Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR CONTROLLING
FOULING IN FCC SLURRY LOOP
.
~ACKGROUND OF THE INVENTION
Th;s invention relates to a method of controlling fouling
' 5 in a FCC Slurry Loop and FCC Main Fractionator Bottoms.
,
The Fluid Catalytic Cracking IFCC) Unit is one of the most
, important refinery operating units. These units, common to mostsl refiner~es, experience process side fouling which affects operations
and reduces operating profît. In most FCC Units, the slurry loop
has historically been the most severe fouling system in the unit.
Factors which affect fouling in the slurry system include feed
composition, main fractionator bottoms temperature, slurry system
viscosity, the slurry settling system, and catalyst loading.
In the processing of petroleum hydrocarbons and feedstocks
such as petroleum processing intermediates, e.g., gasZ oils and
.~ reformer stocks, the hydrocarbons are commonly heated to
temperatures of 100 to 1000F. Similarly, such petroleum
hydrocarbons are frequently employed as heating ~ediums on the "hot
side" of heating and heat exchange systems. In both instances, the
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petroleum hydrocarbon liquids are subjected to elevated temperatures
which produce a separate phase known as fouling deposits, within the
petroleum hydrocarbon. In all cases, these deposits are undesirable
by-products. In many processes, the deposits reduce the bore of
conduits and vessels to impede process throughput, impair thermal
transfer, and clog filter screens, valves and traps. In the case of
heat exchange systems, the deposits form an insulating layer upon
the available surfaces to restrict heat transfer and necessitate
frequent shut-downs for cleaning. Moreover these deposits reduce
throughput, which of course, results in a loss of capacity with a
drastic effect in the yield of finished product. Accordingly, these
deposits have caused considerable concern to the industry.
~ hile the nature of the foreqoing deposits defies precise
analysis, they appear to contain a combination of carbonaceous
phases which are coke-like in nature, polymers or condensates formed
; from the petroleum hydrocarbons or impurities present therein and
salt formations which are primarily composed of magnesium, calcium
and sodium chloride salts. The catalysis of such condensates has
been attributed to metal compounds such as copper or iron which are
present as impurities. For example, such metals may accelerate the
, hydrocarbon oxidation rate by promoting degenerative chain
, branching, and the resultant free radicals may initiate oxidation
1 and polymerization reactions which form gums and sediments. It
-~ further appears that the relatively inert carbonaceous deposits areentrained by the more adherent condensates or polymers to thereby
contribute to the insulating or thermal opacifying effect.
'i Historically, the major area of fouling within the Fluid
Catalytic Cracking Unit is the main fractionator bottoms and the
slurry loop. Attempts to reduce this fouling have included
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! mechanical changes, operational changes, and chemical treatment.
Often, these have met with limited success. Factors which have an
effect on the slurry fouling within this system would include the
stream properties, main fractionator bottoms temperature, catalyst
loadinq, velocity, and viscosity.
Slurry properties and composition are greatly dependent
upon the feedstock processed in the unit, the type of catalyst used,
and the severity of the cracking operation. Feedstock to the FCC
Unit may consist of heavy gas oils, vacuum gas oils, and residuum.
These feedstocks may or may not be hydrotreated, which greatly
affects the unit operation. It has been shown that hydrotreated
feedstocks generalty are less prone to cause fouling in the slurry
, system due to better conversion, lower Conradson carbon, and reduced
' metals content. It is known that when resids are charged to the
un;t, fouling in the slurry loop will increase. Usually, the higher
the resid feedrate, the greater the fouling tendency in the system.
Resids are much higher in solids and in asphaltene levels which are
both primary contributors to a feedstock fouling tendency.
