U.S. patent application number 10/894138 was filed with the patent office on 2005-02-24 for stability of hydrocarbons containing asphal tenes.
Invention is credited to Duggan, George G., Respini, Marco.
Application Number | 20050040072 10/894138 |
Document ID | / |
Family ID | 34107778 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050040072 |
Kind Code |
A1 |
Respini, Marco ; et
al. |
February 24, 2005 |
Stability of hydrocarbons containing asphal tenes
Abstract
Heavy fuel oils or residual fuel oils can be stabilized with
magnesium over-based compounds such as magnesium overbased
carboxylates. It was surprisingly discovered that adding magnesium
overbased carboxylates to the residual fuel oils shortly after
thermal cracking gave much better results than can be achieved
after the application of the carboxylates to the fuel oil after
storage. Further, compounds containing at least about 21 wt %
magnesium also give better results than compounds with 18 wt % or
less, in one non-limiting embodiment. Magnesium overbased compounds
can also be added to coker feedstocks to reduce coker furnace
fouling. Treatment with the methods of this invention reduces
asphaltene deposits and sludges.
Inventors: |
Respini, Marco;
(Casalmorano, IT) ; Duggan, George G.; (Katy,
TX) |
Correspondence
Address: |
MADAN, MOSSMAN & SRIRAM, P.C.
2603 AUGUSTA
SUITE 700
HOUSTON
TX
77057
US
|
Family ID: |
34107778 |
Appl. No.: |
10/894138 |
Filed: |
July 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60488891 |
Jul 21, 2003 |
|
|
|
Current U.S.
Class: |
208/48AA ;
208/132; 208/14 |
Current CPC
Class: |
C10G 75/04 20130101;
C10L 1/2437 20130101; C10G 9/16 20130101; C10L 1/1832 20130101;
C10L 1/1817 20130101; C10L 1/188 20130101; C10G 9/005 20130101;
C10L 1/2493 20130101 |
Class at
Publication: |
208/048.0AA ;
208/132; 208/014 |
International
Class: |
C10G 009/16 |
Claims
We claim:
1. A method for stabilizing a hydrocarbon stream containing
asphaltenes comprising: heating the hydrocarbon stream containing
asphaltenes; and adding to the hydrocarbon stream a magnesium
overbased compound selected from the group consisting of magnesium
overbased carboxylates, magnesium overbased sulfonates, magnesium
overbased phenates, and mixtures thereof, in an amount effective to
improve the stability of the hydrocarbon stream, where the
hydrocarbon stream is subjected to heat after the addition.
2. The method of claim 1 where the magnesium overbased compound is
added in an amount ranging from about 25 to about 2000 ppm based on
the hydrocarbon stream.
3. The method of claim 1 where the magnesium overbased compound
contains at least 21 wt % magnesium.
4. The method of claim 1 where the adding is performed within 40
hours or less after the hydrocarbon stream is thermally
cracked.
5. The method of claim 1 where the hydrocarbon stream is a coke
drum feedstock and the magnesium overbased compound is added to the
feedstock prior to storing the feedstock at an elevated
temperature.
6. The method of claim 1 where the adding is performed within a
temperature range of about 250 to about 490.degree. C.
7. A method for inhibiting coke furnace fouling comprising: heating
a coke drum feedstock containing asphaltenes; adding to the coke
drum feedstock a magnesium overbased compound selected from the
group consisting of magnesium overbased carboxylates, magnesium
overbased sulfonates, magnesium overbased phenates, and mixtures
thereof; and storing the coke drum feedstock at an elevated
temperature.
8. The method of claim 7 where the magnesium overbased compound is
added in an amount ranging from about 25 to about 2000 ppm based on
the coke drum feedstock.
9. The method of claim 7 where the magnesium overbased compound
contains at least 21 wt % magnesium.
10. The method of claim 7 where the adding is performed within a
temperature range of about 250 to about 490.degree. C.
