Note: Descriptions are shown in the official language in which they were submitted.
?6
BACKGROUND OF THE INVENTION
lQ Field Of The Invention
The invention relates to an improvement in the treat-
ment of hydrocarbon distillates, and particularly to an improved
method of sweetening sour hydrocarbon distillates by oxidizing
mercaptans in the distillate to disulfides in the presence of a
phthalocyanine catalygt on a charcoal carrier in the presence of
a basic medium and oxygen. An improved basic medium is disclosed,
along with a process for recovery and reuse of a basic medium
which dissolves in the treated hydrocarbon.
Prior Art
The fixed bed sweetening of hydrocarbons is well known
in the art. A typical fixed bed sweetening process is disclosed
~ J
~0~ 6
in U. S. Patent 2,9~8,50~ ~
In this patent, a sour petroleum
distillate is contacted with a fixed bed of a metal phthalo-
cyanine catalyst composited with a charcoal carrier in the presence
of oxygen and an alkaline reagent. The patentee teaches that any
alkaline reagent may be used, but that aqueous sodium hydroxide
solution is preferred because it is cheapest. The other alkaline
reagents taught were aqueous solutions of lithium hydroxide,
rubidium hydroxide, and cesium hydroxide O The patentee taught
~10 that it was possible to have the alkaline reagent as an alkaline
solution, but that a solution in a non-alkaline solvent may be
'~ used. It is believed that the patentee is referring to a non-
,.~ .
!" ' aqueous solvent, rather than a non-alkaline solvent. See 2 lines
46-69.
;15 The advantage of a fixed bed treating process is that
the refiner has a high degree of control over the sweetening
opexation, and can be reasonably sure that all of the hydrocarbon
passing through his fixed bed treating unit will be treated. The
advantage of a fixed bed process as disclosed in this patent is
that it does not add any significant amount of harmful materials
- to the treated hydrocarbon. 'rhis is in contrast to some other
treating processes, e.g., the plumbite process, wherein sulfur is
one of the treating reagents used, leading to the possibility of
sulfur contamination in the hydrocarbon produ~ts.
~5 Another type of sweetening process~ and one that occurs
almost by accident in a number of refineries~ is inhibitor sweet-
ening. This is a phenomena observed when a refiner adds an
, .
~ -2-
,~
10~4496
inhibitor such as phenylene diamine to his petroleum products
and stores the products in a large tank. After several days,
the mercaptan content of the product declines, and the product
may eventually become doctor sweet. In such a process, it is
necessary to contact the mercaptan with oxygen, usually in the
presence of an alkaline reagent. Perhaps the best way to differ-
entiate between inhibitor sweetening and fixed bed treating is
the time of treating. In a fixed bed treating unit, the duration
of contact of hydrocarbon and catalyst is almost always less
than one hour, i.e., these fixed beds typically operate at a
1.0 or higher liquid hourly space velocity. In contrast, in
inhibitor sweetening, the reaction takes several days to occur.
Although the fixed bed sweetening process, as disclosed
in U. S. Patent 2,988,500, was exceedingly satisfactory for many
hydrocarbon charge stocks, there were a few problems encountered
in the practice of that invention. Specifically, a number of
feeds contained naphthenic acids and other oxidation products
which would react with the strong caustic solutions used to pro-
vide an alkaline reagent. The reaction product of the naphthenic
acid and alkaline reagent formed a soap which could plug the
charcoal bed on which the catalyst is supported. Another problem
associated with the use of strong caustic solution is that means
must be provided to insure removal of all caustic from the hydro-
carbon product. These deficiencies can be overcome without too
much difficulty, however. The naphthenic acids can be removed
from the feed with a simple prewash of the feed with a dilute
1094496
caustic material, Similarly, the pxesence of caustic solution
can be eliminated by passing the treated hydrocarbon throug}l a
two-phase separator, then passing the hydrocarbon phase through
a water-wash zone to remove caustic, followed by another two-
~hase separator, followed by passage of the hydrocarbon stream
through a bed of salt which will remove any water remaining in
the charge stock. Finally, passage of the treated hydrocarbon
through a bed of sand will insure that the last traces of water
are removed from the process.
Another problem encountered in the treating arts, is
that the desirable fixed bed sweetening process is being used to
treat very refractory sour hydrocarbon distillates. The hydro--
carbon distillates encountered by refiners today are becoming
!, ' more difficult to treat because, with the worldwide demand for o~l,
reiners are encountering distillates which are exceedingly
difficult to sweeten. With some hydrocarbon distillate, the only
; way to sweeten them in a conventional fixed bed unit is to pro-
vide for frequent replacement of the catalyst in the bed, and
even more frequent placement of the strong caustic used to wet
:~ 20 the charcoal bed.
