WO1998027071A1 - Method for the preparation of melamine - Google Patents

Method for the preparation of melamine Download PDF

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Publication number
WO1998027071A1
WO1998027071A1 PCT/NL1997/000683 NL9700683W WO9827071A1 WO 1998027071 A1 WO1998027071 A1 WO 1998027071A1 NL 9700683 W NL9700683 W NL 9700683W WO 9827071 A1 WO9827071 A1 WO 9827071A1
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Prior art keywords
melamine
reactor
stream
urea
cooled
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Application number
PCT/NL1997/000683
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French (fr)
Inventor
Julius Gerardus Theodorus Van Wijck
Original Assignee
Dsm N.V.
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Filing date
Publication date
Priority claimed from NL1004814A external-priority patent/NL1004814C2/en
Application filed by Dsm N.V. filed Critical Dsm N.V.
Priority to AU53462/98A priority Critical patent/AU5346298A/en
Publication of WO1998027071A1 publication Critical patent/WO1998027071A1/en

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    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07DHETEROCYCLIC COMPOUNDS
    • C07D251/00Heterocyclic compounds containing 1,3,5-triazine rings
    • C07D251/02Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings
    • C07D251/12Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members
    • C07D251/26Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members with only hetero atoms directly attached to ring carbon atoms
    • C07D251/40Nitrogen atoms
    • C07D251/54Three nitrogen atoms
    • C07D251/56Preparation of melamine
    • C07D251/60Preparation of melamine from urea or from carbon dioxide and ammonia

