U.S. patent application number 11/119518 was filed with the patent office on 2006-04-06 for method to extend the utilization of a catalyst in a multistage reactor system.
Invention is credited to George F. Diffendall, Mayis Seapan.
Application Number | 20060070918 11/119518 |
Document ID | / |
Family ID | 35759319 |
Filed Date | 2006-04-06 |
United States Patent
Application |
20060070918 |
Kind Code |
A1 |
Seapan; Mayis ; et
al. |
April 6, 2006 |
Method to extend the utilization of a catalyst in a multistage
reactor system
Abstract
The invention provides a method to extend the utilization of a
catalyst in a multistage reaction system, provided that a primary
reaction and a secondary (or more) catalyst-poisoning reaction
occur on the same catalyst, and the rate of the secondary (or
more), catalyst-poisoning reaction is faster than the rate of the
primary reaction.
Inventors: |
Seapan; Mayis; (Landenberg,
PA) ; Diffendall; George F.; (Wilmington,
DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
35759319 |
Appl. No.: |
11/119518 |
Filed: |
April 29, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60615083 |
Oct 1, 2004 |
|
|
|
Current U.S.
Class: |
208/210 ;
208/251H; 208/254H; 208/57; 208/58 |
Current CPC
Class: |
B01J 8/0457 20130101;
B01J 35/0006 20130101; C10G 65/02 20130101; B01J 8/0085 20130101;
B01J 2219/0004 20130101; B01J 2208/00707 20130101 |
Class at
Publication: |
208/210 ;
208/251.00H; 208/254.00H; 208/057; 208/058 |
International
Class: |
C10G 65/02 20060101
C10G065/02; C10G 65/04 20060101 C10G065/04 |
Claims
1. A method for extending catalyst utilization comprising: (a)
passing a feedstock and hydrogen through at least two
serially-connected reactors in positions R.sub.1, R.sub.2, . . . .
R.sub.n, wherein n is the number of reactors, each reactor
containing a catalyst, for a period until the catalyst in at least
one most upstream reactor is deactivated for a secondary catalytic
reaction or until the product from the most downstream reactor
fails to meet a desired specification; (b) bypassing the at least
one most upstream reactor containing the deactivated catalyst of
step (a) to pass the feedstock and hydrogen into at least one
downstream reactor; (c) reloading the at least one bypassed reactor
of step (b) with fresh catalyst; (d) placing the at least one
reloaded reactor of step (c) downstream of at least one of the
serially-connected reactors that were not reloaded with fresh
catalyst in step (c); and (e) repeating steps (a) through (d) to
meet the product specification.
2. The method of claim 1, wherein the catalyst is selected from the
group consisting of a zero-valent element of one or more of the
Group VIII elements of the Periodic Table.
3. The method of claim 2, wherein the catalyst is selected from the
group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt.
4. The method of claim 2, wherein the catalyst is a porous metal
structure.
5. The method of claim 4, wherein the catalyst comprises Raney.RTM.
nickel.
6. The method of claim 2, wherein the catalyst is supported on a
support.
7. The method of claim 6, wherein the support is selected from the
group consisting of carbon, alumina, silica, titania,
silica-alumina, silica-titania, titania-alumina, clays,
aluminosilicates, zeolites, water insoluble salts of calcium, water
insoluble salts of barium, water insoluble salts of strontium,
compounds thereof and combinations thereof.
8. The method of claim 7, wherein the catalyst comprises nickel
with heavy nickel loading supported on extrudates of
silica/alumina.
9. The method of claim 1, wherein the pressure is from about 100
kPa to about 20 MPa.
10. The method of claim 1, wherein the hydrogen is fed to one or
more of the reactors.
11. The method of claim 1, wherein the temperature is from about
minus 50.degree. C. to about 400.degree. C.
12. The method of claim 1, further comprising adjusting the
temperature to compensate for the number of serially-connected
reactors in each of steps (b) and (d) for obtaining product with
the desired specifications.
13. The method of claim 1, wherein the feedstock is an organic
liquid comprising a compound that can be hydrogenated by a catalyst
of one or more of the Group VIII elements of the Periodic
Table.
14. The method of claim 1, wherein in step (d) the at least one
reloaded reactor is placed downstream of the most downstream
reactor that was not reloaded with the fresh catalyst in step
(c).
15. A method for extending catalyst utilization comprising: (a)
passing an organic feedstock and hydrogen through at least two
serially-connected reactors in positions, R.sub.1, R.sub.2, . . .
R.sub.n, wherein n is the number of reactors, each reactor
containing a porous metal or supported catalyst, for a period until
the catalyst in at least one most upstream reactor is deactivated
for desulfurization or until the product from the most downstream
reactor fails to meet a desired specification; (b) bypassing the at
least one most upstream deactivated reactor of step (a) to pass the
feedstock and the hydrogen into downstream reactors; (c) reloading
the at least one bypassed reactor of step (b) with fresh catalyst;
(d) placing the at least one reloaded reactor of step (c)
downstream; and (e) repeating steps (a) through (d) to meet a
desired specification.
16. The method of claim 15, wherein the temperature is from about
minus 50.degree. C. to about 400.degree. C.
