Note: Descriptions are shown in the official language in which they were submitted.
2168720
PROCESS FOR DESULFURIZING CATALYTICALLY CRACKED GASOLINE
FIELD OF THE INVENTION
The present invention relates to a process for
desulfurizing catalytically cracked gasoline. More
particularly, the present invention relates to a process for
hydrodesulfurizing catalytically cracked gasoline containing
sulfur compounds and olefin components in the presence of a
catalyst.
BACKGROUND OF THE INVENTION
In the field of petroleum refining, catalytically
cracked gasoline is a stock of high-octane number gasoline
containing a certain amount of olefin components.
Catalytically cracked gasoline is a gasoline fraction
obtained by catalytically cracking a heavy petroleum fraction
as a stock oil, such as a vacuum gas oil or an atmospheric
residual oil, and recovering and distilling the catalytically
cracked products. Catalytically cracked gasoline is a
primary blending stock of automotive gasoline.
However, the stock oil for catalytic cracking has a
relatively high content of sulfur compounds. When an
untreated stock oil is subjected to catalytic cracking, the
resulting catalytically cracked gasoline also has a high
sulfur compound content. The resulting gasoline fraction
would cause environmental pollution if used as a blending
stock of automotive gasoline.
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2I6~720
Consequently, the stock oil is usually subjected to a
desulfurization process prior to catalytic cracking.
On the other hand, a naphtha fraction obtained by
distilling crude oil is generally subjected to catalytic
reforming to at least partially aromatize the same and
increase its octane number. Because a reforming catalyst is
generally poisoned by sulfur compounds, the naphtha fraction
should also be desulfurized prior to catalytic reforming.
A hydrodesulfurization process has hitherto been
carried out to achieve the above-noted desulfurization in the
field of petroleum refining. A hydrodesulfurization process
includes contacting a stock oil to be desulfurized with an
appropriate catalyst for hydrodesulfurization in a
pressurized hydrogen atmosphere at a high temperature.
Catalysts which are typically used for
hydrodesulfurization of heavy petroleum fractions, such as a
stock oil for catalytic cracking (e.g., a vacuum gas oil or
an atmospheric residual oil) and a stock oil for thermal
cracking (e. g., a vacuum residual oil), comprise a group VIII
element (e. g., cobalt and nickel) and a group VI element
(e.g., chromium, molybdenum and tungsten) supported on an
appropriate carrier (e.g., alumina). The
hydrodesulfurization process is usually conducted at a
temperature of about 300 to about 400°C, a hydrogen partial
pressure of about 30 to about 200 kg/cm2, and a liquid hourly
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~~ss7~~
space velocity (hereinafter abbreviated as LHSV) of about 0.1
to about -10 1 /hr .
Catalysts which are typically used for
hydrodesulfurization of naphtha comprise a combination of a
group VIII element and a group VI element (e.g., a
combination of cobalt and molybdenum) supported on an
appropriate carrier (e.g., alumina). The
hydrodesulfurization process is usually carried out at a
temperature of about 280 to about 350°C, a hydrogen partial
pressure of about 15 to about 40 kg/cmz, and an LHSV of about
2 to about 8 1/hr.
In the case of hydrodesulfurization of a heavy
petroleum fraction such as a vacuum gas oil or an atmospheric
residual oil, which is a stock oil for catalytic cracking,
processing is carried out at high temperature and high
pressure as described above. Consequently, strict conditions
are imposed on the apparatus design. Furthermore, an
extension of the apparatus to increase its capacity involves
high construction costs.
On the other hand, when catalytically cracked
gasoline is hydrodesulfurized under the above-described
processing conditions, the olefin components present in the
cracked gasoline fraction are hydrogenated to reduce the
olefin content, and the resulting cracked gasoline fraction
has a reduced octane number. Therefore, the cracked gasoline
fraction following hydrodesulfurization is desirably
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2168720
subjected to catalytic reforming, isomerization, etc. so as
to increase the octane number. That is, two processes are
involved. The technique disclosed in the unexamined
published Japanese patent application No. Hei. 6-509830 based
on a PCT application is an example of such a two process
system.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a
process for effectively hydrodesulfurizing catalytically
cracked gasoline containing sulfur compounds and olefin
components while minimizing the reduction of olefin
components.
