U.S. patent application number 12/845617 was filed with the patent office on 2012-02-02 for multi-stage reforming process with final stage catalyst regeneration.
This patent application is currently assigned to Chevron U.S.A. Inc.. Invention is credited to Cong-Yan Chen, Ann J. Liang, Stephen J. Miller, James N. Ziemer.
Application Number | 20120024754 12/845617 |
Document ID | / |
Family ID | 45525622 |
Filed Date | 2012-02-02 |
United States Patent
Application |
20120024754 |
Kind Code |
A1 |
Chen; Cong-Yan ; et
al. |
February 2, 2012 |
MULTI-STAGE REFORMING PROCESS WITH FINAL STAGE CATALYST
REGENERATION
Abstract
The present invention relates to a multistage reforming process
to produce a high octane product. A naphtha boiling range feedstock
is processed in a multi-stage reforming process, in which said
process involves at least 1) a penultimate stage for reforming the
naphtha feedstock to produce a penultimate effluent 2) a final
stage for further reforming at least a portion of the penultimate
effluent 3) a regeneration step for the final stage catalyst. The
severity of the penultimate stage can be increased during final
stage catalyst regeneration in order to maintain the target RON of
the reformate product and avoid reactor downtime.
Inventors: |
Chen; Cong-Yan; (Alameda,
CA) ; Miller; Stephen J.; (San Francisco, CA)
; Ziemer; James N.; (Martinez, CA) ; Liang; Ann
J.; (Walnut Creek, CA) |
Assignee: |
Chevron U.S.A. Inc.
|
Family ID: |
45525622 |
Appl. No.: |
12/845617 |
Filed: |
July 28, 2010 |
Current U.S.
Class: |
208/65 ;
208/64 |
Current CPC
Class: |
C10G 35/04 20130101;
C10G 2400/02 20130101; C10G 2300/1044 20130101; C10G 59/02
20130101; C10G 35/085 20130101; C10G 35/095 20130101; C10G 35/09
20130101; C10G 2300/305 20130101; C10G 35/065 20130101 |
Class at
Publication: |
208/65 ;
208/64 |
International
Class: |
C10G 59/02 20060101
C10G059/02 |
Claims
1. A reforming process comprising: a. providing a naphtha to a
multi-stage reforming system that includes a penultimate reforming
stage containing a first reforming catalyst and a final reforming
stage containing a second reforming catalyst; b. contacting the
naphtha at a first reforming temperature with the first reforming
catalyst and producing a penultimate effluent; c. contacting at
least a portion of the penultimate effluent at a second reforming
temperature with the second reforming catalyst and producing a
final reformate having an RON of greater than 90; and d.
regenerating the second reforming catalyst in the final reforming
stage while reforming the naphtha in the penultimate reforming
stage and producing a third reformate from the penultimate
reforming stage that has an RON of at least 90.
2. The process of claim 1, wherein step (b) comprises contacting
the naphtha at a first reforming temperature in the range of from
800.degree. F. to 1100.degree. F. (427.degree. C. to 593.degree.
C.).
3. The process of claim 1, wherein step (b) comprises contacting
the naphtha at a first reforming pressure in the range of from 200
psig (1380 kPa) to 400 psig (2760 kPa).
4. The process of claim 1, wherein step (b) comprises contacting
the naphtha with the first reforming catalyst, which comprises
platinum and rhenium on an alumina support.
5. The process of claim 1, wherein step (c) comprises contacting at
least a portion of the penultimate effluent at a second reforming
temperature in the range of from 800.degree. F. to 1100.degree. F.
(427.degree. C. to 593.degree. C.).
6. The process of claim 1, wherein step (c) comprises contacting at
least a portion of the penultimate effluent at a second reforming
pressure in the range of from 40 psig (276 kPa) to 200 psig (1480
kPa).
7. The process of claim 1, wherein step (c) comprising contacting
at least a portion of the penultimate effluent with the second
reforming catalyst comprising silicalite having a silica to alumina
molar ratio of at least 200, a crystallite size of less than 10
microns and an alkali content of less than 5,000 ppm.
8. The process of claim 7, wherein step (c) comprises contacting at
least a portion of the penultimate effluent with the second
reforming catalyst comprising iridium, platinum, palladium or a
combination thereof.
9. The process of claim 1, wherein step (a) comprises providing the
naphtha having an RON of less than 75.
10. The process of claim 1, wherein step (c) further comprises: a.
isolating an intermediate reformate from the penultimate effluent,
the intermediate reformate having an RON within the range of 75 to
90; and b. contacting the intermediate reformate at the second
reforming temperature with the second reforming catalyst and
producing the final reformate having an RON of greater than 90.
11. The process of claim 1, wherein step (c) comprises producing a
final reformate having an RON of at least 95.
12. The process of claim 1, wherein step (d) comprises producing a
third reformate having an RON of at least 95.
13. The process of claim 1, wherein step (d) comprises reforming
the naphtha in the penultimate reforming stage at a temperature
that is at least 5.degree. F. higher than the first reforming
temperature.
14. The process of claim 1, wherein regenerating the second
reforming catalyst in step (d) comprises: a. ceasing the flow of
intermediate reformate to the final reforming stage; b. increasing
the reforming temperature in the penultimate reforming stage by at
least 5.degree. F. (2.8.degree. C.) to produce a third reformate
having an RON of at least 90; and c. regenerating the second
reforming catalyst in the final reforming stage.
15. The process of claim 14, wherein regenerating the second
reforming catalyst in step (d) comprises: a. passing a nitrogen
containing stream through the second reforming stage to remove at
least a portion of the naphtha contained therein; b. passing an
oxygen containing stream through the final reforming stage to
remove at least a portion of the carbon deposited on the second
reforming catalyst contained within the final reforming stage; c.
passing a nitrogen containing stream through the second reforming
catalyst to remove at least a portion of the oxygen contained
therein; d. reducing the temperature of the second reforming
catalyst within the final reforming stage to a temperature of less
than the second reforming temperature; e. introducing at least a
portion of the penultimate effluent to the final reforming stage;
and f. increasing the temperature of the second reforming catalyst
to a temperature in the range of 800.degree. F. to 1100.degree. F.
(427.degree. C.-593.degree. C.).
16. The process of claim 15, further comprising: h. reducing the
reforming temperature in the penultimate reforming stage by at
least 5.degree. F. (2.8.degree. C.).
Description
RELATED APPLICATION
[0001] This application claims priority to U.S. patent application
Ser. No. 12/134,153, filed Jun. 5, 2008. This application claims
priority to and benefits from the foregoing, the disclosure of
which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a multistage reforming
process with minimized down time during final stage catalyst
regeneration. The process uses a medium pore molecular sieve
catalyst in the final stage to enable fast regeneration without a
halogenation step.
BACKGROUND OF THE INVENTION
[0003] Catalytic reforming is one of the basic petroleum refining
processes for upgrading light hydrocarbon feedstocks, frequently
referred to as naphtha feedstocks. Products from catalytic
reforming can include high octane gasoline useful as automobile
fuel, aromatics (for example benzene, toluene, xylenes and
ethylbenzene), and/or hydrogen. Reactions typically involved in
catalytic reforming include dehydrocylization, isomerization and
dehydrogenation of naphtha range hydrocarbons, with
dehydrocyclization and dehydrogenation of linear and slightly
branched alkanes and dehydrogenation of cycloparaffins leading to
the production of aromatics. Dealkylation and hydrocracking are
generally undesirable due to the low value of the resulting light
hydrocarbon products.
[0004] Catalysts commonly used in commercial reforming reactions
often include a Group VIII metal, such as platinum or palladium, or
a Group VIII metal plus a second catalytic metal, which acts as a
promoter. Examples of metals useful as promoters include rhenium,
tin, tungsten, germanium, cobalt, nickel, rhodium, ruthenium,
iridium or combinations thereof. The catalytic metal or metals may
be dispersed on a support such as alumina, silica, or
silica-alumina. Typically, a halogen such as chlorine is
incorporated on the support to add acid functionality. In addition
to Group VIII metals, other reforming catalysts include
aluminosilicate zeolite catalysts. For example, U.S. Pat. Nos.
3,761,389, 3,756,942 and 3,760,024 teach aromatization of a
hydrocarbon fraction with a ZSM-5 type zeolite catalyst. U.S. Pat.
No. 4,927,525 discloses catalytic reforming processes with beta
zeolite catalysts containing a noble metal and an alkali metal.
Other reforming catalysts include other molecular sieves such as
borosilicates and silicoaluminophosphates, layered crystalline
clay-type phyllosilicates, and amorphous clays.
[0005] In addition to selection of catalysts for reforming, various
processes for reforming a naphtha feedstock in one or more process
steps to produce higher value reformate products are known in the
art. U.S. Pat. No. 3,415,737 teaches a process for reforming
naphtha under conventional mild reforming conditions with a
platinum-rhenium-chloride reforming catalyst to increase the
aromatics content and octane number of the naphtha. In U.S. Pat.
No. 3,770,614 there is disclosed a process in which a reformate is
fractionated and the light reformate fraction (C6 fraction) passed
over a ZSM-5-type zeolite to increase aromatic content of the
product. U.S. Pat. No. 3,950,241 discloses a process for upgrading
naphtha by separating it into low- and high-boiling fractions,
reforming the low-boiling fraction, combining the high-boiling
naphtha with the reformate, and contacting the combined fractions
with a ZSM-5-type catalyst. U.S. Pat. No. 4,181,599 discloses a
process for reforming naphtha comprising separating the naphtha
into heavy and light fractions and reforming and isomerizing the
naphtha fractions. U.S. Pat. No. 4,190,519 teaches a process for
upgrading a naphtha-boiling-range hydrocarbon which comprises
separating the naphtha feedstock into a light naphtha fraction
containing C6 paraffins and lower-boiling hydrocarbons and a heavy
naphtha fraction containing higher-boiling hydrocarbons, reforming
the heavy naphtha fraction and passing at least a portion of the
reformate together with the light naphtha fraction over a zeolite
catalyst to produce an aromatics-enriched effluent. Different
catalysts may be employed in different process steps during the
reforming of naphtha feedstocks as described in U.S. Pat. No.
4,627,909, U.S. Pat. No. 4,443,326, U.S. Pat. No. 4,764,267, U.S.
Pat. No. 5,073,250, U.S. Pat. No. 5,169,813, U.S. Pat. No.
5,171,691, U.S. Pat. No. 5,182,012, U.S. Pat. No. 5,358,631, U.S.
Pat. No. 5,376,259 and U.S. Pat. No. 5,407,558, for example.
