WERKWIJZE VOOR HET BEREIDEN VAN UREUM UIT AMMONIAK EN KOOLDIOXIDE.

摘要

Urea is made by reacting ammonia and carbon dioxide at 140-400 ata/160-230 deg.C. The resulting aq. soln. of urea is sepd. from unreacted NH3 and CO2 (stage 1). Liq. or gaseous streams of NH3 and CO2 are sepd. from gases inert to the synthesis of urea and from the purified waste water withdrawn from the process (stage 2); and these sepd. streams are recycled to the synthesis process. The recovered urea soln. is vacuum thickened (stage 3) at 0.04-0.90 ata to give a condensed phase of dehydrated urea and a vapour phase which is a mixt. of water, NH3, CO2 and urea. The dehydrated urea is converted into solid particles and cooled in an airstream; and urea dust is water-washed from the resulting air to form an aq. soln. of urea which is delivered to stage 3. The mixt. of water, NH3, CO2 and urea from the vapour phase of stage 3 is condensed due to its indirect cooling, to form a liquor vapour condensate which is supplied to stage 2. NH3 and CO2 contained in the uncondensed portion of the vapour phase after the indirect cooling are directly contacted with a cooling agent-absorbent at 10-60 deg.C/1.5-18 ata which contains dissolved in water 0.2-3.4 wt.% NH3, 0-1 wt.% CO2 and 0-50% urea; and at least a portion of the resulting soln. is then passed to stage 1, stage 2 or stage 3. The process makes it possible to avoid supplying power steam to the zone of contacting with the vapour-gas stream remaining after completion of the liquor vapour condensation due to indirect cooling (cf. conventional Mitsui Toatsu (FR2099882) or Stamicarbon (FR1184991) processes). Urea is used in mfr. of fertilisers, protein additives for ruminant feedstuffs, resins, etc.