In order to solve the above-described problem, the
present inventors sought to develop a hydrodesulfurization
process for removing sulfur compounds to a permissible level
while minimizing reduction in the content of olefin
components. As a result, the present inventors found that
various sulfur compounds contained in catalytically cracked
gasoline are not equally hydrodesulfurized, and the ease or
difficulty in desulfurization varies depending on the
molecular structure of the sulfur compounds.
In view of the difference in the relative ease or
difficulty in desulfurization among sulfur compounds, the
present inventors have discovered a process for
hydrodesulfurizing catalytically cracked gasoline containing
sulfur compounds and olefin components, which comprises
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21~872~
separating the catalytically cracked gasoline into a
plurality of fractions including at least one of (i) a first
fraction rich in sulfur compounds that are hard to
desulfurize and (ii) a second fraction rich in sulfur
compounds that are easy to desulfurize, next
hydrodesulfurizing at least one of the first and second
fractions in the presence of a catalyst, and then mixing the
hydrodesulfurized fractions) with the remaining fractions.
That is, the present invention relates to a process for
desulfurizing catalytically cracked gasoline comprising
separating the catalytically cracked gasoline into at least
one of a fraction that has a high content of a single or a
plurality of sulfur compounds that are difficult to
desulfurize and a fraction that has a high content of a
single or a plurality of sulfur compounds that are easy to
desulfurize, subjecting at least one of the fractions to
hydrodesulfurization under optimum conditions, and mixing the
fractions.
DETAILED DESCRIPTION OF THE INVENTION
The catalytically cracked gasoline for use in the
present invention is a gasoline fraction distilled at a
temperature of from about 30 to about 250°C. The
catalytically cracked gasoline is obtained by catalytically
cracking a heavy petroleum fraction (e.g., a vacuum gas oil
or an atmospheric residual oil) to mostly convert the heavy
petroleum fraction into a broad range of petroleum fractions,
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and recovering and distilling the catalytically cracked
products: The catalytically cracked gasoline is often
separated into a light fraction and a heavy fraction which
are used depending on the intended application as a gasoline
base. The boiling point of the light fraction is from about
30 to about 180°C, and that of the heavy fraction is from
about 80 to about 250°C.
These catalytically cracked gasoline fractions
contain about 10 to about 1000 ppm of sulfur compounds, such
as thiophene, alkylthiophenes, benzothiophene,
alkylbenzothiophenes, thiacyclopentane,
alkylthiacyclopentanes, mercaptanes and sulfides.
Catalytically cracked gasoline which has been subjected to
sweetening also contains disulfides. These sulfur compounds
can be analyzed and quantified by a GC-AED (a gas
chromatography with an atomic emission detector).
Of these sulfur compounds, thiophene and
alkylthiophenes are compounds that are difficult to
desulfurize. Alkylthiophenes are more difficult to
desulfurize than thiophene. The alkylthiophenes become more
difficult to desulfurize with an increase in the number of
constituent alkyl groups. The present invention is
characterized in that one or more sulfur compounds which are
difficult to desulfurize are identified as such, and one or
more fractions having a high concentration of sulfur
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~16~720
compounds that are hard to desulfurize are handled separately
from other fractions.
On the other hand, benzothiophene,
alkylbenzothiophenes, thiacyclopentane, and
alkylthiacyclopentanes, among the above-described sulfur
compounds, are examples of sulfur compounds that are easy to
desulfurize. Of these, benzothiophene is the easiest to
desulfurize. The alkylbenzothiophenes become more difficult
to desulfurize with an increase in the number of constituent
alkyl groups.
Separating the catalytically cracked gasoline into a
fraction that is rich in sulfur compounds that are hard to
desulfurize and into a fraction that is rich in sulfur
compounds that are easy to desulfurize may be accomplished by
any of distillation, adsorption, crystallization and the
like. Distilling is the most convenient of these methods.