Definitions

  • the invention relates to a method for the preparation of melamine from urea in which solid melamine is obtained by transferring the melamine stream leaving the reactor to a product cooling unit in which the melamine stream is cooled by means of a cooling agent.
  • EP-A-747366 discloses a high-pressure process for the production of melamine from urea.
  • EP-A-747366 describes the pyrolysis of urea in a reactor at a pressure of 10.34 to 24.13 MPa and a temperature of 354 to 454 "C for producing a reactor product.
  • This reactor product contains melamine, C0 2 , and NH 3 and is transferred under pressure, as a mixed stream, to a separator that is operated at virtually the same pressure and temperature conditions as the reactor. In the separator the reactor product is separated into a gaseous stream and a liquid stream.
  • the gaseous stream contains C0 2 and NH 3 off-gases and also melamine vapour and the liquid stream consists substantially of molten melamine.
  • the gaseous stream from the separator is transferred to a scrubber unit that is operated at virtually the same pressure and temperature as the reactor.
  • the scrubber unit the C0 2 and NH 3 off-gases, which contain melamine vapour, are scrubbed with molten urea to pre-heat the urea, cool the off-gases to a temperature of 177-232 °C, and remove the melamine vapour from the off-gases by dissolving it in the molten urea.
  • the pre-heated molten urea which contains the dissolved melamine, is then fed into the reactor.
  • the liquid stream from the separator comprising mainly molten melamine
  • a product cooling unit where it is contacted with a liquid cooling medium.
  • the temperature of the molten melamine is lowered to produce a solid melamine product.
  • EP-A-747366 the purity of the solid melamine end product is higher than 99 wt.%, but these products prove to have a somewhat yellow colour.
  • use is preferably made of liquid ammonia as liquid cooling medium.
  • EP-A-747366 aspires to be an improvement on NL-A-8403843.
  • the products obtained according to the process described in NL-A-8403843 are also somewhat yellow.
  • a 60 gram sample of melamine powder is introduced into a cell of a Hunterlab ColorQUEST ® spectrophotometer and values of parameters L' , a', and b' are determined.
  • the value of b' is a measure of the blue-yellow shift, the b' value being positive if the product is yellow and negative if the product is blue. The greater the positive value, the more yellow the product.
  • the aim of the present invention is to obtain an improved process for the preparation of melamine from urea in which melamine having a high degree of purity is obtained as a dry, virtually white powder directly from the reactor product.
  • the colour of the melamine can be improved substantially by transferring the melamine stream leaving the melamine reactor to a product cooling unit in which the melamine stream is cooled to a temperature below 175 °C, preferably below 150 °C, and, most preferably, below
  • the colour of melamine can be improved substantially in a method for the preparation of melamine via a non- catalytic high-pressure process by transferring the melamine melt leaving the reactor to a product cooling unit in which the melamine is recovered by cooling the melamine melt by means of a cooling medium down to a temperature below 175 °C, preferably below 150 °C, and, most preferably, below 125 °C.
  • the preferred cooling medium for cooling the melamine melt is liquid ammonia.
  • a brief residence time is chosen to ensure that the discolouration of the solid melamine obtained is maintained at a level below that which would correspond to a C.I.E. b' value of 1.2.
  • the residence time of the solid melamine in the product cooling unit should be less than two hours, preferably less than one hour, and, most preferably, less than 30 minutes.
  • the residence time at a given temperature should be sufficiently short to ensure that the resulting degree of discolouration is maintained at a level below that which would correspond to a C.I.E. b' value of about 1. Because the degree of discolouration is a function of the time at temperature, the use of lower temperatures permits longer residence times to be tolerated while still maintaining acceptable colour of the solid melamine product. Conversely, at higher temperatures care must be taken to maintain a brief residence time to avoid unacceptable levels of discolouration in the melamine product .
  • Another customary method for determination of the colour of melamine is the APHA colour measurement conducted according to SCM Method 10. This involves the preparation of a formaldehyde-melamine resin with an F/M ratio of about 3.0, using a formaldehyde solution with 35 wt . % formaldehyde, 7.5-11.2 wt% methanol, and 0.028 wt% of an acid (particularly formic acid) .
  • the theoretical solids content of the solution thus prepared is about 56 wt . % .
  • a 25 gram sample of melamine is then slowly dissolved (the addition taking about 3 minutes) in 51 grams of the above formaldehyde solution while the mixture is being heated.
  • the colour of the resulting mixture is then analyzed with a spectrophotometer such as a Hitachi U100 spectrophotometer using a 4 cm glass cell.
  • Solutions typically used as calibration standards include solutions of cobalt chloride and potassium hexachloroplatinate.
  • the colour of the formaldehyde- melamine resin obtained when using melamine prepared according to the present invention is preferably lower than about 20 APHA, and most preferably lower than about 15 APHA.