[0006] Even with the advances in naphtha reforming catalysts and
processes, a need still exists to develop new and improved
reforming methods to provide higher liquid yield, improve hydrogen
production, and minimize the formation of less valuable low
molecule weight (C.sub.1-C.sub.4) products. It has been discovered
that interstage feed separation in a staged reforming process and
lower pressure in the final stage of a multistage reforming process
can improve the RON (Research Octane Number), aromatics content,
C.sub.5+ liquid yield, hydrogen production, and catalyst life.
SUMMARY OF THE INVENTION
[0007] The present invention is based on the discovery that in a
multi-stage reforming process, the yield of hydrocarbon product and
hydrogen can be optimized by increasing the severity of the
penultimate stage during regeneration of the final stage catalyst.
During regeneration of the final stage catalyst, the RON of the
effluent from the penultimate stage can meet the target RON of the
hydrocarbon product by temporarily increasing the severity of the
penultimate stage reaction conditions. Due to fast regeneration
times of the final stage catalyst, the lifetime of the penultimate
stage catalyst is minimally affected by the increased reaction
severity.
[0008] The present invention relates to processes for catalytically
reforming a naphtha feed to produce a product reformate in a
multistage reforming operation. The reforming process includes
providing a naphtha to a multi-stage reforming system that includes
a penultimate reforming stage containing a first reforming catalyst
and a final reforming stage containing a second reforming catalyst;
contacting the naphtha at a first reforming temperature with the
first reforming catalyst and producing a penultimate effluent;
contacting at least a portion of the penultimate effluent at a
second reforming temperature with the second reforming catalyst and
producing a final reformate having an RON of greater than 90; and
regenerating the second reforming catalyst in the final reforming
stage while reforming the naphtha in the penultimate reforming
stage and producing a third reformate from the penultimate
reforming stage that has an RON of at least 90.
[0009] In embodiments, the first reforming catalyst includes
platinum and rhenium on an alumina support. In embodiments, the
second reforming catalyst includes silicalite having a silica to
alumina molar ratio of at least 200, a crystallite size of less
than 10 microns and an alkali content of less than 5,000 ppm.
[0010] In embodiments, the step of regenerating the second
reforming catalyst includes ceasing the flow of intermediate
reformate to the final reforming stage; increasing the reforming
temperature in the penultimate reforming stage by at least
5.degree. F. (2.8.degree. C.) to produce a third reformate having
an RON of at least 90; and regenerating the second reforming
catalyst in the final reforming stage. In further embodiments, the
step of regenerating the second reforming catalyst includes passing
a nitrogen containing stream through the second reforming stage to
remove at least a portion of the naphtha container therein; passing
an oxygen containing stream through the final reforming stage to
remove at least a portion of the carbon deposited on the second
reforming catalyst contained within the final reforming stage;
passing a nitrogen containing stream through the second reforming
catalyst to remove at least a portion of the oxygen contained
therein; reducing the temperature of the second reforming catalyst
within the final reforming stage to a temperature of less than the
second reforming temperature; introducing at least a portion of the
penultimate effluent to the final reforming stage; and increasing
the temperature of the second reforming catalyst to a temperature
in the range of 800.degree. F. to 1100.degree. F. (427.degree.
C.-593.degree. C.). In further embodiments, the step of
regenerating the second reforming catalyst includes reducing the
reforming temperature in the penultimate reforming stage by at
least 5.degree. F. (2.8.degree. C.).
[0011] Other aspects, features and advantages will be apparent from
the description of the embodiments thereof and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic diagram of one embodiment of the
invention.
[0013] FIG. 2 is a schematic diagram of a second embodiment of the
invention.
DETAILED DESCRIPTION
[0014] In the present process, a naphtha boiling range feedstock is
processed in a multi-stage reforming process, in which said process
involves at least a penultimate stage for reforming the naphtha
feedstock to produce a penultimate effluent and a final stage for
further reforming a portion of the penultimate effluent. The
reforming process is operated at conditions and with catalysts
selected for conducting dehydrocyclization, isomerization and
dehydrogenation reactions of paraffins thus converting low octane
normal paraffins and cycloparaffins into high octane materials. In
this way, a product having increased octane and/or containing an
increased amount of aromatics is produced. In preferred
embodiments, the multi-stage reforming process is operated at
conditions and with one or more catalysts for producing a net
positive quantity of hydrogen. It is a further object of the
invention to provide for a regeneration step during which the final
stage catalyst is regenerated while reformate product of a target
RON is produced by temporarily increasing the severity of the
penultimate stage such that the effluent of the penultimate stage
comprises reformate of the target RON.
[0015] The multi-stage reforming process of the invention comprises
passing a refinery stream through at least two reforming stages in
series. In general, each reforming stage is characterized by one or
more reforming reactor vessels, each containing a catalyst and
maintained at reforming reaction conditions. The product from each
stage before the final stage is passed, at least in part, to the
succeeding stage in the multi-stage process. The temperature of the
product from each stage which is passed to a succeeding stage may
be increased or decreased to meet the particular needs of the
process. Likewise, the pressure of the product which is passed to a
succeeding stage before the final stage may be increased or
decreased. Preferably the final stage is run at a lower pressure
than the penultimate stage.
[0016] The present invention is based in part on the discovery that
selective reforming of C5-C8 paraffins in a separate or additional
reforming stage provides improved performance of the overall
reforming process. Thus, a penultimate reforming stage using a
conventional reforming catalyst is operated at relatively low
severity, since it is not required to reach the high octane levels
normally desired for a naphtha fuel or fuel blend stock. While not
being bound to any theory, we believe that under these conditions
the reforming catalyst of the penultimate stage catalyzes the more
facile reactions, such as cyclohexane and alkycyclohexane
dehydrogenation, while keeping hydrocracking to a minimum.
Generally, a conventional catalyst used to dehydrocyclize paraffins
under more severe conditions produces higher quantities of light
C1-C4 gases, on account of the catalyst being somewhat unselective
for dehydrocyclization. With the present invention, however, an
intermediate reformate comprising at least 70 vol. % C5-C8
hydrocarbons from a penultimate reforming stage is passed to a
final reforming stage containing the same or a different reforming
catalyst as the penultimate stage. The C9+ fraction from the
penultimate stage has higher octane than the C5-C8 fraction, and is
not further reformed in the final stage, thus preventing any
unwanted dealkyation or cracking of the C9+ hydrocarbons. In a
preferred embodiment the final stage is run at a lower pressure
than the penultimate stage. We believe that running the final stage
at a lower pressure than the penultimate stage leads to
improvements including one or more of the following
characteristics--1) increased yield of C5+ liquid products, 2)
minimized unwanted hydrocracking/dealkylation reactions, and 3)
increased hydrogen production. Lower pressure of the final stage
can, in some cases, lead to higher catalyst fouling rates depending
on the type of catalyst used; however, in situ catalyst
regeneration of the final stage catalyst can be used to maintain
catalyst activity. While the final stage catalyst is being
regenerated, the severity of the penultimate stage can be
temporarily increased to meet octane targets for the total blended
reformate which would otherwise be achieved with both the
penultimate and final stages operating. Consequently, the
performance characteristics of the penultimate and final stage
reactors provide complementary benefits, resulting in an overall
process which produces a high octane product at an improved C5+
liquid yield and improved hydrogen production.
[0017] While the discussion which follows relates at times, for
convenience, to operation of penultimate and final reforming
stages, the principles of the invention are applicable as between
any two successive stages and can be applied to several
sequentially connected stages. In essence then, the term final
stage as used herein does not necessarily indicate the last stage
if there are three or more stages, but rather indicates a
succeeding stage which follows a preceding (often referred to for
convenience as "penultimate") stage.
[0018] As disclosed herein, boiling point temperatures are based on
ASTM D-2887 standard test method for boiling range distribution of
petroleum fractions by gas chromatography, unless otherwise
indicated. The mid-boiling point is defined as the 50% by volume
boiling temperature, based on an ASTM D-2887 simulated
distillation.
[0019] As disclosed herein, carbon number values (i.e. C.sub.5,
C.sub.6, C.sub.8, C.sub.9 and the like) of hydrocarbons may be
determined by standard gas chromatography methods.
[0020] As disclosed herein, Research Octane Number (RON) is
determined using the method described in ASTM D2699.
[0021] Unless otherwise specified, as used herein, feed rate to a
catalytic reaction zone is reported as the volume of feed per
volume of catalyst per hour. The feed rate as disclosed herein is
reported in reciprocal hours (i.e. hr-1) which is also referred to
as liquid hourly space velocity (LHSV).
[0022] As used herein, a C.sub.4- stream comprises a high
proportion of hydrocarbons with 4 or fewer carbon atoms per
molecule. Likewise, a C.sub.5+ stream comprises a high proportion
of hydrocarbons with 5 or more carbon atoms per molecule. It will
be recognized by those of skill in the art that hydrocarbon streams
in refinery processes are generally separated by boiling range
using a distillation process. As such, the C.sub.4- stream would be
expected to contain a small quantity of C.sub.5, C.sub.6 and even
C.sub.7 molecules. However, a typical distillation would be
designed and operated such that at least about 70% by volume of a
C.sub.4- stream would contain molecules having 4 carbon atoms or
fewer per molecule. Thus, at least about 70 vol % of a C.sub.4-
stream boils in the C.sub.4- boiling range. As used herein,
C.sub.5+, C.sub.6-C.sub.8, C.sub.9+ and other hydrocarbon fractions
identified by carbon number ranges would be interpreted likewise.
In embodiments, the naphtha that is provided to the multi-stage
reforming system has an RON of less than 80 or less than 75.
[0023] As used herein, the multi-stage reforming system includes at
least two reaction stages, a first (i.e. penultimate) containing a
first reforming catalyst and a second (i.e. final) containing a
second reforming catalyst. Included in the reforming system are the
necessary heaters and furnaces, valves, piping and associated
hardware, and fractionation zones that are necessary for successful
operation of the reforming system.
[0024] The term "silica to alumina ratio" refers to the molar ratio
of silicon oxide (SiO2) to aluminum oxide (Al.sub.2O.sub.3).
[0025] As used herein the term "molecular sieve" refers to a
crystalline material containing pores, cavities, or interstitial
spaces of a uniform size in which molecules small enough to pass
through the pores, cavities, or interstitial spaces are adsorbed
while larger molecules are not. Examples of molecular sieves
include zeolites and non-zeolitic molecular sieves such as zeolite
analogs including, but not limited to, SAPOs
(silicoaluminophosphates), MeAPOs (metalloaluminophosphates),
AlPO4, and ELAPOs (nonmetal substituted aluminophosphate
families).
