U.S. patent application number 11/779500 was filed with the patent office on 2008-01-24 for process for producing hydrogen.
This patent application is currently assigned to Green Hydrotec Inc.. Invention is credited to Chia Yeh Hung, Min Hon Rei, Hang Fu Wang, Guan Ting Yeh.
Application Number | 20080019902 11/779500 |
Document ID | / |
Family ID | 34750255 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080019902 |
Kind Code |
A1 |
Rei; Min Hon ; et
al. |
January 24, 2008 |
PROCESS FOR PRODUCING HYDROGEN
Abstract
A process for producing hydrogen is provided. The process
comprises the introduction of reactants into a reactor with a steam
reforming section containing a steam reforming catalyst to form a
hydrogen-containing product. The process is driven by heat
generated in a combustion section containing an oxidation catalyst,
which comprises a noble metal and boron nitride. According to the
process of the subject invention, the first combustion reaction can
rapidly generate heat and is advantageous for conducting steam
reforming reactions.
Inventors: |
Rei; Min Hon; (Tao Yuan,
TW) ; Yeh; Guan Ting; (Tao Yuan, TW) ; Wang;
Hang Fu; (Tao Yuan, TW) ; Hung; Chia Yeh; (Tao
Yuan, TW) |
Correspondence
Address: |
HOLLAND & KNIGHT LLP
10 ST. JAMES AVENUE
11th Floor
BOSTON
MA
02116-3889
US
|
Assignee: |
Green Hydrotec Inc.
19-2, Wen-Ming Rd. Kweishang
Tao Yuan
TW
333
|
Family ID: |
34750255 |
Appl. No.: |
11/779500 |
Filed: |
July 18, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10761789 |
Jan 21, 2004 |
7252692 |
|
|
11779500 |
Jul 18, 2007 |
|
|
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Current U.S.
Class: |
423/652 ;
423/648.1; 423/651 |
Current CPC
Class: |
C01B 2203/0822 20130101;
C01B 2203/0465 20130101; Y02P 20/10 20151101; C01B 2203/0811
20130101; B01J 2208/00504 20130101; B01J 2208/00716 20130101; C01B
2203/1604 20130101; C01B 2203/1064 20130101; C01B 3/501 20130101;
Y02P 20/128 20151101; C01B 2203/047 20130101; C01B 2203/1247
20130101; C01B 2203/041 20130101; C01B 2203/048 20130101; B01J
8/009 20130101; B01J 8/0285 20130101; C01B 2203/0827 20130101; C01B
2203/1223 20130101; C01B 3/38 20130101; C01B 2203/0475 20130101;
C01B 2203/1058 20130101; B01J 2208/00212 20130101; C01B 2203/0216
20130101; C01B 3/323 20130101; C01B 2203/1076 20130101 |
Class at
Publication: |
423/652 ;
423/648.1; 423/651 |
International
Class: |
C01B 3/26 20060101
C01B003/26 |
Claims
1. A process for producing hydrogen comprising a step of conducting
a steam reforming reaction of reactants, wherein the steam
reforming reaction is driven by a heat generated from a first
combustion reaction, and the first combustion reaction comprises
conducting an oxidation of a first fuel and is catalyzed by an
oxidation catalyst comprising a noble metal and boron nitride.
2. The process according to claim 1, wherein the noble metal is
selected from a group consisting of Pt, Pd, Rh, Ru, and a
combination thereof.
3. The process according to claim 1, wherein the noble metal is
Pt.
4. The process according to claim 1, wherein the oxidation catalyst
is carried by a support consisting essentially of a material
selected from a group consisting of alumina, titania, zirconia,
silica, and a combination thereof.
5. The process according to claim 4, wherein the material is
alumina.
6. The process according to claim 1, wherein the first fuel
comprises a hydrogen-containing gas, an alcohol, a hydrocarbon, or
a combination thereof.
7. The process according to claim 6, wherein the alcohol is
selected from a group consisting of methanol, ethanol, propanol,
isopropanol, butanol, and combinations thereof, and the hydrocarbon
is selected from a group consisting of methane, ethane, propane,
butane, pentane, hexane, gasoline, liquefied petroleum gas (LPG),
and combinations thereof.
8. The process according to claim 6, wherein the first fuel
comprises a portion of a hydrogen-containing product and the
hydrogen-containing product is produced by the steam reforming
reaction.
9. The process according to claim 6, wherein the first fuel
comprises methanol.
10. The process according to claim 6, further comprising conducting
a second combustion reaction in a steam reforming section for
conducting the steam reforming reaction until the steam reforming
section reaches a desired temperature prior to the starting of the
steam reforming reaction.
11. The process according to claim 10, wherein the second
combustion reaction comprises conducting an oxidization of a second
fuel, wherein the second fuel is identical to or different from the
first fuel.
12. The process according to claim 10, wherein the first combustion
reaction and the second combustion reaction are started
simultaneously.
13. The process according to claim 1, wherein the reactants
comprise water as well as an alcohol, a hydrocarbon, or a
combination thereof.
14. The process according to claim 13, wherein the alcohol is
selected from a group consisting of methanol, ethanol, propanol,
isopropanol, ethylene glycol, glycerol, and combinations thereof,
and the hydrocarbon is selected from a group consisting of methane,
hexane, liquefied petroleum gas (LPG), gasoline, naphtha oil,
diesel oil, and combinations thereof.
15. The process according to claim 13, wherein the reactants
comprise water as well as methanol, hexane, or a combination
thereof.
16. The process according to claim 1, wherein the steam reforming
reaction is catalyzed by a catalyst comprising Cu, Zn, Pd, Re, Ni,
or a combination thereof.
17. The process according to claim 16, wherein the steam reforming
reaction is catalyzed by a catalyst comprising K as well as Cu, Zn,
Pd, Re, Ni, or a combination thereof.
18. The process according to claim 1, further comprising a step of
purifying the product obtained from the steam reforming reaction to
provide hydrogen with a relatively high purity and a spent
product.
19. The process according to claim 18, wherein the first fuel
comprises a portion of the spent product.
20. The process according to claim 18, wherein the purifying step
is conducted with the use of at least one palladium membrane
tube.
21. The process according to claim 20, wherein the palladium
membrane tube is formed by depositing a palladium-containing
membrane on a porous support, and the porous support is made of
stainless steel or a ceramic material.
22. The process according to claim 21, wherein the
palladium-containing membrane is made of palladium, a
palladium-silver alloy or a palladium-copper alloy.
23. The process according to claim 20, wherein the hydrogen
obtained from the purifying step has a purity of at least 99%.
24. The process according to claim 18, further comprising a
converting step to convert any carbon-containing compounds
contained in the hydrogen into alkane.
