Note: Descriptions are shown in the official language in which they were submitted.
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~ Descri~tion
Process for Removal of Organo-sulfur
Compounds from ~iquid Hydrocarbons
Technical Field
This invention relates to the purification of
hydrocarbons containing sulfur compounds, and, more
particularly, it relates to a process for desulfurizing
liquid hydrocarbons containing organo-sulfur compounds by
oxidation of the organo-sulfur compounds employing an
ion-oxidant which is electrochemlcally regenerable.
Backqround ~t
For environmental reasons there is an ever-increasing
need for liquid hydrocarbon ruels containing very low levels
of sulfur, e.g., fuels for motor vehicles having sulfur
contents as low as 0.03 wt~ (300 ppm) or even down to 0.003
wt~ (30 ppm).
Presently, hydrorefining is frequently used for
industrial puri~ication of petroleum distillates.
Hydrorefining is known to provide nearly complete removal o~
mercaptans, sulfides and disulfides from liquid hydrocarbons.
But, the use of hydrorefining for reducing the thiophene
- content to a level of 30 ppm is limited because of the
expense, and so the sulfur conten. remains rather high, e.g.,
about 0.1-0.2 wt~.
While it is possible to use a multistage hydrorefining
process employing consequent increased hydrogen partial
pressure and a precious metal catalyst to remove such
difficult to remove sulfur compounds, this is not considered
feasible, due to the expense of installing and operating such
a process.
An alternative approach is to extract and absorb these
latter sulfur compounds using selective solid sorbents. But
thiophenes possess a low reactivity and the customary
sorbents do not provide the necessary efficiency of
purification.
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Some analogs are also known for the electrolytic
desul~urization of petroleum products. For example, U.S.
Patent No. 3,193,484 discloses a process for the electrolytic
oxidation of mercaptans, which is based on the removal of
mercaptans ~rom petroleum fractions via oxidation of
mercaptides into disulfides which remain in the electrolyzer.
This patent also reviews the prior art as covered in U.S.
Patents Nos. 2,140,194; 2,654,706; and 2,856,353. In this
process a stream of fuel is mixed with an electrolyte and the
mixture flows through an anodic cell where the mercaptides
are converted into disul~ides and oxygen is released. More
specifically, a feedstock containing acidic impurities (e.g.,
mercaptans) is subjected to treatment with an alkaline
reagent. The preferred reagent i8 an aqueous solution of an
alkali metal hydroxide such as sodium hydroxide. That alkali
metal hydroxide chemically interacts with the mercaptans
forming e.g. sodium mercaptide, which is then converted into
a disul~ide, according to the following reaction:
2NaSR+O ---> R2S2+Na2O
where the required oxygen atoms are produced by the
electrolytic decomposition of water. Concurrently, the
disulfides are ~ormed via the oxidation of mercaptans on the
anode of an electrolytic cell:
2RS ---> RSSR + 2 electrons
This process runs only at the electrode surface in a two
phase system. The working solution from the anodic cell then
flows into a settling tank where the disul~ides and oxygen
are re~oved from the solution, after which the solution is
washed by ligroin in a scrubber and returned to an extraction
column. Because this process runs only at the electrode
surface in a two phase system, the puri~ication is not very
ef~ective. Also, the method is not appropriate for removing
thiophene derivatives.
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An electrochemical method of purifying petroleum
products is described in U.S. Patent No. 3,915,819.
According to this method, the oil or petroleum products are
mixed with an ionizing organic solvent (e.g. methanol,
toluene, etc.) and the mixt~re is exposed to the action o~ a
DC current having a current density of not less than 0.0001
A/cm2 and a voltage of between 2-120V. To speed up the
process an aqueous salt solution or solution of bases of
alkaline or alkaline-earth metals is introduced into the
stock to ensure a pH value of 8-12. The process is conducted
for not less than 4 hour9 in an electrolyzer containing two
platinum cylindrical electrodes having a definite ratio of
anode/cathode areas. The effectiveness of the
desulfurization can be as high as 90~. The shortcomings of
the method include: (1) constant control over the process
parameters must be provided since the magnitude of current
density, voltage and pH change during the process; (2) high
power consumption (be~ause of the high resistivity of the
electrolyte, most of the consumed electric power is wasted on
heating the electrolyte); and (3) the process requires not
less than 4 hours because the poor conductivity of the
electrolyte does not permit the use o~ high current
densities.
U.S. Patent No. 4,101,635 discloses a method for
oxidizing sulfur dioxide by contacting a sulfur
dioxide-containing gas and an oxygen-containing gas with an
aqueous solution containing pentavalent vanadium and divalent
manganese as an oxidation catalyst, wherein a calcium
compound and an oxygen-containing gas are added to the
aqueous solution, the resulting gypsum is separated, and the
recovered aqueous catalyst solution is recycled for use as
the oxidation catalyst.
U.S. Patent No. 3,793,171 discloses a process for the
destruction of oxidiza~le impurities carried in a gas stream
by contacting the gas stream with an aqueous acid stream
containing an electrolytically regenerable oxidizing agent,
and electrolytically regenerating the oxidizing agent for
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further treatment o~ additional amounts of the gas stream.
Cobalt in the +3 ~alence state (Co III) is said to be the
most preferred oxidizing agent, and other suitable metals
exhibiting at least two different ionic valence states are
stated to be chromium (Cr VI/III), manganese (Mn III/II),
silver (Ag II/I) and cerium (Ce IV/III). The process
disclosed in U.S. Patent No. 3,793,171 differs from the
present invention in that it is not specifically intended for
the selective removal of admixtures of heteroatomic compounds
from hydrocarbons. Instead, it discloses a process designed
to remove oxidizable gases from a gas stream.
At the present time, however, a practical, low-cost and
efficient process has not been developed for purifying liquid
hydrocarbons, such as petroleum distillates used for fuels,
of d'ifficult to remove organo-sulfur compounds.
Pisclosure ~ the Tnvention
A primary object of the present in~ention is a process
for removing organo-sulfur compounds from liquid
hydrocarbons. A further object is a process for efficiently
and economically purifying liquid hydrocarbons used for fuels
and chemical feedstocks of residual, difficult to remove
organo-sulfur compounds such as thiophene. Other objects of
the invention will become apparent from the ~ollowing
description of the invention and the practice thereof.
