Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ 27
r~
~ETHOD FOR REMOVING INSOLUBLE SULFID~
AT OIL/WATER INTERFACE5
~ield of the Invention
Solid metallic sulfides are frequently
S encountered in petroleum processing equipment. In
operations involving water and oil phase separations, such
as in field dehydration systems, desalting plants, and the
like, ~hese solid me~allic sulfides are p~rticularly
troublesome. They have low solubility in water or brines.
The oleophilic chlracteristics of sulfides cause them to
collect at the oil/water interface~ to form sludges of a
complicated nature. These sludges are generally referred
to as "padsnO The pads caused by the presence of the
troublesome metallic sulfides drastic~lly interfere with
the efficient separation of crude oil from the associated
agueous medium. Under thes~ conditions, a clearly defined
interface between the oil and water phases is not present
due to the emulsification effect exerted by the solid
metallic sulfides. As a consequence, phase separation,
desalting, and similar processes required in crude oil
production and refining are slowed or interrupted. The
presence of -solid metallic sulfides at the oil/water
interface ~orces large time, chemical, and energy
expenditures to be utili~ed. This holds true for the oil
phase, which must be purified before entering sefineries,
as well as the aqueous phase prior to dispcsal or
discharge. In addition, these metallic sulfide-containing
pads create fouling of oil handling equipment~ interfere
with control and sensing equipment, and produce inherent
corrosion at the points of contact within oil field
vessels or other metallic equipment. Such ef~ects as these
add to the cost and complexity of petroleum processing. In
addition, the quality and suitability of the oil for
subsequent uses may be reduced by th~ occurrence of these
interfacial sulfide pr~cipitates~
Prior Art
In the past~ a variety of c:hemical methods have
been employed in an attempt to allev.iate the problems
1~227~L~
caused by solid metallic sulfides presellt at oil/water
interfaces. Earlier efforts to 801Ye this problem include
the use of inorganic chloride containing chemicals such as
hydrochloric acid, hypochlorous acid, alkali and alkaline
earth hypochlorites, and chlorine. In addition, organic
chemicals such as acrolein and various nonionic, CAtioniC~
and anionic surfactants have been employed.
Most of the inorganic chlorine-containing
chemicals are required in rela~ively high concentrations
and are very corrosive to the steels and other metals used
in the construction of typical petroleum producing
equipment. The pH's of the treated media are typically low
under these conditions. The chemicals may also react with
the petroleum, yielding hydroehloric acid and organic
chlorides by decomposition. This alteration of the
petroleum composition creates products that are poisonous
to catalysts used in the refining process, which seriously
affects refinery operations. Although the rate of solid
metallic sulfide removal by hydrochloric acid and chlorine
can be economically rapid enough, the action of
hypochlorous acid and hypochlorite salts is quite slow.
Acrolein can be quite useful in removing
insoluble metallic sulfides. Ho~.~ ver/ typical applications
of acrolein generally require long contact periods with
the pads at the oil/water interfac*. Frequently, several
applications cf asrolein are required to eli.~ninate the
total insoluble metallic sulfide pad. The large amounts of
acrolein chemical consumed under these circumstances can
become quite expensive
Most applications involving nonionic, cationic,
and anionic surfactants tend to remove the oil adhering to
the solid metallic sulfide pad present in the oil/water
interface but do not eliminate the solid metallic
sulfides, so the interfacial pads reform quickly.
~hlorine dioxide has been known to successfully
remove hydlogen sulfide from aqueous media for many
decades. U.S. Patent 4,077,87~ discloses a process using
chlorine dioxide to remove undesirable .~oluble sulfides
I
-3 ~22~
fron\ aqueous systems contaminated with small amounts of
petroleum oils. However, removal of oll/water interfaclal
pads in bulk oil/water syst~ms by chlorine dioxide in
order to improve oil recover~ has not previously been
5 k nown .
Furthermore, any use of chlorine dioxide to
treat soluble metallic sulfides is limited to aqueous
media. It is generally known that the ~ffects o~ solvents
on chemical reaction~ can sreatly alter observati~ns.
Chlorine dioxide is not known to he effective in treating
insoluble metallic sulfides in the presence of oils.
Although some chemical approache~ are available
for removing metallic sulfide-contalning pads at an
oil/water interface, high cost or poor performance
characteristics are usually encountered~ The inventive
process described hereinafter utilizes a chlorine dioxide
application to treat the bulk properties of the oil/water
interfacial pad caused by the solid metallic sulfides.
