Note: Descriptions are shown in the official language in which they were submitted.
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CRUDE OIL ANTIFOULANT
FIELD OF THE INVENTION
The present invention relates to methods for inhibiting
the fouling of heat exchangers during the refining of crude oils.
The methods are particularly useful at inhibiting fouling of heat
exchangers processing high carbonyl containing crude oils.
BACKGROUND OF THE INVENTION
Fouling can be defined as the accumulation of unwanted
matter on heat transfer surfaces. This deposition can be very
costly in refinery and petrochemical plants since it increases
fuel usage, results in interrupted operations and production
losses and increases maintenance costs.
Deposits are found in a variety of equipment: preheat
exchangers, overhead condensers, furnaces, heat exchangers,
fractionating towers, reboilers, compressors and reactor beds.
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These deposits are complex but they can be broadly characterized as
organic and inorganic. They consist of metal oxides and sulfides,
soluble organic metals, organic polymerst coke, salt and various
other particulate matter. Chemical antifoulants have been developed
that effectively combat fouling.
The chemical composition of organic foulants is rarely
identified completely. Organic fouling is caused by insoluble
polymers which sometimes are degraded to coke. The polymers are
usually formed by reactions of unsaturated hydrocarbons, although
any hydrocarbon can polymeri~e. Generally, olefins tend to
polymerize more readily than aromatics, which in turn polymeri~e
more readily than paraffins. Trace organic materials containing
hetero atoms such as nitrogen, oxygen and sulfur also contribute to
polymerization, often through a condensation mechanism.
In refineries, deposits usually contain both organic and
inorganic compounds. This makes the identification of the exact
cause of fouling extremely d;fficult. Even if it were possible to
precisely identify every single deposit constituent, this would not
guarantee uncovering the cause of the problem. Assumptions are
often erroneously made that if a deposit is predominantly a certain
compound, then that compound is the cause of the fouling. In
reality, oftentimes a minor constituent in the deposit could be
acting as a binder, a catalyst, or in some other role that
influences actual deposit formation.
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The final form oF the deposit as viewed by analytical
chemists may not always indicate its origin or cause. Before
openings, equipment is steamed, waterwashed, or otherwise readied
for inspection. During this preparation, fouling matter can be
changed both physically and chemically. For example, water-
soluble salts can be washed away or certain deposit constituents
oxidized to another form.
In petrochemical plants, fouling matter is often organic
in nature. Fouling can be severe when monomers convert to
polymers before they leave the plant. This is most likely to
happen in streams high in ethylene, propylene, butadiene, styrene
and other unsaturates. Probable locatinns for such reactions
include units where the unsaturates are being handled or purified,
or in streams which contain these reactive materials only as
contaminants.
Even through some petrochemical fouling problems seem
similar, subtle differences in feedstock, processing schemes,
processing equipment and type of contaminants can lead to
variations in fouling severity. For example, ethylene plant
depropanizer reboilers experience fouling that appears to be
primarily polybutadiene in nature. The severity of the problem
varies significantly from plant to plant, however. ~he average
reboiler run length may vary from one to two weeks up to four to
six months (without chemical treatment~.
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Although it is usually impractical to iden~ify the fouling
problem by analytical techniques alone, this information combined
with knowledye of the process, processing conditions and the
factors known to contribute to fouling, are all essential to
understanding the problem.
There are many ways to reduce fouling both mechanically
and chemically. Chemical additives often offer an effective
anti-fouling means; however, processing changes, mechanical
modifications equipment and other methods available to the plant
should not be overlooked.
Antifoulant chemicals are formulated from several
materials: some prevent foulants from forming, others prevent
foulants from depositing on heat transfer equipment. Materials
that prevent deposit formation include antioxidants, metal
coordinators and corrosion inhibitors. Compounds ~hat prevent
deposition are surfactants which act as detergents or dispersants.
Different combinations of these properties are blended together to
maximize results for each different application. These "poly
functional" antifoulants are generally more versatile and
effective since they can be designed to combat various types of
fouling that can be present in any given system.
Condensation inhibitors include materials that interfere
~ith acidtbase reactions, and others that react with hetero atom
compounds such as carbonyls and pyrroles. These inhibitors
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prevent growth of the hydrocarbon molecules and thus help to
inhibit fouling.
