U.S. patent number RE33,323 [Application Number 07/204,754] was granted by the patent office on 1990-09-04 for reforming process for enhanced benzene yield.
This patent grant is currently assigned to Exxon Research & Engineering Company. Invention is credited to Murray Nadler, John C. Roarty.
United States Patent |
RE33,323 |
Roarty , et al. |
September 4, 1990 |
**Please see images for:
( Certificate of Correction ) ** |
Reforming process for enhanced benzene yield
Abstract
A process for reforming a full boiling range naptha feed to
enhance benzene yield is disclosed which first separates the feed
into a .[.C.sub.6 .]. .Iadd.lighter .Iaddend.fraction .[.containing
at least 10% by volume of C.sub.7+ hydrocarbons.]. .Iadd.,
comprising at least one member selected from the group consisting
of C.sub.6, C.sub.7, and C.sub.8 hydrocarbons, .Iaddend.and a
.[.C.sub.7 +.]. .Iadd.heavier .Iaddend.fraction, then subjecting
the .[.C.sub.6 .]. .Iadd.lighter .Iaddend.fraction to a catalytic
aromatization process .[.and subjecting the C.sub.7 + fraction to a
catalytic reforming process, followed by recovering the aromatics
produced.]..Iadd.in the presence of a non-acidic
catalyst.Iaddend..
Inventors: |
Roarty; John C. (Baton Rouge,
LA), Nadler; Murray (Houston, TX) |
Assignee: |
Exxon Research & Engineering
Company (Florham Park, NJ)
|
Family
ID: |
26899779 |
Appl.
No.: |
07/204,754 |
Filed: |
June 10, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
679500 |
Dec 7, 1984 |
04594145 |
Jun 10, 1986 |
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Current U.S.
Class: |
208/79; 208/133;
208/138; 208/93 |
Current CPC
Class: |
C10G
59/06 (20130101); C10G 61/04 (20130101) |
Current International
Class: |
C10G
61/04 (20060101); C10G 59/00 (20060101); C10G
61/00 (20060101); C10G 59/06 (20060101); C10G
037/06 () |
Field of
Search: |
;208/79,93,133,138 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2323664 |
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Apr 1977 |
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FR |
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2121788 |
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Jan 1984 |
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GB |
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Primary Examiner: Davis; Curtis R.
Attorney, Agent or Firm: Bittman; M. D.
Claims
What is claimed is:
1. A process for reforming a full boiling range hydrocarbon feed to
enhance benzene yield comprising:
(a) separating the hydrocarbon feed into a C.sub.5- fraction, a
C.sub.6 -C.sub.7 fraction containing at least 10% by volume of
C.sub.7+ hydrocarbons, and a C.sub.7+ fraction;
(b) subjecting the C.sub.6 -C.sub.7 fraction to catalytic
aromatization at elevated temperatures in the presence of hydrogen
and utilizing a catalyst containing a non-acidic carrier and at
least one Group VIII noble metal which catalyst converts C.sub.6
paraffins to benzene in a yield of at least 30% by volume and a
selectivity of at least 50% and separating a C.sub.5+ effluent:
(c) subjecting the C.sub.7+ fraction to catalytic reforming at
elevated temperatures in the presence of hydrogen utilizing a
catalyst comprising platinum on an acidic alumina carrier and
separating a C.sub.8- effluent from a C.sub.9+ effluent;
(d) mixing the C.sub.5+ effluent and C.sub.8- effluent from steps
(b) and (c) and recovering an aromatic extract and a non-aromatic
raffinate.
2. Process of claim 1 wherein the C.sub.5+ effluent is separated in
a flash drum.
3. Process of claim 2 wherein the C.sub.6 fraction contains 15 to
35% by volume of C.sub.7+ hydrocarbons.
4. Process of claim 1 wherein the catalyst for catalytic
aromatization converts C.sub.6 paraffins into benzene at a
selectivity of at least 50% of the C.sub.6 paraffins to benzene and
the catalyst for catalytic reforming converts C.sub.6 paraffins
into benzene at a selectivity of less than 35% of C.sub.6 paraffins
to benzene.
5. Process of claim 4 wherein the aromatic extract and non-aromatic
raffinate are recovered in a solvent extraction process.
6. Process of claim 5 wherein the catalytic reforming is carried
out at temperatures sufficient to convert at least 90% of the
C.sub.7 paraffins.
7. Process of claim 6 wherein the catalytic reforming is carried
out with a platinum-rhenium gamma alumina catalyst at temperatures
of from about 480.degree. C. to 510.degree. C.
8. Process of claim 6 wherein the non-aromatic raffinate recovered
in the solvent extraction process is recycled and added to the full
boiling range naphtha prior to the separation of step (a).
9. Process of claim 5 further comprising separating the C.sub.8-
effluent into a C.sub.6- effluent, a C.sub.7 effluent and a C.sub.8
effluent and only the C.sub.6- effluent and the C.sub.8 effluent
are mixed with the C.sub.5+ effluent for the recovery of the
aromatic extract in the solvent extraction process.
10. Process of claim 9 wherein the effluent from the catalytic
reforming are separated by first fractionating the effluent into a
C.sub.6- effluent, a C.sub.7 effluent and a C.sub.8+ effluent, then
fractionating the C.sub.8+ effluent into a C.sub.8 effluent and a
C.sub.9+ effluent.
11. Process of claim 5 wherein the non-aromatic raffinate recovered
in the solvent extraction process is recycled and added to the
C.sub.6 fraction in step (b) for catalytic aromatization.
12. Process of claim 5 wherein the solvent extraction process uses
a solvent selected from the group consisting of sulfolane and tetra
ethylene glycol.