25. The process according to claim 20, the process is conducted in
a reactor comprising a steam reforming section, a combustion
section, and a membrane tube section, the steam reforming reaction
is carried out in the steam reform section, the first combustion
reaction is carried out in the combustion section, and the
purifying step is conducted in the membrane tube section, wherein
the steam reforming section is arranged in the peripheral part of
the reactor, the membrane tube section is arranged in the central
part of the reactor and comprises at least one palladium membrane
tube, and the combustion section is located between the membrane
tube section and the steam reforming section.
26. The process according to claim 1, wherein the reactants
comprise water and methanol.
27. The process according to claim 26, wherein the steam reforming
reaction is conducted at a molar ratio of methanol/water ranging
from about 1.0 to about 1.5.
28. The process according to claim 27, wherein the molar ratio of
methanol/water ranges from about 1.05 to about 1.25.
29. The process according to claim 26, wherein the steam reforming
reaction is conducted at a temperature ranging from about
200.degree. C. to about 330.degree. C.
30. The process according to claim 29, wherein the steam reforming
reaction is conducted at a temperature ranging from about
280.degree. C. to about 300.degree. C.
31. The process according to claim 20, wherein the purifying step
is conducted at a temperature of not higher than about 490.degree.
C.
32. The process according to claim 31, wherein the purifying step
is conducted at a temperature ranging from about 25.degree. C. to
about 490.degree. C.
33. The process according to claim 31, wherein the purifying step
is conducted at a temperature ranging from about 200.degree. C. to
about 380.degree. C.
Description
RELATED APPLICATION
[0001] This application is a continuation-in-part of and claims
priority to U.S. patent application Ser. No. 10/761,789, filed 21
Jan. 2004, which is herein incorporated by reference.
TECHNICAL FIELD
[0002] The subject invention relates to a process for producing
hydrogen. More specifically, the invention relates to a process for
catalytically quick-driving hydrogen production with an integrated
catalyzed oxidation.
BACKGROUND OF THE INVENTION
[0003] Purified hydrogen is an important fuel source for many
energy conversion devices. For instance, fuel cells normally
require hydrogen with an extremely high purity and oxygen (or air)
as the fuel to generate electricity. A widely known process for
providing hydrogen is the steam reforming process. Particularly,
the steam reforming process comprises reacting steam with a fuel
such as an alcohol (e.g., methanol or ethanol) or a hydrocarbon
(e.g., methane, gasoline, or hexane) over a steam reforming
catalyst to form the main product hydrogen and other by-products
(e.g., CO and CO.sub.2). Since the steam reforming reaction is an
endothermic reaction, it requires a substantial amount of heat from
an external heating system to maintain the temperature of the steam
reforming system. Moreover, an additional purification facility is
also necessary to purify the product formed in the steam reforming
reaction to attain the desired purity of hydrogen, typically at
least 95% such as 95% to 99.995%. Obviously, the external
facilities for the steam reforming system, such as heaters and
purifying devices, occupy a larger share of the capital investment
and plant space.
[0004] Since highly-purified hydrogen is desirable in the industry,
numerous studies have been conducted to find an economic and simple
way to efficiently purify hydrogen from steam reforming reactions.
Membrane separators have been proposed to harvest purified hydrogen
from the steam reforming process. Additionally, to reduce the space
of the reaction system, the combination of the membrane separator
with the steam reformer in a single device, such as a membrane
steam reforming reactor, has also been proposed. For example, U.S.
Pat. No. 5,861,137 discloses a steam reformer with internal
hydrogen purification, which comprises a tubular hydrogen-permeable
and hydrogen selective membrane therein.
[0005] Traditional processes normally use external flame in the
endothermic steam reforming reaction mentioned above; however, the
complicated control and the heat transfer efficiency of such system
is not always desirable. It is believed that a rapid and stable
supply of heat is critical in maintaining the desired temperature
of the steam reforming zone and thus the reaction rate therein. If
not, the transfer of heat to the reaction zone fails, causing the
reaction temperature and conversation rate of hydrogen to drop. As
a result, developments have been focused on in-situ heating via
conventional combustion of fuel and/or spent gases from the
reformer to provide the heat required for the endothermic steam
reforming reaction. For example, U.S. Pat. No. 6,821,502 B2
provides a membrane steam reforming reactor using flameless
distributed combustion for generating heat. The flameless burning
can be provided by injecting a fuel and a preheated air stream to
the reactor for automatic ignition. Obviously, said technical means
needs to preheat the air with an additional heater prior to feeding
it into the combustion zone. U.S. Pat. No. 5,861,137 discloses a
small burner that is provided to burn the fuel or vent product
gases to provide the needed thermal energy. Such manner, however,
produces dangerous open flame and polluting products, e.g.,
nitrogen oxide. U.S. Pat. No. 6,585,785 B1 teaches a fuel processor
apparatus comprising a catalyst tubular reactor which is heated
using an infrared radiant burner to provide the endothermic heat of
the reaction needed to reform a mixture of hydrocarbon and steam
for the production of hydrogen. Nonetheless, according to the
teachings of U.S. Pat. No. 6,585,785 B1, to provide an even
distribution of thermal energy or temperature in the reactor
chamber, complicated facility or device such as forced circulation
of hot air is required.
[0006] Apparently, the above mentioned developments concerning the
heat supply to the steam reforming system still have some
shortcomings, such as the use of additional heaters and complicated
devices, naked flames, and polluting products. The subject
invention provides a process for producing hydrogen with high
purity (99.99%) in a simple and economical way. By using the
process of the subject invention, the heat generated from a
catalytic combustion section can rapidly increase the temperature
of a steam reforming section to a sufficient level to initiate an
endothermic steam reforming reaction carried out therein in a very
short time and to maintain the reaction temperature.
SUMMARY OF THE INVENTION
[0007] The objective of the subject invention is to provide a
process for producing hydrogen comprising a step of conducting a
steam reforming reaction of reactants. The steam reforming reaction
is driven by a heat generated from a first combustion reaction, and
the first combustion reaction is catalyzed by a supported oxidation
catalyst comprising a noble metal and boron nitride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic view showing a reactor module for
implementing the process of the subject invention.
[0009] FIG. 2 is a schematic view showing an assembly of reactor
modules for implementing the process of the subject invention.
[0010] FIG. 3 is a schematic view showing a reactor for
implementing the process of the subject invention.
[0011] FIG. 4 is a schematic view showing another reactor for
implementing the process of the subject invention.
[0012] FIG. 5 is a temperature profile showing a first combustion
reaction of methanol using various catalysts and oxygen/methanol
ratios with WHSV=3.2 to start from room temperature, wherein
T.sub.1 represents the temperature at the peak and T.sub.2
represents the temperature at the steady.
[0013] FIG. 6 and FIG. 7 show the temperature distributions of the
combustion section and the membrane tube section at different
conditions of WHSV and air/MeOH ratio exemplified in EXAMPLE
11.