Research indicates that even very small amounts of oxygen
can cause or accelerate polymerization. Accordingly, antioxidant
type antifoulants have been developed to prevent oxygen initiated
foul;ng. Antio~idants act as chain~stoppers by forming inert
molecules with the oxidized free radical hydrocarbons, in
accordance with the following reaction:
Chain Termination
ROO Antioxidant _ ROOH + Antioxidant (H)
Surface modifiers or detergents change metal surface
characteristics to prevent foulants from depositing. Dispersants
or stabili2ers prevent insoluble polymers, coke and other particu-
late matter from agglomerating into large particles which can
settle out of the process stream and adhere to the metal surfaces
of process equipment. They also modify the particle surface so
that polymerizat10n cannot readily take place.
Antifoulants are designed to prevent equipment surfaces
from fouling. They are not designed to clean up existing foulants.
Therefore, an antifoulant should be started immediately after
equipment is cleaned. It is usually advantageous to pretreat the
system at double the recommended dosage for two or three weeks to
reduce the initial high rate of fouling immediately after startup.
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The increased pro~it possible wi~h the use of antifoulants
varies from application to application. It can include an
increase in production, fuel savings, maintenance savings and
other savings from greater operating efficiency.
There are many areas in the hydrocarbon processing
industry where antifoulants have been used extensively; the main
areas of treatment are discussed below.
In a refinery, the crude unit has been the focus of
attention because of increased fuel costs. Antifoulants have been
successfully applied at the exchangers; downstream and upstream of
the desalter, on the produçt side of the preheat train, on both
sides of the desalter makeup water exchanger and at the sour water
stripper.
Hydrodesulfurization units of all types experience preheat
fouling problems. Among those that have been successfully treated
are reformer pretreaters processing both straight run and coker
naphtha, desulfurizers processing catalytically cracked and coker
gas oil, and distillate hydro-treaters. In one case, fouling of a
Unifiner stripper column was solved by applying a corrosion
inhibitor upstream of the problem source.
Unsaturated and saturated gas plants (refinery vapor
recovery units) experience fouling in the various fractionation
columns, reboilers and compressors. In some cases, a corrosion
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control program combined with an antifoulant program gave the best
results. In other cases, an application of antifoulants alone was
enough to solve the problem.
Cat cracker preheat exchanger fouling~ both at the vacuum
column and at the cat cracker itself, has also been corrected by
the use of antifoulants.
The two most prevalent areas for fouling problems in
petrochemical plants are at the ethylene and styrene plants.
In an ethylene plant, the furnace gas compressors, the various
fractionating columns and reboilers are subject to fouling.
Polyfunctional antifoulants, for the most part, have provided good
results in these areas. Fouling can also be a problem at the
butadiene extraction area. Both antioxidants and polyfunctional
antifoulants have been used with good results.
In the different design butadiene plants, absorption oil
fouling and distillation column and reboiler fouling have been
corrected with various types of antifoulants.
Chlorinated hydrocarbon plants, such as V~M, EDC and
perchloroethane and tri-chloroethane have all experienced various
types of fouling problems. The metal coordinating/antioxidant-type
antifoulants give excellent service in these areas.
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SUMMARY OF THE INVENTION
The present invention pertains to methods for inhibiting
fouling in heat exchangers during the processing of crude oils
comprising adding to said crude oils an effective amount for the
purpose of 1-(2-aminoethyl) piperazine.
The present invention is particularly useful at inhibiting
fouling in heat exchangers upstream or downstream of the desalting
unit during the processing of crude oils having a high carbonyl
content.
DESCRIPTION OF THE RELATED ART
The use of 1-(2-aminoethyl) piperazine is known in the
petroleum refining industry. As evidenced ln U.S. Patent No.
4,744,881, Reid, May 1988, 1-(2-am;noethyl) piperazine is used ;n
conjunction with a non-h;ndered or partially h;ndered phenol
compound to reduce foul;ng problems in hydrocarbons, specifically
refined fractions having a brom;ne number greater than 10.
