Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS OF DESULFURIZATION OF HEAVY OIL
[Field of the Invention]
The present invention relates to processes of
desulfurizing heavy oils continuously for a long period
of time. More specifically, the present invention
relates to a process of desulfurizing a heavy oil such
as an atmospheric residual oil continuously for a long
period of time, without exchanging a catalyst.
[Background of the Invention]
Heavy oils such as atmospheric and vacuum residual
oils produced in a petroleum refining process usually
contain a few percent by mass of sulfur components and
thus can not be put in markets as they are. Therefore,
such heavy oils are desulfurized in the presence of high
pressured hydrogen using a catalyst so as to lower the
sulfur concentration. A substantial part of the
reaction product resulting from desulfurization of the
heavy oils is further subjected to a secondary
treatment to be converted to various useful products
such as gasoline, kerosene, and gas oil. The process
of desulfurization of heavy oils thus takes an
important role in the current petroleum refining (see,
for example, Non-Patent Document 1). If the
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desulfurization operation is ceased, other processes
are adversely affected, and in this connection, the
whole refinery is adversely affected in terms of
economical efficiency. Therefore, how the lifetime of
a catalyst is prolonged, i.e., how the operation with
a catalyst once charged can be prolonged has been a
serious issue in the petroleum refining industry. It
is thus necessary to operate a desulfurization unit for
heavy oil stably over an extended period of time in order
to improve the economical efficiency of petroleum
refining.
However, under the current circumstances, the
lifetime of a catalyst can not be prolonged
sufficiently due to deactivation factors mainly caused
by coking on the catalyst and there is thus no other
choice than to cease the operation in a relatively short
period of time for exchanging the catalyst. The
petroleum industry has been vigorously engaged in
studies to prolong the lifetime of a desulfurization
catalyst so as to enable the desulfurization process
of heavy oils to be operated for a long period of time
and has vigorously undertaken research and development
to improve the catalyst, i.e., to prolong the lifetime
thereof by selecting optimum supported metals and
catalyst supports (see, for example, Patent Documents
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.
1 and 2 below). However, no satisfactory result has
been attained, and a view that it is impossible to
prolong the lifetime of the desulfurization catalyst
for heavy oil has been dominating in the industry.
(1) Patent Document 1: Japanese Patent Laid-Open
Publication No. 10-180109
(2) Patent Document 1: Japanese Patent Laid-Open
Publication No. 11-151441
(3) Non-Patent Document 1: "Sekiyu Seisei
Purosesu (Petroleum Refining Process)" by the
Japan Petroleum Institute, 1998, page 88
[Disclosure of the Invention]
The present invention has an object to improve the
economic efficiency of petroleum refining by
prolonging the lifetime of a catalyst for
desulfurization of heavy oils.
As a result of extensive researches and studies,
the present invention was achieved by the finding that
the lifetime of a desulfurization catalyst was able to
be prolonged by a process of desulfurization of a heavy
oil, comprising diluting the heavy oil with a dilution
medium and then cracking the diluted heavy oil at a low
cracking rate.
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That is, the present invention relates to a
process of desulfurizing a heavy oil, comprising
diluting the heavy oil with a dilution medium to 90
percent by mass or less and cracking the diluted heavy
oil at a cracking rate of 10 percent or less.
The present invention also relates to a process
of desulfurizing a heavy oil, comprising diluting the
heavy oil with a dilution medium to 90 percent by mass
or less, cracking the diluted heavy oil at a cracking
rate of 10 percent or less, and desulfurizing the
cracked heavy oil after removal of the dilution medium
therefrom.
The present invention will be described in more
detail below.
The heavy oil used in the present invention
denotes a heavy oil mainly composed of carbon and
hydrogen and containing 90 percent by mass or more of
a fraction with an initial boiling point of 300 C or
higher and a boiling point of 360 C or higher.
There is no particular restriction on the type of
heavy oil used in the present invention. Typical
examples include atmospheric residual oils and vacuum
residual oils, produced during a petroleum refining
process.
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.. , , i
There is no particular restriction on the dilution
medium used in the present invention except that it is
inactive to the heavy oil to be treated. The dilution
medium is preferably compatible with the heavy oil to
be treated at a cracking temperature and particularly
preferably a dilution medium with a boiling point of
120 C or higher.
Preferred examples of the dilution medium include
aromatic hydrocarbons such as benzene and toluene. The
use of the dilution medium can evenly dilute the heavy
oil.
In the present invention, the heavy oil is diluted
with the diluting medium to 90 percent by mass or less,
preferably 85 percent by mass or less, and particular
preferably 80 percent by mass of less. If the
concentration of the heavy oil is in excess of 90 percent
by mass, the effect of prolonging the lifetime of a
catalyst can not be obtained sufficiently. There is
no particular restriction on the lower limit
concentration. However, the concentration is
preferably 20 percent by mass or more and more
preferably 30 percent by mass or more in view of the
process efficiency.
There is no particular restriction on the method
of diluting the heavy oil. However, the heavy oil is
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usually diluted in a mixing bath or through line-mixing.