In order to achieve the objects of the present invention
there is pro~lded a process ~or purifying a liquid
hydrocarbon feedstock containing organo~sul~ur compounds,
which process comprises: (a) forming an aqueous sulfuric acid
solution containing an ion-oxidant with a concentration of
transition metal ions in a first, lower oxidation state; (b)
passing an electric current through the aqueous solution
between an anode and a cathode in an electrolytic cell to
oxidize said ions of said ion- oxidant to a second, oxidation
state higher than said first oxidation state so as to form a
fresh working solution containing the resulting oxidized
ions; (c) introducing said feedstock and said working
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solution into a con-tacting zone and intimately contactlng
said feedstock and said working solution therein under
conditions e~fective to oxidize organo-sulfur compounds in
said feedstock and form watersoluble, or gaseous sulfur-
containing compounds and to reduce said oxidized ions, so asto form a mixture of (i) a 9pent working solution containing
the resulting reduced ions and having said water-soluble
compounds dissolved therein and (ii) a puri~ied hydrocarbon
product containing a reduced level of said organo-sulfur
compounds relative to the level thereof in said ~eedstock;
(d) separating said purified hydrocarbon product and said
spent working solutioni (e) recovering the separated purified
hydrocarbon producti and (f) returning the separated working
solution to step (b) above wherein 9aid reduced ions are
oxidized to a higher oxidation state. Preferably, the
ion-oxidant contains ions of vanadium, chromium, manganese,
cobalt or cerium. The sulfuric acid solution preferably
contains ~rom about 4 to about 15 moles of sulfuric acid per
liter.
As used herein, "ion-oxidant' refers to an active
particle in an electrolyte or in a chemical reagent whose
composition contains one or more types of such active
particles. The ion-oxidant contains one or more metal ions
of varying valence (e.g., V, Cr, Mn, Ce, Co) surrounded in
the electrolyte with a shell of water molecules, oxygen ions,
hydroxyl ions and anions of the electrolyte. The ion-oxidant
can accept one or more electrons ~rom the compound being
oxidized and can transfer water molecules, oxygen ions,
hydroxyl ions and anions of the electrolyte from its shell to
that compound.
~rief Descr;~tion of the Drawings
The present invention is described herein ~elow with
reference to the accompanying drawings, wherein:
Fig. 1 is a general schematic process flow diagram of a
process according to the present invention; and
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Fig. 2 is a schematic process flow diagram of one
preferred process according to the present invention.
Best Mode ~or Carry; n~ Out the Tnvent; ~
As used herein, "hydrocarbon feedstock'~ means any fuel
oil (e.g. gasoline, diesel fuel, propellant), petrochemical
feedstock or the like in the form of a particular oil
~raction or particular hydrocarbon. The liquid hydrocarbon
feedstocks purified by the present process may be derived
from petroleum, coal, oil shale or bituminous sands, etc. and
typically are liquid hydrocarbon mixtures containing
organo-sulfur compounds.
The preferred feedstocks for the present process have
been subjected to a preliminary purification to substantially
reduce the content of heteroatomic compounds by
hydrorefining, or by other suitable preliminary purification
techniques, which also reduce the content of unsaturated or
resin-forming compounds. This is so because the present
process works to oxidize organo-sulfur compounds.
Unsaturated or oxygen-containing compounds also may be
oxidized to yield various by-products (e.g. resins), thus
reducing the selectivity for desul~urization. Thus, it is
generally undesirable ~or fuel oils of complicated
composition (e.g., containing ethers or alcohols) to be
puri~ied by the technology. The present invention is
preferably employed to provide a fine purification of
hydrocarbon feedstocks which have been subjected to
hydrorefining (e.g., fuel oils satisfying standards presently
in force, i.e. sulfur content ~ 1000 ppm or < 10,000 ppm)
which contain no, or only minor amounts of oxidizable
compounds. In such cases, the present process provides a
selective removal of residual sulfur-containing,
oxygen-containing, nitrogen-contalning compounds and
heteroatomic compounds containing heavy metals.
An aqueous sulfuric acid solution is employed in the
present process as a carrier for the ion-oxidant and as an
electrolyte.
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Aqueous solutions of sul~uric acid have been used to
remove organo-sulfur compounds from petroleum products by
so-called "sul~uric acid purification'1. In this process an
aqueous solution of sul~uric acid at an acid concentration
ranging from 2.5 to 18 moles/liter (2.5-18 M) (this
corresponds to 20-96 wt~) is used to remove various organo-
sulfur, unsaturated, or resin-forming compounds. Fuming
sulfuric acid with a monohydrate (S03) concentration of 104.5
~, or dry sul~uric anhydride (S03) as a gas can also be used.
Solutions o~ sulfuric acid with concentrations less than
15M (93 wt~) are used only for removing non-saturated or
oxygen-containing compounds from petroleum products. At
these concentrations, the main mechanisms involved in the
process are polymerization and sulfurization.
In order to remove organo-sul~ur compounds ~rom
petroleum products via oxidation using the sulfuric acid
purification technique, the concentration of sulfuric acid
must be greater than 15 M (93 wt~). In this case, the
sulfuric acid is a spent reagent - its consumption rate
exceeds lO kg per 1 kg of sulfur removed. Moreover,
resin-like products (so-called "acidic tar~) are formed which
are not soluble in the petroleum product and so must be
removed via settling, filtration, or centrifuging. The
ef~iciency of the sulfuric acid puri~ication technique with
respect to thiophenes is less than 40-50~.
The present method of oxidizing organo-sulfur compounds
by means of ion-oxidants preferably uses a sulfuric acid
concentration range of 4 - 15 M, i.e. in those concentrations
of sulfuric acid (viz., c 15 M) where sulfuric acid alone
(without the presence of any ion-oxidants) does not remove
organo-sulfuric compounds ~rom petroleum products.
Also the present method does not use sul~uric acid as a
spent reagent which is consumed to oxidize the organo-sulfur
compounds. During the oxidation of a molecule of an
35 organo-sulfur compound, the following substances take part:
ion-oxidants, hydrogen ions, and water molecules. The
products of the incomplete dissociation of sulfuric acid
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(i.e. HSO~[-] ions)-can participate during the early stages
of the oxidation process (immediately after the organo-sulfur
molecule has been attacked by an ion-oxidant) as a catalyst
of the water molecule addition to the partly oxidized
organo-sulfur molecule. Like any other catalytic process,
the HS04~-] ions are not consumed.
The spent reagents in the present method of oxidizing
organo-sulfur compounds are ion oxidants (i.e. the
ion-oxidants transfer into to a lower oxidation state) and
water. In the case of complete oxidation, sulfur is oxidized
to form sulfuric acid. Thus, sUlfUriC acid is a product of
the present process, which is formed concurrently with the
fuel purification. Some minor consumption of the sulfuric
acid may occur because of possible side-reactions involving
non-saturated compounds, e.g., polymerization of the
non-saturated compounds.
Thus, the results of comparative testing of the present
process and the sulfuric acid purification technique are as
follows:
a) Regime of concentrated sulfuric acid (i.e. 15-18
M). Such concentrated sulfuric acid removes about
40-50~ of the organo-sulfur compounds, and the
addition into the solution of ion-oxidants does not
improve the purification ef~ectiveness.
b) Regime of dilute sulfuric acid (i.e. 4-15 M). The
standard sulfuric acid purification technique is
not e~fective with respect to thiophenes at such
concentrations of sulfuric acid. But the addition
of ion-oxidants into the solution provides almost
complete removal of=all organo-sulfur compounds.