11. A method for stabilizing heavy fuel oils comprising: thermally
cracking a residual oil to provide a heavy fuel oil; and adding to
the heavy fuel oil a magnesium overbased compound selected from the
group consisting of magnesium overbased carboxylates, magnesium
overbased sulfonates, magnesium overbased phenates, and mixtures
thereof, in an amount effective to improve the stability of the
fuel oil, where the adding is conducted sufficiently soon after
thermal cracking to improve stability.
12. The method of claim 11 where the magnesium overbased compound
is added in an amount ranging from about 25 to about 2000 ppm based
on the heavy fuel oil.
13. The method of claim 11 where the magnesium overbased compound
contains at least 21 wt % magnesium.
14. The method of claim 11 where the adding is performed within 40
hours or less of the thermal cracking.
15. The method of claim 11 where the adding is performed within a
temperature range of about 250 to about 490.degree. C.
16. The method of claim 11 where the method is practiced in the
absence of adding a co-promoter reaction product from a succinic
anhydride and a lower carboxylic acid.
17. The method of claim 11 where the magnesium overbased compound
is a magnesium overbased carboxylate.
18. A method for stabilizing heavy fuel oils comprising: thermally
cracking a residual oil to provide a heavy fuel oil; and adding to
the heavy fuel oil a magnesium overbased carboxylate in an amount
effective to improve the stability of the fuel oil, where the
adding is conducted sufficiently soon after thermal cracking to
improve stability, where the magnesium overbased carboxylate
contains at least 21 wt % magnesium and the adding is performed
within 2 hours or less of the thermal cracking.
19. The method of claim 18 where the magnesium overbased
carboxylate is added in an amount ranging from about 25 to about
2000 ppm based on the heavy fuel oil.
20. The method of claim 18 where the adding is performed within a
temperature range of about 250 to about 490.degree. C.
21. The method of claim 18 where the method is practiced in the
absence of adding a co-promoter reaction product from a succinic
anhydride and a lower carboxylic acid.
22. A stabilized heavy fuel oil comprising: a heavy fuel oil
prepared by thermally cracking a residual oil; and a magnesium
overbased compound in an amount effective to improve the stability
of the fuel oil, where the magnesium overbased compound is added to
the heavy fuel oil sufficiently soon after thermal cracking to
produce the residual oil to improve stability, and where the
magnesium overbased compound is selected from the group consisting
of magnesium overbased carboxylates, magnesium overbased
sulfonates, magnesium overbased phenates and mixtures thereof.
23. The heavy fuel oil of claim 22 where the magnesium overbased
compound is present in an amount ranging from about 25 to about
2000 ppm based on the heavy fuel oil.
24. The heavy fuel oil of claim 22 where the magnesium overbased
compound contains at least 21 wt % magnesium.
25. The heavy fuel oil of claim 22 where the magnesium overbased
compound is added within 40 hours or less of the thermal
cracking.
26. The heavy fuel oil of claim 22 where the magnesium overbased
compound is added within a temperature range of about 250 to about
490.degree. C.
27. The heavy fuel oil of claim 22 further comprises an absence of
a copromoter reaction product from a succinic anhydride and a lower
carboxylic acid.
28. The heavy fuel oil of claim 22 where the magnesium overbased
compound is a magnesium overbased carboxylate.
29. A stabilized heavy fuel oil comprising: a heavy fuel oil
prepared by thermally cracking a residual oil; and a magnesium
overbased carboxylate in an amount effective to improve the
stability of the fuel oil, where the magnesium overbased
carboxylate is added to the heavy fuel oil within 2 hours after
thermal cracking to produce the residual oil to improve stability,
and where the magnesium overbased carboxylate contains at least 21
wt % magnesium.
30. The heavy fuel oil of claim 29 where the magnesium overbased
carboxylate is present in an amount ranging from about 25 to about
2000 ppm based on the heavy fuel oil.
31. The heavy fuel oil of claim 29 where the magnesium overbased
compound is added within a temperature range of about 250 to about
490.degree. C.
32. The heavy fuel oil of claim 29 further comprises an absence of
a copromoter reaction product from a succinic anhydride and a lower
carboxylic acid.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application 60/488,891 filed Jul. 21, 2003.
