GEL ASSISTED SEPARATION METHOD AND DEWATERING/DESALTING HYDROCARBON OILS

METHODE DE SEPARATION ASSISTEE PAR GEL ET DESHYDRATATION/DESALAGE D'HYDROCARBURES

English Abstract

A method for separating polar hydrocarbon compounds from a hydrocarbon oil containing polar hydrocarbon compounds comprising the steps of: a) forming a gel in the hydrocarbon oil, and thereafter b) separating the gel from the hydrocarbon oil to produce a separated gel and a separated hydrocarbon oil.

French Abstract

Un procédé de séparation de composés hydrocarbonés polaires d'une huile hydrocarbonée contenant des composés hydrocarbonés polaires comprend les étapes : a) former un gel dans l'huile hydrocarbonée, puis b) séparer le gel de l'huile hydrocarbonée pour produire un gel séparé et une huile hydrocarbonée séparée.

Claims

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CLAIMS:

1. A method for separating polar hydrocarbon compounds from a hydrocarbon oil
comprising polar hydrocarbon compounds comprising the steps of:
a) adding a gel forming agent comprising water to the hydrocarbon oil;
b) subjecting the hydrocarbon oil and the gel forming agent comprising water
to a
process selected from the group consisting of temperature cycling, pressure
cycling, shear
cycling, sonic cycling, and combinations thereof to form a gel comprising at
least a portion
of the polar cydrocarbon compounds, wherein the gel is formed without using a
resin;
c) separating the gel from the hydrocarbon oil to produce a separated gel
comprising water, water soluble salt, and water insoluble salts, and a
separated
hydrocarbon oil, said separation of the gel from the hydrocarbon oil is by a
process
selected from the group consisting of gravity settling, centrifugation,
hydrocyclone
treatment, filtration, and combinations thereof.

2. The method of claim 1 wherein said separated hydrocarbon oil comprises said
polar hydrocarbon compounds that are at least 1 wt% less than in the
hydrocarbon oil.

3. The method of claim 1 wherein said hydrocarbon oil is selected from the
group
consisting of crude oil, crude oil distillate , crude oil residuum and
mixtures thereof.

4. The method of claim 1 wherein said gel has a density greater than the
density of the
hydrocarbon oil at the temperature at which step b) is conducted.
5. The method of claim 1 wherein the amount of gel formed in the hydrocarbon
oil is
in the range of 0.5 to 20wt% based on the weight of the hydrocarbon oil.
6. The method of claim 1 wherein said water is in the range of 0.01 to 10wt%
based
on the weight of the hydrocarbon oil.

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7. The method of claim 1 wherein said temperature cycling is in the
temperature
range of 10°C to 90°C at atmospheric pressure, the number of
cycles is at least 2, and the
total time period of cycling is from 5 minutes to 10 days.

8. A method for dewatering and/or desalting a hydrocarbon oil comprising
polar
hydrocarbon compounds, water and salt comprising the steps of:
a) adding a gel forming agent comprising water to the hydrocarbon oil;
b) subjecting the hydrocarbon oil and the gel forming agent comprising water
to a
process selected from the group consisting of temperature cycling, pressure
cycling, shear
cycling, sonic cycling, and combinations thereof to form a gel comprising at
least a portion
of the polar hydrocarbon compounds, wherein the gel is formed without using a
resin;
c) separating the gel from the hydrocarbon oil to produce a separated gel
comprising water, water soluble salt, and water insoluble salts, and a
separated
hydrocarbon oil, said separation of the gel from the hydrocarbon oil is by a
process
selected from the group consisting of gravity settling, centrifugation,
hydrocyclone
treatment, filtration, and combinations thereof, and thereafter;
d) further separating water and salt from the separated hydrocarbon oil to
provide a
dewatered and desalted hydrocarbon oil.

9. The method of claim 8 wherein said separation of water and salt from the
separated
hydrocarbon oil in step d) is by electrostatic treatment.

10. The method of claim 8 wherein said hydrocarbon oil is selected from the
group
consisting of crude oil, crude oil distillate, crude oil residuum and mixtures
thereof.

11. The method of claim 8 wherein said hydrocarbon oil comprises asphaltenes
and
naphthenic acids.

12. The method of claim 8 wherein said gel is viscoelastic.
13. The method of claim 8 wherein said gel has a density greater than the
density of the
hydrocarbon oil at the temperature at which step b) is conducted.

