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Патент USA US2111276

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amh 11, 1193,
J. H. CASTNER ET AL
‘
291119276
PROCESS FOR THE PRODUCTION OF NITROUSv OXIDE
Filed June 25, 1936
Jepara/or §
7
James ??arsfner
William? 152G125!
INVENTORS '
BY
1
ATTORNEY
Patented Mar. 15, 1938
2,111,276
UNITED STATES PATENT OFFICE
2,111,276
PROCESS FOR THE PRODUCTION OF
NITROUS OXIDE
James B. Castner and William E. Kirst, Wood
bury, N. J., assignors to E. I. du Pont de Ne
mours & Company, Wilmington, Del., a corpo
ration of Delaware
Application June 25, 1936, Serial No. 87,201
'1 Claims. (01. 23—158)
The present invention relates to the manufac
ture of nitrous oxide by the heating of ammo
nium nitrate to its temperature of decomposition
and more particularly to such a process in which
5 improvement in yield, purity and uniformity of
gas evolution is obtained.
‘
.
The commercial methods of the prior art for
the manufacture of nitrous oxide have generally
comprised the heating of ammonium nitrate to
10 its decomposition temperature, with the resulting
formation of gaseous nitrous oxide and water, ac
cording to the equation
since under some conditions of decomposition
nitrogen gas and other impurities may be pro
duced.
The explanation of these sudden semi-explo
sive increases in gas evolution which occasionally
take place is not de?nitely known. Such occur
rences are, of course, due to an increase in re
action rate and are generally accompanied by
an increase in side reactions which give such
undesirable products as ammonia, nitric acid, 10
the higher oxides of nitrogen, or nitrogen itself.
Aside from the effect of local overheating, there
is no general agreement as to the reasons for the
occurrence of these violent reactions. It seems
15 As generally carried out, the method of opera
tion
consists in
introducing
a
considerable
amount of ammonium nitrate, for example 600
pounds, into a retort vessel either in solid lump
form or as a molten material.
Heat is then ap
120 plied until the charge is raised to the decomposi
tion temperature, for example 240 to 260° C.
Since the reaction is exothermic, no further ap
plication of heat is ordinarily necessary when
once it has started. Indeed, a certain amount of
25 cooling may be desirable from this point on in
order to exercise the desired control over the
decomposition velocity. As the process is usually
carried out, it is customary to carry out the de
composition until 60 to 80% of the ammonium
30 nitrate has been decomposed. The process is
then stopped and a fresh charge of ammonium
nitrate is added to bring the amount of the ma
terial to the original quantity. Upon heating,
renewed evolution of nitrous oxide will again
35 occur.
Nitrous oxide is thus obtained as a de
composition product together with water, which
latter material may be largely removed by con
densation.
While the chemistry of this process is simple,
40 the method of operation must be carefully con
trolled for several reasons.
In the ?rst place
It is essential that the nitrous oxide produced
should be of high purity, since the principal de
mand therefor is as an anaesthetic.
A further
‘5 important consideration ‘is that the reaction
should proceed smoothly since the decomposition
reaction involves the conversion of a solid to
gaseous products, a very great increase in vol
ume occurs, and an uncontrolled reaction might,
50 therefore, become explosive in its effects. This
control of the reaction velocity is important not
only from the safety point of View, but also from
the practical consideration. of yield. For the
purity of the product is to a considerable extent
.55 dependent on the even course of the reaction,
probable, however, that the presence of certain 15
impurities in small amounts in the reaction ma
terial exerts an undesirable catalytic effect on
the various side reactions. For it is observed
that the purity of the gas produced falls off
steadily‘ as fresh quantities of ammonium nitrate 20
are added to the heel. Apparently the impurity
which exerts the undesirable catalytic effect is
non-volatile and therefore increases progres
sively in amount as successive quantities of am
monium nitrate are added to the retort.
25
I-leretofore various attempts have been made to
counteract the e?ect of these occasional semi
explosive decompositions. These attempts, how
ever, have not successfully overcome the cause
of the di?iculty and manufacturers have con- 30
tented themselves by providing means for rapid
ly cooling the mixture, pressure vents and releas
able lids, so that the danger to life or permanent
equipment would be minimized.
The object of our invention is an improved 35
process for the production of nitrous oxide by
thermal decomposition of ammonium nitrate. A
further object is such a process characterized by
improved yields, increased purity of product, and
uniform velocity of gas evolution. A still further 40
object is a continuous process for manufacturing
nitrous oxide of high purity in high yields. Ad
ditional objects will be disclosed as our invention
Is hereinafter more fully described.
