Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F7/00—Compounds containing elements of Groups 4 or 14 of the Periodic Table
  • C07F7/02—Silicon compounds
  • C07F7/08—Compounds having one or more C—Si linkages
  • C07F7/10—Compounds having one or more C—Si linkages containing nitrogen having a Si-N linkage
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
  • C07F7/00—Compounds containing elements of Groups 4 or 14 of the Periodic Table
  • C07F7/02—Silicon compounds
  • C07F7/08—Compounds having one or more C—Si linkages

Definitions

• the invention relates to a process for the preparation of organosilazane and ammonium halide.
• DE 26 45 703 B2 describes a process for preparing hexamethyldisilazane by reacting trimethylchlorosilane with gaseous ammonia in the presence of hexamethyldisilazane as solvent.
• the ammonium chloride formed in the reaction is separated from hexamethyldisilane by washing with water.
• the hexamethyldisilazane is then dried with sodium sulfate and the sodium sulfate is filtered off.
• the ammonium chloride is separated from hexamethyldiosilazane by distillation at a bottom temperature below 75 ° C and reduced pressure.
• the distillation conditions selected prevent larger amounts of ammonium chloride from subliming on distilling off the hexamethyldisilazane, thereby clogging the conduit paths.
• the ammonium chloride remaining in the reactor after distillation, which still contains residues of hexamethyldisilazane, is dissolved by addition of dilute hydrochloric acid.
• the remaining hexamethyldisilazane reacts to form hexamethyldisiloxane and is separated off from the aqueous ammonium chloride as a lighter phase.
• a further possibility of salt separation consists in removing the ammonium chloride from the reaction mixture by means of filtration or centrifugal separation.
• the hexamethyldisilazane-containing ammonium chloride is then dissolved in dilute hydrochloric acid, once again hexamethyldisiloxane is formed and ammonium chloride is obtained as an aqueous solution. Yield losses on hexamethyldisilazane also occur in this procedure, since considerable amounts of hexamethyldisilazane remain in the ammonium chloride during filtration or centrifugal separation.
• EP 0 921 127 A1 describes a process for the preparation of organosilazanes and ammonium chloride, in which an organochlorosilane and ammonia are reacted in the presence of organosilazane as solvent, ammonium chloride being separated from the resulting mixture containing organosilazane and ammonium chloride by dissolving before the Separation to the mixture, or after separation of the ammonium chloride, an antiblocking agent will be added.
• the disadvantage of this process lies in the complicated separation of the solid ammonium chloride from organosilazane. Separation processes are thermal processes or the combination of mechanical processes and thermal processes, the combination of mechanical processes and thermal processes being preferred. In the combination of mechanical and thermal processes, the mechanical process is carried out before the thermal process.
• the object was to overcome the disadvantages of the prior art.
• the invention relates to a continuous process for the preparation of organosilazanes in which continuous streams of ammonia and organohalosilane with a molar ratio of at least 7: 1 in a pressure reactor at a temperature> 160 ° C and a pressure> 110 bar ge brought to the reaction are, the final reaction mixture at a temperature> 80 0 C, a pressure> 40 bar and an ammonium halide content of> 1 wt .-% of two phases
• the process according to the invention now provides a simple, economical and environmentally conscious continuous process for the preparation of organosilazanes. It avoids a complicated solid-liquid separation of the reaction products.
• An advantage of the method is that no yield losses of organosilazane occur and the ammonium halide is obtained in a solid, pure and manageable, ie free-flowing and block-stable form and the known mann of which some are listed below.
• Ammonium chloride z. B. is a valuable raw material among others for the fertilizer sector, for explosives and for the production of zinc / ammonium chloride melts. Furthermore, ammonium chloride is used as a nitrogen source in municipal biological wastewater treatment plants.
• the inventive method is based on the surprising discovery that from the final reaction mixture (the reaction mixture after the reaction) containing organosilazane, ammonium halide and ammonia at a temperature> 80 ° C, a pressure> 40 bar and an ammonium halide content of> 1 wt .-%, a liquid phase A deposits, which consists of at least 75 wt .-% of the total amount of ammonium halide formed and at most 20 wt .-% of the total amount of formed organosilazane and ammonia.
• the ammonia phase B has a significantly lower density than the ammonium halide phase A.
• the process allows a selective and continuous deposition of the individual reaction products from the final reaction mixture without addition of foreign substances and at the same time ensures that only a small part of the process ammonia has to be completely evaporated and recondensed. This ensures high product yields or purities at low production costs.