[0014] FIG. 8 shows the temperature variations of the steam
reforming section of the reactor exemplified in EXAMPLE 12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] According to the process of the subject invention, the
production of hydrogen from a steam reforming reaction of reactants
is driven by a first combustion reaction. The first combustion
reaction is normally an oxidation of a first fuel over an oxidation
catalyst comprising a noble metal and boron nitride. In particular,
the first combustion reaction generates heat to allow a section for
conducting the steam reforming reaction, i.e., a steam reforming
section, to reach a desired temperature to initiate and maintain
the steam reforming reaction carried out therein. Optionally, after
the steam reforming reaction is initiated, a portion of a
hydrogen-containing product obtained therefrom is directed back to
the process system as at least a part of the first fuel for the
first combustion reaction, so as to continuously provide heat for
maintaining steam reforming section at the desired temperature.
Accordingly, the steam reforming reaction can be continuously
driven by the heat generated from the first combustion reaction of
the hydrogen-containing product.
[0016] The first fuel may comprise a hydrogen-containing gas (such
as the hydrogen-containing product obtained from the steam
reforming reaction), one or more alcohols (such as C.sub.1-4
alcohols), one or more hydrocarbons (such as C.sub.1-6 alkanes),
and combinations thereof. Specific examples of the first fuel
include methanol, ethanol, propanol, isopropanol, butanol, methane,
ethane, propane, butane, pentane, hexane, gasoline, liquefied
petroleum gas, and combinations thereof, and methanol and hexane
are preferred. Moreover, according to the subject invention, the
first combustion reaction is normally carried out at a molar ratio
of O.sub.2 (from such as air) to C (from the first fuel) ranging
from about 1.0 to about 4.0.
[0017] Any noble metal suitable for oxidation can be used in the
oxidation catalyst for the process of the subject invention.
Generally, the noble metal is selected from a group consisting of
Pt, Pd, Rh, Ru, and a combination thereof. It is preferred that the
noble metal is Pt. In addition to the noble metal, the oxidation
catalyst used in the subject invention comprises boron nitride.
Moreover, in application, the oxidization catalyst comprising the
noble metal and boron nitride is normally carried by a support. For
example, in one embodiment of the supported oxidization catalyst
used in the subject invention, the noble metal is dispersed on a
horizontal boron nitride layer over a support. The material of the
support should be inert and thermally-stable and the support is in
a porous format. The material of the support can be, but is not
limited to, alumina, titania, zirconia, silica, or a combination
thereof. Preferably, the support is consisting essentially of a
material selected from a group consisting of alumina, titania,
zirconia, silica, and a combination thereof. A preferred embodiment
of the support material is alumina because of its excellent thermal
resistance. Moreover, commercial products such as DASH 220 (NE
Chemtec, Inc. Japan) and N220 (Sud Chemie Catalysts, Japan, Inc.)
can be used as the support. Generally, based the total weight of
the oxidation catalyst system (including the noble metal, boron
nitride, and support), the amount of the noble metal is from about
0.05 to about 1.0 wt %, and preferably from about 0.1 to about 0.5
wt % and most preferably from about 0.15 to about 0.25 wt %; and
the amount of boron nitride is about 1 to about 20 wt %, preferably
about 2 to about 10 wt %, and most preferably about 4 to about 6 wt
%.
[0018] The oxidation catalyst can be prepared by any suitable
methods. A method for preparing the oxidation catalyst is
illustrated as followed. A noble metal salt (e.g.,
H.sub.2PtCl.sub.6) and boron nitride are first dissolved in a
suitable solvent, such as a mixture of methanol and dimethyl
formamide (DMF), and then the resulting mixture is stirred for a
while to obtain a slurry. Next, the slurry is coated on a support
(made of such as Al.sub.2O.sub.3). The coated support is dried and
then sintered so as to obtain a supported oxidation catalyst useful
in the subject invention.
[0019] The boron nitride in the oxidation catalyst serves two
functions. Because the oxidization reaction will produce not only
heat but also water, which is adverse to the catalyst system and
will decline the catalyst efficiency, the hydrophobic character of
boron nitride can prevent the generated water from chemisorbing on
the active catalyst sites too long and facilitate turning over of
the sites for new run of reaction. Additionally, since the thermal
conductivity of boron nitride is high, this helps a rapid transfer
of exothermic reaction heat away from the active catalyst center
which avoids the formation of detrimental hot spots on the
catalyst, and also allows an even dispersion of heat in the
combustion section for more effective heat supply to the steam
reforming section. This is particularly appreciated in the reactor
scale up design.
[0020] In addition, the operation of the subject invention is
relatively safe because the first combustion reaction supplies
flameless heat. In other words, no dangerous open flames or harmful
gases will be produced during the steam reforming process.
Furthermore, because the steam reforming reaction is an endothermic
reaction, a rapid and stable supply of heat is critical to the
steam reforming reaction. Using the unique oxidation catalyst of
the subject invention (i.e., comprising the noble metal and boron
nitride), the generated heat can be evenly and directly transferred
to the steam reforming section so as to avoid the complicated
arrangement of forced air circulation for achieving an even
distribution of reaction temperature in the steam reforming
section. Consequently, the process of the subject invention can be
carried out smoothly as a result of a stable and effective heat
supply from the unique oxidation catalyst.
[0021] As mentioned above, the subject invention utilizes the
oxidation of the first fuel (such as methanol) to generate heat for
heating the steam reforming section to a desired temperature, i.e.,
the reaction temperature. The inventors also found that prior to
the starting of the steam reforming reaction, a second combustion
reaction can be carried out in the steam reforming section until
the steam reforming section reaches the desired temperature. In
this way, the time required for attaining the steam reforming
temperature can be extensively shorten. In particular, the second
combustion reaction involves an oxidation of a second fuel (e.g.,
methanol), which can be identical to or different from the first
fuel. Preferably, the first combustion reaction and the second
combustion reaction are started simultaneously. For example, in
comparison with merely utilizing the heat from the oxidation of
methanol in the combustion section, the utilization of the heat
from the oxidation of methanol in the combustion section as well as
that in the steam reforming section can cut the time that the steam
reforming section reaches the desired temperature (i.e., the
temperature of steam reforming reaction) much sooner as much as 50%
of initiation time can be saved.
[0022] In the steam reforming reaction, the relevant technical
contents are well known in the art. Any materials that can be
converted into hydrogen in a steam reforming reaction can be used
in the subject invention as the reactants. Normally, the reactants
comprise water as well as one or more alcohols, one or more
hydrocarbons, or combinations thereof. For example, the alcohol can
be, but is not limited to, methanol, ethanol, propanol,
isopropanol, ethylene glycol, glycerol, or a combination thereof,
and the hydrocarbon can be, but not limited to, methane, hexane,
gasoline, liquefied petroleum gas (LPG), naphtha oil, diesel oil,
or a combination thereof. Preferably, the reactants comprise water
and methanol, hexane, or a combination of methanol and hexane.
