CN1158268C - Process for the preparation of melamine from urea - Google Patents
Process for the preparation of melamine from urea Download PDFInfo
- Publication number
- CN1158268C CN1158268C CNB018023940A CN01802394A CN1158268C CN 1158268 C CN1158268 C CN 1158268C CN B018023940 A CNB018023940 A CN B018023940A CN 01802394 A CN01802394 A CN 01802394A CN 1158268 C CN1158268 C CN 1158268C
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- CN
- China
- Prior art keywords
- trimeric cyanamide
- urea
- cooled region
- ton
- region
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D251/00—Heterocyclic compounds containing 1,3,5-triazine rings
- C07D251/02—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings
- C07D251/12—Heterocyclic 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
- C07D251/26—Heterocyclic 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
- C07D251/40—Nitrogen atoms
- C07D251/54—Three nitrogen atoms
- C07D251/56—Preparation of melamine
- C07D251/60—Preparation of melamine from urea or from carbon dioxide and ammonia
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
Process for the preparation of melamine from urea by reacting urea or thermal decomposition products thereof at elevated temperature in the presence of a catalyst, with process condensate being discharged from the process and characterized in that a proportion of the concentrated aqueous carbamate solution from the absorption zone is returned to the cooling zone or in that the temperature in the cooling zone is lowered to 100-150 DEG C.
Description
The present invention relates to be prepared by urea the method for trimeric cyanamide, this method is to be undertaken by urea is reacted.
Urea can be represented by following reaction equation to the conversion of trimeric cyanamide:
The currently known methods for preparing trimeric cyanamide by urea in the presence of catalyzer is the gaseous melamine method.At this, with the liquid urea in the table metering melamine reactor.The fluidized-bed of granules of catalyst is present in this melamine reactor, makes this maintenance fluidization by adding gaseous ammonia.
In melamine reactor, the temperature that is formed trimeric cyanamide by urea is usually above 325 ℃.Generally speaking, this temperature is not higher than 500 ℃, and more particularly preferred this temperature is 370-450 ℃.In the building-up process in the presence of catalyzer, the pressure that puts on melamine reactor is generally 0.5-3MPa.
Vapor phase process has been documented among the NL-A-6816385 by the implementation method that urea prepares trimeric cyanamide, and the gaseous mixture that wherein contains trimeric cyanamide, ammonia and carbonic acid gas passes melamine reactor and arrives the trimeric cyanamide cooled region.Cool off the gaseous mixture of autoreactor in this cooled region with a kind of aqueous solution, the described aqueous solution is to form in the recovery part of melamine plant.In cooled region, obtained trimeric cyanamide suspension and the air-flow of solid melamine in water-containing solvent according to the method for NL-A-6816385.
In the method for NL-A-6816385, mainly to form from the air-flow of cooled region by ammonia, carbonic acid gas and water vapour, this air-flow arrives absorption column through over-heat-exchanger, has obtained almost pure ammonia stream and ammonium carbamate solution in this absorption column.Melamine reactor is returned in described ammonia recirculation,, and ammonium carbamate solution is transferred to for example contiguous urea equipment here used as fluidized gas.
Ammonium carbamate solution from absorption column is enriched in the water, flows the 2-2.5 ton water of trimeric cyanamide generation per ton through this liquid and discharges from the operation according to NL-A-6816385.
Transferring in one or more hydrocyclones from the trimeric cyanamide suspension of cooled region, there this suspension is separated into suspension and the denseer feeding desorb post or the suspension of stripping columns of dilution, described dilute suspension still contains a spot of trimeric cyanamide, and the suspension that this is rare turns back to cooled region.According to other processing condition, this rare suspension can contain the trimeric cyanamide of the solubilized form of the melamine crystals of 4 weight % for example and 8 weight %.Under same processing condition, above-mentioned dense trimeric cyanamide suspension can contain the trimeric cyanamide of the solubilized form of the melamine crystals of 35 weight % and 5 weight %.
In NL-A-6816385, be collected in from the air-flow that contains trimeric cyanamide of melamine reactor and contain in the water coolant, and be converted into aforesaid suspension (suspension quenching).
Perhaps, be collected in from the air-flow of melamine reactor and contain in the water coolant, and be converted into melamine solution (solution quenching).This method for example is described among the WO96/20933.
