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Trondheim Emulsions 6-23-03 1
Asphaltene and Naphthenate Mechanisms of EmulsionStabilization in water-in-crude oil Emulsions
Marit-Helen Ese, Keith L. Gawrys andPeter K. Kilpatrick
(919) 515-7121; (919) 515-3465 (fax)[email protected]
Symposium Honoring Dr. Jan Czarnecki on theOccasion of his 65th Birthday
4th International Conference on Petroleum Phase Behavior5th International Symposium on the Chemistry and Physics of
Petroleum-Water EmulsionsTrondheim, Norway, June 23-26, 2003
Trondheim Emulsions 6-23-03 2
MotivationProcessing naphthenic acid-based crudes involves:
Emulsion problems - severe separation and transport problems - bad oil quality
Foam problems during transportPrecipitation of metal salts based on naphthenic acids(naphthenates)
- separation problemsCorrosion problems during refining and transportCatalyst problems
- refining problemEnvironmental problems (bad water quality)
Trondheim Emulsions 6-23-03 3
OutlineRecent Observations on PetroleumEmulsions
Naphthenate Molecular Structures
Emulsion Stabilization Results
Optical Polarizing Microscopy
Neutron Scattering of Emulsions: TheCore-Shell Model
Conclusions and Acknowledgements
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CEF Design and Measurement Principles• CEF is a measure of the electric field
strength required to induce the flow ofcurrent through a w/o emulsion
• Surface-active crude components form abarrier to current flow until electromotiveforce causes film rupture and watercoalescence
0
0.005
0.01
0.015
0.02
0.025
0.03
0 0.4 0.8 1.2 1.6
Cur
rent
(mA
)
Electric Field (kV/cm)cef
+
- V
V
V
+
-
+
-critical electric field - water bridges
electrodes, conductivity jumps
+
- droplet chains lengthen and bridge
entire gap
0 kV/cm droplets form short chains parallel to electric field
+
-
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Water-in-Crude Oil Emulsion Stability:Asphaltenic vs Naphthenate Mechanism
0
0.5
1
1.5
2
2.5
3
0 2 4 6 8 10
water
= 0.30, T=60oC, Salinity = 1% NaCl
AHHOB4B6CSABANSTHSJVAlbaSMSCSAfricac.e.f.
y = 0.34582 + 0.27709x R= 0.96401
Cri
tical
Ele
ctri
c Fi
eld
(kV
/cm
)
Asphaltene x Delta H/C
Block 17 Africa Crude – High TAN #
Strong Correlation for Asphaltenic Crudes
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Dalia (Block 17 West Africa) W/O Emulsion Stability:Goldszal et al., TotalFinaElf, Paper 56f, Spring AIChE Meeting (2002)
0
10
20
30
40
50
60
70
80
90
100
4 5 6 7 8 9 10 11 12 13 14final pH
0
0.1
0.2
0.3
0.4
0.5
0.6stability (% non decanted water at 48 h)
surface tension (mJ/m²)
surface tension
stability
TANc
TANc
Sudden Transitions in W/OEmulsion Stability w pH
Trondheim Emulsions 6-23-03 7
Emulsion Stabilization Mechanisms
Solvation Shell
Electrostatic Steric Gibbs-Marangoni 3rd Phase Film
Convective Flow dueto Film Drainage
Surfactant Diffusion dueto Interfacial Tension Gradient
Molecular Aggregate
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Mechanism of Adsorption of AsphaltenesTo O/W Interfaces and Film Formation
bulk asphaltenes (cA)
Fickian diffusion
near-interface asphaltenes
cAs = 2cA(Dt/ )1/2
adsorption (rate constant = ka)
adsorbed, unconsolidated asphaltenes ( 1)
adsorbed, consolidated asphaltenes ( )
consolidation (rate constant = kc)
(CA)
kA
ΓA
kc) ΓC
Trondheim Emulsions 6-23-03 9
Naphthenate’s ability to organize intolamellar structures (LLC)