[0023] To smooth out the steam reforming reaction, the reactants
are normally preheated to a temperature slightly higher than the
temperature of the steam reforming reaction, before being
introduced into the steam reforming section. According to the
process of subject invention, the reactants can be preheated by the
heat generated from the first combustion reaction to effectively
use the heat in the reaction system. If desired, the reactants can
also be preheated using an external heater as described in the
prior art, and then fed into the steam reforming section.
[0024] In addition to the heat supply, the steam reforming reaction
also requires a steam reforming catalyst for lowering the
activation energy of the steam reforming reaction to convert the
reactants into hydrogen. The steam reforming catalyst is normally
selected depending on the species of the reactants to be converted
into hydrogen. Typical steam reforming catalysts that can be used
in the subject invention include, but are not limited to,
transition metals. Optionally, the steam reforming catalyst can be
used in combination with a group IA metal such as potassium (K). It
is noted that the use of the group IA metal reduce the coking of
the catalyst. For example, the steam reforming catalyst used in the
subject invention can comprise Cu, Zn, Pd, Re, Ni, or a combination
thereof. Particularly, in steam reforming of methanol or glycerol,
a combination of Cu and Zn can be used as the catalyst. On the
other hand, in steam reforming of hexane, a combination of K and Ni
can be used to catalyze the reaction.
[0025] Similar to the oxidation catalyst for the first combustion
reaction of the subject invention, it is often desirable that the
steam reforming catalyst is carried by a support, which is normally
an inert compound. Suitable support for the steam reforming
catalyst normally comprises one or more of elements of Group III
and IV of the Periodic Table, for example, oxides or carbides of
Al, Si, Ti, and Zr. A preferred embodiment of the support for the
steam reforming catalyst is alumina. The method for producing a
supported steam reforming catalyst is well known by persons skilled
in the art, such as the sol gel technique or impregnation, and can
be referred to "Production and thermal pretreatment of supported
catalysts," written by J. W. Geus (see Preparation of Catalysts
III, ed. G. Poncelet, P. Grange and P. A. Jacobs, Elsevier,
Amsterdam, 1983, 1-34). For example, the supported steam reforming
catalysts such as CuOZnO/Al.sub.2O.sub.3,
PdOCuOZnO/Al.sub.2O.sub.3, and K.sub.2ONiO/Al.sub.2O.sub.3 can be
used in the subject invention.
[0026] The temperature of steam reforming reaction varies with many
factors including the species of the reactants, the scale and
module of the reactor for implementing the steam reforming process,
and especially, the species of the steam reforming catalyst. For
example, in the case of steam reforming of an alcohol (such as
methanol, isopropanol, or glycerol), the steam reforming catalyst
used typically comprises Cu and Zn, and the temperature should not
go over about 330.degree. C. to prevent the sintering and coking of
the steam reforming catalyst. Hence, the temperature of steam
reforming of an alcohol should stay within the range of about
200.degree. C. to about 330.degree. C., preferably, about
280.degree. C. to about 300.degree. C. On the other hand, for steam
reforming of an alkane (e.g., hexane, methane, or gasoline), the
reaction is generally carried out at a temperature of about
700.degree. C. to about 900.degree. C.
[0027] The steam reforming reaction of the subject invention
provides a hydrogen-containing product. In industrial applications,
such as in fuel cells, the hydrogen-containing product always needs
to be further purified. As a result, the process of the subject
invention preferably further comprises a step of purifying the
hydrogen-containing product obtained from the steam reforming
reaction to produce purified hydrogen and leave a spent product.
Any proper purifying methods, such as catalytic adsorption,
cryogenic cooling, pressure swinging adsorption, or polymer
membrane, can be used to conduct the purification.
[0028] In the case of using a purifying step, a portion of the
spent product obtained from the purifying step can be directed back
to the combustion section as at least a part of the first fuel for
the first combustion reaction, to continuously provide heat for
maintaining steam reforming section at a desired temperature.
Accordingly, the steam reforming reaction can be continuously
driven by the heat generated from the first combustion reaction of
the spent product.
[0029] One preferred embodiment of the process of the subject
invention is to utilize at least one palladium membrane tube to
purify the product of the steam reforming reaction. The palladium
membrane tube can be formed by depositing a palladium-containing
membrane with a thickness of about 3 .mu.m to about 50 .mu.m on a
porous support. The palladium-containing membrane is normally made
from one of the following materials: palladium, a palladium-silver
alloy, and a palladium-copper alloy. The porous support can be made
of such as ceramic material or stainless steel. Stainless steel is
preferred because of its cost effectiveness and convenience in the
fabrication of a reactor.
[0030] The palladium-containing membrane can be deposited on the
porous support using an electroplating method, an electro-less
plating method, a sputtering method, or a cold-rolled method. Many
prior art references, such as TW 1232888, U.S. Pat. No. 6,152,987,
JP 2002-119834, and JP 2002-153740, already describe the technology
for depositing a palladium-containing membrane on a porous support
and their contents are incorporated hereinto for reference.
[0031] As exemplified in Examples 3 and 4 below, in one embodiment
of the palladium membrane tube suitable for the subject invention,
the outside diameter of the tube is 9.525 mm, while the length of
the tube is 150 mm. Furthermore, the palladium membrane tube has
one sealed end, which is arranged upstream to the flowing path to
speed up the flow of hydrogen permeating from the sealed end to the
open end. The crude hydrogen, with a 60-75% purity, from the steam
reforming reaction permeates through the palladium membrane tubes
to yield hydrogen with a purity greater than 99%. The high purity
of hydrogen is directly derived in the membrane tube side without
any additional purification facilities.
[0032] Normally, the temperature of conducting the purification
with the use of one or more membrane tubes is not higher than about
490.degree. C., such as about 25.degree. C. to about 490.degree. C.
Preferably, the purification is carried out at a temperature
ranging from about 200.degree. C. to about 380.degree. C. The heat
for maintaining the purification temperature can also be provided
by the combustion section.
[0033] In the purification step, highly pure hydrogen is separated
from the spent product. The spent product primarily contains CO and
CO.sub.2, and also contains H.sub.2. As mentioned above, a portion
of the spent product can be directed back to the combustion section
to generate heat for continuously supplying heat to the endothermic
steam reforming reaction. The spent product can also be used in
many other applications, such as heating water. The highly pure
hydrogen obtained may contain few undesired carbon-containing
compounds such as CO and CO.sub.2, which are unfavorable to many
energy conversion devices, especially fuel cells, and will reduce
their efficiency. Accordingly, it is preferred to further treat the
highly pure hydrogen with a converter to convert the undesired
carbon-containing compounds into an alkane, such as methane.