In desorption or stripping columns, when heating, the part ammonia and the carbonic acid gas that are dissolved in solution or the suspension are desorbed.Injected steam hitherward provides heat in the post under externally well heater helps or by directly carrying to gas.The direct vapor injection of preferred use is easy to produce fault usually because the applicant has been found that external heater.Have been found that fault is to be accumulated on heating unit by trimeric cyanamide, reduced that hot transfer causes.If use direct vapor injection, as described in the NL-A-6816385, flow velocity is the 0.3-0.9 ton trimeric cyanamide that steam/ton produced, particularly the 0.4-0.8 ton trimeric cyanamide that steam/ton produced.In the embodiment of WO96/20933, the steam consumption in stripping tower is quite high, i.e. the 1.5-2.8 ton trimeric cyanamide that steam/ton produced, particularly the 1.6-1.8 ton trimeric cyanamide that steam/ton produced.
Melamine solution or trimeric cyanamide suspension arrive the purifying (back segment) of trimeric cyanamide through stripping columns.If use suspension is at first with the insoluble impurity of its dissolving filtering.If use solution can directly be removed insoluble impurity by filtering.
At back segment, subsequently solution is fed crystallizer in order, to separate out trimeric cyanamide.At pressure is that 0.02-0.1MPa and temperature are to carry out crystallization under 60-100 ℃.In crystallization, produce dense suspension and almost do not have the crystalline current.These current can loop back cooled region, stripping tower or back segment.
After crystallization, with melamine crystals centrifugation and dry.In centrifugal process, trimeric cyanamide per ton uses 0.3-1 ton, the particularly wash-down water of 0.4-0.8 ton, and it is incorporated in the technology by the trimeric cyanamide recovery part.In this trimeric cyanamide recovery part, form the aqueous solution that turns back to back segment or cooled region.
In this crystallization, also form the vapor phase stream of mainly forming by water vapour.After condensation, this water vapour turns back to operation as the technological process condensation product that does not almost have trimeric cyanamide, makes an appointment with half to get back to back segment, and second half gets back to condenser zone.The technological process condensation product amount of Xing Chenging is the 0.2-4 ton trimeric cyanamide that condensation product/ton produced herein, and it depends on other situation under other processing condition.
The water that in melamine plant, uses, for example as a component of refrigerant, it mainly is incorporated in this operation by centrifugation step, washing water as instrument and pump, if at the direct vapor injection of this use described in NL-A-6816385, it is by introducing in the operation to the direct vapor injection of stripping columns.Final this water is included in the carbamate solution from the absorption region, and described solution for example is transferred to urea equipment.
With regard to the moisture carbaminate circulation that will about 45-50 weight % forms in the absorption region moves on to urea equipment, its economically attractive spot be and can further anhydrate to concentrate this carbamate solution by from solution, removing.The shortcoming of this method is that it needs extra investment, and makes this method costliness more owing to increased the use of air-flow, condensation power and water.
Have been found that this shortcoming can eliminate by the combination measure.
In first embodiment, purpose of the present invention reaches by the following method: eject the technological process condensation product from described operation, the dense moisture carbamate solution in the zone of self-absorption in the future partly turns back to condenser zone.Preferably, in described first embodiment, provide heat to stripping tower by direct vapor injection.The gas that 20-40 weight % offers the absorption region turns back to condenser zone with condensate.
In second embodiment of the present invention, have been found that in the carbamate stream of absorption region, the minimizing of the water yield can also be finished by the following method: eject the technological process condensation product from described operation, the temperature of condenser zone is reduced to 100-150 ℃, preferred 110-140 ℃.In particular, in described second embodiment, provide heat to stripping tower by direct vapor injection.Make the temperature of condenser zone reduce and can carry out by the following method: condenser zone install external condensation device and cooling wherein refrigerant and/or by the refrigerant of cooling before feeding condenser zone at refrigerant from back segment.
The amount of the technological process condensation product of discharging depends on many factors.For example directly under the situation of stripping columns injected steam, the amount of the condensation product of discharge is than by using indirect heating equipment a lot of to the condensation object height that stripping columns provides heat to discharge.
