Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/18—Separation; Purification; Stabilisation; Use of additives
  • C07C263/20—Separation; Purification
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/10—Preparation of derivatives of isocyanic acid by reaction of amines with carbonyl halides, e.g. with phosgene
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C265/00—Derivatives of isocyanic acid
  • C07C265/14—Derivatives of isocyanic acid containing at least two isocyanate groups bound to the same carbon skeleton

Definitions

• the invention relates to a process for the separation and purification of isocyanates from a reaction mixture in the production of aromatic or aliphatic isocyanates.
• aromatic isocyanates these are preferably methylene di (phenyl isocyanate) (MDI) and tolylene diisocyanate (TDI), and in the case of aliphatic hexamethylene diisocyanate (HDI) and isophorane diisocyanate (IPDI).
• aromatic isocyanates TDI tolylene diisocyanate
• MDI methylene diphenyl diisocyanate
• PMDI polymethylene polyphenylene polyisocyanate
• HDI hexamethylene diphenyl diisocyanate
• IPDI isophorone diisocyanate
• Known mixing units include, in particular, nozzles such as the ring slot nozzle, ring hole nozzles, smooth jet mixing nozzles, fan jet nozzles, angular jet chamber nozzles, three-flow nozzles, counterflow mixing chambers, dynamic nozzles and Venturi mixing nozzles.
• nozzles such as the ring slot nozzle, ring hole nozzles, smooth jet mixing nozzles, fan jet nozzles, angular jet chamber nozzles, three-flow nozzles, counterflow mixing chambers, dynamic nozzles and Venturi mixing nozzles.
• Isocyanate synthesis often takes place in the first stage at a very low temperature and in the second at a significantly higher temperature in a residence time apparatus. This process is often referred to as cold-hot phosgenation.
• This process is often referred to as cold-hot phosgenation.
• a description can be found, for example, in W. Siefken, Liebigs Analen der Chemie 562 (1949), page 96.
• a suspension of the intermediates carbamoyl chloride and amine hydrochloride is prepared at low temperature, mostly at 0 ° C or room temperature, maximum 60 ° C, which is then at higher temperatures, usually 100 to 200 ° C, in one Residence apparatus is converted to the isocyanate.
• the reactors customary and known for the preparation of the isocyanates and exemplified above can be used as the residence time apparatus.
• the isocyanates are usually prepared in solution.
• Chlorinated aromatic hydrocarbons such as dichlorobenzene, chlorobenzene, trichlorobenzene or aromatic or aliphatic hydrocarbons such as toluene, xylene, benzene, pentane, hexane, heptane, octane, cyclohexane, biphenyl, ketones such as 2- Butanone, methyl isobutyl ketone, esters such as diethyl isophthalate, ethyl acetate, butyl acetate, nitriles such as acetonitrile, or sulfolane and others used.
• the solvent which usually boils lighter than the isocyanate, is separated from the isocyanate and any residue and worked up by distillation.
• TDI tolylene diisocyanate
• the isocyanate is then removed from the residue by distillation and the isocyanate is distilled off or purified by crystallization (this is also done by competitors in the case of TDI). We should not show too clearly that we are doing distillation ).
• further separation operations can be carried out in order to produce the isomer mixture in the case of TDI or MDI or the oligomer mixture in the case of MDI into individual fractions with different isomer and oligomer compositions.
• the mixture of phosgene and hydrogen chloride obtained in the reaction of aliphatic or aromatic amines with phosgene to give the corresponding isocyanates, which can still contain more or less large amounts of solvent, is generally converted into the mostly gaseous hydrogen chloride and a liquid solution Mixture of phosgene and optionally Solvent separated.
• the phosgene or phosgene / solvent mixture is then returned to the reaction.
• US Pat. No. 3,410,888 describes a process for isolating an aromatic diisocyanate from a reaction mixture, the isocyanate having two phenyl nuclei and the isocyanate groups being bonded to carbon atoms of different phenyl nuclei.
• MDI 4,4'-, 2,4'-, 2, '-methylene di (phenyl isocyanate)
• PMDI polymethylene polyphenylene polyisoeyanate
• the process described therein comprises the steps of firstly the reaction of a corresponding aromatic diamine with phosgene and the distillative removal of part of the aromatic isocyanate thus produced in the course of the solvent removal, secondly the transfer of the distillation residue (bottom product) into a second distillation unit, the is designed as a vessel, over the inner surface of which the residue is distributed as a thin film and the temperature and pressure of which are sufficient to cause evaporation of the isocyanate, and thirdly the removal of the vapor from this second distillation device, which is essentially rich in isocyanate , The steam is condensed and the isocyanate stored. Climbing film evaporators or falling film evaporators are mentioned as possible distillation devices.
• the solvent selected in the isocyanate synthesis usually has a lower boiling point than the isocyanate, it is preferably at least 30 ° C. lower. If the difference in boiling point is smaller, part of the isocyanate produced is also separated off together with the solvent in the solvent separation. This is followed by the distillation of the crude isocyanate obtained as a residue in a thin-film evaporator.
• the partial removal of the isocyanate in the solvent removal has the advantage that undesired middle boilers, possibly colored impurities or components whose boiling point is between that of the isocyanate and the solvent, are also removed in the solvent removal.
• the mixture of the partially separated isocyanate and the solvent is then fed back to the solvent separation as a feed stream, or it is fed in a separate evaporation or fractional distillation to concentrate the isocyanate. The latter is then recycled as a feed into the solvent separation.
• a disadvantage of this process is the partial removal of the isocyanate in the solvent removal, which requires an additional purification of the solvent by distillation. If the solvent for the production of the amine solution contains isocyanate, it forms when the amine and solvent are mixed Urea, which as solids on the one hand leads to constipation and on the other hand leads to poor product quality.
• the invention thus relates to a process for the preparation of isocyanates by reacting amines with phosgene in a reactor, if appropriate separating off the solvent used and subsequently separating and purifying the isocyanate from the reaction mixture, characterized in that the separation and purification of the isocyanate in one Column at a top pressure of 1-950 mbar, preferably 5-50 mbar, particularly preferably 10-20 mbar, and a bottom temperature of 90-250 ° C, preferably 120-170 ° C, particularly preferably 130-150 ° C , and the column is preferably operated in countercurrent gas and liquid.
• the pure isocyanate stream is preferably taken off in liquid or gaseous form in a side draw from the column. A particularly small amount of heavy product is obtained if the residence time in the bottom of the column is not more than six hours, preferably not more than four hours, based on the bottom draw.
• the feed of the reaction mixture is advantageously carried out in the lower part of the column, preferably the column can also be equipped only with a pure rectifying section without stripping section.
• the known internals of distillation and rectification columns are used as internals.
• a tray column or a packing column are used.
• sieve, valve, bell or dual flow bottoms can be used as bottoms and for packs e.g. Sheet, tissue or mesh packs of all types can be used. Packings are particularly advantageous because they have a low pressure drop. However, packed beds are less suitable, but not excluded in principle.
• Sulzer BX, Sulzer CY, Sulzer Mellapak, Sulzer Mellapak Plus, Montz A3, Glitsch 4A, kuhni Rombopak, and others can be used as pack types.
• all types of evaporator types can be used as bottom circulation evaporators, falling film evaporators, long-tube evaporators or thin-film evaporators being particularly advantageous since they can be used to implement evaporation that is gentle on the product. It is advantageous if the column is equipped with a vertical partition. For energy reasons and in order to conserve the product and thus minimize the heavy product accumulation, it can be advantageous to precede the column used according to the invention with one- or multi-stage evaporation. Intermediate evaporation is also advantageous.
• the liquid feed is fed to an evaporator and thereby partially or completely evaporated.
• the steam and possibly the remaining liquid stream is fed to the column.
• the liquid is correspondingly removed from the tray by a tray or collector and fed to a heat exchanger. Both the pre-evaporation and the intermediate evaporation can be carried out in one or more stages.
• the top condenser can be designed externally or integrated into the column. Tube bundle and plate apparatus can be used.
• the solvent used can still be contained in the reaction mixture contained in the column used according to the invention. However, it is advantageous to separate at least part of it beforehand. This can be done, for example, in an upstream column or a similar separation device. At the top of the column, hydrogen chloride, phosgene, solvents, chlorinated by-products and inerts such as nitrogen and carbon dioxide are produced.
• the drawn off at the bottom effluent of the column heavy product contains high-boiling 'oligomeric and polymeric compounds, typically mostly ureas, polyureas, isocyanurates, uretdiones, carbodiimides, and not completely separated isocyanate.
• the discharged bottom product of the column still contains isocyanate, this can advantageously be obtained in a further apparatus, preferably a column, at a pressure of 1-500 mbar, preferably 5-25 mbar, and a temperature of to obtain the isocyanate still remaining in the residue 100-225 ° C, preferred
• the process according to the invention is particularly suitable for working up tolylene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI).
• TDI tolylene diisocyanate
• MDI methylene diphenyl diisocyanate
• HDI hexamethylene diisocyanate
• IPDI isophorone diisocyanate
• other isocyanates can also be purified in this way.
• composition of the feed (1.14 kg / h) was 1.1 kg / h (96.5% by weight) TDI including heavy-boiling TDI homologues, 0.02 kg / h (1.8% by weight) %) Uretdione and 0.02 kg / h (1.8% by weight) chlorinated by-products as well as small amounts of low boilers such as hydrogen chloride, phosgene, and others.
• 1.0 kg / h (99.9% by weight) of TDI with small amounts (0.001 kg / h, 0.1% by weight) of chlorinated by-products were removed from a side draw of the column.