1-(2-am;noethyl) p;peraz;ne can also be used with a
phosphite compound to stab;l;ze d;st;llate fuel oil and ;nhibit
color degradat;on. U.S. Patent No. 4,867,754, Reid, September
1989, teaches that th;s combination is more effective than either
compound used alone, U.S. Patent No. 4,697,290, Reid, March 1987
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teaches a combination of 1-(2-aminoethyl) piperazine and
N,N-diethylhydroxylamine for color stabilized distillate fuel oils.
U.S. Patent No. 4,200,518, Mulvany, April 1980, teaches
the use of a polyalkylene amine compound to reduce fouling in
hydrocarbon streams passing through a heat exchanger. Numerous
amines are disclosed as being effective as antifoulants, however,
1-(2-aminoethyl) piperazine is not taught as an antifoulant. The
polyalkylene amine compounds in Mulvany have molecular weights
ranging from 200 to 2700 and preferably in the range of 1000 to
1500. The compound of the instant invention has a molecular weight
of 12g.
U.S. Patent No. 4,714,793, Van Eijl, December 1987, teaches
a process for inhibiting the polymerization of styrene from
hydrocarbon streams using an N-aminoalkyl piperazine compound.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to methods for inhibiting the
fouling of heat exchangers located upstream or downstream of the
desalting unit in a crude oil having a high carbonyl content
processing system comprising adding to said crude oil an effective
amount for the purpose of an aminoalkyl piperazine compound.
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The preferred aminoalkyl piperazine compound is l-
(2-aminoethyl) piperazine. This co~pound is preferred in certain
crudes as some crudes will foul the heat exchangers of the crude
processing un;t prior to the desalting unit. The specific crude
oils that are treated by the methods of the present invention are
those that contain a high carbonyl content.
The use of aminoethyl piperazine (AEP) is known in the
petroleum refining industry as an antioxidant in hydrocarbon
processing. U.S. Patent No. 4,744,881 Reid which is wholly
incorporated by reference herein teaches the use of a composition
of an unhindered or hindered phenol and a strongly basic amine
compound to control fouling in high temperatures hydrocarbon
fluids having a bromine number greater than ten. U.S. Patent No.
4,647,290 Reid which is wholly incorporated by reference herein
teaches the use of a composition of N-(2-aminoethyl) piperazine
and N,N-d;ethylhydroxyl amine to inhibit color deterioration;of
distillate fuel oils.
Reid '881 teaches the use of a synergistic composition of
a phenol compound and an amine compound to control fouling in
hydrocarbon fluids having bromine numbers in excess of lO. These
systems contain unsaturated or olefinic components which are
induced by oxygen to polymerize or react. The methods of the
present lnvention employ an overpressure of nitrogen to the
system. The resulting crude stream is relatively oxygen free.
Crudes generally have bromine numbers less than 10.
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Reid '290 ;s directed towards color inhibition in distil-
lation fuel oils through the synergistic combination of N-(2-amino-
ethyl) piperazine and N,N-diethylhydroxyolamine. Reid '290
teaches in Col. 5, lines 41-45 and Col. 6, lines 1-2 that neither
of these two chemical species, when used alone, are effective
antioxidants in the hydrocarbon systems taught in Reid '290. This
patent is also directed towards finished products that are in
transit or storage and their protection from color contamination.
The present invention is directed to crude oils that are under
going petroleum re~ining.
The methods are adapted to inhibit formation and
deposition of components that polymerize or react due to the high
temperatures of the heat exchanger. Temperatures from 100 to
~00F are o~ten reached in these systems. These systems are
primarily composed of ferrous metal. Iron, as well as iron alloys
such as low and high carbon steel, stainless steel and nickel-
chromium-iron alloys are customarily used for the production of
hydrocarbon processing equipment such as heat exchangers.
It has been found that fouling on the carbon steel
surfaces utilized in conjunction with the test system described
herein is inhibited by use of the aminoalkyl piperazine compounds
described above. Accordingly, it is to be expected that coking
will also be reduced on iron, nickel and chromium based
metallurgical surfaces in contact with the crude oil.
