CN1659201A - Process for the production of melamine from urea, and particularly to obtain melamine-free off-gas in the first separation step - Google Patents
Process for the production of melamine from urea, and particularly to obtain melamine-free off-gas in the first separation step Download PDFInfo
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- CN1659201A CN1659201A CN03813289.3A CN03813289A CN1659201A CN 1659201 A CN1659201 A CN 1659201A CN 03813289 A CN03813289 A CN 03813289A CN 1659201 A CN1659201 A CN 1659201A
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- 229920000877 Melamine resin Polymers 0.000 title claims abstract description 70
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 title claims abstract description 70
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 title claims abstract description 31
- 239000004202 carbamide Substances 0.000 title claims abstract description 31
- 238000000034 method Methods 0.000 title claims description 28
- 238000000926 separation method Methods 0.000 title claims description 22
- 238000004519 manufacturing process Methods 0.000 title claims description 7
- 238000006243 chemical reaction Methods 0.000 claims abstract description 31
- 238000000197 pyrolysis Methods 0.000 claims abstract description 21
- 238000011282 treatment Methods 0.000 claims abstract description 15
- 239000007791 liquid phase Substances 0.000 claims abstract description 11
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 16
- 229910001868 water Inorganic materials 0.000 claims description 15
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 14
- 229910021529 ammonia Inorganic materials 0.000 claims description 11
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 10
- 239000007788 liquid Substances 0.000 claims description 9
- 239000001569 carbon dioxide Substances 0.000 claims description 4
- 230000001172 regenerating effect Effects 0.000 claims description 2
- 238000005406 washing Methods 0.000 abstract description 9
- 238000000859 sublimation Methods 0.000 abstract description 2
- 239000000110 cooling liquid Substances 0.000 abstract 1
- 239000008246 gaseous mixture Substances 0.000 abstract 1
- 239000007789 gas Substances 0.000 description 42
- 239000012071 phase Substances 0.000 description 14
- 239000000243 solution Substances 0.000 description 13
- 238000010791 quenching Methods 0.000 description 10
- 239000007792 gaseous phase Substances 0.000 description 8
- 239000000203 mixture Substances 0.000 description 7
- 239000000047 product Substances 0.000 description 7
- 238000000746 purification Methods 0.000 description 6
- 230000000171 quenching effect Effects 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 5
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 5
- 238000011084 recovery Methods 0.000 description 5
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 4
- 235000011114 ammonium hydroxide Nutrition 0.000 description 4
- 238000010521 absorption reaction Methods 0.000 description 3
- 239000007795 chemical reaction product Substances 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000000725 suspension Substances 0.000 description 3
- 238000003786 synthesis reaction Methods 0.000 description 3
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 2
- BVCZEBOGSOYJJT-UHFFFAOYSA-N ammonium carbamate Chemical compound [NH4+].NC([O-])=O BVCZEBOGSOYJJT-UHFFFAOYSA-N 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- KXDHJXZQYSOELW-UHFFFAOYSA-N carbonic acid monoamide Natural products NC(O)=O KXDHJXZQYSOELW-UHFFFAOYSA-N 0.000 description 2
- 239000003054 catalyst Substances 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- PAWQVTBBRAZDMG-UHFFFAOYSA-N 2-(3-bromo-2-fluorophenyl)acetic acid Chemical compound OC(=O)CC1=CC=CC(Br)=C1F PAWQVTBBRAZDMG-UHFFFAOYSA-N 0.000 description 1
- YZEZMSPGIPTEBA-UHFFFAOYSA-N 2-n-(4,6-diamino-1,3,5-triazin-2-yl)-1,3,5-triazine-2,4,6-triamine Chemical compound NC1=NC(N)=NC(NC=2N=C(N)N=C(N)N=2)=N1 YZEZMSPGIPTEBA-UHFFFAOYSA-N 0.000 description 1
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 239000001099 ammonium carbonate Substances 0.000 description 1
- 235000012501 ammonium carbonate Nutrition 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- OHJMTUPIZMNBFR-UHFFFAOYSA-N biuret Chemical compound NC(=O)NC(N)=O OHJMTUPIZMNBFR-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000007233 catalytic pyrolysis Methods 0.000 description 1
