Note: Descriptions are shown in the official language in which they were submitted.
ZC55~;6
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T 5418
HEAVY OIL CONVERSION PROCESS
The present invention relates to a process for the conversion
of a heavy hydrocarbon oil by contacting the hydrocarbon oil with
solid partic~es in the presence of hydrogen at elevated temperature
and moderate pressure.
Various processes have been developed in order to convert
heavy hydrocarbons into valuable light fractions. These processes
can be roughly divided into carbon rejecting type of processes,
e.g. thermal cracking, and hydrogen addition type of processes,
e.g. hydrocracking.
Thermal cracking of residual material is usually performed at
a relatively low or moderate pressure (usually 5 to 30 bar) and at
a relatively high temperature (420-520 C) without the use of a
catalyst and in the absence of hydrogen. The middle distillates
obtained from thermal cracking of high boiling residues are of good
quality as far as the ignition properties are concerned. The high
content of olefins and heteroatoms (especially sulphur and
nitrogen), however, make a hydrofinishing treatment necessary for
many applications. An intrinsic problem of thermal cracking is the
occurrence of condensation reactions which lead to the formation of
polyaromatics and at high severity can lead to coke in the cracked
residue.
Hydrocracking is usually performed at a relatively high
hydrogen partial pressure (usually 100-140 bar) and a relatively
low temperature (usually 300 to 400 C). The catalyst used in this
resction has several functions: acid catalyzed cracking of the
hydrocarbon molecules and activation of hydrogen and hydrogenatlon.
; A long reaction time is used (usually 0.3 to 2 l/lJh liquid hourly
space velocity). Due to the high hydrogen pressure only small
amounts of coke are deposited on the catalyst which makes it
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possible to use the catalyst for 0.5 to 2 years in a fixed bed
operation without regeneration. The product slates obtained in this
process are dependent on the mode of operation. In one mode of
operation, predominantly naphtha and lighter products are obtained.
The naphtha fraction contains paraffins with a high iso/normal
ratio, making it a valuable gasoline blending component. In a mode
for heavier products, kerosene and gas oil are mainly obtained. In
spite of the extensive hydrogenation, the quality of these products
is rather moderate, due to the presence of remaining aromatics
together with an undesired high iso/normal ratio of the paraffins
among others.
At the present there is much interest in processes combining
carbon re~ection with hydrogen addition~ Conceptually, these
processes combine the benefits of carbon rejection and hydrogen
addition, both contributing to the desired hydrogen/carbon ratio of
the valuable distillate products. Such processes could be very
attractive because of controlled production of coke and
simultaneous upgrading of the distillates obtained.
Further, in general it is advantageous when a process can be
operated in the absence of a catalyst as catalysts tend to become
deactivated in heavy hydrocarbon conversion processes, due to the
presence of asphaltenes and metals therein. Deactivated catalyst
must then be regenerated, involving metal removal and catalyst
rejuvenation, which leads to higher operating costs.
Therefore, an object of the present invention is to provide a
non-catalytic process wherein the production of liquid hydrocarbons
together with substantial amounts of coke can be controlled and
optimized. Furthermore, it is highly advantageous when part or all
of the coke produced can be used in the production of energy or
hydrogen containing streams for further use in e.g. refineries.
A process has now been found which ls especially suitable for
the conversion of heavy hydrocarbon oils with the help of non-
catalytic solid particles in the presence of hydrogen and at
elevated temperature and moderate pressure. The solid particles and
hydrogen-containing gas must be of such a temperature when in
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contact with the hydrocarbon oil that at least part of the hydrogen
is thermally dissociated. In this way hydrogenation of hydrocarbons
takes place and condensation reactions resulting in the formation
of aromatic components are suppressed. Thus, this process combines
the favourable aspects of carbon re;ection and hydrogen addition in
one process step.
The present invention relates to a process for the conversion
of a heavy hydrocarbon oil, which process comprises:
(i) contacting non-catalytic solid particles of a temperature of
at least 600 C with a hydrogen-containing gas and a heavy
hydrocarbon oil in a reactor which is operated at a hydrogen
partial pressure of between 10 and 80 bar and a temperature
of between 450 and 850 C, in which reactor the bulk
temperature is substantially uniform,
(ii) withdrawing coked solid particles from the reactor and
removing coke from said particles, and
(iii) recycling particles from which coke has been removed in step
(ii~, to the reactor.