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The aminoalkyl piperazine compounds may be added to the
crude oil being processed at any point along the processing
system. The aminoalkyl piperazine compound may be added to the
crude oil either as a concentration or as a solution using a
suitable carrier solvent which is compatible with the piperazine
compound and the crude oil. Heavy aromatic naphtha is
representative of those solvents. The pre~erred solution is
1-(2-aminoethyl) piperazine dissolved in heavy aromatic naphtha.
The amount of aminoalkyl piperazine added to the crude oil
is clearly dependent upon the severity of the fouling problem at
the heat exchanger as well as the concentration of the piperazine
compound employed. Accordingly, it is desirable to ensure that
the aminoalkyl piperazine compound content of the solution is high
enough to ensure that an ample quantity of piperazine compound is
dispersed in the crude oil. As such, product formulation lends
itself to great flexibility
Broadly speaking, the dosage recommendations range from
about 1 to about 1000 parts piperazine compound per million parts
crude oil. More preferably, a range from about 5 to about 200
parts piperazine compound per million parts crude oil.
The antifoulant compound of the invention may include
other additives, if desired. For example, other antifoulants may
be used in combination with the piperazine compounds of this
invention, or corrosion inhibitors, etc., may be combined with the
antifoulants of the invention.
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In order to more clearly illustrate this invention, the
data set forth below was developed. The following examples are
included as being illustrations of the invention and should not be
construed as limiting the scope thereof.
In order to ascertain the antifouling efficacy of the anti-
foulant compounds the materials were subjected to a dual fouling
apparatus test. In the dual fouling apparatus, process fluid
(crude oil) is pumped from a pressure vessel through a heat
exchanger containing an electrically heated rod. Then the process
fluid is chilled back to room temperature in a water-cooled
condenser before being remixed with the fluid in the pressure
vessel. The system is pressurized by nitrogen to minimize
vaporization of the process fluid.
The Oual Fouling Apparatus (DFA) used to generate the data
shown in the following Table contains two heated rod exchangers
that are independent. The Hot Liquid Process Simulator (HLPS)
fouling apparatus contains a single heat exchanger. In both tests,
the rod temperature was controlled while testing. As fouling on
the rod occurs, less heat is transferred to the fluid so that thé
process fluid outlet temperature decreases. Antifoulant protection
was determined by comparing the summed areas between the heat
transfer curves for control and treated runs and the ideal case
for each run. In this method, the temperatures of the oil inlet
and outlet and rod temperatures at the oil inlet (cold end) and
outlet (hot end) are used to calculate U-rig coeFficients of heat
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transfer every ~ minutes during the tests. From these U-rig
coefficients, areas under the fouling curves are calculated and
subtracted from the non-fouling curve for each run. Comparing the
areas of control runs (averaged) and treated runs in the following
equation results in a percent protection value for antifoulants.
Area~ntrol) - Area(treatment) * 100 - % protection
Area(control)
Antifouling protection in various crude oils was determined
as shown in the following tables.
The crude oil tested in Tables I and II was an Australian
crude oil. It was characterized by having a neutralization number
of 0.01 mg KOH/g, a bromine number of 1 mg Br/g, containing 0.~1 wt.
% asphaltenes and having a carhonyl content of 18,000 parts per
million.
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These results are reported in Table I.
TABLE I
Betz Fouling Apparatus
500F Rod Temperature
800 psig Nitrogen Overpressure
23 ml/mn Flow Rate
Heat
Concentration Transfer
(ppm Product/ Oil Tem~. Loss Area
ppm Active~ Chanqe(uE) (BTU/Hr/F~SF) (BTU/Fl % P
- Blank 62 13.5 41.3
500/2501 3 2.7 7.4 82
500/1252 54 11.7 25.5 38
5ûO/1253 52 10.8 27.û 35
1 = 1-(2-aminoethyl) piperazine in heavy aromatic naphtha
2 = Blend of hindered phenols and cyclohexamine
3 - aminoalkyl alcohol
As seen in Table I, a treatment of 1-(2-aminoethyl) piperazine
in heavy aromatic naphtha proved efficacious at inhibiting`fouling in
crude oil containing high concentrations of carbonyl type oxygenates
which are known to take part in condensation polymerization reactions.