- 239000013626 chemical specie Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000003337 fertilizer Substances 0.000 description 1
- 229910000856 hastalloy Inorganic materials 0.000 description 1
- 239000002638 heterogeneous catalyst Substances 0.000 description 1
- 229910001026 inconel Inorganic materials 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- ZFSLODLOARCGLH-UHFFFAOYSA-N isocyanuric acid Chemical compound OC1=NC(O)=NC(O)=N1 ZFSLODLOARCGLH-UHFFFAOYSA-N 0.000 description 1
- 230000007257 malfunction Effects 0.000 description 1
- YSRVJVDFHZYRPA-UHFFFAOYSA-N melem Chemical compound NC1=NC(N23)=NC(N)=NC2=NC(N)=NC3=N1 YSRVJVDFHZYRPA-UHFFFAOYSA-N 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 239000003973 paint Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000003449 preventive effect Effects 0.000 description 1
- 239000012495 reaction gas Substances 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 238000005201 scrubbing Methods 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 230000008022 sublimation Effects 0.000 description 1
- 238000005092 sublimation method Methods 0.000 description 1
- WNVQBUHCOYRLPA-UHFFFAOYSA-N triuret Chemical compound NC(=O)NC(=O)NC(N)=O WNVQBUHCOYRLPA-UHFFFAOYSA-N 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/002—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by condensation
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G12/00—Condensation polymers of aldehydes or ketones with only compounds containing hydrogen attached to nitrogen
- C08G12/02—Condensation polymers of aldehydes or ketones with only compounds containing hydrogen attached to nitrogen of aldehydes
- C08G12/26—Condensation polymers of aldehydes or ketones with only compounds containing hydrogen attached to nitrogen of aldehydes with heterocyclic compounds
- C08G12/30—Condensation polymers of aldehydes or ketones with only compounds containing hydrogen attached to nitrogen of aldehydes with heterocyclic compounds with substituted triazines
- C08G12/32—Melamines
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Health & Medical Sciences (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Treating Waste Gases (AREA)
Abstract
Treatment of off-gas deriving from the pyrolysis reaction of urea to produce melamine, carried out in liquid phase at a high pressure, wherein the melamine content present in the off-gas is separated by washing the off-gas with a cooling liquid stream which rapidly brings the gaseous mixture to de-sublimation temperatures of the gaseous melamine which separates in solution in said stream, thus obtaining melamine-free off-gas on the one hand, and a fraction of high purity de-sublimated melamine in solution, on the other.
Description
The present invention relates to a process for the production of melamine, in particular to the separation stage and treatment of the reaction products.
In the latest industrial practice, melamine is generally obtained by pyrolysis of urea according to the following overall reaction:
the carbon dioxide and ammonia produced from the pyrolysis reaction are commonly referred to as tail gas. The entire pyrolysis reaction requires a supply of heat and, according to the available techniques, they can be carried out both in liquid phase, at high pressure, without catalyst, and in gas phase, at low pressure and with heterogeneous catalysts.
In these techniques, the reaction can be specifically shifted towards the consumption of the urea feedstock by appropriate selection of the operating parameters. 234kg of off-gas, a product of CO, are formed for every 126kg of melamine produced in the reaction, based on the molecular weight of the chemical species concerned2And NH3Composition with a weight ratio off-gas/melamine equal to 1.85. The technical problem posed is therefore the separation of melamine within the technical standards and the recovery and reuse of considerable quantities of off-gas generated from the main reaction. The efficiency and the economics of the separation and treatment of the effluent of this reaction step are crucial for the commercial success of the process for the preparation of melamine. Also in these separation and recovery steps, there is a significant distinction between the various competing processes. In the industrial practice generally adopted at present, the plants for the production of melamine from urea are coupled, or even integrated, with urea plants, so that the off-gases can be reused throughout the cycle.