17. The method of claim 15, wherein the pressure is from about 100
kPa to about 20 MPa.
18. The method of claim 15, further comprising adjusting the
temperature to compensate for the number of serially-connected
reactors in each of steps (b) and (d) to meet the desired product
specifications.
19. The method of claim 15, wherein the feedstock comprises
1,3-propanediol.
20. The method of claim 15, wherein in step (d) the at least one
reloaded reactor is placed last in the reactor series, in position
Rn.
21. The method of claim 15, wherein the catalyst comprises nickel
with heavy nickel loading supported on extrudates of
silica/alumina.
22. A method for extending catalyst utilization comprising: (a)
passing a biochemically-derived organic feedstock containing
1,3-propanediol and hydrogen through at least two
serially-connected reactors in positions R.sub.1, R.sub.2, . . .
R.sub.n, wherein n is the number of reactors, each reactor
containing a catalyst comprising nickel with heavy nickel loading
supported on extrudates of silica/alumina, for a period until the
catalyst in the most upstream reactor is deactivated for
desulfurization or until the product from the most downstream
reactor fails to meet a desired specification; (b) bypassing the
reactor in position R.sub.1 to pass the feedstock and the hydrogen
into the reactor in position R.sub.2; (c) reloading the bypassed
reactor of step (b) with fresh catalyst; (d) placing the reloaded
reactor of step (c) in the reactor series downstream at position
Rn; and (e) repeating steps (a) through (d) to meet a desired
specification.
23. The method of claim 22 further comprising adjusting the
temperature to compensate for the number of serially-connected
reactors in each of steps (b) and (d).
24. The method of claim 22, wherein the temperature is from about
minus 50.degree. C. to about 200.degree. C.
25. The method of claim 22, wherein the temperature is from about
80.degree. C. to about 140.degree. C.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/615,083, filed Oct. 1, 2004, which is hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a method to extend utilization of
a catalyst in a multistage reactor system. More specifically, the
invention relates to a method to extend catalyst utilization in
sets of reactions catalyzed on the same catalyst (i.e.,
hydrogenation and desulfurization), where one reaction causes
catalyst poisoning.
BACKGROUND
[0003] Hydrogenation is a commonly practiced process in petroleum,
chemical, and food industries. Depending on the feedstocks and the
severity of the operating conditions (e.g., temperature, pressure,
and contact time), the hydrogenation process may saturate
unsaturated bonds, reduce aldehydes and ketones, reduce carboxylic
acids and their esters, reduce nitrogen-containing compounds,
reduce sulfur-containing compounds, and cause numerous other
reduction reactions.
[0004] In catalytic hydrogenation processes, the active catalyst is
usually a zero-valent metallic catalyst of one or more of the Group
VIII elements of the periodic table. Catalyst deactivation is a
common phenomenon in catalytic processes (e.g., hydrocracking,
hydrotreating, as well as hydrogenation). For example, sulfur in a
feedstock is a poison for most hydrogenation catalysts. In such
cases, hydrodesulfurization proceeds along with hydrogenation.
Reduction of the organic sulfur compounds in the feedstock converts
the sulfur to its divalent form. The divalent sulfur reacts with
the active zero-valent metal of the catalyst to form a metal
sulfide. At low to moderate temperatures (lower than about
200.degree. C.) of hydrogenation, metal sulfides do not have
practical hydrogenation activity and thus are considered the
poisoned form of the metallic catalysts.
[0005] To preclude or reduce catalyst poisoning, desulfurization of
the feedstock prior to the desired reaction can be achieved by
physical adsorption of the organoo-sulfur compounds on certain
reactive adsorbents. "Reactive adsorption" refers to cases where
the sulfur compounds react with the adsorbent. Various oxides
(including ZnO, CuO, and MnO) can react with the sulfur compounds
(specifically hydrogen sulfide) and remove them from gaseous
streams.
[0006] At temperatures above 200.degree. C., metal sulfides show
hydrodesulfurization and some hydrogenation activity.
Hydrodesulfurization is a widely practiced process in the petroleum
industry to selectively desulfurize feedstocks. In
hydrodesulfurization, the organo-sulfur compounds are converted to
hydrogen sulfide, which is usually removed from the reactor as a
gas mixed with the excess hydrogen. A thorough review of
desulfurization processes has recently been published by I. V.
Babich and J. A. Moulijn (Fuel, 82, pp 607-631, (2003)).
[0007] In a single reactor, the poisoned zone will progress
downstream, gradually diminishing the activity of the upstream
portion of the catalyst bed to the point where the reactor cannot
produce a product with desired specifications. Although the entire
reactor bed cannot meet the required specification, the catalyst
downstream from the poisoned zone still is relatively active and
may only be slightly deactivated.
[0008] In traditional practice, once the quality of the reactor
product falls below the accepted specification, it becomes
necessary to replace the catalyst of the entire reactor bed. This
requires stopping the operation to remove and dispose of the
poisoned catalyst once the quality of the reactor product falls
below the accepted specification, and to load the reactor with
fresh catalyst before resuming operation. Because the rate of the
secondary reaction (for example, hydrodesulfurization) is faster
than the rate of the primary reaction (for example hydrogenation),
the full extent of the useful life of the catalyst is not realized
and the economics of the process are negatively affected.