13. Process of claim 4 wherein the C.sub.6 fraction contains 10 to
50% by volume of C.sub.7+ hydrocarbons.
14. Process of claim 1 wherein the platinum on acidic alumina
catalyst also contains a metal chosen from the group consisting of
rhenium,. iridium, tungsten, tin and bismuth.
15. Process of claim 1 wherein the catalyst for catalytic
aromatization converts the C.sub.6 paraffins into benzene at a
yield of at least 40% by volume of C.sub.6 paraffins in the feed
and at a selectivity of at least 55% of C.sub.6 paraffins to
benzene.
16. Process of claim 15 wherein the catalyst for catalytic
aromatization is a platinum type L zeolite catalyt wherein at least
90% of the exchangeable cations are metal ions selected for sodium,
lithium, barium, calcium, potassium, strontium, rubidium and
cesium.
17. Process of claim 16 wherein the benzene yield is from 5 to 25%
by volume of the C.sub.6+ hydrocarbons and 35 to 80% by volume of
the C.sub.6 hydrocarbons in the full boiling range hydrocarbon
feed.
18. The process of claim 15 where the catalyst is platinum
potassium type L zeolite.
19. Process of claim 1 wherein the hydrocarbon feed is a naphtha
having a boiling range up to about 350.degree. F. .Iadd.
20. A process for reforming a hydrocarbon feed comprising:
(a) separating said hydrocarbon feed into a lighter fraction,
comprising at least one member selected from the group consisting
of C.sub.6, C.sub.7, and C.sub.8 hydrocarbons, and a heavier
fraction;
(b) reforming said lighter fraction under reforming conditions in a
reformer in the presence of a non-acidic catalyst, said non-acidic
catalyst comprising a non-acidic zeolite support, to produce a
first reformate;
(c) reforming said heavier fraction under reforming conditions in
the presence of an acidic catalyst to produce a second
reformate;
(d) introducing said first reformate into an extraction unit;
(e) separating and removing an aromatic extract stream and a
non-aromatic raffinate stream from said extraction unit; and
(f) recycling said non-aromatic raffinate stream to said
hydrocarbon feed for reforming under reforming conditions in the
presence of a non-acidic catalyst to produce a stream comprising
benzene..Iaddend. .Iadd.21. The process as defined by claim 20,
wherein said non-acidic catalyst further comprises at least one
metal selected from the group consisting of Group VIII metals, tin,
and germanium, said at least one metal comprising at least one
Group VIII metal having a dehydrogenating effect..Iaddend.
.Iadd.22. The process as defined by claim 20, wherein said zeolite
is selected from the group consisting of zeolite L, zeolite X, and
zeolite Y..Iaddend. .Iadd.23. The process as defined by claim 22,
wherein said zeolite is zeolite L..Iaddend. .Iadd.24. The process
as defined by claim 23, wherein said zeolite L has exchangeable
cations, at least 90% of said exchangeable cations being metal ions
selected from the group consisting of sodium, lithium, barium,
calcium, potassium, strontium, rubidium and cesium..Iaddend.
.Iadd.25. The process as defined by claim 21, wherein said at least
one metal comprises platinum..Iaddend. .Iadd.26. The process as
defined by claim 20, wherein said lighter fraction comprises
C.sub.6, C.sub.7, and C.sub.8 hydrocarbons..Iaddend. .Iadd.27. The
process as defined by claim 20 wherein said lighter fraction is a
C.sub.6 -C.sub.7 fraction containing at least 10% by volume
C.sub.7+ hydrocarbons, and said heavier fraction is a C.sub.7+
fraction..Iaddend. .Iadd.28. A process for reforming a hydrocarbon
feed comprising:
(a) separating said hydrocarbon feed into a lighter fraction,
comprising at least one member selected from the group consisting
of C.sub.6, C.sub.7, and C.sub.8 hydrocarbons, and a heavier
fraction;
(b) reforming said lighter fraction under reforming conditions in
the presence of a non-acidic catalyst, said non-acidic catalyst
comprising a non-acidic zeolite support, to produce a first
reformate;
(c) reforming said heavier fraction under reforming conditions in
the presence of an acidic catalyst to produce a second
reformate;
(d) introducing said first reformate into an extraction unit;
(e) separating and removing an aromatic extract stream and a
non-aromatic raffinate stream from said extraction unit; and
(f) recycling said non-aromatic raffinate stream to said lighter
fraction for reforming under reforming conditions in the presence
of a non-acidic catalyst to produce a stream comprising
benzene..Iaddend. .Iadd.29. The process as defined by claim 28,
wherein said non-acidic catalyst further comprises at least one
metal selected from the group consisting of Group VIII metals, tin,
and germanium, said at least one metal comprising at least one
Group VIII metal having a dehydrogenating effect..Iaddend.
.Iadd.0. The process as defined by claim 28, wherein said zeolite
is selected from the group consisting of zeolite L, zeolite X, and
zeolite Y..Iaddend. .Iadd.31. The process as defined by claim 30,
wherein said zeolite is zeolite L..Iaddend. .Iadd.32. The process
as defined by claim 31, wherein said zeolite L has exchangeable
cations, at least 90% of said exchangeable cations being metal ions
selected from the group consisting of sodium, lithium, barium,
calcium, potassium, strontium, rubidium and cesium..Iaddend.