,.,
l Catalyst types, which are the commonly used zeolites:,i3 20 either as such or modified, also seem to affect fouling in the
slurry loop - especially when cracking residuum. Higher activity
catalysts will generally crack heavier molecules more efficiently,
thereby reducing the amount of slurry yield, increasing the gravity
and the solids loading in the main fractionator bottoms and, in
~`~ 25 turn, increasing the fouling tendency.
j The FCCU main fractionator bottoms temperature is usually
controlled between 650 and 700F in order to maintain optimum
product separation and to reduce coking in the fractionator~ The
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ma~ior method of controlling this temperature is by cooled slurry
recycle. Therefore, it is most important to maintain a clean slurry
exchanger system. As the slurry recycle temperature increases, the
bottoms temperature also increases promoting a greater fouling rate
in the slurry system which further increases the column temperature
and reduces production rates. A major method of cooling the slurry
is by generating steam where the heat from the slurry (650-700 F)
heats the water to ~roduce the steam, thereby in turn effectively
cooling the slurry.
ln In the process relating to the slurry loop, FCC reactor
vapors which are being discharged from the FCC unit are introduced
into a fractionating column. The vapors are composed of a wide
range of hydrocarbons from the light fractions represented by
methane, ethane, ethylene and the like to the heavy fractions such
as the high molecular weight aromatics.
In the fractionating column the heaviest components of the
mixture condense and are withdrawn from the fractionator. Since the
temperature of the condensed heavy fraction is still quite high9 the
fraction, which itself must be cooled for storage or transportation,
is used as a heat source in process heat exchangers, reboilersy
steam generators and the like. As is apparent, the system of
utilizing residual heat of the heavy fraction improves the economies
' and operations production efficiencies.
However, it appears ~hat because the mixture is composed
. ~5 of the very heavy fractions in combination with the residual
unremoved FCC catalyst, there is a tendency for fouling to occur.
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In the past, additives and different chemistries including
.~ two of the ingredients of the present invent;on have been utilized
with varying degrees of success in treatin~ heavy hydrocarbon FCC
slurry mixtures after the fractionators (distillation columns).
. ~
As will be established by the following case studies,
topping ~he combination treatment with the third component provided
I~ much superior run times.
; DESCRIPTION OF THE INVENTION
The present inventor discovered that if the high molecular
' 10 wei~ht hydrocarbon - FCC catal~yst slurry was treated with a
cnmbination of reaction products after or during removal from the
fractionator, that fouling and deposition could be controlled to an
`? acceptable degree.
The treatment combination is comprised of three reaction
products tProducts I, II, and III~ which are described and prepared
~s follows.
Product I is a Mannich-type product formed via reaction of :
the reactants tA), (B), and (C); wherein (A) is an alkyl substituted
~;, phenol of the structure
` 20 OH FORMULA (A)
,~ I .
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I R
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where;n R and Rl are the same or different and are
;ndependently selected from alkyl, aryl, alkaryl, or aralkyl of From
about 1 to 20 carbon atoms, x is O or l; wherein (B) is a polyamine
` of the structure
H2N(CH-(CH2)y ~CH-NH)z -H FORMULA (B)
R R3
wherein z is a positive integer, R2 and R3 may be the same
or different and are independently selected from H, alkyl, aryl,
~, 10 aralkyl, or alkaryl hav~ng from 1 to 20 carbon atoms, y may be O or
l; and wherein (C) is an aldehyde of the structure
`J
o FORMULA (C)
,~,~ 11
R4 - C - H
wherein R~ is selected from hydrogen and alkyl having from
1 to 6 carbon atoms.
,
As to exemplary compounds falling within the scope of
Formula A supra, p-cresol, 4-ethylphenol, 4-t-butylphenol~
4-t-amylphenol, 4-t-octylphenol, 4-dodecylphenol,
2,4-di-t-butylphenol, 2,4-di-t-amylphenol, and 4-nonylphenol may be
:~ mentioned. ~t present, it is preferred to use 4-nonylphenol as the
;J Formula A component.
'1
Exemplary polyamines which can be used in accordance with
Formula B include ethylenediamine, propylenediamine, diethylene-
triamine, triethylenetetramine, tetraethylenepentamine and the like,with ethylenediamine being preferred.
