U.S. patent number 3,898,299 [Application Number 05/412,099] was granted by the patent office on 1975-08-05 for production of gaseous olefins from petroleum residue feedstocks.
This patent grant is currently assigned to BP Chemicals International Limited. Invention is credited to John Robert Jones.
United States Patent |
3,898,299 |
Jones |
August 5, 1975 |
Production of gaseous olefins from petroleum residue feedstocks
Abstract
Normally gaseous olefins are produced from an atmospheric
petroleum residue feedstock by: A. contacting the feedstock in a
hydrogenation zone with a hydrogenation catalyst, of which
nickel/tungsten/silica/alumina and cobalt/molybdenum/alumina are
most suitable, under conditions which effect hydrogenation of
aromatic hydrocarbons. Typical conditions are a temperature in the
range 50.degree. to 500.degree.C, a pressure in the range 50 to 500
psig, and an LHSV of 0.1 to 5.0 with a hydrogen feed rate of 5 to
10 times the molar feed rate of the feedstock. B. separating from
the hydrogenated feedstock a gaseous phase containing hydrogen and
a liquid phase containing hydrocarbons. C. recycling at least a
portion of said gaseous phase containing hydrogen to said
hydrogenation zone. D. separating the liquid phase from (c) into a
distillate fraction having a boiling range below 650.degree.C and a
residue fraction having a higher boiling range, advantageously by
vacuum distillation. E. subjecting the distillate fraction from (d)
to thermal cracking in the presence of steam thereby converting at
least a portion of the liquid phase to normally gaseous
hydrocarbons and F. recovering the normally gaseous olefins from
the pyrolysis zone effluent.
Inventors: |
Jones; John Robert
(Walton-on-Thames, EN) |
Assignee: |
BP Chemicals International
Limited (GB)
|
Family
ID: |
10460013 |
Appl.
No.: |
05/412,099 |
Filed: |
November 2, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Nov 8, 1972 [GB] |
|
|
51435/72 |
|
Current U.S.
Class: |
585/251; 208/57;
208/89; 585/314; 208/61; 585/269; 585/324 |
Current CPC
Class: |
C10G
45/44 (20130101); C10G 2400/20 (20130101) |
Current International
Class: |
C10G
45/44 (20060101); C10G 69/06 (20060101); C10G
69/00 (20060101); C10g 037/00 () |
Field of
Search: |
;260/683R
;208/57,61,89 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: Spresser; C. E.
Claims
I claim:
1. A process for the production of normally gaseous olefins from an
atmospheric petroleum residue feedstock which process comprises the
steps of:
a. contacting the petroleum residue feedstock in a hydrogenation
zone with a hydrogenation catalyst selected from
nickel/molybdenum/alumina, cobalt/tungsten/alumina,
nickel/tungsten/alumina, cobalt/molybdenum/alumina,
nickel/cobalt/molybdenum/alumina, cobalt/molybdenum/silica/alumina,
nickel/molybdenum/silica/alumina, nickel/tungsten/silica/alumina
and hydrogen at a temperature in the range 50.degree. to
500.degree.C, a pressure in the range 50 to 5,000 psig, a Liquid
Hourly Space Velocity in the range 0.1 to 5.0, and a hydrogen feed
rate of 5 to 10 times the molar feed rate of the atmospheric
petroleum residue feedstock, to effect hydrogenation of aromatic
hydrocarbons,
b. separating from the resulting hydrogenated atmospheric petroleum
residue feedstock a gaseous phase containing hydrogen and a liquid
phase containing hydrocarbons,
c. recycling at least a portion of said gaseous phase containing
hydrogen to said hydrogenation zone,
d. separating said liquid phase containing hydrocarbons into a
distillate fraction having a boiling range below 650.degree.C and a
residue fraction having a boiling range above that of the
distillate fraction,
e. subjecting said distillate fraction in the presence of steam to
thermal cracking in a pyrolysis zone under conditions effecting
conversion of at least a portion of said liquid phase to normally
gaseous olefins and
f. recovering the normally gaseous olefins from the pyrolysis zone
effluent.