.Iadd.33. The process as defined by claim 29, wherein said at least
one metal comprises platinum..Iaddend. .Iadd.34. The process as
defined by claim 28, wherein said lighter fraction comprises
C.sub.6, C.sub.7, and C.sub.8 hydrocarbons..Iaddend. .Iadd.35. The
process as defined by claim 28, wherein said lighter fraction is a
C.sub.6 -C.sub.7 fraction containing at least 10% by volume
C.sub.7+ hydrocarbons, and said heavier fraction is a C.sub.7+
fraction..Iaddend. .Iadd.36. The process for reforming a
hydrocarbon feed comprising:
(a) separating a full boiling range naphtha feed stream into at
least two fractions;
(b) contacting one of said fractions of said naphtha feed in an
aromatizer reactor with a catalyst at process conditions which
favor dehydrocyclization to produce an aromatics product, wherein
said catalyst is a non-acidic catalyst comprising a zeolite
containing at least one Group VIII metal;
(c) reforming another of said fractions of said naphtha feed in the
presence of an acidic catalyst to produce an effluent;
(d) separating components comprising normal paraffins and
single-branched isoparaffins present in said aromatics product as
non-aromatic raffinate; and
(e) recycling said non-aromatic raffinate to said one fraction of
said naphtha feed to said aromatizer reactor..Iaddend. .Iadd.37.
The process as defined by claim 36 wherein said separating in step
(d) is carried out by solvent extraction..Iaddend. .Iadd.38. The
process as defined by claim 37, wherein said solvent is
sulfolane..Iaddend. .Iadd.39. The process as defined by claim 36,
wherein said zeolite is a type L zeolite..Iaddend. .Iadd.40. The
process as defined by claim 39, wherein said catalyst contains a
metal selected from the group consisting of metals of Group VIII of
the periodic table of elements, tin and germanium..Iaddend.
.Iadd.41. The process as defined by claim 40, wherein said metal
includes at least one metal of the periodic table having a
dehydrogenating effect..Iaddend. .Iadd.42. The process as defined
by claim 41, wherein said metal is platinum..Iaddend. .Iadd.43. The
process as defined by claim 42, wherein said catalyst comprises
exchangeable cations selected from the group consisting of sodium,
lithium, barium, calcium, potassium, strontium, rubidium, and
cesium..Iaddend. .Iadd.44. The process as defined by claim 43,
wherein said exchangeable cation is potassium..Iaddend. .Iadd.45.
The process as defined by claim 43, wherein said exchangeable
cation is barium..Iaddend. .Iadd.46. A process for reforming a
hydrocarbon feed comprising:
(a) separating said hydrocarbon feed into a first fraction and a
second fraction;
(b) separating said second fraction into a lighter fraction,
comprising at least one member selected from the group consisting
of C.sub.6, C.sub.7, and C.sub.8 hydrocarbons, and a heavier
fraction;
(c) reforming said lighter fraction under reforming conditions in
the presence of a non-acidic catalyst, said non-acidic catalyst
comprising a non-acidic zeolite support, to produce a first
reformate;
(d) reforming said heavier fraction under reforming conditions in
the presence of an acidic catalyst to produce a second
reformate;
(e) introducing said first reformate into an extraction unit;
and
(f) separating and removing an aromatic extract stream and a
non-aromatic raffinate stream from said extraction unit;
(g) recycling said non-aromatic raffinate stream to said
hydrocarbon feed for reforming under reforming conditions in the
presence of a non-acidic
catalyst to produce a stream comprising benzene..Iaddend. .Iadd.47.
The process as defined by claim 46, wherein said non-acidic
catalyst further comprises at least one metal selected from the
group consisting of Group VIII metals, tin and germanium, said at
least one metal comprising at least one Group VIII metal having a
dehydrogenating effect..Iaddend. .Iadd.48. The process as defined
by claim 46, wherein said zeolite is selected from the group
consisting of zeolite L, zeolite X, and zeolite Y..Iaddend.
.Iadd.49. The process as defined by claim 48, wherein said zeolite
is zeolite L..Iaddend. .Iadd.50. The process as defined by claim
49, wherein said zeolite L has exchangeable cations, at least 20%
of said exchangeable cations being metal ions selected from the
group consisting of sodium, lithium, barium, calcium, potassium,
strontium, rubidium and cesium..Iaddend. .Iadd.51. The process as
defined by claim 47, wherein said at least one metal comprises
platinum..Iaddend. .Iadd.52. The process as defined by claim 46,
wherein said first fraction is a C.sub.5 - fraction, and said
second fraction is a C.sub.6 + fraction..Iaddend. .Iadd.53. The
process as defined by claim 46, wherein said lighter fraction
comprises C.sub.6, C.sub.7, and C.sub.8 hydrocarbons..Iaddend.
.Iadd.54. A process for reforming a hydrocarbon feed
comprising:
(a) separating said hydrocarbon feed into a first fraction and a
second fraction;
(b) separating said second fraction into a lighter fraction,
comprising at least one member selected from the group consisting
of C.sub.6, C.sub.7, and C.sub.8 hydrocarbons, and a heavier
fraction;
(c) reforming said lighter fraction under reforming conditions in
the presence of a non-acidic catalyst, said non-acidic catalyst
comprising a non-acidic zeolite support, to produce a first
reformate; and
(d) reforming said heavier fraction under reforming conditions in
the presence of an acidic catalyst to produce a second
reformate.
(e) introducing said first reformate into an extraction unit;
(f) separating and removing an aromatic extract stream and a
non-aromatic raffinate stream from said extraction unit;
(g) recycling said non-aromatic raffinate stream to said
hydrocarbon feed for reforming under reforming conditions in the
presence of a non-acidic catalyst to produce a stream comprising
benzene..Iaddend. .Iadd.55. The process as defined by claim 54,
wherein said non-acidic catalyst further comprises at least one
metal selected from the group consisting of Group VIII metals, tin,
and germanium, said at least one metal comprising at least one
Group VIII metal having a dehydrogenating effect..Iaddend.
