(19)

&
(11) EP 1 317 435 B1
(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.:

of the grant of the patent: C07D 251/62 (2006.01) B01J 8/02 (2006.01)
11.07.2012 Bulletin 2012/28
(86) International application number:
(21) Application number: 01982252.7 PCT/EP2001/010279

(22) Date of filing: 06.09.2001 (87) International publication number:

WO 2002/022589 (21.03.2002 Gazette 2002/12)

(54) PROCESS FOR THE PRODUCTION OF HIGH PURITY MELAMINE FROM UREA
VERFAHREN ZUR HERSTELLUNG VON HOCHREINEM MELAMIN AUS HARNSTOFF
PROCEDE DE PRODUCTION DE MELAMINE A HAUTE PURETE A PARTIR D’UREE

(84) Designated Contracting States: (72) Inventor: RIPPERGER, Willi

AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU 67227 Frankenthal (DE)
MC NL PT SE TR
Designated Extension States: (74) Representative: Zardi, Marco et al
RO M. Zardi & Co. S.A.
Via Pioda 6
(30) Priority: 13.09.2000 EP 00119891 6900 Lugano (CH)

(43) Date of publication of application: (56) References cited:

11.06.2003 Bulletin 2003/24 WO-A-96/20182 GB-A- 1 174 848

(73) Proprietor: Casale Chemicals S.A.

6900 Lugano-Besso (CH)
EP 1 317 435 B1

Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent
Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the
Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been
paid. (Art. 99(1) European Patent Convention).

Printed by Jouve, 75001 PARIS (FR)

 EP 1 317 435 B1

Description

Field of the invention

5 [0001] According to its general aspect the present invention relates to a high-pressure non-catalytic process for the
production of high purity melamine from urea.
[0002] More in particular, the invention relates to a method for purifying melamine from impurities like ureido-melamine,
oxotriazines, melam, melem and non-converted urea in the form of isocyamic acid by an appropriate physical-chemical
treatment. The treatment is preferably but not exclusively carried out within the non-catalytic process, so as to obtain
10 melamine with a purity of 99% and higher.

Prior Art

[0003] The modern processes of melamine synthesis can be classified into two categories: the catalytic low-pressure
15 processes and the non-catalytic high-pressure processes. All processes are characterised by three process stages: a)
syntheses; b) Melamine purification and recovery; c) the off-gas treatment. An overview of the prior art is given in
(Ulmann’s Encyclopaedia of Industrial Chemistry, Vol. A 16, p.171-181(1990)).
[0004] In a high-pressure non-catalytic process a urea melt from the off-gas scrubber is fed to the high-pressure
reactor, operated at a pressure between 6 and 15Mpa and in the temperature range of 390 - 410°C. The urea is pyrolised
20 to melamine according to the equation