The best results are obtained for a sulfuric acid
concentration range of 6-12 M, and maximum
effectiveness is observed within the range of 7-lO
M, with the concentration of 9 M being most
effective for the feedstock employed.
c) Regime of low sulfuric acid concentration (i.e. < 4
M). Thiophenes are not removed if such low
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concentrations of sulfuric acid are used, although
oxygen-sulfur-organic compounds are removed.
Thus, the preferred range of sulfuric acid concentration
in the solution is 4-15 M, with the range of 6-12 M being
preferable, and the range of 7-10 M providing the maximum
effectiveness.
In the present process the ion-oxidants are in the
aqueous electrolyte, or sulfuric acid solution, and the
organo-sulfur compounds are in the liquid hydrocarbon
feedstock. The electrolyte and the feedstock are, for
practical purposes, mutually insoluble and form a
heterophase system when mixed. ~hus, a liquid interface is
present to enable the oxidation o~ the organo-sul~ur
compounds by the ion-oxidant and subsequent reactions of the
organo-sulfur compounds with water or sulfuric acid. The
purification rate and purification effectiveness are
influenced by the interface area and time the two are in
contact. Conse~uently, it is desirable to mix the feedstock
and the electrolyte, e.g., by forming an emulsion, so that
they are in intimate contact.
Any known method of providing the interface can be
employed to realize the present process of desulfurization.
Thus, the heterophase system involving the hydrocarbon
feedstock and the working solution may be obtained in the
following ways:
1) An emulsion may be formed by mechanical or
acoustical mixing and may contain the hydrocarbon
feedstock as either a disperse or a continuous
phase;
2) Concurrent co-directed flows of the hydrocarbon
feedstock and the electrolyte through a porous
media, the solid phase of whlch exhibits similar
wetting properties with respect to the hydrocarbon
and the working solution (electrolyte);
3) Concurrent co-directed flows of the hydrocarbon
feedstock and the electrolyte through a porous
media, the solid phase of which exhibits dissimilar
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wetting p~operties with respect to the hydrocarbon
and the working solution (electrolyte);
4) Concurrent counterfIow of the hydrocarbon feedstock
and the electrolyte by gravitational or centrifugal =.
forces;
5) Concurrent counterflow of the hydrocarbon feedstock
and the electrolyte along solid surfaces (e.g.,
plates, fibers, etc.) with respect to which the
hydrocarbon and the working solution exhibit
similar or dissimilar wetting properties.
Any known method may be used to separate the purified
petroleum product and the electrolyte. The choice of
extractor type is defined mainly by economics.
The ion-oxidants used in the present process contain
ions which work as carriers of electrons from the
organo-sulfur compounds in the feedstock to an anode of the
electrolytic cell. The ions change their charge during such
interaction, thus requiring electrolytic regeneration.
Such ions are produced by the following method. The
electrolyte is prepared first and consists of, e.g., a 9 M
aqueous solution of sulfuric acid and the dissolved salt of a
transition metal such as V, Cr, Mn, Co, or Ce in which the
metal is in either the lowest or intermediate (but not in the
highest) oxidation state. The metal salt can be of any type
which dissolves in the solution, e.g., chlorides. Since the
main electrolyte is sulfuric acid, it is preferable to use
sulfates of such metals. In such cases no new ions appear in
addition to the ones participating in the chemical process of
purification of the hydrocarbon and additional side-reactions
are avoided.
Thus, VOS04, Cr2 (S04) 3, MnSO4, Ce2(SOq)3, or CoS04 are
dissolved in the electrolyte to create the required
concentration of one of the ions: V4+, Cr3+, Mn2+, Ce3+, Co2+ or
a mixture of these ions.
Another important aspect is that although standard ion
designations are used, such as V4+, Cr3+, Mn2+ or Co2+, the ions
do not exist in the aqueous solution in exactly these forms.
CA 022 j4726 1998 - 09 - 2 j
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11
The ions are bonded-to water molecules, hydroxide (OH-) or
oxygen, or form complexes of two or more ions. Because of
the nature of the process of li~uid hydrocarbon feedstock
purification, such hydrate shells around the ions and their
bonds to oxygen are very important factors in the process.
It is impossible to specify the exact structure or properties
of the shells of the ions or their complexes because they are
subject to change depending on parameters which are
uncontrollable during purification, e.g., the concentration
of hydrogen ions (H+) changes during both the oxidation of
ions on the anode and the oxidation by the ions of the
organo-sulfur compounds. So, the concentration o~ hydrogen
ions and the type and properties of ion-oxidants also change
over time in the reaction space.
Thus, the ion-oxidants contain transition metal ions
(e.g., V, Cr, Mn, Co) in different oxidation states at
dif~erent stages of the process. As noted above, the
ion-oxidant is not just a metal ion, but a structure
containing the metal ion. Also, the oxidation states of the
ions change during the process. Thus, manganese can exist in
several oxidation states: Mn2+, Mn3~, Mn4~, Mn6+, Mn7+. It is
preferable to use ions Mn or Mn in the purification
technology. But, it cannot be guaranteed that, e.g., only
ions Mn3~ are produced because of the possibility of the
spontaneous transition of Mn3 ions into other oxidation
states.
The electrolyte solution containing the metal ions in
the lowest or intermediate oxidation state are subjected to
electrolysis by passing a DC current through the electrolyte
in an electrolytic cell. The metal ions are oxidized on an
anode therein and transferred into a higher oxidation state.
Oxidation o~ ions on an anode can be provided either in
- a regime of constant current density or constant voltage
(potential) applied between an anode and a cathode. The
properties of the generated ions (i.e. metal oxidation state)
are defined by the anode potential. A constant potential (as
opposed to a constant current) was used during laboratory
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12
experiments to produce ions having the desired oxidation
state. However, this approach to ion-oxidant generation may
not be desirable for use in industrial plants. A simpler
approach is to conduct the ion-oxidant generation in a regime
of constant anode current density. This latter approach is
based on a relation between the anode current density and
the electrochemical reaction potential of the ions. This
relation, however, is not a single valued function because
the anode current density depends on many factors, e.g., the
nature of the anode material, the anode sur~ace contamination
(e.g. by organic impurities adsorption), the ion
concentration in the electrolyte, the electrolytic cell
design, the hydrodynamic regime and the presence o~ other
ions in the electrolyte which can also be oxidized (i.e.
side-reactions). The design and operation of the
electrolytic cell are not critical and many variations
thereof may be used, provided that the cell allows the
production of metal ions in the second higher oxidation state
at a rate sufficient for oxidizing the organo-sulfur
compounds in the hydrocarbon feedstock and provides the
desired level of purification of the feedstock.