In addition, direct amount to the stripping columns injected steam depends on how to operate cooled region.If obtain suspended substance (suspended substance quenching) at cooled region, then the quantity of steam to the stripping columns injection is the 0.3-0.9 ton trimeric cyanamide that steam/ton produced, particularly 0.4-0.8 ton steam/ton trimeric cyanamide.If obtain solution (solution quenching) at cooled region, then steam consumption is the 1.5-4 ton trimeric cyanamide that steam/ton produced, particularly 1.7-3.5 ton steam/ton trimeric cyanamide.
After will the water vapor condensation from crystallizer, the output of the technological process condensation product that has formed equals the 0.2-10 ton trimeric cyanamide that condensation product/ton produced, particularly 0.5-8 ton condensation product/ton trimeric cyanamide.
If obtain suspended substance and use direct vapor injection to stripping columns at cooled region, then the technological process condensation product of Pai Chuing will be 1.4 tons of/ton trimeric cyanamides.Yet if obtain solution and use direct vapor injection to stripping columns at cooled region, the technological process condensation product of discharging will be about 3.4 tons of/ton trimeric cyanamides.The amount of the technological process condensation product of discharging can be chosen wantonly by the air-flow to crystallizer or feeding crystallizer provides heat to increase.
Described technological process condensation product almost is a pure water, has dissolved the ammonia that is lower than 2 weight % therein.Before discharging the technological process condensation product, can choose wantonly in desorption procedure and remove deammoniation.
In the method for the invention, have been found that the water content from the dense carbamate solution of absorption region finally equals about 20-35 weight %.This causes the described carbamate solution that turns back to urea equipment partly to be suitable for direct processing.This means enrichment step or can be remaining or can more simplify, and then make design more at a low price.
In addition, have been found that method of the present invention is particularly suitable for so-called gaseous melamine equipment, the working pressure of this equipment is 0.5-3MPa, and more specifically pressure is 0.7-2.5MPa.
Method of the present invention is particularly suitable for improveing existing trimeric cyanamide method as, the method for describing among NL-A-6816385 and the WO96/20933 for example.
Illustrate the present invention with reference to following embodiment.
Example I and II
At an inside diameter is that 1 meter and height are to prepare trimeric cyanamide in 15 meters the cylindrical fluidisation bed.Come fluidized catalyst by the ammonia that will provide through the gas distribution dish, and heat this catalyzer, and fused salt flows by the pipe of this reactor by the heat exchanger tube that is installed in the reactor.Under the help of two-phase atomizer,, use ammonia as atomizing gas with the liquid urea in the table metering reactor.This reactor is 390 ℃ of operations down, and stagnation pressure is 1.7MPa (example I) and 2.0MPa (example II).Measure urea with 1.4 tons/hour speed with table, and the speed of the ammonia of process two-phase atomizer is 0.7 ton/hour.Ammonia through the charging of fluidisation dish equals 0.7 ton/hour.With respect to described balance, anhydrous urea to the transformation efficiency of trimeric cyanamide greater than 98%.Come the air-flow of autoreactor to contain NH
3, CO
2, trimeric cyanamide steam and trace byproduct, with described air-flow in the cooling zone coolant cools.A part is turned back to cooled region from the dense moisture carbamate solution of absorption region.Remaining dense carbamate solution is fed contiguous urea equipment.
The returning part from the ammonium carbamate of absorption region, the water yield, the water-content of described air-flow and the condensation product of from this technology, exporting of discharging have been stipulated in the table 1 to other water (wash-down water and washing water) amount of the quantity of steam of stripping tower injection, introducing, from absorption portion.In example I, used solution quenching in the method for the present invention as describing among the WO96/20933.In example II, used suspension quenching in the method for the present invention as describing among the NL-A-6816385.
Comparative Example A An and B
Prepare trimeric cyanamide similar in appearance to example I and II, except the carbaminate that does not have the zone of self-absorption in the future returns cooled region and provides steam to stripping tower.Used solution quenching in the method that embodiment A is mentioned as describing among the WO96/20933.Used suspension quenching in the method that Embodiment B is mentioned as describing among the NL-A-6816385.In both cases, carbamate stream is too rare and can have under the situation of intermediate steps the urea of feeding equipment.Referring to table 1.