25 [0005] To enhance the reaction and to suppress the formation of byproducts, additional ammonia is fed to the reactor
in an amount of 0,2 - 1,0 Kg ammonia/Kg urea and the residence time in the reactor, referring to the urea feed, is between
0,5 - 2 hours. The reaction products in the reactor consist of molten melamine comprising byproducts like ureido-
melamine, oxotriazines, melam, melem and non-converted urea in the form of Isocyamic Acid. The Melamine melt is
transferred under pressure, together with CO2 and NH3 as a mixed stream, to a gas-liquid separator. In the gas liquid
30 separator which is kept at virtually the same pressure and temperature at the reactor vessel, the reaction gases are
separated from the melamine melt.
[0006] The gaseous stream, which contains the reaction gases ammonia and carbon-dioxide, the added ammonia,
non-converted isocyamic acid and also melamine vapour, is sent to the urea scrubber where it is scrubbed at virtually
the same pressure, with molten urea so as to preheat the urea, cool said off-gases and remove the melamine from the
35 off-gases. Isocyanic acid is reconverted to urea in the scrubber. The preheated urea, which contains the removed
melamine is sent to the reactor.
[0007] The liquid melamine melt from the gas-separators, which contains still the above mentioned impurities, ureido-
melamine, oxotriazines, melam, melem as well as unconverted isocyamic acid besides dissolved ammonia and carbon-
dioxide can not be simply cooled to solid melamine. This melamine would contain too much impurities and could not be
40 used for technical purposes. Normally, customary melamine has a purity > 99.5% more preferably > 99.8%. To produce
such a high-purity melamine, the melamine melt is either: quenched with an aqueous ammonia solution, dissolved,
filtered and recrystallised or molten melamine is vaporised by a stream of ammonia from the melt or transferred to a so
called ageing-unit where the melt or the already solid melamine is treated by increasing the ammonia pressure at higher
temperature and longer residence times.
45 [0008] A water quench for removing and reducing the impurities is used for example, by the Nissan process ("Technical
development of melamine Manufactured by Urea process" by A. Shiroishi et al., Chemical economy & Engineering
review, vol.8, 1976, page 35 ff.), the Montedison process (" The manufacture of Non-fertiliser Nitrogen Products" Nitrogen
No.139, p32-39, (1982)) and lately by the Eurotecnica process ("A Challenging Opportunity", Nitrogen & Methanol, No.
233, page 35 - 40, (1998))..
50 [0009] In principle, in all three processes the mixture of melamine melt and the off-gases coming from the reactor are
separated or not into a gaseous stream and a liquid stream, consisting mainly of melted melamine. The liquid stream is
quenched with an aqueous ammonia solution, in which the melamine is dissolved. The solution is maintained for a
definite period of time at higher temperature and pressure, during which the impurities are said to be eliminated.
[0010] Thereafter follows a further treatment with numerous apparatus, including filtration, crystallisation and a costly
55 waste water treatment section. The number of unit operations in a melamine plant with such quenching units is very
high which rises the investment costs as well as the operating cost considerably. This is a serious drawback of such plants.
[0011] To avoid this costly units for quenching with an aqueous ammonia solution and following purification by crys-

2
 EP 1 317 435 B1

tallisation, a purification by evaporation of the melamine melt has been proposed (WO 95/01345, WO 97/34879). After
separation of the off-gases from the melamine melt, the liquid melamine melt is directed to a vaporiser and is vaporised
therein by lowering the pressure and/or feeding ammonia gas into the vaporiser. The melamine containing ammonia
gas obtained from the vaporiser is cooled in a quencher, preferably with ammonia gas. Though the melamine obtained
5 has a sufficient purity, this process has the disadvantage of a high energy consumption:

To evaporate the melamine from the melt, the heat of vaporisation must be raised which cannot, or only at a very
low temperature level, be recovered.

10 [0012] To enhance the evaporation of the melamine, a minimum of 2,4Kg, ammonia per Kg of melamine is needed
to vaporise the melamine. So, large amounts of gas are to be handled.
[0013] To avoid the above mentioned drawbacks of the different processes Melamine chemicals, US patent 4 565
867, has developed a very simple high pressure process in which the quantity of apparatus is quite small as compared
with the Montedison, Nissan or Eurotecnica process. However, the purity of the melamine obtained is only 95 - 97.5%
15 in a commercial plant.
[0014] To combine the advantage of a simple high-pressure process like the Melamine Chemicals process, with a
high product quality numerous proposals had been made.
[0015] One method described (WO 98/04533, WO 98/52928, WO 98/55465, WO 98/55466, WO 98/20183, WO
96/20183, WO 98/23778, WO 00/21940, US patent 5 514 797) is the after treatment of the already solidified melamine
20 powder or crystals under high ammonia pressure and at elevated temperature. Pressure up to 50Mpa and temperatures
between 270 - 354°C are claimed for the after treatment. A noticeable reduction of the melam and melem content is
only achieved at ammonia pressures above 7,5 MPA, as shown in the examples. Furthermore, because this reaction
takes place in the solid state, long residence time, up to 5 hours, and mechanical agitation are necessary. For all the
persons skilled in the art, these restrictions are serious disadvantages.
25 [0016] As an alternative to the treatment of solid melamine the aftertreatment of the melamine melt under high ammonia
pressure and higher temperatures is described (WO 96723778, WO 96/20182, EP 0808 836 A1). The liquid ,melamine
melt, separated from the reaction gases ammonia and carbon-dioxide, is subjected to a treatment with ammonia at
temperature between 430°C and the melamine melting point under an ammonia partial pressure from 5 to 40 MPa during
a mean resting time up to 8 hours. After that the melamine melt is cooled down with a controlling rate to a temperature
30 from 320°C to 270°C and then expanded and cooled down to room temperature.
[0017] All these methods have the disadvantage that the pressure level within the plant has to be increased considerably
above the reaction pressure of the reactor and gas purification unit and longer residence times of the melt are necessary
to achieve a sufficient reduction of the by-product content. This is a serious handicap for a continuos process operation,
apart from the cost for the compression of the ammonia gas.
35 [0018] On the other side the multitude of published patents show the importance of getting melamine of high purity
from the high-pressure, non-catalytic processes.