This process is especially useful in that it allows rapid
and low cost phase separations in treatment of crude oil
to remove water, solids, salts, and other impurities.
~hese steps are required beEore the petroleum can be sold,
transported, and refined.
Specific references to chlorine dioxide removing
insoluble iron and manganese sulfides in aqueous media can
be found. However, references pertaining to other specific
insoluble metals are not prominent in the literature. The
inventi~e discovery of the fast action of chlorine dioxide
in removing cer~ain insoluble metallic sulfide pads in
oil/water interfaces present in actual oil field tanks was
unpredictable from prior processes and ~uite surprising.
In practicing the inventive process for
removing insoluble metallic sulfides in oil/water
separation equipment, various water quality improvements
may also result as a side effect of the treatment,
depending upon the amount of chlorine dioxide used and its
point of applicationO S~ch improv~ments may include
solu~le sulfide removal, biocidal effects and others.
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However, these benefits are ancil1ary to the inventive
process, which provides oil recovery and phase ~eparation
improvements regardless of whether these ancillary
benefits are achieved.
ummary of_the Invention
Chlorine dioxide is used in a process for
eliminating the ef~ects o insoluble metalllc sulfides in
impeding the separation of oils from aqueous phases
encountered in petroleum processing systems~ This process
involves adding aqueous chlorine dioxide solution to the
oil/water mixture containing an insoluble metallic sulfide
interfaciâl pad. The process results in a clearly defined
oil/water interface.
Descri~tion of the Invention
Insoluble metallic sulfide interfacial pads are
defined âS interfacial interferences caused when metals
and metallic ions combine with sulfur, hydrogen sulfide,
or soluble sulfide salts to form insoluble metallic
- sulfides. Examples of such metals and ions include, but
~ are not limited by, Ag, Ca, Cd, Co, Cr, Cu, Fe, Mn, Ni,
Pb, Sn, Tl, and Zn, separately or in any combined ratio.
These insoluble metallic sulfides become attracted to the
oil phase of an oil/water system, and collect at the
oil/water interface. Typical oils found in oil field
practices combined with these insoluble m~tallic sulfide
pads can experience troublesom~ interacial interferences
in contact with aqueous media. This situation can also
arise when dissolved gases and undissolved yases are
present.
Troublesome interfacial sulfide pads can be
found in oil field tank~, free-water-knockouts, heater
treaters, desalters, refiner~ distillate receivers, sumps,
pits, and the like. These pieces of e~uipment can be
involved in constant-flowing, intermittent-flowing, and
static fluid conditions
Chlorine dioxide solutions can be obtained from
a variety of manufacturing processes. Typical processes
include acid-chlorite, acid-chlorate, acid-hypochlorous
~2;2~71~
--5--
acid-chlorite, acid-hypochlorite salts-chlorit~,
chlorine~chlorite, and the like~ and any vari~tion of
these systems comprised o~ process adjuvants.
The application of chlorine dioxide can be made
into quiet, nonagitated petroleum processing equipment,
Additionally, applications of chlorine dioxide can be
accompanied by agitation of fluids within such equipment.
The temperature of the systems to which chlorine
dioxide may be applied varies w~dely. The effectlveness of
the inventive process is not very dependeZt on the
temperature, and is found to be useful in petroleum-water
separations at temperatures from low am~ient to 200C, or
thereabouts. Some systems are operated under pressures to
allow higher temperatures and lower fluid viscosities,
which is helpful in the sedimentation and separation o~
phases. Higher temperatures appear to ]essen somewhat the
amount of chlorine dioxide required.
By the use of chlorine dioxide, insoluble metal
sulfides are converted to a soluble form. Presumably, the
petroleum oil that wets, i.e., clings to the surface of,
the insoluble metal sulfide is able, after chlorine
dioxide treatment, to migrate to the petroleum oil phase
and is no longer a component oE the emulsion. This then
permits the clean separation of the petroleum oil from
water phases. The mode of action of chlorine dioxide as
described is believed to be ~orrect and ~s given for
better understanding~ but is not intended to limit the
scope of the invention.
Aqueous chlorine dioxide solutions c~n be added
to oil/water systems in a variety of different ways in
order to remove in~oluble interfacial sulfide pads. ~he
chlorine dioxide may be added into the inlet lines
upstream of the equipment containing the troublesome
int rfacial sulide pads. Applications may also be made
directly into the individual oil field eqllipn\ent. The more
cost effective applications appear to be those made into
the oil phase proper.