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14. The method of claim 8 wherein said gel has a density greater than the
density of the
hydrocarbon oil and lower than the density of water at the temperature at
which step b) is
conducted.

15. The method of claim 8 wherein the amount of gel formed in the hydrocarbon
oil is
an amount sufficient to extract at least 1 wt% of the polar hydrocarbons
compounds from
the hydrocarbon oil.

16. The method of claim 8 wherein the amount of gel formed in the hydrocarbon
oil is
in the range of 0.5 to 20wt% based on the weight of the hydrocarbon oil.

17. The method of claim 8 wherein said water is in the range of 0.01 to 10wt%
based
on the weight of the hydrocarbon oil.

18. The method of claim 8 wherein said temperature cycling is in the
temperature
range of 10°C to 90°C at atmospheric pressure, the number of
cycles is at least 2, and the
total time period of cycling is from 5 minutes to 10 days.

19. The method of claim 1 wherein the water soluble salts are selected from
the group
consisting of sodium, potassium, calcium chlorides and any combination thereof
and the
water insoluble salts are selected from the group consisting of calcium
carbonate, calcium
sulfate and any combination thereof and wherein the gel further comprises
crude oil
derived compounds selected from the group consisting of asphaltenes,
naphthenic acids,
naphthenic acids salts such as sodium and calcium naphthenates, organo sulfur
compounds, organo nitrogen containing compounds and any combination thereof
and
organic carbonaceous solids selected from the group consisting of coal, coke,
and any
combination thereof.

20. The method of claim 1 wherein the hydrocarbon oil comprises surface active
polar
hydrocarbon compounds that are surface active at a hydrocarbon water
interface.

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21. The method of claim 8 wherein the water soluble salts are selected from
the group
consisting of sodium, potassium, calcium chlorides and any combination thereof
and the
water insoluble salts are selected from the group consisting of calcium
carbonate, calcium
sulfate and any combination thereof and wherein the gel further comprises
crude oil
derived compounds selected from the group consisting of asphaltenes,
naphthenic acids,
naphthenic acids salts such as sodium and calcium naphthenates, organo sulfur
compounds, organo nitrogen containing compounds and any combination thereof
and
organic carbonaceous solids selected from the group consisting of coal, coke,
and any
combination thereof.

22. The method of claim 8 wherein the hydrocarbon oil comprises surface active
polar
hydrocarbon compounds that are surface active at a hydrocarbon water
interface.

23. The method of claim 8 further comprising adding a demulsifier chemical to
the
separated hydrocarbon oil and subjecting the separated hydrocarbon oil to
electrostatic
treatment to provide the dewatered desalted oil.

24. The method of claim 1 further comprising injecting the separated gel in a
hydrocarbon reservoir.

25. The method of claim 8 further comprising injecting the separated gel in a
hydrocarbon reservoir.

26. A method for recovering crude oil from a subterranean environment
comprising the
steps of:
a) adding a gel forming agent comprising water to a hydrocarbon oil comprising

polar hydrocarbon compounds;
b) subjecting the hydrocarbon oil and the gel forming agent comprising water
to a
process selected from the group consisting of temperature cycling, pressure
cycling, shear
cycling, sonic cycling, and combinations thereof to form a gel comprising at
least a portion
of the polar hydrocarbon compounds, wherein the gel is formed without using a
resin;

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c) separating the gel from the hydrocarbon oil to produce a separated gel
comprising water, water soluble salts, and water insoluble salts, and a
separated
hydrocarbon oil, said separation of the gel from the hydrocarbon oil being by
a process
selected from the group consisting of gravity settling, centrifugation,
hydrocyclone
treatment, filtration, and combinations thereof; and
d) thereafter injecting the separated gel into the subterranean environment
and
recovering crude oil from said environment.

27. The method of claim 1 wherein the gel forming agent further comprises
another gel
forming agent selected from the group consisting of lignin, cellulose, coke
fines, coal
fines, cholesteryl and cholestanyl derived gellation compounds and oxidized
alkyl
aromatic hydrocarbons, and any combination thereof.

28. The method of claim 8 wherein the gel forming agent further comprises
another gel
forming agent selected from the group consisting of lignin, cellulose, coke
fines, coal
fines, cholesteryl and cholestanyl derived gellation compounds and oxidized
alkyl
aromatic hydrocarbons, and any combination thereof.