Summary of the invention

40 [0019] The technical problem underlying the present invention is to provide a method for obtaining melamine at high
purity in a simple and reliable manner, without the drawbacks of the prior art.
[0020] The problem is solved by a method for purifying melamine from impurities like ureido-melamine, oxotriazines,
melam and melem, characterized in that a melamine melt is put into contact at a temperature comprised between 340°C
and 410°C and at a pressure comprised between 8 and 17 MPa with a bed of a catalyst thus obtaining melamine with
45 a purity of at least 99%.
[0021] Preferably, the catalyst is selected from the group comprising alumina, silica, alumina/silica, molecular sieves,
mixtures and derivatives thereof.
[0022] According to a preferred embodiment of the invention, the catalyst also has adsorptive properties.
[0023] Preferably said melamine containing impurities is obtained from urea by a high-pressure non-catalytic process.
50 [0024] Advantageously said melamine containing impurities in the melt state is fed with a continuous flow to a purifi-
cation unit comprising one bed of said catalyst.
[0025] Preferably, said continuous flow of melamine melt is fed to the purification unit with a flow rate comprised
between 0.5 and 10 Kg of melamine melt/ (litre catalyst x hour), for instance between 1 and 10 Kg of melamine melt/
(litre catalyst x hour)
55 [0026] The contact between the melamine melt with the bed of the catalyst is carried out in the presence of NH3,
wherein NH3 is dissolved in said melamine.
[0027] According to the research work carried out by the Applicant, the surprising results obtained with the above
purification method could be explained by the catalyst who promotes the reaction of impurities such as ureido-melamine,

3
 EP 1 317 435 B1

oxotriazines, ammeline, ammelide, cyanuric acid, melam, melem and melon to melamine. Improved results have further
been obtained by the use of a catalyst with additional adsorptive properties: non-converted higher molecular compounds
such as melam, melem and melon are thus removed from the melamine melt by adsorption.
[0028] According to a further embodiment, the present invention relates to a method for purifying melamine comprising
5 impurities like melam, melem, melon, characterized in that a melamine melt is put into contact at a temperature comprised
between 340°C and 410°C and at a pressure comprised between 8 and 17 MPa with a bed of an adsorbent material.
[0029] Preferably, the adsorbent material is selected from the group comprising alumina, silica, alumina/silica, active
carbon, natural clays, molecular sieves, mixtures and derivatives thereof.
[0030] Among the many advantages obtained with the present invention it is worth citing that a melamine conversion
10 yield up to 99.9% may be achieved.
[0031] Moreover, operating pressure and temperature of the present method can be substantially equal to those used
in the non-catalytic melamine synthesis process from urea, so that no changes are required in the operating conditions
during the production process.
[0032] It is also advantageously possible to carry out the melamine purification directly and in continuous within the
15 same plant for the non-catalytic production of high purity melamine from urea.

Brief description of the drawings

[0033]
20
Fig. 1 shows a flow diagram of a melamine plant according to the present invention.

Fig.2 shows a test apparatus to detect melamine purity.