2. A process according to claim 1 wherein the whole of said liquid
phase containing hydrocarbons is, after separation of a gaseous
phase containing hydrogen, fed in the presence of steam directly to
the pyrolysis zone wherein unvapourised feedstock is removed as a
residue fraction in a separation zone prior to entry of the
vapourised distillate fraction into that region of the pyrolysis
zone maintained under conditions which effect thermal cracking.
3. A process according to claim 1 wherein the separation of said
liquid phase containing hydrocarbons into a distillate fraction
having a boiling range below 650.degree.C and a residue fraction
having a boiling range above that of the distillate fraction is
effected by vacuum distillation.
4. A process according to claim 1 wherein said hydrogenation
catalyst is nickel/tungsten/silica/alumina.
5. A process according to claim 1 wherein said hydrogenation
catalyst is cobalt/molybdenum/alumina.
6. A process according to claim 1 wherein said hydrogenation
catalyst is activated before use in the hydrogenation reaction by
contact with a stream of hydrogen at a temperature in the range
100.degree. to 800.degree.C for a period of 1 minute to 24
hours.
7. A process according to claim 1 wherein the temperature is in the
range 300.degree. to 600.degree.C, the pressure is in the range 200
to 3,000 psig and the Liquid Hourly Space Velocity is in the range
0.1 to 0.5.
8. A process according to claim 1 wherein the major portion of the
gaseous phase containing hydrogen is separated from the liquid
phase containing hydrocarbons in a high pressure separator and
recycled either directly or, after scrubbing to remove hydrogen
sulphide and ammonia, to the hydrogenation zone.
9. A process according to claim 1 wherein the hydrogenation zone is
a single zone or a series of zones employing the same or different
hydrogenation catalyst.
10. A process according to claim 1 wherein thermal cracking of the
distillate fraction in the presence of steam is effected at a steam
to hydrocarbon weight ratio of 0.5:1 to 2.0:1 in a heated zone at a
maximum temperature in the range 700.degree. to 1,000.degree.C with
a residence time in this range between 0.01 and 5 seconds.
Description
The present invention relates to a process for the production of
normally gaseous olefins from atmospheric petroleum residue
feedstocks.
In the operation of a typical oil-refinery crude oil is initially
fed to a distillation unit where it is separated at atmospheric
pressure into benzine (motor spirit), naphtha, kerosine and gas
oil. The residue from the atmospheric distillation unit,
hereinafter to be referred to as an atmospheric petroleum residue
feedstock, is composed of fractions boiling under atmospheric
pressure at a temperature greater than 300.degree.C. This residue
may either be used directly as fuel oil or as feedstock to a
distillation unit operating at reduced pressure. The distillate
from the distillation unit operating at reduced pressure, otherwise
known as a vacuum distillate, may be used as catalytic cracker
feedstock or used in lubricating oil manufacture whilst the
residue, hereinafter to be referred to as the vacuum residue, may
be blended for use as fuel oil.
An alternative use for the vacuum distillate is described in Davis
et al. U.S. Pat. No. 3,781,195, which describes a process for the
production of olefins by hydrogenating a petroleum distillate
feedstock in the presence of a hydrogenation catalyst and hydrogen
and thermally cracking the resulting hydrogenated product in the
presence of steam. Whilst this process leads to a number of
substantial advantages there are disadvantages when using high
sulphur feedstock (e.g. from typical Middle East sources). Using
these feedstocks a large quantity of vacuum residue is co-produced
with the vacuum distillate. The vacuum residue contains higher
sulphur levels than the initial petroleum residue feedstock to the
vacuum distillation unit and is more difficult to desulphurise than
either the vacuum distillate or the petroleum residue feedstock.
With increasing restrictions on fuel oil sulphur levels in many
countries high sulphur vacuum residues will become increasingly
difficult to dispose of and will consequently adversely effect the
economics of the overall process. Further only a part of the
atmospheric petroleum residue feedstock is utilised as hydrogenated
petroleum distillate feedstock to the steam cracker, the remaining
carbon in the vacuum residue being lost to olefins production.
It has now been discovered that the first of these disadvantages
can be substantially overcome and the fraction of the atmospheric
petroleum residue feedstock utilised as feedstock to the steam
cracker increased by hydrogenating the atmospheric petroleum
residue feedstock prior to distillation.