[0009] Attempts have been made to extend catalyst utilization.
These methods include external or in-situ regeneration, and various
process modifications, including altering operating conditions
(such as increasing temperatures) to compensate for the lost
primary reaction activity, for example, a process having a
multi-reactor or a single reactor with multi-zone concept for
selective hydrogenation of diolefins in a liquid hydrocarbon. Once
the zone or reactor furthest from the inflow of feedstock loses its
activity, the next closest zone or reactor is brought on stream and
placed upstream of the partially deactivated zone.
[0010] The problem that remains to be solved is how to extend
catalyst utilization when a primary reaction (e.g., hydrogenation)
and a secondary (or more) catalyst-poisoning reaction (e.g.,
hydrodesulfurization) occur on the same catalyst, and when the rate
of the poisoning reaction is faster than the rate of the primary
reaction.
SUMMARY OF THE INVENTION
[0011] A method is provided for extending catalyst utilization in a
multistage reaction system comprising: a) passing a feedstock and
hydrogen through at least two serially-connected reactors in
positions R1, R2, . . . Rn, wherein n is the number of reactors,
each reactor containing a catalyst, for a period until catalyst in
at least one most upstream reactor is deactivated for a secondary
catalytic reaction or until the product from the most downstream
reactor fails to meet a desired specification; b) bypassing the at
least one most upstream reactor of step (a) to pass the feedstock
and hydrogen into at least one downstream reactor; c) reloading the
at least one bypassed reactor of step (b) with fresh catalyst; d)
placing the at least one reloaded reactor of step (c) downstream of
at least one of the serially-connected reactors that were not
reloaded with fresh catalyst in step (c); and e) repeating steps
(a) through (d) to meet the product specification.
[0012] In one embodiment of the invention, the temperature may be
optionally increased after step (a) to continuously meet the
specification for the product as it leaves the most downstream
reactor. Subsequently, after step (d) the temperature is decreased
to its original level. Adjusting the temperature allows the product
specification to be met continuously even during catalyst change
out without interrupting the process.
[0013] The method of the invention uses a catalyst selected from
the group consisting of a zero-valent element of one or more of the
Group VIII elements of the Periodic Table. One embodiment of the
method for extending catalyst utilization provides: a) passing an
organic feedstock and hydrogen through at least two
serially-connected reactors in positions, R1, R2, . . . Rn, wherein
n is the number of reactors, each reactor containing a porous metal
or supported catalyst, for a period until the catalyst in at least
one most upstream reactor is deactivated for desulfurization or
until the product from the most downstream reactor fails to meet a
desired specification; b) bypassing the at least one most upstream
deactivated reactor of step a) to pass the feedstock and hydrogen
into downstream reactors; c) reloading the at least one bypassed
reactor of step b) with fresh catalyst; d) placing the at least one
reloaded reactor of step c) downstream; and e) repeating steps (a)
through (d) to meet the product specification.
[0014] Another embodiment of the invention extends catalyst
utilization in the manufacture of biologically derived
1,3-propanediol comprising the steps: a) passing a biologically
derived organic feedstock comprising 1,3-propanediol and hydrogen
through at least two serially-connected reactors in positions R1,
R2, . . . . Rn, wherein n is the number of reactors, each reactor
containing a catalyst comprising nickel with heavy nickel loading
supported on extrudates of silica/alumina, for a period until the
catalyst in the most upstream reactor is deactivated for
desulfurization or until the product from the most downstream
reactor fails to meet a desired specification; b) bypassing the
reactor in position R1 to pass the feedstock and hydrogen into the
reactor in position R2; c) reloading the bypassed reactor of step
b) with fresh catalyst; d) placing the reloaded reactor of step c)
in the reactor series downstream at position Rn; and e) repeating
steps (a) through (d) as necessary to meet the product
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1a shows the initial arrangement of reactors in series
where the feedstock enters reactor A (in position R1), and then
downstream reactors B and C (in positions R2, . . . Rn), with
optional intermittent hydrogen input.
[0016] FIG. 1b shows a flow diagram for the subsequent arrangement
of the reactors after the deactivated catalyst in reactor A is
replaced with fresh catalyst and is placed back on stream in
position Rn, where the outlet of reactor C supplies the feed for
reactor A.
[0017] FIG. 2 shows the distribution of sulfur on two spent
catalyst beds.
[0018] FIG. 3 shows the activity of fresh and spent catalysts of
varying sulfur content. Catalyst activity (expressed as a percent
reduction in absorbance at UV-270 nm) clearly decreases with
increased sulfur deposited on the catalyst.
[0019] FIG. 4 shows the effect of temperature on the profile of
sulfur deposited on the spent catalyst. At 120.degree. C., most of
the sulfur accumulates near the entrance of the reactor, whereas at
80.degree. C., sulfur deposition is spread more uniformly
throughout the catalyst bed.