In British patent specification 1,460,615 a process is
described for cracking heavy hydrocarbons in a reactor, in which
feed is introduced together with granular solid in an upper zone,
which is maintained at a temperature of not higher than 550 C, and
preheated hydrogen-containing gas is introduced in a lower zone.
Gaseous components are withdrawn from the top of the reactor. In
this way an upper zone is created in which heavy hydrocarbons are
converted under non-hydrogenating conditions and a lower zone in
which hydrogen addition takes place of heavy material. The required
temperature~differences within the reactor will present large
difficulties, both because of the operating conditions which need
to be such that separate reaction zones are maintained and because
of the reactor which has to be made such that it can stand such
differences in process temperature.
Another non-catalytic process is the so-called Dynacracking
Process, described for example in Hydrocarbon Processing, May 1981
pp. 86-92, which is in essence a thermal hydroconversion process
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carried out in a moving particles system. The feed is thermally
converted in the presence of hydrogen in the upper part of the
system in the presence of synthesis gas producing substantial
amounts of coke which are deposited on inert carrier material. In
the lower part of the system coke on the inert material is gasified
to synthesis gas with steam and oxygen. The problems to be faced in
designing and operating such reactor would seem to be quite
formidable.
A further process is the Fluidized Thermal Cracking ~FTC)
process which is, for instance, described in US patent speci-
fication 4,668,378. The process is carried out in a fluidi7edsystem in which residual feedstock is contacted with fine porous
catalytically inactive particles, which particles are fluidized by
steam or a hydrogen-containing gas at a rather low (hydrogen)
partial pressure.
The conversion in the present process leading to molecular
weight reduction is essentially determined by the hydrogen
dissociating role of the solid particles of high temperature and
the hydrogen partial pressure of between 10 and 80 bar. Thereby the
coke make, calculated on Conradson Carbon Content of the feedstock,
usually varies between O.S and 1.4 weight/weight, respectively. The
dissociated hydrogen apparently participates in the radical
reaction mechanisms and contributes to the saturation of the larger
hydrocarbyl radicals resulting in less condensed aromatic
structures and finally a lower coke make.
The middle distillates obtained in the present process are of
good quality due to the high amount of n-paraffins and the low
amount of olefins although they may contain a certain amount of
aromatic compounds. The hydrogen consumption of the process is
relatively low compared to pure hydrogen-addition processes, as the
aromatic components are not substantially hydrogenated. A large
part of the metals and nitrogen components present in the feed is
deposited on the solid particles leaving a high quality distillate
with a low metal(s) and nitrogen content which makes the distillate
very suitable for product blending or as a feedstock for further
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upgrading in, for instance, catalytic cracking or hydrocracking
units.
When compared with a usual thermal cracking process a higher
middle distillate yield is produced with a comparable product
S quality, assuming that the thermal cracking product is~subjected to
an additional hydrofinishing treatment.
When compared with the Dynacracking and FTC processes as
described hereinbefore and the process described in British patent
specification 1,460,615, the present process has the important
advantage that a considerable hydrogenation takes place in the
presence of the dissociated hydrogen at relatively elevated
hydrogen partial pressure. This results in a higher middle
distillate yield of a higher quality and a lower and controllable
coke production on feed.
With regard to the usual hydrocracking process, the process of
the present invention is relatively insensitive to feedstock
impurities, as there are no catalytic sites needed.
A feedstock which can suitably be applied in the present
process is a heavy hydrocarbon oil comprising at least 35 ~wt of
material boiling above 520 C, and usually more than 15 ~wt of
material boiling above 620 C. Vacuum distillates, catalytically
cracked cycle oils and slurry oils, deasphalted oils, atmospheric
and vacuum residues, thermally cracked residues, asphalts
originating from various kinds of deasphalting processes, synthetic
residues and hydrocarbon oils originating from tar sands and shale
oils of any source can suitably be converted as such or in mixtures
in the process according to the present invention. Preference is
given to hydrocarbon oils which comprise at least S0 %wt of
material boiling above 520 C, in particular to hydrocarbon oils
comprising at lesst 90 ~wt of material boiling above 520 C.