FIELD OF THE INVENTION
[0002] The present invention relates to methods and compositions to
stabilize hydrocarbon streams containing asphaltenes, and more
particularly relates, in one embodiment, to methods and
compositions to stabilize residual fuel oils and coker feedstocks
using readily available materials.
BACKGROUND OF THE INVENTION
[0003] The stability of heavy fuel oils obtained from thermally
cracked residual oils is a well known problem with significant
economic ramifications. Residual fuel oil consists predominantly of
an oil phase, the composition of which is almost entirely related
to the crude oil from which it originates. In this oil phase are
dispersed relatively large hydrocarbon molecules called
asphaltenes. It is the nature of asphaltenes to be attracted to one
another, and it is this tendency, along with size and concentration
of the asphaltene molecules, that are consequences of both the
crude oil type and the thermal cracking manufacturing process. The
compositions of the various thermally cracked residual fuel oils
can thus vary widely.
[0004] The stability of a residual fuel oil can be defined as its
ability to resist the formation of carbonaceous sludge during
storage and handling. The effects of sludge formation in a residual
fuel oil in systems where that fuel oil is used to power an engine
can result in choked centrifuges, filter blocking, heater fouling,
and ultimately, engine shut down and damage. However, the simple
formation of sediment over time in the bottom of storage tanks
causes problems because these sludge layers are difficult to
remove. These sediments are due to the aggregation of the unstable,
high molecular weight polynuclear aromatic asphaltenes.
[0005] The traditional approaches of trying to stabilize thermally
cracked fuel oils is to blend them with valuable refinery stocks or
add any one of a variety of different chemicals to the fuel oils
stored in tanks. However, these techniques have the disadvantage of
having to be customized for each particular fuel oil. Moreover
blending of fuel oil with other refinery cutter stocks requires the
availability of aromatic heavy boiling cuts from Fluid Catalytic
Cracking plants. If such streams are not available, any attempt to
blend unstable cracked fuel with atmospheric or vacuum gas-oil will
result in a de-stabilization of asphaltenes. Addition of chemicals
in storage tanks also requires good mixing, which is seldom
available.
[0006] Similar stability problems affect visbreaking and delayed
coking processes, and potentially any bottoms upgrading process
where the feed is stored at elevated temperatures prior to
processing. Although delayed coking is used herein as a specific
embodiment, as delayed cokers are units where the problem is often
seen, it will be appreciated that the problem is present in any
operation where feed is preheated and heat exchangers experience
fouling.
[0007] Delayed coking is a bottoms upgrading process. It involves
raising a feedstock to approximately 950.degree. F. (510.degree.
C.) using a process furnace, and then transferring the hot stream
to a coke drum. The coke drum functions as a residence chamber for
the oil to allow time for cracking to occur. The products of the
cracking are coke (a highly enriched carbon polymer) which forms in
the coke drum, and some quantity of cracked distillates (gasoline
and gas oil boiling range) which are removed by fractionating a
stream that leaves the coke drum. A common problem with this
process is the formation of fouling (coke formation) in the process
furnace.
[0008] Delayed coker furnace fouling is believed to result from at
least two mechanisms. The first involves the pyrolysis of
hydrocarbons, followed by polymerization and dehydrogenation,
leaving behind a nearly pure carbon structure commonly called coke.
The second mechanism involves the destabilization of already
existing asphaltene polymers in the feedstock. These asphaltenes
exist as a colloidal dispersion in the feedstock, with another
class of high boiling hydrocarbons, resins, acting as the
dispersing agent. Any of several changes to which the feedstock is
exposed can disturb this colloidal state, with precipitation of the
asphaltenes on the furnace tubes. These asphaltenes further
dehydrogenate and result in a coke-like residue, very similar to
that derived from the former mechanism.
[0009] The feed to the coker unit is typically composed of crude
unit vacuum tower residue or bottoms (VTB). In most coker units,
the VTB is partly routed directly as coker feed, while a portion is
routed to intermediate storage. The storage exists as a buffer, to
allow the upstream crude unit to continue producing VTB even while
the coker unit is down for furnace tube decoking. This decoking is
periodically necessary to remove the coke formed from the two
mechanisms described above. The primary economic impact of this
furnace coking or fouling includes lost production penalties and
potentially shorter furnace tube life.