[0020] FIG. 5 shows that a reactor filled with partially-poisoned
catalyst can remove most of the sulfur and serve as a guard bed to
protect downstream reactor beds from heavy sulfur deposition
load.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The inventors have solved the stated problem with a method
for extending catalyst utilization in a multistage reactor system
for feedstocks containing organics. When a primary reaction (e.g.,
hydrogenation) and a secondary (or more) catalyst-poisoning
reaction (e.g., hydrodesulfurization) occur on the same catalyst,
and when the rate of the catalyst-poisoning reaction is faster than
the rate of the primary reaction, catalyst poisoning is mainly
restricted to the upstream reactor while the downstream reactor
completes the bulk of hydrogenation needed to meet the product
specification. By "reactor" is meant an individual reactor within a
series of multiple reactors.
[0022] The invention directs the catalyst-poisoning reaction to the
upstream reactor, preventing the downstream reactors from uniform
and/or rapid poisoning. Because the upstream reactor is used as a
guard bed to protect the catalyst in the downstream reactor or
reactors against poisoning, the overall useful life of the catalyst
is extended.
[0023] This method provides two significant advantages for
multistage reaction systems: 1) catalyst utilization can be
significantly extended, and 2) process and equipment downtime
needed to change the catalyst can be significantly reduced or even
eliminated.
[0024] The method uses a multistage reactor system comprised of a
minimum of two reactors in series (in positions R1, . . . Rn, where
n is the number of reactors). (See FIG. 1a.) The reactors are
operated under such conditions as to concentrate or direct the
secondary (or more) catalyst-poisoning reaction to the most
upstream reactor(s). Secondary (or more) reactions may be, for
example, desulfurization or demetallation. When the most upstream
reactor in position R1 is poisoned, it is taken out of service
(bypassed) and its catalyst is changed to fresh catalyst. During
this period, the process continues in the second or downstream
reactors (in positions R2, . . . Rn). To compensate for the removed
or bypassed reactor, the temperature in the reactor now in the most
upstream position R1 can be temporarily increased to meet the
product specification requirements. After reloading the bypassed
reactor with fresh catalyst, it is placed downstream in the train
of reactors (in one embodiment at the most downstream position, Rn)
and the operating temperatures can be adjusted to reflect the
number of reactors in the train. The reloaded reactor in position
Rn now primarily serves as the reactor for the primary reaction
(e.g., hydrogenation). As shown in FIG. 1b, the reactor now most
upstream in position R1 (containing partially-poisoned catalyst)
serves as the primary site for the secondary reaction, thus
protecting downstream reactors in positions R2, . . . Rn. The
cycling of the reactors continues as the next reactor most upstream
in the process train deactivates to a designated level, is removed
or bypassed, refreshed, and replaced downstream in turn.
Catalyst
[0025] Any hydrogenation catalyst known in the art is suitable for
use in this invention, provided that the primary hydrogenation
reaction and a secondary (or more) catalyst-poisoning reaction
occur on the same catalyst, and the rate of the catalyst-poisoning
reaction is faster than the rate of the primary hydrogenation
reaction. By varying the operating conditions (e.g. temperature)
the rate of hydrogenation relative to the rate of one or more
poisoning reactions can be adjusted to remove the bulk of the
poisons in the upstream reactor. In one embodiment of the
invention, the hydrogenation catalyst can remove sulfur in a narrow
band. In this case, the catalyst's ability to remove sulfur in a
narrow band is used to vary the relative rate of hydrogenation
relative to the rate of desulfurization and the affinity of the
catalyst to react with the sulfur to remove it. The relative rates
of the reactions in each set can be determined by one of ordinary
skill in the art by varying the reaction temperature, pressure, and
the feedstock contact time with the catalyst without generating
undesirable side reactions.
[0026] The catalyst used in the invention is comprised of at least
one zero-valent element of the Group VIII elements of the Periodic
Table. In embodiments of the invention the catalyst is at least one
of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt, with or without various
promoters. The catalyst need not be present in its elemental form.
The promoter may be any element of the periodic table or a compound
thereof that could be added to the catalyst to enhance its activity
or selectivity. "The Handbook of Heterogeneous Catalytic
Hydrogenation for Organic Synthesis," by Shigeo Nishimuru, John
Wiley (2001), ISBN: 0471-39698-2, extensively discusses such
catalysts and conditions.
[0027] The catalyst may be a porous metal structure, a Raney.RTM.
catalyst, or supported on a substrate. The catalyst support could
be from any support material known in the art, such as at least one
of carbon, alumina, silica, titania, silica-alumina,
silica-titania, titania-alumina, clays, aluminosilicates, zeolites,
water insoluble salts of calcium (such as calcium carbonate),
barium (such as barium sulfate), strontium (such as strontium
carbonate), and compounds and combinations thereof. The catalyst
may have various shapes or sizes, such as fine powder, granules,
tablets, pellets, extrudates, or other structured supports.
Feedstocks
[0028] Suitable feedstocks for the process of this invention are
those comprising compounds that can be hydrogenated, as well as
other materials or compounds that poison the catalyst in a
secondary reaction. The invention is useful for
hydrogenation/desulfurization systems in which the feedstocks
contain sulfur compounds. The sulfur-containing feedstock is not
limited to petroleum-based hydrocarbons and may be any organic
fluid/s derived from fossil and/or biological sources. The
inventive technique is more advantageously applied to feedstocks
characterized by low but still undesirable levels of sulfur. The
lower the undesirable sulfur level in the feedstock, the longer the
life of the catalyst can be extended by use of the invention.
