Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates to a process for the continuous
production o~ nitroguanidine from guanidine nitrate through the
action of aqueous sulfuric acid and possibly nitric acid thereby
reusing the recovered concentrated sulfuric acid from -the pre-
ceding step, the conversion i.s carried out using 2.5 to 3.5 moles
sulfuric acid per mole of guanidine nitrate.
Such process for the producti.on of nitroguanidine from
guanidine nitrate is already well-known. Here conversion is
carried out with a 75% to 85% sulfuric acid within a period of
4 to 24 hours and is performed at a temperature of ~5-35C. Then
the reaction mixture is diluted to a sulfuric acid concentration
of 25% to 30% with water or with wash-water consisting of 2% to
5% sulfuric acid of the preceding step, the nitroguanidine is
precipitated within a temperature range of 18C to 25C and the
sulfuric acid i5 concentrated for the following batch. This re-
covered and concentrated sulfuric acid is reused for the next
batch.
It is a disadvantage of this process that when chosing
a reaction temperature not exceeding 35C, the reaction period
will amount to 4 to 24 hours if a nitroguanidine recovery of as
much as 98% is to be obtained.
It is the purpose of this invention to find a more
economic process for the recovery of nitroguanidine whereby the
reaction period is considerably reduced for the same yield.
This is achieved by carrying out the dehydratation using
a 82% to 85% sulfuric acid, maintaining a temperature of 40-80C,
preerably 40-60C for a period of 1 to 3 hours and subsequently
diluting the sulfuric acid to 25~35% by adding water or wash-acid
of 0-5C from a preceding step and concentrating the diluted 25-
35% sulfuric acid recovered after the separation of the precipi-
tated nitroguanidine for reusage.
By chosing a reaction temperature of 40 to 80C the
-- 1 --
~ ~54E~
reaction process could be reduced to l to 3 hours but this means
that opposite to the well-known process in the same times about
4 to ~ times the conversion of the known process is obtained.
The process of the invention therefore is already much more eco-
nomic than the previous process only for this reason.
Contrary to previous assumptions it appeared that when
using a 82% to 85% dehydratation acid for the reaction step no
spontaneous disintegration has to be feared but that the temper-
ature can be raised to 60% without the danger of an explosive
reaction process and that even a temperature increase up to 80C
is not yet dangerous.
When carrying out the well-known process in a circula-
tion, it appeared that guanidine salt as well as ammonium sulfate
and other organic or inorganic impurities result in the concen-
trated sulfuric acid. This requires the removal of the total
concentrated sulfuric acid after repeated circulation and its
replacement by fresh acid. For this reason it is not possible
to perform this process for a longer period of time continuously
and make it economic but a still-stand results after one or some
circules due to decreasing quality of the product and bad yields-,
the number of the permissible circles is dependent on the purity
of the raw materials and the materials used for the plant.
For the recovery of the dissolved nitroguanidine rest
in the precipitation acid obtained after separation of the nitro-
guanidine, already a slow stepwise concentration of the 20% to
30% sulfuric acid has been carried out at rising temperature and
higher vacuum. This process is carried out in a period of lO-17
hours to reduce the danger of a spontaneous dissolution of the
nitroguanidine dissolved in the sulfuric acid and furthermore to
remove the nitric acid released during the conversion from the
reaction mixture.
Nevertheless a slow disintegration of the nitroguani-
dine in the presence of concentrated sulfuric acid as per the
below scheme cannot be avoided by the well-known process:
/ H2\ (92-98%) / ~I2
1. ~I-~=C I-~03 -~ EI2S04 ~ HN=C ~ H20
2 above 35-40C NH , N02
/NH2
2. ~=C ~ ? H N - C - N ~ N 0 + H 0
NH , N02
3. H2N - C - N + 2 H20 , 2 ~I3 + C02
.. . . ~
10 Molecular formula:
NH2 \ conc.
IIN-C ~IN03 + H2S04 __~ N20 -~ 2 NH3 + C02
\ \ ~I2J above 35
~ ccording to a preferable performance of the process
of the invention the recovered 25-35% sulfuric acid is concentra-
ted to `30-82%. 10-25% of this concentrated acid are replaced by
~7-98% fresh sulfuric acid or oleum and the sulfuric acid having
a concentration of 82-85% is reused.
The 25-33% sulfuric acid centrifuged off after the first
step still contains about 0.5 to 2% nitroguanidine, 1 to 4% ammo-
nium sulfate and ammonium bisulfate respectively as well as or-
ganic and inorganic contaminants included during this workir~ proce-
dure, like NH4N03 from the guanidine nitrate, further impurities
and metal salts from the apparatus and small disintegration pro
ducts of the nitroguanidine which form rela-tively much ammonium
bisulfate and ammonium sulfate resp. due to the high nitrogen
content of nitroguanidine.
By permanently replacing a certain part of the concen-
trated sulfuric acid by concentrated fresh acid an enrichrnent of
these impurities during the continuous perforrnance of the process
can be avoided and it is possible to obtain the final produc-t
r - 3 -
nitroguanidine always in the same form.
The share of the con~entrated sulfuric æid to ke ~ placed
by concentrated fresh acid is between 10% and 25%. If, for ex-
ample, a guanidine nitrate with 95% purity is used for the pro-
duction of nitroguanidine according to the well-known process
only one, at the utmost two circules would be possible to achieve
a nitroguanidine purity of at least 99.0%. If one proceeds ac-
cording to the preferred performance of the process of the inven-
tion and replaced 10-25% of the concentrated wash-acid ineach case
by 98% fresh acid or oleum and repeats this procedure in each
circle, the acid will stay in the circulation and a nitroguani-
dine of minimum 98% purity will be obtained whereby the process
can be continued continuously without changing the yield of 97_
98% of the the~y related to used guanidine nitrate of 100% and
the purity of the recovered nitroguanidine.
