Note: Descriptions are shown in the official language in which they were submitted.
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Sulfur Removal Process
Field of the Invention
This invention relates to a process for producing a product of reduced sulfur
content from a liquid feedstock wherein the feedstock is comprised of a
mixture of
hydrocarbons and contains organic sulfur compounds as unwanted impurities.
More
particularly, it involves converting at least a portion of the organic sulfur
compounds in the feedstock to products of a higher boiling point and removing
these high boiling products by distillation.
Background of the Invention
The catalytic cracking process is one of the major refiriing operations which
is currently employed in the conversion of petroleum to desirable fuels such
as
gasoline and diesel fuel. The fluidized catalytic cracking process is an
example of
this type of process wherein a high molecular weight hydrocarbon feedstock is
converted to lower molecular weight products through contact with hot, finely-
divided solid catalyst particles in a fluidized or dispersed state. Suitable
hydrocarbon feedstocks typically boil within the range of from about 205 C
to
about 650 C, and they are usually contacted with the catalyst at temperatures
in the
range from about 450 C to about 650 C. Suitable feedstocks include various
mineral oil fractions such as light gas oils, heavy gas oils, wide-cut gas
oils,
vacuum gas oils, kerosenes, decanted oils, residual fractions, reduced crude
oils and
cycle oils which are derived from any of these as well as fractions derived
from
shale oils, tar sands processing, and coal liquefaction. Products from the
process
are typically based on boiling point and include light naphtha (boiling
between about
10 C and about 221 C), kerosene (boiling between about 180 C and about 300
C), light cycle oil (boiling between about 221 C and about 345 C), and heavy
cycle oil (boiling at temperatures higher thar., about 345 C).
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Not only does the catalytic cracking process provide a significant part of the
gasoline pool in the United States, it also provides a large proportion of the
sulfur
that appears in this pool. The sulfur in the liquid products from this process
is in
the form of organic sulfur compounds and is an undesirable impurity which is
converted to sulfur oxides when these products are utilized as a fuel. These
sulfur
oxides are objectionable air pollutants. In addition, they can deactivate many
of the
catalysts that have been developed for the catalytic converters which are used
on
automobiles to catalyze the conversion of harmful emissions in the enaine
exhaust to
gases which are less objectionable. Accordingly, it is desirable to reduce the
sulfur
content of catalytic cracking products to the lowest possible levels.
The sulfur-containing impurities of straight run gasolines, which are
prepared by simple distillation of crude oil, are usually very different from
those in
cracked gasolines. The former contain mostly mercaptans and sulfides, whereas
the
latter are rich in thiophene derivatives.
Low sulfur products are conventionally obtained from the catalytic cracking
process by hydrotreating either the feedstock to the process or the products
from the
process. The hydrotreating process involves treatment with elemental hydrogen
in
the presence of a catalyst and results in the conversion of the sulfur in the
sulfur-
containing organic impurities to hydrogen sulfide which can be separated and
converted to elemental sulfur. Unfortunately, this type of processing is
typically
quite expensive because it requires a source of hydrogen, high pressure
process
equipment, expensive hydrotreating catalysts, and a sulfur recovery plant for
conversion of the resulting hydrogen sulfide to elemental sulfur. In addition,
the
hydrotreating process can result in an undesired destruction of olefins in the
feedstock by conversion to saturated hydrocarbons through hydrogenation. This
destruction of olefins by hydrogenation is undesirable because it results in
the
consumption of expensive hydrogen, and the olefins are valuable as high octane
components of gasoline. As an example, naphtha of a gasoline boiling range
from a
catalytic cracking process has a relatively high octane number as a result of
the
presence of a large olefin content. Hydrotreating such a material canses a
reduction
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in the olefin content in addition to the desired desulfurization, and octane
number
decreases as the degree of desulfurization increases.
During the early years of the refining industry, sulfuric acid treatment was
an important process that was used to remove sulfur, precipitate asphaltic
material,
and improve stability, color and odor of a wide variety of refinery stocks. At
page
3-119 of the Petroleum Processing Handbook, W.F. Bland and R.L. Davidson,
Ed., McGraw-Hill Book Company, 1967, it is reported that low temperatures (-4
to 10 C) are used in this process with strong acid, but that higher
temperatures
(21 to 54 C) may be practical if material is to be rerun. It is disclosed
in the Oil
and Gas Journal, November 10, 1938, at page 45 that sulfuric acid treatment of
naphtha is effective in removing organic sulfur-containing impurities such as
isoamyl mercaptan, dimethyl sulfate, methyl-p-toluene sulfonate, carbon
disulfide,
n-butyl sulfide, n-propyl disulfide, thiophene, diphenyl sulfoxide, and n-
butyl
sulfone. The chemistry involved in sulfuric acid treatment of gasoline is
extensively
discussed by G.E. Mapstone in a review article in the Petroleum Refiner, Vol.
29,
No. 11 (November, 1950) at pp. 142-150. Mapstone reports at page 145 that
thiophenes may be alkylated by olefins in the presence of sulfuric acid. He
further
states that this same reaction appears to have a significant effect in the
desulfurization of cracked shale gasoline by treatment with sulfuric acid in
that a
large proportion of the sulfur reduction obtained occurs on the redistillation
of the
acid treated gasoline. with the rerun bottoms containing several percent of
sulfur.
U.S. Patent No. 2,448.211 (Caesar et al.) discloses that thiophene and its
derivatives can be alkylated by reaction with olefinic hydrocarbons at a
temperature
between about 140 and about 400 C in the presence of a catalyst such as an
activated natural clay or a synthetic adsorbent composite of silica and at
least one
amphoteric metal oxide. Suitable activated natural clay catalysts include clay
catalysts on which zinc chloride or phosphoric acid have been precipitated.
Suitable
silica-amphoteric metal oxide catalysts include combinations of silica with
materials
such as alumina, zirconia, ceria, and thoria. U.S. Patent No. 2,469,823
(Hansford
et al.) teaches that boron trifluoride can be used to catalyze the alkylation
of
thiophene and alkyl thiophenes with alkylating agents such as olefinic
hydrocarbons,
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alkyl halides, alcohols, and mercaptans. In addition, U.S. Patent No.
2,921.081
(Zi.mmerschied et al.) discloses that acidic solid catalysts can be prepared
by
combining a zirconium compound selected from the group consisting of zirconium
dioxide and the halides of zirconium with an acid selected from the group
consisting
of orthophosphoric acid, pyrophosphoric acid, and triphosphoric acid. It is
further disclosed that thiophene can be alkylated with propylene at a
temperature of 227 C
in the presence of such a catalyst.
U.S. Patent No. 2,563,087 (Vesely) discloses that thiophene can be removed
from mixtures of this material with aromatic hydrocarbons by selective
alkylation of
the thiophene and separation of the resulting thiophene alkylate by
distillation. The
selective alkylation is carried out by mixing the thiophene-contaminated
aromatic
hydrocarbon with an alkylating agent and contacting the mixture with an
alkylation
catalyst at a carefully controlled temperature in the range from about
-20 C to about 85 C. It is disclosed that suitable alkylating agents
include
olefins, mercaptans, mineral acid esters, and alkoxy compounds such as
aliphatic
alcohols, ethers and esters of carboxylic acids. It is also disclosed that
suitable
alkylation catalysts include the following: (1) The Friedel-Crafts metal
halides,
which are preferably used in anhydrous form; (2) a phosphoric acid, preferably
pyrophosphoric acid, or a mixture with sulfuric acid in which the volume ratio
of
sulfuric to phosphoric acid is less than about 4:1; and (3) a mixture of a
phosphoric
acid, such as orthophosphoric acid or pyrophosphoric acid, with a siliceous
adsorbent, such as kieselguhr or a siliceous clay, which has been calcined to
a
temperature of from about 400 to about 500 C to form a silico-phosphoric
acid
combination which is commonly referred to as a solid phosphoric acid catalyst.