Operating Conditions
[0029] The operating conditions for the invention are first
selected to meet the specification for the product produced by the
particular catalytic reactions. Those skilled in the art will be
well aware of the methods to adapt the invention to yield a
particular product, for instance, conducting a series of
experiments to determine the best temperature, pressure, and the
feedstock contact time to concentrate the catalyst-poisoning
reaction in the upstream reactor(s). Additionally, it will be
further beneficial to test the activity of the partially poisoned
catalyst from the downstream reactor to demonstrate and measure its
remaining activity available for the primary hydrogenation
reaction. Once these two conditions are established and verified, a
train of multiple reactors can be designed to implement this
invention for a particular product.
[0030] The claimed invention describes a multistage reactor system
to manage catalyst poisoning from the secondary reaction (i.e.,
hydrodesulfurization) in a more economical way than previously
known. Instead of one large reactor typically used in conventional
systems, at least two smaller reactors having a combined catalyst
volume equivalent to that of the one large reactor are placed in
series. The reactors are used as disclosed to hydrogenate the
feedstock until catalyst is poisoned for the secondary reaction or
the product fails to meet the product specification as it exits the
most downstream reactor. The first reactor(s) is then bypassed and
the feedstock is directed instead into the next reactor(s)
downstream in the series.
[0031] Increasing the processing temperature to compensate for the
removal or bypassing of the upstream reactor enables the remaining
reactor(s) to continuously meet the product specification during
catalyst change out without any interruption in the process. During
this operating period, the first reactor(s) is reloaded with fresh
catalyst. The renewed reactor(s) is/are then returned to service,
but placed downstream of the partially deactivated reactor(s),
preferably in the most downstream position in the train and the
temperature is adjusted to the desired original level such that the
product specifications are met. The reactor(s) containing partially
poisoned catalyst, now at the most upstream position in the series,
act(s) as the primary desulfurization reactor, while the renewed
reactor(s) with the fresh catalyst provides primarily hydrogenation
activity. A schematic of a multi-feed embodiment of the process is
shown in FIGS. 1a and 1b. The hydrogen may be fed into individual
reactors or may be fed to the most upstream reactor.
[0032] When the primary reaction is hydrogenolysis (such as
hydrodesulfurization, hydrodenitrogenation or hydrodeoxygenation),
the operating temperature is usually at or below 400.degree. C.
When the primary reaction is hydrogenation, the operating
temperature of this invention is usually at or below 200.degree. C.
(preferably in the range of about minus 50.degree. C. to about
140.degree. C.). During hydrogenation, the removed sulfur may
deposit as adsorbed elemental sulfur or as a reacted compound
(usually as a metal sulfide). Hydrogen flow rate and hydrogen
pressure must be maintained to deliver adequate hydrogen to the
catalyst surface to accomplish the desired hydrogenation. In
general, the hydrogen feed rate depends on the hydrogen demand of
the process. The operating hydrogen pressure for the process of
this invention is above 100 kPa with a preferred range of 800-4240
kPa. In the hydrogenation of 1,3-propanediol, the hydrogen to crude
PDO feed ratio is above 0.5 scc H2/g PDO with a preferred range of
1-20 scc H2/g PDO.
[0033] The process of this invention can be applied to any
multi-reaction system where a primary reaction and a secondary (or
more) catalyst-poisoning reaction occur on the same catalyst, and
when the rate of the catalyst-poisoning reaction is faster than the
rate of the primary reaction. These reactions can be of any
chemistry where catalyst deactivation can be narrowed to a band (or
portion) of the bed and only the contents of that deactivated band
can be changed while the remainder of the reaction bed continues
functioning. Examples of such multi-reaction systems include
hydrocracking, hydrotreatment, hydrodeoxygenation,
hydrodenitrogenation, and hydrodesulfurization reactions, where the
catalyst may be poisoned by secondary hydrodemetallation
reactions.
Reactor System
[0034] The invention can be applied to any type of reactor in
multistage configuration, provided that the reactor configuration
allows for the determination of the operating conditions that will
concentrate the catalyst-poisoning phenomenon into the first
reactor. Such reactors include fixed-bed catalytic reactors with
upflow or down-flow arrangement, where the hydrogen can be fed
individually into each reactor or fed just into one reactor. The
hydrogen may flow co-currently or counter-currently with the liquid
feedstock. The reactors may alternatively be of slurry-type or
fluidized-bed or any other reactor type known in the literature
(see, for example, Perry's Chemical Engineer's Handbook, Sixth
Edition, R. H. Perry and D. Green, Ed.). An industrially
advantageous reactor uses a packed-bed of catalyst wherein the
liquid and gas flow co-currently or counter-currently, in an
up-flow or down-flow (trickle-bed) mode of operation.