In the present description, reference is made to the high-pressure pyrolysis technique, which operates in the liquid phase by feeding molten urea into a heated reactor in the presence of an excess of ammonia and without the use of a catalyst. The pyrolysis reactor for the conversion of urea to melamine is generally operated at a temperature of 380-450 ℃ and a pressure of 80-150 bar.
Several methods have been proposed in the known art for the treatment of off-gas after separation and recovery of the melamine still present in the gaseous phase. For example, the off-gas may be absorbed in water to form ammonium carbamate or ammonium carbonate, which may be condensed and fractionated to separate the carbon dioxide from the ammonia, or they may be used to produce ammonium nitrate or ammonium sulfate which may be used as a fertilizer. These processes in general have considerable disadvantages due to high investment and high energy costs.
A more recent system for treating off-gas, which involves the synthesis of melamine in liquid phase at high pressure, seeks to wash the gas phase separated from the reaction effluent with molten urea in order to separate off the melamine present in the off-gas. The content is not negligible, since it can reach 10-20% of the total amount of melamine produced, depending on the operating conditions. The above process allows this part of the melamine to be recovered and the off-gas in anhydrous state to be recycled to the urea plant section, which has a pressure matching the pressure of the off-gas thus obtained. The molten urea containing the recovered melamine is then sent to the same melamine synthesis reactor.
These recovery systems using molten urea are described, for example, in US3,700,672 and US4,565,867. This washing processwith molten urea operates on the gaseous phase separated from the reaction effluent, under the same synthesis pressure and temperature conditions, generally around 180 ℃. The choice of the washing temperature reflects a compromise between preventing ammonium carbamate condensation and limiting the conversion of urea degradation into undesired products such as biuret, 1, 3-di-carbamylurea or cyanuric acid which cause great disadvantages in the operating unit. Under the operating conditions described with molten urea absorption, a considerable amount of the substances in the off-gas separated from the liquid phase, mainly melamine, are condensed and solidified, but are still dispersed in the molten urea which is then fed to the reaction. However, under these conditions, there is also a parallel apparent dissolution of the above off-gases in the molten urea. For example, the data available in the prior art show that the molten urea originating from the melamine separation plant contains about 5% by weight of dispersed melamine and that about 20% by weight of off-gas is in solution, causing an undesirable recycling of off-gas which should be separated and sent to subsequent treatment.
The recovery treatment of melamine from off-gas with molten urea, making the anhydrous off-gas obtained reusable, seems to be of relative interest, but it is complex and inconvenient. The washing section of the molten urea system requires machines and equipment operating at almost the same pressure conditions as the pyrolysis reactor for the conversion of urea into melamine and employs substances that cause significant corrosion phenomena, even for stainless steel materials; it is therefore sought to use expensive materials such as alloys known as INCONEL and HASTELLOY and extremely expensive devices.
The efficiency of such a pyrolysis unit itself is significantly reduced by recycling the recovered melamine (which itself is recycled byabout 15-20% under dynamic conditions) and the off-gas (which recycle represents about 40-50% of the off-gas produced by the "useful" pyrolysis reaction). Such circulation not only requires an increase in the reaction volume but also disturbs the circulation inside the reactor and reduces the heat exchange efficiency due to an unfavorable change in the gas/liquid ratio inside the reactor. A significant increase of the heat exchange surface is therefore required for the same net production of melamine.
There are also considerable disadvantages with regard to the reduced reliability of the overall system, in which the pyrolysis zone is integrated with the washing zone of the molten urea (which constitutes the pyrolysis feedstock). A malfunction in the washing zone, which operates under very precise conditions, usually causes an immediate stop of the main pyrolysis zone and a subsequent interruption of production. Also the stoppage of the pyrolysis main zone, whether programmed or accidental, involves complex procedures, such as emptying the reactor, usually by sublimating the melamine by injecting ammonia at high temperature. When the washing device with molten urea is integrated with the reaction step, this emptying by sublimation method is no longer applicable, since the molten urea used for washing cannot be treated by feeding it into the reactor which is not in operation: it is therefore necessary to install an additional specific area which is receptive to the sublimation products and which can only be activated in the event of such an accident.