.Iadd.56. The process as defined by claim 54, wherein said zeolite
is selected from the group consisting of zeolite L, zeolite X, and
zeolite Y..Iaddend. .Iadd.57. The process as defined by claim 56,
wherein said zeolite is zeolite L..Iaddend. .Iadd.58. The process
as defined by claim 57, wherein said zeolite L has exchangeable
cations, at least 90% of said exchangeable cations being metal ions
selected from the group consisting of sodium, lithium, barium,
calcium, potassium, strontium, rubidium and cesium..Iaddend.
.Iadd.59. The process as defined by claim 55, wherein said at least
one metal comprises platinum..Iaddend. .Iadd.60. The process as
defined by claim 54, wherein said first fraction is a C.sub.5 -
fraction, and said second fraction is a C.sub.6 +
fraction..Iaddend. .Iadd.61. The process as defined by claim 54,
wherein said lighter fraction comprises C.sub.6, C.sub.7, and
C.sub.8 hydrocarbons..Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to a process for reforming a full-boiling
range hydrocarbon feed to enhance benzene yield by a combination of
steps including separating the hydrocarbon feed into fractions,
then separately treating the fractions by catalytic reforming the
recovering the products. More particularly, the invention relates
to a process for integrating a catalytic aromatization process
which uses a catalyst superior in reforming C.sub.6 .[.and C.sub.7
.]..Iadd.,C.sub.7, and C.sub.8 .Iaddend.paraffins with a catalytic
reforming process utilizing a conventional reforming catalyst in a
manner which enhances the benzene yield, increases energy
efficiency and efficiently recovers the resulting products.
In a conventional reforming process, pentanes and lighter
hydrocarbons (C.sub.5-) are first removed with the C.sub.6+ stream
sent to a reformer followed by fractionation with the overhead sent
to an extraction unit as shown in FIG. 2. While a substantial
amount of aromatics (primarily toluene, xylenes and C.sub.9
aromatics) are produced using a conventional reforming catalyst
such as a Pt-Re gamma alumina catalyst, this process is not
designed to maximize benzene yields.
FIELD OF THE INVENTION
The reforming of petroleum hydrocarbon streams is an important
petroleum refining process which is employed to provide high octane
hydrocarbon blending components for gasoline. The process is
usually practiced on a straight run naphtha fraction which has been
hydrodesulfurized. Straight run naphtha is typically highly
paraffinic in nature but may contain significant amounts of
naphthenes and minor amounts of aromatics or olefins. In a typical
reforming process, the reactions include dehydrogenation,
isomerization, and hydrocracking. The dehydrogenation reactions
typically will be the dehydroisomerization of alkylcyclopentanes to
aromatics, the dehydrogenation of paraffins to olefins, the
dehydrogenation of cyclohexanes to aromatics, and the
dehydrocyclization of paraffins and olefins to aromatics. The
aromatization of the n-paraffins to aromatics is generally
considered to be the most important because of the high octane of
the resulting aromatic product compared to the low octane ratings
for n-paraffins. The isomerization reactions include isomerization
of n-paraffins to isoparaffins, the hydroisomerization of olefins
to isoparaffins, and the isomerization of substituted aromatics.
The hydrocracking reactions include the hydrocracking of paraffins
and hydrodesulfurization if any sulfur compounds remain in the
feedstock. On lighter naphtha streams, it is often desirable to
avoid hydrocracking because of the resulting low carbon number of
gaseous products which are the result.
It is well known that several catalysts are capable of reforming
petroleum naphthas and hydrocarbons that boil in the gasoline
boiling range. Examples of known catalysts useful for reforming
include platinum and optionally rhenium or iridium on an alumina
support, platinum on type X and Y zeolites (provided the reactants
and products are sufficiently small to flow through the pores of
the zeolites), platinum on intermediate pore size zeolites as
described in U.S. Pat. No. 4,347,394, and platinum on cation
exchanged type L zeolites. U.S. Pat. No. 4,104,320 discloses the
dehydrocyclization of aliphatic hydrocarbon to aromatics by contact
with a catalyst comprising a type L zeolite containing alkali metal
ions and a Group VIII metal such as platinum.
The conventional reforming catalyst is a bi-functional catalyst
which contains a metal hydrogenation-dehydrogenation component
which is usually dispersed on the surface of a porous inorganic
oxide support, notably alumina. Platinum has been widely used
commercially in recent years in the production of reforming
catalysts, and platinum on alumina catalyst have been commercially
employed in refineries for the past few decades. In the last
decade, additional metallic components have been added to platinum
as promoters to further the activity or selectivity, or both, of
the basic platinum catalyst, e.g., iridium, rhenium, tin and the
like. Some catalysts possess superior activity, or selectivity, or
both, as contrasted with other catalysts. Platinum-rhenium
catalysts, by way of example, possess high selectivity in contrast
to platinum catalysts. Selectivity is generally defined as ability
of the catalyst to produce yields of C.sub.5+ liquid products with
concurrent low production of normally gaseous hydrocarbons, i.e.,
methane and propane.
There exist several processes for dividing naphtha feedstock into a
higher boiling and a lower boiling cut and reforming these cuts
separately. U.S. Pat. No. 2,867,576 discloses separating straight
run naphtha into lower and higher boiling cuts, in which the higher
boiling cuts are reformed with a hydrogenation-dehydrogenation
catalyst with the liquid reformate produced being passed to an
aromatics separation process. The paraffinic fraction obtained from
the separation process is blended with the lower boiling naphtha
fraction and the resulting blend is reformed with a reforming
catalyst which may or may not be the same type employed in
reforming the high boiling cut.