1,3-Propanediol Processed in a Hydrogenation/Desulfurization
System
[0035] A suitable feedstock processed in a
hydrogenation/desulfurization system comprises 1,3-propanediol
(also hereinafter termed "PDO"), a monomer useful in the production
of a variety of polymers including polyesters, polyurethanes,
polyethers, and cyclic compounds. Homo- and co-polyethers of
polytrimethylene ether glycol are examples of such polymers. The
polymers are ultimately used in various applications including
fibers, films, etc.
[0036] PDO may be obtained from non-renewable resources, typically
petrochemical products. Chemical routes to generate PDO include
hydroformylation of ethylene oxide over a catalyst or hydration of
acrolein. Both of these synthetic routes to PDO involve the
intermediate synthesis of 3-hydroxypropionaldehyde. The
3-hydroxypropionaldehyde is reduced to PDO in a final catalytic
hydrogenation step. Subsequent purification involves several
processes, including vacuum distillation. Hereinafter, the PDO from
chemical processes is termed "chemical PDO" or "chemically derived
PDO".
[0037] PDO is also derived from renewable resources, including
glucose or glycerol from such sources as corn or other biomass.
Such PDO is hereinafter referred to as "biochemical PDO",
"bio-PDO", or "biochemically-derived PDO". The technique is
disclosed in several patents, including U.S. Pat. Nos. 5,633,362;
5,686,276; and 5,821,092, all of which are incorporated in their
entirety by reference herein. The PDO formed via biochemical routes
contains numerous organic compounds and several organic sulfur
compounds in the parts-per-million (ppm) range.
[0038] Applicants' invention is usefully practiced where
hydrogenation is used as a polishing step in the production of PDO,
for instance to obtain PDO of suitable quality for polymer
production. (See WO2004/101479, WO2004/101482, and WO2004/101468,
all of which are incorporated in their entirety by reference
herein.) In the bio-PDO process, hydrogenation comprises contacting
biochemically-derived PDO with hydrogen in the presence of a
hydrogenation catalyst. The catalyst in the polishing process
serves two purposes: 1) to hydrogenate the color and color
precursor compounds, and 2) to remove the sulfur from the
feedstock. The extent of hydrogenation can be determined as a
function of color, residual carbonyls, iodine number, and similar
indicators known to those of skill in the art.
[0039] The catalyst used in the invention is comprised of at least
one zero-valent element of Group VIII of the periodic table. In
embodiments of the invention the catalyst is at least one of Fe,
Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt. Various mixed metal oxides such
as mixed copper, chromium, and zinc oxides are also effective
catalysts for color removal. An embodiment of the invention
utilizes a nickel catalyst with heavy nickel loading. Another
embodiment of the invention utilizes a catalyst comprising nickel
supported on extrudates of silica/alumina.
[0040] In another embodiment of the invention, the catalyst may be
present with at least one promoter. The promoter may be any element
of the periodic table or compound thereof that could be added to
the catalyst to enhance its activity or selectivity. In other
embodiments of the invention promoters are iron, chromium, and
molybdenum.
[0041] The sulfur compounds contained in the crude PDO are reduced
in the hydrogenation process. The reduced sulfur may then react
with the hydrogenation catalyst, poisoning its active sites. This
poisoning of the catalyst for hydrogenation by the desulfurization
of the feedstock represents a significant cost in the manufacture
of PDO. Previously when the catalyst lost its color-removing
capacity, it was replaced with fresh catalyst regardless of any
remaining ability to hydrogenate or remove sulfur from the
feedstock. The replacement protocol required equipment downtime. In
terms of materials and time, replacement of the underutilized
catalyst was relatively expensive in light of the overall process.
Cycling the reactors in the manner of the invention extends the
overall utilization of the catalyst and can reduce or eliminate
equipment downtime.
[0042] The temperature for the process ranges from about minus
50.degree. C. to about 200.degree. C. In another embodiment, the
temperature for the process ranges from about 80.degree. C. to
about 140.degree. C.
[0043] Other Sets of Multiple Reactions on the Same Catalyst
[0044] In petroleum feedstocks containing vanadium and/or nickel
porphyrins, hydrotreatment and hydrodemetallation reactions are
catalyzed on the same catalyst. The secondary reaction removes
these metals and deposits them on the catalyst, poisoning the
catalyst for the primary reaction. Similarly, in the upgrading of
coal-derived liquids, the organometallic compounds of titanium and
other elements present in the coal liquids are converted to metals
by the secondary reaction, poisoning the catalyst for use in the
primary reaction. Other sets of reactions that are catalyzed on the
same catalyst are known to those of skill in the art of industrial
catalysis.
[0045] Usually hydrodemetallation reactions are relatively faster
than the hydrotreatment reactions on the same catalyst. By
determining and selecting a set of suitable operating conditions,
the deposition of metals can be concentrated in the most upstream
reactor(s) of a multiple stage reactor system, allowing the
downstream reactor(s) to complete the desired degree of
hydrotreatment.
[0046] Initially, a set of experiments is conducted under typical
hydrotreatment conditions (where the Liquid Hourly Space Velocity
(LHSV) is varied, for example, from 0.1 to 10 1/h and the
temperature is varied, for example, from 200.degree. C. to
400.degree. C.) to accomplish hydrodemetallation of the metal(s)
contained in the feedstock and to concentrate the deposition of the
metals in the most upstream reactor(s).