Feedstocks comprising at least 3 ~wt of asphaltènic constituents,
in particular at least 10 ~wt, can suitably be processed. Wieh the
asphaltenic constituents mentioned hereinbefore "C7-asphaltenes"
are meant, i.e. the asphaltenic fraction removed from the oil
fraction by precipitation with heptane.
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The solid particles to be applied in the present process can
comprise any non-catalytic solid material which can withstand the
high temperatures applied, e.g. coke, alumina, silica and zirconia.
Preferably, the particles substantially consist of coke. Suitably,
the process is initially carried out with the help of ex-situ coke
particles on which in-situ coke deposits during the reaction, which
in-situ coke is thereafter (partly) removed. Before recycling, the
particles may be ground and sieved in order to obtain particles of
a preferred diameter. When the non-catalytic solid particles are
contacted with the hydrogen-containing gas and the heavy
hydrocarbon oil, the particles should have a temperature of at
least 600 C, in order to dissociate the hydrogen present.
Preferably, the particles have a temperature of at least 650 C.
The process according to the present invention is suitably
carried out at a hydrogen partial pressure of between 10 and 80
bar, preferably between 12 and 50 bar, and a temperature of between
450 and 850 C and at a substantially uniform bulk temperature
within the reactor. Suitably a difference in bulk temperature of
not more than 100 C can be measured within the reactor, more
specifically not more than 50 C.
It will be appreciated that a higher conversion will be
obtained when the temperature is higher, as the rate of cracking of
hydrocarbons will be higher at higher temperatures.
The process according to the present invention can suitably be
carried out in various types of moving bed reactors: a fluidized
bed reactor and a riser reactor. Each type of moving bed reactor
has its specifically preferred reaction conditions.
In case the process according to the present invention is
carried out in a fluidized bed reactor, i.e. in which part or all
of the feed is sprayed on the non-catalytic solid particles, a
suitable temperature is between 450 and 650 C, preferably between
470 and 600 C. The hydrogen partial pressure i9 then suitably
chosen between 10 and 80 bar, preferably between 12 and 50 bar,
more preferably between 15 and 40 bar. The non-catalytic solid
particles/oil ratio can suitably be chosen between 1-20
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weight/weight, preferably between 2-12 weight/weight, more
preferably between 2-8 weight/weight. Suitably the particles
residence time in the fluidized bed reactor is chosen between 0.2
a~d 10 minutes, preferably between 0.4 and 5 minutes. A hydrogen
containing gaseous stream is supplied to the fluidized bed reactor
to provide the hydrogen required for the desired reactions and to
maintain a good fluidization, this is suitably achieved at a
superficial gas velocity between 0.01 and 3.S0 m/s.
If the present process is carried out in a riser reactor, in
which the liquid feed is sprayed onto the incoming hot non-
catalytic solid particles, the temperature is suitably between 450and 850 C, preferably between 500 and 750 C. The hydrogen partial
pressure is suitably chosen between 10 and 80 bar, preferably
between 12 and 50 bar, most preferably between 15 and 40 bar. The
non-catalytic solid particles/oil ratLo is suitably chosen between
1-20 weight/weight, preferably between 2 and 12 weight/weight, most
preferably between 2 and 8 weight/weight. Suitably, the particles
residence time in the riser reactor is below 2 minutes, preferably
between 0.1 and 10.0 seconds. The hydrogen containing gaseous
stream is suitably supplied to the riser reactor at a superficial
gas velocity of between 0.6 and 3.5 m/s to provide the hydrogen
required for the desired process reactions and to maintain a good
fluidization and aeration.
The hydrogen-containing gas applied in the present process
suitably comprises molecular hydrogen. Hydrogen containing refinery
streams can be applied. They may also contain lower hydrocarbons,
steam and/or mixtures thereof.
Removal of coke from the coked non-catalytic solid particles
can suitably be carried out by burning off or gasifying coke. The
synthesis gas obtalned in the gasification o$ the coke can suitably
be used as A refinery fuel gas or as a hydrogen source for hydro-
processes in the refinery, or as a feedstock for hydrocarbon
synthesis processes. If desired, the removal step can suitably be
carried out by supplying the heat required for gasification via hot
particles which preferably have a larger diameter and a higher
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density than the solid particles from which coke is to be removed.