  • the pressure in the product cooling unit at which cooling of the melamine to below 175 °C takes place is not critical.
  • the invention therefore, is equally applicable to both low-pressure and high- pressure cooling processes. If the invention is applied in a high-pressure process, the pressure caused by the evaporating cooling medium, preferably liquid ammonia, is preferably higher than 1.5 MPa, and most preferably higher than 5 MPa.
  • NL-A-8403843 describes a method in which the liquid melamine melt is cooled to a temperature of 50- 75 "C using liquid ammonia at a pressure of 1.38-
  • the melamine preparation can be carried out at a low pressure, preferably between 0.1 and 2.5 MPa, in the presence of a catalyst such as aluminium oxide, or at a high pressure, preferably between 5 and 80 MPa, without utilizing a catalyst.
  • the temperature at which the reaction occurs may be between 325 and 450 "C and is preferably between 350 and 425 °C.
  • the NH 3 and C0 2 byproducts are usually separated and returned to an adjoining urea plant.
  • a plant suitable for the present invention may comprise a scrubber unit, a reactor in combination with a gas/liquid separator or with a separate gas/liquid separator, optionally a post-reactor or an aging vessel and a product cooling unit .
  • melamine is prepared from urea in a plant consisting of a scrubber unit, a melamine reactor, optionally in combination with a gas/liquid separator or a separate gas/liquid separator and a product cooling unit .
  • Urea melt from a urea plant is fed to a scrubber unit at a pressure of 5 to 80 MPa, preferably 8 to 30 MPa, and at a temperature above the melting point of urea.
  • This scrubber unit may be provided with a jacket so as to provide extra cooling in the scrubber.
  • the scrubber unit may also be provided with internal cooling bodies.
  • the liquid urea comes into contact with reaction gases from the melamine reactor or from a separate gas/liquid separator installed downstream of the reactor.
  • the reaction gases consist primarily of C0 2 and NH 3 and will also contain an amount of melamine vapour.
  • the molten urea scrubs the melamine vapour from the reaction gases and carries this melamine back to the reactor.
  • the reaction gases are cooled from the temperature of the reactor, i.e from 350- 425 °C, to 170-240 °C, and the molten urea is pre-heated to 170-240 °C.
  • the reaction gases are preferably removed from the top of the scrubber unit and returned to a urea plant for use as a starting material for the production of urea.
  • the pre-heated urea is withdrawn from the scrubber unit and fed, for instance via a high-pressure pump, together with the dissolved melamine scrubbed from the reaction gases, into the reactor, which has a pressure of 5 to 80 MPa, and preferably of 8 to 30 MPa.
  • the scrubber unit can be placed above the melamine reactor to permits the use of gravity to accomplish or assist in transferring the pre-heated urea into the reactor.
  • the molten urea is heated to a temperature of 325 to 450 °C, preferably to a temperature of about 350 to 425 °C, at a pressure within the range described above. Under these conditions, the urea is converted into melamine, C0 2 , and NH 3 .
  • An amount of ammonia can be metered into the melamine reactor as either a liquid or a hot vapour.
  • the ammonia metered into the melamine reactor can, for instance, serve both to prevent the formation of melamine condensation products such as melam, melem, and melon, and to promote mixing in the reactor.
  • the amount of ammonia fed into the melamine reactor may be as much as 10 moles of NH 3 per mole of urea, preferably, less than about 5 moles of NH 3 per mole of urea, and most preferably less than about 2 moles of NH 3 per mole of urea.
  • the C0 2 and NH 3 formed as a result of the reaction, as well as any additional ammonia supplied, may be separated from the liquid melamine in a separation section of the reactor, typically at the top of the reactor, or may be separated in a gas/liquid separator located downstream of the reactor.
  • the C0 2 and NH 3 gas mixture, as well as any melamine vapour, once separated from the liquid melamine, is then sent to a scrubber unit for removal of melamine vapour and for preheating of the urea melt as described above.
  • the liquid melamine is withdrawn from the reactor, or optionally from a gas/liquid separator downstream from the reactor, and transferred to a product cooling unit.
  • the liquid melt is cooled by means of liquid ammonia to a temperature below 175 °C, preferably below 150 °C, and most preferably below 125 °C.
  • the residence time of the melamine in the product cooling unit is between 2 and 60 minutes, preferably below 5 and 30 and in particular between 5 and 15 minutes.
  • the pressure in the product cooling unit is generally at least 1 MPa and preferably between 3 and 25 MPa.
  • a evaporator is added between the reactor or post-reactor and the product cooling unit.
  • the melamine melt leaving the reactor or post-reactor is fed into the evaporator where it is heated to form melamine vapour.
  • the melamine vapour is then fed into the product cooling unit where it is cooled with liquid ammonia to produce solid melamine according to the present invention.
  • the present invention is suitable for use in both low-pressure catalytic and high-pressure non- catalytic melamine processes.
  • the present invention is also suitable for use in processes that feed a melamine melt to the product cooling unit and those that feed a melamine vapour to the product cooling unit .