25 Detailed description of the drawings

[0034] With specific reference to Fig.1 is a detailed description of a preferred embodiment of the present invention.
[0035] It is shown a flow diagram of a complete plant-system for the manufacture of melamine from urea in a high-
pressure process and shows how the invention can be integrated into an existing plant or in a new one.
30 [0036] Liquid urea is fed to a gas scrubber (2) via line (1). Via line (5), a gas stream consisting mainly of NH3, CO2
and gaseous melamine is transferred from the melamine reactor (3), which is connected directly with the gas-liquid
separator (4) to the gas scrubber (2). In the gas-scrubber (2) the melamine is scrubbed from the gas stream by means
of the urea supplied via line (1). Via line (6) the liquid urea with the melamine and dissolved NH3 and CO2 enters through
a nozzle the melamine reactor (3). Via line (8) additional NH3 can be fed to the melamine reactor.
35 [0037] A gas stream consisting of NH3 and CO2 leaves the gas scrubber (2) via line (7) to an adjoining urea plant. In
the reaction vessel (3) the urea is reacted at 390°C-410°C and 8-17 MPa to NH3, CO2 and melamine. The liquid melamine
is separated from the reaction gases on the top of the melamine reactor (3) and in the connected gas-separator (4). To
strip off the last traces of CO2 from the melamine melt, pressurised NH3 is fed via line (9) to the gas separator (4).
[0038] The liquid melamine melt from the gas- separator (4), which is practically free of CO2 and saturated with NH3,
40 is directed via line (10) to the purification unit (11) according to this invention. In this unit a catalyst removes the impurities
by catalytic conversion and - depending on the catalyst used - also by adsorption. The purification unit (11) has practically
the pressure as the melamine reactor (3) and gas-separator (4). The temperature of the purification unit (11) can be
adjusted to the amount of impurities, preferably the temperature is between 360 and 410°C. In other words, the pressure
and the temperature in unit (11) can be substantially the same as in the melamine reactor (3). It is also possible that
45 lower pressure and/or temperature are used in unit (11).
[0039] To enhance the catalytic conversion of the impurities additional ammonia can be fed to the purification unit via
line (12). Via dashed line (13) low pressure steam, when necessary, can be introduced into the purification unit to
regenerate the catalyst.
[0040] In the subsequent product cooler (14) the melamine melt, saturated with ammonia, is cooled slightly above its
50 melting point under the reaction conditions. In another embodiment of the invention the product cooler (14) is installed
directly after the gas-separator (4) and before the purification unit (11).
[0041] After passing the product cooler (14) the melamine melt is sent via line (15) to the quenching section (16),
where the melamine melt is de-pressurised and cooled with liquid ammonia, added by line (19). The resulting solid
melamine powder is discharged via line (17), the gaseous ammonia is discharged via line (18), liquefied and recycled
55 to the quenching section (16).
[0042] With specific reference to Fig. 2, it is shown a test apparatus wherein the effectiveness of the invention was
demonstrated.
[0043] Solid melamine is filled in the autoclave (20). Then the autoclave is pressurised with NH3 via line (21) to the

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 EP 1 317 435 B1

desired pressure and heated to the desired temperature, normally in the range of 360°- 410°C. During the heating up
period the pressure increases, surplus NH3 is released by valve (22). After reaching the desired temperature and pressure
and all the melamine is melted, valve (23) is opened and the melamine melt is fed to the purification unit (24), which is
filled with the catalyst (25). Line (26) indicates a NH3 feed to the purification unit (24).
5 [0044] After passing the catalyst (25), the melamine melt is expanded via valve (27) into the quencher (30). In the
quencher the melamine melt is effectively cooled by liquid ammonia fed via line (28) below 250°C. The pressure in the
quencher (30) is appropriately adjusted to the pressure in the purification unit. Evaporated ammonia is released by the
valve (29).
[0045] At the end of the test, the accumulated melamine is taken from the quencher and analysed by High Pressure
10 Liquid Chromatography (HPLC). The following examples demonstrate the effectiveness of the invention.