The boiling points of typical sulfur compounds that
are hard to desulfurize are as follows. Thiophene: 84.16°C;
2-methylthiophene: 112.56°C; 3-methylthiophene: 115.44°C; 2-
ethylthiophene: 134.00°C; 3-ethylthiophene: 136.00°C; 2,5-
dimethylthiophene: 136.70°C; 2,4-dimethylthiophene: 140.70°C;
2,3-dimethylthiophene: 141.60°C; 3,4-dimethylthiophene:
145.00°C; 2-isopropylthiophene: 153.00°C; 3-
isopropylthiophene: 157.00°C; 3-ethyl-2-methylthiophene:
157.00°C; 5-ethyl-2-methylthiophene: 160.10°C; 2,3,5-
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216~7~0
trimethylthiophene: 164.50°C; and 2,3,4-trimethylthiophene:
172.70°C:
The boiling points of typical sulfur compounds that
are easy to desulfurize are as follows. Thiacyclopentane:
121.12°C; 2-methylthiacyclopentane: 133.23°C; 3-
methylthiacyclopentane: 138.64°C; 2,trans-5-
dimethylthiacyclopentane: 142.00°C; 2,cis-5-
dimethylthiacyclopentane: 142.28°C; 3,3-
dimethylthiacyclopentane: 145.00°C; 2,3-
dimethylthiacyclopentane: 148.00°C; 3-ethylthiacyclopentane:
165.00°C; benzothiophene: 219.90°C; methylbenzothiophene:
243.90°C.
Thus, some of the sulfur compounds that are hard to
desulfurize and some of the sulfur compounds that are easy to
desulfurize have boiling points that are close together.
Accordingly, it is necessary to first determine the
distribution of sulfur compounds by analysis, and to then
select a distillation apparatus and distillation conditions
that would provide the greatest degree of separation
possible. After separation, the fraction that is rich in
sulfur compounds that are hard to desulfurize desirably
contains sulfur compounds that are hard to desulfurize in an
amount of more than 50 mold, preferably at least 60 mold, of
the total sulfur compound content. Likewise, the fraction
that is rich in sulfur compounds that are easy to desulfurize
desirably contains sulfur compounds that are easy to
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z1~8~~0
desulfurize in an amount of more than 50 mold, preferably at
least 60-mol~, of the total sulfur compound content. To
separate a sample containing both sulfur compounds that are
hard to desulfurize and sulfur compounds that are easy to
desulfurize having close boiling points, a multi-stage
distillation apparatus is preferred to a single distillation
apparatus for carrying out separation and concentration at
increased efficiency.
The method used for desulfurizing a fraction that is
rich in sulfur compounds that are hard to desulfurize and a
fraction that is rich in sulfur compounds that are easy to
desulfurize is selected according to the intended purpose.
The language "rich in sulfur compounds that are hard
to desulfurize" might be defined as a fraction containing
sulfur compounds that are hard to desulfurize in an amount of
more than 50 mold, preferably at least 60 mold, of the total
content of sulfur compounds contained in the fraction.
The language "rich in sulfur compounds that are easy
to desulfurize" might be defined as a fraction containing
sulfur compounds that are easy to desulfurize in an amount of
more than 50 mold, preferably at least 60 mold, of the total
content of sulfur compounds contained in the fraction.
For example, where the sulfur content is to be
reduced to a limited extent, only a fraction that is rich in
sulfur compounds that are easy to desulfurize is subjected to
hydrodesulfurization under mild conditions, for example, in
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~1687~0
the presence of a catalyst for hydrodesulfurization at a
temperature of about 200 to about 300°C, a hydrogen partial
pressure of about 5 to about 20 kg/cm2, and an LHSV of about
4 to about 20 1/hr.
Hydrodesulfurization of the fraction that is rich in
sulfur compounds that are easy to desulfurize can be
performed while retaining the olefin components that are
originally present in the fraction. More particularly, if
proper reaction conditions are selected, a desulfurization
rate as high as 70~ or even more can be achieved while
controlling hydrogenation of the olefins to 10~ by volume or
lower, thus minimizing a reduction in octane number.
It is necessary to select the conditions of
hydrodesulfurization for each fraction, taking into
consideration the kinds and amounts of sulfur compounds
contained therein and the kinds and amounts of olefin
components concurrently contained therein, in order to
achieve the desired desulfurization rate and a permissible
reduction in octane number.
The reaction conditions of hydrodesulfurization are
selected from a temperature range of from about 200 to about
350°C, a hydrogen partial pressure range of from about 5 to
about 30 kg/cm2, an LHSV range of from about 1 to about
20 1/hr, and a hydrogen/oil ratio range of from about 300 to
about 5000 scf/bbl. The lower the temperature or pressure,
or the higher the hydrogen/oil ratio, the more effectively
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olefin hydrogenation can be suppressed to minimize a
reduction- in octane number.
