Note: Descriptions are shown in the official language in which they were submitted.
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lo The present invention relates to a process or reacting
nitric oxide with hydrogen.
The reaction of N0 with H2 in acid solution in the
presence of noble-metal catalysts is carried out for preparing
hydroxylamine salts. The choice of a suitable catalyst is a pre-
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requisite, selective hydrogenation o~ the ~0 to yield hydroxylamine
'~, bein~ also necessary in addit~n to high reaction activity.
Economically carrying out the reaction to produceh~droxylamine salts which serve, for example, as a starting product
for the commercially important synthesis of caprolactam may be ;
;~ 20 achieved, inter alia, in bubble columns. In this case, if a
~ suitable apparatus is used for distributing the gases in the liquid,
i the production of a flow of liquid in the opposite direction to the
ascending bubbles yields the following advantages: -
It makes it possible to carry the heat of reaction off
vutside the reaction chamber by means of cooling
r~ devices of simple design;
It allows an increase in the dwell time of the gas bubbles
in the, reaction chamber, along with the higher mass
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t~ansfer associated therewith.
When continuously carrying out the reaction in a counter~
current bubble column, adequate conversion values of the NO
gas will not generally occur, so far as it is desired to
achieve economically reasonable volume-time yields. However,
the amount of reacted NO can be increased by uslng a gas
circuit.
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i Complete conversion cannot be obtained even by using
a gas circuit, however, since the recirculation ratio of -
10 the amount of recycle gas to amount of top gas cannot be
increased to any degree that may be desired. The reason
for this is that the gaseous by-pyoducts formed during the
~1 reaction and, in particular, the inert constituents present
in the charging gases in industrial operations must be
removed as waste gas. No gas is in addition lost in the
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process of removing the waste gas. ~:
; It has been found that when a counter-current bubble
column is employed, gas is discharged from the reaction
3 chamber with the liquid if certain liquid charges are
20 exceeded. Analysis shows that this gas contains little if ;~
any NO, which is surprising.
Accordingly, the present invention relates to a process `
-i for reacting nitric oxide with H2 in the presence of noble-
~ metal catalysts which are suspended in an acid liquid. The
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novel feature comprises introducing said liquid adjacent `
the upper end of a bubble column and fIowing said liquid ~;
~, downwardly at a liquid flow rate, introducing said NO and
` H2 adjacent the lower end of said column whereby large ;
and small bubbles are formed in said liquid~ adjusting
~ 30 said flow rate so as to permit said larger gas bubbles
`¦ to rise and collect adjacent the top of said column to
~ 3859~
form top gas and to aarry said smaller bubbles entrained ~:~
~` in said liquid to the lower end of said column,
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removing said liquid and said smaller bubbles from the ~;
~`~ bottom of said column, separating said smaller bubbles ;:
i from said liquid to form bottom gas,
`1 returning at least a part of said bottom gas and said ~
top gas to said lower end of said column, returning part .
of said liquid to the upper end of said column and with~
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;. drawing the rest of said liquid, which liquid contains
``. 10 said hydroxylamine. ` :~;
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~38597
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According to a preferred embodiment, the was~e.gas ~o be .- : :
separated is produced by means of liquid char~es of 80 - 350 ;:~
m3/m2 per hour.
Advantageously, only a proportion o:E the separated gas
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is removed as waste gas and the remainder is passed back into the
. gas circuit.
Taking advantage of these circumstances and further
.. in accordance with this invention, in the catalytic hydrogenation
of NO, an apparatus according to Figure 1 was set up comprising a
`~ counter-current bubble column with a gas circuit, a liquid charge ; ;.
'1 which entrained at least an amount of gas corresponding to the inert ;.~: ~
~ ~constituents to be discharged which, after the separation of the . :
.~ gas from the liquid, was discharged as waste gas. The waste gas
yield was free from NO and allowed complete-NO conversion to be
achieved, which is a sLgnificant technical advance. ..
In an apparatus operated on the principle described, the . :.
lowest specific consumption of NO per quantity of hydroxlamine
produced is achieved.
In addition to this economically favorable aspect, `;
another prime advantage of the described process is that in a ;
~ process in which NO is reacted with H2, a waste gas is obtained~ ~.?;` '. ~'
~ which is free from NO and does not have to undergo any costly
.~ treatments before being given off:into the atmosphere
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In a preferred embodLment of the inven~ion, the gas
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mixture in the counter-current bubble column is split up by :~
adjusting the flow of liquid such that a mixture of H2 and inert
gas with a comparatively high NO content is i-ormed as top gas at ;
the upper end of the column. As a result, a gas mixture practically .
free of NO is formed in conjunction with the liquid at the lower ~:
end of the counter-current bubble column. The gas mixture is then
withdrawn at the bottom and separated from the suspension. This
i last mentioned gas mixture is divided into~
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a) a portion which is returned to the gas circuit, and :
b) waste gas which is so adjusted in quantity that the
inert gases introduced with the fresh gases or
formed in secondary reactions are discharged .
The process ac~ording to the invention will be explained
with reference to Fig. l. In the counter-current bubble column
~ 4 there is produced a flow of liquid which is conveyed in the
X direction of the arrow from top to bottom,then through the
¦ line 7, the gas separator 6, the line 14 and the pump 5 and
:3 back to the upper end of the counter~current bubble column 4.
i 20 A portion of the liquid which, in addition to the suspended
3 catalyst, contains the ~esired end product ~say hydroxylamine
salt) and, if occasion arises, by-product (such as ammonium
salt), is drawn off through the line 12 and replaced by a
corresponding quantity of fresh liquid via the line ll.