[0047] Under such suitable operating conditions, the metals can be
deposited in a relatively narrow band in the most upstream
reactor(s) of a multi-stage reactor system. Once the upstream
catalyst loses its secondary reactivity for metals removal, it can
be removed or bypassed in the process reactor train and the reactor
reloaded with fresh catalyst. This reactor can now be placed
downstream in the reactor train (preferably at the most downstream
position), to provide the primary catalytic reaction to complete
the desired degree of hydrotreatment. Cycling the reactors in this
manner extends the overall utilization of the catalyst and can
reduce or eliminate equipment downtime.
General Materials, Equipment, and Test Methods
Feedstock
[0048] The biochemically-derived PDO is from E.I. du Pont de
Nemours and Company. Four different batches of the biochemical PDO
made at a pilot plant in Decatur, Ill., were used in the examples
below. These batches were 99.4 to 99.8% pure PDO with over 60
unidentified impurities comprising from about 0.2 to about 0.6% of
the crude PDO and had an initial UV absorption at 270 nm (20%
solution in water (v/v)) varying from 0.61 to 1.83 and a sulfur
content varying from 1.3 to 16 ppm.
Catalyst
[0049] The catalyst was a commercially available, supported nickel
material, C-28-1-01-RS-CDS catalyst (Sud-Chemie Inc., Louisville,
Ky.). It is a reduced and stabilized high nickel-content catalyst
containing nominally 52% Ni on silica/alumina. It is an extrudate
of 1.6 mm size with a surface area of about 250-350 m2/g. The fresh
catalyst contains about 200 ppm sulfur.
Reactor
[0050] The laboratory reactor is a jacketed stainless steel tube of
17.3 mm inside diameter packed with either 129 or 250 mm height of
catalyst. The reactor was heated by hot oil flowing through the
reactor jacket. Both PDO and hydrogen entered at the bottom of the
reactor and the flow direction was upflow.
Test Method 1. UV absorption
[0051] The PDO color quality was measured by a UV/VIS
spectrophotometer. Specifically, the broad UV absorption peak at
around 270-280 nm correlates strongly with the presence of color
precursors in the PDO and color in the polymers made therefrom.
Hydrogenation converts the color precursors and color compounds,
reducing the UV-270 nm absorption. Therefore, absorption at UV-270
nm is used as a measure of the extent of hydrogenation. All the UV
analyses were measured using a HP 8453 UV/VIS (Hewlett-Packard,
Palo Alto, Calif.) spectrophotometer after diluting the PDO to a
20% concentration by volume with water. The results are reported in
the Examples at this 20% dilution.
Test Method 2. Sulfur Analysis
[0052] The sulfur was analyzed by a Perkin-Elmer 3300RL Inductively
Coupled Plasma (ICP) analyzer. Liquid samples were analyzed by
direct injection into the analyzer. Catalyst samples were dissolved
in acids and then analyzed as aqueous solution. TABLE-US-00001
Glossary AU Absorption Unit kPa Kilo Pascal MPa Mega Pascal LHSV
Liquid Hourly Space Velocity, 1/h ppm Part per million of weight
scc/g Standard cubic centimeters per gram .degree. C. Degree
Celsius mm millimeter g gram h hour approx approximately
EXAMPLES
Example 1
[0053] Run-36 was conducted in a single reactor with 250 mm
catalyst packing at various temperatures (80.degree. C.,
100.degree. C., and 120.degree. C., but mostly at 100.degree. C.)
at 2860 kPa, 0.8 1/h LHSV with H2 to PDO flow ratio of 6.1 scc/g.
The feed had 16 ppm sulfur and the run continued until the catalyst
was significantly deactivated. At the end of the run, the catalyst
was taken out in segments and analyzed for its sulfur content.
[0054] FIG. 2 shows the sulfur profile in the reactor, indicating
that sulfur deposition is predominantly near the reactor
entrance.
[0055] Furthermore, this test showed that the desulfurization rate
is much faster than the hydrogenation rate to remove color. The
following Table 1 shows that at various conditions of operation
while the percentage reduction in UV-270 nm varies from 65 to 94%,
the sulfur concentration in the PDO exiting the reactor is below
the detection limit of 1 ppm. TABLE-US-00002 TABLE 1 Temperature
LHSV % Reduction % Reduction .degree. C. 1/h UV-270 Sulfur 80 0.8
65.3 approx. 100 100 0.4 91.4 approx. 100 100 0.8 87.4 approx. 100
100 1.2 78.1 approx. 100 120 0.8 94.2 approx. 100
Example 2
[0056] Run-37 was conducted in a single reactor with 250 mm
catalyst packing at various temperatures (80.degree. C.,
100.degree. C., and 120.degree. C., but mostly at 100.degree. C.)
at 2860 kPa, 0.8 1/h LHSV with H2/PDO=6.1 scc/g. The run continued
until the reactor bed was partially deactivated but was still able
to meet the desired UV specifications. The run was stopped and the
catalyst was removed in segments and analyzed for sulfur.