The ion-oxidants are generated by an electrochemical
reaction on the anode of the electrolytic cell, whlch
reaction changes the metal ions in the ion-oxidant to a
higher oxidation state, i.e., to an oxidation state higher
than the initial one. Such processes and apparatus for the
oxidation o~ metal ions are well known and need not be
described herein in detail. See, for example U.S. Patent No.
3,793,171, which is incorporated herein ~y reference.
The present process of desulfurization is not truly a
catalytic one, since the ion-oxidants are a chemical reagent
which is consumed during the time when the electrolyte and
liquid hydrocar~on feedstock are in contact in the
he~erophase mixture. The term "consumedl' means that this
reagent is trans~ormed during oxidation o~ the organo-sulfur
compounds into another form (i.e. to ions of a lower
oxidation state). While such ion-oxidants are present in the
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13
electrolyte and in-contact with the organo-sulfur containing
feedstock, the oxidation of organo-sulfur compounds proceeds.
So, the lower limit of the ion concentration in the
electrolyte can be considered as slightly greater than zero
(operability of the present process was demonstrated at a
concentration of ion-oxidant as low as 0.002 moles per liter
of electrolyte).
The rate at which the ion-oxidant is consumed will
de~ine the purification rate. For example, if the feedstock
contains 3000 ppm of sulfur (i.e. about 0.1 mole of sulfur
per liter of the feedstock) and this sulfur is present in the
~orm of thiophene derivatives, then 2 moles o~ electrons
(i.e. 20 electrons per atom o~ sulfur) should be accepted by
the ion-oxidant from the organo-sulfur compounds. If the
ion-oxidant includes chromium ions of the oxidation state 6+
(i.e. Cr6+), then about 0.6 mole of ion-oxidant is required to
purify one liter of the feedstock (since 3 electrons are
accepted during Cr6+ ~$ Cr3 transition). It does not matter
what the particular concentration of the ion-oxidant is,
e.g., if the concentration of the ions is 0.1 mole per liter
o~ electrolyte, then 6 liters of the electrolyte are
required to purify 1 liter o~ the feedstock product from
sulfur. And if this concentration is less by a factor of 10
or 100 then proportionally more electrolyte is needed.
~owever, the above ratio also provides only an estimate
of the specific ion consumption, because in a commercial
hydrocarbon feedstock sulfur can exist in the form of other
organo-sulfur compounds, or there may be incomplete removal
of sulfur. Uncontrollable side-reactions are also possible,
affecting the specific ion-oxidant consumption. So the range
of 10-40 is a reasonable rough estimate of the preferred
range of electrons accepted from the organo-sulfur compound
per one atom of sulfur removed.
According to the above and to the fact that the
concentration of ion-oxidant in the sulfuric acid solution is
a difficult parameter to control, the concentration of the
parent metal ions in the electrolyte may range from slightly
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14
greater than zero u-p to a concentration corresponding to the
saturation point of the metal salt used in the solution. In
order to generate ion-oxidants most ef~ectively, a saturated
solution of the parent metal ions ~i.e., V, Cr, Co, Mn, Ce),
or their mixtures, in the electrolyte is preferable. The
saturated solution can be prepared by dissolving the metal
oxides, or their salts, in the electrolyte consisting of the
selected sulfuric acid concentration (e.g., 9M) until a
nonsoluble salt residue is observed. The produced solution
can then be dissolved with pure electrolyte of the same or a
differe~t sulfuric acid concentration to provide a lower
concentration o~ the metal ions (e.g., down to 1~ of the
metal ion concentration in the saturated solution). This
method was tested experimentally for various electrolytic
solutions. At least down to 1~ of the metal ion
concentration in the saturated metal ion solution was tested,
but no lower limit o~ the metal ion concentration was
observed.
The sulfuric acid solution containing the metal ions is
sub~ected to electrolysis to generate ion-oxidants containing
metal ions in an oxidation state higher than that of the ions
before the electrolysis. The optimal hydrocarbon
feedstock/electrolyte volumetric ratio is derived ~rom the
initial concentration o~ sul~ur in the ~eedstock and the
desired sulfur concentration in the purified product. In
practice, an electric current is passed through the
electrolytic cell in an amount and at a voltage which is
required to accept about 1 to 200 electrons from the
organo-sul~ur compound per atom of sulfur contained in the
feedstock, with the preferred value being 10-40 electrons per
atom of sulfur. It is thi~ parameter, viz., the number of
electrons accepted from the organo-sul~ur compound per atom
of sulfur removed, that is important. The particular amount
of ion-oxidants in the higher oxidation state compared to the
amount of ion-oxidants in the lower oxidation state (see U.S.
Patent No. 3,793,171) is not important. The corresponding
value of the amount o~ electric current passed through the
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electrolytic cell can be easily calculated from the following
relation: the condition of one electron per one atom of
sulfur removed corresponds to the amount of electric current
passed being equal to Faraday's Constant (i.e., 96520
coulombs per one mole of sulfur). Thus, the claimed value of
about 10-40 electrons per atom of sulfur removed corresponds
to that amount of electric current passed through the
electrolytic cell which is equal to about (1-4) x 106
coulombs per one mole of sulfur removed.
The present process preferably is conducted at ambient
temperature. Although electrolysis may result in some
heating of the electrolyte, this generally causes only a
minor temperature rise which may be disregarded in most
instances.
Higher electrolyte temperatures will result in higher
rates of ion oxidation on the anode and faster kinetics in
the heterophase reaction at the hydrocarbon/electrolyte
interface. Also, highçr temperature affects the concentration
of saturated metal salt solutions, thus increasing the
maximum allowed concentration of parent metal ions in the
electrolyte. Because of this and the fact that the oxidation
potential of Co3+ is 1.5 to 2 times higher than the oxidation
potentials of the other ions used in the present invention,
Co3+ ions are less suitable for the purpose of the present
invention than are Vs+, Cr6+, Mn3+, or Ceq+ ions. (Higher
values of the oxidation potential affect the selectivity of
the oxidation reactions of heteroatomic compounds.) This is
in sharp contrast to the process disclosed in U.S. Patent No.
3,793,171, in which the Co3+ ion is claimed to be the
preferred one.
All these effects are positive from the point of view of
the rate of the purification process. However, a temperature
rise will also increase the rates of side-reactions, thus
making the process less selective (e.g. resulting in higher
resins yield). In addition, ion-oxidants (e.g. Co3+) can
decompose molecules of water at elevated temperatures and
thus be wasted. Thus lower temperatures, e.g. about 25OC or
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16
lower are generally preferred to improve the process
selectivity, and it is preferable to generate the metal ions,
e.g., Co3+, at an even lower electrolyte temperature, e.g.
about 0 ~C.