29. The method of claim 26 wherein the gel forming agent further comprises
another
gel forming agent selected from the group consisting of lignin, cellulose,
coke fines, coal
fines, cholesteryl and cholestanyl derived gellation compounds and oxidized
alkyl
aromatic hydrocarbons, and any combination thereof.

30. The method of claim 1 wherein the gel forming agent consists essentially
of water
and optionally one or more of lignin, cellulose, coke fines, coal fines,
cholesteryl and
cholestanyl derived gellation compounds, and oxidized alkyl aromatic
hydrocarbons.

31. The method of claim 8 wherein the gel forming agent consists essentially
of water
and optionally one or more of lignin, cellulose, coke fines, coal fines,
cholesteryl and
cholestanyl derived gellation compounds, and oxidized alkyl aromatic
hydrocarbons.

Description

CA 02512822 2005-07-21
~ 1
GEL ASSISTED SEPARATION METHOD AND
DEWATERING/DESALTING HYDROCARBON OILS
FIELD OF THE INVENTION
[0001] The invention relates to separating polar hydrocarbons from
hydrocarbon oils.The invention also relates to desalting and/or dewatering
s hydrocarbon oils.
BACKGROUND
[0002] Hydrocarbon oils, particularly heavy crude oils, contain polar
io hydrocarbon compounds such as naphthenic acids, nitrogen and sulfur
containing hydrocarbon compounds and pose problems in refining. There is a
need to upgrade such hydrocrabon oils. Separation of polar hydrocarbon
compounds such as naphthenic acids, nitrogen and sulfur containing
hydrocarbon compounds from crude oils results in upgrading. The present
~s invention addresses this need.
[0003] Hydrocarbon oils, particularly crude oils when produced comprise
varying amounts of water and inorganic salts like halogens, sulfates and
carbonates of Group I and Group II elements of The Periodic Table of Elements.
20 ( The Periodic Table of Elements is the common long form of the periodic
table;
Advanced Inorganic Chemistry by F.A Cotton and G. Wilkinson Interscience
Publishers, 1962) Removal of water from produced crude oils is termed
dewatering and salt removal is termed desalting. Often, the process of
dewatering also desalts the crude oil since water-soluble salts are removed
with
25 the water.
[0004] Dewatering the produced crude oil is desired at crude oil production
facilities as it impacts the value of crude oil and its economic
transportation. The

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presence of salts, especially chlorides of Group I and Group II elements of
The
Periodic Table of Elements, corrode oil processing equipment. In order to
mitigate the effects of corrosion, it is advantageous to reduce the salt
concentration to the range of 1 to 5 ppm or less and water content to about
0.25
to 1 wt% by weight of the crude oil prior to transportation and processing of
the
oil.
[0005] Among the crude oil dewatering and/or desalting methods in use
today, electrostatic separation methods are commonly used. Heavy crude oils
~o containing high concentrations of asphaltenes, resins, waxes, and napthenic
acids
are difficult to dewater and desalt and usually require longer processing
times,
higher process operation temperatures and higher concentrations of demulsifier
chemicals to effect the desired dewatering and desalting. As a result of these
processing requirements for heavy crude oils the process throughput is lowered
1s and costs for dewatering and desalting increased. Consequently, there is a
need
for improved crude oil dewatering and/or desalting methods that improve the
efficiency of dewatering andJor desalting especially with heavy crude oils
containing asphaltenes and naphthenic acids. The present invention also
addresses this need.
SUMMARY OF THE INVENTION
[0006] In one embodiment is a method for separating polar hydrocarbon
compounds from a hydrocarbon oil containing polar hydrocarbon compounds
2s comprising the steps of:
a) forming a gel in the hydrocarbon oil, and thereafter

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b) separating the gel from the hydrocarbon oil to produce a
separated gel and a separated hydrocarbon oil.
[0007] In another embodiment is a method for dewatering and/or desalting a
s hydrocarbon oil containing water and salt comprising the steps of:
a) forming a gel in the hydrocarbon oil,
b) separating the gel from the hydrocarbon oil to produce a
io separated gel and a separated hydrocarbon oil, and thereafter
c) separating water and salt from the separated hydrocarbon oil to
provide a dewatered and desalted hydrocarbon oil.
is DETAILED DESCRIPTION OF THE PRFERRED EMBODIMENTS
[0008] The gel separation method of the instant invention is useful for
hydrocarbon oils comprising polar hydrocarbon compounds. It is particularly
useful for crude oils that contain polar hydrocarbon compounds such as
2o naphthenic acids, asphaltenes and metalloprophyrins. Separation of the
polar
hydrocarbon compounds from the crude oil results in a upgraded crude oil.
Preferred hydrocarbon oils are hydrocarbon oils selected from the group
consisting of crude oil, crude oil distillate , crude oil residuum or mixtures
thereof.
[0009] The desalting and/or dewatering method of the instant invention is
useful for hydrocarbon oils comprising salts, water and mixtures thereof. It
is
particularly useful for heavy and waxy crude oils that are generally difficult
to