[0010] There is thus a need to find a method and/or composition
that will help stabilize thermally cracked fuel oils and coker
feedstocks that is more effective than current techniques.
SUMMARY OF THE INVENTION
[0011] Accordingly, it is an object of the present invention to
provide a chemical composition for improving the stability of
thermally cracked residual fuel oils.
[0012] It is another object of the present invention to provide a
method for treating thermally cracked residual fuel oils that
improves their stability.
[0013] An additional object of the invention is to provide a fuel
oil that has improved stability.
[0014] In carrying out these and other objects of the invention,
there is provided, in one form, a method for stabilizing a
hydrocarbon stream containing asphaltenes that involves heating the
hydrocarbon stream containing asphaltenes; and adding to the
hydrocarbon stream a magnesium overbased compound. The magnesium
overbased compound may be a magnesium overbased carboxylate, a
magnesium overbased sulfonate, a magnesium overbased phenates, or
mixtures thereof. The magnesium overbased compound is added in an
amount effective to improve the stability of the hydrocarbon
stream. The hydrocarbon stream is subjected to heat after the
addition.
[0015] Further provided in another non-limiting embodiment is a
method for inhibiting coke furnace fouling that includes heating a
coke drum feedstock containing asphaltenes and then adding to the
coke drum feedstock a magnesium overbased compound. The magnesium
overbased compound can be a magnesium overbased carboxylate, a
magnesium overbased sulfonate, a magnesium overbased phenate, or
mixtures thereof. The coke drum feedstock is then stored at an
elevated temperature.
[0016] There is additionally provided a method for stabilizing
heavy fuel oils that involves thermally cracking a residual oil to
provide heavy fuel oil; and adding to the thermally cracked heavy
fuel oil a magnesium overbased compound that is a magnesium
overbased carboxylate, a magnesium overbased sulfonate, and/or a
magnesium overbased phenate, in an amount effective to improve the
stability of the fuel oil, where the adding is conducted
sufficiently soon after thermal cracking to improve stability. In
one non-limiting embodiment of the invention, the magnesium
overbased carboxylate is added within about 2 hours or less of
thermally cracking the fuel oil. In another non-limiting embodiment
of the invention, the magnesium overbased carboxylate is added
within about 40 hours or less of thermally cracking the fuel
oil.
[0017] There is additionally provided in another non-restrictive
form of the invention a stabilized heavy fuel oil that includes a
thermally cracked residual oil. The stabilized heavy fuel oil also
includes a magnesium overbased compound in an amount effective to
improve the stability of the fuel oil. The magnesium overbased
compound is added to the thermally cracked residual oil
sufficiently soon after thermal cracking to produce the residual
oil to improve stability. The magnesium overbased compound may be a
magnesium overbased carboxylate, a magnesium overbased sulfonate,
and/or a magnesium overbased phenate.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The present invention relates to the addition of overbased
magnesium compounds relatively soon after the heavy fuel oil is
produced by thermal cracking before it is stored and/or blended, if
blending is necessary. In particular, the invention is concerned
with the treatment of visbreaker tars. According to one embodiment
of the invention, the application of these compounds is much more
effective if they are applied to the visbreaker tars before storage
and blending of the tar. In particular, early application of these
compounds helps prevent or reduce aging difficulties, resulting in
far better results than attempts to cure aging and stability
problems after their occurrence.
[0019] In one non-limiting embodiment of the invention, the method
operates by treating heavy fuel oils from fractionation of
thermally cracked atmospheric or vacuum residuals. By "heavy" is
meant with a boiling range above 350.degree. C., a density ranging
from 0.9 to 1 kg/m.sup.3 and a viscosity range from 200 to 500
centistokes at 50.degree. C. These properties are averages reported
as non-limiting examples only; it should be clear that these
parameters are not comprehensive of all thermally cracked residuals
to which the present invention applies. The exact method of
production of the fuel oils and their characteristics are not
critical to the method of this invention. Producing heavy fuel oils
by thermal cracking of residual oil is a well-known process in the
industry. Within the context of this invention, it will be
understood that the term "heavy fuel oil" includes, but is not
necessarily limited to, visbreaker tars (or vistars), thermally
cracked resids (residual fuel oils), turbine fuels, and the
like.