[0026] When used in this disclosure, the Periodic Table of the
Elements referred to is the CAS version published by the Chemical
Abstract Service in the Handbook of Chemistry and Physics, 72nd
edition (1991-1992).
[0027] As used herein, naphtha is a distillate hydrocarbonaceous
fraction boiling within the range of from 50.degree. (10.degree.
C.) to 550.degree. F. (288.degree. C.). In some embodiments,
naphtha boils within the range of 70.degree. (21.degree. C.) to
450.degree. F. (232.degree. C.) or within the range of 80.degree.
(27.degree. C.) to 400.degree. F. (204.degree. C.) or even within
the range of 90.degree. (32.degree. C.) to 360.degree. F.
(182.degree. C.). In some embodiments, at least 85 vol % of naphtha
boils within the range of from 50.degree. (10.degree. C.) to
550.degree. F. (288.degree. C.) or within the range of from
70.degree. (21.degree. C.) to 450.degree. F. (232.degree. C.). In
embodiments, at least 85 vol % of naphtha is in the C4-C12 range,
or in the C5-C11 range, or in the C6-C10 range. Naphtha can
include, for example, straight run naphthas, paraffinic raffinates
from aromatic extraction or adsorption, C6-C10 paraffin-rich feeds,
bioderived naphtha, naphtha from hydrocarbon synthesis processes,
including Fischer Tropsch and methanol synthesis processes, as well
as naphtha from other refinery processes, such as hydrocracking or
conventional reforming.
[0028] The reforming catalyst used in the penultimate reforming
stage may be any catalyst known to have catalytic reforming
activity. In one embodiment, the penultimate stage catalyst
comprises a Group VIII metal disposed on an oxide support. Examples
of Group VIII metals include platinum and palladium. The catalyst
may further comprise a promoter, such as rhenium, tin, tungsten,
germanium, cobalt, nickel, iridium, rhodium, ruthenium, or
combinations thereof. In some such embodiments, the promoter metal
is rhenium or tin.
[0029] The above mentioned metals can be disposed on a support
comprising one or more of (1) a refractory inorganic oxide such as
alumina, silica, titania, magnesia, zirconia, chromia, thoria,
boria or mixtures thereof; (2) a synthetically prepared or
naturally occurring clay or silicate, which may be acid-treated;
(3) a crystalline zeolitic aluminosilicate, either naturally
occurring or synthetically prepared such as FAU, MEL, MFI, MOR, MTW
(IUPAC Commission on Zeolite Nomenclature), in hydrogen form or in
a form which has been exchanged with metal cations; (4) a spinel
such as MgAl.sub.2O.sub.4, FeAl.sub.2O.sub.4, ZnAl.sub.2O.sub.4,
CaAl.sub.2O.sub.4; (5) a silicoaluminophosphate; and (6)
combinations of materials from one or more of these groups. The
refractory support of the reforming catalyst preferably comprises
an inorganic oxide, more preferably alumina. In embodiments, the
reforming catalyst used in the penultimate reforming stage includes
platinum on an alumina-containing support.
[0030] Halogen may be incorporated into the catalyst by combining
it with a source of halogen such as alkali or alkaline earth
chlorides, fluorides, iodides or bromides. Other halogen sources
include compounds such as hydrogen halide, e.g., hydrogen chloride,
and ammonium halides, e.g., ammonium chloride. The preferred
halogen source is a source of chlorine. The amount of halogen
source combined with the catalyst should be such that the catalyst
contains from about 0.1 to 3 wt % halogen, more preferably from
about 0.2 to about 1.5 wt % halogen, and most preferably between
0.5 to 1.5 wt % halogen.
[0031] The catalyst, if it includes a promoter metal, suitably
includes sufficient promoter metal to provide a promoter to
platinum ratio between 0.5:1 and 10:1, more preferably between 1:1
and 6:1, most preferably between 2:1 and 5:1. The precise
conditions, compounds, and procedures for catalyst manufacture are
known to those persons skilled in the art. Some examples of
conventional catalysts are shown in U.S. Pat. Nos. 3,631,216;
3,415,737; and 4,511,746, which are hereby incorporated by
reference in their entireties.
[0032] The reforming catalyst in the penultimate stage and final
stage may be employed in the form of pills, pellets, granules,
broken fragments, or various special shapes, disposed as a fixed
bed within a reaction zone, and the charging stock may be passed
through in the liquid, vapor, or mixed phase, and in either upward,
downward or radial flow. Alternatively, the reforming catalysts can
be used in moving beds or in fluidized-solid processes, in which
the charging stock is passed upward through a turbulent bed of
finely divided catalyst. However, a fixed bed system or a
dense-phase moving bed system are preferred due to less catalyst
attrition and other operational advantages. In a fixed bed system,
the feed is preheated (by any suitable heating means) to the
desired reaction temperature and then passed into a reaction zone
containing a fixed bed of the catalyst. This reaction zone may be
one or more separate reactors with suitable means to maintain the
desired temperature at the reactor entrance. The temperature must
be maintained because reforming reactions are typically endothermic
in nature.
[0033] The actual reforming conditions in the penultimate stage
will depend, at least in part, on the feed used, whether highly
aromatic, paraffinic or naphthenic and upon the desired octane
rating of the product and the desired hydrogen production.
[0034] The penultimate stage is maintained at relatively mild
reaction conditions, so as to inhibit the cracking of the stream
being upgraded, and to increase the useful lifetime of the catalyst
in the penultimate stage. The naphtha boiling range feedstock to be
upgraded in the penultimate stage contacts the penultimate stage
catalyst at reaction conditions, which conditions include a
temperature in the range from about 800.degree. F. (427.degree. C.)
to about 1100.degree. F. (593.degree. C.), a pressure in the range
from about 70 psig (482 kPa) to about 400 psig (2760 kPa), and a
feed rate in the range of from about 0.5 LHSV to about 5 LHSV. In
some embodiments, the pressure in the penultimate stage is in the
range from about 200 psig (1380 kPa) to about 400 psig (2760
kPa).
[0035] The effluent from the penultimate stage is an upgraded
product, in that the RON has been increased during reaction in the
penultimate stage as compared to the RON of the naphtha feedstock.
The penultimate stage effluent comprises hydrocarbons and hydrogen
generated during reaction in the penultimate stage and at least
some of the hydrogen, if any, which is added to the feed upstream
of the penultimate stage. The effluent hydrocarbons may be
characterized as a mixture of C4- hydrocarbons and C5+
hydrocarbons, the distinction relating to the molecular weight of
the hydrocarbons in each group. In embodiments, the C5+
hydrocarbons in the effluent have a combined RON of at least
85.
[0036] The effluent from the penultimate stage (otherwise termed
the "penultimate effluent") comprises C5+ hydrocarbons which are
separated into at least an intermediate reformate and a heavy
reformate. The effluent further comprises hydrogen and C4-
hydrocarbons. In some embodiments, a hydrogen-rich stream is
separated from the effluent in a preliminary separation step,
using, for example, a high pressure separator or other flash zone.
C.sub.4- hydrocarbons in the effluent may also be separated in a
preliminary separation, either along with the hydrogen or in a
subsequent flash zone. The intermediate reformate is characterized
as having a lower mid-boiling point than that of the heavy
reformate. In some embodiments, the intermediate reformate boils in
the range from about 70.degree. F. (21.degree. C.) to about
280.degree. F. (138.degree. C.). In some such embodiments, the
intermediate reformate comprises at least 70 vol % C5-C8
hydrocarbons. In some embodiments, the intermediate reformate boils
in the range from about 100.degree. F. (38.degree. C.) to about
280.degree. F. (138.degree. C.). In some such embodiments, the
intermediate reformate comprises at least 70 vol % C6-C8
hydrocarbons. In some embodiments, the intermediate reformate boils
in the range from about 100.degree. F. (38.degree. C.) to about
230.degree. F. (110.degree. C.). In some such embodiments, the
intermediate reformate comprises at least 70 vol % C.sub.6-C.sub.7
hydrocarbons. Recovery of an intermediate reformate fraction may be
accompanied by the further recovery of a largely C5 light reformate
fraction. The light reformate is characterized as having a lower
mid-boiling point than that of the intermediate reformate. In some
embodiments, the light reformate fraction boils in the range from
about 70.degree. F. (21.degree. C.) to about 140.degree. F.
(60.degree. C.). In some such embodiments, the light reformate
fraction comprises at least 70 vol % C5 hydrocarbons. The heavy
reformate that is produced during separation of the upgraded
product boils in the range of about 220.degree. F. (14.degree. C.)
and higher. In some such embodiments, the heavy reformate comprises
at least 70 vol % C9+ hydrocarbons.
[0037] The RON of the intermediate reformate is indicative of the
mild reforming conditions in the penultimate stage. As such, the
intermediate reformate typically has an RON within the range of
about 65 to 90. In one embodiment the intermediate reformate has a
RON of 70 to 90. In a further embodiment the intermediate reformate
has an RON within the range of 70 to 85.
[0038] The reforming catalyst used in the final stage may be any
catalyst known to have catalytic reforming activity. Catalysts
described above for the penultimate stage can be used in the final
stage. Examples of catalysts useful in the final stage include: (1)
molecular sieves such as zeolites, borosilicates, and
silicoaluminophosphates; (2) amorphous Group VIII metal catalysts
with an optional promoter metal selected from the group consisting
of a non-platinum Group VIII metal, e.g. rhenium, germanium, tin,
lead, gallium, indium, and mixtures thereof; and (3) additional
catalysts comprising acid catalysts and clays. The final stage
catalyst may include a single catalyst or a mixture of more than
one of the above catalysts. In an embodiment the final stage
catalyst comprises a zeolite and a group VIII metal. In another
embodiment the final stage catalyst is a platinum rhenium catalyst
supported on alumina.