We have found that the foregoing objects are 45
accomplished by carrying out the reaction in the
presence of the catalyst disclosed and claimed in
our copending application, Serial No. 87,202 ?led
June 25, 1936, in such a manner that a substan
tially constant ratio is maintained between the 50
amount of ammonium nitrate being decomposed
and the amount of catalyst present in the reac
tion mixture.
In the copending case above referred to, a
great many materials are disclosed which not 55
2
2,111,276
only increase the rate of decomposition of am
monium nitrate to nitrous oxide, but also inhibit
the side reactions which result in the formation
of nitrogen and other impurities. Various com
pounds containing phosphorous, arsenic, molyb
denum, silver, and manganese which exhibit this
catalytic effect are therein disclosed.
The phos
phorous- and arsenic-containing compounds are
especially effective particularly water-soluble
10 substantially non-volatile derivatives which con
tain these elements in the acid» radical’, for ex
ample arsenates and phosphates of ammonia and
the alkali metals.
According to the present invention'ade?nite
15 improvement both in smoothness, of decomposi
tion and purity of product is obtained by placing
in the reaction vessel a suitable amount of the
catalyst described and claimed in the above men
tioned copending application.
Preferably pure
ammonium nitrate is then added to the retort
and the mixture is heated until decomposition
takes place. As'the ammonium nitrate in the re
tort decomposes, ammonium nitrate is fedto the
vessel, either continuously or at short intervals,
25 so that substantially the same quantities of am
monium nitrate and catalyst are present in the
reaction vessel at all times. By operating inthis
manner, the reaction may be carried out continu
ously or semi-continuously to obtain nitrous ox
30 ide of high purity in excellent yields.
In order to describe our invention more clear
ly, reference is made to the accompanying draw
ing which illustrates a preferred embodiment
thereof. It is to be understood, however, that
35 this is done solely by way of illustration and is
not to be regarded as a limitation upon the scope
of our invention.
.
.
,
The single ?gure oi the. drawing represents a
vertical section of a suitable apparatus for carry
40 ing out the process of our invention. The ap
paratus comprises a suitable reaction vessel l of
metal, for example iron or aluminum, provided
with a man hole 2, a gas outlet 3, and an am
monium nitrate inlet 4. Heat is supplied beneath
45 the retort by means of the gas burner 5. The gas
outlet 3 is connected through the condenser 6 to
the separating chamber 1' whereinthe condensate
is separated from the gaseous nitrous oxide.
From the separating chamber 1 the gas proceeds
50 through the line 8 to the compressor or storage
tank (not shown).
‘
In operation, 60 pounds of ammonium dihy
drogen phosphate for example, and 540 pounds of
ammonium nitrate are introduced into the re
55 tort l. Heat is supplied to the retort. by means
of the gas burner 5 until the ammonium nitrate
is brought to the temperature of decomposition.
As the nitrous oxide and water ‘vapor are evolved,
they pass through the gas exit line 3 into the
cooler condenser 6 where the water vapor is con
densed. The condensedwater is separated from
the gaseous nitrous oxide in the separating
chamber 1 and the N20 thence passes through
the line 8 to the storage tank or to the com
65 pressors. As the ‘ammonium nitrate is decom
posed, additional quantities of ammonium nitrate
are added through the line 74 so that substan
tially the same volume of ammonium nitrate is
maintained in the retort I throughout the course
of the reaction.
1
V
The ammonium nitrate fed to the retort I may
be added either in a solid or molten'condition, or
as an aqueous solution, as desired. Preferably
the ammonium nitrate is added continuously.
75 In~ view of the fact, however, that the catalyst is
present in a small percentage, it is possible to
maintain the ratio between the amount of cata
lyst and the amount of ammonium nitrate sub
stantially constant, by operating in a semi-con
tinuous manner, as for example, by adding the
ammonium nitrate at suitable intervals, so that
the quantity of material in the retort remains
substantially constant. When operating in this
manner, the quantities added and the intervals
between successive additions will, of course, de
pend on the rate at which the reaction is pro
ceeding.
, Since the ammonium phosphate is substantially
non-volatile under these conditions there will be
no loss of the catalyst.
The particular advan
15
tage of this procedure, therefore, arises from the
fact that substantially constant amounts of cat
alyst andv ammonium nitrate are present in the
reaction vessel l at all times. In other words,
the ratio of the amount of catalyst to the amount 20
of ammonium' nitrate is substantially constant.