The prior art also proposes a system for separating off-gases from the crude effluent of the pyrolysis reaction, by separation with water or cold aqueous ammonia or ammonia solution, in a rapid cooling tower, commonly known as a quench tower, in which melamine and off-gases are still present in the gaseous phase. Such a separation system is depicted in the scheme of fig. 1.
The reaction is carried out in reactor a, which is fed with molten urea via line 1 and with more ammonia via line 2. The crude reaction effluent produced in step A is discharged overhead via line 3 and is rapidly cooled in the quenching tower B to a temperature at which the melamine, which enters solution or suspension in the aqueous separation stream, can be completely recovered. Column B feeds the aqueous stream at the bottom of column C, while the gas produced in stripper D is separated in column C. Condensed melamine is obtained in the aqueous liquid phase stream leaving column B, together with ammonia and saturated carbon dioxide. The remaining off-gas rises up the column and is released overhead together with a certain amount of water vapour, but the stream is substantially free of melamine. Column B can be operated over an extremely wide range of pressures, from reaction pressures up to that required by the subsequent system receiving the tail gas1-2 bar. The operating temperature, in turn, corresponds to the pressure and composition of the gas phase. The quench operation is generally carried out at 20-30bar (about 2-3X 10)6Pa) and 165 ℃. But this system also has its drawbacks. Which results in the formation of a melamine aqueous solution containing unacceptable levels of CO in downstream steps2Amount of the compound (A). As described in WO 01/36397A1, which has to be removed before the purification step to obtain a product with a low content of polycondensates, of which melam, melem and melom are the main ones, CO is removed in a stripper D2. In which the melamine solution/suspension is stripped and NH-containing is produced3And CO2Is fed to the absorption column C via line 7 and is separated with recycled water from line 8. The product at the bottom of column C contains stripped CO2And recycled to the quenching tower B through a line 5. The bottom product of column D contains melamine and is then sent to a purification step, indicated by E in simplified form. It can be seen that CO2Need for removal ofAdditional stripping and separation steps, thereby increasing capital costs and energy consumption. The steam consumption in the stripper D alone was 1kg NH/stripping3And CO2About 1kg of steam.
It is an object of the present invention to provide a process for treating off-gas which overcomes the disadvantages of the prior art processes in a simple and economical way. The process according to the invention aims at recovering the melamine still in the gaseous phase from the off-gas after said off-gas has been separated directly in the upper part of the same reactor or in a downstream separator immediately following it.
This object is achieved with the method of the invention, which is defined in claim 1 of the present invention in its most general sense; preferred embodiments or possible variations thereof are defined in the dependent claims.
The characteristics and advantages of the process according to the invention for treating off-gas in order to recover the melamine contained therein and send it to the subsequent sections of the plant will be apparent from the following description, given by way of illustration and not of limitation, with reference to the scheme of the attached drawings.
Figure 1 shows a prior art method according to the above. Fig. 2 depicts an embodiment of the present invention, while fig. 3, 4 and 5 show possible variations thereof.
The pyrolysis reaction takes place in a reactor a, which consists of a vertical vessel to which molten urea is fed from its bottom through line 1, while anhydrous ammonia, preferably in the gaseous phase, is fed together through line 2. The pyrolysis reaction for the formation of melamine from urea takes place in reactor a at an operating temperature of 380-450 c and an operating pressure of 80-150bar, and the necessary heat is supplied to maintain the pyrolysis reaction.
In the pyrolysis reactor a mixed phase is formed, which mainly consists of the liquid melamine formed, the off-gas produced in the reaction and the excess ammonia injected from the bottom through line 2. This mixed phase remains constantly circulating due to the hydraulic pressure of the gases formed and the specific internal structure of the pyrolysis reactor.