[0020] Suitable overbased magnesium compounds include, but are not
necessarily limited to, magnesium overbased carboxylates, magnesium
overbased sulfonates and/or magnesium overbased phenates and the
like. In one non-limiting embodiment, magnesium overbased
carboxylates may be used. A particularly suitable magnesium
overbased carboxylate is KI-85 available from Baker Petrolite. In
another non-limiting embodiment of the invention, the overbased
magnesium compound contains from about 21 to about 26 wt %
magnesium. In another non-limiting embodiment of the invention, the
magnesium content is from about 24 to about 25 wt %. In a
particular non-limiting embodiment of the invention, the compound
has at least about 21 wt % magnesium, and in another non-limiting
embodiment, has at least about 25 wt % Mg. Typically, these
magnesium proportions are average amounts. These magnesium
overbased compounds may be readily produced by methods well known
in the art.
[0021] In another non-limiting embodiment of the invention, the
residual fuel oil is treated by the addition of about 25 to about
2000 ppm of a suitable magnesium overbased compound, based on the
heavy fuel oil. In another non-limiting embodiment, the proportion
of the magnesium overbased compound ranges from about 150 to about
2000 ppm of based on the heavy fuel oil.
[0022] An important part of the method of the invention is to add
the magnesium overbased carboxylate (or other compound) to the
thermally cracked heavy fuel oil sufficiently soon after thermal
cracking to improve its stability. The optimal time or time range
of addition will vary depending on the nature of the overbased
magnesium compound, how much is added, how much magnesium is
present in the compound, the temperature of addition and the nature
of the thermally cracked fuel oil. In one non-limiting embodiment,
the overbased magnesium compound is added at least within about 40
hours or less. In another non-limiting embodiment the overbased
magnesium compound is added at least within about 2 hours or less
after separation of heavy fuel oil from other thermally cracked
streams. In another non-limiting embodiment of the invention, the
magnesium overbased compound is added within 20 hours or less after
thermal cracking, and in an alternate embodiment, within 10 hours
or less.
[0023] In one other non-limiting embodiment of the invention, the
adding of the overbased magnesium compound is performed within a
temperature range of about 250 to about 490.degree. C. Typically,
this temperature will be at or near the temperature of the
thermally cracked residual fuel oil shortly after it is produced.
In yet another non-limiting embodiment, the overbased magnesium
compound is added within a temperature range of about 250 to about
380.degree. C.
[0024] Although it is acceptable to use the overbased magnesium
compounds made according to the methods of U.S. Pat. No. 6,197,075,
incorporated herein by reference, it will be appreciated that in
another non-limiting embodiment of the present invention, the
method is practiced in the absence of adding a copromoter reaction
product of a succinic anhydride and a lower carboxylic acid, in all
of the forms described in the '075 patent. It is also noted that
the method of the '075 patent does not appreciate the need for
adding the overbased magnesium compounds very shortly after the
residual fuel oils are produced by thermal cracking.
[0025] Further, it will be appreciated that it is not necessary for
the heavy fuel oils to completely prevent asphaltene sediments or
aggregation or to produce a heavy fuel oil that is stable forever
for the invention to be considered successful. Rather, the methods
and compositions of this invention are successful if the stability
of the heavy fuel oils is simply improved.
[0026] The present invention also relates to inhibiting or
preventing furnace fouling caused by asphaltenes in other
hydrocarbon streams including coker feedstocks. Again, it will be
appreciated that fouling need not be entirely prevented for the
invention to be considered successful in this context.
[0027] It has been observed that furnace fouling rates are
correlated to the amount of coker unit feed that comes from
storage. Higher amounts of feed from storage result in generally
higher rates of furnace fouling. The basis for the invention is the
possibility that a significant portion of the coker furnace fouling
results due to the 10-20% of feed that comes from the storage tank.
