U.S. patent application number 12/029183 was filed with the patent office on 2008-06-05 for method for preparing hydroxylamine.
This patent application is currently assigned to China Petrochemical Development Corporation, Taipei (Taiwan). Invention is credited to Shou-Li Luo, Shu-Hung YANG.
Application Number | 20080131339 12/029183 |
Document ID | / |
Family ID | 38559239 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080131339 |
Kind Code |
A1 |
YANG; Shu-Hung ; et
al. |
June 5, 2008 |
METHOD FOR PREPARING HYDROXYLAMINE
Abstract
A method for preparing hydroxylamine by reducing nitric acid or
its salt with hydrogen gas in an aqueous medium in the presence of
a catalyst, wherein reduction of nitric acid or its salt is
performed in a reactor comprising a reaction section, a cooler
disposed at the lower portion of the reactor, and a middle gas
distributor and a lower gas distributor respectively disposed above
and below the cooler for introducing hydrogen gas into the reaction
section. According to the present invention, gas distribution
become more uniform by disposing the gas distributors at different
positions of the reactor, which results in higher yield of
hydroxylamine.
Inventors: |
YANG; Shu-Hung; (Taipei,
TW) ; Luo; Shou-Li; (Taipei, TW) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
China Petrochemical Development
Corporation, Taipei (Taiwan)
Taipei City
TW
|
Family ID: |
38559239 |
Appl. No.: |
12/029183 |
Filed: |
February 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11534167 |
Sep 21, 2006 |
|
|
|
12029183 |
|
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Current U.S.
Class: |
422/198 |
Current CPC
Class: |
C01B 21/1418
20130101 |
Class at
Publication: |
422/198 |
International
Class: |
B01J 19/00 20060101
B01J019/00; F28D 21/00 20060101 F28D021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2006 |
TW |
095110888 |
Claims
1-9. (canceled)
10. A reactor for preparation of hydroxylamine, in which the
preparation is performed by reducing nitric acid or its salt with
hydrogen gas in an aqueous medium in the presence of a catalyst,
and unreacted hydrogen gas is recovered, the reactor comprising: a
reaction section; a cooler disposed at a lower portion of the
reactor; a lower gas distributor disposed below the cooler and
configured for introducing a first fresh hydrogen gas into the
reaction section; and a middle gas distributor disposed above the
cooler and configured for recovering and circulating the unreacted
hydrogen gas back to the reaction section.
11. The reactor according to claim 10, wherein the middle gas
distributor is configured for introducing a mixture of the
unreacted hydrogen gas and a second fresh hydrogen gas.
12. The reactor according to claim 10, further comprising an upper
gas distributor disposed above the middle gas distributor and
configured for introducing part of the first fresh hydrogen gas and
the rest of the first fresh hydrogen gas is introduced into the
reaction section through the lower gas distributor.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for preparing
hydroxylamine, and more particularly, to a method for preparing
hydroxylamine by reduction of nitric acid or its salt with hydrogen
gas.
BACKGROUND OF THE INVENTION
[0002] Hexanolactam is an important starting material for
manufacturing polyamide (also referred to as nylon). Hexanolactam
is conventionally prepared by a method comprising reacting
hydroxylamine with cyclohexanone to give cyclohexanone oxime, and
then subjecting said cyclohexanone oxime to Beckman rearrangement
to yield hexanolactam. Therefore, hydroxylamine is one of the
important starting materials for hexanolactam production.
Hydroxylamine is usually prepared by reducing nitric acid or its
salt with hydrogen gas in presence of a mono metal catalyst such as
palladium/carbon, or a double metal catalyst such as
palladium-platinum/carbon. However, pure hydroxylamine is unstable
and decomposes automatically upon heating, which may result in
explosion. So, hydroxylamine is usually prepared in a form of its
salt with an acid, such as hydroxylammonium sulfate,
hydroxylammonium chloride, or hydroxylammonium phosphate, wherein
hydroxylammonium phosphate is preferred.