The reaction gas containing melamine in the gaseous phase in a ratio of 6-8% by weight is separated as in the upper part of reactor a as shown in the scheme of figure 2 or by means of an immediately downstream gas/liquid separator a' as shown in the scheme of figure 3 and is then sent to gas scrubbing unit B via line 3. The crude melamine in the melt, containing a small portion of dissolved gases containing NH in a ratio of 2-3% by weight with respect to the total, is sent through line 4 to decomposition and quenching unit C3And CO2. This strand of molten raw melamine can be subjected to an intensive purification treatment before being fed to the dissolution and quenching apparatus C, as described in US 6,252,074 and italian patent application MI 01a001216 by the same applicant. As shown in the schemes of figures 2, 3, 4 and 5, an aqueous ammonia stream is fed from the bottom to unit C via line 6.
As shown in fig. 2-5, the present invention is characterized by the following fact with respect to the prior art flow shown in fig. 1: the quenching tower C operates in liquid phase and is obtained by means of CO in the mixture of crude melamine fed through line 42Has very low solubility, so CO2The concentration is very low. Under these conditions, the treatments comprising ammonia injection through line 6, operating as described in patent application WO 001/36397A1, are effective in removing the polycondensates and thus do not require the preventive stripping of CO as in the scheme of FIG. 12。
A purified melamine stream is withdrawn from the upper part of the plant C and is sent to the crystallizer through line 7 together with the melamine separated in the plant B and discharged through line 9.
The total separation of melamine takes place in the plant B, which is fed from the top by means of the line 8 with a suitable quantity of regenerating water, commonly called make-up water, and by means of the line 9' with a recycle stream of aqueous melamine solution taken from the stream of aqueous melamine solution discharged by means of the line 9 and separated in the column B. The regeneration or make-up stream may consist of deionized water which may be supplied to the apparatus from an external source or may be taken from an appropriate stream within the apparatus as long as it has a composition suitable for use in column B.
According to a preferred embodiment of the invention, stream 9' is cooled by heat exchanger F before being recycled to the upper part of column B, which makes it possible to limit the make-up at the same separation efficiency. In typical applications, the heat exchanger F provides mainly the cooling required in column B for separating the condensed components from the gaseous reaction effluent, and said condensed components are discharged through line 9. The quantity of make-up water required is generally extremely reduced, with a weight ratio to the off-gas treated in column B of between 0.2 and 1.5, preferably between 0.3 and 0.5, and a weight ratio of the melamine solution recycled via line 9' to the off-gas treated of between 4 and 40,preferably between 10 and 15. The separation of melamine in column B is generally carried out at a temperature in the range from 120 ℃ to 180 ℃, preferably in the range from 155 ℃ to 165 ℃ and at a pressure in the range from 2 to 30bar, preferably at about 25 bar.
The melamine recovered in the gaseous phase in the stream of line 9 has a very high purity, which contains neither the oxyaminotriazine, commonly known as OAT, nor the polycondensate. Which consists of a suspension/solution, can be fed directly to the crystallization zone.
In the embodiments shown in fig. 4 and 5, the portion of the stream of line 9 that is not recycled to the separation zone of column B with line 9' is fed to the bottom of purification column C together with the ammonia solution fed through line 6. This alternative embodiment of the invention provides a significant improvement in both the stability and the uniformity of the quality of the melamine produced. Since there is no longer a large amount of CO in the solution2The apparatus C can be used as an efficient purifier for separating the polycondensate from the product.
Examples
With reference to the scheme of figure 2, melamine is produced by non-catalytic pyrolysis of molten urea in a reactor with internal circulation, at 390 ℃ and 80bar (about 8 x 10)6Pascal) (gauge pressure). The reaction product consists of a liquid phase (a) and a gas phase (b), andthe paint comprises the following components in parts by weight:
phase (a) phase (b)
Melamine 92.5% 6.9%
NH31.5％ 44.5％
CO21.0％ 48.6％
5.0% of urea-
The gas phase (b) is cooled and washed with water, which may be recycled water, in order to desublimate and dissolve the melamine contained therein.