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

The invention relates to a method for the preparation of melamine from urea in which solid melamine is obtained by transferring the melamine stream leaving the reactor to a product cooling unit where the melamine stream is cooled to a temperature below 175 °C. More in particular it relates to a method for the preparation of melamine from urea via a non-catalytic high-pressure process by transferring the melamine melt leaving the reactor to a product cooling unit where the melamine is recovered by cooling the melamine melt using a cooling medium, the melamine melt being cooled to a temperature below 175 °C.

Description

METHOD FOR THE PREPARATION OF MELAMINE
The invention relates to a method for the preparation of melamine from urea in which solid melamine is obtained by transferring the melamine stream leaving the reactor to a product cooling unit in which the melamine stream is cooled by means of a cooling agent.
Such a method is described in, inter alia, EP-A-747366, which discloses a high-pressure process for the production of melamine from urea. In particular, EP-A-747366 describes the pyrolysis of urea in a reactor at a pressure of 10.34 to 24.13 MPa and a temperature of 354 to 454 "C for producing a reactor product. This reactor product contains melamine, C02, and NH3 and is transferred under pressure, as a mixed stream, to a separator that is operated at virtually the same pressure and temperature conditions as the reactor. In the separator the reactor product is separated into a gaseous stream and a liquid stream. The gaseous stream contains C02 and NH3 off-gases and also melamine vapour and the liquid stream consists substantially of molten melamine.
The gaseous stream from the separator is transferred to a scrubber unit that is operated at virtually the same pressure and temperature as the reactor. In the scrubber unit the C02 and NH3 off-gases, which contain melamine vapour, are scrubbed with molten urea to pre-heat the urea, cool the off-gases to a temperature of 177-232 °C, and remove the melamine vapour from the off-gases by dissolving it in the molten urea. The pre-heated molten urea, which contains the dissolved melamine, is then fed into the reactor. The liquid stream from the separator, comprising mainly molten melamine, is transferred to a product cooling unit where it is contacted with a liquid cooling medium. Through contact with the liquid cooling medium and a reduction in pressure, the temperature of the molten melamine is lowered to produce a solid melamine product. By selecting a liquid cooling medium that forms a gas at the temperature and pressure, generally higher than 41.4 bar, present in the product cooling unit, the solid melamine produced requires no further washing or purification.
According to EP-A-747366 the purity of the solid melamine end product is higher than 99 wt.%, but these products prove to have a somewhat yellow colour. In EP-A-747366 use is preferably made of liquid ammonia as liquid cooling medium. EP-A-747366 aspires to be an improvement on NL-A-8403843. The products obtained according to the process described in NL-A-8403843 are also somewhat yellow.
The disadvantage of these methods is that melamine produced tends to have a pale yellow colour. For more demanding applications, however, and in particular melamine-formaldehyde resins used in laminates, this yellowish discolouration renders the melamine unsuitable. For universal applicati n, therefore, the solid melamine must have almost no discernable discolouration and should be essentially white in colour. Research by the applicant has shown that this pale yellow colour is partly caused by the combination of storage temperature and storage time in the product cooling unit. Experiments conducted by the applicant prove that there is a relationship between yellowness of the melamine product and the storage temperature and the storage time. The yellowness of the product was measured according to the Hunterlab C.I.E. method. According to this method, a 60 gram sample of melamine powder is introduced into a cell of a Hunterlab ColorQUEST® spectrophotometer and values of parameters L' , a', and b' are determined. In the Hunterlab C.I.E. method, the value of b' is a measure of the blue-yellow shift, the b' value being positive if the product is yellow and negative if the product is blue. The greater the positive value, the more yellow the product.
The aim of the present invention is to obtain an improved process for the preparation of melamine from urea in which melamine having a high degree of purity is obtained as a dry, virtually white powder directly from the reactor product. In particular, it is the aim of the present invention to obtain an improved high-pressure process for the preparation of melamine from urea in which melamine having a high degree of purity is obtained as a dry, virtually white powder directly from the liquid melamine melt through cooling by means of a cooling medium. The applicant has now found that the colour of the melamine can be improved substantially by transferring the melamine stream leaving the melamine reactor to a product cooling unit in which the melamine stream is cooled to a temperature below 175 °C, preferably below 150 °C, and, most preferably, below