U.S. Pat. No. 2,944,959 discloses fractionating a full straight run
gasoline into a light paraffinic fraction (C.sub.5 and C.sub.6)
which is hydroisomerized with hydrogen and a pt-alumina catalyst, a
middle fraction (end point of 320.degree. to 360.degree. F.) which
is catalytically reformed with hydrogen and a pt-alumina catalyst,
and a heavy fraction which is catalytically reformed with a
molybdinum oxide catalyst and recovering the liquid products. U.S.
Pat. Nos. 3,003,949, 3,018,244 and 3,776,949 also disclose
fractionating a feed into a C.sub.5 and C.sub.6 fraction which is
isomerized and a heavier fraction which is reformed.
Other processes for dividing feedstocks and separately treating
them include: U.S. Pat. Nos. 3,172,841 and 3,409,540 which disclose
separating fractions of a hydrocarbon feed and catalytically
hydrocracking and catalytically reforming various fractions of the
feed; U.S. Pat. No. 4,167,472 which discloses separating straight
chain from non-straight chain C.sub.6 -C.sub.10 hydrocarbons and
separately converting to aromatics; and U.S. Pat. No. 4,358,364
which discloses catalytically reforming a C.sub.6 to 300.degree. F.
B.P. fraction and producing additional benzene by hydrogasifying a
C.sub.5- fraction, a fraction with a B.P. above 300.degree. F. and
the gas stream produced from the catalytic reforming.
U.S. Pat. No. 3,753,891 discloses fractionating a straight run
naphtha into a light naphtha fraction containing the C.sub.6 and a
substantial portion of the C.sub.7 hydrocarbons and a heavy naphtha
fraction boiling from about 200.degree. to 400.degree. F.; then
reforming the light fraction to convert naphthenes to aromatics
over a pt-alumina catalyst or a bimetallic reforming catalyst;
separately reforming the heavy fraction; then upgrading the
reformer effluent of the low boiling fraction over a ZSM-5 type
zeolite catalyst to crack the paraffins; and recovering an effluent
with improved octane rating.
While these patents disclose split feed reforming, these patents do
not disclose enhancing benzene yield by: splitting a feed into a
.Iadd.lighter fraction, such as a .Iaddend.C.sub.6 fraction
containing at least 10% by volume of C.sub.7+ hydrocarbons and a
.Iadd.heavier fraction, such as a .Iaddend.C.sub.7+ fraction;
catalytically aromatizing the .[.C.sub.6 .]. .Iadd.lighter
.Iaddend.fraction over a catalyst superior in reforming C.sub.6
.[.and C.sub.7.]. , C.sub.7, and C.sub.8 paraffins; catalytically
reforming the .[.C.sub.7+ .]. .Iadd.heavier .Iaddend.fraction; and
recovering the effluents.
SUMMARY OF THE INVENTION
It has now been found that the benzene yields produced upon
reforming a full boiling range hydrocarbon feed can be increased
with improved efficiencies by first separating the feed into three
.[.fractions,.]. .Iadd.fractions: first fraction, such as a
.Iaddend.C.sub.5- .[.fraction,.]. .Iadd.fraction; lighter fraction,
such as .Iaddend.a C.sub.6 fraction containing at least 10% by
volume of C.sub.7+ .[.hydrocarbons,.]. .Iadd.hydrocarbons;
.Iaddend.and a .Iadd.heavier fraction, such as a .Iaddend.C.sub.7+
fraction. The .[.C.sub.6.]. lighter fraction is subjected to a
catalytic aromatization process and a C.sub.5+ effluent is
separated. The .[.C.sub.7+.]. heavier fraction is subject to a
catalytic reforming process and a C.sub.8- effluent is separated
from a C.sub.9+ effluent. The C.sub.5+ effluent from the catalytic
reformer are then mixed and the aromatic content is recovered. This
process maximizes the benzene production by efficiently producing
benzene from a .[.C.sub.6.]. lighter fraction by catalytic
aromatization and also obtains the benefits of benzene production
of the .[.C.sub.7+ .]. .Iadd.heavier .Iaddend.fraction in a
catalytic reformer.
DESCRIPTION OF THE DRAWINGS
The reforming processes will be described in more detail by
reference to the drawings of which:
FIG. 1 is a flow diagram of the reforming process of the
invention.
FIG. 2 is a flow diagram of a conventional reforming process.
DETAILED DESCRIPTION OF THE INVENTION
In accord with this invention, the first step of this process
involves separating a full boiling range hydrocarbon feed into
three fractions (cuts). The three fractions are a C.sub.5- fraction
(hydrocarbons having a five carbon atom content or less), a C.sub.6
fraction containing at least 10% by volume of C.sub.7+ hydrocarbons
and a C.sub.7+ fraction (hydrocarbons containing seven carbon atoms
and greater). This separation is suitably and preferably carried
out in distillation columns to give the specified fractions. Unless
otherwise specified, the fractions contain greater than 90%,
preferably at least 95% of the stated hydrocarbons. Advantageously,
the C.sub.6 fraction containing at least 10 vol. % of C.sub.7+
hydrocarbons can be separated in a fractionator with less energy
being required as compared to having a C.sub.6 fraction with a
lower C.sub.7+ content. For example, fractionating a C.sub.6
fraction containing 15% C.sub.7+ hydrocarbons requires 15% less
energy that fractionating a C.sub.6 fraction containing 5% C.sub.7+
hydrocarbons. Generally, the C.sub.6 fraction contains from 10 to
50% by volume of C.sub.7+ hydrocarbons, and preferably from 15 to
35% by volume of C.sub.7+ hydrocarbons. The fractionation can be
carried out, as shown in FIG. 1, wherein the hydrocarbon feed is
first fractionated into the C.sub.5- fraction and a C.sub.6+
fraction in the first column and then in a second column separated
into the C.sub.6 fraction and the C.sub.7+ fraction.