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The aldehyde component can comprise, for example
formaldehye, acetaldehyde, propionaldehyde, butyraldehyde,
hexaldehyde, heptaldehyde, etc. with the most preferred being
formaladehyde which may be used in its monomeric form, or, more
conveniently, in its polymeric form (;.e., paraformaldehyde).
As is conventional in the art, the condensation reaction
may proceed at temperatures from about 50 to 200C, with a
preferred temperature range being about 75-175 C. As is stated in
! U S. Pat. No. 4,166,726, the t;me required for completion of the
reaction usually varies from about 1-8 hours, varying of course with
the specific reactants chosen and the reaction temperature.
As to the molar range of components (A):(B):(C) which may
be used, this may fall within 0.5-5:1:0.5-5.
Product I, which is described and taught as a transition
15 metal deacti~ator in U.S. Patent No. 4,749,468, the Specific
Embodiment which follows, was prepared utilizing molar ratios of
2:1:2 of p-nonylphenol, ethylenediamine and formaldehyde.
,` .
Product II is a polyalkenylthiophosphonic acid rompound or
alcohol/polyglycol esters thereof. The methods of preparation of
~0 these type compounds are described in U.S. Patents 3,281,359;
4,578,178; and 4,775,458 the latter of which also establishes the
use of the compounds as antifoulnts.
. !
As is expressed in the patents, the polyalkenyl-P2Ss
reaction products may be prepared by reacting alkenyl polymers such
as polyethylene, polypropylene, polyisopropylene, polyisobutylene,
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polybutene or copolymers comprising such alkenyl repeat unit
moieties with P2Ss (at about 5-40 wt. percent of the reaction mass)
at a temperature of from about 100 to about 320 C in the presence
of between about 0.1-5.0 wt. percent sulfur.
The resulting reaction mixture ;s then diluted with
mineral oil and is then steam hydrolyzed. If desired, the
hydrolyzed polyalkenyl-P2Ss reaction product may then be esterified~
by further reaction with lower alkyl lCl-C5) alcohols such as
methanol, ethanol, propanol, butanol, etc. or with a polyglycol such
ln as hexylene glycol or pentaerythritol.
`
As the '359 patent states, it is highly desirable to
employ, as a precursor material, an alkenyl polymer having an
averaqe molecular weight of between about 600 and 5,000.
The reaction product preferred for use is the
15 pentaerythritol ester of polyisobutenylthiophosphonic acid which was
used in the Specific Embodiments and use studies below. This
particular ester is com~ercially available and is hereinafter
referred to as PETPA. The polyisobutenyl moiety of PETPA has been
reported as having an average molecular weight of about 1300. The
, 20 product is sold as a 40 vol 7O solution in mineral oil. It has a
J specific gravity of 0.92 at 60F, and a viscosity of 63.9 CST at
} 210 F
;l,
PETPA is prepared by mixing polyisobutene (average
molecular weight of 750-2000) with P2Ss (po1ybutene-P2Ss molar ratio
of 0.9-1.25) in the presence of sulfur at 300-600F until the
reaction product is soluble in n-pentane. The product is di luted
with paraffin base distillate, steamed for 4-10 hours at 350-375F~
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then dried with N2 at 350-375F. The product is extracted with
50-100~0 by volume of methanol at 75-150F to leave a lubricating
oil raffinate containing a polyisobutenylthiophosphonic acid. This
material is reacted with pentaerythritol to yield PETPA.
Product III is an alkyl or alkenyl substituted succinimide
which is prepared by reacting a substituted succinic anhydride
having the following formula:
~', O O
~', 10 C C
I
Rs - CH - CH2
or a substituted succinic acid having the following
formula:
, COOH COOH
t
Rs - CH - CH2
in which Rs is an alkyl or alkenyl radical having from 30
to ~00 carbon atoms in the carbon chain with a polyamine of the
formula:
' 20
H2N - (CnH2n - N~m H
H
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in which
n is an integer between 2 and 10 inclusive,
m is an integer between 1 and 10 inclusive, and CnH2n is a straight
chain hydrocarbon group.
