Water in the urea reactor — During conversion of ammonium carbamate to urea, what is the effect of a large excess of water in the reacting solution?

Introduction:
The urea synthesis liquid contains NH3, CO2, ammonium carbamate, water, and urea. Water plays a dual role: it is a product of dehydration and a solvent. However, too much water negatively affects the equilibrium conversion to urea.

Given Data / Assumptions:

• Liquid-phase reversible dehydration: NH2COONH4 ⇌ NH2CONH2 + H2O.
• High pressure, moderate temperature; downstream stripping/evaporation present.
• Activity effects: higher water concentration shifts equilibrium.

Concept / Approach:
Le Châtelier’s principle applies: since water is a product, adding excess water drives the equilibrium back toward ammonium carbamate, lowering urea yield at a given temperature and pressure. Moreover, excess water increases the duty of downstream concentrators and can slow kinetics by dilution. Plants therefore control water balance and use high NH3/CO2 ratios and stripping to enhance conversion.

Step-by-Step Solution:
Consider equilibrium: adding product (water) shifts left.Assess process impact: more water → lower conversion, higher evaporation duty.Conclude that large excess water adversely affects yield.

Verification / Alternative check:
Simulation and plant data show conversion drops with higher water content at fixed T, P, and NH3/CO2, validating the adverse effect.

Why Other Options Are Wrong:

• Increasing yield would require removal of water/volatile components, not addition.
• “No yield penalty” ignores equilibrium and kinetic dilution effects.
• Corrosion mitigation is separate and does not inherently raise conversion.

Common Pitfalls:
Assuming dilution always helps reactions; overlooking that water is a reaction product here.

Final Answer:
It adversely affects (reduces) the yield of urea