Accordingly, I realized that it would be very desir-
able to find a way to operate the fixed bed treating process
without using an aqueous solution of sodium hydroxide. It
:j would also be desirable if a substitute could be found which
would be soluble in hydrocarbons, and perhaps eliminating the
necessity for a separate alkaline phase in the fixed bed
- sweetening process.
.;~
. .
: ~ ' `.,
4~6
I also realized that it would be desirable to eliminate, if
possible, the waste disposal problem associated with the use of
aqueous sodium hydroxide solutions.
I conducted a series of tests, and discovered that the
~ 5 use of quaternary ammonium hydroxides would permit complete
; elimination of the conventional alkaline reagent, i.e., aqueous
sodium hydroxide solution, used in a fixed bed treating process.
; Accordingly, the present invention provides in a pro-
`~ cess for treating a sour hydrocarbon distillate containing mer-
captans by reacting the mercaptans with an oxidizing agent by
- passing the distillate, oxidizing agent and an alkaline medium
through a fixed bed of a phthalocyanine catalyst composited with
a carbon carrier at a liquid hourly space velocity of 0.1 to 20,
the improvement which comprises use of a quaternary ammonium
compound as the alkaline medium.
In one embodiment, the present invention provides a
process for oxidizing mercaptans present in a liquid hydrocarbon
`~ stream comprising: (a) contacting the hydrocarbon stream with an
oxidizing agent in the presence of a metal chelate catalyst and
an organic alkaline reagent to produce a treated hydrocarbon
stream with reduced mercaptan content and containing dissolved
organic alkaline reagent; (b) contacting the treated hydrocarbon
phase with water and recovering an aqueous phase containing at
least 50% of the organic alkaline reagent present in the treated
hydrocarbon; (c) passing the aqueous phase from step (b) to a
fractionation means and separately recovering therefrom water
- and concentrated organic alkaline reagent; (d) recycling the
10~ 96
water from step (c) to step (b); and (e) recycling the concen-
trated organic alkaline reagent from step (c) to step (a).
It is believed that any highly alkaline quaternary
ammonium compound may be used. The preferred compound is a
quaternary ammonium hydroxide, and particularly, tetrabutyl
ammonium hydroxide.
Another excellent quaternary ammonium hydroxide is
one in which a benzene ring is at least one of the substituents
on the ammonium hydroxide. Thus, benzyl trimethyl ammonium
; 10 hydroxide is another excellent alkaline reagent for use in the
present invention.
The quaternary ammonium compounds may be used in an
; aqueous or alcoholic solution, and substitute for the conventional
aqueous solution of sodium hydroxide. Thus, the fixed bed of
catalyst used in the sweetening process may be wetted, either
continuously or intermittently with an aqueous or alkaline
- solution of the quaternary ammonium compound. In the preferred
embodiment, the quaternary ammonium compounds are dissolved in
the hydrocarbon feed to the fixed bed unit. This permits elim-
ination of an aqueous or alcoholic phase within the fixed bed
treating reactor.
When the quaternary ammonium compounds are used in an
aqueous or alcoholic solution, the concentration should be 0.1
to 10 normal. The upper limit is a function of how much quater-
nary amine will dissolve in the aqueous or alkaline medium usedto contain the alkaline reagent, while the lower limit is set
10~
by the minimum concentration required to provide a basic medium.
Optimum concentration secms to bc around 1 n~mal.
In th~ preferre~ embodiment, quaternary ammonium
hydroxide is used without any solvent, i.e., dissolved in the
feed. Thus, small amounts of QAH, or quaternary ammonium hy-
droxide, may be added to a storage tank supplying feed to the unit,
or to the feed as it comes to the unit, or injected in the reactor
upstream of the charcoal. The QAH may be dissolved in a hydro-
carbon, aqueous or alcoholic solvent to permit easy metering of
the QAH into the charge stock. However, once injected into the
feed, the QAH would dissolve in the feed.
The fixed bed of catalyst will operate in substantially
the same way as in prior art units, i.e., the temperatures, LHSV,
pressure, and amounts of oxidizing agents added will be conven-
'~ 15 tional. In practice, the preferred conditions are a low pressure,
but sufficient to maintain liquid operation within the reactor,
'~ typically one to ten atm, absolute. Temperatures will generally
be ambient, or slightly above ambient, which will speed up the
rate of reaction somewhat. Temperatures of 20 to 60 C work
well. The LHSV may range from 0.1 to 20. The amount of oxidiz-
ing agent added should be at least enough to satisfy the stoichio-
metric amount needed to oxidize the mercaptans contained in the
feed to disulfides. Usually air is added in an amount equal to
100 to 250 percent of the amount of air required to oxidize all
of the mercaptans.