Applications of chlorine dioxide can be made
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into oil field vessels experiencing continuous flowing,
intermittent flowing, and stagnarlt fluid conditions. The
time required for complete pad removal is lessened if the
ve~sel can be agitated, e.~., such as rolling tank
contents with gas.
Successful applications utilize up to about
three moles chlorine dioxide per mole of insoluble
metallic sulfide. Th~se conditions result in lowering the
pH of a given system by tWQ or less pH units for an
initial system pH ran~e of A to lC for metallic substances
containing chromium, iron, manganese and Yanadium. Systems
comprised of cadmium, ~obalt, lead, silver, tin, and
tantalum appear to require more aoidic final pH values.
Lower amounts of chlorine dioxide, and subsequently lower
drops in system pH levels, are realized if the process is
carried out at higher temperatures.
The invention describing a method for removing
insoluble metallic sulfide pads at oil/water interfaces is
demonstrated by the following non-limiting examples
XAMPLE 1
Ten screw cap test tubes were each filled with
1.0 mL ferric chloride solution ~0.037M) and l.OmL freshly
prepared sodium sulfide solution (0.037M). ~lack iron
sulfide precipitates formed immediately. These
heterogeneous mixtures were diluted with 5.0 mL ASTM brine
solution t4.2%, American Society Testing Materials~
formula a, A.S.T.~. D-1141-52, Table 1, section 4). These
solutions gave 3.7xlO 5 moles of sulfide and had a pH of
7Ø Then, 1.0 mL Nujol (trademark) mineral oil was added,
the tubes were capped, and shaken vigorously for one
minute. A heavy iron sulfide pad formed at the oil/water
interface in all tubes. Next, various amounts of chlorine
dioxide solution (0.0266M) were added to each of the tubes
and the results recorded.
`~J
7 ~3L2~27~
T~BLE 1
Moles C102 Einal Moles 5ulf.id~
added ~ H to mole~ Observations
1.33 x 10-6 7 27.8 P~d Present
51.99 x 10-6 6.6 18.~ Pad broke, but
rapidly reformed
2.39 x 10-6 6.3 15.0 Pad broke, but
slowly reformed
2.66 x 10-6 6.1 13.7 Pad disappeared
102.79 x 10-6 6.0 13.3 Pad disappeared
2.92 x 10-6 5.0 12.7 Pad disappeared
3.32 x 1n~5 4.5 11~1 Pad disappeared
3.98 x 10~6 4,0 9.3 Pad disappeared
7.96 x 10-6 3.0 4.6 Pad disappeared
151.06 x 10-5 2.0 3.5 Pad dis~ppeared
2.12 x 10-5 1.0 1.7 Pad disappeared
This example demonstrates the ability of
chlorine dioxide to remove an iron sulfide pad in a
synthetic oil/water system. It is Rlso clearly shown the
pad can be removed without causing the p~ of the aqueous
solution to drop by ~ore ~han 0.9 of a p~ uni~.
EXAMPLE 2
Three screw cap test tubes wer~ each filled with
0.5 mL ferric chloride solution (0.037M) and 0.5 mL
~reshly prepared sodium suli~e solution (0.C37M). The
black iron sulfide precipitat~s were dilu~ed with 2.0 mL
deionized water and vi.gorously shaken with 9,5 mL various
oils to provide a heavy pad at ~he oil/water interfaces.
Then, 3,0x10-6 moles chlorine dioxide were added. The
initial pH of 6.5 fell to 6~0 after treatment with the
chlorine dioxide, at a ratio of 0.62 moles o$ sulfide to
1~0 moles of chlorine dioxide~
TABLE 2
~il Used _ Results
Mineral oil Pad remoYed; did not reform
23 API California Cr~ude ~ad removed; did not re$orm
35 API Arkansas Crude Pad remo~e~; ~id not reform
This e~ample dernonstrates that chlorine dioxide
~22;~
is effective in removing pads not only at the oil/water
interface oi synthetic oils, but also ~t interfaces
between aqueous phases and actual crude oils.
EXAMPL~ 3
Eight screw cap test tubes were charged with
equal amounts of 0.037M ferric chloride and 0.037M sodium
sulfide ~olutions. Then, 4.2~ ~STM brine solution and
mineral oil were added. The tub~s were capped and shaken
to obtain a heavy oil/water interfacial pad. These
solutions had an initial pH of 7~0. Then, l.llx10 5 M
chlorine dioxide solution was added, and the observations
recorded.