In principle, for each type of hydrocarbon feedstock, an
optimal process temperature range can be readily determined,
depending on the selected criteria of effectiveness (e.g.
minimal resins yield or minimal electric power consumption,
etc.).
Typically, the present process will be conducted at
normal atmospheric pressure. However, it is well known that
pressure can affect the processing. Thus, higher oxygen
partial pressure in the anode area may be employed to reduce
the rate of oxygen releasing side-reactions, thus increasing
the hpper limit of the allowed anode current density.
A purpose of the present invention is to increase the
effectiveness of hydrocarbon feedstock desulfurization and so
increase the productivity of the purification unit. These
goals may be achieved by the preferred embodiment of the
present invention described hereinbelow.
The ion-oxidant is electrolytically generated in the
aqueous sulfuric acid solution as described above. After
that, the aqueous solution containing that ion-oxidant is
mixed with a liquid hydrocarbon feedstock to produce an
emulsion. Desulfurization is provided by the oxidized ions
of the ion-oxidant which are reduced during oxidation of the
sulfur-containing compounds in the feedstock. The sulfur is
removed from the feedstock by forming water-soluble compounds
of sulfur which go into the aqueous working solution in the
form of ion compounds or gaseous compounds of sulfur (e.g.
S02) which evolve from the solution. After the emulsion
decays and the hydrocarbon and aqueous phases are separated,
a purified petroleum product and a spent aqueous working
solution containing reduced metal ions are formed. The ions
in the spent working solution are regenerated via
electrolytic oxidation. One or more of the following ions
CA 022~4726 l998-09-2~
W097l3594s PCT~U97/~08C
17
may be used as the Ion-oxidant: manganese, vanadium,
chromium, cobalt and cerium.
The present process can be realized by the apparatus
described with reference to the schematic diagram shown in
5 Fig. 1.
Such apparatus includes an electrolytic cell (1), an
emulsion generator ~2), a source for supplying liquid
hydrocarbon feedstock (3), a de-emulsifying unit (4), an
adsorber or filter (5) and a tank for the puri~ied product
(6). If desired, a column may be provided for the
distillation of the purified hydrocarbon product.
In the process the sulfuric acid solution containing the
desired concentration of the transition metal ions in a high
oxidation state is fed to the emulsion generator (2) from the
electrolytic cell (l). Concurrently, the hydrocarbon
feedstock is also fed into the emulsion generator (2) from
the feedstock source (3). The feedstock comes into intimate
contact with the electrolyte solution to form an emulsion.
The contact between the feedstock and the working solution is
maintained for a period of time sufficient to permit the
ion-oxidant to oxidize the organo-sulfur compounds in the
feedstock. The oxidation of sulfur-containing compounds in
the feedstock occurs along the liquid-liquid interphase
boundaries in the presence of an ion-oxidant, the ions of
which are reduced during that reaction, and the produced
water-soluble ionic compounds of sulfur go into the aqueous
phase.
The reaction mixture then flows into the de-emulsifying
unit (4) where the emulsion is broken down. The spent
working solution and the purified hydrocarbon product are
separated, and the isolated spent working solution then flows
into the electrolytic cell (1) to regenerate the ion-oxidant
via oxidation of the ions. Purified hydrocarbon products
flow through an adsorber or filter (5) (where additional
purification may occur) to remove acidic components and/or
resinous by-products resulting from the oxidation of the
CA 022~4726 l998-09-2~
W097l35945 PCT~U97/00086
18
organo-sulfur compounds. The purified hydrocarbon products
then flow into the tank (6) for storage.
The recovered purified hydrocarbon product may be passed
through a filter (5) comprising an alkaline material which is
effective in neutralizing any acidic components and is also
effective in removing any resinous products remaining in the
purified product. For some applications, such a filter may
be made of an inert material, such as silicon oxide or
fiberglass.
After being filtered, the purifled product may be passed
to a distillation column not shown where it is distilled in
the presence of an alkaline material, or passed through a
particulate adsorbent material (e.g., alumina), to achieve a
more complete removal of acids and/or resins. If desired,
the 'adsorbed contaminants may be burned from the adsorbent ~y
contact with an oxygen-containing gas at an elevated
temperature.
Alternatively, the separated purified hydrocarbon
product may be centrifuged to remove the acidic components
and/or resinous by- products.
The following examples demonstrate the effectiveness of
the present process for the removal of organo-sulfur
compounds from hydrocarbon feedstocks.
~x~m~le
A sample feedstock consisting of decane mixed with +0.1
by volume of thiophene was treated as described below.
An electrolytic cell with a graphite anode of 6 cm2and a
nickel wire cathode of a small area was used to prepare a
fresh working solution containing a vanadium ion-oxidant.
The process parameters were: current density of 20-30 mA/cm2;
the electrolyte was a o.1 M solution of vanadium (III)
sulfate in a 5 M aqueous solution of sulfuric acid.
Electrolysis was conducted for l hour to form a working
solution. After that, the feedstock was intimately mixed
with the electrolyte solution containing the ion-oxidant for
CA 022~4726 l998-09-2~
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19
30 minutes. After Beparating the phases, a purified
petroleum product was obtained (see Table 1).
Table 1
Raw Material Sul~ur Content of Sulfur Content of
Effectiveness
(Feed stock) Feedstock Puri~ied Product (~)
(ppm) (ppm)
Decane + Thiophene 380 40 89
~ le 2.
A diesel ~uel containing O.13~ sul~ur was treated. An
electrolytic cell with a lead anode of 6 cm2and a nickel wire
cathode of a small area was used to prepare a fresh working
solution containing a manganese ion-oxidant. The process
parameters were: current density o~ 20-80 mA/cm2; the
electrolyte was a 0.1 M solution of manganese (II) sul~ate in
a 15 M a~ueous solution of sul~uric acid.
Electrolysis wa5 conducted for 1 hour to ~orm a working
solution. After that, the diesel fuel was intimately mixed
with the working solution containing the manganese ion-
oxidant for 30 minutes. A~ter separating the phases, apurified petroleum product was obtained (see Table 2).
Table 2
- 25 Raw Material Sul~ur Content o~ Sulfur Content of
Ef~ectiveness
(Feed stock) Feedstock Puri~ied Product (~)
(ppm) (ppm)
Diesel Fuel 1300 340 74
CA 022~4726 l998-09-2~
W097/3S945 PCT~U97/00086
Example 3.
A diesel fuel containing 0.13 ~ of sulfur was treated. An
electrolytic cell with a lead anode of 6 cm2 and nickel wire
cathode of small area was used to prepare a cobalt working
solution. Process parameters were: current density of 20-80
mA/cm2; the electrolyte was a 0.1 M solution of cobalt (II)
sulfate in 9 M aqueous solution of sulfuric acid.
Electrolysis was conducted for 1 hour. After that the
feedstock was mixed with the solution containing the cobalt
ion- oxidant for 30 minutes. After separating the phases a
purified petroleum product was obtained (see Table 3).