The catalyst used can be any catalyst which will speed
up the rate of mercaptan oxidation in the presence of an alkaline
~0~44~6
reagent enough to permit sweetening of a sour hydrocarbon dis-
tillate over a fixed bed of the catalyst. Some metal chelates
possess sufficient activity to permit their use as in such a
process. Preferred among the metal chelates are the phthalo-
~- 5 cyanines. Especially preferred are the monosulfonated deriva-, tives of cobalt phthalocyanine. ~he sulfonation of the cobalt
phthalocyanine makes the material soluble enough in various sol-
vents to permit the impregnation of a fixed bed of charcoal with
the catalyst. The monosulfonate derivative is preferred because
the more highly sulfonated derivatives are more soluble in the
water which is periodically used to wash out accumulated impuri-
tles permitting the leeching away of catalyst from the bed.
Recent work done with polyphthalocyanine catalysts, and mixtures
of different metal phthalocyanines, indicates that these catalyst
too may be acceptable for use in the present invention, although
,~ forming no part thereof.
The catalyst material may be composited with any suit-
able form of charcoal by conventional means. An excellent way
of preparing the catalyst is to dissolve, e.g., cobalt phthalo-
cyanine monosulfonate in methanol and pass the methanol-catalyst
solution repeatedly over a bed of activated charcoal. The pre-
cise type of catalyst used, its method of preparation and its
incorporation onto a bed of charcoal support form no part of
- the present invention.
EXA~PLES
To evaluate the effectiveness of the alkaline medium
of the present invention, a number of experiments were run. A
-8-
10~4~6
,
'
kerosene which was very difficult to sweeten was used as the
` reference feedstock. The kerosene contained 180 wt. ppm mer-
captan sulfur.
The test procedure used was not meant to be indicative
; 5 of commercial operation, rather it was meant to be a simplified
procedure which would quickly separate good alkaline reagents
from bad ones. The test procedure was to put 2 grams of catalyst,
wetted with 5 ml of the alkaline reagent being tested, plus 100
i ml of feedstock in a 300 ml flask. The flasks were then capped
and placed in an automated shaking device. Temperature was not
measured, but all tests were conducted at ambient temperature in
a room maintained at about 25 C, so changes in temperature are
not believed to be significant. The contents of the flasks
were sampled at uniform intervals and the mercaptan sulfur con-
tent of the hydrocarbon determined.
To insure the validity of the test, a number of blanks
were run, i.e., operation with charcoal which contained no metal
phthalocyanine catalyst on it, and operation with and without
conventional alkaline reagent (aqueous sodium hydroxide solution).
The same lot charcoal material was used throughout the test, a
vegetable derived charcoal sold by the Westvaco Co. known in the
trade as Nuchar WA. The catalyst was prepared by impregnating
the charcoal with a cobalt phthalocyanine monosulfonate. The
catalyst was prepared by dissolving 0.15 grams of cobalt phthalo-
cyanine sulfonate in 100 cc of methanol. The cobalt phthalo-
cyanine was difficult to dissolve, so to insure that all of it
_9_
, ~ ~ ,~ ,. :.,
1094496
.
! ~ went into solution, the dissolu-tion proceeded step-wise, i.e ,
one-fourth of the alcohol was mixed with the phthalocyanine,
then decanted, then the next o,ne-fourth portion was added to
the cobalt phthalocyanine remaining in the bottom of the flask
with grinding of the cobalt compound. This was repeated a
third and a fourth time to make sure that all of the active
material was dissolved in the alcohol. The alcohol was then
placed in a container with 15 yrams (100 cc) of charcoal, stirred
slightly, and allowed to stand overnight. The alcohol was then
drained from the material, and the charcoal dried under a water
pump vacuum. The filtrate had only a faint blue color, but did
not contain any significant amount of cobalt, so the catalyst
contained 1 wt. ~ of the cobalt phthalocyanine sulfonate. This
catalyst was divided into several 2 gram portions for use in
carrying out the activity tests. The bases used, and the
results of the test are reported in the following table,
., .