U.S. Patent No. 2,943,094 (Birch et al.) is directed to a method for the
removal of alkyl thiophenes from a distillate which consists predominately of
aromatic hydrocarbons, and the method involves converting the alkyl thiophenes
to
sulfur-containing products of a different boiling point which are removed by
fractional distillation. The conversion is carried out by contacting the
mixture with
a catalyst at a temperature in the range from 500 to 650 C, wherein the
catalyst is
prepared by impregnating alumina with hydrofluoric acid in aqueous solution.
It is
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disclosed that the catalyst functions to: (1) convert alkyl thiophenes to
lower alkyl
thiophenes and/or unsubstituted thiophene by dealkylation; (2) effect the
simultaneous dealkylation and alkylation of alkyl thiophenes; and (3) convert
alkyl
thiophenes to aromatic hydrocarbons.
U.S. Patent No. 2,677,648 (Lien et al.) relates to a process for the
desulfurization of a high sulfur olefuiic naphtha which involves treating the
naphtha
with hydrogen fluoride to obtain a raffinate, defluorinating the raffinate,
and then
contacting the defluorinated raffinate with HF-activated alumina. The
treatment
with hydrogen fluoride is carried out at a temperature in the range from about
-51
to -1 C under conditions which result in the removal of about 10 to 15 % of
the
feedstock as a high sulfur content extract, and about 30 to 40% of the
feedstock is
simultaneously converted by polymerization and alkylation to materials of the
gas
oil boiling range. After removal of HF from the raffinate, the raffinate is
contacted
with an HF-activated alumina at a temperature in the range from about 316 to
482 C to depolymerize and dealkylate the gas oil boiling range components
and to
effect additional desulfurization.
U.S. Patent No. 4,775,462 (Imai et al.) is directed to a method for
converting the mercaptan impurities in a hydrocarbon fraction to less
objectionable
thioethers which are permitted to remain in the product. This process involves
contacting the hydrocarbon fraction with an unsaturated hydrocarbon in the
presence of an acid-type catalyst under conditions which are effective to
convert the
mercaptan impurities to thioethers. It is disclosed that suitable acid-type
catalysts
include: (1) acidic polymeric resins such as resins which contain a sulfonic
acid
group; (2) acidic intercalate compounds such as antimony halides in graphite,
aluminum halides in graphite, and zirconium halides in graphite; (3)
phosphoric
acid, sulfuric acid or boric acid supported on silica, alumina, silica-
aluminas or
clays; (4) aluminas, silica-aluminas, natural and synthetic pillared clays,
and natural
and synthetic zeolites such as faujasites, mordenites, L, omega, X and Y
zeolites;
(5) aluminas or silica-aluminas which have been impregnated with aluminum
halides
or boron halides; and (6) metal sulfates such as zirconium sulfate, nickel
sulfate,
chromium sulfate, and cobalt sulfate.
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Summary of the Invention
Hydrotreating is an effective method for the removal of sulfur-containinc,
impurities from hydrocarbon liquids such as those which are conventionally
encountered in the refining of petroleum and those which are derived from coal
liquefaction and the processing of oil shale or tar sands. Liquids of this
type, which
boil over a broad or narrow range of temperatures within the range from about
10
C to about 345 C, are referred to herein as "distillate hydrocarbon
liquids." For
example, light naphtha, heavy naphtha, kerosene and light cycle oil are all
distillate
hydrocarbon liquids. Unfortunately, hydrotreating is an expensive process and
is
usually unsatisfactory for use with highly olefinic distillate hydrocarbon
liquids.
Accordingly, there is a need for an inexpensive process for the removal of
sulfur-
containing impurities from distillate hydrocarbon liquids. There is also a
need for
such a process which can be used to remove sulfur-containing impurities from
highly olefinic distillate hydrocarbon liquids.
We have found that many of the sulfur-containing impurities which are
typically found in distillate hydrocarbon liquids can be easily and
selectively
converted to sulfur-containing materials of a higher boiling point by
treatment with
an acid catalyst in the presence of olefins or alcohols. We have also found
that a
large portion of the resulting higher boiling sulfur-containing materials can
be
removed by fractional distillation.
One embodiment of the invention is a method for producing a product of
reduced sulfur content from a liquid feedstock, wherein said feedstock is
comprised
of a mixture of hydrocarbons which boils below about 345 C and contains a
minor
amount of organic sulfur compounds, and wherein said process comprises: (a)
adjusting the composition of said feedstock so that it contains an amount of
alkylating agent which is at least equal on a molar basis to that of the
organic sulfur
compounds, and wherein said alkylating agent is comprised of at least one
material =
selected from the group consisting of alcoholc and olefms; (b) contacting the
resulting mixture with an acidic solid catalyst at a temperature in excess of
100 C
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for a contact time which is effective to result in conversion of at least a
portion of
said organic sulfur compounds to a higher boiling sulfur-containing material;
and
(c) fractionally distilling the product of said contacting step to remove high
boiling
suifur-containing material and produce a product which has a reduced sulfur
content
relative to that of said feedstock.
Another embodiment of the invention is a method for producing a product of
reduced sulfur content which comprises: (a) producing catalytic cracking
products
which include sulfur-containing impurities by catalytically cracking a
hydrocarbon
feedstock which contains sulfur-containing impurities; (b) separating at least
a
portion of the catalytic cracking products which is comprised of at least 1
weight
percent of olefins and contains organic sulfur compounds as impurities; (c)
contacting the separated catalytic cracking products with an acidic solid
catalyst at a
temperature in excess of 50 C for a period of time which is effective to
convert at
least a portion of the sulfur-containing impurities in said separated
catalytic cracking
products to a sulfur-containing material of higher boiling point; and (d)
fractionally
distilling the product of said contacting step to remove high boiling sulfur-
containing material and produce a product which has a reduced sulfur content
relative to that of said separated catalytic cracking products.
A further embodiment of the invention is a method for producing a product
of reduced sulfur content which comprises: (a) producing catalytic cracking
products by catalytically cracking a hydrocarbon feedstock which contains
sulfur-
containing impurities; (b) passing the catalytic cracking products to a
distillation
unit and fractionating said catalytic cracking products into at least two
fractions
which comprise: (1) a liquid boiling below about 345 C which contains sulfur-
containing impurities and (2) material of higher boiling point; (c) producing
a
treated liquid by contacting a portion of said fraction (1) from the
distillation unit
with an acidic solid catalyst at a temperature in excess of 50 C for a period
of time
which is effective to convert at least a portion of the sulfur-containing
impurities in
said fraction (1) to a sulfur-containing material of higher boiling point; and
(d)
returning the treated liquid to said distillation unit and fractiorating 'he
treated
liquid simultaneously with the catalytic cracking products, whereby at least a
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portion of the sulfur-containing material of higher boiling point in the
treated liquid
is removed and a product of reduced sulfur content is produced.
An object of the invention is to provide a method for the removal of sulfur-
containing impurities from distillate hydrocarbon liquids which does not
involve
hvdrotreating with hydrogen in the presence of a hydrotreating catalyst. An
object of the invention is to provide an inexpensive method for producing-
distillate hydrocarbon liquids of a reduced sulfur content.
Another object of the invention is to provide a method for the removal of
mercaptans, thiophene and thiophene derivatives from distillate hydrocarbon
liquids.
Another object of the invention is to provide an improved method for the
removal of sulfur-containing impurities from catalytic cracking products.
A further object of the invention is to provide a method for the removal of
sulfur-containing impurities from the light naphtha product of a catalytic
cracking
process without significantly reducing its octane.
Brief Description of the Drawings
FIG. 1 of the drawings illustrates the use of a solid phosphoric acid catalyst
on kieseiguhr to increase the boiling point of sulfur-containing impurities in
a
stabilized heavy naphtha feedstock that was blended with a mixture of C3 and
C4
olefins.
FIG. 2 of the drawings illustrates the use of a solid phosphoric acid catalyst
on kieselguhr to increase the boiling point of sulfur-containing impurities in
an
olefin-containing, stabilized, heavy naphtha feedstock.