On the other hand, where a high overall rate of
desulfurization is required, both a fraction that is rich in
sulfur compounds that are hard to desulfurize and a fraction
that is rich in sulfur compounds that are easy to desulfurize
are subjected to hydrodesulfurization. In this case, the
conditions of hydrodesulfurization are optimized for each
fraction to achieve the desired high rate of desulfurization
while controlling hydrogenation of olefins to minimize a
reduction in octane number.
The catalyst for use in the present invention
includes those ordinarily used for hydrodesulfurization in
the field of petroleum refining. That is, the catalyst
generally comprises a desulfurization active metal supported
on a porous inorganic oxide carrier.
The porous inorganic oxide carrier includes alumina,
silica, titania, magnesia and mixtures thereof. Alumina and
silica-alumina are preferred.
The desulfurization active metal includes chromium,
molybdenum, tungsten, cobalt, nickel and mixtures thereof.
Cobalt-molybdenum and nickel-cobalt-molybdenum are preferred.
These metals can have the form of a metal, an oxide, a
sulfide or a mixed form thereof on the carrier. The active
metal can be supported on the carrier by a known method, such
as impregnation or co-precipitation.
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216~'~20
In the present invention, a catalyst comprising
cobalt-molybdenum or nickel-cobalt-molybdenum supported on an
alumina carrier is preferred. The amount of the active metal
supported on the oxide carrier is preferably about 1 to about
30~ by weight, more preferably about 3 to about 20~ by
weight, in terms of the oxide of the active metal. The
metals may be preliminarily converted to sulfides in a known
manner before use in hydrogenation.
The reaction tower for hydrogenation may be of a
fixed bed type, a fluidized bed type or a boiling bed type.
A fixed bed type reactor is preferred. The catalytically
cracked gasoline fraction can be contacted with the catalyst
in any of a parallel upward flow system, a parallel downward
flow system or a countercurrent flow system. These
operations are well known in the field of petroleum refining,
and known techniques can be selected as appropriate.
EXAMPLES
The present invention will now be illustrated in
greater detail by way of the following Examples. However,
the present invention should not construed as being limited
to those Examples.
COMPARATIVE EXAMPLE 1
A catalytically cracked gasoline light fraction
(about a 30 to 80°C fraction) was obtained by catalytically
cracking a stock oil containing an atmospheric residual oil.
The term "about a 30 to 80°C fraction" as used herein is a
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216~7~0
nominal designation. This fraction actually contained 11.9
by weight of a fraction having a boiling point of 30°C or
lower and 3.2~ by weight of a fraction having a boiling point
exceeding 80°C (hereinafter referred to as an 80+°C cut) as
shown in Table 1 below. The about a 30 to 80°C fraction had
a density of 0.675 g/cm3 at 15°C, a sulfur content of 27 ppm,
an olefin content of 65~ by volume, and a research method
octane number of 93.8.
A commercially available catalyst comprising an
alumina carrier having supported thereon 5$ by weight of Co0
and 17~ by weight of Mo03 was used for hydrodesulfurization
after it was preliminarily converted to a sulfide form in a
usual manner. The above-described catalytically cracked
gasoline fraction was hydrodesulfurized using a fixed bed
parallel downward flow type hydrogenation reaction apparatus
under relatively mild conditions, i.e., at a reaction
temperature of 250°C, a partial hydrogen pressure of
kg/cmz, an LHSV of 5 1/hr, and a hydrogen/oil ratio of
1000 scf/bbl.
As a result, a hydrodesulfurized catalytically
cracked gasoline light fraction was obtained having a sulfur
content of 12 ppm, an olefin content of 44~ by volume, and a
research method octane number of 86.1. There was no loss of
liquid components due to the treatment.
EXAMPLE 1
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~1687~0
The same catalytically cracked gasoline as used in
Comparative Example 1 was distilled to divide the same into 7
cuts each by a difference in distillation temperature of
10°C. The yield, sulfur content and olefin content of each
cut are shown in Table 1 below.
TABLE 1
Distillation Sulfur Olefin
Temperature Yield Content Content
( C) (n''t~ ) (PPm) (volt
)
I.B.P. to 30 11.9 0 82
30 to 40 36.0 1 73
40 to 50 1.9 7 84
50 to 60 7.7 3 42
60 to 70 28.3 24 55
70 to 80 11.0 129 62
80+ 3.2 154 51
total 100.0 27 65
On analysis of the sulfur content of the 70 to 80°C
cut, it was found that 90 mold of the sulfur content was
thiophene, a sulfur compound that is hard to desulfurize.