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

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• 2002
  • 2002-12-19 DE DE10260093A patent/DE10260093A1/de not_active Withdrawn
• 2003
  • 2003-12-13 JP JP2004561289A patent/JP4324559B2/ja not_active Expired - Fee Related
  • 2003-12-13 CN CNA2003801067827A patent/CN1729166A/zh active Pending
  • 2003-12-13 ES ES03789263T patent/ES2330518T3/es not_active Expired - Lifetime
  • 2003-12-13 PT PT03789263T patent/PT1575905E/pt unknown
  • 2003-12-13 EP EP03789263A patent/EP1575905B1/de not_active Expired - Lifetime
  • 2003-12-13 AU AU2003293872A patent/AU2003293872A1/en not_active Abandoned
  • 2003-12-13 MX MXPA05006056A patent/MXPA05006056A/es active IP Right Grant
  • 2003-12-13 DE DE50311902T patent/DE50311902D1/de not_active Expired - Lifetime
  • 2003-12-13 WO PCT/EP2003/014186 patent/WO2004056757A1/de not_active Ceased
  • 2003-12-13 AT AT03789263T patent/ATE442350T1/de not_active IP Right Cessation
  • 2003-12-13 KR KR1020057011102A patent/KR101016737B1/ko not_active Expired - Fee Related
  • 2003-12-13 US US10/538,119 patent/US20060089507A1/en not_active Abandoned

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