Table 3
Raw Material Sulfur Content of Sulfur Content of
Effectiveness
(Feed stock) Feedstock Purified Produc~
(ppm) (ppm)
Diesel Fuel 1300 280 78
~ s seen from the above, these experimental data indicate that
the present process can be used for the purification of liquid
hydrocarbon feedstocks containing organo-sulfur compounds,
including thiophenes, even though purification from thiophenes
is a most difficult task. The purification effectiveness is
high. The efficiency of the operation is also high, and power
consumption is low because of:
- conductivity of the electrolyte is good, causing no
heating;
- high yield by the current of the electrode reaction of
generating the ion-oxidant;
-
CA 022~4726 l998-09-2~
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21
- high effectiveness of ion-oxidant ~or oxidation o~ sulfur-
containing compounds.
The electrodes of the electrolytic cell need not be made of
precious metals, and they can be made of any material which is
c 5 not readily soluble in the electrolyte (e.g. graphite,
titanium, etc.). Since the magnitude of voltage, current
density, electrolyte concentration, and electrolyte pH are
constant during the electrolysis process, there is no need to
control these parameters.
10 Preferred parameters for designing the purification
apparatus and process regimes are:
- concentration of sulfuric acid in electrolyte: 4...15 M;
- electrode materials: anode made from lead covered by oxide;
cathode made ~rom nickel;
- DC current density at anode: 200.. 800 A/m2;
- DC current density at cathode: 10000...20000 A/m2;
- total voltage drop across electrolyte including electrodes
and porous membrane separating the anode and cathode regions:
1Ø..6 V;
Fi~. 2 schematically illustrates apparatus and the process
flow of a preferred embodiment of the present invention
wherein organo-sulfur compounds and, if desired, other
cont~m~n~nt compounds in hydrocarbon feedstocks can be reduced
to varying levels. This preferred embodiment comprises: an
~ 25 electrolyzer (11) which is fed from a DC power supply (12), an
emulsi~ier unit (13) into which an electrolyte is ~ed from the
electrolyzer (11) and petroleum product is fed from a
petroleum feedstock source (14), a de-emulsifier unit (15)
W097/35945 PCT~U97/00086
22
connected to both ~he emulsi~ier unit (i.e. petroleum
product/electrolyte emulsion input to de-emulsifier) and the
electrolyzer (i.e. spent electrolyte output ~rom de-
emulsifier.
The petroleum product outlet from the de-emulsifier unit (15)
is equipped with a mechanical filter (16), an alkali filter
(17), an adsorber (18) and a storage tank (19) for purified
petroleum product. The system also includes a centrifuge
(20), connected to a tank (21) for storing the separated
resinous products, a sorbent regeneration unit (22) connected
to an adsorber (18) a hot air supply (23) and a condenser
(24). The condenser is also provided with a cooling water
supply (25) and a cold air ventilation unit (26). Petroleum
product separated in the condenser is returned and mixed with
the petroleum feedstock.
The electrolyzer (11) is also connected to a vessel (27)
containing hydrogen gas and to a reactor (28) designed to
neutralize the excess electrolyte. This reactor is, in turn,
connected to a vacuum ~ilter (29) and to a tank (30) for
storing the neutralized electrolyte products (e.g. gypsum).
This tank (30) is also connected to an alkaline filter (17) to
store the spent alkaline sorbent. The reactor (28) is also
connected to an alkaline ~eed source (31) which also feeds the
alkaline filter (17).
The electrolyzer (11) is also provided with supplies of water
(32), electrolyte (33) and metal ions (34). The outlets from
the de-emulsifier unit (15) and the centrifuge (20) (for
removing spent electrolyte) are connected to the electrolyzer
WO 97135945 PCT/RU97100086
23
(11). The inlet o~ the centrifuge (20) is connected both to
the de-emulsifier unit (15) and the mechanical filter (16).
The outlet of the centrifuge is also connected to the
mechanical filter (16). The outlet of the alkaline filter
(17) can be connected to a distillation unit (still or
fractionator) (35) and to a condenser (36). The still (35) is
connected to an alkaline supply (31), a heat source (37) and a
storage tank for neutralized products (30). The condenser
(36) is connected to the cold water supply (25) and the
storage tank (19) holding the puri~ied petroleum product.
This system operates as follows:
Oxidation of the metal ions dissolved in the electrolyte
(which changes the oxidation state of the ions from the lower
or intermediate state to a higher state) occurs on the anode
of the electrolyzer (ll). Reduction of hydrogen ions and the
formation of hydrogen molecules occurs on the cathode of the
electrolyzer, and the produced hydrogen is collected in the
storage vessel (27). This hydrogen can be used as feedstock
for the initial hydro-refining of the petroleum product or
saved ~or other purposes. The oxidation of the metal ions and
the reduction of the hydrogen ions proceed via the consumption
of DC electric power supplied by unit (12) which is connected
to the electrolyzer anode and cathode appropriately. The
total voltage drop between the anode and cathode consists of
the following components:
o Electric potential di~ferences corresponding to the
equilibrium oxidation reaction of the metal ions;
CA 022~4726 1998-09-2~
W097/35945 PCT~U97/~086
24
~ Additional po~ential differences produced during the
oxidation o~ the metal ions due to non-equilibrium
reaction conditions (e.g. non-zero anode current
density);
5 o Voltage drop generated by passing the electric (ionic)
current between the anode and cathode through the
electrolyte;
~ Additional potential differences produced by
non-equilibrium reaction conditions during the
reduction of hydrogen ions (e.g., non-zero cathode
current density) - (Note that the equilibrium
potential difference inherent in the reduction of
the hydrogen ions is zero).
The equilibrium difference of oxidation potentials of the
metal ions is defined by the thermodynamic parameters of the
initial and final oxidation products and are as follows:
V[4+] -> V[5+] 1-1.3 V
Cr~3+~ -~ Cr[6+] 1.3 V
Ce[3+] -~ Ce(4+] 1.6 V
Mn[2+] -> Mn[3+] 1.5 V
Co[2+] -> Co[3+] 1.8 V
The additional potential difference produced by the oxidation
of the electrolytic metal ions is determined mainly by two
~actors: the anode current density and the ratio of the
concentrations of ions in the initial and in the higher
oxidation state. Such potential differences, as well as those
inherent to the reduction of the hydrogen ions or the voltage
drop through the electrolyte, increases electric power
consumption required. In addition, these potential
differences also increase the rate of side-reactions, e.g.
CA 022~472W097/35945 PCT~U97~00086
oxygen generation, which reduce the target reaction yield and
therefore the efficiency of the process.