[0034] It is unexpectedly observed that the structure of the
reactor will influence the temperature for conducting the steam
reforming reaction. Particularly, it is observed that when the
hydrogen purification is achieved by using palladium membrane tubes
and the tubes are configured in the steam reforming section, the
temperature necessary to conduct the steam reforming reaction can
be reduced. For example, when gasoline is used as the reactant for
the steam reforming reaction, the steam reforming temperature can
be reduced from at least about 700.degree. C. (e.g., from about
700.degree. C. to about 900.degree. C.) to less than about
650.degree. C. (e.g., from about 500.degree. C. to about
650.degree. C.). Without limited by theory, it is believed that the
reduction of hydrogen in the steam reforming section due to the
hydrogen-permeable palladium membrane can break the limits of
thermodynamic control on the conversion level and attain the same
conversion of hydrogen at a lower temperature.
[0035] The apparatus for carrying out the process of the subject
invention mainly comprises three sections, i.e., the steam
reforming section, the hydrogen purification section, and the
combustion section. It should be mentioned that the three sections
can be arbitrarily arranged according to different needs of scales
and temperature requirements given that the combustion section can
be positioned inside, outside, or between the other two
sections.
[0036] For implementing the process of the subject invention, a
3-in-1 reactor module can be used. In brief, the reactor used
combines three sections, namely, a steam reforming section for
producing a hydrogen-containing product, a membrane tube section
containing at least one palladium membrane tube for purifying the
hydrogen-containing product, and a combustion section for providing
the heat required for driving the steam reforming reaction. For
example, the membrane tube section can be arranged within the steam
reforming section. In other words, the palladium membrane tube and
the steam reforming section are positioned in the same compartment.
Alternatively, the membrane tube section and the steam reforming
section can be arranged in separate compartments of the reactor. As
for the combustion section, as mentioned above, it can be
configured inside, outside, or between the membrane tube section
and the steam reforming section as required.
[0037] One reactor module for implementing the process of the
subject invention is shown in FIG. 1. Reactor module 1 comprises a
reactor 15 with a shell 11 that has an inlet 12, an outlet 13 and a
vent 14; a flowing path 17 extending from the inlet 12 to outlet
14; and several palladium membrane tubes 16. The palladium
membranes deposited on each of the tubes 16 are used for purifying
hydrogen, wherein each tube 16 has one sealed end located upstream
to the flowing path 17. The reactor module 1 further includes a
combustion section 18 for heating the reactor 15. The inlet 12 is
configured to receive reactants composed of steam and a fuel, such
as gasoline, after the reactants are pumped from the feed tank 121
and is properly heated to the desirable reaction temperature by the
heat generated in the combustion section 18. The outlet 13 is
configured to discharge pure hydrogen, while the vent 14 is
configured to discharge a spent product, including H.sub.2, CO and
CO.sub.2. The spent product discharged from the vent 14 is passed
through a pressure reducer 191 and forwarded into the combustion
section 18 through a connection 19 for combustion. A proper amount
of air is pumped first through a fuel reservoir 182 and a check
valve 183 and then into the connection 19 to mix with the spent
product. The gases from the combustion section 18 are further
vented through an outlet 181 for discharge as waste gases or heat
exchanged with the feed stream. Moreover, reactor module 1 can
further include a heat conductive perforated metal plate 151 welded
to the wall of the reactor 15. The heat conductive perforated metal
plate 151 facilitates heat transfer from the warmer reactor wall to
the steam reforming catalyst zone for the endothermic reaction. In
the case of steam reforming of hexane or gasoline, the reactor
module 1 is suitable.
[0038] It is observed that hydrogen flux through the palladium
membrane is drastically decreased when the hydrogen concentration
is low. This means that the palladium membrane tube is very
inefficient in the low hydrogen concentration region. This
surprising discovery practically limits the use of long length
membrane tubes during hydrogen production on a large scale.
Accordingly, another reactor module with a short palladium membrane
tube can be used to conduct the process of the subject invention.
Preferably, the length of the palladium membrane tube is about 3 cm
to about 120 cm. Moreover, in order to avoid using a long tube, an
assembly 2 of the reactor modules is useful as shown in FIG. 2.
[0039] Referring to FIG. 2, an assembly 2 includes two reactor
sections 28 and 29, both with an extended common shell 21, an inlet
22, two vents 24 and 25, and two outlets 26 and 27. The two reactor
sections 28 and 29 are assembled to share the common inlet side and
have flowing paths extending from the inlet to the outlet opposite
in direction to the reactor sections 28 and 29, respectively. Each
reactor section, 28 or 29 has a plurality of palladium membrane
tubes 30. The palladium membrane tube 30 is formed by depositing a
palladium membrane on the porous support for purifying hydrogen,
wherein each palladium membrane tube 30 has one sealed end located
upstream to the flowing path. Assembly 2 further includes a
combustion section 31 for heating the reactor sections 28 and 29.
The inlet 22 is configured to receive reactants. The reactants can
comprise ethanol, methanol, isopropanol, methane, hexane, gasoline,
LPG, glycerol, or a combination thereof. The outlets 24 and 25 are
configured to discharge pure hydrogen, and the vents 26 and 27 are
configured to discharge spent products including H.sub.2, CO, and
CO.sub.2. The spent products discharged from the vents 26 and 27
are introduced into the combustion section 31 through a connector
(not shown) for combustion. The waste gases are discharged from the
combustion section 31 via a vent (not shown). Moreover, the
assembly 2 further includes a heat conductive perforated metal
plate 23 welded into the reactor wall in each reactor section. The
heat conductive perforated metal plate 23 facilitates heat transfer
from the warmer reactor wall to the steam reforming catalyst zone
in the endothermic reaction.
[0040] In addition to the above reactors having the configuration
that the palladium membrane tubes are arranged inside the steam
reforming section, other reactor types can be used in the subject
invention. One embodiment of the reactors is depicted in FIG. 3. As
shown in FIG. 3, a reactor 300 comprises a membrane tube section
340 with at least one palladium membrane tube 350 located in the
central part of the reactor 300, a steam reforming section 310
located in the peripheral part of the reactor 300, and a combustion
section 330 located between the membrane tube section 340 and steam
reforming section 310. A first fuel, such as methanol, and air are
first introduced into the combustion section 330 via a line 331 for
combustion. The combustion section 330 is filled with the oxidation
catalysts. In this aspect, the first fuel and air can be introduced
into the combustion section 330 using different inlets. For
example, the first fuel can be pumped into the combustion section
330 at the bottom and the middle of the reactor 300 and air can be
fed at the bottom of the reactor 300. Then, the first fuel is
reacted with the oxygen subject in the air over the oxidation
catalyst in the combustion section 330 to rapidly generate heat.
Then, reactants comprising a fuel and water are pumped into a
preheating coil 320 located in the combustion section 330 via a
line 311 that is heated to a predetermined temperature of about
20.degree. C. to about 50.degree. C. higher than the temperature of
the steam reforming reaction. The space velocity of the reactants
depends on many factors, such as the size of the reactor and the
components of reactants. Generally, the reactants are introduced
into the reactor 300 with a space velocity of about 0.9 to about
5.0 hr.sup.-1, preferably about 2.0 to about 4.0 hr.sup.-1. Then,
the pre-heated reactants are introduced into the steam reforming
section 310 via a line 312. Meanwhile, the steam reforming reaction
will be quickly driven by the heat generated in the combustion
section 330 and is conducted smoothly due to the stable heat
supply.