The two streams then leave a cooling and washing unit of phase (b) operating at 25bar (gauge) and 160 ℃: a liquid phase (c) and a gaseous phase (d) having the following composition by weight:
photo (c) photo (d)
Melamine 20.0% - -
NH315.0％ 36.3％
CO24.0％ 43.5％
H2O 61.0％ 20.2％
The solution of phase (c) contains pure desublimated melamine and is sent directly to the crystallization step.
Phase (a) contains mainly liquid melamine, which is sent to a quenching step where it is cooled with water and dissolved. Since there is no significant carbon dioxide in the quench apparatus, the apparatus is fed with an amount of ammonia such that there is at least 13 wt% NH in phase (e) in solution3Content, and has the following composition:
photo (e)
10.10 percent of melamine
0.55 percent of urea
NH313.10％
CO20.11％
H2O 76.14％
The operating conditions were 25bar and 172 ℃ and corresponded to the conditions necessary for the purification given in WO 01/36397A 1.
By way of comparison, if the same reaction product is fed directly to the quench apparatus B as a liquid/gas phase mixture according to the scheme shown in FIG. 1, while the other conditions remain unchanged, the resulting liquid phase contains 3.8 wt.% CO2Thus, it is necessary to carry out a stripping in column D in order to remove this portion of CO before sending it with ammonia to the subsequent purification step2。
Comparing the scheme of figure 1, which describes the prior art, and figure 2, which describes an embodiment of the present invention, the results show that: the solution according to the invention requires lower investments, since it requires a smaller amount of equipment to operate at high pressure and thus a smaller amount of expensive materials; since the solution of the invention does not require stripping of CO in the stripper D as shown in the solution of FIG. 12And NH3Thus avoiding the consumption of cooling water for absorption and steam for stripping in the column C shown in the scheme of figure 1, so that the energy consumption and the corresponding cost are also greatly reduced.
Claims (8)
1. Process for treating off-gas from a pyrolysis reaction for the production of melamine from urea, said off-gas containing carbon dioxide and ammonia from the reaction, said reaction being carried out in the liquid phase at a temperature of 380-450 ℃ and a pressure of 80 to 150bar, said process comprising an initial separation step in which a liquid reaction effluent containing crude melamine is separated from a gaseous effluent of the reaction, said gaseous effluent consisting essentially of the off-gas resulting from the pyrolysis, said process being characterized in that: the off-gas separated from the reactor effluent is treated in a melamine separation column (B) with a stream of regenerating water fed from above through line (8), while utilizing a recycle stream of melamine solution fed through line (9')taken from the stream of melamine solution discharged through line (9) separated in column B.
2. The process for the treatment of off-gas according to claim 1, characterized in that the initial separation step of the liquid effluent from the gaseous effluent is carried out in the upper part of the reactor (A).
3. The process for the treatment of off-gas according to claim 1, characterized in that the initial separation step of the liquid effluent from the gaseous effluent is carried out in a gas/liquid separator (A') immediately downstream of the reactor (A).
4. Process for the treatment of off-gas according to claim 1, characterized in that the ratio by weight of the quantity of make-up water fed by line (8) to the quantity of off-gas treated in column (B) is comprised between 0.2 and 1.5, while the ratio by weight of the quantity of melamine solution recycled through line (9') to the quantity of off-gas treated is comprised between 4 and 40.
5. Process for the treatment of off-gas according to claim 4, characterized in that the ratio by weight of the quantity of make-up water fed by line (8) to the quantity of off-gas treated in column (B) is comprised between 0.3 and 0.5, while the ratio by weight of the quantity of melamine solution recycled through line (9') to the quantity of off-gas treated is comprised between 10 and 15.
