2. Combustion of fuels with air at high temperatures can produce nitrogen/oxygen compounds (NOₓ) as unwanted by-products. Because these compounds are pollutants, they must be removed, and one process for doing so is called selective catalytic reduction (SCR). A researcher claims to have developed a new SCR catalyst that uses ammonia (NH₃) as a reactant to convert NO into nitrogen and water via the reaction: \[ 6\text{NO(g)} + 4\text{NH}_3\text{(g)} \rightarrow 5\text{N}_2\text{(g)} + 6\text{H}_2\text{O(g)} \] We are working on the design for a process using this reaction in which 120 mol/hr of an equimolar mixture of NO and NH₃ (i.e., 60 mol/hr NO and 60 mol/hr NH₃) at 450°C is fed to the reactor. We may assume that the reaction goes to completion in the limiting reactant. The reactor is jacketed to maintain the temperature at 450°C, and we may assume that the pressure is held constant at 1 atm. Use the following constant heat capacities for the gases: | Species | $ \bar{C}_p $(J/mol K) | |----------|--------------------------| | NO (g) | 30.5 | | NH₃ (g) | 37.0 | | N₂ (g) | 29.1 | | H₂O (g) | 34.2 | (a) Determine the composition (species molar flow rates) of the product stream. (b) Determine the standard enthalpy change for the reaction at 298 K ($ \Delta H_{298}^\circ $). (c) Determine the rate at which heat must be added to or removed from the reactor.

Introduction to Chemical Engineering Thermodynamics

8th Edition

ISBN:9781259696527

Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart

Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart

Chapter1: Introduction

Section: Chapter Questions

Problem 1.1P

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Question

2. Combustion of fuels with air at high temperatures can produce nitrogen/oxygen compounds (NOₓ) as unwanted by-products. Because these compounds are pollutants, they must be removed, and one process for doing so is called selective catalytic reduction (SCR). A researcher claims to have developed a new SCR catalyst that uses ammonia (NH₃) as a reactant to convert NO into nitrogen and water via the reaction:

\[ 6\text{NO(g)} + 4\text{NH}_3\text{(g)} \rightarrow 5\text{N}_2\text{(g)} + 6\text{H}_2\text{O(g)} \]

We are working on the design for a process using this reaction in which 120 mol/hr of an equimolar mixture of NO and NH₃ (i.e., 60 mol/hr NO and 60 mol/hr NH₃) at 450°C is fed to the reactor. We may assume that the reaction goes to completion in the limiting reactant. The reactor is jacketed to maintain the temperature at 450°C, and we may assume that the pressure is held constant at 1 atm.

Use the following constant heat capacities for the gases:

| Species | $ \bar{C}_p $(J/mol K) |
|----------|--------------------------|
| NO (g) | 30.5 |
| NH₃ (g) | 37.0 |
| N₂ (g) | 29.1 |
| H₂O (g) | 34.2 |

(a) Determine the composition (species molar flow rates) of the product stream.

(b) Determine the standard enthalpy change for the reaction at 298 K ($ \Delta H_{298}^\circ $).

(c) Determine the rate at which heat must be added to or removed from the reactor.

Expert Solution

Step 1: Composition of the product stream

Given, Reaction is

$6 N O left parenthesis g right parenthesis plus 4 N H subscript 3 open parentheses g close parentheses space rightwards arrow 5 N subscript 2 left parenthesis g right parenthesis space plus space 6 H subscript 2 O left parenthesis g right parenthesis$

In the feed there is 60 mol/hr of NO and 60 mol/hr of NH₃.

From the reaction stoichiometry, NOis the limiting reactant.

For 60 mol/hr of NO

NH₃ required = $4 over 6 cross times 60 equals 40 space fraction numerator m o l over denominator h r end fraction$

Product stream composition will be

N₂ formed = $5 over 6 cross times 60 equals 50 space fraction numerator m o l over denominator h r end fraction$

H₂O formed = $6 over 6 cross times 60 equals 60 space fraction numerator m o l over denominator h r end fraction$

NH₃ remaining = $60 minus 40 equals 20 space fraction numerator m o l over denominator h r end fraction$

Total molar flow rate of products = 130 mol/hr