Urea

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Urea
aka diamino carbonyl
Urea struct.png
Chemical formula OC(NH2)2
Molar Mass(g/mol) 60 
Melting Point(°C) 135 
Density(g/cc) 1.32 
Solubility in water(g/L) ≥1000 
Solubility in ethanol(g/L) 50
NFPA 704
NFPA704.png
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Thermal Decomposition
urea
unk°C
NH3,CO2

A major source of organic nitrogen.

Uses

Primary

  • Industrial chemical
  • Fertilizer (46-0-0)

Secondary

  • Feedstock (through natural decomposition) to ammonia
  • Feedstock for urea nitrate for cold packs
  • Pharm: (ointment) Skin treatment

Natural occurrence

  • Appears naturally in urine and to a lesser degree in compost

Hazards

Production

Extraction

from urine

Approximately 9.3g are expected in a liter of fresh human urine. Delay in processing allows bacteria to convert the urea to ammonia.

simple evaporation
  1. Dry urine to solids
  2. Repeat
    1. Dissolve in ethanol
    2. filter
    3. discard residue
    4. evaporate alcohol
    5. gather crystals
  3. Until nothing but clear crystals remains

The crystals are urea

further separation
Reactants
Products
Equipment
  • Liquid Dryer/Evaporater
  • Gas bubbling equipment
  • (Optional) Distillation equipment
Process
  1. Boil 10L of urine down to 1L (containing ~93g, 6.6M of urea)
  2. Filter
  3. Residue contains organics, calcium and other phosphates, can be retained to produce phosphorus or burned and disposed
  4. Filtrate contains sodium chloride and urea
  5. Evaporate water by gentle heating (≤ 133°C)
  6. Residue is mostly sodium chloride and urea
  7. Wash residue with hot concentrated ethanol several times, combine washings
    NB: Urea dissolves easily, salt does not.
  8. IF (two layers form in the washings)
    1. Separate the aqueous layer and evaporate separately, producing mineral salts
  9. ENDIF
  10. Evaporate ethanol washings
    NB: It may be worth condensing the ethanol vapors
  11. The residue is urea. It should crystallize
via oxalic acid
  • Precipitate from urine using oxalic acid, then extract again using calcium hydroxide. Detoxify the calcium oxalate by thermal decomposition.
    CO(NH2)2 + H2(COO)2 C3H6N2O5
    C3H6N2O5 + Ca(OH)2 CO(NH2)2 + Ca(COO)2 + 2 H2O
    Ca(COO)2
    {
    ≥600°C}
    CaCO3 + CO
via nitric acid
  1. Combine urine and nitric acid, producing urea nitrate crystals
  2. Filter
  3. Discard filtrate
  4. Repeat
    1. Prepare a saturated solution of urea nitrate in boiling water
    2. Mix in charcoal fines
    3. Stir
    4. Cool
    5. Filter through charcoal
    6. Discard residue
    7. Dry solution to crystals
  5. Until no further residue is collected and the crystals are as pure as desired

Synthesis

Wohler

See Also

References