Analysis of the sulfur content~of the 80+°C cut revealed that
94 mold of the sulfur content also was thiophene. The 70 to
80°C cut and 80+°C cut which were rich in sulfur compounds
that are hard to desulfurize were mixed together and
hydrodesulfurized using the same reaction apparatus and the
same catalyst as used in Comparative Example 1 at a
temperature of 300°C, a hydrogen partial pressure of
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~168'~~~J
30 kg/cmz, an LFiSV of 5 1/hr, and a hydrogen/oil ratio of
1000 scf/bbl.
The mixture of the 70 to 80°C cut and the 80+°C cut
had a sulfur content of 145 ppm and an olefin content of 59~
by volume. The hydrodesulfurization treatment reduced the
sulfur content and the olefin content to 3 ppm and 5~ by
volume, respectively. The treated oil was added to the
remaining cuts to obtain catalytically cracked gasoline
having a sulfur content of 8 ppm, an olefin content of 62~ by
volume, and a research method octane number of 91.8. There
was no loss of liquid components due to the treatment.
EXAMPLE 2
The same catalytically cracked gasoline as used in
Comparative Example 1 was distilled into 7 cuts each by a
difference in distillation temperature of 10°C in the same
manner as in Example 1. The 70 to 80°C cut and the 80+°C cut
rich in sulfur compounds that are hard to desulfurize were
mixed and treated under the same conditions as in Example 1.
Separately, as a result of analysis, 95 mold of the
sulfur content of the 60 to 70°C cut was found to be n-
propylmercaptane. The 60 to 70°C cut was hydrodesulfurized
using the same apparatus and catalyst as used in Comparative
Example 1 at a reaction temperature of 250°C, a hydrogen
partial pressure of 5 kg/cm2, an LHSV of 5 1/hr, and a
hydrogen/oil ratio of 1000 scf/bbl.
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The sulfur content and the olefin content of the 60
to 70°C cut were 24 ppm and 55~ by volume, respectively,
while those of the hydrodesulfurized oil were 5 ppm and 41~
by volume, respectively.
The treated oil of the mixture of the 70 to 80°C cut
and the 80+°C cut and the treated oil of the 60 to 70°C cut
were added to the remaining cuts to obtain catalytically
cracked gasoline having a sulfur content of 3 ppm, an olefin
content of 57~ by volume, and a research method octane number
of 89.5. There was no loss of liquid components due to the
treatment.
COMPARATIVE EXAMPLE 2
A catalytically cracked gasoline whole fraction
(about a 30 to 210°C fraction) obtained by catalytically
cracking stock oil containing an atmospheric residual oil was
used as a catalytically cracked gasoline. The term "about a
30 to 210°C fraction" as used herein is a nominal
designation. This fraction actually contained 4.9~ by weight
of a fraction having a boiling point of 30°C or lower and
1.5~ by weight of a fraction having a boiling point exceeding
210°C (hereinafter referred to as 210+°C cut) as shown in
Table 2 below. The whole fraction had a density of
0.731 g/cm3 at 15°C, a sulfur content of 92 ppm, an olefin
content of 43~ by volume, and a research method octane number
of 92Ø
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21687~Q
A commercially available catalyst comprising an
alumina carrier having supported thereon 3.8~ by weight of
Co0 and 12.5 by weight of Mo03 was used for
hydrodesulfurization after it was preliminarily converted to
a sulfide form in a usual manner. The above-described
catalytically cracked gasoline was hydrodesulfurized using
the same reaction apparatus as used in Comparative Example 1
under mild conditions, i.e., at a reaction temperature of
240°C, a hydrogen partial pressure of 10 kg/cm2, an LHSV of
7 1/hr, and a hydrogen/oil ratio of 1000 scf/bbl.
As a result, a hydrodesulfurized catalytically
cracked gasoline whole fraction was obtained having a sulfur
content of 63 ppm, an olefin content of 38~ by volume, and a
research method octane number of 90.3. There was no loss of
liquid components due to the treatment.
COMPARATIVE EXAMPLE 3
The same catalytically cracked gasoline whole
fraction as used in Comparative Example 2 was
hydrodesulfurized under more severe conditions than those
employed in Comparative Example 2, i.e., at a reaction
temperature of 270°C, a hydrogen partial pressure of
kg/cm2, an LHSV of 5 1/hr, and a hydrogen/oil ratio of
1000 scf/bbl. The apparatus and catalyst used were the same
as those used in Comparative Example 2.
