Classifications

• • 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
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/18—Separation; Purification; Stabilisation; Use of additives

Definitions

• the invention relates to a process for the preparation of polyisocyanates by reacting the corresponding amines with phosgene.
• Polyisocyanates are produced in large quantities and serve mainly as starting materials for the production of polyurethanes. They are usually prepared by reacting the corresponding amines with phosgene.
• the continuous embodiment of this method is two-stage.
• the first stage of phosgenation the amine is reacted with phosgene to form carbamoyl chloride and hydrogen chloride and in a parallel reaction to amine hydrochloride.
• the reaction between amine and phosgene is very fast, strongly exothermic and proceeds even at very low temperatures.
• amine and phosgene if appropriate in a mixture with organic solvent, must therefore be rapidly mixed.
• the first stage of phosgenation generally takes place in a mixing device, preferably a nozzle.
• the second stage of phosgenation involves both the decomposition of the carbamoyl chloride, which is usually present as a solid, to the desired isocyanate and hydrogen chloride, and also the phosgenation of the amine hydrochloride to the carbamoyl chloride.
• the temperature of the second phosgenation stage is generally higher than that of the first.
• a variety of reactors have been developed.
• the hydrogen chloride formed in the reaction is usually removed from the reaction mixture very rapidly in order to reduce the pressure in the reaction system and to shift the equilibrium of the reaction in the direction of the isocyanates.
• the reaction is usually carried out in the presence of solvents.
• solvents such as toluene or chlorobenzenes, are most frequently used. These solvents must be separated from the reaction mixture after the reaction.
• isocyanates as a solvent. This is described, for example, in DE 1 192 641, DE 100 27 779 and DE 101 29 233. In this variant, the separation of the solvents after the phosgenation be waived.
• the disadvantage is that a reaction of the polyisocyanates with the amines used to ureas can not be excluded.
• a constant requirement in the production of isocyanates by reacting the corresponding amines with phosgene is the reduction of the amount of phosgene present in the reaction system, also referred to as phosgene hold-up. Furthermore, a constant requirement in the production of polyisocyanates is to reduce the side reactions and thus to obtain a higher yield and products having an improved quality.
• the invention accordingly provides a process for preparing isocyanates by reacting the corresponding amines with phosgene in the presence of solvents, characterized in that the solvents used are those compounds which form molten salts with hydrogen chloride and from which the hydrogen chloride is reversibly released again leaves.
• Suitable solvents which form interme ⁇ diary salt melts with the hydrogen chloride formed during the reaction are in particular ethers and polyethers.
• the ethers may be chain or cyclic ethers. Examples of these are dioxane, tetrahydrofuran, and glycol ethers, such as diethylene glycol dimethyl ether (diglyme), ethylene glycol dimethyl ether (glyme).
• the solvents mentioned can be used alone or in a mixture with other organic solvents. If other organic solvents are used, the content of the solvents used in accordance with the invention which form salts with hydrogen chloride salt should be at least 10% by weight, based on the total amount of the solvent.
• the conversion of the solvents into salts or molten salts can be carried out before the reaction and the dissolution of the starting compounds. It is also possible to first dissolve the starting compounds in the solvent and then, by adding hydrogen chloride, the solvent into the salt or the molten salt convert.
• the formation of the salts or salt melts preferably takes place intermediately by the hydrogen chloride formed in the reaction of the amines with phosgene.
• the formation of the salts or molten salts is reversible, that is, they can be converted back into solvent and hydrogen chloride. This can be done for example by pressure reduction and / or temperature increase.
• the equilibrium is on the side of the molten salt.
• the reaction system is depressurized and thus the solvent is separated from the hydrogen chloride.
• the separation of the hydrogen chloride and the solvent from the reaction system can be carried out, for example, in a flash with a subsequent evaporator. In this case, the solvent and the hydrogen chloride are liberated from the salt or the molten salt and can be separated by distillation from the isocyanate.
• the separation of the solvent from the hydrogen chloride can also be effected by increasing the temperature. However, this embodiment is not preferred for energetic reasons.