The separated C.sub.6 fraction which contains at least 10% by
volume of C.sub.7+ hydrocarbons, is then subject to a catalytic
aromatization process wherein it is contacted with a catalyst which
at elevated temperatures and in the presence of hydrogen causes the
C.sub.6 and greater paraffins to form into six carbon atom rings
and thereafter causes these rings to dehydrogenate to aromatics.
The aromatization catalyst for this process include catalysts which
convert the C.sub.6 paraffins to benzene at a high selectivity and
yield generally converting C.sub.6 paraffins at a yield of at least
30% by volume of C.sub.6 paraffins in the feed and a selectivity of
at least 50% of the C.sub.6 paraffins to benzene, preferably
converting C.sub.6 paraffins to benzene at a yield of at least 40%
by volume of C.sub.6 paraffins in the feed and at a selectivity of
at least 55% of C.sub.6 paraffins to benzene. Suitable catalysts
include non-acidic catalysts which contain a non-acidic carrier and
at least one noble metal of Group VIII of the periodic table. In
general the catalyst employed will comprise other elements
including those from Groups 6-B, 7-B, 1-B, 4-A, 6-A of the periodic
table, loaded on an amorphous silica, amorphous alumina or zeolitic
supports with the preferred catalysts being chosen for its ability
to maximize benzene yield.
The preferred catalyst is a platinum-zeolite L (see U.S. Pat. No.
4,104,320 which is incorporated herein by reference). This catalyst
has been shown to have high yields and selectivity in producing
aromatic compounds from paraffins, more specifically providing
efficient dehydrocyclization of C.sub.6 paraffins. The Zeolite L
and its preparation is described in U.S. Pat. Nos. 3,216,789 and
3,867,512 and in U.K. Application No. 82-14147, filed May 14, 1982.
The aromatization is carried out with a catalyst comprising a Type
L Zeolite having an exchangeable cations and a noble metal having a
dehydrogenating effect. Generally at least 90% of the exchangeable
cations are metal ions selected from sodium, lithium, barium,
calcium, potassium, strontium, .[.rhubidium.]. .Iadd.rubidium
.Iaddend.and cesium with the preferred metal ion being potassium.
The Zeolite L also contains at least one metal selected from the
group consisting of metals of Group VIII of the periodic table of
elements, tin and germanium, said metal or metals including at
least one metal from Group VIII of the periodic table having a
dehydrogenating effect with the preferred noble metal being
platinum, preferably at a range of 0.1-1.5% by weight. With a pt-K
Zeolite L catalyst yields of 40 to 50% by volume of C.sub.6
paraffins in the feed and a selectivity of 55 to 70% of the C.sub.6
paraffins to benzene have been observed. The dehydrocyclization is
carried out in the presence of hydrogen, generally at hydrogen to
hydrocarbon mole ratios of 2 to 20, preferably 3 to 10, pressures
of from about 110 to 1750 KPa and at temperatures of about
430.degree. to 550.degree. C.
The effluent from the catalytic aromatization of the C.sub.6
fraction contains a high yield of benzene from which a C.sub.5+
effluent is separated. In addition, the C.sub.7+ hydrocarbons in
the C.sub.6 fractions are efficiently converted to aromatics such
as toluene. A C.sub.5+ effluent is efficiently separated from the
effluent of the aromatization unit due to the level of C.sub.7+
hydrocarbons present in the effluent. The C.sub.7+ hydrocarbons
present in the C.sub.5+ effluent act as a heavy oil wash in the
flash drum to efficiently remove the C.sub.5+ hydrocarbons from the
effluent.
Recovery of C.sub.5+ hydrocarbons especially benzene from a stream
containing a high benzene yield, (i.e. greater than 30 vol. %)
using conventional techniques, is difficult. For example, in a
reforming process containing 50 vol. % benzene (<1% C.sub.7+
hydrocarbons), conventional recovery techniques utilizing a flash
drum result in the recovery of only about 80% by volume of the
benzene in the effluent. In this process, with the presence of at
least 10% C.sub.7+ hydrocarbons in the effluent, the recovery of
C.sub.5+ hydrocarbons, especially benzene is dramatically improved.
For example where the effluent containing 50 volume % benzene and
25 volume % C.sub.7+ hydrocarbons about 90% by volume of the
benzene in the effluent is recovered in a flash drum.
The separated C.sub.7+ fraction is subjected to catalytic reforming
with conventional reforming catalyst. That is, it is contacted with
a catalyst which at elevated temperatures and in the presence of
hydrogen causes the dehydrogenation of the C.sub.7+
alkylcyclohexanes to alkylaromatics, the dehydroisomerization of
alkylcyclopentanes to alkylaromatics, the dehydrocyclization of
C.sub.7+ paraffins to alkylaromatics and the isomerization of
normal paraffins to iso-paraffins. Suitable catalysts for this
purpose are acidic noble metal catalysts such as platinum on an
acidic alumina carrier. Such catalysts may contain more than one
noble metal and additionally may contain other metals, preferably
transition metals such as rhenium, iridium, tungsten, tin, bismuth
and the like and halogens such as chlorine or fluorine. Catalysts
of this type are available commercially. A preferred reforming
catalyst is a platinum-rhenium on gamma alumina catalyst. The
conventional reforming catalysts are generally efficient in
converting C.sub.7+ hydrocarbons but are generally not as effective
in producing benzene from C.sub.6 paraffins as the aromatization
catalyst. In general, the reforming catalysts convert C.sub.6
paraffins at a yield of less than 30% by volume of C.sub.6
paraffins in the feed and a selectivity of less than 35% of C.sub.6
paraffins to benzene.