' 5 In the above reaction, from 1/2 to 2 chemical equivalents
; of polyamine are used for 1 chemical equivalent of succinic compound.
The preferred Product III is obtained by reaction of
triethylenetetramine with polyisobutenyl succinic anhydride. This
product was incorporated in the formulation tested in the Specific
;~10 Embodiment, The preparation and use of Product III type compounds
~'as antifoulants are described in U.S. Patent No.'s 3,271,295 and
j 3,271,296.
;The combination product of the invention may be dispersed
¦within the petroleum hydrocarbon slurry within the range of about
0.5-10,000 ppm based upon one million parts hydrocarbon slurry.
Preferablv, the product is added in an amount of from about 1 to 500
ppm.
The exact combination of the specific ingredients and the
A,~ effective dosage rates for the combination product will depend upon
~-20 the severity of the fouling problem. The relative weight ratios of
~- Products I to II to III which would appear to be effective are
6:1:12 to 40:12:1.
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As earlier indicated, both Product II and Product III have
heen used ;ndependently and in co~binat;on ;n FCC hydrocarbon slurry
applications as a dispersant or antifoulant, with minor success
being experienced in each instance.
SPECIFIC EMBODIMENTS
The treatment as specified below was tested in accordance
with the test procedure, set forth to establish the fouling
inhibitory capacity of the inventive mixture.
Pressurized Hot Filament Fouling Test
A weighed nickel chromium wire was suspended between two
electrodes in an autoclave. 500 mL of FCC slurry and the
appropriate amount of treatment was added to the vessel. Stirring
was started, the vessel was pressurized with nitrogen and a current
of 10 amps was applied across the wire for 24 hours. The wire was
then removed, washed, dried and weighed.
FCC SLURRY FOULING RESULTS
Treatment Deposit Weight (mg)
~ l None (Blank*) 92 (average~
i 2 Inventive Treament: 10 ,
, 20 250 ppm comprised of 40qo
'; weight active Product I
~ ~100 npm active)
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Treatment Deposit Weight (mg)
and
750 ppm of a combination
comprised of 19% weight active
Product III (142,5 ppm active) and
1.8X weight active Product II
~13.5 ppm active)**
3 None (~lank ~ 2-1/2 wt. ~ 395
spent catalyst)
10 * ~lank slurry contained 49.7 lb. of zeolite catalyst per thousand
BBL of Hydrocarbon
** weight ratio of Products I:II:III=8:1:12
Case History No. 1
Fouling in the FCC slurry loop of a Texas refinery became
15 so severe that exchanaer run lengths were reduced to 2-3 weeks.
~ecause of this fouling problem, a Composition X was fed to
determine whether the heat exchanger run lengths could be
increased. Composition X, which was a 2570 by weight Product II
(earlier described) in 75% solvent was fed at a level of 200 ppm to
' 20 the slurry. The treatment resulted in a doubling of exchanger run¦ lengths (4-6 weeks) between cleanin~s.
j Since the first treatment was considered to be successful~ to a degree, the refinery agreed to the treatment of the slurry
I system with another composition, Composition Y, to see whether even
25 longer run lengths were possible. Composition Y, which was a
combination of 19% by weight Product III and 1.8% by weight Product
remainder solven~) was fed at 200 ppm to the slurry.
Performance with the treatment using Composition Y was essentially
the same as that obtained with Composition X.
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Again, in order to establish whether run lengths could be
lengthened, the refinery agreed to a third evaluation. However,
iprior to the third evaluation, several slurry characterizations were
made to establish what mechanisms could be involved which might be
resulting in the shortened run lengths. The characterizations of
the slurry follow.
Although it was not clear just what phenomena which might
be occurring to establish the fouling problem3 it was decided that
perhaps the addit;on of a third component to the treatment might
have some effect. At that time, Product I in the form of
Composition Z ~40~ by weight Product I with 60~o solvent) was used at
`I50 ppm to the slurry in con~iunction with Composition Y at 200 ppm.