125 °C. In particular, the applicant has found that the colour of melamine can be improved substantially in a method for the preparation of melamine via a non- catalytic high-pressure process by transferring the melamine melt leaving the reactor to a product cooling unit in which the melamine is recovered by cooling the melamine melt by means of a cooling medium down to a temperature below 175 °C, preferably below 150 °C, and, most preferably, below 125 °C. The preferred cooling medium for cooling the melamine melt is liquid ammonia. Further, a brief residence time is chosen to ensure that the discolouration of the solid melamine obtained is maintained at a level below that which would correspond to a C.I.E. b' value of 1.2. The residence time of the solid melamine in the product cooling unit should be less than two hours, preferably less than one hour, and, most preferably, less than 30 minutes. Preferably, the residence time at a given temperature should be sufficiently short to ensure that the resulting degree of discolouration is maintained at a level below that which would correspond to a C.I.E. b' value of about 1. Because the degree of discolouration is a function of the time at temperature, the use of lower temperatures permits longer residence times to be tolerated while still maintaining acceptable colour of the solid melamine product. Conversely, at higher temperatures care must be taken to maintain a brief residence time to avoid unacceptable levels of discolouration in the melamine product .
Another customary method for determination of the colour of melamine is the APHA colour measurement conducted according to SCM Method 10. This involves the preparation of a formaldehyde-melamine resin with an F/M ratio of about 3.0, using a formaldehyde solution with 35 wt . % formaldehyde, 7.5-11.2 wt% methanol, and 0.028 wt% of an acid (particularly formic acid) . The theoretical solids content of the solution thus prepared is about 56 wt . % . A 25 gram sample of melamine is then slowly dissolved (the addition taking about 3 minutes) in 51 grams of the above formaldehyde solution while the mixture is being heated. The colour of the resulting mixture is then analyzed with a spectrophotometer such as a Hitachi U100 spectrophotometer using a 4 cm glass cell. Solutions typically used as calibration standards include solutions of cobalt chloride and potassium hexachloroplatinate. The colour of the formaldehyde- melamine resin obtained when using melamine prepared according to the present invention is preferably lower than about 20 APHA, and most preferably lower than about 15 APHA.
The pressure in the product cooling unit at which cooling of the melamine to below 175 °C takes place is not critical. The invention, therefore, is equally applicable to both low-pressure and high- pressure cooling processes. If the invention is applied in a high-pressure process, the pressure caused by the evaporating cooling medium, preferably liquid ammonia, is preferably higher than 1.5 MPa, and most preferably higher than 5 MPa.
NL-A-8403843 describes a method in which the liquid melamine melt is cooled to a temperature of 50- 75 "C using liquid ammonia at a pressure of 1.38-
2.76 MPa. Residence times are not disclosed in the application. However, application EP-A-747366, noted above in the preamble, teaches that products according to NL-A-8403843 do not have a good purity. The advantage of the method according to the present invention is that virtually white, powdery melamine is obtained, which can be used in virtually all melamine applications without the need for further purification. In the preparation of melamine, urea is preferably used as starting material in the form of a melt. NH3 and C02 are byproducts obtained during the melamine preparation, which proceeds according to the following reaction equation:
6 C0(NH2) C3N6H6 + 6 NH, + 3 CO,
The melamine preparation can be carried out at a low pressure, preferably between 0.1 and 2.5 MPa, in the presence of a catalyst such as aluminium oxide, or at a high pressure, preferably between 5 and 80 MPa, without utilizing a catalyst. The temperature at which the reaction occurs may be between 325 and 450 "C and is preferably between 350 and 425 °C. The NH3 and C02 byproducts are usually separated and returned to an adjoining urea plant.
The above-mentioned aim of the invention is achieved in a plant suitable for the preparation of melamine from urea. A plant suitable for the present invention may comprise a scrubber unit, a reactor in combination with a gas/liquid separator or with a separate gas/liquid separator, optionally a post-reactor or an aging vessel and a product cooling unit .