[0003] Hydroxylamine is prepared in a gas/liquid/solid triple phase
bubbling reaction system. As such a reaction system is a
heterogeneous system, the reaction is affected not only by catalyst
concentration, hydrogen pressure, hydrogen ion concentration, and
the surface area of the catalyst, but also affected by mass
transfer among gas, liquid and solid phases. The reaction scheme
for preparation of hydroxylamine is as shown below:
NH.sub.4NO.sub.3+2H.sub.3PO.sub.4+3H.sub.2.fwdarw.NH.sub.3OHH.sub.2PO.su-
b.4+NH.sub.4H.sub.2PO.sub.4+2H.sub.2O
[0004] In the prior art, hydroxylamine was prepared, for example,
in a reactor as shown in FIG. 1. Referring to FIG. 1, a reactor 10'
includes a reaction section 12', a cooler 14' disposed at the lower
part of the reactor 10', and a gas distributor 16' disposed above
the cooler 14'. An phosphate-buffered aqueous medium containing
nitrate ions is fed to the reactor 10' through a pipe 22'. Fresh
hydrogen gas is delivered to a gas distributor 16' of the reactor
10' through a pipe 24' and then introduced into the reaction
section 12'. In the reaction section 12', nitric acid or its salt
contained in the phosphate-buffered aqueous medium is reduced by
hydrogen gas to form hydroxylammonium phosphate. The aqueous medium
containing the produced hydroxylammonium phosphate leaves the
reactor 10' through a pipe 30'. The unreacted hydrogen gas leaves
the reactor 10' through a pipe 32' at the top of the reactor 10',
and is treated in a separator (not shown). The treated hydrogen gas
after mixing with fresh hydrogen gas is circulated back to the gas
distributor 16' of the rector 10' and reintroduced into the
reaction section 12'.
[0005] In said method for preparation of hydroxylammonium
phosphate, the hydrogen gas is fed into a reactor 10' through a gas
distributor 16' at the middle part of the reactor, resulting in
uneven distribution of hydrogen gas in the reactor 10', and
occurrence of wall flow, channeling phenomenon etc., which
adversely affects the efficiency of mass transfer among gas, liquid
and solid phases during the reaction, and lowers the yield of
hydroxylamine.
[0006] Therefore, it is desired to provide a method for preparing
hydroxylamine in a gas/liquid/solid triple phase reaction system
with high yield.
SUMMARY OF THE INVENTION
[0007] To overcome the above-mentioned problems of the prior art,
it is an object of this invention to provide a method for preparing
hydroxylamine with high yield.
[0008] Another object of this invention is to provide a method for
preparing hydroxylamine, in which mass transfer among gas, liquid
and solid phases is enhanced.
[0009] A further object of this invention is to provide a method
for preparing hydroxylamine, in which catalyst activity is
increased.
[0010] Still another object of this invention is to provide a
method for preparing hydroxylamine, in which reaction selectivity
is increased.
[0011] To achieve the aforementioned and other objects, provided is
a method for preparing hydroxylamine by reducing nitric acid or its
salt with hydrogen gas in an aqueous medium in the presence of a
catalyst, said reduction of nitric acid or its salt is performed in
a reactor comprising a reaction section, a cooler disposed at the
lower part of the reactor, and a middle gas distributor and a lower
gas distributor respectively disposed above and below the cooler
for introducing hydrogen gas into the reaction section. As hydrogen
gas is introduced into the reaction section respectively from the
middle gas distributor and the lower gas distributor, gas
distribution will become more uniform, resulting in higher
efficiency of mass transfer among gas, liquid and solid phases in
the reactor, which leads to increased catalyst activity and
increased selectivity to hydroxylamine; in turn, leads to higher
yield of hydroxylamine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic diagram of a conventional reactor for
production of hydroxylamine;
[0013] FIG. 2 is a schematic diagram of a reactor according to the
first embodiment of the present invention;
[0014] FIG. 3 is a schematic diagram of a reactor according to the
second embodiment of the present invention; and
[0015] FIG. 4 is a schematic diagram of a reactor according to the
third embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention provides a method for preparing
hydroxylamine by reducing nitric acid or its salt with hydrogen gas
in an aqueous medium in the presence of a catalyst, said reduction
of nitric acid or its salt is performed in a reactor comprising a
reaction section, a cooler disposed at the lower portion of the
reactor, and a middle gas distributor and a lower gas distributor
respectively disposed above and below the cooler for introducing
hydrogen gas into the reaction section.
[0017] Reduction of nitric acid or its salt to hydroxylamine can be
performed at any proper temperature, for example, at a temperature
from 20.degree. C. to 100.degree. C., preferably from 30.degree. C.
to 90.degree. C., and more preferably from 40.degree. C. to
65.degree. C.
[0018] The catalyst used in the reaction is a noble metal catalyst
supported by a catalyst carrier. Examples of the catalyst include a
mono metal catalyst such as palladium/carbon, a double metal
catalyst such as palladium-platinum/carbon, and the like. Examples
of the catalyst carrier include, but not limited to, a carbon
carrier or an aluminum carrier, preferably a carbon carrier. The
amount of noble metal in the catalyst, based on the total amount of
noble metal and the carrier, is in the range from 1 to 25% by
weight, and preferably from 5 to 15% by weight. The noble metal
catalyst is used in an amount of 0.2 to 5% by weight, based on the
total weight of the aqueous medium.