[0057] FIG. 2 shows more distinctly that sulfur deposits
predominantly near the entrance of the bed. The partially used bed
(Run-37) shows most of the sulfur accumulated in the front one
third of the bed. The extensively used catalyst bed (Run-36) shows
most of the sulfur accumulated in the first half of the bed.
Example 3
[0058] Three segments of the spent catalyst from Run-36 were
sampled to represent poisoned catalysts with different levels of
sulfur on the catalyst. The hydrogenation activities of these
samples and that of a sample of the fresh catalyst were measured
under identical conditions of 3.8 1/h LHSV, 100.degree. C., and
2860 kPa.
[0059] FIG. 3 shows that the catalyst activity for color removal,
as measured by percent reduction in the absorption at UV-270 nm,
decreases with increasing level of sulfur accumulated on the
catalyst.
Example 4
[0060] Run-46 and Run-47 were conducted at 80.degree. C. and
120.degree. C., holding all other operating parameters, including
the run duration identical (1.2 1/h LHSV, 2860 kPa, H2/PDO of 7.8
scc/g, for a duration corresponding to about 380 kg of PDO/kg of
catalyst).
[0061] FIG. 4 shows the distribution of sulfur in the bed. At
higher temperatures the rate of desulfurization increased,
depositing the sulfur closer to the reactor entrance. This example
demonstrates that by selecting the proper temperature, the sulfur
deposition profile in the bed can be changed to accumulate the
sulfur in a selected zone of the bed, thus protecting the entire
bed from deactivation.
Example 5
[0062] Run-70 was carried out in two reactors arranged in series.
The first reactor was packed with a portion of the poisoned
catalyst from Run-36, which was well deactivated and had 6700 ppm
of sulfur. This reactor served as a guard bed for the second
reactor. The second reactor was packed with fresh catalyst
containing 330 ppm sulfur. The run was carried out at 100.degree.
C., 1.2 1/h LHSV, 2860 kPa, H2/PDO of 7.8 scc/g for a duration
corresponding to 1000 kg of PDO/kg catalyst.
[0063] Analysis of the poisoned catalyst in the guard bed reactor
showed significant additional sulfur removal. The sulfur profile of
the downstream reactor, which was protected by the guard bed,
showed substantially lower sulfur deposition, as shown in FIG.
5.
Example 6
[0064] In order to evaluate the effect of guard bed in protecting
the downstream bed, Run-71 was carried out in a single reactor,
identical to the second reactor of Example 5, except that no guard
bed was placed upstream of this reactor. The run conditions were
identical to those of Run-70.
[0065] FIG. 5 shows the effect of the guard bed in protecting the
fresh catalyst. In this example, the guard bed reduced the average
sulfur deposition on the catalyst from 3000 ppm to about 1350 ppm,
or by 55%.
Example 7
[0066] Run-76 was made with two reactors in series, both loaded
with fresh catalyst, with a combined LHSV of 1.2 1/h at 120.degree.
C., 2860 kPa, and 6.9 scc of H2/g of PDO for a duration
corresponding to 2100 kg PDO/kg catalyst. During this period the
UV-270 of the product increased to 0.1 Absorption Units (AU). After
completion of the run, the catalyst in the upstream reactor was
replaced with fresh catalyst and this reactor was placed downstream
of the reactor originally positioned downstream. The run with spent
catalyst in the first reactor, Run-77, was carried out under
conditions identical to those in Run-76 to a point where the UV-270
of the product reached the same level (0.1 AU) as in Run-76. This
duration corresponded to 1600 kg PDO/kg catalyst. Since this was
achieved by replacing only one reactor with fresh catalyst, two
catalyst change outs would have given 3200 kg PDO/kg catalyst
utilization. Thus compared with Run-76, it presented about 52%
increased utilization of catalyst.
[0067] The exact percent increase in catalyst utilization may vary
somewhat with the targeted product quality and operating
conditions. This example clearly showed that application of the
invention results in a significant increase in overall utilization
of the catalyst relative to that achievable without the
invention.
Example 8
Prophetic
[0068] For the hydrotreatment of petroleum feedstocks containing
organometallic poisons, the following example is proposed. A set of
experiments is conducted under typical hydrotreatment conditions
(where the LHSV is varied, for example, from 0.01 to 10 1/h and the
temperature is varied, for example, from 200.degree. C. to
400.degree. C.) to accomplish hydrodemetallation of the metal(s)
contained in the feedstock and to concentrate the deposition of the
metals in the most upstream reactor(s).
[0069] Under such suitable operating conditions, the metals can be
deposited in a relatively narrow band in the most upstream
reactor(s) of a multi-stage reactor system. Once the catalyst in
the upstream loses its secondary reactivity for the removal of
metals, the reactor can be removed or bypassed in the process
reactor train and the reactor is then reloaded with fresh catalyst.
This reloaded reactor is now placed downstream in the reactor train
(preferably at the most downstream position), to provide the
primary catalytic reaction to complete the desired degree of
hydrotreatment. Cycling the reactors in this manner extends the
overall utilization of the catalyst.
* * * * *