In an embodiment of the method, melamine is prepared from urea in a plant consisting of a scrubber unit, a melamine reactor, optionally in combination with a gas/liquid separator or a separate gas/liquid separator and a product cooling unit . Urea melt from a urea plant is fed to a scrubber unit at a pressure of 5 to 80 MPa, preferably 8 to 30 MPa, and at a temperature above the melting point of urea. This scrubber unit may be provided with a jacket so as to provide extra cooling in the scrubber. The scrubber unit may also be provided with internal cooling bodies.
In the scrubber unit the liquid urea comes into contact with reaction gases from the melamine reactor or from a separate gas/liquid separator installed downstream of the reactor. In the case of a separate gas/liquid separator, the pressure and temperature are virtually the same as the temperature and pressure in the melamine reactor. The reaction gases consist primarily of C02 and NH3 and will also contain an amount of melamine vapour. The molten urea scrubs the melamine vapour from the reaction gases and carries this melamine back to the reactor. In the scrubbing process the reaction gases are cooled from the temperature of the reactor, i.e from 350- 425 °C, to 170-240 °C, and the molten urea is pre-heated to 170-240 °C. The reaction gases are preferably removed from the top of the scrubber unit and returned to a urea plant for use as a starting material for the production of urea. The pre-heated urea is withdrawn from the scrubber unit and fed, for instance via a high-pressure pump, together with the dissolved melamine scrubbed from the reaction gases, into the reactor, which has a pressure of 5 to 80 MPa, and preferably of 8 to 30 MPa. To reduce the necessary high-pressure pump capacity, the scrubber unit can be placed above the melamine reactor to permits the use of gravity to accomplish or assist in transferring the pre-heated urea into the reactor.
In the reactor the molten urea is heated to a temperature of 325 to 450 °C, preferably to a temperature of about 350 to 425 °C, at a pressure within the range described above. Under these conditions, the urea is converted into melamine, C02, and NH3. An amount of ammonia can be metered into the melamine reactor as either a liquid or a hot vapour. The ammonia metered into the melamine reactor can, for instance, serve both to prevent the formation of melamine condensation products such as melam, melem, and melon, and to promote mixing in the reactor.
The amount of ammonia fed into the melamine reactor may be as much as 10 moles of NH3 per mole of urea, preferably, less than about 5 moles of NH3 per mole of urea, and most preferably less than about 2 moles of NH3 per mole of urea. The C02 and NH3 formed as a result of the reaction, as well as any additional ammonia supplied, may be separated from the liquid melamine in a separation section of the reactor, typically at the top of the reactor, or may be separated in a gas/liquid separator located downstream of the reactor. The C02 and NH3 gas mixture, as well as any melamine vapour, once separated from the liquid melamine, is then sent to a scrubber unit for removal of melamine vapour and for preheating of the urea melt as described above.
The liquid melamine is withdrawn from the reactor, or optionally from a gas/liquid separator downstream from the reactor, and transferred to a product cooling unit. In the product cooling unit the liquid melt is cooled by means of liquid ammonia to a temperature below 175 °C, preferably below 150 °C, and most preferably below 125 °C. The residence time of the melamine in the product cooling unit is between 2 and 60 minutes, preferably below 5 and 30 and in particular between 5 and 15 minutes. The pressure in the product cooling unit is generally at least 1 MPa and preferably between 3 and 25 MPa.
In another embodiment, as described in O- 95/01345, a evaporator is added between the reactor or post-reactor and the product cooling unit. The melamine melt leaving the reactor or post-reactor is fed into the evaporator where it is heated to form melamine vapour. The melamine vapour is then fed into the product cooling unit where it is cooled with liquid ammonia to produce solid melamine according to the present invention. As shown through the discussion of these embodiments, the present invention is suitable for use in both low-pressure catalytic and high-pressure non- catalytic melamine processes. The present invention is also suitable for use in processes that feed a melamine melt to the product cooling unit and those that feed a melamine vapour to the product cooling unit .
The invention will be elucidated with reference to the following examples.
Examples
Melamine powder (standard DSM melamine) was transferred into a container and subjected to various temperature, pressure, and residence time combinations. Table 1 presents the results of comparative experiment A and experiments 1-6. The C.I.E. b' value was measured using the Hunterlab ColorQUEST® spectrophotometer in accordance with the procedure described above. TABLE 1
Figure imgf000011_0001

