Ammonia–urea complexes — Industrial fertilizer plants meet their nitrogen (N2) requirement primarily by obtaining nitrogen via which route?

Introduction:
Nitrogen is the primary feed for ammonia synthesis (Haber–Bosch), which underpins the global fertilizer industry. Large-scale, reliable supply of high-purity N2 is essential. Understanding the standard industrial source clarifies front-end integration in ammonia–urea complexes.

Given Data / Assumptions:

• High-purity nitrogen is required continuously at significant flow rates.
• Co-product oxygen may be valuable but is not mandatory.
• Plant scales are typically hundreds to thousands of tonnes per day of NH3.

Concept / Approach:

The standard source of nitrogen for large fertilizer complexes is cryogenic air separation units (ASU), which liquefy and distill air to supply N2 (and often O2/Ar). Alternative sources such as decomposition of NOx or recovery from process gases are impractical or insufficient. Membranes can supply moderate-purity nitrogen for inerting, not typically for ammonia synthesis where high purity is demanded to avoid catalyst poisoning.

Step-by-Step Solution:

Verification / Alternative check:

Process flow diagrams for ammonia plants routinely show an ASU or purchase of pipeline nitrogen produced cryogenically.

Why Other Options Are Wrong:

B: Dissociating NOx is not an industrial nitrogen source. C/D: Producer/coke-oven gases do not provide bulk, pure N2. E: Membranes are typically for lower-purity inerting, not synthesis-grade nitrogen.

Common Pitfalls:

Assuming small packaged nitrogen generators (membranes/PSA) can meet the purity/flow needed for ammonia synthesis—these are rarely suitable for base-load NH3 plants.

Final Answer:

fractionation (cryogenic distillation) of liquefied air