TABI.E 3
Moles of
Ferric Chloride mL 4.2% mL Final
15 & Sodium Sulfide ASTM Brine Nu~ pH Observations
3.7 x 10 6 5.0 1.0 - No pad formed
initially
1.85 x 10 5 5.5 1.0 4~0 Pad removed
3.7 x 10-5 6.0 1.0 4.0 Pad removed
203.7 x 10 6 10.0 1.0 _ No pad formed
initially
3.7 x 10 5 21.0 1.0 ~.0 Pad removed
3.7 x 10 5 6.0 S.0 6.0 Pad removed
3.7 x 10 5 4~U 13.0 7.0 Pad removed
253.7 x 10 5 11.0 1~,0 7,0 Pad removed
These exa~nples demonstrate the ability of
chlorine dioxide to remove various amounts of interfacial
pads in varying ~il to water systems~
EXAMPLE 4
The ability of chlorine dioxide to remove
oil/water interfacial sulfide pads in systems with varying
pH's can also be demonstrated. Several screw cap test
tubes were charged with 1.48x10 6 moles of ferric chloride
and 1.48x10 6 moles sodium sulfide. Each of these mixtures
was diluted with 1.0mL various pH buffer solutions and
0.5mL mineral oil. Upon shaking, heavy interfacial pads
formed. Then, 0.037M chlorine dioxide solution was added
27~
and, in all cases, the pad was removed~
TABLE 4
Initial Moles Final
~o~ L~m æ~l ~a~
~.
Deionized System 6 9.74 x lQ 7 5
4.2% ASTM brine 5 9.74 x 10 7 5
Phthalate 4 9.74 x 10 7 4
Phthalate 5 9.74 x 10 7 S
Acetate 5.5 9.74 x 10~7 5.5
Phosphate/Citrate 6.5 1.95 x 1~ 6 6
Phosphate 6 2.9~ x lQ 6
Phosphate 7 3~9 x 10 ~ 6
Tris 6.5 9~74 x 10--7 5.5
Phosphate ~ ~.87 x 10 6 7
Tris 8.5 5.84 x 10 6 7
Borate 8 3.8~ x 10 6 7
Borate 8.S 4~85 x 10 6 8
Tris 9 6.01 x 10 ~ 8.5
~orate 10 6.Ul x 10-6 8
Carbona~e 10 4.~7 x 10 6 8
EXAMPLE 5
Chlorine dioxide can remove oil/water
interfacial sulfide pads under a wide variety of
temperatures. Several screw cap test tubes were charged
with l.OmL ferric chloride (0.037M~ and l~O~IL freshly
prepared sodium sulfide (0.037M). The re.sulting mixtures
were diluted with 5.0mL of aqueous medium and l.OmL
mineral oil. Upon vigorous shaking, heavy sulfide
interfacial pads formed. Then, the tubes were heated to
various temperatures. Chlorine dioxide solution was then
added at the elevated temperature and r in all cases, the
sulfide interfacial pad was removed.
TABLE 5
Initial Temperature Moles Final
Medium pH _ (~C~
4.2% AST~ 7 21 7.~ x 10 6 6
4.2% ASTM 7 35 5~57 x 10 6 7
4.2% ASTM 7 4b 5.13 x 10 6 7
!
~2~7~.~
--10`-
Initial Temperature Moles FinalMedium ~ (C) _ _C~ E~
4.2~ ASTM 7 554.46 x 10 6 7
4.2% ASTM 7 644.23 x 10 6 7
54.2~ ASTM 7 804.12 x 10 6 7
4.2% ASTM 7 964.12 x 10 6 7
0.42~ ASTM 7 211.0 x 10 5 4
O . 42% ASTM 7 4~8 . 91 x 10 5 5
0.42% ASTM 7 558.36 x 10 6 5
lQ0.42~ ASTM 7 708.36 x 10 6 5
n . 42~ ASTM 7 947.8 x 10 ~ 5.5
Phosphate ~uffer 6 ~1 1.78 x 10 5 4
Phosphate Buffer 6 40 1.73 x 10 5 5
Phosphate Buffer 6 55 1.67 x 10 5 6
Phosphate Buffer 6 66 1.67 x 10 5 6
Phosphate Buffer 6 90 1~67 x 10 5 6
Tris Buffer 7 216.13 x 10 6 6,5
Tris Buffer 7 425,5 ~ 10-6 7
Tris Buffer 7 535.5 x 10 6 7
Tris Ruffer 7 645.35 x 10 6 7
Tris Buffer 7 885.35 x 10 6 7
~orate Buffer 8 211.39 x 10 5 5
Borate huffer ~ 371.23 x 10 5 5.5
Borate Buffer 8 501.11 x 10 5 6
Borate Buffer ~ 701~11 x 10 5 6
Borate ~uffer 8 341.~ x 10 5 6
These results demonstrate the effect of higher
temperature on the ability o~ chlorine dioxide to remove
interfacial ~ulfide pads. Adding heat to the oil/water
system allows less chlorine dioxid~ to be used to
accomplish pad removal. This decrease in the amount o~
chlorine dioxide produces an aqueous system with a higher
pH.