The use of relatively large particles (e.g. 3-20 times the diameter
of the solid particles from which coke is to be removed) allows
easy separation by fluidization and/or centrifugation in a cyclone.
S The hot particles which provide the external heat for the removal
step are suitably brought to the desired temperature by heating in
a combustive atmosphere (e.g. in an air/fuel gas system).
In order to prevent accumulation of contaminants, such as
metals originally present in the heavy hydrocarbon oils, it is
preferred to continuously remove a small amount of coked particles
from the process of the present invention. Such coked particles are
preferably replaced by fresh solid particles. Preferably, at least
90 ~ of the coked solid particles being withdrawn from the reactor
is replaced by particles from which coke has been removed.
The present invention will now be illustrated by means of the
following Example.
EXAMPLE
An Arabian light vacuum residue and a Maya vacuum residue,
respectively, were used as feedstock to demonstrate the conversion
process according to the present invention. The feed properties are
described in Table l.
Experiments were carried out using coke particles having a
diameter between 0.01 and 5 mm.
The feedstock and the liquid product were analyzed for the
boiling point distribution using a TBP-GLC (true boiling point
measured by gas liquid chromatography) method. On basis thereof
conversions and product yields were calculated. The 520 C+
conversion has been defined as the amount of 520 C material
present in the feedstock minus the amount of 520 C material
present in the total liquid product, divided by the amount of 520
C+ material present in the feedstock. The product slate was split
up into gas (Cl-C4), the total liquid product (C5 ) and the coke
deposited on the catalyst. The respective fractions have been
calculated as the amount of product in question, divided by the
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g
total amount of products. The following experiments were carried
out:
Experiment 1
The Arabian light vacuum residue was contacted with coke
particles having a temperature of 650 C. The reaction was carried
out at a temperature of 500 C, a hydrogen partial pressure of
25 bar and at substantially uniform bulk temperature. The product
obtained is described in Table 2.
Experiment 2
The Arabian light vacuum residue was contacted with coke
particles having a temperature of 650 C. The reaction was carried
out at a temperature of 500 C, a hydrogen partial pressure of 50
bar and at substantially uniform bulk temperature. The product
obtained is described in Table 2.
Experiment 3
The Maya vacuum residue was contacted with coke particles
having a temperature of 700 C. The reaction was carried out at a
temperature of 540 C, a hydrogen partial pressure of 25 bar and at
substantially uniform bulk temperature. The product obtained is
described in Table 2.
Experiment 4
The Maya vacuum residue was contacted with coke particles
having a temperature of 700 C. The reaction was carried out at a
temperature of 540 C, a hydrogen partial pressure of 50 bar and at
substantially uniform bulk temperature. The product obtained is
described in Table 2.
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TABLE 1
Arabian light Maya vacuum
vacuum residue residue
Specific gravity (d 15/4) 1.014 1.052
Sulphur content (%wt) 4.11 5.24
Nitrogen content ~%wt) 0.4303 0.9401
Vanadium content (%wt) 0.0078 0.0615
C7-asphaltenes (%wt)6.7 23.0
Conradson Carbon test (~wt) 15.62 26.7
Viscosity at 100 C (cSt) 618.5
Viscosity at 150 C (cSt) - 1226.7
Distillation TBP/GLC:
350 C - 520 C 9.8 4.7
520 G 90.2 95.3
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TABLE 2
Experiment 1 2 3 4
520 C+ Conversion ~%w) 93.694.5 96.8 97.0
Product yields:
Total gas make (~w)5.5 5.611.2 10.9
H2S (%w) 1.1 1.4 3.1 3.8
Cl-C4 (%w) 4.4 4.2 8.1 7.1
Total liquid product:72.6 78.273.0 75.0
C5-250 C (~w) 14.417.3 23.827.8
250-370 C (%w) 19.624.3 26.428.2
370-520 C (%w) 32.831.6 19.716.2
520 C+ (%w) 5.8 5.0 3.1 2.8
Coke (%w) 21.916.2 l5.814.1
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