Note: Descriptions are shown in the official language in which they were submitted.
so~ ,
The present ~nvention relates to an :Lmproved method
of thermally cracking a heavy petroleum oil.
Various methods have been suggested in the past for
therma}ly cracking heavy petroleum oil. One of these methods
is disclosed in German Offenlegungsshrift 2,215,432, in which
a gas which does not react with the heavy petroleum oil, is
contacted with the heavy petroleum oil at a temperature of
400 - 2000C to thermally crack the oil at a temperature lower
than 500 C, thereby producing hydrocarbon gases, aliphatic hydro-
carbon oils and aromatlc hydrocarbon pitches. To be morespecific, the heavy petroleum oil is heated to a temperature
of 450 - 520 C and is introduced into a reactor and then contacted
with the gas at a temperature of 400 - 2000C within the reactor
to bring about thermal cracking at a temperature of 350 - 450 C, :`
preferably of 400 - 440 C.
This method, however, has the disadvantage that the
aromatic hydrocarbon pitches thus produced are of reduced quality
because of unwanted contamination by a substance approximating
the raw material and by a granular co~ed substance resulting
from excessive thermal cracking of the raw material.
An object of this invention, ~herefore, is to provide
a method ~or thermally cracking heavy petroleum oil, which method
causes the thermal cracking to proceed moderately and thereby
affords pitches having high aromaticity and good homogeneity
and which produces, in good yields, distillates composed pre-
dominantly of aliphatic hydrocarbon oils.
The inventors of this invention have now found that
the thermal cracking of a heavy petroleum oil carried out by
the convent-ional technique described above can be made to proceed
moderately when the thermal cracking is performed by using, as
the reaction system, a plurality of reactor vessels arranged
in series and by having the interior temperatures of these
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reactor vessels gradually lowered, each by a fixed step, in the
direction of the transfer of the feed oil. The present invention
has been accomplished on the basis of this knowledge.
According to the present invention, there ls provided
a method of thermally cracking a heavy petroleum oil by intro-
ducing the heavy petroleum oi~ into a reactor system and ~ringi~g
the oil therein into contact with a gas which does not react
with the heavy petroleum oil, at a ~emperature in the range of
from 40~ to 2000C, the improvement comprising the steps of:
(a) introducing ~said heavy petroleum oil successively
into a plurality of reactor vessels arranged in series; and
(b) arranging for the interior temperatures of said
plurality of reactor vessels in the series to be successively
lowered by steps of not less than 3C so that the interior
temperature of the second reactor vessel is at least 3 C lower
than that of the first reactor vessel, that of the third reactor
vessell is at least 3 C lower than that of the second reactor
vessel, and so on.
In the accompanying drawings:
Fig. 1 is a flow sheet illustrating one preferred
embodiment of the method of this invention; and
Fig. 2 is a graph showing the relationship between
the number of reactor vessels used and the highest softening
point of pitches produced, in the thermal cracking of a heavy
petroleum oil in accordance with the present invention.
The heavy petroleum oils which are usable for the
present invention include all the products of petroleum refineries
classified as heavy distillates and residues such as, for example,
residues from atmospheric distillation, residues from vacuum
distillation, residues from thermal cracking, slurry oil from
catalytic cracking and various refinery resldues. These heavy
petroleum oils are generally composed predominantly of components
having boiling points not lower than 350C.
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The gas which is used for contact with the heavy
petroleum oil inside the reactor vessels has only to satisfy
the requirement that it should remain stable at the reaction
temperature, avoid reacting with the heavy petroleum oil under
treatment, function as an effective heat medium for the heavy
petroleum oil and accelerate thermal cracking of the oil. Examples
of the gases ~hich are usable for this purpose include inert
gases such as nitrogen and argon; steam; and complete combustion
gases containing substantially no oxygen.
In the present invention, the heavy petroleum oil
is successively introduced into the plurality of reactor vessels
arranged in series and is brought into contact, inside the
reactor vessels, with the gas maintained at a temperature in the
range of from 400 to 2000 C, with the interior temperatures of
the reactor vessels so ad~usted that they are successively
lowered in the various reactors by steps of not less than 3 C.