~ 10 -
10~9~
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109 1~96
A dash indicates that the mercaptan content was not
tested. The results reported under test 3, i.e., use of aqueous
NaOH solution, indicate the standard activity for a convcntional
fixed bed process. Surprisingly, the use of an alcoholic NaO~I
solution gives much better results than use of an aqueous NaOH
solution, however, the use of an alcoholic sodium hydroxide solu-
tion forms no part of the present invention. Not all solutions
showed an improvement in going from an aqueous to an alcoholic
phase, as can be observed by comparing the results of aqueous
NH40H to alcoholic NH40H. The alcoholic NH40H appeared to give
slightly higher initial activity, but after a 60 minute period,
the mercaptan content was 100 to 20% higher for the alcoholic
solution than for the aqueous solution.
A number of organic bases were tested. The results
are presented in Table II.
-12-
10~ 96
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10~4496
In addition to this accelerated testing, a test of one
embodiment of the present invention was conducted at a refinery.
The refiner had experienced extreme difficulty in sweetening a
heavy gasoline produced from an FCC unit. The gasoline contained
large amounts of materials which would oxidize to form gum, which
would plug the bed, and color bodies, which made the gasoline
unacceptable. In addition, the gasoline contained very high
levels of mercaptan sulfur, which were difficult to oxidize. The
refiner's treating unit was a fixed bed sweetening system using
a catalyst similar to that prepared for the batch shake test
discussed previously in this specification. The refiner used
naturally occurring basic nitrogen compounds present in the hy-
drocarbon feed to the unit, to provide the alkalinity needed.
The catalyst rapidly deactivated, probably due to formation of
, 15 gum or other polymeric material upon the bed of charcoal cata-
lyst. In addition, the gasoline product contained an unacceptable
~ gum content. The gum content was probably due to over oxidation
3 of treated feed. At the very start of a run, air injection equiv-
alent to 150~ of stoichiometric would convert mercaptans to di-
sulfide, while at the end of a run, the gasoline product would
not be doctor sweet even with a 400 or 500 percent of stoichio-
metric air condition. Even increasing the temperature~ to
125 F and decreasing the throughput to 45% of design capacity
could not produce a sweet gasoline. In addition, the catalyst
appeared to lose activity irreversibly because operation between
regenerations went from eight days, to about three days, to one
day. Catalyst regeneration was effected by steaming of the
catalyst bed with 50 psig plant steam to desorb gum material.
:
; -14-
.~ ~
The treating unit was designed to process about 20,000
barrels per day of a heavy gasoline from an FCC unit. The tem-
perature of the gasoline entering the unit was 117 F. Oxygen
was added by adding compressed air in an amount equivalent to
1.1 times the amount of air required to convert mercaptan sulfur
to disulfides. The Saybolt color of the feed was, on average,
about +20. The feed did not come from storage, but came primarily
from another operating unit, the FCC unit in the refineryO Ac-
cordingly, the feed composition varied during day-to-day opera-
tion. On average, the boiling range of the charge stock was 125,180, 285, 382 and 434 F for an initial boiling point, 10 LV %
distilled, 50 LV %, 90 LV % and end point respectively. The
feed contained from 40 to 70 ppm basic nitrogen. The gum con-
tent of the feed was determined by two methods, air jet gum and
nitrogen jet gum. The air jet gum content of the gasoline feed
ranged from 12 to 33 mg/100 ml, while the nitrogen jet gum con-
tent ranged from 0 to 1 mg/100 ml. The great difference in gum
content by the two methods indicated that the feed contained an
exceptionally large amount of material which would oxidize in
the presence of air to form gum.
The quaternary ammonium compound used was tetramethyl
ammonium hydroxide, or TMAH. T~H has a molecular weight of 91.15
and is soluble in water and hydrocarbons. It was available as
a 26 wt. % solution in methanol. Reagent grade material was
used for this test, though it is believed that ~chnical grade
of TM~H will work as well.
-15-
~0~4~
The test was conducted in several phases, the first
phase was with injection of TMAH, the second phase was without,
and the third phase was again with TMAH injection. This
sequenc~ of operation did illustrate how the unit worked with
and without TMAH injection. The reason for the discontinuous
addition of TMAII was more accidental than intended. Three 55
yallon drums of the 26 wt. ~ solution of TMAII in methanol were
readily available, while de]ivery of two or more drums required
several days. Consequently, the amount of TMAI-I available was
used, and when more came in later, it was also used. The data
taken during this test run are presented in greater detail in
Table III. These data are averages for each day of operation,
and are the be~t available.
.
.: .
- 16 -
~10~ L~ 4 ~?6
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,, .
10!~ 6
As a supplement to the data, the notes made by a
chemical engineer supervising the test run are also reported.