[0039] Molecular sieves particularly useful in the practice of the
present invention include zeolites, zeolite analogs, and
nonzeolitic molecular sieves. By "zeolite analog" it is meant that
a portion of the silicon and/or aluminum atoms in the zeolite are
replaced with other tetrahedrally coordinated atoms such as
germanium, boron, titanium, phosphorus, gallium, zinc, iron, or
mixtures thereof. The term "nonzeolitic molecular sieve" as used
herein refers to molecular sieves whose frameworks are not formed
of substantially only silicon and aluminum atoms in tetrahedral
coordination with oxygen atoms. Zeolites, zeolite analogs, and
nonzeolitic molecular sieves can be broadly described as
crystalline microporous molecular sieves that possess
three-dimensional frameworks composed of tetrahedral units (TO4/2,
T=Si, Al, or other tetrahedrally coordinated atom) linked through
oxygen atoms. Depending on the identity of the T atoms in the
zeolite, zeolite analog, or nonzeolitic molecular sieve the
properties of the material are affected. For example, the presence
of aluminum in a zeolite introduces a negative charge in the
zeolite framework and affects the acidity and activity of the
zeolite as a reforming catalyst. The Si/Al ratio in zeolites can
vary from about 1 to infinity. The lower limit arises from the
avoidance of neighboring tetrahedral units with negative charges
(Al--O--Al). It is generally accepted that the linking of two
AlO.sub.4 tetrahedra is energetically unfavorable enough to
preclude such occurrences. Negative charges in a zeolite, zeolite
analog, or nonzeolitic molecular sieve framework are compensated by
extraframework cations such as protons and alkali cations. The
properties of zeolites, zeolite analog, or nonzeolitic molecular
sieve can be altered through exchange of these extraframework
cations with other positively charged species. The type of cations
present in the zeolite, zeolite analog, or nonzeolitic molecular
sieve framework help determine the acidity of the molecular
sieve.
[0040] Strong acidity in the molecular sieve can be undesirable for
catalytic reforming because it promotes cracking, resulting in
lower selectivity. To reduce acidity, the molecular sieve
preferably contains an alkali metal and/or an alkaline earth metal.
The alkali or alkaline earth metals are preferably incorporated
into the catalyst during or after synthesis of the molecular sieve.
Preferably, at least 90% of the acid sites are neutralized by
introduction of the metals, more preferably at least 95%, most
preferably at least 99%. In one embodiment, the intermediate pore
molecular sieve has less than 5,000 ppm alkali. Such intermediate
pore silicate molecular sieves are disclosed, for example, in U.S.
Pat. No. 4,061,724 and in U.S. Pat. No. 5,182,012. These patents
are incorporated herein by reference, particularly with respect to
the description, preparation and analysis of silicates having a
specified silica to alumina molar ratio, having a specified
crystallite size, having a specified crystallinity, and having a
specified alkali content.
[0041] Prior art techniques have resulted in the formation of a
great variety of synthetic zeolites. Many of the zeolites have come
to be designated by letter or other convenient symbol, as
illustrated by zeolite Z (U.S. Pat. No. 2,882,243); zeolite X (U.S.
Pat. No. 2,882,244); zeolite Y (U.S. Pat. No. 3,130,007); zeolite
ZK-5 (U.S. Pat. No. 3,247,195); zeolite ZK-4 (U.S. Pat. No.
3,314,752); zeolite ZSM-5 (U.S. Pat. No. 3,702,886); zeolite ZSM-11
(U.S. Pat. No. 3,709,979); zeolite ZSM-12 (U.S. Pat. No.
3,832,449); zeolite ZSM-20 (U.S. Pat. No. 3,972,983); zeolite
ZSM-35 (U.S. Pat. No. 4,016,245); and zeolite ZSM-23 (U.S. Pat. No.
4,076,842). Zeolite Beta is described in U.S. Pat. No. 3,308,069
and RE 28,341 both to Wadlinger, and reference is made to these
patents for a general description of zeolite Beta. The zeolite Beta
of Wadlinger is described as having a silica-to-alumina ratio going
from 10 to 100 and possibly as high as 150. Highly silicious
zeolite Beta described as having silica-to-alumina ratios within
the range of 20-1000 is disclosed in Valyocsik et al, U.S. Pat. No.
4,923,690.
[0042] In addition to cation-exchange, the catalytic properties of
the zeolitic molecular sieve can be altered by isomorphous
substitution of at least some of the tetrahedral atoms to make
zeolite analogs or nonzeolitic molecular sieves wherein a portion
or all of the silicon or aluminum atoms of the zeolite framework
are replaced with, for example, germanium, titanium, boron,
phosphorus, gallium, iron, or zinc. The use of these different
elements in zeolite synthesis has often led to materials with novel
topologies or to materials with properties that are very different
from their aluminosilicate (zeolite) counterparts which have
equivalent framework topologies. For example, the aluminosilicate
zeolite RHO cannot currently be synthesized with a Si/Al ratio much
below 3. However, the aluminogermanate and gallosilicate analogues
of zeolite RHO can be made with a Ge/Al ratio and a Si/Ga ratio of
1.0 and 1.3 respectively. The cation-exchange capacities of these
RHO materials are therefore very different. Aluminophosphate and
gallophosphate analogues of zeolites are other example of molecular
sieves based on replacement of silicon with other atoms. These
materials are usually composed of strictly alternating AlO.sub.4
(or GaO.sub.4) and PO4 tetrahedral units, but they can be altered
by isomorphous substitution of silicon, magnesium, beryllium, or
transition metal ions.
[0043] Molecular sieves have uniformly sized pores (3 to 10 .ANG.)
which are determined by their unique crystal structures. The pores
in zeolites and zeolite analogs are often classified as small (8 T
atoms), medium (10 T atoms), large (12 T atoms), or extra-large
(.gtoreq.14 T atoms) according to the number of tetrahedral atoms
that surround the pore apertures. Zeolite A (LTA) and zeolite Rho
are examples of molecular sieves with small pores delimited by
8-membered rings, wherein the pore aperture measures about 4.1
.ANG., while zeolite X (FAU) and zeolite Beta are examples of
zeolites with large pores delimited by 12-membered rings wherein
the pore aperture measures about 7.4 .ANG.. While the final stage
catalyst can comprise large pore molecular sieves such as zeolite
X, in a preferred embodiment the final stage catalyst comprises a
medium pore molecular sieve. The phrase "medium pore" as used
herein means having a crystallographic free diameter in the range
of from about 3.9 to about 7.1 Angstrom when the molecular sieve is
in the calcined form. Shape selective medium pore molecular sieves
used in some embodiments of the practice of the present invention
have generally 1-, 2-, or 3-dimensional channel structures, with
the pores characterized as being 9 or 10-ring structures. The
crystallographic free diameters of the channels of molecular sieves
are published in the "Atlas of Zeolite Framework Types", Fifth
Revised Edition, 2001, by Ch. Baerlocher, W. M. Meier, and D. H.
Olson, Elsevier, pp 10-15, which is incorporated herein by
reference.
[0044] Non-limiting examples of medium pore molecular sieves
include ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48,
ZSM-57, MCM-22, SSZ-20, SSZ-25, SSZ-32, SSZ-35, SSZ-37, SSZ-44,
SSZ-45, SSZ-47, SSZ-57, SSZ-58, SSZ-74, SUZ-4, EU-1, NU-85, NU-87,
NU-88, IM-5, TNU-9, ESR-10, TNU-10 and combinations thereof.
[0045] The crystallite size of the molecular sieve can vary
depending on preparation conditions and may be tuned depending on
the desired product and reactor conditions in the final stage of
the reforming process. By way of illustration only, in the medium
pore zeolite ZSM-5, manipulating crystal size in order to change
the selectivity of the catalyst has been described in U.S. Pat. No.
4,517,402 which is incorporated herein by reference. Additional
references disclosing ZSM-5 are provided in U.S. Pat. No. 4,401,555
to Miller, hereby incorporated by reference in its entirety and in
U.S. Pat. No. 5,407,558. In one embodiment, the final stage
catalyst is a high silica to alumina ZSM-5 having a silica to
alumina molar ratio of at least 40:1, preferably at least 200:1 and
more preferably at least 500:1. In an embodiment the final stage
catalyst is high silica to alumina ZSM-5 with a small crystallite
size wherein the crystallite size less than 10 microns, more
preferably less than 5 microns, and most preferably less than 1
micron.
[0046] Other molecular sieves which can be used in the final
reforming stage include those as listed in U.S. Pat. No. 4,835,336;
namely: ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, and
other similar materials such as CZH-5 disclosed in Ser. No. 166,863
of Hickson, filed Jul. 7, 1980 and incorporated herein by
reference.
[0047] SSZ-20 is disclosed in U.S. Pat. No. 4,483,835, and SSZ-23
is disclosed in U.S. Pat. No. 4,859,442, both of which are
incorporated herein by reference.
[0048] ZSM-5 is more particularly described in U.S. Pat. No.
3,702,886 and U.S. Pat. Re. 29,948, the entire contents of which
are incorporated herein by reference.
[0049] ZSM-11 is more particularly described in U.S. Pat. No.
3,709,979 the entire contents of which are incorporated herein by
reference.
[0050] ZSM-12 is more particularly described in U.S. Pat. No.
3,832,449, the entire contents of which are incorporated herein by
reference.
[0051] ZSM-22 is more particularly described in U.S. Pat. Nos.
4,481,177, 4,556,477 and European Pat. No. 102,716, the entire
contents of each being expressly incorporated herein by
reference.
[0052] ZSM-23 is more particularly described in U.S. Pat. No.
4,076,842, the entire contents of which are incorporated herein by
reference.
[0053] ZSM-35 is more particularly described in U.S. Pat. No.
4,016,245, the entire contents of which are incorporated herein by
reference.
[0054] ZSM-38 is more particularly described in U.S. Pat. No.
4,046,859, the entire contents of which are incorporated herein by
reference.
[0055] ZSM-48 is more particularly described in U.S. Pat. No.
4,397,827 the entire contents of which are incorporated herein by
reference.
[0056] Other zeolites useful in the practice of the present
invention include, but are not limited to: Y zeolite, mordenite,
offretite, omega, ferrierite, heulandite, SSZ-24, SSZ-25, SSZ-26,
SSZ-31, SSZ-32, SSZ-33, SSZ-35, SSZ-37, SSZ-42, SSZ-44, EU-1,
NU-86, NU-87, UTD-1, MCM-22, MCM-36, MCM-56, and mixtures
thereof.
[0057] Examples of zeolite analogs useful in the process of the
invention include borosilicates, where boron replaces at least a
portion of the aluminum of the zeolitic form of the material.
Examples of borosilicates are described in U.S. Pat. Nos.
4,268,420; 4,269,813; 4,327,236 to Klotz, the disclosures of which
patents are incorporated herein.
[0058] Silicoaluminophosphates (SAPOs) are an example of
nonzeolitic molecular sieves useful in the practice of the present
invention. SAPOs comprise a molecular framework of corner-sharing
[SiO4] tetrahedra, [AlO.sub.4] tetrahedra and [PO.sub.4] tetrahedra
linked by oxygen atoms. By varying the ratio of P/Al and Si/Al the
acidity of the SAPO can be modified to minimize unwanted
hydrocracking and maximize advantageous isomerization reactions.