Example 1

[0046] Melamine with the following composition (wt%):

15
Melamine 97,5
Melam 1,91
Melem 0,14
Ureido-Melamine 0,05
20
Oxotriazines 0,4

was melted in the autoclave and the melamine melt passed at different flow rates over a catalyst in the purification unit
according to Figure 2 under the following conditions:
25
Catalyst Volume (ml) 500
Catalyst Type Al2O3 (activated
alumina)
Temperature (°C) 400
30
Pressure (MPa) 15
NH3added (wt% of melamine) 5

[0047] The "flow rate" is defined as the hourly melamine feed in Kg per volume of catalyst, given in litres. In several
35 test runs the following results have been received (mean values)

Flow rate 4 7
Product Composition (wt%)
Melamine 99,9% 99,6%
40 Melam - -
Melem <0,01 <0,01
Ureido-Melamine - -
Oxotriazines - -
45
"-" means not detectable by HPLC

Example 2

[0048] Melamine with the following composition (wt%)

50

Melamine 95,3
Melam 1,30
Melem 0,74
Ureido-Melamine 1,53
55
Oxotriazines 0,90

[0049] Was melted and treated in the purification unit as described in example 1 under the following reaction conditions:

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 EP 1 317 435 B1

Catalyst Volume (ml) 500

Catalyst Type Al2O3/SiO3 (Silica/ alumina)
Temperature (°C) 400
5
Pressure (MPa) 8
NH3 added (wt% of melamine feed) 5

[0050] The following results had been received depending on the flow rate:
10
Flow rate 2 4
Product Compostion (wt%)
Melamine 99,6% 99,3%
Melam 0,1 0,4
15
melem <0,01 <0,01
Ureido-Melamine - -
Oxotriazines - 0,01

20 Example 3

[0051] The example shows the possibility to remove melam and melem from a liquid melamine melt essentially by
adsorption. Melamine with 1000 ppm melem and 1500 ppm melam was molten and fed to the purification unit as described
above under the following conditions:
25
Adsorbent Volume (ml) 500
Adsorbent Type Al2O3(γ Alumina)
Temperature (°C) 360
Pressure (MPa) 15
30
Flow rate 4 Kg Melamine/l adsorbent  h

[0052] Under these conditions the melem content was reduced to 40-80 ppm, the content of melam in the product
was reduced to 350 - 500 ppm.
35 [0053] As it is apparent to one skilled of the art various modifications are possible within the scope of this invention.
For example, the invention can be applied to all existing high-pressure process with quite different compositions of the
melamine melt coming from the synthesis section of a high pressure process.
[0054] In particular, the purifying unit (11) can be installed later into an existing melamine plant. There is a high flexibility
concerning pressure, temperature and amount and type of impurities to be removed, on the one hand by the selection
40 of suitable catalysts and or adsorbent materials, on the other hand by varying the dimension of the reactor and/or the
flow rate.
[0055] Furthermore, it is possible to operate various modifications on said catalysts and or adsorbent materials, e.g.
surface area, pore volume, pore diameter, acid properties etc.

45
Claims

1. Method for purifying melamine comprising impurities like ureido-melamine, oxotriazines, melam, melem, charac-
terized in that a melamine melt is put into contact at a temperature comprised between 340°C and 410°C and at
50 a pressure comprised between 8 and 17 MPa with a bed oft a catalyst selected from the group comprising alumina,
silica, alumina/silica, molecular sieves, mixtures and derivatives thereof, in the presence of NH3 thus obtaining
melamine with a purity of at least 99%.

2. Method according to claim 1, characterized in that said catalyst has adsorptive properties.
55
3. Method according to claim 1, characterized in that said melamine containing impurities is obtained from urea by
a high-pressure non-catalytic process.

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 EP 1 317 435 B1

4. Method according to claim 1, characterized in that said melamine melt is fed with a continuous flow to a purification
unit comprising at least one bed of said catalyst.

5. Method according to claim 4, characterized in said continuous flow of melamine melt is fed to said purification unit
5 with a flow rate comprised between 0.5 and 10 Kg of melamine melt/ (litre catalyst x hour), preferably between 1
and 10 Kg of melamine melt/ (litre catalyst x hour).