FIG. 3a of the drawings illustrates the distribution of sulfur content as a
function of boiling point in a low olefin content synthetic hydrocarbon
feedstock
which contains 2-propanethiol, thiophene, 2-methylthiophene, and isopropyl
sulfide
as impurities. FIG. 3b illustrates the use of a solid phosphoric acid catalyst
on
kieselguhr to increase the boiling point of the sulfur-containing impurities
in this
synthetic feedstock.
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FIG. 4a of the drawings illustrates the distribution of sulfur content as a
function of boiling point in a high olefin content synthetic hydrocarbon
feedstock
which contains 2-propanethiol, thiophene, 2-methylthiophene, and isopropyl
sulfide
as impurities. FIG. 4b illustrates the use of a solid phosphoric acid catalyst
on
kieselguhr to increase the boiling point of the sulfur-containing impurities
in this
synthetic feedstock.
FIG. 5 of the drawings illustrates the ability of six different solid acidic
catalysts to increase the boiling point of sulfur-containing impurities in a
synthetic
feedstock (which contained 12.9 wt. % of C6 and C7 olefins) both before and
after
the feedstock was blended with propene at a 0.25 volume ratio of propene to
synthetic feedstock.
Detailed Description of the Invention
We have discovered a process for the production of a product of reduced
sulfur content from a liquid feedstock wherein the feedstock is comprised of a
mixture of hydrocarbons and contains organic sulfur compounds as unwanted
impurities. This process comprises converting at least a portion of the sulfur-
containing impurities to sulfur-containing products of a higher boiling point
by
treatment with an alkylating agent in the presence-of an acid catalyst and
removing
at least a portion of these higher boiling products by distillation.
Suitable alkylating agents for use in the practice of this invention include
both alcohols and olefins. However, olefins are generally preferred since they
are
usually more reactive than alcohols and can be used in the subject process
under
milder reaction conditions. Suitable olefins include cyclic olefms,
substituted cyclic
olefins, and olefins of formula I wherein R, is a hydrocarbyl group and each
R2 is
independently selected from the group consisting of hydrogen and hydrocarbyl
groups. Preferably, R, is an alkyl group and each R2 is independently selected
from
the group consisting of hydrogen and alkyl groups. Examples of suitable cyclic
olefins and substituted cyclic olefins include cyclopentene, 1-
methylcyclopentene,
cyclohexene, 1-methylcyclohexene, 3-methylcyclohexene, 4-methylcyclohexene,
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cycloheptene, cyclooctene, and 4-methylcyclooctene. Examples of suitable
olefins
of the type of formula I include propene, 2-methylpropene, 1-butene, 2-butene,
2-methyl-l-butene, 3-methyl-l-butene, 2-methyl-2-butene, 2,3-dimethyl-l-
butene,
3,3-dimethyl-l-butene, 2,3-dimethyl-2-butene, 2-ethyl-l-butene, 2-ethyl-3-
methyl-
1-butene, 2,3,3-trimethyl-l-butene, 1-pentene, 2-pentene, 2-methyl-l-pentene,
3-methyl-l-pentene, 4-methyl-l-pentene, 2,4-dimethyl-l-pentene, 1-hexene, 2-
hexene, 3-hexene, 1,3-hexadiene, 1,4-hexadiene, 1,5-hexadiene, 2,4-hexadiene.
1-heptene, 2-heptene, 3-heptene, 1-octene, 2-octene, 3-octene, and 4-octene.
Secondary and tertiary alcohols are highly preferred over primary alcohols
because
they are usually more reactive than the primary alcohols and can be used under
milder reaction conditions. Materials such as ethylene, methanol and ethanol
are
less useful than most other olefins and alcohols in the practice of this
invention
because of their low reactivity.
Ri., R2
c= c (1)
R.;/ R2
Preferred alkylating agents will contain from about 3 to about 20 carbon
atoms, and highly preferred alkylating agents will contain from about 3 to
about 10
carbon atoms. The optimal number of carbon atoms in the alkylating agent will
usually be determined by both the boiling point of the desired liquid
hydrocarbon
product and the boiling point of the sulfur-containing impurities in the
feedstock.
As previously stated, sulfur-containing impurities are converted by the
alkylating
agents of this invention to sulfur-containing materials of a higher boiling
point.
However, alkylating agents which contain a large number of carbon atoms
ordinarily result in a larger increase in the boiling point of these products
than
alkylating agents which contain a smaller number of carbon atoms. Accordingly,
an
alkylating agent must be selected which will convert the sulfur-containing
impurities
to sulfur-containing products which are of a sufficiently high boiling point
that they
can be removed by disiillation. For example, propylene may be a highly
satisfactory alkylating agent for use in the preparation of a liquid
hydrocarbon
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product of reduced sulfur content which has a maximum boiling point of 150 C
but
may not be satisfactory for a liquid hydrocarbon product which has a maximum
boiling point of 345 C.
In a preferred embodiment, a mixture of alkylating agents, such as a mixture
of olefins or of alcohols, will be used in the practice of this invention.
Such a
mixture will often be cheaper and/or more readily available than a pure olefin
or
alcohol and will often yield results which are equally satisfactory to what
can be
achieved with a pure olefin or alcohol as the alkylating agent. However, when
it is
desired to optimize the removal of specific sulfur-containing impurities from
a
specific hydrocarbon liquid, it may be advantageous to utilize a specific
olefin or
alcohol which is selected to: (1) convert the sulfur-containing impurities to
products which have a sufficiently increased boiling point that they can be
easily
removed by fractional distillation; and (2) permit easy removal of any
unreacted
alkylating agent, such as by distillation or by aqueous extraction. in the
event that
this material must be removed. It will be appreciated, of course, that in many
refinery applications of the invention, it will not be necessary to remove
unreacted
alkylating agent from the resulting distillate products of reduced sulfur
content.
Although the invention is not to be so limited, it is believed that the
principal
mechanism for conversion of the sulfur-containing impurities to higher boiling
products involves the alkylation of these impurities with the alkylating
agent. By
way of example, simple alkylation of an aromatic sulfur compound such as
thiophene would yield an alkyl-substituted thiophene. This type of reaction is
illustrated in equations II and III wherein the conversion of thiophene to
2-isopropylthiophene is illustrated using propene and 2-propanol,
respectively, as
the alkylating agent. It will be appreciated, of course, that monoalkylation
of
thiophene can take place either a or R to the sulfur atom, and that
polyalkylation
can also take place. The alkylation of a mercaptan would yield a sulfide, and
this
type of reaction is illustrated in equations IV and V wherein the conversion
of
n-butylmercaptan to isopropyl(n-butyl)sulfide is illustrated using propene and
2-propanol, respectively, as the alkylating aà nt.
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+
CH'= CHCH3 S (II)
S 0_](CF~~
+ (CH3),CHOH S ~
( (IID
S C_13)2_
CH3(CH2)3SH + CHy= C~LH3 -~ C113(CHZ)3SCH(CH3), (IV)
CH3(CE-~)3SH + (CHACHOH CH3(CHZ~SCH(CH3)2 (V)
The alkylation process results in the substitution of an alkyl group for a
hydrogen atom in the sulfur-containing starting material and causes a
corresponding
increase in molecular weight over that of the starting material. The higher
molecular weight of such an alkylation product is reflected by a higher
boiling point
relative to that of the starting material. For example, the conversion of
thiophene to
2-t-butylthiophene by alkylation with 2-methylpropene results in the
conversion of
thiophene, which has a boiling point of 84 C, to a product which has a
boiling
point of 164 C and can be easily removed from lower boiling material in the
feedstock by fractional distillation. Conversion of thiophene to di-t-
butylthiophene
by dialkylation with 2-methylpropene results in a product which has an even
higher
boiling point of about 224 C. Alkylation with alkyl groups that add a large
rather
than a small number of carbon atoms is preferred since the products will have
higher molecular weights and, accordingly, will usually have higher boiling
points
than products which are obtained through alkylation with the smaller alkyl
groups.