Preferably, therefore, the thermal cracking of the heavy
petroleum oil aimed at by this invention can be carried out by
heating the heavy petroleum oil in a heating furnace to a
20 temperature in the range of from 450 to 520 C, delivering the
preheated heavy petroleum oil into the first reactor vessel,
and allowing the oil to undergo thermal cracking at successively
decreasing reaction temperatures in the range of from 350 to
450 C under a pressure in the range of from 300 mm Hg Abs. to
15 kg/cm .G for an overall retention time of from 1 to 10 hours.
The interior temperatures of these reactor vessels can be
adjusted, for example, by properly controlling the volumes of
the gas having a temperature of from 400 to 2000C introduced
into the respective reactor vessels. It is also necessary that
the interior temperatures of these reactor vessels should be
successively lowered by steps of not less than 3C, preferably
by steps in the range of from 5 to 50C. Although the number
of such reactor vessels to be used for the present thermal
cracking is not specifically limited, it is generally preferred
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to be in the range of from 2 to 5.
Now, the present invention will be speclfically described
with reference to the flow sheet of Fig. l.
Heavy petroleum oil as the raw material is continu-
ously transferred from a ra~ material tank 1 into a tubular
heating furnace 3 by means of a pump 2. In the heating fur~ace
3~ ~he feed oil is heated to a temperature in the range of from
450 to 520 C and then forwarded continuously to th~ ~lrst
reactor vessel 4. The liquid in the first reactor 4 is further
forwarded continuously into the second reactor vessel 5 and then
into the third renctor vessel 6. During the travel through the
successlve reactor vessels, the liquld is gradually conver~ed
into a pitchy mass owing to the thermal cracking reaction. The
pitchy mass is received in a pitch cooling tank 7, in which it
is cooled to a temperature in the range of from 300 to 350 C
so as to terminate the thermal cracking reaction. The pitchy
mass kept in a liquid state in the pitch cooling tank 7 is
continuously forwarded through the bottom of the tank to a
storage unit 10 by way of a pump 8.
The heat-medium gas is heated in advance in a gas
heating furnace 9 and is continuously blown through inlets in
the bottoms of the reactor vessels 4, 5 and 6, to serve the
purpose of providing heat for the cracking reac~ion and
distilling cracked oils formed by the reaction.
Generally, the operating conditions for the reaction
vessels 4, 5 and 6 are 350 to 450C of temperature, 300 mm ~g Abs.
to 15 kg~cm2.G of pressure and 1 to 10 hours of overall reten-
tion time. Preferable operating conditions are 380 to 440 C
of temperature, 0 to 2 kg~cm2.G of pressure and 1 to 5 hours
of overall retention time. The regulation of the overall
retention time can be accomplished by causing the liquid under-
going treatment to be continuously transferred at a suitablycontrolled rate from one reactor vessel to another and thereby
keeping constant the levels of liquid within the respective
- reactor vessels.
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The regulation of the operating temperatures within
the reactor vessels 4; S and 6 can be accomplished by properly
adjusting the temperature of the oil at the outlet of the
tubular heating furnace in the range of from 450 to 520 C and
the temperature of the heat-medium gas being blown into the
reactor vessels in the range of from 400 to 2000C~
What should be noted at this point is that the temper-
a~ures of the reactor vessels in the series should be definitely
and gradually lowered in the direction of the transfer of the
charge, by steps oE not less than 3 C, preferably steps in the
range of from 5 to 50 C.
Of the products occurring in the course of the cracking
reaction, the light distillates are expelled out of the upper
ends of the reactor vessels 4, 5 and 6 in the form of vapor with
the heat-medium gas being blown upwardly through the reactor
vessels. The expelled light distillates are forwarded to a
fractional distillation unit 11, there to be divided into
cracked gas and cracked oil.
One of the most important characteristics of this
invention is that the interior temperature of the second reactor
vessel should be lower than that of the first reactor vessel.