This result was unexpected since this material is ineffective in crude
oils with low carbonyl contents. Another example ûf a crude oil with
high carbonyl content is shown in Table II. This treatment proved more
effective than known antifoulant compositions.
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TABLE II
ALCOR HLPS Fouling Apparatus
500F Rod Temperature
3 ml/min Flow Rate, 800 psig Nitrogen Overpressure
S 5 Hour Run Times
Heat
Treatment Transfer
Concentration Oil Temp. Loss Area
(ppm Active) Chanqe(~E) (BTU/Hr/F.SF) (~LF) % P
Avg. Blank -22~/-I 0.9+/-0.2 1.0~/-0.2
nispersant 1 (62.5) 17 0.9 0.9 10
Dispersant 1 (125) 4 0.1 0.2 80
Dispersant 2 (62.5) 15 0.6 1.2 0
Dispersant 2 (125) 7 0.3 2.0 0
Dispersant 1~
1-(2-aminoethyl) 4 0.2 0.2 80
piperazine (62.5/62.5
1-(2-aminoethyl)
piperazine (62.5) 7 0.5 0.5 50
Dispersant 1 = cyclic succinimide dispersant
Dispersant 2 = long chain phosphorous dispersant
The aminoethyl piperazine compounds of the present invention
proved unexpectedly effective in the high carbonyl content crude
oil. These compounds were also effective with known dispersant
compounds.
The results of Table II indicate that the aminoalkyl
piperazine compounds of the present invention are effective when
used in combination with other dispersant compositions.
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The crude oil tested in Tables III and IV was desalted crude
oil ~rom Texas. This crude possessed a neutralization number of
0.12 mg KO~/g, a bromine number of O mg Br/gl an asphaltene content
of 0.32 wt. % and less than 100 parts per million carbonyls.
TABLE IIT
Desalted Crude from Texas
Side 2 of Dual Fouling Apparatus
800F Rod Temperature, 900 psig N2 at 23 ml/min flow rate
Heat
Concentration Transfer
(ppm Product/ Oil TemP. Loss Area
pPm Active! Chanqe(F) ~BTUlHr/~E) (BTU/F) % p
Blank 35 6.0 13.3 --
1000~2501 23 4.4 8.7 29
5~/2002 29 5.5 16.6 0
Blank 29 4.9 11.2 --
1000/250 and
500/2503 17 1.8 3.1 75
1000/2504 21 3.1 5.1 58
500/125 and
250/1255 21 3.4 7.6 38
1 = Long-chained phosphorous based dispersant and 30% heavy
aromatic naphtha
2 = 50% 1-(2-aminoethyl) piperazine and 50% heavy aromatic naphtha
5 3 = Long-chained phosphorous based dispersant and 30% heavy
aromatic naphtha with 50% am;noethyl piperazine and 50% heavy
aromatic naphtha
4 - same composition as 1
5 = same composition as 3
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TABL~ IV
Betz Fouling Apparatus
500F Rod Temperature
800 psig Nitrogen Overpressure
23 ml/mn Flow Rate
Heat
Concentration Transfer
Oil Temo. Loss Area
(~e~ Active) ChanqeL~E) (BTU/Hr/F~SF) (BTU/F~ % P
Avg. Blank 32t/-4 5.5+/-0.8 12.3+/-1.5
Avg. Dispersant (250) 22~/-1 3.8+/-0.9 6.9~/-2.5 44
1-~2-aminoethyl)
piperazine (250) 29 5.5 16.6 0
Dispersant 2 and
1-(2-aminoethyl~
piperazine (250/250) 17 1.8 3.1 75
Dispersant 2 and
1-(2-aminoethyl)
piperazine (125/125) 21 3.4 7.6 38
Dispersant 2 = Long Chain phosphorous dispersant
These results show that 1-(2-aminoethyl) piperazine is
ineffective in low carbonyl content crude oils. Further, it
proved only slightly more effective when used with a known
antifoulant dispersant.
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While this invention has been described with respect to
particular embodiments thereof, it is apparent that numerous other
forms and modifications of this invention will be obvious to those
skilled in the art. The appended claims and this invention
generally should be construed to cover all such obvious forms and
modifications which are within the true spirit and scope of the
present invention.
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