This stored-feed-stock-induced fouling is believed to result from
degradation of the feedstock during this storage time. These
materials are very viscous, and, as such, must be kept at elevated
temperatures (250.degree. F. and higher; 121.degree. C. and higher)
while stored to allow pumping to the coker unit. Storage times can
range from a few days to several weeks.
[0028] The degradation of the stored materials is believed to
involve several possible mechanisms:
[0029] 1. Thermal destruction of the resins, followed by
aggregation of asphaltenes.
[0030] 2. Oxidative destruction of the resins, followed by
aggregation of asphaltenes.
[0031] 3. Oxidation and polymerization of hydrocarbons to form
additional, poorly soluble polymers.
[0032] In all three cases, metal catalysis may promote the chemical
reactions. The metal catalysis may be caused by impurities in the
hydrocarbon stream or possibly the metal conduits and vessels.
Also, in cases 1 and 2, the stability of asphaltenes is negatively
affected, which causes this portion of the coker feed to exhibit a
higher degree of asphaltene destabilization and precipitation than
the portion of feed that does not experience extended storage time.
In case 3, a polymer is formed that, like asphaltenes, has poor
solubility in the oil, and with the extreme temperatures seen in
the furnace, can precipitate as foulant.
[0033] Finally, it has been discovered that these forms of
degradation can be successfully inhibited using the magnesium
overbased compounds previously described. A variety of thermally
stable dispersants such as the magnesium overbased compounds have
shown promise in controlling this degradation, thus greatly
reducing this component of the furnace fouling. Laboratory testing
thus far has shown that two magnesium overbased compounds within
the definition of this invention, both thermally stable
dispersants, give significant inhibition to the degradation, as
measured by solids by hot filtration.
[0034] Previous attempts to control or reduce furnace fouling in
delayed coking units and visbreakers have generally met with little
success. Only sporadic success has been reported. The prior
attempts have involved adding either a dispersant, anti-coking or
antioxidant additive directly to the feed that goes to the furnace
in the delayed coker unit. Additionally, previous attempts to
improve on the furnace treatment by moving the injection point back
up stream, as far as the vacuum tower bottom, to enhance mixing of
additive and oil and to provide additional residence time appear to
have shown some benefit. The benefit may well have occurred as a
result of some of the additive going with the feed that was stored.
This invention involves introducing a more concentrated chemical
treatment into the stored feed or just prior to the hydrocarbon
stream being stored. By "more concentrated" is meant the
high-magnesium content compounds of this invention.
[0035] Typically in a delayed coking operation, the stored feed
comes from a pair of storage tanks. One embodiment of this
invention would involve concentrating the treatment chemicals in
the rundown to storage, rather than treating the furnace
directly.
[0036] The invention will now be further described with respect to
particular Examples that are not meant to limit the invention, but
rather are intended to illustrate it further with respect to
certain, more specific non-limiting embodiments.
[0037] Hot Filtration Test
[0038] The Hot Filtration Test (HFT) is a relatively standard test
to determine the stability of a particular fuel oil.
[0039] Materials
[0040] Four Whatman fiber glass GF/A type filters, 1.6 micrometers
porosity or equivalent
[0041] Hot filtration test equipment
[0042] Heating plate
[0043] Analytical balance, 0.0001 grams
[0044] 100.degree. C. thermometer with 1.degree. C. precision
[0045] n-Heptane, analytical grade
[0046] Mixture of 85% n-heptane, 15% xylene by volume, analytical
grade
[0047] Procedure:
[0048] Install on a hot filtration test apparatus four pre-weighed
(0.0001 grams precision) filters, two for each filtration heated
flask. Heat the filtration flasks at 100.degree. C. with vacuum
applied to the hot filtration test filter holders.
[0049] Heat the fuel to about 70-80.degree. C. to have a fluid
fuel. Weigh 10 grams of heavy fuel oil sample, with 0.0001 grams
precision. Heat fuel oil in a range of 99-101.degree. C. and pour
about half of the fuel oil in the first HFT filter holder, with the
two Whatman filters. Register, by weight, the exact quantity
poured. Repeat the operation with the other filter holder. Wait for
complete filtration under vacuum. Cool filter holders to ambient
temperature. Wash each filter couple, with filters on the filter
holder, with two washings of 25 mls each of n-heptane/xylene
mixture and two washing of 10 mls each of n-heptane. Dry each
filter couple, and reweigh, with 0.0001 gram precision.
