Urea synthesis chemistry:\nIn the industrial manufacture of urea, the immediate intermediate formed from NH3 and CO2 inside the high-pressure reactor is ________.

Introduction / Context:
Urea production integrates ammonia synthesis with CO2 capture by converting these two streams to urea. The reaction proceeds via a key intermediate, knowledge of which is essential for understanding recycle loops, heat integration, and safety in urea plants.

Given Data / Assumptions:

• Reagents: NH3 and CO2 at high pressure and elevated temperature.
• Closed-loop design with carbamate formation and decomposition/recovery sections.
• We seek the chemical intermediate formed before dehydration to urea.

Concept / Approach:
The first step is exothermic formation of ammonium carbamate: CO2 + 2 NH3 → NH2COONH4. The second step is endothermic dehydration of ammonium carbamate to urea and water. Ammonium carbonate is not the controlled process intermediate in modern urea synthesis; biuret and cyanuric acid are side products arising from urea condensation at elevated temperatures and are not desired intermediates.

Step-by-Step Solution:
NH3 + CO2 in the reactor → ammonium carbamate.Ammonium carbamate → urea + H2O by dehydration.Recycle unconverted carbamate and excess NH3 for efficiency.

Verification / Alternative check:
All major licensor packages (e.g., Stamicarbon, Saipem) describe the same two-step mechanism featuring ammonium carbamate as the immediate intermediate.

Why Other Options Are Wrong:
Ammonium carbonate is not the targeted intermediate; biuret/cyanuric acid are thermal condensation by-products and are controlled to low levels.

Common Pitfalls:
Confusing carbamate with carbonate or assuming biuret is part of the intended pathway; it is a quality-limiting impurity formed in finishing if overheated.

Final Answer:
Ammonium carbamate