Preferred molar ratios of P/Al are from about 0.75 to 1.3 and
preferred molar ratios of Si/Al are from about 0.08 to 0.5.
Examples of a silicoaluminophosphate useful to the present
invention include SAPO-11, SAPO-31, and SAPO-41, which are also
disclosed in detail in U.S. Pat. No. 5,135,638.
[0059] The molecular sieves optionally include an amorphous support
or binder such as amorphous alumina or amorphous silica. Other
examples of amorphous supports are selected from the group
consisting of alumina, silica, titania, vanadia, chromia, zirconia,
and mixtures thereof. Other supports such as naturally occurring or
synthetic clays including, but not limited to, bentonite, kaolin,
sepiolite, attapulgite, and hallyosite can be used in the process
of this invention. The support may make up to 80% by weight of the
catalyst.
[0060] The molecular sieve catalysts according to the present
invention may also contain one or more Group VIII metals, e.g.,
nickel, ruthenium, rhodium, palladium, iridium or platinum. The
preferred Group VIII metals are iridium, palladium, and platinum.
Most preferred is platinum due to its high selectivity with regard
to dehydrocyclization and stability under the dehydrocyclization
reaction conditions. The preferred percentage of the Group VIII
metals, such as platinum, in the catalyst is between 0.1 wt. % and
5 wt. %, more preferably from 0.3 wt. % to 2.5 wt. %.
[0061] Examples of amorphous Group VIII metal catalysts include
those detailed in "penultimate zone catalyst" above. Suitable
catalysts for the final stage include platinum-containing amorphous
reforming catalysts which optionally contain a promoter metal
selected from the group consisting of a non-platinum Group VIII
metal, e.g. rhenium, germanium, tin, lead, gallium, indium, and
mixtures thereof. The platinum may exist within the catalyst as a
compound such as the oxide, sulfide, halide, oxyhalide, in chemical
combination with one or more other ingredients of the catalytic
composite, or as an elemental metal. Preferably, substantially all
of the platinum exists in the catalytic composite in a reduced
state. The preferred platinum component generally comprises from
about 0.01 wt. % to 2 wt. % of the catalytic composite, preferably
0.05 to 1 wt. %, calculated on an elemental basis.
[0062] The catalyst can also include a binder material. Binders
include inorganic oxide supports such as alumina, silica,
silica-alumina, titania, vanadia, chromia, zirconia, clays,
zeolites, non-zeolitic molecular sieves, and mixtures thereof. The
binder may make up to 80% by weight of the catalyst.
[0063] Any conventional impregnation, mulling, ion exchange or
other known methods for adding the metals to the binder may be
used. The Group VIII noble metals may be introduced into the
amorphous binder by, for example, ion exchange, impregnation,
carbonyl decomposition, adsorption from the gaseous phase,
introduction during synthesis, and adsorption of metal vapor. The
preferred technique is ion exchange or impregnation by the
so-called incipient witness method. Preparations of such catalysts
are taught, e.g., in U.S. Pat. Nos. 3,415,737; 4,636,298; and
4,645,586, the disclosures of which are incorporated herein by
references.
[0064] The catalyst optionally contains a halogen component. The
halogen component may be either fluorine, chlorine, bromine, iodine
or mixtures thereof. Chlorine is the preferred halogen component.
The halogen component is generally present in a combined state with
the inorganic-oxide support. The halogen component is preferably
well dispersed throughout the catalyst and may comprise from more
than 0.2 wt. % to about 15 wt. %, calculated on an elemental basis,
of the final catalyst.
[0065] Conventional acid catalysts such as solid acid catalyst
including, but not limited to, acidic clays and acidic zeolites may
also be used in the practice of the present invention as a final
stage catalyst or as a component of the final stage catalyst. The
zeolite molecular sieves discussed above with protons as
counterions in the anionic zeolite framework are examples of solid
acid catalysts. MCM-22 is an example of a layered aluminosilicate
clay which can act as a solid acid.
[0066] The final stage catalyst may comprise acidic or non acidic
phyllosilicate clay compositions derived from the smectites such as
those described in U.S. Pat. Nos. 4,248,739 and 5,414,185. Final
stage catalysts may comprise any natural or synthetic clays having
a lamellar structure, examples of which include, but are not
limited to, bentonite, montmorillonite, berdellite, hectorite,
vermiculite and the like. Layered clays can be delaminated or
pillared to produce high surface area materials with a majority of
their active sites or cations exposed at the crystal surface.
[0067] The clays may further comprise active metals such as Group
VIII metals, preferably platinum or palladium. The clays mentioned
above may be used alone or admixed with inorganic oxide matrix
components such as silica, alumina, silica-alumina, hydrogels and
other clays. The clays may be any suitable size or shape as to
ensure good contact with the reactants. Examples include powder,
pellets, granules, extrudates, and spheres.
[0068] The final stage catalyst is selected to provide a high
selectivity for the production of aromatic compounds at a reduced
pressure, which increases the selectivity of C.sub.6 to C.sub.8
paraffin dehydrocyclization while maintaining low catalyst fouling
rates. In embodiments, the final stage catalyst comprises at least
one medium pore molecular sieve. The molecular sieve is a porous
inorganic oxide characterized by a crystalline structure which
provides pores of a specified geometry, depending on the particular
structure of each molecular sieve. In embodiments, the medium pore
molecular sieve is a zeolite, which is a crystalline material that
possess three-dimensional frameworks composed of tetrahedral units
(TO.sub.4/2, T=Si, Al, or other tetrahedrally coordinated atom)
linked through oxygen atoms. An medium pore zeolite that is useful
in the present process includes ZSM-5. Various references
disclosing ZSM-5 are provided in U.S. Pat. No. 4,401,555 to Miller.
Additional disclosure on the preparation and properties of high
silica ZSM-5 may be found, for example, in U.S. Pat. No. 5,407,558
and U.S. Pat. No. 5,376,259.
[0069] A type of ZSM-5 that is useful includes a silicate having a
form of ZSM-5 with a molar ratio of SiO2/M.sub.2O.sub.3 of at least
40:1, or at least 200:1 or at least 500:1, or even at least 1000:1,
where M is selected from Al, B, or Ga. In embodiments, the ZSM-5
has a silica to alumina molar ratio of at least 40:1, or at least
200:1, or at least 500:1, or even at least 1000:1. A type of ZSM-5
that is useful further is characterized as having a crystallite
size of less than 10 .mu.m, or less than 5 .mu.m or even less than
1 .mu.m. Methods for determining crystallite size, using, for
example Scanning Electron Microscopy, are well known. A type of
ZSM-5 that is useful is further characterized as having at least
80% crystallinity, or at least 90% crystallinity, or at least 95%
crystallinity. Methods for determining crystallinity, using, for
example, X-ray Diffraction, are well known.
[0070] Strong acidity is undesirable in the catalyst because it
promotes cracking, resulting in lower selectivity to C5+ liquid
product. To reduce acidity, a type of ZSM-5 that contains an alkali
metal and/or an alkaline earth metal is useful for reforming the
hydrocracked naphtha. The alkali or alkaline earth metals may be
incorporated into the catalyst during or after synthesis of the
molecular sieve. Suitable molecular sieves are characterized by
having at least 90% of the acid sites, or at least 95% of the acid
sites, or at least 99% of the acid sites being neutralized by
introduction of the metals. In one embodiment, the medium pore
molecular sieve contains less than 5,000 ppm alkali. Such molecular
sieves are disclosed, for example, in U.S. Pat. No. 4,061,724, in
U.S. Pat. No. 5,182,012 and in U.S. Pat. No. 5,169,813. These
patents are incorporated herein by reference, particularly with
respect to the description, preparation and analysis of molecular
sieves having the specified silica to alumina molar ratios, having
a specified crystallite size, having a specified crystallinity and
having a specified alkali content.
[0071] Other medium pore molecular sieves that are useful for
reforming include high silica to alumina mole ratio types of ZSM-11
and crystalline borosilicates. ZSM-11 is more particularly
described in U.S. Pat. No. 3,709,979, the entire contents of which
are incorporated herein by reference. The crystalline molecular
sieve may be in the form of a borosilicate, where boron replaces at
least a portion of the aluminum of the more typical aluminosilicate
form of the molecular sieve. Borosilicate molecular sieves are
described in U.S. Pat. Nos. 4,268,420; 4,269,813; 4,327,236 to
Klotz, the disclosures of which patents are incorporated herein,
particularly those disclosures related to borosilicate
preparation.
[0072] The final stage catalyst further contains one or more Group
VIII metals, e.g., nickel, ruthenium, rhodium, palladium, iridium
or platinum. In embodiments, the Group VIII metals include iridium,
palladium, platinum or a combination thereof. These metals are more
selective with regard to dehydrocyclization and are also more
stable under the dehydrocyclization reaction conditions than other
Group VIII metals. When employed in the final stage catalyst, these
metals are generally present in the range of between 0.1 wt. % and
5 wt. % or between 0.3 wt. % to 2.5 wt. %. The catalyst may further
comprise a promoter, such as rhenium, tin, germanium, cobalt,
nickel, iridium, tungsten, rhodium, ruthenium, or combinations
thereof.
[0073] In forming the final stage catalyst, the crystalline
molecular sieve is preferably bound with a matrix. The matrix is
not catalytically active for reforming or other hydrocarbon
conversion. Satisfactory matrices include inorganic oxides,
including alumina, silica, naturally occurring and conventionally
processed clays, such as bentonite, kaolin, sepiolite, attapulgite
and halloysite. Such materials have few, if any, acid sites and
therefore have little or no cracking activity.
[0074] Reaction conditions in the final reforming stage are
specified to effectively utilize the particular performance
advantages of the catalyst used in the stage. Preferably the
reaction pressure of the final reforming stage is less than the
pressure in the penultimate stage. Low pressure in the final stage
may lead to increased catalyst fouling. However, as the process of
the invention requires at least two stages--a penultimate and a
final stage--catalyst regeneration in the final stage reactor can
occur as needed to maintain high catalyst activity in the final
stage. For example, as naphtha reforming is taking place in the
penultimate reactor, catalyst regeneration can take place in the
final reactor. While the final stage catalyst is being regenerated,
the severity of the penultimate stage can be temporarily increased
to meet RON targets for the total blended reformate which would
otherwise be achieved with both the penultimate and final stages in
operation. Operating the final reforming stage at a lower relative
pressure than the penultimate stage minimizes the formation of
light (C.sub.4-) products while increasing the yield of high octane
naphtha and overall liquid yield in the two stage process of the
invention. Because the penultimate stage is operated at relatively
mild conditions, catalyst life in that stage is lengthened while
giving good yields of desired high octane products.