Table 1
| Embodiment | I | n/a | A | B |
| Pressure (MPa) | 1.7 | 2.0 | 1.7 | 2.0 |
| Turn back to the gas part (weight %) of cooled region from cooled region with condensate | 34 | 25 | 0 | 0 |
| Quantity of steam (kilogram/every kilogram of trimerization ammonia amine) to the stripping columns injection | 2.5 | 2.6 | 2.0 | 0.6 |
| Other water (wash-down water and washing water) amount (kilogram/every kilogram of trimeric cyanamide) of introducing | 1.5 | 1.5 | 1.5 | 1.6 |
| Absolute magnitude (kilogram/every kilogram of trimeric cyanamide) from the water of absorption region | 0.74 | 0.70 | 2.5 | 2.2 |
| Water-content (weight %) from the carbaminate of absorption region | 25 | 24 | 49 | 42 |
| The condensation product amount (kilogram/every kilogram of trimeric cyanamide) of output | 3.26 | 1.4 | 1.0 | 0 |
Claims (5)
1. the method that is prepared trimeric cyanamide by urea, this method are to be undertaken by urea is reacted, and it is characterized in that the technological process condensation product is discharged and the temperature of cooled region is reduced to 100-150 ℃ from described technology.
2. according to the method for claim 1, it is characterized in that making the temperature of cooled region reduce and can followingly carry out: cooled region install external condensation device and cooling wherein refrigerant or by the refrigerant of cooling before feeding cooled region at refrigerant from back segment.
3. according to the method for claim 1, it is characterized in that part is turned back to cooled region from the dense moisture carbamate solution of absorption region.
4. according to the method for claim 3, the 20-40 weight % that it is characterized in that feeding the gas of absorption region turns back to cooled region with condensate.
5. according to the method for claim 1 or 2, it is characterized in that providing heat to stripping columns by direct vapor injection.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL1015929 | 2000-08-14 | ||
| NL1015929A NL1015929C2 (en) | 2000-08-14 | 2000-08-14 | Process for the preparation of melamine from urea. |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1388803A CN1388803A (en) | 2003-01-01 |
| CN1158268C true CN1158268C (en) | 2004-07-21 |
Family
ID=19771888
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNB018023940A Expired - Fee Related CN1158268C (en) | 2000-08-14 | 2001-06-27 | Process for the preparation of melamine from urea |
Country Status (4)
| Country | Link |
|---|---|
| CN (1) | CN1158268C (en) |
| AU (1) | AU2001269613A1 (en) |
| NL (1) | NL1015929C2 (en) |
| WO (1) | WO2002014289A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL1019913C2 (en) * | 2002-02-07 | 2003-08-08 | Dsm Nv | Process for the preparation of melamine. |
| EP1688411A1 (en) * | 2005-02-04 | 2006-08-09 | DSM IP Assets B.V. | Process for the preparation of melamine |
| WO2009132750A1 (en) * | 2008-04-29 | 2009-11-05 | Dsm Ip Assets B.V. | Process for recovering solid melamine |
| EP3208264A1 (en) | 2016-02-19 | 2017-08-23 | Casale SA | Method for revamping a high pressure melamine plant |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL161750C (en) * | 1968-11-16 | 1980-03-17 | Stamicarbon | Process for separating melamine from a gaseous reaction mixture of melamine, ammonia and carbon dioxide. |
| US4138560A (en) * | 1975-06-10 | 1979-02-06 | Basf Aktiengesellschaft | Process for cooling melamine synthesis waste gases |
| NL8204979A (en) * | 1982-12-24 | 1984-07-16 | Unie Van Kunstmestfab Bv | METHOD FOR DETERMINING AND CONTROLLING THE COMPOSITION OF AQUEOUS SOLUTIONS OF NH3 AND CO2. |
| US5384404A (en) * | 1993-11-05 | 1995-01-24 | Lee; Jing M. | Process for manufacturing melamine from urea |
-
2000
- 2000-08-14 NL NL1015929A patent/NL1015929C2/en not_active IP Right Cessation
-
2001
- 2001-06-27 WO PCT/NL2001/000481 patent/WO2002014289A1/en active Application Filing
- 2001-06-27 AU AU2001269613A patent/AU2001269613A1/en not_active Abandoned
- 2001-06-27 CN CNB018023940A patent/CN1158268C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| AU2001269613A1 (en) | 2002-02-25 |
| CN1388803A (en) | 2003-01-01 |
| NL1015929C2 (en) | 2002-02-18 |
| WO2002014289A1 (en) | 2002-02-21 |
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