On the other side, a gas mixture consisting of NO, H2 `
and inert gases flows via the line 3 into the lower end of the
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~ counter-current bubble column. The last-mentioned gases, such as
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nitrogen, are partly introduced from the start and are partly formed
during the reaction3 such as nitrous oxide The rate of flow of
the liquid is so adjusted that larger bubbles ascend slowly and `
i their content accumulates at the top of the column 4, while smailer
bubbles are retained in the lower part of the column by the flow or
brought back again into the lower part of the column by the said flow
Surprisingly, there accumulates in this way in the lower part of the
; column a gas mixture which is practically completely free of nitric
lo oxide. The nitric oxide its-elf ascends, together with part of the ;~
- hydrogen and inert gas. As far as the nitric oxide has not reacted -
through the catalyst suspended in the liquid to form the end product, -~
it accumulates as top gas at the top of the column together with
parts of the remainlng constituents of the gas mixture, that is
with part of the hydrogen and of the inert gases.
The gas which has accumulated in the lower part of the
column is'carried by the said flow of liquid via the line 7 into
the gas separator 6.
The design of the gas separator is also adapted to take
1 20 care of the problems which normally occur in practice, such as for ~`
instance high foam formation, which is done in conventional manner.
The gas is separated from the liquid in the separator 6
and conveyed through the line 8 into the line 9. Part of this gas
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(about 10-80% by mass) escapes, generally via a pressure relief
valve, through the line 10. The remainder flows to the bubble ~ -
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~1 column 4 via the line 9, then through the line 13, the gas circuit
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lQ38S97 ,~ ~
compressor 2 and the line 3. The liquid charge is so adjusted
that the amount of gas separated in the gas separator 6 is
greater than the amount discharged at 10
The top gas, which has a NO content of about 5 - 15%
by volume, escapes upwardly via the line 15 and is supplied
to the circuit via the lines 13 and 3 ~ogether with the gas
flowing from the line 9.
The introduction of the recycle branch 6-8-9 is novel.
In this way, the top gas is prevented from being able to pass unused
lo into the open air via the line 15-9-10, because in fact gas free
from NO flows downwardly in the line 9, which prevents the ascent
of the N0. As a result, with ~ull assurance of pressure equaliza- ; `.
tion in the system, firstly the yield of reacted N0 is improved and
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secondly pollution of the environment by N0 is avoided, which
~signiies a considerably technical advance
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Fresh N0/H2 mixture of the conventional commercial purity
i~ received in the part 13-2-3 of the gas circuit via the line 1
and introduced into the bubble column. In quantity, it corresponds
approximately to those parts which are converted in the reaction `~
20 chamber, plus those which!are carried off via the line 10 for the
purpose of dLscha~ging the inert gas constituents.
~ . The advantages of the described principle in comparison
3s with the conventional operation of a counter-current bubble column~
having a gas circuit, in which the waste gas is removed at the top ~:
of the column, will be illustrated with the aid of the following :~
~¦: Examplqs.
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103B597 `~
; In these Examples, "N" - "normal", i,e. condi~ions at '';
760 mm'Hg and 0C. ''
Exam~le 1
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In an apparatus according to Fig. 1, 7.018 Nm3 of H2, `
3.793 Nm3 of N0 and 0.789 Nm3 of inert gases were fed per hour
, via the line 1 together with the recycle gas flowing in from
the line 13, on the suction side of the gas circuit compress,or 2,
I via the 'line 3 to the counter-current bubble column 4. The
;? ~ ~ :column was filled for the ~ajor part (4/5 of its height~ with ',
ii lo one of the known acid catalyst suspensions. This suspension,
for its part, flowed downwardly in the direction of the arrow
through the bubble column 4, then through the line 7 and the
gas separator (or one of the conventional gas separator systems) 6
and back into the bubble column 4 via the line 14 and the pumy 5, ,'
A ~mall part of the end-product containing liquid corresponding to
the reacted NG plus H2 was drawn off by means of the line 12, a ` ~ ~'
corresponding amount of fresh catalyst suspension belng supplie~ to ',',~
~ the liquid circuit via the line Ll. The amount of this catalyst ~ ,
'I suspension was so adjuted by means of the pump 5 that a liquid
, 20 charge of 250 m3/m2 per hour was obtained in the bubble column.
'; The quan~ity of gas separated from the flow of liquid by means of
, the gas separator 6 (Nm3/hour) was conveyed via the line 8,
"1 for the larger part via the lines 9 and 13 to the suction side ',''~ of the gas circuit compressor 2, and for the smaller part
(1.916 Nm3/hour~ was discharged through the line ~0 as waste
~-t . gas. The waste gas was free from N0, corresponding to a N0 ,;
`' conversion of 100%. '
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-;, Example 2 ~Comparison Example) . ... ~
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~ Under similar conditions for the amounts of gas supplied
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:~ and the liquid circuit as those indicated in Example 1, in an ; .
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-' a~paratus according to Fig. 1, which, however, was operated
~,j without a gas separator .6 and a line 8 for separating ~he
entrained gas, the waste gas was discharged direc~ly as a
., proportion of the top gas (in line 15) through the line 10 in
an amount of 2.691 Nm3/hour. . -;~
,l, The NO content of the waste gas was 11~3~/o by volume, .
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o corresponding to 0.303 Nm3/hour. The degree of NO conversion .
was 92%. ~,
;l Modiications in and to the above described embodiments .: ;
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"! may be,made by those skilled in the art. It is .intended to
'''`if cover all such modiications which do not depar~ rom the spirit
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~1 and scope of the invention as defined in the claims appended hereto.
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