[0041] After, the product formed in the steam reforming section 310
is fed into a membrane tube section 340 via a line 313. The product
includes hydrogen, un-reacted reactants, and by-products. In the
membrane tube section 340, the hydrogen in the product will
permeate the palladium membranes on the palladium membrane tubes
350, and flow in and exit from the palladium membrane tubes 350.
Purified hydrogen can then be obtained via a line 314. The
palladium membrane tubes 350 have one sealed end, which is arranged
upstream to the flowing path to speed up the flow of hydrogen from
the sealed end to the open end. Also, since the presence of CO and
CO.sub.2 in a fuel cell is undesirable, the purified hydrogen from
the palladium membrane tubes 350 is further treated with a
methanizer 360 to convert CO and CO.sub.2 in the purified hydrogen
to CH.sub.4. The heat for maintaining the methanizer 360 at a
desired temperature can also be provided by the combustion section
330. By using the reactor 300 for implementing the process of the
subject invention, the purity of the resulting purified hydrogen is
above 99.98%.
[0042] The spent product, which does not permeate through the
palladium membrane, exits from the membrane tube section 340 via a
line 315. Some of the spent product can be directed back into the
combustion section 330 for conducting catalytic oxidization so as
to generate heat. Then, the spent gas which is generated in the
combustion section 330 exits from the reactor 300 via a line 332.
The reactor 300 is particularly suitable for use in steam reforming
of methanol because the steam reforming section 310 deposited in
the peripheral part can be maintained at a lower temperature (e.g.,
about 280.degree. C. to about 300.degree. C.).
[0043] FIG. 4 shows another reactor for use in conducting the
process of the subject invention. The reactor 400 comprises a
membrane tube section 440 deposited in the peripheral part of
reaction 400 and a steam reforming section 410 positioned in a
combustion section 430. The steam reforming section 410 is in
tubular form. As described in FIG. 3, the first fuel and air for
combustion are introduced into the combustion section 430 via lines
433 and 431, respectively. Then, the reactants are first fed into
the preheating zone 420 via a line 411 and then into the steam
reforming section 410. The product formed in steam reforming
section is introduced into the membrane tube section 440 with the
palladium membrane tubes (not depicted) via a line 412 for hydrogen
purification. After hydrogen purification, the purified hydrogen is
obtained via a line 414, while the spent product is directed back
into the combustion section 430 via a line 415. Waste gases in the
combustion section 430 exit the reactor 400 via a line 432. The
reactor 400 further includes a heat conductive perforated metal
plate 460 welded into the reactor wall to facilitate the uniform
distribution of the generated heat.
EXAMPLES
Example 1
Hydrogen Permeation of a H.sub.2--CH.sub.4 Mixture
[0044] The hydrogen mixture with different concentrations of
hydrogen, i.e., 99.995%, 80%, 75%, and 66%, were used to study
hydrogen permeation through the palladium membrane tube at
330.degree. C. under a pressure of 5, 6, 7 and 8 bar at the shell
side. The resultant hydrogen flux through the palladium membrane is
shown in Table 1. The permeability was calculated in units of
M3/M2-hr-bar1/2. The experiment was carried out in a stainless
steel tubular reactor that was 25 mmOD.times.350 mL (outside
diameter.times.length) with a palladium membrane tube of 9.525
mmOD.times.110 mmL. The hydrogen mixture is fed into the shell side
of membrane, and then the pure hydrogen permeates through the
membrane into the interior of the membrane tube. The permeation
pressure is set by adjusting the back pressure regulator in the
spent gas mixture stream before leaving the reactor system.
TABLE-US-00001 TABLE 1 Hydrogen permeation of a H.sub.2/CH.sub.4
mixture with a palladium membrane Perme- Flux, ability, % H in %
M.sup.3/M.sup.2-hr P1, absol., bars M.sup.3/M.sup.2-
H.sub.2/CH.sub.4 H.sub.2 purity 6 7 8 hr-bar.sup.1/2 99.995 Flux,
18.30 21.28 24.00 12.6 M.sup.3/M.sup.2-hr H.sub.2 purity 99.99999+
80 Flux, 13.85 16.66 18.96 11.85 M.sup.3/M.sup.2-hr H.sub.2 purity
99.96 75 Flux, 12.71 14.83 16.94 11.45 M.sup.3/M.sup.2-hr H.sub.2
purity 99.92 66 Flux, 10.86 12.96 14.28 10.8 M.sup.3/M.sup.2-hr
H.sub.2 purity 99.92
Example 2
Hydrogen Permeability of a H.sub.2--Y Mixture with Y: N.sub.2,
CO.sub.2 and Cyclohexanol (CXL)
[0045] The palladium membrane tube, which was 9.525 mm.times.30 mm
(outside diameter.times.length), was used for the hydrogen
permeability test at 310.degree. C. The results are shown in Table
2. The observed drop in hydrogen permeability was far more than
that could be accounted for by the decrease of the partial pressure
of hydrogen. Moreover, the dilution of hydrogen concentration
brought about not only a decrease in hydrogen flux, but also a
deterioration of the hydrogen purity via the permeation. Through
the palladium membrane, an industrial grade of hydrogen with
99.995% purity can be purified into an electronic grade with
99.9999+purity. The purity was decreased to 99.9999% and 99.99%
when the hydrogen concentration was decreased to 75% and 50%,
respectively, as the Y was CXL. TABLE-US-00002 TABLE 2 Hydrogen
permeability in a mixed feed of H.sub.2/Y (Y = CO.sub.2, CXL, or
N.sub.2).sup.[a] Perme- Flux, ability, % H in % cc/min P1, absol.,
bars M.sup.3/M.sup.2- H.sub.2/Y Y H.sub.2 purity 3 4 5
hr-bar.sup.1/2 99.995 Flux, 87.3 122 152 8.66 cc/min H.sub.2 purity
99.9999+ 75 CXL.sup.[b] Flux, 81 113 140 9.30 cc/min H.sub.2 purity
99.9999 50 CXL Flux, 24 35 47 5.08 cc/min H.sub.2 purity 99.992
99.994 99.996 50 N.sub.2 Flux, 20 34 42 4.48 cc/min H.sub.2 purity
>99.9.sup.[c] 50 CO.sub.2 Flux, 13 23 32 3.60 cc/min H.sub.2
purity 99.94 99.95 99.96 .sup.[a]The permeability test was
conducted at 310.degree. C. with a Pd-membrane of 9.575 mm .times.
