HRP950605A2

HRP950605A2 - Melamine purifying process

Info

Publication number: HRP950605A2
Application number: HRA2393/94A
Authority: HR
Inventors: Helmut Fingrhut; Martin Muellner; Lorenzo Canzi; Gerhard Coufal; Silvano Giacomuzzo
Original assignee: Agrolinz Melamin Gmbh
Priority date: 1994-12-23
Filing date: 1995-12-19
Publication date: 1997-10-31
Also published as: PL320790A1; AT402295B; WO1996020183A1; CN1068315C; IL116516A0; EP0799213A1; DE59504292D1; JPH10511369A; RO115521B1; DK0799213T3; ATA239394A; HRP950605B1; RU2161610C2; ATE173474T1; IL116516A; BR9510606A; ES2124034T3; TW299324B; KR100374731B1; EP0799213B1

Abstract

In a melamine purifying process, impure melamine is heated up to a temperature above 200 DEG C but below the ammonia pressure-dependent, momentary melting point of melamine, and is kept in a solid state in said temperature range under an ammonia pressure from 5 to 350 bars for a period from 1 minute to 20 hours. It is then expanded and cooled down to room temperature, in whatever order, to produce pure melamine in powder form.

Description

Iz literature je poznat velik broj postupaka za proizvodnju melamina. Preporučljiv polazni materijal je pri tome urea, koja se ili pri visokom tlaku i nekatalitički, ili pri niskom tlaku i uz upotrebu katalizatora, pretvara u melamin, amonijak i CO2. Također je poznato, da kod tih postupaka, osobito kod postupaka koji se vrše pod visokim pritiskom, nastaju različiti nuz-proizvodi odnosno nečistoće, kao što je npr. melem, melam, amelin, amelid ili ureidomelamin, koji loše djeluju na čistoću melamina. A large number of procedures for the production of melamine are known from the literature. The recommended starting material is urea, which either at high pressure and non-catalytically, or at low pressure and with the use of a catalyst, turns into melamine, ammonia and CO2. It is also known that during these procedures, especially during procedures performed under high pressure, various by-products or impurities are formed, such as, for example, salve, melam, amelin, amelide or ureidomelamine, which have a bad effect on the purity of melamine.

Do sada uobičajeni postupci čišćenja, kao što je prekristalizacija, povezani su sa nedostacima. Tako se naročito kod prekristalizacije pojavljuje taj nedostatak, da se nečistoće gomilaju u osnovnoj otopini i da se zbog toga znatan dio te otopine, koji sadrži i melamin, mora ukloniti ili naknadno obraditi. Nadalje je u CH 345.894 opisano da su nečistoće kao melem, melam ili ureidomelamin netopive ili teško topive u vodi i vodenim alkalil otopinama, tako da se ti spojevi putem prekristalizacije mogu teško i uz gubitke melamina ukloniti iz melamina koji treba čistiti. Until now, common cleaning procedures, such as recrystallization, are associated with disadvantages. Thus, especially during recrystallization, the disadvantage is that impurities accumulate in the basic solution and, as a result, a significant part of that solution, which also contains melamine, has to be removed or subsequently processed. Furthermore, in CH 345.894 it is described that impurities such as salve, melam or ureidomelamine are insoluble or difficult to dissolve in water and aqueous alkali solutions, so that these compounds can be difficult to remove from the melamine to be cleaned by means of recrystallization and with loss of melamine.

Zadatak ovog izuma je pronalaženje postupka pri kojem se nečistoće koje su netopive Ui teško topive u vodi ili vodenim alkalil otopinama, naročito melam i ureidomelamin, u melaminu koji treba čistiti, mogu znatno smanjiti bez većih gubitaka melamina. The task of this invention is to find a process in which impurities that are insoluble and difficult to dissolve in water or aqueous alkali solutions, especially melamine and ureidomelamine, in the melamine to be cleaned, can be significantly reduced without major losses of melamine.