Thus according to the present invention there is provided a process
for the production of normally gaseous olefins from an atmospheric
petroleum residue feedstock which process comprises contacting the
atmospheric petroleum residue feedstock in a hydrogenation zone
with a hydrogenation catalyst and hydrogen under conditions which
effect hydrogenation of aromatic hydrocarbons, separating from the
resulting hydrogenated atmospheric petroleum residue feedstock a
gaseous phase containing hydrogen and a liquid phase containing
hydrocarbons, recycling at least a portion of said gaseous phase to
said hydrogenation zone, separating said liquid phase into a
distillate fraction and a residue fraction, subjecting said
distillate fraction in the presence of steam to thermal cracking in
a pyrolysis zone under conditions effecting conversion of at least
a portion of said liquid phase to normally gaseous olefins and
thereafter recovering the normally gaseous olefins from the
pyrolysis zone effluent.
Distillate fraction within the context of the present application
means that fraction of the liquid phase containing hydrocarbons
having a boiling range below 650.degree.C at atmospheric pressure
and residue fraction that fraction having a boiling range above
that of the distillate fraction.
The term 'normally gaseous olefins' within the context of the
present application is intended to mean olefins which exist in the
form of gases at normal temperature and pressure.
The whole of the liquid phase containing hydrocarbons resulting
from the hydrogenation of the atmospheric petroleum residue
feedstock may, after separation of a gaseous phase containing
hydrogen, be fed in the presence of steam directly to the pyrolysis
zone wherein unvapourised feedstock is removed as a residue
fraction in a separation zone prior to entry of the vapourised
distillate fraction into that region of the pyrolysis zone
maintained under conditions which effect thermal cracking. The
temperature of the liquid phase containing hydrocarbons/steam
mixture fed to the pyrolysis zone is preferably regulated to
maximise the proportion of hydrocarbons in the distillate fraction
without promoting incipient thermal cracking of the mixture.
It is preferred however to separate the liquid phase containing
hydrocarbons resulting from hydrogenation of the atmospheric
petroleum residue fraction, after separation of a gaseous phase
containing hydrogen, into a distillate fraction and a residue
fraction by distillation under reduced pressure and feed only the
vacuum distillate fraction in the presence of steam to the
pyrolysis zone.
Thermal cracking within the context of this application is intended
to include steam cracking but not catalytic cracking.
Hydrogenation of the petroleum residue feedstock not only achieves
hydrogenation of aromatics thereby leading to a reduction in
boiling point of the compounds involved and an increase in the
proportion of the feedstock available for thermal cracking to
gaseous olefins but also effects desulphurisation of the feedstock,
leads to substantially increased yields of useful olefins for a
given quantity of feedstock and results in a reduction of coke
laydown in the cracking coil and of tar deposits in transfer lines
and heat exchangers.
It is important to avoid excessive breakdown of the feedstock in a
hydrocracking type of reaction. A limited amount of hydrocracking
can be tolerated and may even give the benefit of producing a more
mobile product but excessive hydrocracking leads to the use of
larger quantities of hydrogen with increased manufacturing costs
and to the formation of products which do not give corresponding
benefits in further increases in the yield of olefins.
Any catalyst which is capable of catalysing the hydrogenation of
compounds containing aromatic rings without substantial structural
alteration or breakdown may be used. Since most feedstocks contain
sulphur and nitrogen compounds it is desirable that the catalyst
should also possess some tolerance to these materials and their
hydrogenation products. Hydrogenation catalysts embodying these
requisites include for example nickel/molybdenum/alumina,
cobalt/tungsten/alumina, nickel/tungsten/alumina,
cobalt/molybdenum/alumina, nickel/cobalt/molybdenum/alumina,
cobalt/molybdenum/silica/alumina, nickel/molybdenum/silica/alumina,
cobalt/tungsten/silica/alumina and nickel/tungsten/silica/alumina.
Particularly active hydrogenation catalysts are
nickel/tungsten/silica/alumina and cobalt/molybdenum/alumina of
which nickel/tungsten/silica/alumina is preferred.
A typical nickel/tungsten/silica/alumina catalyst may have the
composition 1-6 per cent by weight of nickel and 9-27 per cent by
weight of tungsten, with a silica to alumina ratio in the range
90:10 to 25:75 but compositions outside this range are also
effective. Cobalt/molybdenum/alumina catalysts produced
commercially may contain up to 0.5% silica.