Feedstocks which can be used in the practice of this invention include any
liquid which is comprised of one or more hydrocarbons and contains organic
sulfur
compounds, such as mercaptans or aromatic sulfur compounds, as impurities. In
addition, a major portion of the liquid should be comprised of hydrocarbons
boiling
below about 345 C and preferably below about 230 C. Suitable feedstocks
include any of the various complex mixtures of hydrocarbons which are
conventionally encountered in the refining of petroleum such as natural gas
liquids,
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naphtha, light gas oils, heavy gas oils, and wide-cut gas oils, as well as
hydrocarbon fractions derived from coal liquefaction and the processing of oil
shale
or tar sands. Preferred feedstocks include the liquid products that contain
organic
sulfur compounds as impurities which result from the catalytic cracking or
cokina
of hydrocarbon feedstocks.
Aromatic hydrocarbons can be alkylated with the alkylating agents of this
invention in the presence of the acidic catalysts of this invention. However,
aromatic sulfur compounds and other typical sulfur-containing impurities are
much
more reactive than aromatic hydrocarbons. Accordingly, in the practice of this
invention, it is possible to selectively alkylate the sulfur-containing
impurities
without significant alkylation of aromatic hydrocarbons which may be present
in the
feedstock. However, any competitive alkylation of aromatic hydrocarbons can be
reduced by reducing the concentration of aromatic hydrocarbons in the
feedstock.
Accordingly, in a preferred embodiment of the invention, the feedstock will
contain
less than 50 weight percent of aromatic hydrocarbons. If desired, the
feedstock can
contain less than about 25 weight percent of aromatic hydrocarbons or even
smaller
amounts.
Catalytic cracking products are preferred feedstocks for use in the subject
invention. Preferred feedstocks of this type include liquids which boil below
about
345 C, such as light naphtha, heavy naphtha, distillate and light cycle oil.
However, it will also be appreciated that the entire output of volatile
products from
a catalytic cracking process can be utilized as a feedstock in the subject
invention.
Catalytic cracking products are a desirable feedstock because they typically
contain
a relatively high olefin content, which makes it unnecessary to add any
additional
alkyiating agent. in addition, aromatic sulfur compounds are frequently a
major
component of the sulfur-containing impurities in catalytic cracking products,
and
aromatic sulfur compounds are easily removed by means of the subject
invention.
For example, a typical light naphtha from the fluidized catalytic cracking of
a
petroleum derived gas oil can contain up to about 60% by weight of olefins and
up
to about 0.5% by weight of sulfur wherein most of the sulfur will be in the
form of
aromatic sulfur compounds. A preferred feedstock for use in the practice of
this
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invention will be comprised of catalytic cracking products and will be
additionally
comprised of at least 1 weight percent of olefins. A highly preferred
feedstock will
be comprised of catalytic cracking products and will be additionally comprised
of at
least 5 weight percent of olefins. Such feedstocks can be a portion of the
volatile
products from a catalytic cracking process which are separated by
distillation.
The sulfur-containing impurities which can be removed by the process of
this invention include but are not limited to mercaptans and aromatic sulfur
compounds. Examples of aromatic sulfur compounds include thiophene, thiophene
derivatives, benzothiophene, and benzothiophene derivatives, and examples of
such
thiophene derivatives include 2-methyithiophene, 3-methylthiophene, 2-
ethylthiophene and 2,5-dimethylthiophene. In a preferred embodiment of the
invention, the sulfur-containing impurities in the feedstock will be comprised
of
aromatic sulfur compounds and at least about 20% of these aromatic sulfur
compounds are converted to higher boiling sulfur-containing material upon
contact
with the alkylating agent in the presence of the acid catalyst. If desired at
least
about 50% or even more of these aromatic sulfur compounds can be converted to
higher boiling sulfur-containing material in the practice of this invention.
Any acidic material which can catalyze the reaction of an olefin or alcohol
with mercaptans, thiophene and thiophene derivatives can be used as a catalyst
in
the practice of this invention. Solid acidic catalysts are particularly
desirable, and
such materials include liquid acids which are supported on a solid substrate.
The
solid acidic catalysts are generally preferred over liquid catalysts because
of the
ease with which the sulfur-containing feedstock can be contacted with such a
material. For example, the feedstock can simply be passed through a
particulate
fixed bed of a solid acidic catalyst at a suitable temperature. In contrast,
the use of
a liquid acid on a large scale is frequently more difficult because of the
problems
which are inherent in handling a corrosive liquid and because of the problems
involved in separating the liquid acid from the products which are generated
upon
contact of the feedstock with the liquid acid catalyst.
Catalysts which are suitable for use in the practice of the invention can be
comprised of materials such as acidic polymeric resins, supported acids, and
acidic
= CA 02248159 2006-02-24
-15-
inorganic oxides. Suitable acidic polymeric resins include the polymeric
sulfonic
acid resins which are well-known in the art and are commercially available.
Amberlyst 35, a product produced by Rohm and Haas Co., is a typical example
of
such a material.
Supported acids which are useful as catalysts include, but are not limited to,
Bronsted acids (examples include phosphoric acid, sulfuric acid, boric acid,
HF,
fluorosulfonic acid, trifluoromethanesulfonic acid, and dihydroxyfluoroboric
acid)
and Lewis acids (examples include BF3, BC13, A1C13, AIBr3, FeC12, FeCI3,
ZnC1,,
SbF5, SbC15 and combinations of AIC13 and HCI) which are supported on solids
such as silica, alumina, silica-aluminas, zirconium oxide or clays. When
liquid
acids are employed, the supported catalysts are typically prepared by
combining the
desired liquid acid with the desired support and drying. Supported catalysts
which
are prepared by combining a phosphoric acid with a support are highly
preferred
and are referred to herein as solid phosphoric acid catalysts. These catalysts
are
preferred because they are both highly effective and low in cost. U.S. Patent
No.
2,921,081 (Zimmerschied et al.)
discloses the preparation of'solid phosphoric acid catalysts by combining a
zirconium compound selected from the group consisting of zirconium oxide and
the
halides of zirconium with an acid selected from the group consisting of
orthophosphoric acid. pyrophosphoric acid and triphosphoric acid. U.S. Patent
No.
2,120,702 (Ipatieff et al. ) discloses the
preparation of solid phosphoric acid catalysts by combining a phosphoric acid
with
a siliceous material. Finally. British Patent No. 863,539
also discloses the preparation of a solid phosphoric acid
catalyst by depositing a phosphoric acid on a solid siliceous material such as
diatomaceous earth or kieselguhr.
Acidic inorganic oxides which are useful as catalysts include, but are not
limited to, aluminas, silica-atuminas, natural and synthetic pillared clays,
and
natural and synthetic zeolites such as faujasites, mordenites, L, omega, X, Y,
beta,
and ZSM zeolites. Tiighly suitable zeolites include beta, Y, ZSM-3, ZSM-4, ZSM-
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5, ZSM-18, and ZSM-20. If desired, the zeolites can be incorporated into an
inorganic oxide matrix material such as a silica-alumina. Indeed, equilibrium
cracking catalyst can be used as the acid catalyst in the practice of this
invention.
Catalysts can comprise mixtures of different materials, such as a Lewis acid
(examples include BF3, BC13, SbF5, and AIC13), a nonzeolitic solid inorganic
oxide
(such as silica, alumina and silica-alumina), and a large-pore crystalline
molecular
sieve (examples include zeolites, pillared clays and aluminophosphates).
Feedstocks which are used in the practice of this invention will occasionally
contain nitrogen-containing organic compounds as impurities in addition to the
sulfur-containing impurities. Many of the typical nitrogen-containing
impurities are
organic bases and, in some instances, can cause deactivation of the acid
catalyst by
reaction with it. In the event that such deactivation is observed, it can be
prevented
by removal of the basic nitrogen-containing impurities from the feedstock
before it
is contacted with the acid catalyst.
