A community can get ammonia without the high-pressure Haber loop from three sources the carrier names: urine allowed to decompose so bacteria turn urea into ammonia, ammonium chloride heated with slaked lime, and guano. Heating 107 g of ammonium chloride with lime releases at most 34 g of ammonia, caught by bubbling the gas through water. Ammonia gas is toxic and corrosive to eyes and lungs, so every route is done outdoors with an open vent.
Part of Industrial Chemistry
Low-pressure routes to ammonia and ammonium compounds that avoid the hazards of high-pressure hydrogen synthesis.
Three Routes Without A Pressure Loop
The carrier lists “alternative ammonia sources” to consider before building a Haber plant. The honest reason to start here is that the Haber Process needs pressures and temperatures a settlement cannot contain safely.
- Urine decomposition. Collect urine and let it decompose; bacteria convert urea to ammonia. The carrier says distilling concentrates it, giving small but usable quantities.
- Ammonium chloride plus lime. The carrier says to heat sal ammoniac (found near volcanic vents or produced from urine) with calcium hydroxide (slaked lime, see Slaking); ammonia gas is released and is captured by bubbling through water.
- Guano. Bat caves and seabird colonies hold nitrogen-rich guano; dissolve and process for ammonia or nitrate. See Guano.
Where the aim is fertilizer, the corpus sources for nitrogen are Nitrogen Sources and Fertilizers and Soil Amendments; where the aim is the soda-ash process, ammonia is recycled rather than consumed (see Solvay Chemistry).
What You Need
- A source of nitrogen: decomposed urine, ammonium chloride, or guano.
- For the lime route: slaked lime, dry.
- A vented heating vessel and a delivery tube to a water trap, with the vessel never sealed.
- A receiver of cold water, with the delivery tube ending in an inverted funnel that just touches the surface, because ammonia is so soluble that a deeper tube would suck water back.
- An outdoor, upwind workplace.
Method: The Ammonium Chloride And Lime Route
Step 1: Mix the ammonium chloride and lime in a vented vessel.
Step 2: Heat gently. Ammonia gas, with its sharp smell, is released.
Step 3: Lead the gas by tube to cold water. It is very soluble; the water becomes ammonia solution.
Step 4: Stop heating, disconnect the tube from the water side first to avoid suck-back, and label the solution.
Worked Example: How Much Ammonia From Each Source
The reaction for the lime route is 2NH4Cl + Ca(OH)2 → CaCl2 + 2NH3 + 2H2O. With rounded atomic masses N 14, H 1, Cl 35.5, Ca 40, O 16:
- NH4Cl = 14 + 4 + 35.5 = 53.5 g per mole; 2 mol = 107 g.
- NH3 = 14 + 3 = 17 g per mole; 2 mol = 34 g.
- Ammonia per gram of ammonium chloride: 34 ÷ 107 = 0.318 g.
- Lime needed: Ca(OH)2 = 40 + 34 = 74 g per 107 g of NH4Cl, or 0.69 g per gram.
For urine, the reaction is CO(NH2)2 + H2O → 2NH3 + CO2. Urea is 12 + 16 + 28 + 4 = 60 g per mole, giving 34 g of ammonia: 34 ÷ 60 = 0.567 g per gram of urea. If urine holds 20 g of urea per litre (a recalled figure that varies with diet and water intake), full conversion gives 20 × 0.567 = 11.3 g of ammonia per litre. Real recovery is lower because ammonia is lost to the air while the urine decomposes.
Common Mistakes
- Sealing the heating vessel. Gas and steam build pressure.
- Leaving the delivery tube deep in the water. Cooling the vessel then draws water back into the hot mixture.
- Mixing ammonia with bleach. It makes toxic gases (Chlorination says never to mix chlorine with acid or ammonia).
- Working indoors.
Safety
Ammonia is a toxic, corrosive gas
Ammonia irritates and burns eyes, throat and lungs and is lighter than air, so it spreads upward and on the wind; strong solutions burn skin. It is flammable only in a narrow range of mixtures with air, but it is a poison long before that matters. Work outdoors upwind, wear eye protection, and keep ammonia solutions away from bleach and acids. See Toxic Gases.
What’s Next
- Learn next: Soda Ash Production — a use for recycled ammonia
- Combine with: Toxic Gases — handling ammonia safely