This is essential because the pitchy mass is more likely to be
coked in the second reactor vessel than in the first reactor
vessel and, in order to prevent this unwanted coking from
occurring, the temperature inside the second reactor vessel
must be lower than that in the first reactor vessel. As is
readily understood, therefore, the interior temperature of
the third reactor vessel must be lower than that of the second
reactor vessel for the same reason. Particularly important in
this respect is the fact that, in the plurality of reactor
vessels arranged in series, the interior temperatures of the
individual reactor vessels should be lowered in the direction
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of the transfer of the charge, by steps of not less than 3 C,
preferably by steps in the range of from 5 to 50 C.
Pitches having high aromaticity and high quality
are consistently obtained by the method described and, at the
same time, distillates of good quality are produced in high
yields. Further, from the operatlonal point of view, the
present invention offers the advantage that the reactor vessels
may effectively function with relatively small inner volumes
and a relatively small quantity of the heat-medium gas is required.
Besides, since the thermal cracking can be performed under
normal conditions, the operation eminently excels in controllability.
The present invention will be described herein below
with reference to a working example.
Example:
The heavy petroleum oil indicated below was subjected
to thermal cracking by the procedure illustrated in Fig. 1 in
three different tests using one, two and three reactor vessels,
respectively. The operating conditions involved, the yields
of products obtained and the attributes of the produced pitches
are compared below in Table 1.
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Table 1 Number of reactor vessels and attributes
of produced pitches
. ~ .. . __ _
Number of reactor vessels 1 2 3
_ _ _ . _ ... .. ~_ . ~
Operating conditions
Kind of oil as raw Residue from Residue from Residue fro
material , vacuum vacuum vacùum
distillation distillation distillation
of ~-~JI oil of ~FJI oil of K~JI oil
Flow rate of oil (kg/hr) 300 300 300
Outlet temperature of
heatiny furnace (C)480 480 4~0
Operat-ing temperature of
first reactor vessel (C) 412 415 421
Operating temperature of .
second reactor vessel
(C) _ 395 397
Opera-ting temperature of
third reactor vessel (C) _ _ . 392
Yields _ _ ___ _
Cracked gas (wt%) 3.5 3.3 3.4
Cracked light oil (wt%~ 11.7 12.1 12.8
Cracked heavy oil (wt~) 54.2 53.8 53.5
Pitches (wt%) 30.6 30.8 30.3
Attrlbutes of pitches .
Softening point* (C)169 173 174
Fixed carbon (wt%)58.0 57.2 56.1
Heptane insolubles (wt~) 75.7 75.7 76.0
Benzene insolubles (wt~) 55.1 51.1 48.9
Quinoline insolubles (wt%' 25.3 18.4 15.8
*Softening point - The temperature at which, when 1 g of a
given sample was placed in a KOKA typ~ flow
tester using a nozzle 1 mm in diameter and the
tester was heated at a temperature increase
rate of 6C/min. under a load of 10 kg/cm2,
the descent of the piston in the tester
ceased, l.e. the piston came -to a stop.
00
As is evident from Table 1, the pitches from the oper-
ation of one reactor vessel had a larger content of quinollne
insolubles than those from the operation of three reactor
vessels, with those from the operation of two reactor vessels
intervening therebetween. This clearly shows that use of a
plurality of reactor vessels arranged in series resuLts in
improved homogeneity of produced pltches.
As regards the operational efficiency, in the production
of pitches hAvlng softening points over 160C, the operation
using one reactor vessel could not be continued for more than
10 hours because the reaction in the reactor vessel produced
coking and gave rise to mechanical trouble, whereas the operation
using three reactor vessels could be easily continued for five
days because the interior temperatures of the second and third
reactor vessels were successively lowered. When the three
vessels used in the latter operation were disassembl~d after
the operation and carefully inspected~ no sign of abnormality
was observed anywhere.
Through experimental operations performed under various
conditions, it has been ascertained that for the reaction system
to be operated without trouble, the relations between the number
of reactor vessels and the softening points of produced pitches
indicated in the graph of Fig. 2 is preferably satisfied.
Fig. 2 is a graph showing the relationship between
the number of reactor vessels used and the softening point of
produced pitches. In the graph of ~ig. 2, the area designated
as I represents easy operation and the area designated as II
represents difficult operation. In this graph, the vertical
axis is graduated for the softening point ( C) of pitches and
the horizontal axis for the number of reactor vessels.
