Feedstocks for nitric acid (Ostwald process): Which raw materials are required to manufacture nitric acid at industrial scale?

Introduction / Context:
Nitric acid is produced by the Ostwald process, which begins with the catalytic oxidation of ammonia to nitric oxide, followed by further oxidation and absorption in water to yield aqueous HNO3. Recognising the true raw materials clarifies mass balances and ties ammonia production to downstream fertiliser manufacture (e.g., ammonium nitrate, nitrates, and nitrophosphates).

Given Data / Assumptions:

• Ammonia feed is typically anhydrous and vaporised.
• Air provides oxygen for oxidation reactions and diluent for temperature control on the catalyst.
• Water is required to absorb nitrogen oxides to form nitric acid.

Concept / Approach:
Process sequence: NH3 + O2 (over Pt–Rh) → NO; NO + O2 → NO2; absorption of NO2 and related species in water → HNO3 with NOx recycle in the absorber. Thus, the essential raw materials are anhydrous ammonia, air, and water. Hydrogen peroxide is not a feedstock for the Ostwald process; “wet ammonia only” without oxidation cannot produce nitric acid; nitrous oxide is not used as the principal oxidised nitrogen feed for HNO3 manufacture.

Step-by-Step Solution:

Verification / Alternative check:
Standard flowsheets show ammonia vaporizer, air preheater, Pt–Rh converter, NOx cooler/oxidiser, and an absorption tower with water feed—confirming the three raw materials.

Why Other Options Are Wrong:

• Hydrogen peroxide route (a): not industrial for nitric acid.
• Ammonia and air only (b): lacks the absorber feed (water).
• Wet ammonia only (d): no oxidation means no HNO3.
• N2O + steam (e): not the Ostwald route.

Common Pitfalls:
Omitting water because its role seems “downstream”; forgetting that absorption is integral to acid formation.

Final Answer:
Anhydrous ammonia, air and water