Ovaj se zadatak može riješiti uz postupak, pri kojem se onečišćen kruti melamin određeno vrijeme u prisustvu amonijaka može držati na povišenoj temperaturi, koja se nalazi ispod točke taljenja melamina. This task can be solved with a procedure in which contaminated solid melamine can be kept for a certain time in the presence of ammonia at an elevated temperature, which is below the melting point of melamine.

Predmet ovog izuma je prema tome, postupak za čišćenje melamina, naznačen time, da se onečišćeni melamin drži na temperaturi, koja je iznad 200°C i ispod točke taljenja melamina koja ovisi o tlaku amonijaka, i da se kod tlaka amonijaka od 5 do 350 bar drži u trajanju od 1 minute do 20 sati u tom temperaturnom području, pri čemu se melamin pojavljuje kao kruta tvar, pri čemu se redoslijedom koji nije striktno određen širi i hladi na temperaturu okoline i dobiva čisti melamin u obliku praha. The subject of this invention is therefore a process for cleaning melamine, indicated by the fact that the contaminated melamine is kept at a temperature above 200°C and below the melting point of melamine, which depends on the ammonia pressure, and that at an ammonia pressure of 5 to 350 the bar is kept for 1 minute to 20 hours in that temperature range, whereby the melamine appears as a solid substance, whereby it expands and cools to ambient temperature in a sequence that is not strictly determined, and obtains pure melamine in the form of a powder.

Postupak prema ovom izumu je prikladan za čišćenje melamina, a dobiva se iz postupka poznatog iz tehnike, koji sadrži nečistoće kao melam i ureidomelamin. Pronađeno je, da se sadržaj melama i ureidomelamina može smanjiti na taj način, da se onečišćeni melamin, koji se pojavljuje u obliku kristala ili praha, zagrijava i u prisustvu amonijaka određeno vrijeme drži u temperaturnom području ispod točke taljenja melamina i ovisi o pritisku amonijaka (stvrdnjavanje). Međutim moguće je melamin, koji ima temperaturu koja je iznad tog područja, ohladiti na to temperaturno područje. Temperaturno područje u kojem se vrši stvrdnjavanje, nalazi se pri tome iznad 200°C, a ispod točke taljenja melamina. Preporuča se temperaturno područje između 240°C, a naročito se preporuča između 250°C i temperature ispod točke taljenja melamina. Melamin se pri tome dovodi na početnu temperaturu, koja je u tom području. Temperatura se za vrijeme stvrdnjavanja može držati konstantnom, ali se može mijenjati unutar gore definiranog temperaturnog područja. Tako primjerice temperatura može kontinuirano ili diskontinuirano padati ili rasti unutar granica temperaturnog područja. The process according to this invention is suitable for cleaning melamine, and it is obtained from a process known in the art, which contains impurities such as melam and ureidomelamine. It was found that the content of melamine and ureidomelamine can be reduced by heating contaminated melamine, which appears in the form of crystals or powder, and in the presence of ammonia is kept for a certain time in a temperature range below the melting point of melamine and depends on the ammonia pressure (hardening ). However, it is possible to cool melamine, which has a temperature above that range, to that temperature range. The temperature range in which hardening takes place is above 200°C and below the melting point of melamine. A temperature range between 240°C is recommended, and it is especially recommended between 250°C and temperatures below the melting point of melamine. The melamine is brought to the initial temperature, which is in that area. The temperature can be kept constant during curing, but can be varied within the temperature range defined above. Thus, for example, the temperature can continuously or discontinuously fall or rise within the limits of the temperature range.

Vrijeme u kojem se melamin drži u tom temperaturnom području, može jako varirati. Ono uglavnom ovisi o željenoj konačnoj vrijednosti melama i ureidomelamina, kao i o pritisku amonijaka te privrednim faktorima i nalazi se između 1 minute i 20 sati, a preporučivo između 10 minuta i 10 sati, osobito između 0,5 i 3 sata. Tlak amonijaka može također varirati u velikom području i nalazi se između 5 i 350 bar. Preporuča se tlak između 10 i 100 bar. The time in which melamine is kept in this temperature range can vary greatly. It mainly depends on the desired final value of melam and ureidomelamine, as well as on ammonia pressure and economic factors and is between 1 minute and 20 hours, and preferably between 10 minutes and 10 hours, especially between 0.5 and 3 hours. Ammonia pressure can also vary over a wide range and is between 5 and 350 bar. A pressure between 10 and 100 bar is recommended.