The catalytic reforming of the C.sub.7+ fraction is suitably
carried out at temperatures of from about 400.degree.-600.degree.
C., preferably at a temperature at least sufficient to convert at
least 90% of the C.sub.9 paraffins. For a platinum-rhenium gamma
alumina catalyst, a temperature sufficient to convert the C.sub.9
paraffins is generally at least 480.degree. C. Conversion of the
C.sub.9 paraffins is desired in order to eliminate enough of the
C.sub.9 paraffins from the reformer effluent to produce in the
solvent extraction process at aromatic extract containing a low
level of non-aromatics. Since the C.sub.9 paraffins boil in the
same range as the C.sub.8 aromatics they are difficult to remove by
fractionation and in a solvent extraction process, solvents such as
sulfolane do a poor job in separating C.sub.9 paraffins from the
aromatics. Thus, an effective way of obtaining an aromatic extract
from the solvent extraction unit with a low or non-specification
level of non-aromatics, such as C.sub.9 paraffins, is to insure the
C.sub.9 paraffins are converted during catalytic reforming. The
catalytic reforming is generally carried out with pressures of from
about 700 to 2750 KPa and at weight hourly space velocities of 0.5
to 10 and hydrogen to feed molar ratios from about 2 to 15.
The effluent from the catalyst reforming of the C.sub.7+ fraction
is then separated into a C.sub.8- effluent and a C.sub.9+ effluent.
Then the C.sub.5+ effluent from the catalytic dehydrocyclization
unit and the C.sub.8- effluent from the catalytic reforming unit
are mixed and an aromatic extract and non-aromatic raffinate are
recovered. The resultant aromatic extract contains a high yield of
benzene which has been produced in an energy efficient manner. The
benzene yield thus achieved for the process of this invention is in
the range of 5 to 25% by volume of the C.sub.6+ hydrocarbons and 35
to 80% by volume of the C.sub.6 hydrocarbons in the full boiling
range hydrocarbon feed, which compares to a benzene yield in a
conventional reforming process as shown in FIG. 2, of about 2 to
10% by volume of C.sub.6+ hydrocarbons and 10 to 35% by volume of
the C.sub.6 hydrocarbons in the full boiling range hydrocarbon
feed. In general, for the same hydrocarbon feed, with the process
of this invention there will be an increase of the benzene yield of
about 1.5 to 3 times the benzene yield of a conventional reforming
process as shown in FIG. 2.
The aromatic extract and non-aromatic raffinate are efficiently
recovered in an aromatics recovery unit, i.e. a solvent extraction
process which uses a solvent selective for aromatics such as
sulfolane or tetraethylene glycol. The C.sub.8- effluent is
preferably further separated into a C.sub.6- effluent and a C.sub.8
effluent, with the C.sub.6- and C.sub.8 effluent being mixed with a
C.sub.5+ effluent from the catalytic aromatization unit for
subsequent recovery of an aromatics extract in the solvent
extraction unit. In this way the effluent containing the C.sub.7
hydrocarbons (mostly toluene) and the effluent containing C.sub.9+
hydrocarbons are not processed in the solvent extraction process
which increases the efficient use of the solvent extraction process
to recover the more valuable aromatics of benzene, xylenes and
ethylbenzene. The separation of the effluent from the catalytic
reforming unit can be efficiently carried out by first
fractionating the effluent, as shown in FIG. 1, into a C.sub.6-
effluent, a C.sub.7 effluent and a C.sub.8+ effluent, then
fractionating the C.sub.8+ effluent into a C.sub.8 effluent and a
C.sub.9+ effluent.
The non-aromatic raffinate recovered from the solvent extraction
process may be recycled and added to the C.sub.6 fraction feed for
catalytic dehydrocyclization which increases the benzene yield of
the process.
EXAMPLE 1
This example shall be described with reference to the flow diagram
of FIG. 1 and the various hydrocarbon streams and units identified
therein. A full boiling range naptha feedstream, comprising a range
of hydrocarbons from C.sub.3 to those boiling up to about
350.degree. F. and containing 51.2% paraffins, 36% naphthenes and
12.8% aromatics is fed into distillation tower 1 to separate a
C.sub.5- fraction from a C.sub.6+ fraction. The resultant C.sub.6+
fraction contains 0.7% of C.sub.5 hydrocarbons 5.4% C.sub.10+
hydrocarbons, 17.9% C.sub.6 hydrocarbons and 76% C.sub.7 to C.sub.9
hydrocarbons while the C.sub.5- fraction contains 6% C.sub.6
hydrocarbons and the remainder C.sub.5- hydrocarbons (all % by
volume). The tower 1 utilizes 0.15 MBTU per barrel of feed.
The C.sub.6+ fraction from distillation tower 1 is then fed into
distillation tower 2 to separate a C.sub.6 fraction which contains
at least 10% C.sub.7+ hydrocarbons from a .[.C.sub.730.]. C.sub.7 +
fraction. The resultant C.sub.6 fraction contains .Badd.3.2%
C.sub.5 hydrocarbons, 72.7% C.sub.6 hydrocarbons and 24.1% C.sub.7+
hydrocarbons, with the C.sub.7+ fraction containing 1.5% C.sub.6
hydrocarbons, 91.9% C.sub.7 to C.sub.9 hydrocarbons and 6.6%
C.sub.10+ hydrocarbons (all % by volume). The tower 2 energy usage
was 0.36 MBTU/barrel of feed. To decrease the C.sub.7+ content in
the C.sub.6 fraction to 5% would require an energy usage of 0.46
MBTU/barrel of feed.