As a result, a hydrodesulfurized catalytically
cracked gasoline whole fraction was obtained having a sulfur
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content of 27 ppm, an olefin content of 31~ by volume and a
research method octane number of 87.8. There was no loss of
liquid components due to the treatment.
EXAMPLE 3
The same catalytically cracked gasoline as used in
Comparative Example 2 was distilled to obtain 20 divided cuts
each different in distillation temperature by 10°C. The
yield, sulfur content and olefin content of each cut are
shown in Table 2.
As a result of analysis, it was found that: 85 mold
of the sulfur content of the 120 to 130°C cut was
thiacyclopentane, a sulfur compound that is easy to
desulfurize; 70 mold of the sulfur content of the 130 to
140°C cut was C1, C2 thiacyclopentane, sulfur compounds that
are easy to desulfurize; and the proportion of
benzothiophene, a sulfur compound that is easy to
desulfurize, of the sulfur content of the 190 to 200°C cut,
200 to 210°C cut and 210+°C cut was 85 mold, 95 mold, and
73 mold, respectively.
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TABLE 2
Dist-illation Sulfur Olefin
Temperature Yield Content Content '
(PPm) (volt)
I.B.P. to 30 4.9 0 82
30 to 40 14.8 1 73
40 to 50 0.8 7 84
50 to 60 3.2 3 42
60 to 70 11.6 24 55
70 to 80 4.5 130 60
80 to 90 2.3 151 51
90 to 100 9.5 14 50
100 to 110 4.2 93 40
110 to 120 5.5 210 32
120 to 130 4.6 60 50
130 to 140 4.2 145 27
140 to 150 7.3 160 23
150 to 160 2.0 123 35
160 to 170 6.1 153 18
170 to 180 3.6 126 17
180 to 190 3.8 185 15
190 to 200 3.0 152 16
200 to 210 2.6 340 13
210+ 1.5 324 12
total 100.0 27 65
The cuts that were rich in sulfur compounds that are
easy to desulfurize, i.e., the 120 to 130 C cut, 130 to 140C
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cut, 190 to 200°C cut, 200 to 210°C cut, and 210+°C cut
were
mixed together and subjected to hydrodesulfurization using
the same apparatus and catalyst as used in Comparative
Example 2 at a reaction temperature of 240°C, a hydrogen
partial pressure of 10 kg/cmz, an LHSV of 7 1/hr, and a
hydrogen/oil ratio of 1000 scf/bbl.
The mixture of the cuts rich in sulfur compounds that
are easy to desulfurize had a sulfur content of 171 ppm and
an olefin content of 28$ by volume, which were reduced by
hydrodesulfurization to 33 ppm and 26~ by volume,
respectively. The oil thus treated was added to the
remaining cuts to obtain catalytically cracked gasoline
having a sulfur content of 69 ppm, an olefin content of 42.5
by volume, and a research method octane number of 91.7.
There was no loss of liquid components due to the treatment.
EXAMPLE 4
The same catalytically cracked gasoline as used in
Comparative Example/2 was distilled to obtain 20 divided cuts
each different in distillation temperature by 10°C in the
same manner as in Example 3. A mixture of the cuts rich in
sulfur compounds that are easy to desulfurize, i.e., the 120
to 130°C cut, 130 to 140°C cut, 190 to 200°C cut, 200 to
210°C cut, and 210+°C cut, was treated under the same
conditions as in Example 3.
As a result of analysis, it was found that: the
proportion of thiophene, a sulfur compound that is hard to
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~16g'~20
desulfurize, of the sulfur content of the 70 to 80°C cut and
the 80 to 90°C cut was 85 mold and 90 mold, respectively; the
proportion of methylthiophene, a sulfur compound that is hard
to desulfurize, of the 110 to 120°C cut was 87 mold; the
proportion of dimethylthiophene, a sulfur compound that is
hard to desulfurize, of the 140 to 150°C cut was 87 mold; the
total proportion of trimethylthiophene, methylethylthiophene,
and propylthiophene, which are sulfur compounds that are hard
to desulfurize, of the sulfur content of the 160 to 170°C cut
was 69 mold; and the total proportion of
tetramethylthiophene, dimethylethylthiophene,
diethylthiophene, and methylpropylthiophene, which are sulfur
compounds that are hard to desulfurize, of the sulfur content
of the 180 to 190°C cut was 56 mold.