Po završetku stvrdnjavanja brzim hlađenjem, ovisno o tehničkim uvjetima, prvo se hladi i zatim stvrdnjava ili obratnim redoslijedom se prvo stvrdnjava a zatim hladi. Ove faze se mogu vršiti i u slijedećim reakcijskim aparatima. Melamin se pri tome hladi na sobnu temperaturu, primjerice pomoću izmjenjivača topline, jednostavnim uklanjanjem grijaćeg medija i stajanjem medija ili miješanjem hladnim plinovima. Melamin se prema ovom postupku dobiva u obliku kristala odnosno praha i ima izrazito smanjen sadržaj melama i ureidomelamina, koji se nalazi ispod granice dokazivanja. Upon completion of hardening by rapid cooling, depending on the technical conditions, it is first cooled and then hardened, or in the reverse order it is first hardened and then cooled. These phases can also be performed in the following reaction apparatuses. Melamine is then cooled to room temperature, for example using a heat exchanger, simply by removing the heating medium and letting the medium stand or mixing with cold gases. According to this process, melamine is obtained in the form of crystals or powder and has a significantly reduced content of melamine and ureidomelamine, which is below the proof limit.

Postupak prema ovom izumu se može povezati s bilo kojim postupkom melamina poznatim iz tehnike. U preporučivom obliku izvedbe se postupak prema ovom izumu može kombinirati s visokotlačnim postupcima poznatim iz tehnike, kao što je opisano u Ullmann Encyclopedia of Industrial Chemistry, peto izdanje, vol. A-16, pp 174-179. Naročito se preporuča vršenje postupka prema ovom izumu vezano na poznatu ponovnu obradu visokotlačnim postupkom. Ove faze ponovne obrade sadrže: The process according to the present invention can be combined with any melamine process known in the art. In a preferred embodiment, the process according to the present invention can be combined with high pressure processes known in the art, as described in the Ullmann Encyclopedia of Industrial Chemistry, fifth edition, vol. A-16, pp. 174-179. It is particularly recommended to carry out the process according to this invention in connection with the known high-pressure reprocessing. These stages of reprocessing include:

a) odvajanje NHs/CO2-plinske mješavine dobivene kod pretvaranja uree od tekućeg melamina, a) separation of the NHs/CO2-gas mixture obtained during the conversion of urea from liquid melamine,

b) smanjenje CO2 otopljenog u melaminu stavljanjem NH3, kao i b) reduction of CO2 dissolved in melamine by adding NH3, as well as

c) ostavljanje tekućeg melamina u prisustvu amonijaka i c) leaving liquid melamine in the presence of ammonia i

d) hlađenje melamina primjerice naglim hlađenjem hladnom vodom ili tekućim amonijakom ili miješanjem hladnim plinom. d) cooling of melamine, for example by sudden cooling with cold water or liquid ammonia or mixing with cold gas.

Te faze ponovne obrade su primjerice opisane u US 3,116,294. These stages of reprocessing are for example described in US 3,116,294.

Postupak prema ovom izumu se vrši vezano na fazu d), pri čemu broj provedenih faza ponovne obrade a) do c) može varirati ovisno o datostima. Ponovna obrada melamina dobivenog visokotlačnim postupkom iz uree do faze hlađenja d) može obuhvaćati faze a) do c), kao i sve moguće binarne kombinacije ili samo jednu od tih faza. The process according to the present invention is carried out in connection with phase d), whereby the number of performed reprocessing phases a) to c) may vary depending on the data. The reprocessing of melamine obtained by the high-pressure process from urea to the cooling stage d) can include stages a) to c), as well as all possible binary combinations or only one of these stages.