Thereupon, the mixing temperature is preferably 60 C
or higher in order to mix the dilution medium with the
heavy oil with a sufficiently lowered viscosity.
Next, the heavy oil diluted to 90 percent by mass
or less with the dilution medium is cracked. The
cracking is necessarily carried out at a low cracking
rate such as 10 percent or lower. The cracking rate
used herein denotes the rate (on the basis of mass) of
a fraction resulting from the cracking, which is
lighter than the feedstock heavy oil (i.e. a fraction
with a boiling point lower than the initial boiling
point of the feedstock heavy oil but not including the
diluting medium), in the produced oil.
In the present invention, the cracking rate is
adjusted to 10 percent or lower and more preferably 8
percent or lower. If the cracking rate is higher than
percent, the effect of prolonging the lifetime of
a catalyst would be insufficient. There is no
particular restriction on the lower limit cracking rate.
However, the lower limit cracking rate is preferably
1 percent or higher and more preferably 2 percent or
higher.
In the present invention, the cracking of the
heavy oil is carried out by thermal cracking. The
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F temperature range at which the thermal cracking is
carried out is preferably from 400 to 600 C and more
preferably from 420 to 540 C. The LHSV range is from
6 to 20 h-1 and more preferably from 8 to 15 h-1. There
is no particular restriction on the pressure. The
cracking may be carried out at a pressure ranging from
atmospheric pressure to slight pressure but is usually
carried out at atmospheric pressure.
As mentioned above, after the diluted heavy oil
is cracked at a low cracking rate, the diluted medium
is removed from the resulting oil, followed by
desulfurization thereof.
There is no particular restriction on the method
of removingthe dilutionmedium. However, the dilution
medium is removed using atmospheric distillation.
There is no particular restriction on the catalyst
or conditions for the desulfurization. There may be
used any known catalyst and conditions which are used
for a conventional desulfurization reaction of heavy
oils. Examples of such a catalyst include those
supportingmolybdenum ortungsten on alumina. Typical
examples of the reaction conditions include a reaction
temperature of 380 to 480 C, a reaction pressure of 5
to 20 MPa, and an LHSV of 0.1 to 2.0 h-1.
The desulfurized oil is then subjected to a
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secondary treatment like as usual. The resulting oil
can be used as a base oil for various products such as
gasoline, kerosene, gas oil, and heavy fuel oil.
[Applicability in the Industry]
As described above, the deactivation rate of the
catalyst can be retarded by cracking a heavy oil diluted
with a dilution medium at a low cracking rate and then
desulfurizing the cracked oil, thereby making it
possible to prolong the lifetime of the catalyst.
[Best Mode for Carrying out the Invention]
The present invention will be described in more
details with reference to the following examples but
is not limited thereto.
(Example 1)
Into a tower for cracking with its inlet
temperature kept at 480 C was fed a vacuum residual oil
(initial boiling point: 580 C, sulfur content: 4.3
percent by mass) diluted to 78 percent by mass with
benzene at an LHSV of 10 h-1. After the benzene is
distilled out, the resulting oil contained 7.7 percent
by mass (cracking rate: 7.7 percent) of a cracked
product with a boiling point of lower than 580 C. The
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resulting oil is fed together with hydrogen to a
reaction tower charged with a commercially available
catalyst for desulfurizing heavy oil. The reaction
tower was operated for 30 days under conditions of an
LHSV of 0.2 h-1 and a reaction pressure of 15 MPa,
controlling the reaction temperature so that the
resulting oil after the reaction was reduced in sulfur
content to 0.4 percent by mass. The reaction
temperature was gradually increased substantially at
a constant rate, from 452.0 C at the time of the
initiation of the reaction and was higher by 1. 6 C than
the initial reaction temperature when the reaction was
completed. The average deactivation rate of the
catalyst during the reaction was 0.053 C/day.
(Comparative Example 1)
The operation same as that of Example 1 was carried
out except for omitting the dilution and cracking steps.
The reaction temperature was increased by 4.8 C. The
average deactivation rate of the catalyst was
0.160 C/day.
(Comparative Example 2)
The vacuum oil same as that used in Example 1 was
cracked at a low cracking rate without using benzene,
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i.e., without dilution. The resulting oil contained
9. 7 percent by mass of a cracked product. The resulting
oil was desulfurized similarly to Example 1. The
reaction temperature was increased by 3.5 C for 30 days.
The average deactivation rate of the catalyst was
0.117 C/day.
(Comparative Example 3)
The cracking of Example 1 was carried out except
that the LHSV was changed to 5 h-1. The resulting oil
contained 14.7 percent by mass of a cracked product.
The resulting oil was desulfurized similarly to Example
1. The reaction temperature wasincreasedby4.6 Cfor
30 days. The average deactivation rate of the catalyst
was 0.153 C/day.
(Example 2)
The cracking operation same as that of Example 1
was carried out except that toluene was used instead
of benzene. The resulting oil contained 8.7 percent
by mass of a cracked product. The resulting oil was
desulfurized similarly to Example 1. The reaction
temperature was increased by 1.9 C for 30 days. The
average deactivation rate of the catalyst was
0.063 C/day.
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