The catalyst may conveniently be prepared by impregnating the
support with an aqueous solution of a salt of each of the metals,
either consecutively or simultaneously. Thus nickel may be added in
the form of nickel nitrate, tungsten as ammonium metatungstate,
cobalt as cobalt nitrate, acetate etc. and molybdenum as ammonium
molybdate. It will usually be found convenient to impregnate the
support first with the salt of the metal which is to be present in
the highest concentration in the finished catalyst though this is
not essential. Other methods of preparing the catalyst include
precipitating the metals on the support from a solution of their
salts and co-precipitation of the metals with the hydrated support
material.
It is preferred that the catalysts be activated before use in the
reaction by contact with a stream of hydrogen at a temperature in
the range 100.degree. to 800.degree.C, more preferably 300.degree.
to 600.degree.C for a period of 1 minute to 24 hours.
Although the metallic components of the aforementioned
hydrogenation catalysts are defined in terms of the elemental
metals present therein, after activation, at least, the metals will
be present in the form of oxides. The precise nature of the active
species in the hydrogenation catalysts after contact for some time
with the atmospheric petroleum residue feedstock under
hydrogenation conditions is now known, though it is possible that
they contain in addition to the support, elemental metal, metal
oxides, metal sulphides and complex aluminium or silicon/metal
compounds.
Although it will usually be convenient to employ the hydrogenation
catalyst without prior exposure to materials containing sulphur at
least initially, the catalyst may also be used in the sulphided
form. The sulphided form of the catalyst may conveniently be
prepared by passing hydrogen through liquid tetrahydrothiophene and
then over the catalyst maintained at a temperature in the range
100.degree.C to 800.degree.C, preferably 300.degree.C to
600.degree.C for a period of 1 minute to 24 hours.
Using nickel and cobalt catalysts the hydrogenation temperature may
be in the range 50.degree. to 500.degree.C, preferably 300.degree.
to 400.degree.C and the pressure may be in the range 50 to 500
psig. preferably 200 to 3000 psig.
The hydrocarbon Liquid Hourly Space Velocity (LHSV) may be in the
range 0.1 to 5.0 preferably 0.1 to 2.0, even more preferably 0.1 to
0.5. For catalysts other than those containing cobalt or nickel the
reaction conditions may be different.
Hydrogen is preferably fed to the hydrogenation zone at about 5 to
10 times the molar rate of the atmospheric petroleum residue
feedstock. The major portion of the gaseous phase containing
hydrogen may be separated from the liquid phase containing
hydrocarbons in a high pressure separator and recycled either
directly or, after scrubbing to remove hydrogen sulphide and
ammonia, to the hydrogenation zone. Hydrogen dissolved in the
liquid phase may be separated in a low pressure separator and
either recycled to the hydrogenation zone or used as fuel gas.
Whilst the process will normally be operated continuously other
methods of operation may also be used such as batch operation in an
autoclave.
Hydrogenation may be carried out in a single stage or in a series
of two or more operations using the same or different
catalysts.
Thermal cracking of the distillate fraction in the presence of
steam may suitably be effected at a steam to hydrocarbon weight
ratio of about 0.5:1 to 2.0:1 in a heated zone, preferably a tube,
at a maximum temperature in the range 700.degree. to 1000.degree.C
with a residence time in the temperature range between 0.01 and 5
seconds, preferably 0.1 to 2.0 seconds. The products may be rapidly
cooled in a heat exchange system and separated and purified by
conventional means.
Normally gaseous olefins e.g. ethylene and propylene are used as
feedstocks for the production of a wide variety of chemical and
polymeric products.
The process of the invention is illustrated by the following
Examples:
COMPARISON TEST
A sample of Kuwait atmospheric residue with a hydrogen to carbon
ratio of 1.59 and a sulphur content of 4.26 per cent weight was
vacuum distilled. The initial boiling point of the atmospheric
residue was 296.5.degree.C, and 54 per cent volume distilled up to
a cut-point temperature of 550.degree.C (corrected to atmospheric
pressure). The distillate had a hydrogen to carbon atomic ratio of
1.70 and a sulphur content of 3.15 per cent weight. Analysis
indicated that the carbon content in aromatic rings was 19.0 per
cent weight of the total carbon, whereas the atmospheric residue
contained 18.8 per cent weight of aromatic carbon.
