Maintaining stability of urea above melt point

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  • #96496
    mohit
    Participant
      • Participant

      put beaker air tight so when ammonia will vaporise it will create pressure and solution will reach in equilibrium and will be stable

      #96217
      imran-idris
      Participant
        • Participant

        As far as I know Urea chemistry, maintaining molten Urea above its boiling point and not letting the formation of by-products can be achieved by storing molten Urea under positive pressure of Ammonia above its boiling point. In this way you can avoid the formation of Biuret and Ammonia(g) which are favored by low pressure.
        As we know the reaction
        Urea (molten) <=> Biuret + Ammonia
        So according to LeChatlier’s principle, increasing pressure and adding Ammonia above molten urea solution would shift the reaction equilibrium towards left side of the equation hence preventing formation of by products.

        #96190
        Mark Brouwer
        Keymaster
          • Expert

          There are (at least) two reactions taking place at temperatures higher than the melt temperature in the urea melt:

          2 urea <=> NH3 + Biuret

          and

          urea <=> NH3 + HNCO

          When knowing what happens if one introduces an acid in the urea melt, the following topic might be of interest:
          https://www.ureaknowhow.com/urea_j/en/round-table/viewtopic.php?p=1463#p1463

          #92554
          drost1
          Participant
            • Participant

            Hello,
            I am working with urea slightly above its melting point (~140-145C). I need to maintain it in liquid phase for prolonged periods (4-8 hours) until used in my process. What recommendations does anyone have to maintain the urea, so as to minimize formation of other compounds (ammonia, biuret, etc.). I can potentially add anything needed, such as acids, alkalis, other materials. Not a urea expert, but looking for some guidelines. Also, any ideas as to what happens to urea when mixed with polyethylene glycol above the urea melt point. I see a temperature rise, and some gassing from my beaker. Thank you.

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