30 mm (outside diameter .times. length). The products were analyzed
with a GC-FID capable of detecting an impurity up to 1 ppm of COx
(CO and CO.sub.2) and other organic compounds. .sup.[b]CXL =
cyclohexanol .sup.[c]Analyzed with a TCD that has a nitrogen
sensitivity >0.5% in the permeation.
Example 3
Direction of Hydrogen Permeation in a Pd-Membrane Tube with Respect
to the Membrane Sealing
[0046] A palladium membrane tube (9.525 mmOD.times.150 mL) with one
sealed end was inserted into a tubular reactor (25.4 mmID.times.450
mL) via two modes of connections, [A] and [B]. In the [A]-mode, the
sealed end of the membrane tube was arranged upstream to the
hydrogen flow, while the hydrogen flowed into both the shell-side
and the tube-side co-currently. In the [B]-mode, the sealed end of
the membrane tube was arranged downstream to the hydrogen flow. The
hydrogen flowed into both the shell-side and tube-side. When the
permeation pressure in the shell side was set at 3 bar, the
hydrogen flux in the tube side in the [A]-mode was 210 cc/min,
while the corresponding hydrogen flux in the [B]-mode was 192
cc/min.
Example 4
Direction of Hydrogen Permeation in the Pd/Ag-Membrane Tube with
Respect to the Membrane Sealing
[0047] A similar experiment to Example 3 was further tested with a
67/33 weight ratio of a Pd/Ag alloy membrane tube that was 25 .mu.m
thick. The membrane tube had a similar porous support (9.525
mmOD.times.150 mL) with the sealed end inserted into a tubular
reactor of 25.4 mmID.times.450 mL via two modes of connections, [A]
and [B] as described above. In the [A]-mode, the sealed end of the
membrane tube was arranged upstream to the hydrogen flow, while the
hydrogen flowed into the shell-side and tube-side co-currently. In
the [B]-mode, the sealed end of the membrane tube was arranged
downstream of the hydrogen flow, while the hydrogen flowed into the
shell-side and tube-side. When the permeation pressure in the shell
side was set at 3, 4, and 6 bar, the hydrogen flux in the tube side
in [A]-mode was 95, 136, and 189 cc/min, respectively. The
corresponding hydrogen flux in the [B]-mode was 80, 112, and 170
cc/min, respectively.
Example 5
Preparation of an Oxidation Catalyst on a Supporting Material
[0048] Five grams (5 g) of H.sub.2PtCl.sub.6 and 50 grams of boron
nitride were dissolved in a solvent comprising 800 ml of methanol
and 200 ml of dimethyl formamide, and then stirred to obtain a
slurry. The slurry was then coated on alumina (948 g), and the
coated alumina was dried at a temperature of 100.degree. C. to
remove the solvent. Next, the dried alumina was sintered in an oven
at a temperature of 450.degree. C. with an air flow of 5 L/min for
8 hours to obtain the oxidation catalyst on alumina.
Example 6
Cold Start Heating with a PBN Oxidation Catalyst
[0049] Six grams (6 g) of Pt/BN/.gamma.-Al.sub.2O.sub.3 was used as
the oxidation catalyst and was placed in a stainless steel tube
with a 1/2-inch OD (outside diameter). The whole tube was insulated
with mineral wool. Two sets of temperatures were measured by
thermocouples as T.sub.a and T.sub.b. T.sub.a indicated the
temperature at the top of catalyst bed, while T.sub.b indicated the
temperature outside of the tube and adjacent to the top of
catalyst. An appropriate amount of methanol was pumped into the
stainless steel tube at a desired space velocity (WHSV, hr.sup.-1)
and air was introduced to provide a molar ratio of O.sub.2/Methanol
close to 1.65 or 1.80 (corresponding to 10% and 20% excess of
theoretical demand). As a result, the reaction temperatures
indicated as T.sub.a and T.sub.b rose rapidly from room temperature
to about 800.degree. C. and then stabilized to a lower temperature
of about 400.degree. C. to 450.degree. C. when a molar ratio of
O.sub.2/Methanol close to 1.65 or 1.80 was introduced at an
appropriate space velocity of 2 hr.sup.-1 to 4 hr.sup.-1 (WHSV). In
addition, the oxidation catalysts in the catalytic combustion
section were either Pt/BN--N-220 and Pt/BN-Dash-220. The heating
effect and cold start capability of Pt/BN--N-220 and Pt/BN-Dash-220
are shown in FIG. 5, wherein T.sub.1 represents the temperature at
the peak and T.sub.2 represents the steady temperature.
Example 7
High Temperature from the Cold Started Catalytic Combustion of
Hexane with Pt/BN--N-220
[0050] Six grams (6 g) of PtBN/N-220 were used as the oxidation
catalyst, and was placed in the combustion section according to the
subject invention. N-hexane, as the first fuel, was pumped onto the
oxidation catalyst at a velocity of 1.66 gm/min. Then, airflow was
introduced at a velocity of 2.35 L/min to give an O.sub.2/hexane
ratio close to 10.45 (10% excess of theoretical demand). The
temperature indicated as T.sub.3 in the catalyst zone rose to
630.degree. C. in 4 min, and then to 970.degree. C. in another 5
min. The temperature indicated as T.sub.4 was maintained between
980.degree. C. to 960.degree. C. for the next 110 min until the
reaction was terminated. Apparently, heat from the combustion of
hexane for maintaining the steady temperature, T.sub.4 was much
more than that of methanol. On the other hand, it was easier for
methanol to initiate the oxidation reaction. Initially, T.sub.1
rose faster and higher than T.sub.3.
Example 8
Cold Start of the Methanol Steam Reforming Reaction Using Catalytic
Combustion of Aqueous Methanol
[0051] Twelve grams (12 g) of Pt/BN-.gamma.-Al.sub.2O.sub.3, as the
oxidation catalyst, was placed into the combustion section of the
subject invention. 120 g of CuO-ZnOAl.sub.2O.sub.3, as the steam
reforming catalyst, was placed in the reactor. The reactor was then
wrapped with a thick layer of mineral wool for insulation. Both the
inner catalyst zone and annular catalyst zone were independently
connected with metering pumps for delivery of a methanol-water
mixture for the reforming and combustion fuel, respectively.
Initially, methanol, as the fuel, at a feeding rate of 7.5
mmol/min. with WHSV=1.2, was introduced into the combustion reactor
at room temperature to set the oxidation reaction by reacting with
air at a O.sub.2/CH.sub.3OH ratio close to 1.65 in 12 minutes. The
temperature, T.sub.OX, of the oxidation catalyst in the catalytic
combustion section rose to 560.degree. C. and almost simultaneously
the temperature, T.sub.SR, in the reactor reached 380-390.degree.