"Initially, the following conditions were established
on the unit:
Heavy FCC gasoline flow = 19,500 BPD
Gasoline temperature = 117F
Air rate = 1.1 x theory
RSH-S = 310 ppm
Color = +19 Saybolt
T~iAH injection rate = 6 gal/hr
T~H concentration in gasoline = 8.8 ppm as N or
` 10.7 ppm as OH
"Within an hour of initiating Tl~AH injection, gasoline
product RSH-S was reduced to 20 ppm. Air rate was increased
to 1.3 x theory and within five hours the product gasoline
was doctor negative.
"The unit charge rate was increased to 29,800 BPD
which reduced the fixed TMAH injection to a concentration of
5.6 ppm. as nitrogen or 6.8 ppm. as OH in the gasoline charge
to the reactor. The air rate was reduced to 1.1 x theory.
The above conditions were maintained for about 16 hours until
the first three drums of Tl~AH had been used.
"The effect of the small quantity of alkali added
was dramatic. Color loss during the above trial was only
3 to 6 Saybolt numbers. Product mercaptan was 1 to 2 ppm.
Existent gum and peroxide number were minimal. Product
alkalinity was low, e.g., pH = 6.1. In summary this plant
trial confirmed previous pilot plant trials conducted at
Des Plaines.
-18-
10~'t4~36
hile waiting for the remaining two drums of TMAH
to arrive at the unit, the effect of deleting T~H injection
on the unit performance was noted. Product gasoline remained
sweet for 10 hours at 1.1 x theory air rate after TMAH injec-
tion stopped. It was then necessary to raise air rate to 2.1x theory to maintain sweet product another 10 hours at which
time reactor LHSV was halved and air rate increased to 3 x
theory to maintain sweet product for another 12 hours. The
, gasoline remained sour for another day during which time
product color loss, existent gum and peroxide number quickly
increased. At that time the additional two drums of T~H
were added to the unit at reduced injection rate.
"TMAH injection at 3 ppm as Nitrogèn and 4 ppm as
Nitrogen even at 3 x theory air rate failed to sweeten the
gasoline, e.g., 10 ppm. RSH-S. This no doubt results from
the short duration of T~H injection after the bed had been
allowed to become fouled following the first TMAH trial. From
the reduced existent gum and peroxide number and improved
color in the product, the Ti~H was benefiting operation at the
reduced injection rate."
In the refinery test of the present invention wherein
tetramethylammonium hydroxide was continuously added to the
feed to the treating unit, no complaints were noted of any
objectionable odor or characteristics imparted to the feed
via dissolution of the T~H in the product. The test run,
however, was of short duration, and on only one feedstock.
-19-
~0~ 6
Because many organic alkaline reagents, and especially the
quaternary ammonium compounds, are soluble in the oil, they
may appear in the treated product. A significant amount of
the organic alkaline medium may be present in the treated
product when a highly alkaline medium is required for the
- treating process. Similarly, the end use of the treated
hydrocarbon may put very stringent limitations of the amounts
of organic alkaline reagent which may be present. This is
particularly true when using tetramethylammonium hydroxide
which can impart a "fishy" odor to some types of hydrocarbon
stocks.
It also may be desirable to recover the organic
~ alkaline medium used to permit its reuse within the process.
; In general, it is believed that the small quantities of QAH
used in the process of the present invention will not normally
justify elaborate QAH recovery facilities, but the economics
of each refinery unit will be different.
When it is desired, for reasons of economics, or
to meet a stringent product specification, to remove the or-
ganic alkaline reagent dissolved in the feed, this can beaccomplished by washing the organic alkaline reagent from the
treated product with water. The washwater can then be frac-
tionated to recover a water phase and an alkaline reagent
rich phase. The alkaline reagent rich phase may be recycled
to the feed to the unit to sati~fy some or substantially all
of the process's requirement for alkaline reagent. The water
recovered from the fractionation zone may be reused to wash
-20-
~09~96
organic alkaline reagent from the treated product. It will
probably be necessary to continuously remove a small portion
of the alkaline reagent rich stream, containing acidic impuri-
;~ ties such as naphthenic acids, phenols, aliphatic acids, and
the like, and dispose of it by mixing it with fuel oil forburning in the refinery. The net consumption of organic
alkaline reagent will then be only a function of the non-mer-
captan acidic components of the feed to the unit, in addition
to any loss of organic alkaline reagent in the dissolved
product. In general, it will not be worthwhile to recover
organic alkaline reagent unless at least about 50~ of the
alkaline organic reagent remaining in the treated product is
removed therefrom in the water-wash step.
The relative solubilities of the organic alkaline
reagent in water and in hydrocarbon, the product specifica-
tions, and the price of organic alkaline reagent will deter-
mine the exact percentage recovery of organic alkaline reagent
desired, and the ratio of wash-water to treated product needed.
-21-
'