Claims

C L A I S
1. Method for the preparation of melamine from urea in which solid melamine is obtained by transferring the melamine stream leaving the reactor to a product cooling unit where the melamine stream is cooled by means of a cooling agent, characterized in that the melamine stream is cooled to a temperature below 175 °C, the residence time being chosen so that the discolouration is less than the discolouration corresponding to a b' of 1.2.
2. Method according to claim 1, characterized in that the melamine stream is cooled to a temperature below 150°C.
3. Method according to claims 1-2, characterized in that the melamine stream is cooled to a temperature below 125 °C.
4. Method according to claims 1-3, characterized in that the residence time of the solid melamine in the product cooling unit is less than two hours.
5. Method according to claim 4, characterized in that the residence time of the solid melamine in the product cooling unit is less than one hour.
6. Method according to claims 4-5, characterized in that the residence time of the solid melamine in the product cooling unit is less than 30 minutes.
7. Method for the preparation of melamine from urea via a non-catalytic high-pressure process by transferring the melamine melt leaving the reactor to a product cooling unit where the melamine is recovered by cooling the melamine melt using a cooling medium, characterized in that the melamine stream is cooled to a temperature below 175 'C.
8. Method according to claim 8, characterized in that liquid ammonia is used as cooling medium.
9. Method for the preparation of melamine from urea in which solid melamine is obtained by transferring the melamine stream leaving the reactor to a product cooling unit where the melamine melt is cooled by means of a cooling agent, characterized in that the melamine stream is cooled to a temperature below 175 °C, the residence time being chosen so that the discolouration is less than the discolouration corresponding to an APHA of about 20.
10. Method for the preparation of melamine from urea in which solid melamine is obtained by transferring the melamine stream leaving the reactor to a product cooling unit where the melamine stream is cooled using a cooling agent, characterized in that the melamine stream is cooled at a temperature and a residence time that is chosen so that the discolouration is less than the discolouration corresponding to a b' of about 1.
11. Method for the preparation of melamine from urea in which solid melamine is obtained by transferring the melamine stream leaving the reactor to a product cooling unit where the melamine stream is cooled by means of a cooling agent, characterized in that the melamine stream is cooled at a temperature and a residence time that is chosen so that the discolouration is less than the discolouration corresponding to an APHA of about 20.
12. Method as substantially described and elucidated in the specification and the examples.
PCT/NL1997/000683 1996-12-16 1997-12-11 Method for the preparation of melamine WO1998027071A1 (en)

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US3273696P 1996-12-16 1996-12-16
US60/032,736 1996-12-16
NL1004814 1996-12-18
NL1004814A NL1004814C2 (en) 1996-12-18 1996-12-18 High purity, white coloured melamine preparation from urea

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6380385B1 (en) 1995-12-07 2002-04-30 Agrolinz Melanin Gmbh Process for the preparation of pure melamine
AU2003304057B2 (en) * 2003-04-24 2009-07-16 Egi Contracting Engineering Co. Ltd Combined air cooled condenser

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3302833A1 (en) * 1983-01-28 1984-08-02 Basf Ag, 6700 Ludwigshafen Process for the preparation of melamine
NL8403843A (en) * 1984-01-05 1985-08-01 Melamine Chemicals Inc PROCESS FOR PREPARING MELAMINE.
US4565867A (en) * 1984-01-05 1986-01-21 Melamine Chemicals, Inc. Anhydrous high-pressure melamine synthesis
WO1995001345A1 (en) * 1993-07-01 1995-01-12 Kemira Oy Process for the preparation of melamine
EP0747366A2 (en) * 1995-06-07 1996-12-11 Melamine Chemicals, Inc. Melamine of improved purity produced by high-pressure, non-catalytic process

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3302833A1 (en) * 1983-01-28 1984-08-02 Basf Ag, 6700 Ludwigshafen Process for the preparation of melamine
NL8403843A (en) * 1984-01-05 1985-08-01 Melamine Chemicals Inc PROCESS FOR PREPARING MELAMINE.
US4565867A (en) * 1984-01-05 1986-01-21 Melamine Chemicals, Inc. Anhydrous high-pressure melamine synthesis
WO1995001345A1 (en) * 1993-07-01 1995-01-12 Kemira Oy Process for the preparation of melamine
EP0747366A2 (en) * 1995-06-07 1996-12-11 Melamine Chemicals, Inc. Melamine of improved purity produced by high-pressure, non-catalytic process

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6380385B1 (en) 1995-12-07 2002-04-30 Agrolinz Melanin Gmbh Process for the preparation of pure melamine
AU2003304057B2 (en) * 2003-04-24 2009-07-16 Egi Contracting Engineering Co. Ltd Combined air cooled condenser

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