6. Process for the treatment of off-gas according to claim 1, characterized in that the recycle stream of melamine solution fed through line (9') is cooled by means of a heat exchanger (F) before being recycled to the upper part of column (B).
7. Process for the treatment of off-gas according to claim 1, characterized in that the separation of melamine in column (B) is carried out at a temperature of 120 ℃ and 180 ℃ and a pressure of 2 to 30 bar.
8. Process for the treatment of off-gas according to claim 7, characterized in that the separation of melamine in column (B) is carried out at a temperature of 155 and 165 ℃ and a pressure of about 25 bar.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT2002MI001026A ITMI20021026A1 (en) | 2002-05-14 | 2002-05-14 | MELAMINE PRODUCTION PROCESS FROM UREA AND PARTICULARLY TO OBTAIN MELAMINE-FREE OFF-GAS IN THE FIRST SEPARATION STAGE |
| ITMI2002A001026 | 2002-05-14 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1659201A true CN1659201A (en) | 2005-08-24 |
| CN1300122C CN1300122C (en) | 2007-02-14 |
Family
ID=11449893
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNB038132893A Expired - Lifetime CN1300122C (en) | 2002-05-14 | 2003-04-29 | Process for the production of melamine from urea, and particularly to obtain melamine-free off-gas in the first separation step |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP1504045A1 (en) |
| CN (1) | CN1300122C (en) |
| AU (1) | AU2003232234A1 (en) |
| IT (1) | ITMI20021026A1 (en) |
| WO (1) | WO2003095516A1 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102285929A (en) * | 2010-05-06 | 2011-12-21 | 欧洲技术设于伊特根的三聚氰氨-卢森堡-分支机构 | Low-energy-consumption process for the production of high-purity melamine, through the pyrolysis of urea, and relative equipment |
| CN102946990A (en) * | 2010-06-24 | 2013-02-27 | 博里利斯阿格罗林茨三聚氰胺有限公司 | Horizontal high-pressure melamine reactor |
| CN108602784A (en) * | 2016-02-19 | 2018-09-28 | 卡萨勒有限公司 | The method that high-pressure melamine equipment is transformed |
| CN109761922A (en) * | 2017-11-09 | 2019-05-17 | 欧洲技术设于伊特根的三聚氰氨，卢森堡，分支机构 | Pass through the improved method and relevant apparatus of the pyrolysis production high-purity melamine of urea |
| CN110613952A (en) * | 2019-11-06 | 2019-12-27 | 河南省中原大化集团有限责任公司 | Novel crystallizer ammonia preparation device and ammonia preparation method |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1902163B (en) | 2004-02-20 | 2010-05-26 | 乌里阿·卡萨勒有限公司 | Integrated process for urea and melamine production |
| ITMI20082294A1 (en) * | 2008-12-22 | 2010-06-23 | Eurotecnica Melamine Luxemburg Zwe Igniederlassun | IMPROVED PROCEDURE FOR THE PRODUCTION OF HIGH PURITY MELAMINE BY UREA PYROLYSIS |
| US9869403B2 (en) | 2011-05-09 | 2018-01-16 | Hamilton Sundstrand Corporation | Valve having pressure-relieving vent passage |
| HUE053647T2 (en) | 2015-04-23 | 2021-07-28 | Stamicarbon | Method and system for the integrated production of urea and melamine |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3315442A (en) * | 1964-10-05 | 1967-04-25 | American Cyanamid Co | Quenching of crude melamine gases |
| NL161750C (en) * | 1968-11-16 | 1980-03-17 | Stamicarbon | Process for separating melamine from a gaseous reaction mixture of melamine, ammonia and carbon dioxide. |
| NL8201479A (en) * | 1982-04-07 | 1983-11-01 | Stamicarbon | METHOD FOR PREPARING MELAMINE. |