The C.sub.6 fraction is fed into the aromatizer reactor 3 which
contains a K Zeolite L catalyst containing 0.6% by weight of
platinum with the dehydrocyclization reaction taking place at a
temperature of 510.degree. C., a weight hourly space velocity of
2.5, a pressure of 860 KPa and a hydrogen to hydrocarbon mole ratio
of 6. The effluent from the aromatizer reactor 3 contains 32%
benzene, 12%, toluene (all % by volume). The effluents is then fed
into a flash drum 4 to separate a C.sub.5+ effluent with about 90%
of the benzene being recovered in the flash drum. The C.sub.4-
stream containing hydrogen from the flash drum 4 is then recycled
as needed to the aromatizer reactor 3 with excess used as make gas.
The C.sub.5+ effluent is then fed into a stabilizer 5 to further
purify and remove any C.sub.4- hydrocarbons.
The C.sub.7+ fraction is fed into a conventional reformer 6 which
contains a pt-Re gamma-alumina catalyst with the reforming reaction
taking place at temperatures of 919.degree. F. (493.degree. C.), a
weight hourly space velocity of 1.3, a pressure of 1413 KPa, a
recycle gas rate of 2.3 KSCF/Bbl with the unit operated to give an
octane of 103. The reformer effluent contains C.sub.5-
hydrocarbons, 1.8% benzene, 3.2% other C.sub.6 hydrocarbons
(excluding benzene), 12.3% toluene, 25.1% xylenes and 24% C.sub.9+
hydrocarbons (all % by volume of reformer feed). The reformer
effluent is then fed into a toluene rejection tower 7 from which a
C.sub.7 effluent containing 92% C.sub.7 hydrocarbon (mostly
toluene) is taken as a sidestream, a C.sub.6- effluent containing
14.1% C.sub.5- hydrocarbons, 11.8% benzene, 22.3% other C.sub.6
hydrocarbons (excluding benzene) and 51.8% C.sub.7 hydrocarbons is
taken overhead and a C.sub. 8+ effluent containing 3.6% C.sub.7,
49.5% C.sub.8 hydrocarbons (mostly xylenes) and 46.9% C.sub.9+
hydrocarbons (mostly aromatics) is taken from the bottom (all % by
volume). The .[.C.sub.830.]. C.sub.8 + effluent is then further
distilled in a C.sub.8 /C.sub.9 splitter tower 8 from which a
C.sub.8 effluent containing .Badd.96% C.sub.8 hydrocarbons and 4%
C.sub.9+ and a C.sub.9+ effluent containing 1% C.sub.8 hydrocarbons
and 99% C.sub.9+ hydrocarbons is recovered.
The C.sub.5+ effluent from the aromatizer and the C.sub.6- effluent
and C.sub.8 effluent from the reformer are then mixed and fed into
the extraction unit 9 which utilizes sulfolane to solvent extract
aromatics with the aromatics extract stream containing 30% benzene,
18% toluene and 51.8% C.sub.8 aromatics while the non-aromatic
raffinate stream contains 0.2% aromatics. The non-aromatic
raffinate stream is then advantageously feed back to tower 2 to
produce benzene. The resultant benzene yield is 12.9% by volume of
the C.sub.6+ hydrocarbons in the feedstream and 66% by volume of
the C.sub.6 hydrocarbons in the full boiling range naptha
feedstream.
EXAMPLE 2
This comparative example shall be described with reference to the
flow diagram of FIG. 2. The full boiling range naptha feedstream of
Example 1 is fed into distillation tower 10 to produce a C.sub.6+
fraction as in Example 1.
The C.sub.6+ fraction is fed into conventional reformer 11 which
contains a Pt-Re gamma-alumina catalyst with the reforming reaction
operated at a temperature of 920.degree. F. (493.degree. C.), a
weight hourly space velocity of 1.3, a pressure of 1400 KPa, a
recycle gas rate of 2.3 KSCF/B with the unit operated to give an
octane of 101. The resultant effluent contains 4% benzene, 11%
other C.sub.6 hydrocarbons, 11.6% toluene, 4.5% other C.sub.7
hydrocarbons, 20% C.sub.8 aromatics, 19% C.sub.9+ hydrocarbons and
balance being C.sub.5- hydrocarbons (all % by volume of feed).
The reformer effluent is fed into a C.sub.8 /C.sub.9 splitter tower
12 to separate the C.sub.8- effluent from the C.sub.9+ effluent.
The C.sub.8- effluent contains 2% C.sub.5 hydrocarbons, 28.6%
C.sub.6 hydrocarbons, 66.2% C.sub.7 hydrocarbons and 3.2% C.sub.9+
hydrocarbons and the C.sub.9+ effluent contains 1% C.sub.8 and the
balance C.sub.9+ hydrocarbons.
The C.sub.8- effluent is fed to a sulfolane extraction unit 13 from
which an aromatic extract containing 12.8% benzene, 31.3% toluene,
53.4% C.sub.8 aromatics, 2.3% C.sub.9+ aromatics and the balance
C.sub.9+ non-aromatics hydrocarbons. The resultant benzene yield is
5.2% by volume of the .[.C.sub.630.]. C.sub.6 + hydrocarbons in the
feedstream and .Badd.27.5% by volume of the C.sub.6 hydrocarbons in
the full boiling range naptha feedstream.
* * * * *