Primjer 1-20 Example 1-20

U jedan mini-autoklav od 10 ml volumena se stavlja odredena količina (EW) melamina s polaznim sadržajem od 18300 ppm melama i 10600 ppm ureidomelamina, kao i količina amonijaka potrebna za održavanje određenog tlaka p. Konačno se autoklav dovodi na temperaturu T i drži na toj temperaturi t minuta. Nakon toga se autoklav brzo hladi uranjanjem u hladnu vodu i zatim otpušta (smanjuje tlak). Tako očišćen melamin se ispituje na sadržaj melama i ureidomelamina, pri čemu se sadržaj ureidomelamina stalno nalazi ispod granice dokazivanja od 100 ppm. Parametri postupka kao, izvagana količina melamina (EW), tlak p, vrijeme t, temperatura T, krajnji sadržaj melama (MA) se vide iz tabele 1. A certain amount (EW) of melamine with an initial content of 18300 ppm melamine and 10600 ppm ureidomelamine is placed in a mini-autoclave of 10 ml volume, as well as the amount of ammonia required to maintain a certain pressure p. Finally, the autoclave is brought to temperature T and kept at at that temperature for t minutes. After that, the autoclave is quickly cooled by immersion in cold water and then released (reduces pressure). The melamine thus cleaned is tested for the content of melam and ureidomelamine, whereby the content of ureidomelamine is constantly below the detection limit of 100 ppm. The process parameters such as weighed amount of melamine (EW), pressure p, time t, temperature T, final melamine content (MA) can be seen from table 1.

Tabela 1 Table 1

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Primjer 21-26 Example 21-26

U jednom autoklavu od 2 1 volumena stavlja se određena količina (EW) melamina s polaznim sadržajem od MA0 melama i UMo ureidomelamina, kao i količina amonijaka potrebna za održavanje određenog tlaka p. Konačno se autoklav dovodi na temperaturu T i drži na toj temperaturi t minuta. Nakon toga se autoklav hladi i zatim otpušta (smanjuje tlak). Tako očišćen melamin se ispituje na sadržaj melama (MA) i ureidomelamina (UM). Parametri postupka, kao izvagana količina melamina (EW), pritisak p, vrijeme t, temperatura T, početni sadržaj melama (MA0) i ureidomelamma (UM0) i krajnji sadržaj melama (MA) i ureidomelamina (UM) se vide iz tabele 2. In one autoclave of 2 1 volume, a certain amount (EW) of melamine is placed with a starting content of MA0 melamine and UMo ureidomelamine, as well as the amount of ammonia required to maintain a certain pressure p. Finally, the autoclave is brought to temperature T and kept at that temperature for t minutes . After that, the autoclave is cooled and then released (reduces pressure). The melamine thus cleaned is tested for the content of melamine (MA) and ureidomelamine (UM). The process parameters, such as the weighed amount of melamine (EW), pressure p, time t, temperature T, initial content of melam (MA0) and ureidomelamine (UM0) and final content of melam (MA) and ureidomelamine (UM) can be seen from Table 2.

Tabela 2: Table 2:

[image] [image]

Claims

1. Process for cleaning melamine, indicated by the fact that the contaminated melamine is kept at a temperature above 200°C and below the melting point of melamine, which depends on the existing ammonia pressure, and that it is kept at an ammonia pressure of 5 to 350 bar for a duration of 1 minute to 20 hours in that temperature range, during which melamine appears as a solid substance, then it is released in an arbitrary order and cooled to room temperature, and pure melamine in powder form is obtained.

2. The process according to patent claim 1, characterized in that the solid melamine is kept at a temperature between 240°C and below the melting point of melamine, which is dependent on the existing ammonia pressure.

3. Process according to patent claim 1, characterized in that the ammonia pressure is between 10 and 100 bar.

4. The process according to patent claim 1, characterized in that the process is connected to the process for the production of melamine.

5. The process according to patent claim 1, characterized in that the process is followed by a high-pressure process for the production of melamine from urea