The basic nitrogen-containing impurities can be removed from the feedstock
by any conventional method such as an acid wash or the use of a guard bed
which is
positioned in front of the acid catalyst. Examples of effective guard beds
include A-
zeolite, Y-zeolite, L-zeolite, mordenite and acidic polymeric resins. If a
guard bed
technique is employed, it is often desirable to use two guard beds in such a
manner
that one guard bed can be regenerated while the other is being used to
pretreat the
feedstock and protect the acid catalyst. If an acid wash is used to remove
basic
nitrogen-containing compounds, the feedstock will be treated with an aqueous
solution of a suitable acid. Suitable acids for such use include, but are not
limited
to, hydrochloric acid, sulfuric acid and acetic acid. The concentration of
acid in the
aqueous solution is not critical, but is conveniently chosen to be in the
range from
about 0.5 to about 30% by weight.
In the practice of this invention, the feedstock which contains sulfur-
containing impurities is contacted with the acid catalyst at a temperature and
for a
period of time which are effective to result in conversion of at least a
portion of the
sulfur-containing impurities to a higher boiling sulfur-containing material.
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Desirably, the contacting temperature will be in excess of about 50 C,
preferablv
in excess of 100 C, and more preferably in excess of 125 C. The contacting
will
generally be carried out at a temperature in the range from about 50 to about
350
C, preferably from about "100 to about 350 C, and more preferably from about
125 to about 250 C. It will be appreciated, of course, that the optimum
temperature will be a function of the acid catalyst used, the alkylating agent
or
agents selected, and the nature of the sulfur-containing impurities that are
to be
removed from the feedstock.
The sulfur-containing impurities are highly reactive and can be selectively
converted to sulfur-containing products of higher boiling point by reaction
with the
alkylating agent of this invention. Accordingly, the feedstock can be
contacted with
the acid catalyst under conditions which are sufficiently mild that most
hydrocarbons will be substantially unaffected. For example, aromatic
hydrocarbons
will be substantially unaffected and significant olefin polymerization will
not take
place. In the case of a naphtha feedstock from a catalytic cracking process,
this
means that sulfur-containing impurities can be removed without significantly
affecting the octane of the naphtha. However, if desired, the temperature and
concentration of alkylating agent can be increased to a point where
significant
alkylation of aromatic hydrocarbons can also be produced. If, for example, the
feedstock contains both sulfur-containing impurities and modest amounts of
benzene, the reaction conditions can be selected so that the sulfur-containing
impurities are converted to higher boiling products and a major portion of the
benzene is converted to alkylation products.
Any desired amount of alkylating agent can be used in the practice of this
invention. However, relatively large amounts of alkylating agent relative to
the
amount of sulfur-containing impurities will promote a rapid and complete
conversion of the impurities to higher boiling sulfur-containing products upon
contact with the acid catalyst. Before contacting with the acid catalyst, the
composition of the feedstock is desirably adjusted so that it contains an
amount of
alkylating agent which is at least equal on a molar basis to that of the
organic sulfur
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compounds in the feedstock. If desired, the molar ratio of alkylating agent to
organic sulfur compounds can be at least 5 or even larger.
In the practice of this invention, the feedstock can be contacted with the
acid
catalyst at any suitable pressure. However, pressures in the range from about
0.01
to about 200 atmospheres are desirable, and a pressure in the range from about
1 to about 100 atmospheres is preferred. In a highly preferred embodiment of
the
invention, the temperature and pressure at which the feedstock is contacted
with the
solid acidic catalyst are selected so that the feedstock is maintained in a
liquid state.
Although the invention is not to be so limited, it is believed that coke
formation is
minimized when the feedstock is kept in a liquid state during contacting with
the
acid catalyst. More specifically, it is believed that coke precursors are
dissolved
and removed from the catalyst when the feedstock is maintained in the liquid
state.
In contrast, if the feedstock is contacted with the solid acidic catalyst as a
vapor, it
is believed that coke precursors can be deposited on the catalyst and remain
there
until they are ultimately converted to coke which can deactivate the catalyst.
The contacting of the acid catalyst with the feedstock and alkylating agent of
this invention can be carried out in any conventional manner. For example, the
feedstock and alkylating agent can be contacted with the acid catalyst in a
batch
process. However, in a highly preferred embodiment, the feedstock and
alkylating
agent are simply passed through a fixed bed.of solid acidic catalyst which is
placed
either in a vertical or a horizontal reaction zone. Desirably, the solid
acidic catalyst
will be used in a physical form, such as pellets, beads or rods, which will
permit a
rapid and effective contacting with the feedstock and alkylating agent without
creating substantial amounts of back-pressure. Although the invention is not
to be
so limited, it is preferred that the catalyst be in particulate form wherein
the largest
dimension of the particles has an average value which is in the range from
about 0.1
mm to about 2 cm. For example, substantially spherical beads of catalyst can
be
used which have an average diameter from about 0.1 mm to about 2 cm.
Alternatively, the catalyst can be used in the form of rods which have a
diameter in
the range from about 0.1 mm to about 1 cm and a length in the range from about
0.2 mm to about 2 cm.
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This invention represents a method for concentrating the sulfur-containing
impurities of a hydrocarbon feedstock into a high boiling fraction which is
separated
by fractional distillation. As a result of concentration, the sulfur can be
disposed of
more easily and at lower cost, and any conventional method can be used for
this
disposal. For example, the resulting high sulfur content material can be'
blended
into heavy fuels where the sulfur content will be less objectionable.
Alternatively,
this high sulfur content material can be efficiently hydrotreated at
relatively low cost
because of its reduced volume relative to that of the original feedstock.
A highly preferred embodiment of this invention comprises its use to remove
sulfur-containing impurities from the hydrocarbon products that occur in the
products from the fluidized catalytic cracking of hydrocarbon feedstocks which
contain sulfur-containing impurities. The catalytic cracking of heavy mineral
oil
fractions is one of the major refining operations employed in the conversion
of
crude oils to desirable fuel products such as high octane gasoline fuels which
are
used in spark-ignition internal combustion engines. In fluidized catalytic
cracking
processes, high molecular weight hydrocarbon liquids or vapors are contacted
with
hot, finely-divided, solid catalyst particles, typically in a fluidized bed
reactor or in
an elongated riser reactor, and the catalyst-hydrocarbon mixture is maintained
at an
elevated temperature in a fluidized or dispersed state for a period of time
sufficient
to effect the desired degree of cracking to low molecular weight hydrocarbons
of
the kind typically present in motor gasoline and distillate fuels.
Conversion of a selected hydrocarbon feedstock in a fluidized catalytic
cracking process is effected by contact with a cracking catalyst in a reaction
zone at
conversion temperature and at a fluidizing velocity which limits the
conversion time
to not more than about ten seconds. Conversion temperatures are desirably in
the
range from about 430 to about 700 C and preferably from about 450 to about
650 C. Effluent from the reaction zone, comprising hydrocarbon vapors and
cracking catalyst containing a deactivating quantity of carbonaceous material
or
coke, is then transferred to a separation zone. Hydrocarbon vapors are
separated
from spent cracking catalyst in the separation zone and are conveyed to a
fractionator for the separation of these materials on the basis of boiling
point.
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These hydrocarbon products typically enter the fractionator at a temperature
in the
range from about 430 to about 650 C and supply all of the heat necessary for
fractionation.
In the catalytic cracking of hydrocarbons, some non-volatile carbonaceous
material or coke is deposited on the catalyst particles. As coke builds up on
the
cracking catalyst, the activity of the catalyst for cracking and the
selectivity of the
catalyst for producing gasoline blending stocks diminishes. The catalyst can,
however, recover a major portion of its original capabilities by removal of
most of
the coke from it. This is carried out by burning the coke deposits from the
catalyst
with a molecular oxygen-containing regeneration gas, such as air, in a
regeneration
zone or regenerator.