C. The endothermic steam reforming reaction of methanol was then
started up by introducing liquid methanol (15 mmol/min) together
with water (18 mmol/min) into the reforming catalyst bed. The
reaction temperature, T.sub.SR, dropped slightly to 350.degree. C.
and kept steady for the next 60 minutes. Hydrogen and carbon oxides
were produced from the reforming side of the reactor. Thereafter,
T.sub.OX in the combustion section dropped to 420-460.degree. C.
and T.sub.SR in the reformer decreased to 310.degree. C. The lower
temperature reactions were continued for another 30 minutes while
the gaseous products evolved smoothly.
Example 9
Steam Reforming Reaction of Hexane
[0052] According to the subject invention, a steam reforming
reaction of hexane was carried out at 500.degree. C. under a
pressure of 9 bars and VHSV of 10,000 to 30,000 hr.sup.-1. Five
steam reforming catalysts were tested for their carbon coking rate,
conversion and their selectivity to hydrogen product. The
characteristics of these catalysts are shown in Table 3 and their
performance is presented in Table 4 for comparison. As shown in
Tables 3 and 4, both commercial catalysts had a higher decaying
rate by coking than the three homemade catalysts with a higher
surface area. In addition, the commercial catalysts also brought
about higher a hydrogen partial pressure and higher selectivity to
the hydrogen product. With regard to the Y-2 catalyst, the use of
palladium membrane tube showed a much higher conversion, hydrogen
partial pressure and the selectivity to hydrogen. TABLE-US-00003
TABLE 3 Characteristics of catalysts used for the steam reforming
of hexane G-56H-1 FCR-4-02 Y1 Y2 Y3 Specific 2.3 3.0 2.0 2.0 2.0
gravity (kg/l) Surface 27.41 6.73 145.32 133.6 131.44 area
(m.sup.2/g) Pore volume 0.054 0.014 0.365 0.338 0.32 (c.c./g) Pore
size (A) 78.8 87.6 100.33 101.1 97.3 Support
.alpha.-Al.sub.2O.sub.3 .alpha.-Al.sub.2O.sub.3
.gamma.-Al.sub.2O.sub.3 .gamma.-Al.sub.2O.sub.3
.gamma.-Al.sub.2O.sub.3 Content Ni 17.0 12.0 15.0 15.0 17.0 (%)
K.sub.2O 0.4 - 0.4 1.0 0.4 MgO -- -- -- -- 5.0
[0053] TABLE-US-00004 TABLE 4 The performance of steam reforming
reaction of n-hexane.sup.[a] Av. Coking rate n-Hexane Partial Press
Gas composition (vol %) Catalyst (mgC/gCat-hr).sup.[b] Conv. (%
mol) of H.sub.2 (%) CO CO.sub.2 CH.sub.4 H.sub.2 FCR-4-02 128.3
48.02 14.93 0.59 22.55 38.69 38.18 G-56-H-1 13.29 65.84 12.15 0.56
21.64 50.23 27.57 Y-1 8.23 40.48 21.31 0.15 21.52 17.50 59.49 Y-2
3.20 42.39 21.16 0.97 22.35 12.67 64.00 Y-2/Membr 3.20 46.05 31.94
0.02 23.18 9.51 68.29 Y-3 7.70 39.69 18.38 1.51 21.92 3.57 72.99
.sup.[a]VHSV = 20000 h.sup.-1, H.sub.2O/C = 1.5, 9 atm, 500.degree.
C. .sup.[b]Coking time of 6 hr under the conditions of [a]
Example 10
[0054] A reactor (Green Hydrotec Inc., Model: GHR500LPH100) with a
structure as shown in FIG. 3 was used in this example. Methanol was
introduced into the combustion section of the reactor. Upon
achieving a temperature of 260.degree. C., methanol and water in a
molar ratio of 1:1.2 was introduced into the steam reforming
section of the reactor with a feeding rate of 10 g/min. The amount
of the purified hydrogen from the palladium membrane tubes was 7.5
L/min. The amount of the spent product (containing H.sub.2 and
CO.sub.2) was 10 L/min. After calculations, H.sub.2 recovery yield
was 57.1%.
[0055] The spent product (10 L/min) was divided into two streams.
One stream (5.2 L/min) was introduced back into the combustion
section to generate heat for preheating coil and steam reforming.
Another stream (4.8 L/min) was introduced into another oxidation
zone to heat 162 g of water from 20.degree. C. to 49.degree. C. The
thermal energy provided by the stream (4.8 L/min) was 19.6 KJ/min.
The total thermal efficiency of the reactor was 78%.
Example 11
Different Values of WHSV and Air/MeOH Ratio on the Temperature
Distribution of Combustion Section and Membrane Tube Section
[0056] In the case of GHT500LPH100, the space velocity, WHSV and
Air/MeOH ratio were changed to test the optimal temperature
distribution of the reactor. Table 5 lists the experimental
conditions for this example. The temperature distribution of the
combustion section and the membrane tube section are shown in FIGS.
6 and 7. All four conditions can have smooth temperature
distributions without hot spots. The air flow rate was reduced to
cut heat loss by the excess air vent as indicated by EXP1 and EXP3.
Furthermore, EXP2 using the most methanol or fuel input with enough
oxygen for combustion exhibited the highest temperature profile.
EXP4 provides a high enough temperature profile for heat transfer
with lower excess air, and is most efficient. The higher WHSV, on
the other hand, provides a higher reactor temperature for faster
heat time therefore, it is useful in bringing up the reaction
temperature in the initial stage. TABLE-US-00005 TABLE 5 Air MeOH
WHSV EXP No. (L/min) (g/min) (1/hr) O.sub.2/C Excess air 1 60 5
0.375 3.29 119% 2 30 4.16 0.312 1.98 32% 3 30 3.52 0.264 2.34 56% 4
20 3.52 0.264 1.56 4%
Example 12
Introduction of a First Fuel and Air into the Steam Reforming
Section and the Combustion Section
[0057] The conditions are as listed below:
[0058] For the steam reforming section (SRR):
[0059] WHSV (feeding rate of methanol/catalyst weight): 1.54
hr.sup.-1
[0060] Catalyst weight: 50 g of CuOZnO/Al.sub.2O.sub.3
[0061] Feeding rate of air: 6 L/min
[0062] For the combustion section (OXD):
[0063] WHSV (feeding rate of mathanol/catalyst weight): 3.8
hr.sup.-1
[0064] Catalyst weight: 20 g of Pt--BN/Al.sub.2O.sub.3
[0065] Feeding rate of air: 6 L/min
[0066] As shown in FIG. 8, the results show that introducing the
methanol and air into the steam reforming section prior to feeding
the raw material of the first fuel and water can shorten the time
for heating the steam reforming section to the reaction
temperature.
[0067] The above disclosure is related to the detailed technical
contents and inventive features thereof. People skilled in this
field may proceed with a variety of modifications and replacements
based on the disclosures and suggestions of the invention as
described without departing from the characteristics thereof.
Nevertheless, although such modifications and replacements are not
fully disclosed in the above descriptions, they have substantially
been covered in the following claims as appended.
* * * * *