Thus, it is important to maintain a relatively low anode
current density (e.g. 200-800 A/m2), to use a high
concentration of metal ions in the lower oxidation state (e.g.
approximately equal to the concentration in a saturated
solution), and to have a low concentration of metal ions in
the higher oxidation state (e.g. 10-100 times lower than the
metal ion concentration occurring in a saturated solution).
The anode current density should be controlled via the
appropriate variation of the output parameters o~ the DC
current supply (12). The required concentrations of ions is
controlled via controlling the electrolyte flow rate (and,
therefore, the residence time) through the electrolyzer (ll),
regulating the reagents fed into the electrolyzer from the
various sources, viz., water (32), sulfuric acid (33), and
metal ions (34), and the withdrawal rate of the excess
electrolyte into the neutralizer (28).
In order to reduce the voltage drop across the electrolyte,
the gap between the anode and cathode in the electrolyzer (ll)
should be small. Although the use of semipermeable membranes
separating the anode and cathode is also possible, it is
generally not practical. In order to suppress the possible
reduction of the oxidized metal ions on the cathode, the
- 25 cathode surface area should be much less than the surface area
of the anode. Consequently, the cathode current density will
be high, e.g. 10,000-20,000 A/m2. Under these conditions
.
CA 02254726 1998-09-2~
W O 97/35945 PCT~RU97/00086
26
mainly hydrogen ion-s are discharged, since their mobility in
the electrolyte is much higher than that of the metal ions.
The working electrolyte solution is ~ed from
electrolyzer (11) into the emulsifier unit (13) along with the
petroleum feedstock introduced through line (14).
In the emulsion the working electrolyte solution and the
petroleum feedstock are in intimate contact. The oxidation by
the metal ions, of the organo-sul~ur compounds (which occurs
along the interphase boundary between the feedstock and the
electrolyte) changes the organo-sulfur compounds into water
soluble compounds, gaseous products and water (i.e. S02, C~2,
H20) .
The resulting water soluble compounds flow into the
electrolyte where the oxidation of said compounds by metal
l~ ions proceeds further until the formation of gaseous products
and sulfuric acid.
Concurrently with the oxidation of the organo-sulfur
compounds at the interphase boundaries, reactions can proceed
between the sulfuric acid and non-saturated (e.g., aromatic)
hydrocarbons. This results in the formation of sulfonic
acids, which are surface-active substances. These sulfonic
acids and the oxygen-containing products, which result from
the incomplete oxidation of hydrocarbons, can form resinous
products which are insoluble in the electrolyte and in the
petroleum product. These products then collect at the
petroleum product/electrolyte interphase boundary.
The main factor which defines the predominate type of
oxidation reaction is the sulfuric acid concentration in the
CWO 97/35945 PCT/~U97/00086
27
electrolyte. Thus, if the concentration of sulfuric acid is
high (i.e.~ 15 M), then mainly sulfurization reactions take
place and resins are formed. If the sulfuric acid
concentration is less than 4 M, then essentially no oxidation
- 5 reactions occur. Thus, the working range of sulfuric acid
concentration is 4-15 M. A preferable concentration is 7-10
M; in this regime the oxidation of organo-sul~ur compounds
proceeds reasonably fast and resins or other sulfonic acids
are essentially not produced. However, any concentration of
sulfuric acid within the range of 4-15 M can be used as would
be appropriate for the particular petroleum feedstock or
required degree of purification.
The concentration of ion-oxidants has a slight affect on the
type of oxidation reaction that will predominate (i.e. the
selectivity of the oxidation process). Thus, this parameter
may be varied within a wide range of possible values (i.e.
from zero to that concentration which occurs in a saturated
solution). The lower the concentration of ion-oxidants in the
working solution the more solution is needed to pass through
the electrolyzer (11) and through the emulsifier unit (12) to
purify the same volume of petroleum product. The particular
value of the ratio of the petroleum product and working
solution flow rates is determined by the fact that 10-40
electrons are needed to oxidize an organo- sulfur molecule
- 25 containing 1 atom of sulfur; these electrons are transferred
from that molecule to the ion-oxidants. Depending of the
nature (i.e., the composition) of the petroleum feedstock,
this vaiue can vary from 1-200 electrons per one atom of
CA 02254726 1998-09-2~
W O 97/35945 PCT~RU97/00086
28
sulfur removed with the range o~ 10-40 electrons per one atom
of sulfur removed being the most representative.
The petroleum/electrolyte emulsion runs ~rom the emulsifier
unit (13) to the de-emulsifier unit (15), where the spent
working solution is separated from the petroleum product and
resins. The spent working solution then goes into the
electrolyzer with the water soluble oxidation products which
are further oxidized in the electrolyzer and converted into
sul~uric acid and gaseous products. Thus in the electrolyzer
the successive sul~uric acid can be formed. In this case some
part o~ the solution should be withdrawn into the neutralizer
(28) where it is mixed with alkali fed ~rom the source (31).
Neutralization reaction products formed in the reactor (28),
e.g. gypsum (CaS04), are then 5eparated ~rom the residual
working solution by a vacuum ~ilter (29) and stored in storage
tank (30).
The petroleum product containing resins and sulfonic acids
runs from the de-emulsifier unit ~15) to the mechanical filter
(16) which can be a vessel ~illed with an inert material such
as silicon oxide or ~iberglass. The resins and sulfonic acids
separated-by the filter (16) and the same separated from the
petroleum products in the de-emulsifier unit (lS) flow into
the centrifuge (20) where they are separated ~rom the residual
working solution, and are then stored in a storage tank (21)
These resins and sul~onic acids can then be used as a
feedstock for other processes including various petrochemical
processes.
CA 02254726 1998-09-25
W O 97/35945 PCT~RU97/00086 29
Another option in~olves running the petroleum product
containing resins and sul~onic acids from the de-emulsifier
unit (15) first to the centrifuge (20), where the main parts
of the resinous and acidic components are separated, and then
- 5 to a mechanical filter (16).
Normally at this stage of the purification process the sulfur
content can be reduced from an initial level of 1000 ppm to
300-500 ppm, depending on the feedstock composition. However,
the preferred embodiment, which provides a higher level of
desulfurization of the petroleum product, employees additional
purification as follows.
The petroleum product puri~ied from the resins flows from the
inert filter (16~ into the alkaline filter (17) which is fed
with an alkaline powd-er such as NaOH, Ca(OH) 2 ~ or Mg(OH) 2 from
the source (31).
The residual sulfuric acid, dissolved in the petroleum
product is neutralized in the alkaline filter and precipitates
in the form of solid products. Spent alkaline powder should
then be removed from the filter (17) and stored in the storage
tank (30).
