build-up of the asphaltenic film. This demulsifier successfully resolved freshly prepared water-in-Buchan crude oil emulsions. The rheology results showed that a significant reduction in the shear viscosity of the
interfacial films followed the addition of the demulsifier. The incorporation of the IL2 in formulating Unidem120 asphaltenic
was to ensure that films at the interface
well-developed would be dis-
turbed, allowing the other components of the blend to occupy the area of the interface and form weak films. This is the reason why the demulsifier blend Unidem120 is effective in destabilising aged emulsions. Thus it would seem from the results that the blend Unidem120 is a general-type demulsifier that functions by reducing the viscosity of the interfacial film, independent of its age. However, BJ18 is a specific-type demulsifier that should be added before creating the interface in order to prevent the development of asphaltenic viscoelastic films. Hence BJ18 would be suitable for desalting Buchan crude oil when added at relatively low concentrations.
R.A. Mohammed et al./Colloids Surfaces A: Physicochem. Eng. Aspects 83 (1994 ) 261-271
Conclusions The separation is achieved
of water from crude oil emulsions
by the addition
of demulsifier
chemicals
in the oil field. In the first paper of this series, the effects of these chemicals properties
on the shear rheological
of the water/Buchan
have been evaluated. two demulsifier
showed
Unidem120
that the
is to prevent
asphaltenic
a general-
the formation
films at the interface
of the
in the first place
(film inhibitor). It is believed that these films are developed by the adsorption of the indigenous material present in the crude oil at the interface. The way in which this study function the interfacial
the demulsifiers is by reducing
Acknowledgements
and BJ18 func-
ways. Unidem120,
type demulsifier, is able to displace aged interfacial films between water and Buchan crude oil, whereas the function of the demulsifier BJ18, a specific-type demulsifier,
concluded that excessive levels of added demulsifiers (overdosing) may produce the reverse effect. This depends on the concentration and the type of demulsifier. Some demulsifiers may form aggregates in water or in oil to give a viscous phase or to stabilise the emulsion sterically.
crude oil interface
The results
blends
tion in two different
employed
We acknowledge the support from the Arabian Gulf University in Bahrain for the award of a scholarship to R.A.M. and BP International for financial support and permission to publish. We also thank Mr. D. Owen of Grace Dearborn Ltd for supplying the demulsifiers. References 1
in
the viscosity
of
2
film.
In the present work, bottle tests on 10% waterin-Buchan crude oil emulsions using different types of demulsifiers have been performed. At low or moderate
concentrations
of added
emulsion
resolution
However,
at high concentrations
test revealed stant water tration; increased
type
increased
demulsifiers,
with concentration. (overdosing),
this
two types of behaviour: type I, conseparation with increased concenII, reduced
concentration.
uted to the nature
water
separation
with
These effects were attrib-
of the demulsifier.
of this test were combined
The results
with microscopic
8 9 10
obser-
vations on the behaviour of water drops dispersed in the emulsion during the injection of the demulsifier chemicals.
Dissolution
of water
drops
and
subsequent formation of a liquid crystalline phase were mainly responsible for type I behaviour, and steric stabilisation mainly responsible
271
of grown water drops was for type II behaviour. It is
11 12
13
C.G. Sumner, Clayton’s Emulsions and their Technical Treatment, 5th Edn., J. & A. Churchill, London, 1954, Chapter 13. K.J. L&ant, Demulsification Industrial Applications, Surfactant Sci. Ser. 13, Marcel Dekker, New York, 1983, p. 101. S.E. Taylor, Colloids Surfaces, 29 (1988) 29. SE. Taylor, Chem. Ind. (London), October 19 (1992) 770. A.S.C. Lawrence and W. Killner, J. Inst. Petrol., 34 (1948) 821. R.C. Little, Environ. Sci. Technol., 18 (1981) 1184. D.E. Graham, E.L. Neustadter, A. Stockwell, K.P. Whittingham and R.J.R. Cairns, Symp. Surface Active Agents, Sot. Chem. Ind. Colloid Surface Chem. Group, London, 1979, p. 127. R. Aveyard, B.P. Binks, P.D.I. Fletcher and J.R. Lu, J. Colloid Interface Sci., 139 (1990) 128. J. Sjiiblom, H. Soderlund, S. Lindblad, E.J. Johansen and I.M. Skjlrvo, Colloid Polym. Sci., 268 (1990) 389. E.E. Isaacs and R.S. Chow, in L.L. Schramm (Ed.), Practical Aspects of Emulsion Stability, Fundamentals and Application in the Petroleum Industry, Adv. Chem. Ser. 231, American Chemical Society, Washington, DC, 1991, Chapter 2. E.E. Isaacs, H. Huaing, A.J. Babachin and R.S. Chow, Colloids Surfaces, 46 (1990) 177. R.A. Mohammed, AI. Bailey, P.F. Luckham and SE. Taylor, Colloids Surfaces A: Physicochem. Eng. Aspects, 80 (1993) 223. S. Friberg, P.O. Jansson and E. Cederberg, J. Colloid Interface Sci., 55 (1976) 614.