Illustrated as
β-Cholanic Acid (CA)
Acid/Soap Ratio ca. 4-6
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Experimental Procedure: Emulsion Type Studies
Oil-phase
Water-phase
Equilibrate for about 24 hbefore EMULSIFICATION(15,000 rpm for 3 min)
Centrifugation
Emulsion
Characterization:Water- or Oil continuous
Watercontinuous
Oilcontinuous
Oilcontinuous
Watercontinuous
Pure water Pure oil
Trondheim Emulsions 6-23-03 11
0
0.5
1
1.5
2
2.5
3
3.5
8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13
Initial pH in Aqueous phase
Tran
sitio
n C
once
ntra
tion
(wt%
CA-
mat
eria
l in
emul
sion
)
Water
Brine (3.5 wt% NaCl)
CA-concentrations where oil continuous emulsions first appear Studied as a function of initial pH in the aqueous phase
A/S~35A/S~15
A/S~4
A/S~8A/S~2
A/S~3
A/S~320
A/S~80
A/S~1330
A/S~0.4
A/S~0.15
A/S~910
A/S~8770
A/S~54400
W/O Emulsions
O/W Emulsions
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Polarizing Micrograph: 1.5 % (w/w) CA; pH 11.5 W/O Emulsion
30 µm
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Emulsion Studies of Asphaltenic Filmswith Added Cholanic Acid/Soap
0.5 % (w/w) HO asphaltenes in 50:50 (v/v)heptane: tolueneIncreasing amounts of β-cholanic acid(0.025 – 1.5 %, w/w)Varying pH (9-13) of aqueous phase; 50:50(v/v) water:oil in emulsion
Trondheim Emulsions 6-23-03 14
Emulsion StabilityCA and Asphaltene stabilized emulsions at varying pH
(centrifuged at 10 000 rpm for 30 min)
(oil/water = 50%/50%)
Emulsion Stability - CA+Asph in Brine at varying pH
0
10
20
30
40
50
60
70
80
90
100
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
wt% CA-material in the emulsion
wt%
Brin
e re
cove
red
pH = 13.2pH = 12.5pH = 12.0pH = 11.5pH = 10.8pH = 10.0
E4
E1
E2E5
E6
Unstable
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Experimental Design: SANS
Deuteratedwater with
Hydrogenated CA-soap andHydrogenated
HO Asphaltenes
DeuteratedHepTol
Equilibrate for about 24 hbefore EMULSIFICATION(15,000 rpm for 3 min)
Trondheim Emulsions 6-23-03 16
SANS of Emulsions Stabilized by Different Mechanisms
0.01 0.10.01
0.1
1
10
100
1000
10000
Q (Å-1)
I(Q
) (cm
-1)
E1 - A E2 - A+0.025% CA E3 - A+0.05% CA E5 - A+1% CA E6 - A+1.4% CA E7 - 1% CA E8 - 1.5% CA E9 - 2% CA
E4 was destabilized,making SANS-measurement of this emulsion impossible
Jump in Intensity E3 to E5; morethan order of magnitude
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Emulsionsstabilized by
0.5 wt%asphaltene in the
oil phase andincreasing amountof CA added to the
aqueous phase(brine at pH = 12)
The emulsions were diluted in mineraloil (1:3) before the
pictures were taken
35.7µm
E40.1% CA + Asph
E51% CA + Asph
E61.4% CA + Asph
E81.5% CA
E30.05% CA + Asph
E10.5% Asph
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Drop Size Distribution data obtained for Emulsion E6 total CA-concentration in the emulsion is 1 wt%
Aqueous phase: brine at pH = 12Oil phase: 0.5wt% Asphaltenes in 45/55 Heptane/Toluene
E6
0
20
40
60
80
100
120
140
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 1010.5 11
Droplet Diameter (µm)
Dro
plet
Fre
quen
cy
Mean: 3.71 Median: 3.67Min: 0.69Max: 10.59
d32 = 5.01
skewness0 = 83
35.7µm
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Emulsion Stability & Sauter Mean Droplet Diameters (d32)(water phase: brine at pH = 12)
44915.2701.5E8
461135.6001.0E7
43835.010.51.4E6
702567.520.51.0E5