A wide variety of process conditions can be used in the practice of the
fluidized catalytic cracking process. In the usual case where a gas oil
feedstock is
employed, the throughput ratio, or volume ratio of total feed to fresh feed,
can vary
__ from about 1.0 to about 3Ø Conversion level can vary from about 40% to
about
100% where conversion is defined as the percentage reduction of hydrocarbons
boiIing above 221 C at atmospheric pressure by formation of lighter
materials or
coke. The weight ratio of catalyst to oil in the reactor can vary within the
range
from about 2 to about 20 so that the fluidized dispersion will have a density
in the
range from about 15 to about 320 kilograms per cubic meter. Fluidizing
velocity
can be in the range from about 3.0 to about 30 meters per second.
A suitable hydrocarbon feedstock for use in a fluidized catalytic cracking
process in accordance with this invention can contain from about 0.2 to about
6.0
weight percent of sulfur in the form of organic sulfur compounds. Suitable
feedstocks include, but are not limited to, sulfur-containing petroleum
fractions such
as light gas oils, heavy gas oils, wide-cut gas oils, vacuum gas oils,
naphthas,
decanted oils, residual fractions and cycle oils derived from any of these as
well as
sulfur-containing hydrocarbon fractions derived from synthetic oils, coal
liquefaction and the processing of oil shale.and tar sands. Any of these
feedstocks
can be employed either singly or in any desired combination.
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A preferred embodiment of the present invention involves passing the
volatile products from the catalytic cracking of a sulfur-containing feedstock
to a
fractionator where they are separated on the basis of boiling point into at
least two
fractions which comprise: (1) a liquid boiling below about 345 C which
contains
sulfur-containing impurities, and (2) material of higher boiling point. A
treated
liquid is then prepared by contacting a portion of fraction (1) with an acidic
solid
catalyst at a temperature in excess of 50 C for a period of time which is
effective
to convert at least a portion of the sulfur-containing impurities in fraction
(1) to a
sulfur-containing material of higher boiling point. The resulting treated
liquid is
then returned to the fractionator and fractionated together with the original
volatile
products from the catalytic cracking process. In this manner, at least a
portion of
the sulfur-containing material of higher boiling point in the treated liquid
is
removed in the higher boiling fractions and a product of reduced sulfur
content is
produced. This embodiment can be thought of as a recycle process wherein a
recycle stream from the fractionator is contacted with the acid catalyst in
order to
convert sulfur-containing impurities to higher boiling products which are then
removed in the high boiling fractions from the fractionator. In a highly
preferred
embodiment, fraction (1) will be a liquid boiling below about 230 C and
fraction
(2) will be material of a higher boiling point.
The previously mentioned recycle process -embodiment is advantageous
because it can be implemented at very low capital cost. More specifically, the
recycle stream can be withdrawn from the fractionator at a temperature which
is
approximately equal to the preferred temperature for use in contacting the
recycle
stream with the acidic solid catalyst of this invention in order to convert
sulfur-
containing impurities to higher boiling point products. Accordingly, a
furnace, heat
exchanger or other means for heating the recycle stream is not required. In
addition, a separate fractionator is not required. In the practice of this
embodiment,
the recycle stream will, preferably, be from about 5%a to about 90% by volume
of
the above-mentioned fraction (1) from the fractionator.
The following examples are intendect only to illustrate the invention and are
not to be construed as imposing limitations on the invention.
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EXAMPLE I
Polymeric sulfonic acid resin.-- A macroreticular, polymeric, sulfonic acid
resin was obtained from the Rohm and Haas Company which is sold under the name
Amberlyst 35 Wet. This material was provided in the form of spherical beads
which have a particle size in the range from 0.4 to 1.2 mm and has the
following
properties: (1) a concentration of acid sites equal to 5.4 meq/g; (2) a
moisture
content of 56%; (3) a porosity of 0.35 cc/g; (4) an average pore diameter of
300 A.;
and a surface area of 44 m2/g. The resin was used as received and is
identified
herein as Catalyst A.
EXAMPLE II
Solid phosphoric acid alkvlation catalyst on kieselguhr.-- A solid phosphoric
acid catalyst on kieselguhr was obtained from UOP which is sold under the name
SPA-2. This material was provided in the form of a cylindrical extrudate
having a
nominal diameter of 4.75 mm and has the following properties: (1) a loaded
density
of 0.93 g/cm3; (2) a free phosphoric acid content, calculated as P'O5, of 16
to 20
wt. %; and (3) a nominal total phosphoric acid content, calculated as P205, of
60
wt. %. The catalyst was crushed and sized to 12 to 20 mesh size (U.S. Sieve
Series) before use, and is identified herein as Catalyst B.
EXAMPLE III
Preparation of ZSM-5 Zeolite.-- A solution of 1.70 kg of sodium
hydroxide, 26.8 kg of tetrapropyl ammonium bromide, 2.14 kg of sodium
aluminate, and 43.5 kg of silica sol (Ludox HS-40 manufactured by E.I. duPont
de
Nemours Co. Inc.) in 18.0 kg of distilled water was prepared in an autoclave.
The
autoclave was sealed and maintained at a temperature of about 149 C,
autogenous
pressure, and a mixer speed of about 60 rpm for a period of about 120 hours.
The
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slurry was filtered and washed, and the resulting filter cake was dried in an
oven at
121 C for a period of 16 hours. The dried filter cake was then calcined at
538 C
for a period of 4 hours. The calcined material was ion exchanged three times
with
ammonium nitrate in water by heating, under reflux, to a temperature of about
85
C for a period of one hour, cooling while stirring for 2 hours, filtering, and
washing with 1 liter of water, and reexchanging. The resulting solid was
washed
with 4 liters of water, dried in an oven at 121 C for a period of 4 hours
and
calcined at 556 C for 4 hours to yield ZSM-5 zeolite as a powder.
Preparation of alkvlation catalyst comprised of ZSM-5 zeolite in an alumina
malLiZt.-- A 166 g portion of the above-described ZSM-5 zeolite was mixed with
125 g of Catapal SB alumina (alpha-alumina monohydrate manufactured by V ista
).
The mixture of solids was added to 600 g of distilled water, mixed well and
dried in
an oven at 121 C for a period of 16 hours. The solids were then moistened
with
distilled water and extruded as a cylindrical extrudate having a diameter of
1.6 tnm.
The extrudate was dried at 121 C for 16 hours in a forced air oven and
calcined at
538 C for 4 hours. The resulting material was crushed and sized to 12-20 mesh
size (U.S. Sieve Series). This material, which is comprised of ZSM-5 zeolite
in an
alumina matrix, is identified herein as Catalyst C.
EXAMPLE IV
Preparation of beta zeolite.-- A solution of 0.15 kg of sodium hydroxide,
22.5 kg of tetraethyl ammonium hydroxide, 0.90 kg of sodium aluminate, and
36.6
kg of silica sol (Ludox HS-40 manufactured by E.I. duPont de Nemours Co. Inc.)
in 22.5 kg of distilled water was prepared in an autoclave. The autoclave was
sealed and maintained at a temperature of about 149 C, autogenous pressure,
and a
mixer speed of about 60 rpm for a period of about 96 hours. The slurry was
filtered and washed, and the filter cake was dried in an oven at 121 C for a
period
of 16 hours. The resulting solid was ion exchanged three times with ammonium
nitrate in water by heating, under reflux, to a temperature of about 60 C for
a
period of three hours, cooling while stirring for 2 hours, decanting and
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reexchanging. Upon drying in an oven at 121 C for a period of 4 hours, the
desired beta zeolite was obtained as a powder.
Preparation of aljylation catalyst comprised of beta zeolite in an alumina
II1~SLix.-- An 89.82 g portion of the above-described beta zeolite powder was
mixed
with 40 grams of Catapal SB alumina (alpha-alumina monohydrate manufactured by
Vista). The mixture of solids was added to 300 g of distilled water, mixed
well and
dried at 121 C for 16 hours in a forced air oven. The solids were then
moistened
with distilled water and extruded as a cylindrical extrudate having a diameter
of 1.6
mm. The extrudate was dried at 121 C for 16 hours in a forced air oven and
calcined at 538 C for 3 hours. The resulting material was crushed and sized
to 12
to 20 mesh size (U.S. Sieve Series). This material, which is comprised of beta
zeolite in an alumina matrix, is identified herein as Catalyst D.