[0075] The naphtha feed to the final stage is the intermediate
reformate which is separated from the effluent of the penultimate
stage. In the process, the intermediate reformate contacts the
catalyst in the final stage at reforming reaction conditions, which
reaction conditions include a temperature in the range from about
800.degree. F. to about 1100.degree. F. (427.degree. C. to
593.degree. C.), a pressure in the range from about 40 psig to
about 400 psig (276 kPa to 2760 kPa) to and a feed rate in the
range of from about 0.5 LHSV to about 5 LHSV. In some embodiments,
the pressure in the final reforming stage is less than 100 psig
(690 kPa). Preferably the pressure in the final reforming stage is
from about 40 psig (276 kPa) to about 200 psig (1380 kPa), and more
preferably from about 40 psig (276 kPa) to about 100 psig (690
kPa). Hydrogen is preferably added as an additional feed to the
final reforming stage, but it is not required. In embodiments,
hydrogen added with the feed is recovered from the process and is
recycled to the final stage.
[0076] Depending on the particular process, the effluent from the
final reforming stage may contain light (i.e. C.sub.4- products
and/or hydrogen) products which may be removed from the reformate
prior to further processing or blending to make a fuel product. The
C.sub.5+ reformate, herein referred to as the final reformate,
which is produced in the final reforming stage has an increased RON
relative to that of the intermediate reformate which is the feed to
the final reforming stage. Preferably, at least 75 vol % of the
final reformate boils in the C.sub.5+ range. The final reformate
may be used as a fuel or a fuel component by blending with other
hydrocarbons. In embodiments, the RON of the final reformate is 80
or higher, or 90 or higher, or 95 or higher.
[0077] The reformate is useful as a fuel or as a blend stock for a
fuel. In some embodiments, at least a portion of the reformate from
the final reforming stage is blended with at least a portion of the
heavy reformate, which is recovered from the penultimate reforming
stage; the blend may be used as a fuel or as a blend stock for a
fuel.
[0078] Depending on the particular process, the effluent (otherwise
termed the "final effluent") from the final reforming stage may
contain light (i.e. C.sub.4- products and/or hydrogen) products
which may be removed from the reformate in a final separation step
prior to further processing for blending or use as a fuel. A
hydrogen-rich stream may be separated from the effluent prior to
the separation step, using, for example, a high pressure separator
or other flash zone. C.sub.4- hydrocarbons in the effluent may also
be separated in a preliminary flash zone, either along with the
hydrogen or in a subsequent flash zone. The reformate which is
produced in the final reforming stage has an increased RON relative
to that of the intermediate reformate which is the feed to the
final reforming stage. In embodiments, the RON of the final
reformate is greater than 90 or at least 95, or at least 98. In
some embodiments, the final reformate boils in the range from about
70.degree. F. (21.degree. C.) to about 280.degree. F. (138.degree.
C.). In some such embodiments, the final reformate comprises at
least 70 vol % C.sub.5-C.sub.8 hydrocarbons. In some embodiments,
the final reformate boils in the range from about 100.degree. F.
(38.degree. C.) to about 280.degree. F. (138.degree. C.). In some
such embodiments, the final reformate comprises at least 70 vol %
C.sub.6-C.sub.8 hydrocarbons. In some embodiments, the final
reformate boils in the range from about 100.degree. F. (38.degree.
C.) to about 230.degree. F. (110.degree. C.). In some such
embodiments, the final reformate comprises at least 70 vol %
C.sub.6-C.sub.7 hydrocarbons. In addition to the final reformate
stream, a final light stream may also be recovered from the final
effluent. In such cases, the final light stream boils in the range
of about 70.degree. (21.degree. C.) to about 140.degree. F.
(60.degree. C.). In some such embodiments, the final light stream
comprises at least 70 vol % C.sub.5 hydrocarbons.
[0079] The reformate is useful as a fuel or as a blend stock for a
fuel. In some embodiments, at least a portion of the reformate from
the final reforming stage is blended with at least a portion of the
heavy reformate, which is recovered from the penultimate reforming
stage; the blend may be used as a fuel or as a blend stock for a
fuel.
[0080] The gradual accumulation of coke and other deactivating
carbonaceous deposits on the catalyst will eventually reduce the
activity and/or selectivity of the catalyst. Typically, catalyst
regeneration becomes desirable when from about 0.5 to about 5.0 wt.
% or more of carbonaceous deposits are laid down upon the catalyst.
At this point, it is typically necessary to take the hydrocarbon
feedstream out of contact with the catalyst and purge the
hydrocarbon conversion zone with a suitable gas stream. Catalyst
regeneration can then performed either by unloading the catalyst
from the conversion zone and regenerating in a separate vessel or
facility or performing regeneration in-situ. Alternatively, the
catalyst may be continuously withdrawn from the reactor for
regeneration in a separate vessel, to be returned to the reactor as
in a Continuous Catalytic Reformer. Preferably, the catalyst is
regenerated in situ.
[0081] Various regeneration procedures are known in the art.
Generally, the temperature of the final stage catalyst is gradually
lowered to below the temperature of regeneration. The final stage
reformer is taken offline, for example by the use of a valve. The
penultimate reformer continues to operate at reforming reaction
conditions, and to produce both a hydrocarbon product of the
desired RON as well as hydrogen while the final stage is bypassed.
However, reforming severity in the penultimate stage is increased
so that the intermediate reformate has an RON of at least 90 or at
least 95 or even at least 98. In embodiments, the reforming
temperature in the penultimate stage is increased by at least
5.degree. F. (2.8.degree. C.), or by at least 10.degree. F.
(5.6.degree. C.) or even by at least 15.degree. F. (8.3.degree. C.)
while regenerating the final stage catalyst. In embodiments, the
reforming pressure in the penultimate stage is decreased by at
least 10 psig (69 kPa), or at least 20 psig (138 kPa) or even at
least 30 psig (207 kPa) while regenerating the final stage
catalyst. During regeneration, the intermediate reformate bypasses
the final stage, and to be used, for example, as a fuel or fuel
blendstock. Likewise, hydrogen which is recovered from the
penultimate stage bypasses the final stage, to be used, for
example, in other refinery processes.
[0082] The final stage catalyst is then regenerated by
depressurizing the final stage reactor, purging the final stage
reactor with nitrogen, and then introducing a low level of oxygen,
generally between 0.1 to 2%, and preferably between 0.5 to 1%. The
temperature of the final stage is raised to initiate a carbon burn
to remove coke deposits. During catalyst regeneration, the coked
catalyst is contacted with a predetermined amount of molecular
oxygen. A desired portion of the coke is burned off the catalyst,
restoring catalyst activity. Flue gas formed by combustion of coke
in the catalyst regenerator may be treated for removal of
particulates and conversion of carbon monoxide, after which it is
normally discharged into the atmosphere. After the carbon burn the
final stage reactor is purged with nitrogen, the temperature is
reduced to below the start of run temperature, and the final stage
is put back on-line, i.e. the effluent of the penultimate stage now
flows through the final stage. The temperature of the final stage
is gradually raised to run temperature while the temperature of the
penultimate stage is gradually lowered so as to maintain the
desired RON of the final product coming off of the final stage
reactor. In accordance with the invention, the final stage catalyst
does not undergo chloriding or other halogen treatment during
regeneration. Preferably, the final stage catalyst comprises a
medium pore zeolite and at least one noble metal. In an embodiment
the final stage catalyst comprises ZSM-5, ZSM-11, and mixtures
thereof. It is an object of the invention to minimize the amount of
time the multi-stage reforming process is run without the final
stage due to catalyst regeneration. It has been found that avoiding
a chloriding step during regeneration of the final stage catalyst
minimizes the time the multi stage reforming process is run without
the final stage reactor during final stage catalyst
regeneration.
[0083] The regeneration is performed in a halogen-free environment.
By halogen-free, it is meant that chlorine, fluorine, bromine, or
iodine or their compounds including for example, hydrogen chloride,
carbon tetrachloride, ethylene dichloride, propylene dichloride,
are not added at anytime during the catalyst regeneration process.
Halogen free methods to regenerate reforming catalysts are known in
the art. For example, U.S. Pat. No. 5,155,075 discloses a process
for regenerating a medium pore zeolite catalyst and is herein
incorporated by reference in its entirety. Regeneration of coked
catalyst may be effected by any of several procedures. The catalyst
may be removed from the reactor of the regeneration treatment to
remove carbonaceous deposits or the catalyst may be regenerated
in-situ in the reactor. For example, the final stage reformer unit
may be operatively connected with a source of oxidizing gas at
elevated temperature. The catalyst is regenerated by burning off
coke, producing CO.sub.2 and H.sub.2O. Reactor effluent can be
cooled in a feed/effluent exchanger and/or in an air cooler. Final
cooling can occur in a trim cooler. The effluent then enters a
separator. Gas is released from the separator to maintain system
pressure through pressure-response venting. By the time it reaches
the separator, water vapor formed during the burn has condensed and
is separated from the recycle gas. Because water vapor at high
temperatures may damage the catalyst, a relatively low separator
temperature is generally maintained in order to minimize the
H.sub.2O partial pressure in the recycle gas returning to the
reactor. In an embodiment the separator temperature can be between
about 20.degree.-90.degree. C., preferably between about
30.degree.-70.degree. C., and most preferably between about
40.degree.-50.degree. C. at 800 kPa pressure.
[0084] In a typical regeneration process, the final stage reactor
is brought up to pressure with an inert gas, preferably nitrogen.
The reactor inlet temperature is gradually decreased to a
temperature of from 140.degree. C. to no more than about
420.degree. C. Oxygen is then introduced into the reactor. The
oxygen is typically derived from air and an inert gas serves as a
diluent, such that oxygen concentration is from about 21 mole %
oxygen to a lower limit of about 0.1 mole % oxygen. Higher levels
of oxygen may be used in methods where oxygen is supplied in a more
pure form such as from cylinders or other containing means. Typical
inert gases useful in the carbon burn step may include nitrogen,
helium, carbon dioxide, and like gases or any mixture thereof;
nitrogen being preferred. The regeneration gases should be
substantially sulfur-free as they enter the reactor, and preferably
contain less than 100 part per million by volume water. Because the
oxygen content determines the rate of burn, it is desirable to keep
the oxygen content low so as not to damage the catalyst by
overheating and causing metal agglomeration, while still conducting
the carbon burn step in a manner that is both quick and effective.