[0019] The aqueous medium is generally adjusted to acidic pH with
sulfuric acid or phosphoric acid; preferably the aqueous medium is
buffered with phosphoric acid.
[0020] The reactors suitable for use in preparation of
hydroxylamine are illustrated by the following embodiments. The
present invention can also be performed or applied by other
different embodiments. The present invention may be modified and
varied on the basis of different points and applications without
departing from the spirit of the present invention.
[0021] As used herein, selectivity to hydroxylamine and catalyst
activity are defined as follows:
[0022] selectivity to hydroxylamine=yield of
hydroxylamine/consumption of nitric acid or its
salt.times.100%,
[0023] catalyst activity=yield of hydroxylamine per unit time per
gram of palladium catalyst.
[0024] In the first embodiment of the present invention, a reactor
10 as shown in FIG. 2 is used. The reactor 10 includes a reaction
section 12 comprising a catalyst, a cooler 14 disposed at the lower
part of the reactor 10, and a middle gas distributor 16 and a lower
gas distributor 18 disposed above and below the cooler 14,
respectively. A phosphate-buffered aqueous medium containing nitric
acid or its salt is fed to the reaction section 12 through a pipe
22. Fresh hydrogen gas is delivered to the lower gas distributor 18
of the reactor 10 through a pipe 26 and then introduced into the
reaction section 12. In the reaction section 12, nitric acid or its
salt in the phosphate-buffered aqueous medium is reduced by
hydrogen gas to form hydroxylammonium phosphate. The aqueous medium
containing the produced hydroxylammonium phosphate leaves the
reactor 10 through a pipe 30. The concentration of hydroxylammonium
phosphate in the aqueous medium is usually amounted to more than
0.9 mole/kg, preferably more than 1.0 mole/kg, and more preferably
more than 1.1 moles/kg. The unreacted hydrogen gas is discharged
from the reactor 10 through a pipe 32, and then treated in a
separator (not shown). The treated hydrogen gas is circulated back
to the middle gas distributor 16 of the reactor 10 through a pipe
24 and reintroduced into the reaction section 12. The heat produced
during the reaction is removed by a cooler 14.
[0025] In the first embodiment of the present invention, the
circulated hydrogen gas and fresh hydrogen gas are introduced into
the reaction section 12 of the reactor 10 respectively from the
middle gas distributor 16 and the lower gas distributor 18 such
that gas distribution will become more uniform, resulting in higher
efficiency of mass transfer among gas, liquid and solid phases in
the reactor 10, which leads to increased catalyst activity and
increased selectivity to hydroxylamine; in turn, leads to higher
yield of hydroxylamine.
[0026] In the second embodiment of the present invention, a reactor
110 as shown in FIG. 3 is used. The structure and operation of the
reactor 110 is the same as those of the reactor 10 in the first
embodiment, except the unreacted hydrogen gas, after discharged
from the reactor 110 through the pipe 32 and treated in a separator
(not shown), is mixed with a part of the fresh hydrogen gas and
then reintroduced into the middle gas distributor 16 of the reactor
110 through the pipe 24; and the rest fresh hydrogen gas is
introduced into the lower gas distributor 18 of the reactor 110
through the pipe 26.
[0027] In the third embodiment, a reactor 210 as shown in FIG. 4 is
used. The reactor 210 has the same structure as the reactor 10 in
the first embodiment, except an upper gas distributor 20 is further
disposed at the upper part of the reaction section 12, preferably
above the pipe 22 for delivering phosphate-buffered aqueous medium.
The reactor 210 is operated in the same manner as in the first
embodiment, except part of the fresh hydrogen gas is delivered to
the upper gas distributor 20 through a pipe 28 and the rest fresh
hydrogen gas is delivered to the lower gas distributor 18 through
the pipe 26. The unreacted hydrogen gas is recovered through a pipe
32 and is circulated back to the middle gas distributor 16 through
the pipe 24. The ratio of the hydrogen gas delivered to the lower
gas distributor:the hydrogen gas delivered to the upper gas
distributor can be varied depending on the operating conditions,
and is usually, for example, about 2:1.