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dewater and/or desalt. The salts present in the hydrocarbon oil are inorganic
salts
including halogens, sulfates and carbonates of Group I and Group II elements
of
The Periodic Table of Elements. The concentration of the salts can vary from
about 0.001 to lOwt% based on the weight of the hydrocarbon oil. The process
is
s effective for both water-soluble and water insoluble salts that are
suspended in
the hydrocarbon oil. The water content of the hydrocarbon oil-water mixture
can
vary in the range of 0.5 wt% to 20 wt% based on the weight of the hydrocarbon-
water mixture. The hydrocarbon oil required to be dewatered and/or desalted
can
be a crude oil, crude oil distillate, and crude oil residuum obtained from
~o distillation or mixtures thereof. Generally the water of the hydrocarbon
oil is in a
form wherein the water is dispersed as droplets in the hydrocarbon oil. In
this
form of occurrence the hydrocarbon oil -water mixture is generally a water-in
oil
emulsion.
~5 [0010] The gel of the invention is a complex fluid comprising hydrocarbon
oil, water, water soluble salts such as sodium, potassium and calcium
chlorides,
water insoluble salts such as calcium carbonate and calcium sulfate, organic
carbonaceous solids like coal and coke, crude oil derived compounds such as
asphaltenes, naphthenic acids, naphthenic acids salts such as sodium and
calcium
2o naphthenates, organo sulfur compounds, organo nitrogen containing compounds
and metalloporphyrins. The crude oil derived compounds in the gel are polar
hydrocarbon compounds, preferably surface active polar hydrocarbon
compounds, and more preferably surface active polar hydrocarbon compounds
that are surface active at a hydrocarbon - water interface. Surface activity
of the
25 polar hydrocarbon compounds can be determined using known tensiometric
techniques such as hydrocarbon /water interfacial tension by one of ordinary
skill in the art of interfacial science.

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[0011] The gel has physical properties suitable for separation from the
hydrocarbon oil from which it is formed. Preferably the density of the gel is
greater than that of the hydrocarbon oil at the temperature the method is
conducted. More preferably the density is greater than that of the hydrocarbon
oil
and less than that of water at the temperature the method is conducted. The
density of the gel being greater than that of the hydrocarbon oil and less
than that
of water allows easy separation of the gel from the hydrocarbon oil. The gel
is
preferably viscoleastic. Viscoelastic properties of materials is known to one
of
ordinary skill in the art of theology. By virtue of its viscoelastic nature
the gel
io has an elastic modulus and a viscous modulus. The elastic modulus and
viscous
modulus of the viscoelastic gel can be measured by one of ordinary skill in
the
art of fluid theology using oscillatory visometry techniques. Preferably the
viscous modulus of the gel is at least two times that of the hydrocarbon oil
from
which it is formed at a given temperature. Preferably the elastic modulus of
the
is gel is at least two times that of the hydrocarbon oil from which it is
formed at a
given temperature.
[0012] The first step of the method is to form a gel in a hydrocarbon oil. To
form the gel, a variety of methods can be employed. One non-limiting example
2o includes adding gel forming agents including but not limited to lignin,
cellulose,
coke fines, coal fines, synthetic cross linked polymers, cholesteryl and
cholestanyl derived gellation compounds and oxidized alkyl aromatic
hydrocarbons and water. Water is a preferred gel-forming agent. The amount of
gel forming agent to be added can vary in the range of 0.01 to 20 wt% based on
25 the weight of the hydrocarbon oil. When water is the gel forming agent it
is
preferred to add water also the range of 0.01 to 20 wt% based on the weight of
the hydrocarbon oil. More preferrably water is in the range of 0.01 to 10 wt%
based on the weight of the hydrocarbon oil. Water addition can be in one lot
or in