In an embodiment, the oxygen level in the inlet to the regeneration
vessel is between 0.2 to 4.0 mole % In another embodiment, air or
oxygen is injected at a controlled rate to give a maximum oxygen
concentration of between about 0.1% and up to about 2%, preferably
between about 0.25% and up to about 1%, and most preferably between
about 0.5% and up to about 0.7% at the reactor inlet. The
temperature is then increased to facilitate coke removal through a
"burn." As burning begins, a temperature rise of about 85.degree.
C. is generally observed. As the burn dies off the inlet
temperature is raised to and maintain at about 455.degree. C. The
pressure of the reactor can vary, but generally, a pressure
sufficient to maintain the flow of the gaseous oxygen containing
mixture through the catalyst zone is selected. Generally, pressures
can range from between about 1.0 to 50.0 atmospheres and preferably
from about 2 to about 15 atmospheres. A gas hourly space velocity
of about 100 to about 10,000 per hour, with a preferred value of
about 500 to about 5,000 per hour is generally used, although this
can vary depending on the catalyst and amount of coking.
[0085] When the main burn is completed, as evidenced by no
temperature rise across the catalyst bed, the temperature is raised
over 500.degree. C. and the O.sub.2 content can be raised. In an
embodiment the O.sub.2 content is raised to at least 3%, preferably
at least 4%, and more preferably at least 5%. This condition is
held at least one hour (or until all evidence of burning has
ceased). Generally, the regeneration process continues for a
sufficient period of time such that the aromatization activity is
restored to within 20.degree. F. (11.degree. C.) of the
aromatization activity the catalyst possessed at the start of the
previous run cycle. By the term "aromatization activity" we mean
the extrapolated start of run temperature where the run conditions
and the feed as well as the aromatics yield are substantially the
same as in the previous run cycle. The platinum on the catalyst
remains sufficiently dispersed on the support to allow for an
activity change of not more than 10.degree. C. upon termination of
the regeneration procedure, and return of the catalyst to
hydrocarbon conversion service. Thus, the catalyst aromatization
activity is based upon the temperature needed to achieve a desired
constant aromatics production. Regeneration by the process of the
present invention results in a catalyst which has an aromatization
activity, as defined above, which is within 10.degree. C. of the
temperature needed in the previous run to achieve the same constant
aromatics production.
[0086] When the regeneration is complete, the temperature is
reduced, generally to less than 500.degree. C., and the system
purged free of O.sub.2 with an inert gas, preferably nitrogen to
displace the oxygen and any water therefrom. The exit gas is easily
monitored to determine when the catalyst zone is substantially free
of oxygen and water. After the carbon burn-off and purge, the
catalyst is activated by treatment with hydrogen. In the initial
reduction step, the catalyst is contacted with a hydrogen
containing stream at a temperature of from about 150.degree. C. to
about 380.degree. C. for a period of at least of about 0.1 to about
10.0 hours. Preferred conditions for the reduction step are from
about 200.degree. C. to about 320.degree. C. for a period from
about 0.1 to about 2.0 hours. The pressure and gas rates utilized
in the reduction step are preferably very similar to those above
described in the carbon burn step. Following the initial reduction,
the catalyst may be further reduced and dried by circulating a
mixture of inert gas and hydrogen while raising the temperature to
between 480.degree. and 540.degree. C. In the reduction step,
metallic components are returned to their elemental state and the
resulting regenerated catalyst possesses activity, and selectivity
characteristics quite similar to those occurring in a fresh
catalyst.
[0087] After completing the reduction step, the temperature is
lowered to 450.degree. C. or less. The reforming process in which
the catalyst is employed may be resumed by charging the hydrocarbon
feedstream to the catalyst zone and adjusting the reaction
conditions to achieve the desired conversion and product yields.
The reactor is brought up to reaction pressure and the temperature
decreased to below the reaction temperature during the multi-stage
reforming process. The final stage reactor is put back online, i.e.
at least a portion of the effluent from the penultimate reactor
flows through the final stage reactor to produce a hydrocarbon
product of the desired RON.
[0088] In order to avoid a metal re-dispersion step, the ultimate
temperature in the carbon burn regeneration procedure is generally
less than 415.degree. C., and preferably between 315.degree. C. to
400.degree. C. This procedure allows the catalyst to be restored to
an activity very close to that of the fresh catalyst, without noble
metal agglomeration which would require a metal re-dispersion step.
It is further preferred the carbon burn be initiated at a
temperature of less than about 260.degree. C. and further that the
recycle gas be dried to achieve a water concentration in the
recycle gas of less than 100 ppm water, prior to the recycle gas
entering the reforming reactor train.
[0089] Reference is now made to an embodiment of the invention
illustrated in FIG. 1. A naphtha boiling range fraction 5 which
boils within the range of 50.degree. F. (10.degree. C.) to
550.degree. F. (288.degree. C.) passes into the reaction stage 10
at a feed rate in the range of about 0.5 hr.sup.-1 to about 5
hr.sup.-1 LHSV. Reaction conditions in the reforming stage 10
include a temperature in the range from about 800.degree. F.
(427.degree. C.) to about 1100.degree. F. (593.degree. C.) and a
total pressure in the range of greater than 70 psig (483 kPa) to
about 400 psig (2760 kPa).
[0090] The effluent 11 from the penultimate stage is an upgraded
product, in that the RON has been increased during reaction in the
penultimate stage 10. The penultimate stage effluent 11 comprises
hydrocarbons and hydrogen generated during reaction in the
penultimate stage and at least some of the hydrogen (if any) added
to the feed upstream of the penultimate stage. In the embodiment
illustrated in FIG. 1, the effluent is separated in separation zone
20 into a hydrogen-rich stream 21, a C.sub.4- stream 22, an
intermediate reformate 26 and a heavy reformate 26. In embodiments,
this separation occurs in a single separation zone. In other
embodiments, this separation is done in sequential zones, with the
hydrogen, and optionally the C.sub.4- stream, separated in one or
more preliminary separation zones prior to the separation of the
intermediate reformate 25 and the heavy reformate 26.
[0091] In the embodiment illustrated in FIG. 1, the intermediate
reformate 25 comprises a substantial amount of the C.sub.5-C.sub.8
hydrocarbons contained in the effluent, with smaller quantities of
C.sub.4 and C.sub.9 hydrocarbons. At least a portion of
intermediate reformate 25 is passed to final reforming stage 30.
Heavy reformate 26 contains a substantial amount of the C.sub.9+
hydrocarbons contained in the effluent 11, and has an RON of
greater than 98, preferably greater than 100.
[0092] Intermediate reformate 25 is passed to final reforming stage
30 for contact with a catalyst comprising platinum and at least one
medium pore molecular sieve, at reaction conditions which include a
temperature in the range from about 800.degree. F. (427.degree. C.)
to about 1100.degree. F. (593.degree. C.) and a pressure in the
range from about 50 psig (345 kPa) to about 250 psig (1725
kPa).
[0093] Effluent 31 from the final reforming stage is separated in
separation zone 40, yielding at least a hydrogen-rich stream 41, a
C.sub.4- stream 42, and a final reformate stream 45. In
embodiments, the final reformate stream boils in the C.sub.5+
boiling range. As described above, this separation may take place
in one, or multiple, separation zones, depending on the specific
requirements of a particular process. In an embodiment, the final
reformate stream 45 may be further combined with the heavy
reformate 26 before further processing or use as a fuel or fuel
blend stock. Hydrogen-rich stream 41 is combined with hydrogen-rich
stream 21 before using in other refinery processes, and C.sub.4-
stream 42 is combined with C.sub.4- stream 22.
[0094] Reference is now made to an embodiment of the invention
illustrated in FIG. 2. A naphtha boiling range fraction 5 which
boils within the range of 50.degree. F. (10.degree. C.) to
550.degree. F. (288.degree. C.) passes into the reaction stage 10
at a feed rate in the range of about 0.5 hr.sup.-1 to about 5
hr.sup.-1 LHSV. Reaction conditions in the reforming stage 10
include a temperature in the range from about 800.degree. F.
(427.degree./c) to about 1100.degree. F. (593.degree. C.) and a
total pressure in the range of greater than 70 psig (483 kPa) to
about 400 psig (2760 kPa).
[0095] The effluent 11 from the penultimate stage is an upgraded
product, in that the RON has been increased during reaction in the
penultimate stage 10. The penultimate stage effluent 11 comprises
hydrocarbons and hydrogen generated during reaction in the
penultimate stage and at least some of the hydrogen (if any) added
to the feed upstream of the penultimate stage. In the embodiment
illustrated in FIG. 2, the effluent is separated in separation zone
20 into a hydrogen-rich stream 21, a C.sub.4- stream 22, a light
reformate 23, an intermediate reformate 24 and a heavy reformate
26. In embodiments, this separation occurs in a single separation
zone. In other embodiments, this separation is done in sequential
zones, with the hydrogen, and optionally the C.sub.4- stream,
separated in one or more preliminary separation zones prior to the
separation of the light reformate 23, the intermediate reformate 24
and the heavy reformate 26.
[0096] In the embodiment illustrated in FIG. 2, the light reformate
23 comprises a substantial amount of the C.sub.5 hydrocarbons
contained in the effluent, with smaller quantities of C.sub.4 and
C.sub.6 hydrocarbons. The intermediate stream comprises a
substantial portion of the C.sub.6-C.sub.8 hydrocarbons contained
in the effluent; the heavy reformate 26 contains a substantial
amount of the C.sub.9+ hydrocarbons contained in the effluent 11.
Intermediate reformate 24 is passed to final reforming stage 30 at
a feed rate in the range of from about 0.5 hr.sup.-1 to about 5
hr.sup.-1 LHSV, for contact with a catalyst comprising platinum and
at least one medium pore molecular sieve, at reaction conditions
which include a temperature in the range from about 800.degree. F.
(427.degree. C.) to about 1100.degree. F. (593.degree. C.) and a
pressure in the range from about 50 psig (345 kPa) to about 250
psig (1725 kPa). During regeneration of the final stage catalyst,
the severity of the penultimate stage can be increased to increase
the RON of the intermediate reformate. The RON of the intermediate
under increased severity of the penultimate stage (i.e. increased
temperature and/or pressure) would meet the target RON of the final
reformate stream.
