Question

What is undesirable in urea production?

• A. Ammonium carbamate formation
• B. Biuret formation
• C. Dehydration of ammonium carbamate
• D. Liquid NH\( _3 \)

Hint:

Think of urea production as a two-step process. The first step creates an intermediate, and the second step converts it to the desired product. Biuret is a side product that detracts from the main goal.

Answer 1

The Correct Option is B

Step 1: Understand the process of urea production. 
Urea is commercially produced by the reaction of ammonia (NH\( _3 \)) and carbon dioxide (CO\( _2 \)) under high temperature and pressure. The process involves two main steps: 1. Formation of ammonium carbamate: \[ 2 NH_3 + CO_2 \rightleftharpoons NH_2COONH_4 \quad (\text{exothermic}) \] 2. Dehydration of ammonium carbamate to urea: \[ NH_2COONH_4 \rightleftharpoons NH_2CONH_2 + H_2O \quad (\text{endothermic}) \] 
Step 2: Analyze each of the given options in the context of urea production. 
Option 1 (Ammonium carbamate formation): Ammonium carbamate is an intermediate in the production of urea. It is a necessary step for the synthesis of urea from ammonia and carbon dioxide. Therefore, it is not undesirable; it is essential. Option 2 (Biuret formation): Biuret is a byproduct formed by the condensation of two urea molecules with the elimination of ammonia: \[ 2 NH_2CONH_2 \rightarrow NH_2CONHCONH_2 + NH_3 \] Biuret is an undesirable impurity in urea, especially when urea is used as a fertilizer, as it can be toxic to some plants at high concentrations. Its formation reduces the yield of urea and requires additional separation steps. Option 3 (Dehydration of ammonium carbamate): The dehydration of ammonium carbamate is the main reaction that produces urea. While the equilibrium of this reaction is not very favorable under typical industrial conditions (requiring high pressure and excess ammonia), it is the desired transformation to obtain urea. Therefore, it is not undesirable; it is the target reaction. Option 4 (Liquid NH\( _3 \)): Liquid ammonia is one of the primary reactants in urea production. It is essential for the formation of ammonium carbamate and subsequently urea. Therefore, it is not undesirable; it is a necessary feedstock. 
Step 3: Identify the undesirable component or reaction. 
Based on the analysis, biuret formation is the undesirable aspect in urea production as it is an impurity that reduces yield and can have negative effects on the application of urea. 
Step 4: Select the correct answer. 
Biuret formation is undesirable in urea production.