Those cuts rich in sulfur compounds that are hard to
desulfurize, i.e., the 70 to 80°C cut, 80 to 90°C cut, 110 to
120°C cut, 140 to 150°C cut, 160 to 170°C cut, and 180 to
190°C cut were mixed and hydrodesulfurized using the same
apparatus and catalyst as used in Comparative Example 2 at a
reaction temperature of 300°C, a hydrogen partial pressure of
30 kg/cm2, an LHSV of 5 1/hr, and a hydrogen/oil ratio of
1000 scf/bbl.
The mixture of the cuts rich in sulfur compounds that
are hard to desulfurize had a sulfur content of 166 ppm and
an olefin content of 31~ by volume, which were reduced to
14 ppm and 4~ by volume, respectively, by the
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hydrodesulfurization treatment. The treated oil was added to
the remaining cuts to obtain catalytically cracked gasoline
having a sulfur content of 25 ppm, an olefin content of 35~
by volume, and a research method octane number of 89.2.
There was no loss of liquid components by the treatment.
COMPARATIVE EXAMPLE 4
A catalytically cracked gasoline whole fraction
(about a 30 to 230°C fraction) was obtained by catalytically
cracking a stock oil containing an atmospheric residual oil.
The whole fraction had a density of 0.748 g/cm3 at 15°C, a
sulfur content of 352 ppm, an olefin content of 38~ by
volume, and a research method octane number of 91.7. The
whole fraction was hydrodesulfurized using the same apparatus
and catalyst as in Comparative Example 1 at a reaction
temperature of 250°C, a hydrogen partial pressure of
kg/cmz, an LHSV of 7 1/hr, and a hydrogen/oil ratio of
1000 scf/bbl.
As a result, a hydrodesulfurized catalytically
cracked gasoline whole fraction was obtained having a sulfur
content of 115 ppm, an olefin content of 33~ by volume, and a
research method octane number of 89.4. There was no loss of
liquid components due to the treatment.
EXAMPLE 5
The same catalytically cracked gasoline as used in
Comparative Example 4 was divided by.distillation into a 30
to 100°C cut and a 100 to 230°C cut. The ratio of the 30 to
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~m~~~o
100°C cut to the whole fraction was 32~k by weight, and the 30
to 100°C cut had a sulfur content of 62 ppm and an olefin
content of 53~ by volume. The ratio of the 100 to 230°C cut
to the whole fraction was 68~ by weight, and the 100 to 230°C
cut had a sulfur content of 488 ppm and an olefin content of
31~ by volume. The sulfur content of the 100 to 230°C cut
was found by analysis to consist of 28 mold o~
benzothiophene, 31 mold of methylbenzothiophene, 2 mold of
thiacyclopentane, and 3 mol$ of methylthiacyclopentane, which
are sulfur compounds that are easy to desulfurize, and the
balance of thiophene compounds which are sulfur compounds
that are hard to desulfurize.
The 100 to 230°C cut rich in sulfur compounds that
are easy to desulfurize was hydrodesulfurized using the same
apparatus and catalyst as used in Comparative Example 1 at a
reaction temperature of 250°C, a hydrogen partial pressure of
kg/cm2, an LHSV of 5 1/hr, and a hydrogen/oil ratio of
1000 scf /bbl .
By carrying out the hydrodesulfurization treatment,
the sulfur content and the olefin content were reduced to
135 ppm and 28~ by volume, respectively. The treated oil was
mixed with the 30 to 100°C cut to obtain catalytically
cracked gasoline having a sulfur content of 112 ppm, an
olefin content of 36~ by volume, and a research method octane
number of 90.5. There was no loss of liquid components due
to the treatment.
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~16~'~~0
The catalytic hydrodesulfurization process for
treating-catalytically cracked gasoline containing sulfur
compounds and olefin components according to the present
invention is characterized in that the catalytically cracked
gasoline is separated into a fraction rich in sulfur
compounds that are hard to desulfurize and a fraction rich in
sulfur compounds that are easy to desulfurize. One or both
of the fractions are subjected to hydrodesulfurization under
optimum conditions, and the fractions are then mixed together
again. The process of the present invention makes it
possible to efficiently desulfurize stock oil while
suppressing a reduction in olefin content, to thereby
minimize a reduction in octane number.
It should further be apparent to those skilled in the
art that various changes in form and detail of the invention
as shown and described above may be made. It is intended
that such changes be included within the spirit and scope of
the claims appended hereto.
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