Normally the petroleum product ~rom the alkaline filter (17)
is pure enough to be used in most applications. If the
hydrocarbon feedstock contains less than 1000 ppm of sulfur,
then after the alkaline ~ilter (17) the pet~oleum will contain
2~ from 50 to 300 ppm of sulfur, depending on the nature of the
original feedstock. At the 5ame time that sulfur is removed
from ~he feedstock the pre5ent process also removes other
heteroatomic compounds such as nitrogen and heavy me~als. The
CA 022S4726 1998-09-2~
W O 97/35945 PCTnRU97/00086
effectiveness of this process also depends on the nature of
the original feedstock. In fact, some heteroato~ic compounds,
e.g. those containing nitrogen, are removed from the petroleum
feedstock even more ef~iciently than the organo-sulfur~ compounds.
In those cases in which the amount of organo-sulphur
compounds in the petroleum product after the alkaline filter
(17) is still too high, the petroleum product can be ~urther
purified to reduce the sulfur concentration to less than 50
ppm. Also, in some cases (e.g. in diesel ~uel) it is
desirable to reduce the content of aromatic or polyaromatic
compounds in the petroleum product. To address this
situation, it is possible to route the petroleum product from
the alkaline filter (17) into the adsorber (18) which is
filled with a material, such as alumina, that sel~ctively
absorbs aromatic compounds and thiophenes. If the sul~ur
content in the petroleum product before adsorber~(18) is in
the range of 50-300 ppm, then after the adsorber it is reduced
to 5-50 ppm. If required, the sulfur content can be further
reduced to 0.5-5 ppm. However, for most cases this is not
advisable since the rate of consumption of the alumina sorbent
(viz., more than 1 liter of alumina powder per 1 liter of
petroleum product) is high.
Purified petroleum product flows from the adsorber (18)
2~ into the product storage tank (19). The spent sorbent is
removed from the adsorber (18) to the regeneration unit (22)
where it is treated with hot air supplied from source (23).
Regeneration of the spent sorbent is best performed at varying
CA 022W O 97/3~945 P~1/K~fi/00086
31
temperatures, i.e. air (or steam~ having temperature o~
200-400 ~C should be used ~irst and then the air temperature
should be increased to 500 oC or higher. At the lower
temperature, the organic and heteroatomic compounds are
~ 5 removed ~rom the alumina without being decomposed and
there~ore these compounds can be separated ~rom the air (or
steam) in the condenser (24), which is cooled by cold water
supplied from a source (25). These separated compounds may be
either used as a feedstock ~or the petrochemical industry or
mixed with petroleum product feedstock to repeat the
purification cycle. When the lower temperature sorbent
regeneration is completed, heavier products (e.g. coke) can be
removed by burning with an air stream having temperature of
500 ~C or higher. Puri~ied sor~ent is then returned to
adsorber (18) and the cooled air is exhausted into the ambient
atmosphere.
In those cases where there is no need to reduce the
concentration of aromatic compounds in the petroleum product
a~ter the alkaline ~ilter (17), but the sul~ur content should
be ~urther reduced, then additional purification can be
accomplished by using a distillation technique in the presence
o~ an alkaline material. In this case, the petroleum product
~lows to the still (35), which is loaded with dry alkali
provided ~rom stock (31). The petroleum product is heated,
- 25 along with the alkali, by heater (37) and evaporated. ~he
petroleum product vapors are then cooled using cold water
provided from source (25) and condensed in condenser (36).
-
CA 022~4726 l998-09-2~
~097/3S945 PCT~U97/00086
32
The liquid petrole-um product then runs into the storage tank
(19a).
Heating the petroleum product in the presence of the alkaline
material increases the reaction rate between the residual
sulfuric acid dissolved in the petroleum product and the
alkaline material and so the removal of acidic compounds from
the petroleum product in the 9till (35) ls even more efficient
than in the alkaline filter (17). After evaporation of the
petroleum product, the sulfuric acid salts remain in the still
(35) and are thermally decomposed into products which normally
do not contain sulfur since the sul~ur is strongly bound to
the alkali.
As a result of this additional purification, the total sulfur
content in the petroleum product can be reduced from 300 ppm
(after alkaline filter (17)) to 30-50 ppm (after condenser
(36)).
Thus, the system shown in Figure 2 reduces the amount of
organo-sul~ur compounds in petroleum feedstocks to varying
levels depending on the details of the process, i.e. it
reduces the sulfur content from an initial level o~ about 1000
ppm to 50-300 ppm a~ter alkaline filter (17), or 30-50 ppm
after the.still (35), or 5-50 ppm after the adsorber (18). In
addition, it removes heteroatomic compounds, including
nitrogen and heavy metals, and, if required, can also reduce
the amount of aromatic compounds in the petroleum product.
By-products of the puri~ication system are as follows:
~ Minor amounts of co~bustion products which normally need
no additional purification are released into the air;
CA 02254726 1998-09-25
W O 97135945 PCTnRU97100086
33
~ Salts of sulfuric acid (e.g. gypsum) with an admixture
(not more than 0.1~) o~ metals (i.e. V, Cr, Co, Ce, Mn)
are accumulated in storage tank (30);
~ Resinous products containing sulfonic acids and
oxygen-containing compounds are accumulated in storage
tank ~21);
o Concentrated organo-sulfur and aromatic compounds at the
outlet of the condenser (24);
~ ~ydrogen gas (essentially with no pollutants) are
accumulated in vessel (27).
Some of these by-products can be possibly used as feedstocks
for the petrochemical industry.
Consumed resources include electric power, heat power, clean
water (to prepare working solutions), lime, metals (i.e. V,
Cr, Co, Ce, Mn) and cooling water. Sulfuric acid is
essentially not consumed in the process.
Purification of 1 m3O~ diesel fuel with an initial
sulfur content of less than 1000 ppm can ~e characterized by
the following typical rates for consumed resources and final
20 products yields:
In~llt:
Diesel fuel 10001
Electric power 20 kW hour
2~ Clean water 51
Metals (e.g. V, Cr, Co, Ce, Mn) 0.03 kg
Lime (CaO) 5 kg
Air 300m3
CA 022S4726 1998-09-25
W O 97/35g45 PCTnRU97/00086
34
Heat power 0.03 - 0.0~ GCal
Cooling water 2 m3
Alumina 0.05 - 0.10 kg
Ol~t~llt:
Purified diesel fuel 950 - 9901
Resins and sulfonic acids 10-70kg
Hydrogen 2 m3
Gypsum 5 kg
Concentrated organo-sulfur compounds
and-aromatic compounds 10 - 301
Air containin~ less than 30 ppm
sulfur oxides 300 m3
Water (after drying of gypsum) 51
These rates of resource consumption and final product
yields can be used to estimate the cost of the puri~ication
process. The parameters ~or the removal of thiophenes from
others petroleum products, e.g., rough benzene, would differ
20 ~rom those specified above.
Having described preferred embodiments o~ the present
invention, various modi~ications thereof ~alling within the
scope o~ the invention may become apparent to those skilled in
this art, and the scope of the invention is to be determined
25 by the appended claims and their e~uivalents.