92155520.10.50.10E4
891276.910.50.050E3
571656.490.50.025E2
292468.160.50E1
% waterresolved
Skewnessabout origin
d32 (µm)wt% asphin the oil phase
wt% CAin the emulsion
Sample
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Transition from Asphaltene- to Liquid Crystal Stabilized Emulsions
E40.1% CA + Asph
E51% CA + Asph
E61.4% CA + Asph
E71% CA
35.7 µm
Trondheim Emulsions 6-23-03 21
The Core-Shell Model
rcore
ρcore
t
ρshell
ρoil
d-Water(Brine)
d-HepTol(45/55)
Fixed parameters:ρoil ρcore rcore
Varying parameters:ρshell t
Hydrogenated Surfactant Film, w/ or w/o Entrained d-Solvent
Trondheim Emulsions 6-23-03 22
Polydisperse Core-Shell Model Fits
0.01
0.1
1
10
100
1000
Inte
nsity
(cm
-1)
3 4 5 6 7 8 90.01
2 3 4 5 6 7 8 9
Q (Angstrom-1)
E7 (1% wt CA emulsion)
avg core rad (A) = 28000 (fixed)avg shell thickness (A) = 115.37 ± 0.126overall polydispersity (0,1) = 0.44 (fixed)
SLD core (A-2) = 5.89e-06 (fixed)SLD shell (A-1) = 4.1193e-06 ± 1.18e-09
SLD solvent (A-2) = 6.08e-06 (fixed)bkg scattering (cm-1) = 0.001 (fixed)
E6 (1.5% wt CA + 0.5% wt HOA emulsion)
avg core rad (A) = 25100 (fixed)avg shell thickness (A) = 116.57 ± 0.137overall polydispersity (0,1) = 0.44 (fixed)
SLD core (A-2) = 5.89e-06 (fixed)SLD shell (A-2) = 1.0558e-06 ± 3.51e-09
SLD solvent (A-2) = 6.08e-06 (fixed)bkg scattering (cm-1) = 0.001 (fixed)
Water drivenfrom interface
Consistent with~2-5 % CA inlamellar film
Trondheim Emulsions 6-23-03 23
Emulsion StabilityCA and Asphaltene stabilized emulsions at varying pH
(centrifuged at 10 000 rpm for 30 min)
(oil/water = 50%/50%)
Emulsion Stability - CA+Asph in Brine at varying pH
0
10
20
30
40
50
60
70
80
90
100
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
wt% CA-material in the emulsion
wt%
Brin
e re
cove
red
pH = 13.2pH = 12.5pH = 12.0pH = 11.5pH = 10.8pH = 10.0
E4
E1
E2E5
E6
Unstable
Trondheim Emulsions 6-23-03 24
Effect of blending B6 and Africa crude oilon emulsion stability
0.0 0.2 0.4 0.6 0.8 1.00
20
40
60
80
Africa StockB6 Stock
% W
ater
res
olve
d
ΦAfrica
Destabilization of asphaltene-stabilizedemulsions by acidicresins
Napthenic acidand naphthenate-stabilizedemulsions
Trondheim Emulsions 6-23-03 25
ConclusionsMixtures of naphthenates and naphthenic acids formextremely stable emulsions of water-in-oil stabilized by a“third phase” liquid cyrstalline film mechanism
The concentration and pH range over which this occurs ismodest and very sensitive to details of molecular architec-ture, consistent with simple molecular packing arguments
Naphthenates dramatically destabilize asphaltenic filmemulsions in a window of composition and pH, suggestingjudicious blending of crudes and petroleum fluids tominimize emulsion formation
Trondheim Emulsions 6-23-03 26
Conclusions (con’t)Small Angle Neutron Scattering (SANS) of Deuteratedwater in Deuterated oil emulsions, but stabilized byHydrogenated films of surfactants with or without entrainedDeuterated solvents, provides a very effective means ofcontrast variation to elucidate film structure andcomposition
Our results on very simple model systems are consistentwith obervations on crude oil systems of great currentinterest
Trondheim Emulsions 6-23-03 27
NSF Grant CTS-981727
Shell, ChevronTexaco, ExxonMobil, Ondeo-Nalco, Champion Technologies
NIST and ExxonMobil – Eric Sirota, Min Lin
Argonne National Lab -- Papannan Thiyagajaran, Dennis Wozniak
Acknowledgements