(Molar ratio of Product I to Product II to Product III was 6:1:12).
The results of the treatment with Compositions Y and Z
were and have been quite unexpectedly excellent with run lengths
extended from 4-6 weeks to over 40 weeks with no exchanger cleanings
necessary as a result of slurry foulings. Refinery personnel have
been quite pleased with the results of the evaluation and are
currently purchasing the combination treatment.
Case History No. 2
.,
~!FCC slurry fouling at another Texas refinery caused
significant losses in exchanger heat transfer efficiency. Heat
exchange losses in two key exchanger bundles were 0.55 BTU/hr./ft2/
F. Because of the prior experience as described in the foregoing
,15 Case History No. 1, the slurry was characterized and it was decided
to again treat the system with a combination of Composition Y and
Z. In this instance Composition Y was fed at 150 ppm to the slurry
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with 100 ~p~ of Composition Z Performance of the treatment was
considered satisfactory by refinery personnel since the
U-Coefficient decline was reduced to 0.14 BTU/hr/ft2/F. It was
believed that most of the decline in heat transfer efficiency was
;5 related to fouling on the untreated side of the exchanger. The
-molar ratio of Product I~ III for combination treatment was
16:1:12.
It is apparent from the foregoing that the three component
system ~ and Y or (I, II, and III) was quite superior in performance
over Compositions X or Y (the use and sale of both of which occurred
more than one year from the filing date of this application).
The characterization of the slurries used for the
laboratory testing and the case studies appear hereinafter.
While the compositions representing the inventive
treatment were fed independently for a while, a composition
containin~ the three ingredients was also fed.
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` PETROLEUM ANALYSIS REPORT
`~ Description: Laboratory Hot Wire Test
:1 FCC Sl urry
Filterable solids, ptb 49.7
Bromine No. 31.5
Ash, wt YD 0.03
API gravity, 60F 7.2
V~scosity, SFS @ 122 F 77.4
~ 25 Conradson carbon, wt qO 4.73
-i Asphaltenes, wt 70 0.02
' Sulfur, wt qO 0.68
- Carbonyls, % < 0.01
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Metals, ppm
Aluminum 14.4
Calcium 0.9
Chromium < 0.1
Copper 0.2
Iron 40
Lead < 0-1
Magnesium 0.2
Manqanese 0.1
Nickel 0.1
Po~assium 0.7
Sodium 3.9
` Tin 0.3
Vanadium < 0.1
Zinc 1.1
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.PETROLEUM ANALYSIS ~EPORT
i Description: Case History No. 1
; FCC Slurry
Fllterable solids, ptb 384.3
~:~ 20 Bromine No. 15.5
. Conradson carbon, wt ~ 10.0
Basic nitrogen, ppm < 10
Asphaltenes, wt % 1.93
. Mercaptan sulfur, ppm 40
i 25 Carbonyls, ~ 0.085
Metals, ppm
Aluminum< 0.10
Calcium 7.44
. Chromium 0.30
Copper 0.95
. Iron 43
Lead 0.29
-; Magnesium 2.18
. Man~anese 0.23
Y. 2S Nickel 1.0
;i Potassium 1.2
~ Sodium 14.8
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Case History No. l (Cont'd)
Tin <0.10
Yanadium 0.43
- Zinc 1.8
PETROLEUM ANALYSIS REPORT
Description: Case History No. 2
FCC Slurry
Filterable solids, ptb 1,929.2
Bromine No. 73.1
ln Conradson carbon, wt % 18.31
Asphaltenes, wt % 5.08
Metals, ppm
Aluminum 413
Calcium lO.O
lS Chromium 0.5
Copper 0.6
; Iron 29
Lead l.l
. Magnesium 3.1
20 Manganese 0.2
Nickel 6.8
Potassium l.9
. Sodium 9.5
Tin 0.4
1 25 Vanadium 4.7
Zinc 3.5
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 inventlon.
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