EXAMPLES
Example 1
[0028] A reactor 10 as shown in FIG. 2 was used. An aqueous medium
containing 0.04 mole of hydroxylammonium phosphate, 2.89 moes of
hydrogen ions, 2.46 moles of phosphoric acid and 0.26 mole of free
nitric acid, per kilogram of the total weight of the aqueous
medium, was fed to the reaction section 12 of the reactor 10
through a pipe 22 at a flow rate of 130M.sup.3 per hour. Fresh
hydrogen gas was delivered to the lower gas distributor 18 of the
reactor 10 through a pipe 26 and then introduced into the reaction
section 12. In the reaction section 12, nitric acid or its salt
contained in the phosphate-buffered aqueous medium is reduced by
hydrogen gas in the presence of a 10 wt % palladium/active carbon
catalyst at 55% hydrogen partial pressure and 53.degree. C. The
unreacted hydrogen gas was recovered through a pipe 32 and
circulated back to the middle gas distributor 16 of the reactor 10
through a pipe 24. The concentration of the produced
hydroxylammonium phosphate in the aqueous medium at the exit of the
reactor 10 was 1.15 moles per kilogram of the total weight of the
aqueous medium, the selectivity to hydroxylamine was 85.5%, and the
catalyst activity was 26.6 g of hydroxylamine per hour per gram of
palladium.
Example 2
[0029] A reactor 210 as shown in FIG. 4 was used. An aqueous
reaction medium containing 0.04 mole of hydroxylammonium phosphate,
2.89 moles of hydrogen ions, 2.46 moles of phosphoric acid and 0.26
mole of free nitric acid, per kilogram of the total weight of the
aqueous medium, was fed to the reactor 10 through a pipe 22 at a
flow rate of 130M.sup.3 per hour. Fresh hydrogen gas was delivered
to the lower gas distributor 18 of the reactor 210 and the upper
gas distributor 20 of the reactor 210 through a pipe 26 and a pipe
28 respectively. The ratio of the fresh hydrogen gas delivered to
the lower gas distributor 18:the fresh hydrogen gas delivered to
the upper gas distributor 20, was 2 to 1. In the reaction section
12, nitric acid or its salt contained in the phosphate-buffered
aqueous medium is reduced by hydrogen gas in the presence of a 10
wt % palladium/active carbon catalyst at 55% hydrogen partial
pressure and 53.degree. C. The unreacted hydrogen gas was recovered
and circulated back to the middle gas distributor 16 of the reactor
210 through a pipe 24. The concentration of the produced
hydroxylammonium phosphate in the aqueous medium at the exit of the
reactor 210 was 1.06 moles per kilogram of the total weight of the
aqueous medium, selectivity to hydroxylamine was 83.5%, and
catalyst activity was 25.3 g of hydroxylamine per hour per gram of
palladium.
Comparative Example 1
[0030] A reactor 10' as shown in FIG. 1 was used. An aqueous
reaction medium containing 0.04 mole of hydroxylammonium phosphate,
2.89 moles of hydrogen ions, 2.46 moles of phosphoric acid and 0.26
mole of free nitric acid, per kilogram of the total weight of the
aqueous medium, was fed to the reactor 10' through a pipe 22' at a
flow rate of 130M.sup.3 per hour. Fresh hydrogen was delivered to
the middle gas distributor 16' of the reactor 10' through a pipe
24' and then introduced into the reaction section 12'. In the
reaction section 12', nitric acid or its salt contained in the
phosphate-buffered aqueous medium is reduced by hydrogen gas in the
presence of a 10 wt % palladium/active carbon catalyst at 55%
hydrogen partial pressure and 53.degree. C. The unreacted hydrogen
gas was recovered through a pipe 32', which is then mixed with
fresh hydrogen gas and delivered to the middle gas distributor 16'
of the reactor 10' through a pipe 24' for reintroduction into the
reaction section 12'. The concentration of the produced
hydroxylammonium phosphate in the aqueous medium at the exit of the
reactor 10' was 0.83 mole per kilogram of the total weight of the
aqueous medium, selectivity to hydroxylamine was 76.6%, and
catalyst activity was 19.4 g of hydroxylamine per hour per gram of
palladium.
[0031] From comparison of the results of Examples 1 and 2 and
Comparative Example, it can be seen that catalyst activity and
selectivity to hydroxylamine are significantly increased and higher
yield of hydroxylamine are obtained according to the present
invention. It is believed that such higher yield results from more
uniform gas distribution by disposing the gas distributors at
different positions of the reactor, which will increase efficiency
of mass transfer among gas, liquid and solid phases and avoid
occurrence of wall flow, channeling phenomenon, and the like in the
reactor.
[0032] The foregoing detailed description of the embodiments is for
illustrating the features and effects of the present invention and
not for limiting the scope of the present invention. Those skilled
in the art will appreciate that modifications and variations
according to the spirit and principle of the present invention
could be made. All such modifications and variations are considered
to fall within the spirit and scope of the present invention as
defined by the appended claims.
* * * * *