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aliquots. After addition of the gel forming agent the hydrocarbon oil is mixed
and allowed to stand for a period of time and at a temperature sufficient to
promote gel formation. Mixing can be conducted during or after addition of the
gel forming agent. The preferred temperature of addition and mixing is in the
range of about IS°C to about 85°C and preferred period of time
of addition and
mixing is in the range of 5 minutes to 10 days.
[0013] Another example of forming a gel from a hydrocarbon oil is to
subject the hydrocarbon oil to temperature cycles i.e., increase and decrease
the
io temperature of the hydrocarbon oil in a temperature range several times.
Preferrably the temperature cycling is in the temperature range of 10 °
C to 90 ° C
at atmospheric pressure and the number of cycles is at least 2 and the total
time
period of cycling is from 5 minutes to 10 days. In another example a
hydrocarbon
oil is subject to pressure cycles in a suitable pressure range. A pressure in
the
is range of 14 psia ( 96.46 kPa) to 150 psia ( 1033.5 kPa) is preferred. The
hydrocarbon oil can be subject to both temperature and pressure cycles at the
same time. In yet another example the hydrocarbon oil can be subject to
electrostatic fields. Preferably the electrostatic field is at potentials
ranging from
about 10,000 volts to about 40,000 volts, A.C. or D.C. Voltage gradients in
the
2o electrostatic field range from about 500 volts per inch to about 5,000
volts per
inch, preferably ranging from about 500 to about 1,000 volts per inch.
Residence
times in the electrostatic fields range from about 0.5 to about 120 minutes,
preferably from about 0.5 to about 15 minutes. In yet another example the
hydrocarbon oil can be subject to shear cycling i.e., subject the hydrocarbon
oil
2s to shearing forces of varying intensities. This can be accomplished for
example
by subjecting the hydrocarbon oil to turbulent force field followed by a
quiescent
force field. The hydrocarbon oil can also be subject to sonic treatment
cycles. In
this embodiment the hydrocarbon oil is subject to cycles of ultrasonic waves
by

CA 02512822 2005-07-21
turning on and turning off the ultrasonicator alternately for a period of time
sufficient to form the gel. The temperature, pressure, electrostatic, sonic
and
shear treatments can be conducted on the hydrocarbon oil or on the hydrocarbon
oil treated with gel forming agents. For example, one can treat the
hydrocarbon
oil with water and then subject it to the temperature, pressure,
electrostatic, sonic
or shear treatments to promote gel formation.
(0014] The amount of gel formed in the hydrocarbon oil is an amount
sufficient to extract at least 1 weight percent of polar hydrocarbon compounds
in
~o the starting hydrocarbon oil, preferably at least 1 weight percent surface
active
polar hydrocarbon compounds, and more preferably at least 1 weight percent
surface active polar hydrocarbon compounds that are surface active at a
hydrocarbon - water interface. Preferably the surface active polar hydrocarbon
compounds are nitrogen, oxygen , sulfur and metals containing surface active
is compounds of the hydrocarbon oil. The total amount of polar hydrocarbon
compounds of the hydrocarbon oil can be measured by one of ordinary skill in
the art of organic compound analyses. Preferably, the amount of gel that is
formed is in the range of 0.5 to 20wt% based on the initial weight of the
hydrocarbon oil. More preferrably the the amount of gel that is formed is in
the
2o range of 0.5 to lOwt% based on the initial weight of the hydrocarbon oil.
[0015] The second step of the method comprises separating the gel from the
hydrocarbon oil to produce a separated gel and a separated hydrocarbon oil.
This separation can be accomplished by methods known to one of ordinary skill
2s in the art of separations. The system for separation can be considered as a
liquid -
viscoelastic gel system. Because of the favorable density and viscoelastic
properties of the formed gel the preferred separation method is gravity
settling
followed by removal of the top oil phase. Centrifugation or hydrocyclone