By limiting the final concentration of the waste acid
to 80-85% the above disintegration of the nitroguanidine can be
avoided completely or limited to a minimum. The consumption of
fresh acid therefore can be reduced considerably. As only 10-
25% of the total sulfuric acid employed have to be removed afterone working step, the process can, in addition to its compara-
tively excellent economic aspects, be considered non-polluting.
By the above procedure the impurities in -the sulfuric
acid remaining in circulation will enrich only to a tolerable
figure and stay at this figure. Therefore the new process can be
circulated for an unlimited period of time whereby no stillstand
will occur by itself as is the case with the described well-known
process.
Particulars and details of the invention can be realized
from the below examples.
Exam~le 1
Into 82 to 85% sulfuric acid 75-90% of which consisting
of 75-82% concentrated waste sulfuric acid and 10-25% of which
_~_
consisting of fresh sulfurlc acid of 96-98% or oleum and ~ossi-
bly containing 3-10% concentrated nitric acid, within a period
of one hour beginning at room temperature 0.25 to 0.30 parts
guanidine nitrate 98% pure per one part sulfuric acid are added
under cooling the present acid mixture and the temperature is
allowed to ri~e to 50C. The guanidine nitrate dissolves in the
82% to 85% acid and is converted into nitroguanidine.
The hereby obtained reaction mixture reduces the acid
concentration by about 3% to 79-82%. After another one or two
hours the reaction is complete. The reaction mass is mixed with
3-10% acid water of 0.5C from previous steps. After completion
of the process, a 25-35% acid is present in which the precipi-
tated nitroguanidine is suspended. It is cooled to 3-0C and
the nitroguanidine is separated by means of a centrifuge. Sub-
sequently washings are made with wash-water from previous batches
and finally with fresh water so long until the nitroguanidine is
free of acid.
The first centrifuged off 25-35% acid containing about
0.5-2% nitroguanidine and 1-4% ammonium sulfate and ammonium bi-
sulfate resp. and other impurities in a dissolved form, is addedto a rotary evaporator with three steps, connected in a series
and is in steps distilled under reduced pressure and a end temp-
erature up to maximum 140C in such a way that the residence time
in the three steps, however, particularly in the last step is on-
ly a few minutes in each case. The 82% to 85% sulfuric acid per-
manently running off is water-clear. 10-25% of the acid are re-
moved after each nitration cycle and replaced by the same quanti-
ty of concentrated fresh acid or oleum.
By thls method the sulfuric acid returning to the ni-
tration cycle remains the ~same in its composition and for thisreason also the final product nitroguanidine always has the same
desired consistency. The purity of the nitroguanidine will be at
least 99% and the yield at least 97% of the theory related -to used
guanidine nitrate of 100%~ The sulfuric acid thus can be pe~mane~ly
-5-
8~
circulated without the necessity to remove it as a whole.
The share of added ~resh acid is adjusted to 10-25%
depending on the purity of the employed guanidine nitrate and on
the quantity of the organic and inorganic materials added during
the procedure, like ammonium nitrate from the guanidine ni-trate,
impurities, metal salts from the equipment and little disin-te-
gration products of the nitroguanidine containing relatively
much ammonium bisulfate and ammonium sulfate respectively due to
the high nitrogen content of the nitroguanidine.
Example 2
This example corresponds to a running production.
Operation is carried out with three ~,000 liters corro-
sion-resistant 4,000 litres stirrers in a series with the usual
accessories and connected with two feed pumps. In stirrer 1 per-
manently 82-85% sulfuric acid as described is added in such a
quantity as corresponding guanidine nitrate is added via a feeder.
While in a period of 60 minutes 1,250 k~s guanidine
nitrate are added to the reaction mixture with a temperature of
40-50C in the stirrer filled to vOo/O, in the same period of time
4,200 kgs 84% acid of a temperature of 10-30C depending on de-
sired reaction speed are added. The time of the addition is
furthermore depending on the cooling activity of the stirrer as
the weakly exothermic reaction is to be kept to 40-60C.
From the filled stirrer 1 in intervals of 60 minu-tes in
each case 5,450 kgs reaction material are pumped into container
2 filled to 60% and from container 2 the same quantity into con-
tainer 3 with the same volume. By this method, a total reaction
time for the conversion amounting to 3 hours can be achieved.
All three stirrers are continuously filled to 60-90%~
From stirrer 3 permanently reaction mass is pumped off in such a
way that the volume in stirrer 1 practically remains constant.
The hereby obtained diluted acid of a concen-tration of
25-35% is continuously separa-ted from precipi-tated nitroguani-
dine after coolin~ to about 0-5C by rneans of a centrifuge and
is ~ashed free of acid with wash-waters from previous washings
and with water~
The off-running first acid o~ 25-35% is returned -to
the distillation plant with its three steps. 75-90% of th.is acid
are concentrated to 80 82% and mixed with 10-25% of 96% fresh
acid or oleum and the resulting 82-85% acid again is used for the
dehydratation of guanidine nitrate.
The product guanidine has a purity of at least 98.5%
and the yield is about 97-98% of the theory related to used
guanidine nitrate of 100%. Its purity is at least 98.5%.