[0050] Sediments are determined by average of the weight difference
after and before filtration. Hot filtration results can be
calculated as follows.
HF1=First couple of filters weight after HFT test procedure-First
couple of filters, 1 weighed after HFT, 1 before HFT
HFT1=100*(HF1)/Fuel oil filtered
HF2=Second couple of filters 1 weight after HFT test
procedure-Second couple of filters, 1 weighed after HFT, 1 before
HFT
HFT2=100*(HF2)/Fuel oil filtered
Hot Filtration Test Result, HFT=(HFT1+HFT2)/2
[0051] Results
[0052] As widely recognized, the acceptable sediment content for
fuel oil is less than 0.5% by hot filtration test (HFT). These
sediments are due to aggregation of unstable high molecular weight
polynuclear type aromatics known as asphaltenes. Higher contents
than 0.5% have a negative impact on fuel filters (plugging) and on
the burning quality of fuel. High contents of sediments also have a
negative impact on storage tanks as they tend to settle out on the
bottom of the tank with a layer of sludge that is difficult to
remove.
[0053] The invention consists in limiting the content of sediment
formation with time in storage tanks for fuel oil. Particularly,
the invention is concerned with treatment of residues from thermal
cracking, used as heavy fuels or blended with gas-oils for fuel oil
no. 6 production, in one non-limiting embodiment. More
particularly, this invention is related to the treatment of resids
from visbreaking, commonly known as vistar or tar.
[0054] These feedstocks are very problematic with respect to
sediment formation since thermal cracking in the furnace gives rise
to instability. This can be partially solved by decreasing thermal
cracking temperatures or reaction time at cracking temperatures
(about 430-490.degree. C.), although this leads to a strong
decrease in the yield of valuable 360.degree. C.+distillates from
thermal cracking.
[0055] In attempts to limit the problem of sludge formation,
several products were tested: oil soluble magnesium carboxylate
overbased products (having 14-18% magnesium), oil soluble magnesium
carboxylate overbased formulations with a higher magnesium content
(23-26%; average 25%), an asphaltene dispersant (Baker Petrolite
BPR34260) and a sterically hindered phenol, which acts as a radical
stopper-scavenger, commonly marketed as antioxidant.
[0056] To test the products' effectiveness, samples of vistar and
vistar blended with gas-oil streams were submitted to meet no. 6
fuel oil viscosity specifications, the blank (untreated) samples
and treated samples were subjected to controlled "aging", that is,
keeping them at 80.degree. C. for a period of time of more than 100
hours. This is well representative of typical storage tank
temperatures and after more than 60-80 hours aging
(sludge/aggregates) is complete.
[0057] Products are qualitatively considered to be effective
whenever they are able to keep a sediment content of less than 0.5%
by Hot Filtration Test.
[0058] Reported results are from duplicated measurements with
differences in measurements of less than 10%.
[0059] The results on samples from storage tanks, immediately after
storage, show an unexpected ineffectiveness of these products. The
charge from which the tar sample came had been processed in a
visbreaker plant about 10 hours before the sampling of finished
product, the tar. In fact, the initial Hot Filtration Test value of
the tar is low (0.07%), and products are ineffective even at higher
dosages as reported in Table I below.
1TABLE I HFT Data for Samples Partially Aged, From Storage Sample,
after Dosage, storage (10 hours Aged, Ex. Product ppm after
production) 108 hours 1 None 0 0.07 1.25% 2 Overbased 24-26% Mg
2000 0.93% 3 Overbased 23-26% Mg 200 0.95% 4 Overbased 14-18% Mg
2000 1.01% 5 Dispersant BPR34260 5000 0.01 1.25% 6 Sterically
hindered phenol 5000 0.01 1.23% antioxidant BPR34017 BPR34260 and
BPR34017 are available from Baker Petrolite.