The rate of decomposition is therefore uniform
and the nitrous oxide produced is characterized
by an exceptionally high purity throughout the
course of the reaction.
25
In the foregoing detailed description of our in
vention it is apparent that many variations in de
tail may be made without departing from the
spirit and scope thereof. Thus, for example, any
of the other catalysts described and claimed in 30
ourcopending application above referred to may
be employed in place of ammonium phosphate.
Furthermore, the ammonium nitrate added to
the reaction vessel may itself contain a small per
centage of catalyst, for example.0.01%.
The 85
amount of catalyst added in this manner‘ will, of
course, not materially alter the ratio between
catalyst and ammonium nitrate, due to the rela
tively large amount of catalyst (60 pounds) which
was originally placed in the reaction vessel. It
is also apparent that our improved process for
the efficient production of nitrous oxide makes no
claims as to temperature limits which must be ob
served during the decomposition period, but sim
ply requires heating to the temperature where 45
the decomposition of the ammonium nitrate pro
duces the desired gas generating rate. Other
variations in detail will be apparent to any one
skilled in the art. We, therefore, intend to be
50
limited only by the following patent claims:
We claim:
1. The process for the production of substan
tially pure nitrous oxide by thermal decomposi
tion of ammonium nitrate, which‘ process com
prises maintaining at the decomposition tem T55
perature a composition comprising ammonium
nitrate and a catalyst comprising a compound
containing an element selected from the group
consisting of phosphorous and arsenic, and add
ing ammonium nitrate thereto at a rate su?icient 60
to maintain, a substantially constant ratio be
tween the amount of catalyst and the amount of
ammonium nitrate present in the reaction vessel.
2. The process for the production of substan
tially pure nitrous oxide by thermal decomposi
tion of ammonium nitrate, which process com
prises maintaining at the decomposition tempera
ture of ammonium nitrate a composition com
prising ammonium nitrate and a phosphate and
adding ammonium nitrate thereto at a rate suffi
cient to maintain a substantially constant ratio
between the amount of catalyst and the amount
of ammonium nitrate present in the reaction
vessel.
3. The process for the‘production of substan- “~76
2,111,276
tially pure nitrous oxide by thermal decomposi
tion of ammonium nitrate which process com
prises charging into a reaction vessel a catalyst
comprising a compound containing an element
selected from the group consisting of phosphorus
and arsenic, subsequently adding ammonium ni
trate to said vessel, heating the resultant com
position to its decomposition temperature, and
adding to said reaction vessel ammonium nitrate
10 at a rate substantially equal to the rate of de
composition of the ammonium nitrate present in
said vessel.
4. The process for the production of substan
tially pure nitrous oxide by thermal decomposi
15 tion of ammonium nitrate which process com
prises charging into a reaction vessel a catalyst
comprising a phosphate, subsequently adding
ammonium nitrate to said vessel, heating the re
sultant composition to its decomposition tem
perature, and adding to said reaction vessel am
monium nitrate at a rate substantially equal to
the rate of decomposition of the ammonium ni
trate present in said vessel.
5. The process for the production of substan
25 tially pure nitrous oxide by thermal decomposi
tion of ammonium nitrate which process com
prises charging into a reaction vessel a catalyst
comprising ammonium phosphate, subsequently
adding ammonium nitrate to said vessel, heating
3
the resultant composition to its decomposition
temperature, and adding to said reaction vessel
ammonium nitrate at a rate substantially equal
to the rate of decomposition of the ammonium
nitrate present in said vessel.
6. The process for the production of substan
tially pure nitrous oxide by thermal decomposi
tion of ammonium nitrate, which process com
prises maintaining at the decomposition tem
perature a composition comprising ammonium 10
nitrate and a catalyst comprising a compound
containing phosphorous, and adding ammonium
nitrate thereto at a rate sui?cient to maintain a
substantially constant ratio between the amount
of catalyst and the amount of ammonium nitrate 15
present in the reaction vessel.
'7. The process for the production of substan
tially pure nitrous oxide by thermal decomposi
tion of ammonium nitrate which process com
prises charging into a reaction vessel a catalyst 20
comprising a compound containing phosphorous,
subsequently adding ammonium nitrate to said
vessel, heating the resultant composition to its
decomposition temperature, and adding to said
reaction vessel ammonium nitrate at a rate sub
stantially equal to the rate of decomposition of
the ammonium nitrate present in said vessel.
JAMES B. CASTNER.
WILLIAM E. KIRST.
25
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