EXAMPLE V
Preparation of silica-alumina alkylation catalyst.-- A 75.0 g portion of
tetraethyl orthosilicate and 500 g of n-hexane were mixed with 375 g of a low
silica
alumina which had a surface area of 338 m"/g and was in the form of a
cylindrical
extrudate having a diameter of 1.3 mm (manufactured by Haldor-Topsoe). The n-
hexane was allowed to evaporate at room temperature. The resulting material
was
dried in a forced air oven at 100 C for 16 hours and then calcined at 510 C
for 8
hours. The calcined material was impregnated with a solution containing 150 g
of
ammonium nitrate in 1000 ml of water, allowed to stand for 3 days, dried in a
forced air oven at 100 C for 16 hours and calcined at 538 C for 5 hours. The
resulting material, which is comprised of silica-alumina, is identified herein
as
Catalyst E.
EXAMPLE VI
Preparation of alkylation catalys co prised of Y zeolite in an alumina
maSrix.-- A 100.12 g portion of LZY-82 zeolite powder (LZY-82 is an
ultrastable
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Y zeolite manufactured by Union Carbide) was dispersed in 553.71 g of PHF
alumina sol (manufactured by Criterion Catalyst Company), and the dispersion
was
dried in a forced air oven at 121 C for 16 hours. The resulting material was
moistened with distilled water and was then extruded as a cylindrical
extrudate
having a diameter of 1.6 mm. The extrudate was dried at 121 C for 16 hours
in a
forced air oven and then calcined at 538 C for 3 hours. The resulting
material was
crushed and sized to 12-20 mesh size (U.S. Sieve Series). This material, which
is
comprised of LZY-82 zeolite in an alumina matrix, is identified herein as
Catalyst
F.
EXAMPLE VII
The data which are set forth below for the sulfur content of samples as a
function of boiling point were obtained using a gas chromatograph equipped
with a
flame ionization detector, a wide-bore fused-silica capillary column, direct
injector,
and a sulfur chemiluminescence detector. The analytical method is based on a
retention time versus boiling point calibration of the chromatographic system.
The ability of various acidic solid catalysts to convert the sulfur-containing
impurities in a hydrocarbon feedstock to sulfur-containing products of a
higher
boiling point was evaluated using the following feedstocks:
Stabilized Heavy Naphtha.-- This material, boiling over the range from
-21 to about 249 C, was obtained by :(1) partial stripping of the C4
hydrocarbons
from a heavy naphtha that was produced by the fluidized catalytic cracking of
a gas
oil feedstock which contained sulfur-containing impurities; and (2) treatment
with
caustic to remove mercaptans. Analysis of the stabilized heavy naphtha using a
multicolumn gas chromatographic technique showed it to contain on a weight
basis:
4% paraffins, 18% isoparaffins, 15% olefins, 15% naphthenes, 45% aromatics,
and
3% unidentified C13+ high boiling material. The total sulfur content of the
stabilized heavy naphtha, as determined by X-ray fluorescence spectroscopy,
was
730 ppm. This sulfur content, as a function of boiling point, is set forth in
Table I.
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TABLE I. Sulfur Content of Heavy Naphtha Feedstock
as a Function of Boiling Point.
Amount of Sulfur in Higher
Boiling Fractions, wt. % Temperature, C
95 113
90 114
85 132
80 139
75 142
70 163
65 168
60 182
55 201
50 219
45 220
40 220
35 226
30 227
229
20 232
15 233
10 247
25 5 264
1 365
The principal sulfur-containing impurities were identified chromatographically
by
discrete peak identification, and these results are set forth in Table II.
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TABLE II. Principal Sulfur-Containing Impurities In
Stabilized Heavy Naphtha Feedstock.
Component Component Concentration, ppm
Thiophene 18
2-Methylthiophene 33
2-Ethylthiophene 15
3-Ethylthiophene 21
Benzothiophene 111
Tetrahydrothiophene 4
2,5-Dimethylthiophene 11
Experiments with the stabilized heavy naphtha feedstock were carried out
using the following procedure. A 7 g portion of the selected catalyst was
packed
into a 9.5 mm internal diameter tubular reactor which was constructed of
stainless
steel and held in a vertical orientation. The catalyst bed was placed in the
reactor
between beds of silicon carbide which were held in place with plugs of quartz
wool.
Operating temperatures were varied from 93 to 204 C, and the pressure within
the reactor was maintained at 75 to 85 atm. The feedstock was introduced at
the
top of the reactor and was passed downward through the catalyst bed at a space
velocity of 1-2 LHSV. A syringe pump was used to inject the feedstock into the
reactor. The experimental apparatus included a back-pressure regulator which
was
downstream from the reactor and was positioned at a higher elevation than the
top
to the catalyst bed in order to ensure that the catalyst bed was completely
filled with
liquid.
Synthetic Feedstocks.-- Two synthetic feedstocks, one of low olefin content
and the other of high olefin content, were prepared by blending model
compounds
which were selected to represent the principal groups of organic compounds
which
are found in a.typical heavy naphtha which is produced by the fluidized
catalytic
cracking process. The proportions of these principal groups in the ':iigh
olefin
content synthetic feedstock are typical of what would be expected in such a
heavy
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naphtha from a fluidized catalytic cracking process. The synthetic feedstocks
are
very similar in composition except that the low olefin content synthetic
feedstock
contains very little olefin. The compositions of these synthetic feedstocks
are set
forth in Table III.
TABLE HI. Composition of Synthetic Feedstocks.
Component Concentration, wt. %
High Olefm Low Olefin
Component Content Feedstock Content Feedstock
2-Propanethiol 0.39 0.22
1-Hexene 4.10 0.38
Methylcyclopentane 8.54 6.81
2,3-Dimethyl-2-butene 4.17 0.44
Benzene 10.32 13.44
Thiophene 0.49 0.41
1-Heptene 4.63 0.56
n-Heptane 43.37 47.86
Toluene 22.53 28.74
2-Methylthiophene 0.45 0.50
Isopropyl sulfide 0.48 0.29
Experiments with the synthetic feedstocks were carried out using the
following procedure. A 10 cm3 volume of the selected catalyst was packed into
a
1.43 cm internal diameter tubular reactor which was constructed of stainless
steel
and held in a vertical orientation. The catalyst bed was placed in the reactor
between beds of alpha alumina which were held in place with plugs of quartz
wool.
Prior to use, catalysts C, D, E and F were activated in the reactor at a
temperature
of 399 C in a stream of nitrogen at a flow rate of 200 cm3/min for one hour.
Operating temperatures were varied from 93 to 204 C, and the pressure
within
the reactor was maintained at either 17 or 54 atm. The feedstock was
introduced at
the bottom of the reactor and was passed upward through the catalyst bed.