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_g_
techniques can also be employed to increase the rate of separation of the gel
from
the treated oil. Suitable centrifugal force fields can be applied for the
separation.
Suitable filtration methods can also be employed. For example, for gels formed
from crude oils one can use a mineral or rock bed such as a gravel bed as a
s filtration medium to filter off or separate the gel from the oil. Other
filtration
media such as membrane filters can also be used. After gel formation and
separation, the separated hydrocarbon oil contains polar hydrocarbon compounds
that are at least 1 wt% less than the starting hydrocarbon.
~o [0016] The last step of the method for dewatering and desalting is
separating water and salt from the separated hydrocarbon oil. Methods known
for
separating water and salt from the hydrocarbons oils can be employed. These
include methods such as electrostatic separation, centrifugation and
hydrocyclone treatment. Electrostatic separation is the preferred method to
~s separate the water and salts from the separated hydrocarbon oil. Preferably
demulsifier chemicals known to one of ordinary skill in the art of dewatering
and
desalting hydrocarbon oils are added to the separated hydrocarbon oil and
subject
to electrostatic treatment to provide the dewatered desalted oil.
20 [0017] The following non-limiting examples illustrate one embodiment of
the invention.
Step - 1: Gel Formation
25 [0018] 100 grams of a crude oil from Canada was used. To the crude oil
was added 1 wt% water based on the weight of the crude oil. The crude oil was
subject to temperature cycling by heating the crude oil to 60°C and
holding the
temperature at 60°C for 30 minutes. The sample was then cooled to
25°C. The

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heating and cooling was conducted five times. The sample was then allowed to
gravity settle for 5 days.
[0019] After 5 days a gel layer was observed to settle at the bottom of the
s jar containing the temperature cycled oil. The amount of gel formed was Swt%
based on the initial weight of the crude oil. A bright light source held in
front or
behind the jar containing the oil was sufficient to detect the gel layer.
Step - 2: Separation of Oil and Gel
io
[0020] The oil residing on top of the gel was carefully siphoned off to
provide the separated oil (denoted , sample-1). The gel was at the bottom of
the
jar and is the separated gel (denoted , gel sample -G).
~5 Step - 3: Separation of water and salts from the separated oiI
(electrostatic
treatment
[0021] Two samples were examined. Sample-1 was the separated oil
(obtained from step 2) and Sample-2 untreated Canadian crude oil.
Water (5 wt% ) was added to samples 1 and 2 and both samples shaken for 5
minutes on a wrist shaker. A phenol formaldehyde ethoxylated alcohol
demulsifier formulation sold by BASF Corporation as Pluradyne DB7946 was
added to both samples at a treat rate of 100 ppm based on the weight of crude
oil
and the mixture shaken on a wrist shaker for an additional 10 minutes. Both
samples were subject to electrostatic demulsification by applying 830
volts/square inch AC current to the samples at 60C for 1 hour. After
completion
of the procedure the samples were examined and amount of water separating out
recorded. The samples were also analyzed for sodium content by Inductively

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Coupled Plasma (ICP) analyses. Sample -2 did not demulsify under the
conditions of the experiment and no water was observed to split out at the
bottom
of the demulsifier vessel. In Sample-1, 97% dewatering and 80% reduction in
salt content was observed. Thus, formation and separation of the gel results
in
effective dewatering and desalting whereas the untreated crude oil does not
demulsify under the same conditions.
Analyses of the separated gel
[0022] The separated gel ( gel sample -G) from step 2 was subject to
rheological analyses using oscillatory viscometry. A Haake viscometer in the
oscillating mode was used and analyses conducted at 25°C. The separated
gel
( gel sample -G) had a viscous modulus of 32.5 Pascal and an elastic modulus
of
4.4 Pascal. In contrast, the separated oil (sample-2) had a viscous modulus of
7.7
Pascal an elastic modulus of 0.7 Pascal. Thus the formed gel has a
significantly
higher elastic and viscous modulus compared to the crude oil.
[0023] Next, the gel phase was subject to component analysis. The gel was
found to contain 95% oil and 5% water. The oil and water from the separated
gel
o was analyzed. The oil of the gel (Gel Oil) was itself observed to have a
micro-
concarbon residue (MCCR), naphthenic acid (TAN), basic nitrogen and sulfur
level higher than the separated oil (sample-2) obtained from step -2.
Additionally, the surface activity of the oil from the gel was an order of
magnitude higher than the surface activity of the separated oil. This is
evident in
~s the oil/water interfacial tension { IFr (o/w) } values. Thus, in the method
of the
invention the gel extracts the most surface active sulfur, nitrogen and
naphthenic
acid compounds. Results of the analyses are shown in Table-1..

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Table-1
Oil S (1o) Total N Basic TAN MCCR IFT (o/w)
N


(ppm) (ppm) dynes/cm


Separated Oil 3.0 3800 960 0.99 6 20


Gel Oil 4.0 4700 1200 1.82 13 2