| AT397214B (en) * | 1992-03-30 | 1994-02-25 | Chemie Linz Gmbh | DEVICE FOR DEPOSITING MELAMINE |
| US5384404A (en) * | 1993-11-05 | 1995-01-24 | Lee; Jing M. | Process for manufacturing melamine from urea |
| NL1003328C2 (en) * | 1996-06-13 | 1997-12-17 | Dsm Nv | Process for preparing melamine. |
| EA003233B1 (en) * | 1998-11-13 | 2003-02-27 | Агролинц Меламин Гмбх | Method for producing pure melamine |
-
2002
- 2002-05-14 IT IT2002MI001026A patent/ITMI20021026A1/en unknown
-
2003
- 2003-04-29 WO PCT/EP2003/004556 patent/WO2003095516A1/en not_active Application Discontinuation
- 2003-04-29 CN CNB038132893A patent/CN1300122C/en not_active Expired - Lifetime
- 2003-04-29 EP EP03749861A patent/EP1504045A1/en not_active Withdrawn
- 2003-04-29 AU AU2003232234A patent/AU2003232234A1/en not_active Abandoned
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102285929A (en) * | 2010-05-06 | 2011-12-21 | 欧洲技术设于伊特根的三聚氰氨-卢森堡-分支机构 | Low-energy-consumption process for the production of high-purity melamine, through the pyrolysis of urea, and relative equipment |
| CN102285929B (en) * | 2010-05-06 | 2014-11-05 | 欧洲技术设于伊特根的三聚氰氨-卢森堡-分支机构 | Low-energy-consumption process for the production of high-purity melamine, through the pyrolysis of urea, and relative equipment |
| CN102946990A (en) * | 2010-06-24 | 2013-02-27 | 博里利斯阿格罗林茨三聚氰胺有限公司 | Horizontal high-pressure melamine reactor |
| CN102946990B (en) * | 2010-06-24 | 2015-08-26 | 卡萨利股份公司 | Horizontal high-pressure melamine reactor |
| CN108602784A (en) * | 2016-02-19 | 2018-09-28 | 卡萨勒有限公司 | The method that high-pressure melamine equipment is transformed |
| CN108602784B (en) * | 2016-02-19 | 2022-03-25 | 卡萨勒有限公司 | Method for revamping a high-pressure melamine plant |
| CN109761922A (en) * | 2017-11-09 | 2019-05-17 | 欧洲技术设于伊特根的三聚氰氨，卢森堡，分支机构 | Pass through the improved method and relevant apparatus of the pyrolysis production high-purity melamine of urea |
| CN109761922B (en) * | 2017-11-09 | 2023-11-21 | 欧技三聚氰胺有限公司 | Improved process for the production of melamine in high purity by pyrolysis of urea and related plant |
| CN110613952A (en) * | 2019-11-06 | 2019-12-27 | 河南省中原大化集团有限责任公司 | Novel crystallizer ammonia preparation device and ammonia preparation method |
Also Published As
| Publication number | Publication date |
|---|---|
| ITMI20021026A1 (en) | 2003-11-14 |
| ITMI20021026A0 (en) | 2002-05-14 |
| WO2003095516A1 (en) | 2003-11-20 |
| AU2003232234A1 (en) | 2003-11-11 |
| EP1504045A1 (en) | 2005-02-09 |
| CN1300122C (en) | 2007-02-14 |
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| Date | Code | Title | Description |
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| C06 | Publication | ||
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| SE01 | Entry into force of request for substantive examination | ||
| ASS | Succession or assignment of patent right |
Owner name: MELAMINE - LUXEMBOURG - BRANCH LOCATED IN ITGEN B Free format text: FORMER OWNER: EUROTECNICA GROUP S. A. Effective date: 20060609 |
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| C41 | Transfer of patent application or patent right or utility model | ||
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Effective date of registration: 20210422 Address after: Swiss Wollerau Patentee after: Ouji melamine Co.,Ltd. Address before: Itgen, Switzerland Patentee before: EUROTECNICA MELAMINE |
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Granted publication date: 20070214 |