• the involved phases A and B can be separated from one another by common methods of liquid-liquid separation.
• the pressure at the separation of the final reaction mixture is at least 80 and at most 400 bar.
• the ammonium halide phase A can be extracted during the separation with pure ammonia in order to remove a residual content of organosilazane.
• the still up to 20 wt .-% of the total amount of organosilazane-containing phase A is preferably discharged continuously under relaxation from the process, wherein preferably the contained ammonia is evaporated and recycled. If appropriate, the ammonium halide obtained in crystalline form may be freed from any adhering organosilazane by washing with an organic solvent.
• the liquid phase C formed contains much organosilazane, little ammonium halide and ammonia and, because of a significant difference in density, can be separated from the less dense ammonia phase D by customary methods.
• the separated pure ammonia phase D is preferably compressed and returned to the process.
• the organosilazane phase C under relaxation After discharging the organosilazane phase C under relaxation, it is preferably freed of residual ammonia continuously under reduced pressure.
• the organosilazane can be further purified by a rectification step.
• the molar ratio of ammonia and organohalosilane is at least 7: 1.
• the molar ratio of ammonia and organohalogenosilane is at most 150: 1.
• the streams of ammonia and organohalogenosilane are preheated prior to entry into the pressure reactor.
• the reaction temperature is at least 16O 0 C and vor ⁇ preferably at most 400 0 C, in particular at most 300 0 C.
• Hexamethydisilazane or 1,3-divinyltetramethyldisilazane is preferably prepared by the process according to the invention.
• the organohalosilane is preferably trimethylchlorosilane or vinyldimethylchlorosilane or mixtures thereof.
• the ammonium halide is preferably ammonium chloride.
• the process according to the invention has the advantage that it is simple to carry out on a production scale, gives a high yield of organosilazane and is environmentally aware, since the ammonium halide obtained can be recycled.
• a further advantage is that the ammonium halide obtained without the addition of anti-blocking agents has a high blocking resistance and flowability and thus no difficulties in handling even after prolonged storage, for example when emptying from containers.
• the process according to the invention produces ammonium halide was a non-hazardous commodity according to current regulations and can therefore be supplied in a simpler manner to a universal recycling.
• the ammonium halide prepared by the processes according to the invention has a purity with respect to the content of environmentally relevant impurities, such as the heavy metals lead, cadmium, chromium, nickel, zinc, copper and mercury, the conventional ammonium halide, such as the chemicals retailer is distributed, is comparable.
• the heavy, lower phase A is separated off from the two-phase reaction mixture at a pressure of 160 bar and a temperature of 16O 0 C and extracted with 3.0 kg / h of pure ammonia.
• the extracted phase A is then transferred under relaxation to a drying apparatus, whereby the phase decomposes into 3.9 kg / h of solid salt and gaseous ammonia, which is recycled.
• the purity of the ammonium chloride obtained is 99.9% by weight.
• the first separation stage leaving Organosilazan--containing ammonia stream B is depressurized to 50 bar and heated to 100 0 C rationsease before entry into the second Sepa ⁇ , wherein once again forms a two-phase mixture.
• the heavy, lower organosilazane and ammonia-containing phase C is separated from the ammonia stream D under relaxation, wherein the ammonia escapes in gaseous form and is recycled.
• the ammonia-containing organosilazane is freed from dissolved ammonia in a degassing vessel under reduced pressure.
• the product flow obtained of 5.7 kg / h (96% of theory) consists of hexamethyldisilazane with a purity of 99.0% by weight.
• the ammonia stream D escaping from the second separation stage is compressed, adjusted again to the target stoichiometry with fresh ammonia and returned to the process.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)

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Citations (2)

• 2004
  • 2004-10-26 DE DE102004051899A patent/DE102004051899A1/de not_active Withdrawn
• 2005
  • 2005-10-13 WO PCT/EP2005/011036 patent/WO2006045444A1/de not_active Ceased
  • 2005-10-13 KR KR1020077006521A patent/KR100839552B1/ko not_active Expired - Fee Related
  • 2005-10-13 EP EP05794420A patent/EP1805189B1/de not_active Expired - Lifetime
  • 2005-10-13 DE DE502005004757T patent/DE502005004757D1/de not_active Expired - Fee Related
  • 2005-10-13 JP JP2007537167A patent/JP2008517012A/ja not_active Withdrawn
  • 2005-10-13 CN CNA2005800352777A patent/CN101039950A/zh active Pending

Patent Citations (2)

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