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EXPERIMENT VIII
The stabilized heavy naphtha feedstock was blended with a mixed C,/C4
stream (containing, on a weight basis, 55 % propane, 27% propene, 9.5 % 2-
butene,
6% 1-butene and 2.5% 2-methylpropene) at a 1.0 volume ratio of C3/C4 stream to
naphtha. The resulting blend was contacted, as described above, with Catalyst
B
(solid phosphoric acid catalyst on kieselguhr) at a pressure of 85 atm, a
space
velocity of 2 LHSV, and at temperatures of 93 , 149 and 204 C. The
distribution of sulfur content as a function of boiling point in the feedstock
and in
the products obtained at reaction temperatures of 93 , 149 and 204 C is
set forth
in FIG. 1 (boiling point is plotted as a function of the percentage of the
total sulfur
content which is present in higher boiling fractions). These results
demonstrate
that, at a reaction temperature of either 149 or 204 C, the sulfur-
containing
impurities in the feedstock are converted to higher boiling sulfur-containing
products, and that this increase in boiling point is about 25 C over the
entire
boiling range of the naphtha. In contrast, there is relatively little
conversion of the
sulfur-containing impurities to higher boiling products at a reaction
temperature of
93 C.
EXPERIMENT IX
The stabilized heavy naphtha was contacted with Catalyst B (solid
phosphoric acid catalyst on kieselguhr) at a pressure of 75 atm, a temperature
of
204 C and a space velocity of 1 LHSV. The distribution of sulfur content as a
function of boiling point in the feedstock and in the product is set forth in
FIG. 2
(boiling point is plotted as a function of the percentage of the total sulfur
content
which is present in higher boiling fractions). These results demonstrate that
the
olefin content of this heavy naphtha feedstock from a catalytic cracking
process is
sufficiently high to permit conversion of the sulfur-containing impurities to
higher
boiling sulfur-containing products. It will also be noted that 30% of the
sulfur in
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the product boils above 288 C in contrast to only about 20% in the product
which
was obtained when the feedstock was blended with a mixture of propene and
butenes as described in Experiment VIII. It is believed that the higher
molecular
weight olefins present in the feedstock yield sulfur-containing products which
are
higher in boiling point than the products that are obtained when large amounts
of C:
and C4 olefins are added to the feedstock as in Experiment VIII.
EXPERIMENT X
A low olefin content synthetic feedstock having the composition which is set
forth in Table III was contacted, as described above, with Catalyst B (solid
phosphoric acid catalyst on kieselguhr) at a pressure of 54 atm, a temperature
of
204 C, and a space velocity of 2 LHSV. The distribution of sulfur content as
a
function of boiling point in the low olefin content synthetic feedstock is set
forth in
FIG. 3a (boiling point is plotted as a function of the percentage of the total
sulfur
content which is present in higher boiling fractions). FIG. 3b sets forth the
sulfur
distribution as a function of boiling point in the product from this
feedstock.
Comparison of FIGS. 3a and 3b, demonstrates that there was very little
conversion
of the sulfur-containing components of the synthetic feedstock to higher
boiling
sulfur-containing products.
EXPERIMENT XI
A high olefin content synthetic feedstock having the composition which is set
forth in Table III was contacted, as described above, with Catalyst B (solid
phosphoric acid catalyst on kiesetguhr) at a pressure of 54 atm, a temperature
of
204 C, and a space velocity of 2 LHSV. The distribution of sulfur content as
a
function of boiling point in the high olefin content synthetic feedstock is
set forth in
FIG. 4a (boiling point is plotted as a function of the percentage of the total
sulfur
content which is prezent in higher boiling fractions). FIG. 4b sets forth the
sulfur
distribution as a function of boiling point in the product from this
feedstock.
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Comparison of FIGS. 4a and 4b demonstrates that there was substantial
conversion
of the sulfur-containing components of the synthetic feedstock to higher
boiling
sulfur-containing products. Except for olefin content, the high olefin content
synthetic feedstock of this experiment has a composition which is very similar
to
that of the low olefin content synthetic feedstock of Experiment X above. A
comparison of the results of this experiment with those of Experiment X will
demonstrate that there is very little conversion of the sulfur-containing
feedstock
components in the absence of the olefins.
EXPERIMENT XII
Catalysts A, B, C, D, E and F, which are described in detail above and
whose properties are briefly summarized in Table IV, were each tested as
described
above at a pressure of 17 atm, a temperature of 204 C, and a space velocity
of 2 LHSV with the following two feedstocks: (1) a high olefin content
synthetic
feedstock having the composition which is set forth in Table III; and (2) the
same
high olefin content synthetic feedstock after blending with propene at a 0.25
volume
TABLE IV. Catalyst Characteristics.
Catalyst Type Pore Size Relative Acidity
A Amberlyst 35 Wet > 6A Medium
B Solid phosphoric acid > 6A Strong
on kieselguhr
C ZSM-5 zeolite in <6A Strong
alumina matrix
D Beta zeolite in > 6A Strong
alumina matrix
E Silica-alumina > 6A Medium
F Y zeolite in alumina > 6A Strong
matrix
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ratio of propene to synthetic feedstock. In each such test, the conversion of
thiophenes (thiophene and 2-methylthiophene) to other materials was determined
from an analysis of the resulting product for thiophene and methylthiophene
content. The results of these tests are set forth in FIG. 5. These results
suggest
that the conversion of thiophene and 2-methylthiophene in the absence of added
propene is highest over the most acidic catalysts which have a pore size
greater than
about 6A (Catalysts B, D and F). Although the invention is not to be so
limited,
these results suggest that the size of the alkylated product may be too large
to form
in the pores of the catalyst which has a pore size smaller than about 6A
(Catalyst C)
and that the acidity of the moderately acidic catalysts (Catalysts A and E)
may be
insufficient to fully activate the C6 and C7 olefins of the high olefin
synthetic
feedstock. However, when propene is added to the synthetic feedstock, the
conversion of thiophene and 2-methyithiophene over both Catalyst C ( < 6A pore
size) and the moderately acidic Catalyst E is approximately doubled.
EXPERIMENT XIII
A high olefin content synthetic feedstock having the composition which is set
forth in Table III was blended with propene at a 0.13 volume ratio of propene
to
synthetic feedstock, and the resulting blend was contacted with Catalyst B
(solid
phosphoric acid catalyst on kieselguhr) at a pressure of 54 atm, a temperature
of
149 C, and a space velocity of 2 LHSV. This experiment was then repeated at a
temperature of 204 C. In each experiment, the conversion of thiophenes
(thiophene and 2-methylthiophene), benzene, and toluene to other products was
determined from an analysis of the resulting product. At 149 C, the
conversion of
thiophenes (thiophene and 2-methylthiophene), benzene and toluene was 54%, 15%
and 7%, respectively. At 204 C, the conversion of thiophenes (thiophene and 2-
methyithiophene), benzene and toluene was 73%, 36% and 26%, respectively.
Accordingly, under these conditions, the aromatic sulfur compounds (thiophene
and
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2-methylthiophene) are converted in preference to the aromatic hvdrocarbons
(benzene and toluene).
EXPERIMENT XIV
In a series of tests, the stabilized heavy naphtha was blended with varying
amounts of a mixed C3/C4 stream (containing, on a weight basis, 55 % propane.
27% propene, 9.5 %a 2-butene, 6% 1-butene, 2.5% 2-methylpropene, and 1500 ppm
2-propanol), and the various blends were contacted with Catalyst B (solid
phosphoric acid catalyst on kieselguhr) at a pressure of 82 atm, a temperature
of
204 C, and a space velocity of 1 LHSV. The ratio by volume of the mixed C3/C4
stream to naphtha used in these tests is set forth in Table V. The product of
each
test was analyzed with respect to: (1) the conversion of sulfur-containing
impurities
to higher boiling sulfur-containing material; and (2) its content of benzene
and
cumene. These analytical results are also set forth in Table V. The ratio of
cumene
to benzene in the product is an indicator of the extent to which the aromatic
hydrocarbons in the naphtha feedstock have been alkylated under the conditions
of
TABLE V. Effect of Varying Amounts of Mixed C3/C4 Olefins on
Alkylation of Heavy Naphtha.
Volume Ratio Sulfur in Products Weight Ratio
Run of C3/CQ Stream Boiling above 260 C, of Cumene
No. to Naphtha wt. % to Benzene
1 0.02 23 0.01
2 0.03 25 0.03
3 0.14 23 0.04
4 0.24 25 0.14
5 0.50 36 0.83
6 1.0 42 1.6
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each test (the cumene is formed by alkylation of benzene in the naphtha
feedstock
with propene from the mixed C3/C4 stream). For comparison purposes, the
feedstock had a 0.01 weight ratio of cumene to benzene and 5 weight percent of
its
sulfur content had a boiling point above 260 C. The results indicatethat the
sulfur-
containing impurities can be converted to higher boiling sulfur-containing
material
in a selective manner which does not cause significant alkylation of the
aromatic
hydrocarbons which are also in the feedstock.