[0097] Effluent 31 from the final reforming stage is separated in
separation zone 40, yielding at least a hydrogen-rich stream 41, a
C.sub.4- stream 42, a final C.sub.5 stream 43 and a final reformate
stream 44. In embodiments, the final reformate stream boils in the
C.sub.6+ boiling range. As described above, this separation may
take place in one, or multiple, separation zones, depending on the
specific requirements of a particular process. As shown in the
embodiment illustrated in FIG. 2, the final reformate stream 44 is
further combined with the heavy reformate 26 before further
processing or use as a fuel or fuel blend stock, hydrogen-rich
stream 41 is combined with hydrogen-rich stream 21 before using in
other refinery processes, C.sub.4- stream 42 is combined with
C.sub.4- stream 22 and final C.sub.5 stream 43 is combined with
C.sub.5 stream 23.
[0098] The following examples are presented to exemplify
embodiments of the invention but are not intended to limit the
invention to the specific embodiments set forth. Unless indicated
to the contrary, all parts and percentages are by weight. All
numerical values are approximate. When numerical ranges are given,
it should be understood that embodiments outside the stated ranges
may still fall within the scope of the invention. Specific details
described in each example should not be construed as necessary
features of the invention.
EXAMPLES
[0099] In the following examples, the RON values are calculated
values, based on RON blending correlations applied to a composition
analysis using gas chromatography. The method was calibrated to
achieve a difference between measured RON values, determined by
ASTM D2699, and calculated RON values of within .+-.0.8.
Example 1
[0100] A naphtha feed, with an API of 54.8 (0.76 g/cm.sup.3), RON
of 53.3 and an ASTM D-2887 simulated distillation shown in Table 1
was reformed in a penultimate stage using a commercial reforming
catalyst comprising platinum with a rhenium promoter on an alumina
support. The catalyst contained about 0.3 wt. % platinum, and about
0.6 wt. % rhenium on an extruded alumina support. Reaction
conditions included a temperature of 840.degree. F., a pressure of
200 psig, a 5:1 molar ratio of hydrogen to hydrocarbon and a feed
rate of 1.43 hr.sup.-1 LHSV. The C.sub.5+ liquid yield was 92.7 wt
%. The hydrogen production was 975 standard cubic feet per barrel
feed (0.16 m.sup.3 H.sub.2/liter oil).
[0101] This C.sub.5+ liquid product (penultimate effluent)
collected from the penultimate stage had an API of 46.6 (0.79
g/cm.sup.3), an RON of 89 and an ASTM D-2887 simulated distillation
as given in Table 2.
TABLE-US-00001 TABLE 1 Simulated Distillation of naphtha feed
Temperature, Vol % .degree. F. (.degree. C.) IBP 182 (83) 10 199
(93) 30 227 (108) 50 258 (126) 70 291 (144) 90 336 (169) EP 386
(197)
TABLE-US-00002 TABLE 2 Simulated Distillation of the C5+ liquid
product from the penultimate stage (penultimate effluent)
Temperature, Vol % .degree. F. (.degree. C.) IBP 165 (74) 10 189
(87) 30 234 (112) 50 257 (125) 70 289 (143) 90 336 (169) EP 411
(211)
Example 2
[0102] The C5+ liquid product from Example 1 was distilled into an
intermediate reformate and a heavy reformate. The intermediate
reformate was found to represent 80 vol % of the C5+ liquid product
from Example 1. The intermediate reformate, had an API of 55.7
(0.76 g/cm3), an RON of 85 and an ASTM D-2887 simulated
distillation as shown in Table 3, and was used as feed in a final
reforming stage in Examples 3-6. The heavy reformate was found to
represent 20 vol. % of the C5+ liquid product from Example 1. The
heavy reformate had an API of 28.9 (0.88 g/cm3) and an RON of 105,
and is further described in Table 4.
TABLE-US-00003 TABLE 3 Simulated Distillation of intermediate
reformate Temperature, Vol % .degree. F. (.degree. C.) IBP 168 (76)
10 190 (88) 30 235 (113) 50 240 (116) 70 284 (140) 90 296 (147) EP
336 (169)
Example 3
[0103] The intermediate reformate produced in Example 2 was used as
feed to the final reforming stage which used a ZSM-5 zeolite based
catalyst composited with 35% alumina binder material. The ZSM-5 had
a SiO.sub.2/Al.sub.2O.sub.3 molar ratio of .about.2000 and was ion
exchanged to the ammonium form before incorporating in a 65%
zeolite/35% alumina extrudate. The extrudate was impregnated with
0.8% Pt, 0.3% Na, and 0.3% Mg by an incipient wetness procedure to
make the final catalyst. The reaction conditions and experimental
results are listed in Tables 4 and 5.
Example 4
[0104] A product which was produced in the final stage reforming of
the intermediate reformate in Example 3 was blended with the heavy
reformate (Example 2) which was not subjected to the final stage
reforming. The total RON of C.sub.5+, total C.sub.5+ yield and
total H.sub.2 production of the blended final product are given in
Table 4 based on using the total C.sub.5+ penultimate effluent as
feed (which is distilled into intermediate reformate and heavy
reformate in Example 2). The results are compared to those obtained
from Comparative Example 1 where the total C.sub.5+ product was
produced from the total C.sub.5+ penultimate effluent as feed,
without distillation into an intermediate and heavy reformate.
Example 5
[0105] The intermediate reformate produced in Example 2 was
contacted with the platinum/rhenium on alumina based catalyst
described in Example 1 in a final reforming stage. The reaction
conditions and experimental results are listed in Table 5 and
compared with Example 3.
Example 6
[0106] The intermediate reformate produced in Example 2 is
contacted with the platinum/rhenium on alumina based catalyst
described in Example 1 in a final reforming stage wherein the final
reforming stage pressure is less than 200 psig (1380 kPa). The
final reforming stage is run at the same temperatures, LHSV, and
hydrogen to hydrocarbon ratio as in Example 5. The C.sub.5+ liquid
yield for Example 6 is higher than the C.sub.5+ liquid yield for
Example 5 at the same or similar RON. The higher C.sub.5+ liquid
yield of Example 6 as compared to Example 5 illustrates the
benefits of running the final stage at a lower pressure than the
penultimate stage with a platinum/rhenium on alumina catalyst.
Comparative Example 1
[0107] The total C.sub.5+ product produced in Example 1, without
distillation into an intermediate and heavy reformate, was
contacted with the ZSM-5 based catalyst of Example 3 in a final
reforming stage at 930.degree. F. (499.degree. C.), 80 psig (550
kPa), 2:1 molar ratio of hydrogen to hydrocarbon and 1.5 hr.sup.-1
LHSV feed rate. The C.sub.5+ liquid yield was 89.9 wt. % and RON of
the C.sub.5+ liquid product from the final reforming stage was
97.4. The hydrogen production was 190 standard cubic feet per
barrel feed.
TABLE-US-00004 TABLE 4 Comparison of results from Example 4 and
Comparative Example 1 Example 4 Comparative Example 3 Example 2
Example 1 Feedstock Intermediate Heavy Total C.sub.5+ reformate
reformate penultimate (Example 2, (Example 2, effluent Table 3)
Table 3) (Example 1, Table 2) Catalyst Pt/Na/Mg/ZSM-5 Not subjected
Pt/Na/Mg/ZSM-5 with alumina to the final with alumina binder stage
binder reforming Temperature, .degree. F. 900 .sup. -- 930 .sup.
Pressure, psig 80 .sup. -- 80 .sup. LHSV, hr.sup.-1 1.5 -- 1.5
Molar 2:1 -- 2:1 H.sub.2/hydrocarbon Ratio RON of C.sub.5+ 97.0
.sup.(1) 105 .sup.(2) 97.4 .sup.(3) C.sub.5+ Yield, wt % 92.7
.sup.(1) 100 .sup.(2) 89.9 .sup.(3) H.sub.2 Yield, scf/bbl 300
.sup.(1) -- 190 .sup.(3) feed Total RON of C.sub.5+ 98.7 .sup.(4)
97.4 .sup.(3) Total C.sub.5+ Yield, wt % 94.2 .sup.(4) 89.9
.sup.(3) Total H.sub.2 Yield, 240 .sup.(4) 190 .sup.(3) scf/bbl
feed Notes to Table 4: .sup.(1) For Example 3: RON of C.sub.5+,
C.sub.5+ yield and H.sub.2 production of the product are given
based on the intermediate reformate as feed. .sup.(2) For Example
2: RON of C.sub.5+ and C.sub.5+ yield are given based on the heavy
reformate which is not subjected to the final stage reforming.
.sup.(3) For Comparative Example 1: RON of C.sub.5+, C.sub.5+ yield
and H.sub.2 production of the product are given based on the total
C.sub.5+ penultimate effluent as feed. .sup.(4) For Example 4:
Total RON of C.sub.5+, total C.sub.5+ yield and total H.sub.2
production are given based on the total C.sub.5+ penultimate
effluent as feed (which is distilled into intermediate reformate
and heavy reformate in Example 2). The final product of Example 4
consists of a blend of (i) the product from the final stage
reforming of the intermediate reformate and (ii) the heavy
reformate which is not subjected to the final stage reforming.
[0108] Table 4 demonstrates the benefits of the present invention
when using the intermediate reformate as the feedstock at lower
reaction temperature (900.degree. F. vs. 930.degree. F.)
(482.degree. C. vs/499.degree. C.) by showing improved hydrogen
yield, higher C.sub.5+ liquid yield and higher RON versus the full
boiling range C.sub.5+ feedstock.
TABLE-US-00005 TABLE 5 Comparison of results from Example 3 and
Example 5 Example 3 Example 5 Catalyst Pt/Na/Mg/ZSM-5 Pt/Re with
alumina binder with alumina binder Feedstock Intermediate
Intermediate Intermediate Intermediate reformate reformate
reformate reformate (Example 2) (Example 2) (Example 2) (Example 2)
Temperature, .degree. F. (.degree. C.) 900 (482) 950 (510) 910
(488) 940 (504) Pressure, psig (kPa) 80 (552) 80 (552) 200 (1380)
(1380) LHSV, hr.sup.-1 1.5 1.5 1.5 1.5 Molar H.sub.2/hydrocarbon
2:1 2:1 5:1 5:1 Ratio RON of C.sub.5+ 97.0 100.6 96.9 101.8
C.sub.5+ Yield, wt % 92.7 88.4 88.9 85.2 H.sub.2 Yield, scf/bbl
feed 300 430 130 175
[0109] Table 5 demonstrates a preferred embodiment of the present
invention, wherein the pressure of the final stage reactor is lower
than the pressure in the penultimate stage Improvements at the
lower pressure with the ZSM-5 based catalyst in terms of C5+ yield
and hydrogen production at similar C5+RON are seen versus the Pt/Re
catalyst at higher pressure.
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