6. Method according to claim 4, characterized in that said melamine melt is obtained from a high-pressure non-
catalytic process and directly fed to said purification unit.
10
7. Method for purifying melamine comprising impurities like melam, melem, melon, characterized in that a melamine
melt is put into contact at a temperature comprised between 340°C and 410°C and at a pressure comprised between
8 and 17 MPa with a bed of an adsorbent material.

15 8. Method according to claim 7, characterized in that said adsorbent material is selected from the group comprising
alumina, silica, alumina/ silica, active carbon, natural clays, molecular sieves, mixtures and derivatives thereof.

9. High-pressure non-catalytic process for the production of melamine from urea characterized by the fact of com-
prising a melamine purification step according to claim 1 or 7.
20
10. Plant for producing in continuous high-purity melamine, comprising a melamine reactor (3) in fluid communication
with a gas scrubber (2) and a gas separator (4), characterized by the fact of comprising at least a purification unit
(11) comprising at least a bed of a catalyst or an adsorbent material, said unit being in fluid communication with
said gas separator (4).
25

Patentansprüche

1. Verfahren zum Reinigen von Melamin, umfassend Verunreinigungen, wie Ureidomelamin, Oxotriazine, Melam,
30 Melem, dadurch gekennzeichnet, dass eine Melaminschmelze bei einer Temperatur, die zwischen 340°C und
410°C umfasst, und bei einem Druck, der zwischen 8 und 17 MPa umfasst, mit einem Bett eines Katalysators, der
aus der Gruppe umfassend Aluminiumoxid, Siliziumdioxid, Aluminiumoxid/Siliziumdioxid, Molekularsiebe, Gemische
und Derivate davon ausgewählt wird, in Gegenwart von NH3 in Kontakt gebracht wird, um so Melamin mit einer
Reinheit von mindestens 99 % zu erhalten.
35
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass der Katalysator adsorptive Eigenschaften besitzt.

3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das Verunreinigungen enthaltende Melamin aus
Harnstoff mittels eines nicht katalytischen Hochdruckverfahrens erhalten wird.
40
4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Melaminschmelze mit einem kontinuierlichen
Strom einer Reinigungseinheit zugeführt wird, die mindestens ein Katalysatorbett umfasst.

5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass der kontinuierliche Strom der Melaminschmelze der
45 Reinigungseinheit mit einer Strömungsrate zugeführt wird, die zwischen 0,5 und 10 kg Melaminschmelze/(Liter
Katalysator x Stunde), vorzugsweise zwischen-1 und 10 kg Melaminschmelze/(Liter Katalysator x Stunde), umfasst.

6. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass die Melaminschmelze von einem nicht katalytischen
Hochdruckverfahren erhalten wird und der Reinigungseinheit direkt zugeführt wird.
50
7. Verfahren zum Reinigen von Melamin, umfassend Verunreinigungen, wie Melam, Melem, Melon, dadurch gekenn-
zeichnet, dass die Melaminschmelze bei einer Temperatur, die zwischen 340°C und 410°C umfasst, und bei einem
Druck, der zwischen 8 und 17 MPa umfasst, mit einem Bett eines Adsorbentmittels in Kontakt gebracht wird.

55 8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, dass das Adsorptionsmaterial aus der Gruppe umfassend
Aluminiumoxid, Siliziumdioxid, Aluminiumoxid/Siliziumdioxid, Aktivkohle, natürliche Tone, Molekularsiebe, Gemi-
sche und Derivate davon, ausgewählt ist.

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 EP 1 317 435 B1

9. Nicht katalytisches Hochdruckverfahren zur Herstellung von Melamin aus Harnstoff, dadurch gekennzeichnet,
dass es einen Melaminreinigungsschritt nach Anspruch 1 oder 7 umfasst.

10. Anlage zum kontinuierlichen Herstellen von hochreinem Melamin, umfassend einen Melaminreaktor (3) in Fluidver-
5 bindung mit einem Gaswäscher (2) und einem Gasabscheider (4), dadurch gekennzeichnet, dass mindestens
eine Reinigungseinheit (11) umfasst ist, die mindestens ein Bett eines Katalysators oder eines Adsorbentmaterials
umfasst, wobei die Einheit in Fluidverbindung mit dem Gasabscheider (4) ist.