• the molten salt is more polar than the usual inert solvents and can better dissolve the solids that occur during phosgenation as intermediates.
• the solids in particular amine hydrochlorides and carbamoyl chlorides, can react faster here, which increases the space-time yield and reduces the problem of deposits of solids.
• the conversion of the solvents into salts or salt melts can be carried out both before and during the reaction of the amines with phosgene.
• phosgene is used to prepare the solution containing phosgene, which is recycled from the reaction and still contains hydrogen chloride.
• the process step of the separation of phosgene and hydrogen chloride after the preparation of the isocyanates can be dispensed with.
• the solvent is brought into contact with hydrogen chloride before or after the solution of the starting compounds and thus the salts or salt melts are formed.
• the inventive method can be easily carried out in the existing facilities.
• the process according to the invention can be used to prepare the customary industrially prepared polyisocyanates.
• these are, for example, the aromatic isocyanates TDI (toluene diisocyanate) and MDI (methylene diphenyl diisocyanate), PMDI (polymethylene polyphenylene polyisocyanate) and mixtures of MDI and PMDI (crude MDI) and also the aliphatic isocyanates HDI (hexamethylene diphenyl diisocyanate) and isophorone diisocyanate (IPDI).
• TDI toluene diisocyanate
• MDI methylene diphenyl diisocyanate
• PMDI polymethylene polyphenylene polyisocyanate
• mixtures of MDI and PMDI crude MDI
• HDI hexamethylene diphenyl diisocyanate
• IPDI isophorone diisocyanate
• the temperature range which is advantageous for the process according to the invention depends inter alia on the nature and amount of the solvent and the isocyanate to be prepared.
• the mixing unit is a temperature between -20 0 C and 300 0 C, preferably between 10 ° C and 200 0 C and more preferably between 80 0 C and 150 0 C before.
• the temperature in the reactor is generally between 10 0 C and 360 0 C and preferably between 4O 0 C and 21O 0 C and particularly preferably at 80 ° C and 150 0 C.
• the absolute pressure is generally between 0.2 bar and 50 bar, preferably between 1 bar and 25 bar, more preferably between 3 and 17 bar before.
• the residence time of the liquid in the mixing device and in the reactor is in the sum of between 12 seconds and 20 minutes, preferably in the range of 36 seconds to 16 minutes, and more preferably between 60 seconds and 12 minutes.
• the molar ratio of phosgene used to amino groups is 1: 1 to 12: 1, preferably 1.1: 1 to 6: 1.
• the starting materials amine and phosgene are dissolved in the solvent according to the invention; alternatively, only the amine can be dissolved in the solvent.
• the two streams of amine in solution and phosgene, pure or in solution, are combined, preferably by means of a mixing nozzle.
• the mixing nozzle device used is an axially symmetrical mixing tube device with an axial amine feed and a phosgene feed, which takes place via two non-axially arranged annular gaps.
• the amount of solvent used for the process according to the invention is generally from 10 to 1000% by weight, preferably from 50 to 500% by weight, more preferably from 100 to 400% by weight, based on the amount of amine used .
• the mixture of substances is preferably separated by rectification into isocyanate, solvent, phosgene and hydrogen chloride.
• isocyanate solvent, phosgene and hydrogen chloride.
• the decomposition of the salts or molten salts in the solvent and hydrogen chloride Small amounts of by-products remaining in the isocyanate can be separated from the desired isocyanate by means of additional rectification or crystallization.
• the solvent and phosgene can be recycled and reused for the reaction. As described, it is not necessary to recycle hydrogen chloride-free phosgene into the reaction.
• the crude end product may contain inert solvent, carbamoyl chloride and / or phosgene and be further processed by the known methods, as described, for example, in WO 99/40059. It may also be advantageous to pass the product through a heat exchanger when it is withdrawn.

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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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• 2004
  • 2004-11-03 DE DE102004053661A patent/DE102004053661A1/de not_active Withdrawn
• 2005
  • 2005-10-22 MX MX2007004953A patent/MX2007004953A/es unknown
  • 2005-10-22 EP EP05794877A patent/EP1812380A1/de not_active Withdrawn
  • 2005-10-22 KR KR1020077011954A patent/KR20070084595A/ko not_active Application Discontinuation
  • 2005-10-22 US US11/718,520 patent/US20090112018A1/en not_active Abandoned
  • 2005-10-22 CN CNA2005800380851A patent/CN101056847A/zh active Pending
  • 2005-10-22 JP JP2007539495A patent/JP2008518983A/ja active Pending
  • 2005-10-22 WO PCT/EP2005/011367 patent/WO2006048141A1/de not_active Application Discontinuation

Non-Patent Citations (1)

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