This vacuum distillate was steam cracked in an 8 ml. quartz reactor
at a maximum temperature of 830.degree.C. The steam to hydrocarbon
feed weight ratio was 1.0 to 1.0 with an average hydrocarbon feed
rate of 27 g. per hour. The ethylene and propylene yields were 23
and 10 per cent weight on feed respectively with a total conversion
to cracked gas of 53 per cent weight on feed.
This example is provided for purposes of comparison and is not an
example according to the invention.
EXAMPLE 1
A 300 g sample of the Kuwait atmospheric residue used in the
comparison test was hydrogenated in a 1 litre rocking autoclave at
370.degree.C under 2500 psig. of hydrogen during 24 hours using 75
g of a cobalt oxide/molybdenum oxide/alumina catalyst. The catalyst
containing 3.9 per cent weight cobalt, 19.7 per cent weight
molybdenum, and less than 0.1 per cent weight silica, and after
calcination in air at 550.degree.C for 2 hours was activated in a
stream of hydrogen at 400.degree.C for 24 hours. The recovered
hydrogenated atmospheric residue had a hydrogen to carbon atomic
ratio of 1.86 and a sulphur content of 0.14 per cent weight.
Analysis indicated that the carbon content in aromatic rings was
8.5 per cent weight of the total carbon. This material was vacuum
distilled; the initial boiling point of the distillate was
230.degree.C, and 72 per cent volume distolled up to a cut-point
temperature of 550.degree.C (corrected to atmospheric pressure).
The distillate had a hydrogen to carbon atomic ratio of 1.88 and a
sulphur content of 0.15 per cent weight. Analysis indicated that
the carbon content in aromatic rings was 10.8 per cent weight.
The vacuum distillate was steam cracked under the same conditions
as were used in the comparison test. The ethylene and propylene
yields were 24 and 11 per cent weight on feed respectively with a
total conversion to cracked gas of 57 per cent. There was also a
substantial reduction in the coke and tar deposited in the reactor
system compared with that formed from the untreated vacuum
distillate.
EXAMPLE 2
A 300 g sample of the Kuwait atmospheric residue used in the
comparison test was hydrogenated in a 1 litre rocking autoclave at
370.degree.C under 2500 psig. of hydrogen during 24 hours using
54.5 g. of a nickel oxide/tungsten oxide/silica/alumina catalyst.
The catalyst contained 4.9 per cent weight nickel, 15.9 per cent
weight tungsten and the silica to alumina ratio was 3:1. The
catalyst was again first calcined in air at 550.degree.C for 2
hours and then immediately before use it was activated at
400.degree.C in a stream of hydrogen for 24 hours. The recovered
hydrogenated atmospheric residue had a hydrogen to carbon atomic
ratio of 1.79 and a sulphur content of 0.28 per cent weight.
Analysis indicated that the carbon content in aromatic rings was
11.5 per cent weight of the total carbon. This material was vacuum
distilled; the initial boiling point of the distillate was
229.degree.C, and 80 per cent volume distilled up to a cut-point
temperature of 550.degree.C (corrected to atmospheric pressure).
The distillate had a hydrogen to carbon atomic ratio of 1.78 and a
sulphur content of 0.21 per cent weight. Analysis indicated that
the carbon content in aromatic rings was 12.4 per cent weight.
This vacuum distillate was steam cracked under the same conditions
as were used in the comparison test. The ethylene and propylene
yields were 251/2 and 12 per cent weight on feed respectively with
a total conversion to cracked gas of 58 per cent. There was a
further reduction in the coke and tar deposited in the reactor
system compared with that formed in Example 1.
The Examples show that hydrogenation of the atmospheric residue
leads to a substantial increase in the percentage of vacuum
distillate recoverable as feedstock for thermal cracking. When
combined with the increased yield and conversion to ethylene and
propylene in the thermal cracking step it can be seen that the
overall yield of normally gaseous olefins is substantially
increased.
* * * * *