10 Revendications

1. Procédé destiné à purifier de la mélamine comprenant des impuretés telles que l’uréidomélamine, les oxotriazines,
le mélam, le mélem, caractérisé en ce qu’une matière fondue de mélamine est mise en contact à une température
comprise entre 340°C et 410°C et à une pression comprise entre 8 et 17 MPa avec un lit d’un catalyseur sélectionné
15 dans le groupe comprenant l’alumine, la silice, l’alumine/silice, les tamis moléculaires, les mélanges et les dérivés
de ceux-ci, en présence de NH3, obtenant ainsi de la mélamine avec une pureté d’au moins 99 %.

2. Procédé selon la revendication 1, caractérisé en ce que ledit catalyseur a des propriétés d’adsorption.

20 3. Procédé selon la revendication 1, caractérisé en ce que ladite mélamine contenant des impuretés est obtenue à
partir d’urée par un procédé non catalytique haute pression.

4. Procédé selon, la revendication 1, caractérisé en ce que ladite matière fondue de mélamine est amenée avec un
flux continu à une unité de purification comprenant au moins un lit dudit catalyseur.
25
5. Procédé selon la revendication 4, caractérisé en ce que ledit flux continu de matière fondue de mélamine est
amené à ladite unité de purification avec un débit compris entre 0,5 et 10 kg de matière fondue de mélamine/(litre
de catalyseur x heure), de préférence entre 1 et 10 kg de matière fondue de mélamine/(litre de catalyseur x heure).

30 6. Procédé selon la revendication 4, caractérisé en ce que ladite matière fondue de mélamine est obtenue à partir
d’un procédé non catalytique haute pression et directement amenée à ladite unité de purification.

7. Procédé destiné à purifier de la mélamine comprenant des impuretés telles que le mélam, le mélem, le mélon,
caractérisé en ce qu’une matière fondue de mélamine est mise en contact à une température comprise entre
35 340°C et 410°C et à une pression comprise entre 8 et 17 MPa avec un lit d’un matériau adsorbant.

8. Procédé selon la revendication 7, caractérisé en ce que ledit matériau adsorbant est sélectionné dans le groupe
comprenant l’alumine, la silice, l’alumine/silice, le charbon actif, les argiles naturelles, les tamis moléculaires, les
mélanges et les dérivés de ceux-ci.
40
9. Procédé non catalytique haute pression destiné à la production de mélamine à partir d’urée, caractérisé par le fait
qu’il comprend une étape de purification de la mélamine selon la revendication 1 ou 7.

10. Usine de production de mélamine de haute pureté en continu, comprenant un réacteur de mélamine (3) en com-
45 munication fluidique avec un laveur (2) et un séparateur de gaz (4), caractérisée par le fait qu’elle comprend au
moins une unité de purification (11) comprenant au moins un lit d’un catalyseur ou d’un matériau adsorbant, ladite
unité étant en communication fluidique avec ledit séparateur de gaz (4).

50

55

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9
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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European
patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be
excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• WO 9501345 A [0011] • WO 9620183 A [0015]

• WO 9734879 A [0011] • WO 9823778 A [0015]
• US 4565867 A [0013] • WO 0021940 A [0015]
• WO 9804533 A [0015] • US 5514797 A [0015]
• WO 9852928 A [0015] • WO 96723778 A [0016]
• WO 9855465 A [0015] • WO 9620182 A [0016]
• WO 9855466 A [0015] • EP 0808836 A1 [0016]
• WO 9820183 A [0015]

Non-patent literature cited in the description

• Ulmann’s Encyclopaedia of Industrial Chemistry. • The manufacture of Non-fertiliser Nitrogen Products.

1990, vol. A 16, 171-181 [0003] Nitrogen, 1982, 32-39 [0008]
• A. SHIROISHI et al. Technical development of mela- • A Challenging Opportunity. Nitrogen & Methanol,
mine Manufactured by Urea process. Chemical econ- 1998, 35-40 [0008]
omy & Engineering review, 1976, vol. 8, 35 ff [0008]

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