EXAUPLE 6
Agitation of the oil/water system can greatly
decrease the time required for a given amount of chlorine
dioxide to remove an interfacial sulfjde pad. Two 250mL
flasks were charged with 5,0~L each of ferric chloride
~2~714
~0.037M) and ~odium sulfide (0.037M) solutions. These
mixtures were then diluted with 100ml ASTM brine ~4.2~
and 50ml mineral oil. These sy~tems were shaken tn create
a heavy interfacial sulfide p~d. Then, 8.1 x 10-6 moles of
chlorine dioxide solution was added to the top portion of
one flask without agitation. Six minute~ were required to
completely remove the pad under the undis~urbed
conditions.
Again, 8.1x10 6 moles chlorine dioxide was added
to top portion of the other flask. A magnetic stirring bar
was used to create a minor agitation condition at a
spinning rate of 20 cps. Under these conditions, the pad
disappeared in 30 seconds.
EXA~PLE 7
Chlorine dioxide can be used to remove oil/water
interfacial sulfide pads containing metals other than
iron Several screw cap test tubes were charged with a
soluble metallic salt and an equimolar amount of freshly
prepared sodium ~ulfide solution. These mixtures were
diluted with 4.2% ASTM bri.ne and mineral oil. Then,
chlorine dioxide solution was added which caused removal
of the interfacial sulfide pad in all casefi. The data are
~isplayed below.
Metal Moles mL ASTM mL Init.ial Moles Final
Salt Sulfide Brine Oil _ pH ~ Z____ __E~L
MnCl~ 3.7x10 5 7 1 7 2.655 x 10 6 6.9
CrC13 3.7x10-5 7 1 7 l.~6 x 10-6 6.9
VC13 3.7x10-5 8 1 7 2.655 x 10-6 6
MnC12 3.7x10 5 12 1 8 2.78 x 10 5 8
MnC12 3.7x10-5 5 10 8 2 23 x 10 5 8
MnC12 3.7x10 5 7 15 ~ 2.23 x 10 5 8
CdC13 3.7x10-5 7 1 7 3.1 x 10-5
CoC12 3.7x10-5 7 1 7 5.31 x 10-4
Pb(OAc)2 3.7x10 5 7 1 7 1.06 x 10 3
AgNO3 3.7x10-5 7 1 7 5.31 x 10 4
SnCl~ 3.7x10-5 7 1 7 1.06 x 10-3
Tl(OAc) 3.7x10 5 7 1 7 1.33 x 10 4
~2Z7~4
-12- -
Metal Moles mL ASTM mL Initial Moles Final
Salt Sulfide _ ine oil pH
Complex Mixture:
FeCl3 1.85xlO 5 110 50 7 ~.1 x 10 6 5.5
CoC12 1.85xlO 5 110 50 7 8~ x 10-6 5.5
MnC12 1.85xl0 5 110 50 7 8~1 x 10 6 5.5
NiSO4 1.85xlO 5 110 50 7 8.1 x 10 6 5.5
ZnC12 1.85x10-5 llO 50 7 8.1 x 10-6 5.5
These observations demonstrate that chlorine
dioxide can remove interfacial pads formed from a variety
of soluble metallic salts, including complex mixtures of
these materials (not shown in this example). Chlorine
dioxide is effective when added to oil/water systems at pH
1 to pH ll in ratios of from as low as 1:100 moles of
chlorine dioxide per mole of sulfide to as high as three
moles of chlorine dioxide per mole of sulfide. These are
not necessarily critical upper and lower limits, but
generally define the most effective range of chlorine
dioxide to sulfide ratios suitable for use in this
invention. The concept of the invention, however,
contemplates the use of effective amounts of chlorine
dioxide being added to oil/water systems either in the oil
phase or the water phase, or both, to contact the sulfide
oil/water pad and to thereby elim:inate the pad or prevent
the formation of the sulfide pad.
Indu~tria~_~E~L~ion
._ _
This invention finds wide application in
petroleum produ~tion an~ refining.