[0060] It was discovered with several trials that for thermally
cracked resids (tar), magnesium carboxylates products are
surprisingly effective when added immediately (within about 2 hours
or less) after separation of tar from other thermal cracking
(visbreaking) products, before sending tar to storage in tanks, as
shown below in Table II.
2TABLE II HFT Data for Fresh Samples from Plant, Treated
Immediately After Tar Fractionation Dosage, Fresh Aged, Ex. Product
ppm Sample 108 hrs 7 None 0 0.01 1.21% 8 Overbased 25% Mg 2000 0.01
0.31% 9 Overbased 25% Mg 200 0.01 0.38% 10 Overbased 25% Mg 150
0.01 0.38% 11 Overbased 25% Mg 100 0.01 0.71% 12 Overbased 25% Mg
50 0.01 0.79% 13 Overbased 14-18% Mg 2000 0.01 0.7% 14 Overbased
14-18% Mg 200 0.01 0.95% 15 Dispersant BPR34260 2000 0.01 1.0% 16
Sterically hindered phenol antioxidant 2000 0.01 1.05% BPR34017
[0061] It should be noted that magnesium carboxylate with a 25%
average magnesium content was effective to keep asphaltenes
aggregation resulting in Hot Filtration Test sediments below 0.5%
with dosages of 2000 ppm, 200 ppm, and 150 ppm (Examples 8, 9 and
10, respectively). For the magnesium over-based based products of
these Examples, 25% is an average value, as this product has some
variability in the exact magnesium content, typically between 23
and 26%.
[0062] It was also discovered that treatment on fuel oil no. 6 from
blending of gas oil and tar and tar itself is ineffective to reduce
Hot Filtration Test content with samples from storage tanks that
have been aged for more than 60 hours and are beyond the 0.5% HFT
content limit, as shown in Table III.
3TABLE III HFT Data on Samples from Storage Tank after 60 hrs for
Tar and for Blended Tar to Meet No. 6 Fuel Oil Viscosity
Specifications Sample, from Ex. Product Dosage, ppm storage tank 17
None 0 >0.5% 18 Overbased, 24-26% Mg 2000 >0.5% 19 Overbased,
24-26% Mg 200 >0.5% 20 Overbased, 14-18% Mg 2000 >0.5% 21
Overbased, 14-18% Mg 200 >0.5% Generally, blended tars (fuel oil
no. 6) showed a greater HFT than unblended tars.
Example 22
Prevention of Furnace Fouling
[0063] A commercial coker currently takes approximately 15% of its
feed from storage. In a 5 year period, numerous additive treatments
have been tried, at the furnace, to control furnace fouling. The
severity of the problem is such that a spalling (a cleanup process)
is necessary, on average, every 12 days. Furnace fouling is
measured by the rate of skin temperature change for several
thermo-couples attached to furnace tubes. A typical starting
temperature is 1000.degree. F. (538.degree. F.). The limitation is
an upper limit on the skin temperature, typically around
1200.degree. F. (649.degree. C.). When the limit is reached, a
spall or a decoke operation to remove coke is required. When either
cleanup process is carried out, production is lost, and furnace
tube life is shortened. These costs are what drive the refiner to
seek solutions. It is expected that injection of an effective
amount of a magnesium overbased carboxylate, such as the
proportions previously mentioned, would inhibit fouling
sufficiently the time between cleanings is increased from 12 days
to 3 months.
[0064] In the foregoing specification, the invention has been
described with reference to specific embodiments thereof, and has
been demonstrated as effective in providing a method of improving
the stability of heavy fuel oils and other hydrocarbon streams
containing asphaltenes. However, it will be evident that various
modifications and changes can be made to the inventive compositions
and methods without departing from the broader spirit or scope of
the invention as set forth in the appended claims. Accordingly, the
specification is to be regarded in an illustrative rather than a
restrictive sense. For example, particular magnesium-containing
overbased compounds falling within the claimed parameters and added
at different times and dosages, or with particular co-components,
but not specifically identified or tried in a particular
composition or under specific conditions, are anticipated to be
within the scope of this invention.
* * * * *