Mass balance on oxidation of ammonia for production of nitric acid

• Mangoes
In summary: Atkins-In summary, the chemical reaction takes place where NH3 and O2 are fed into a reactor at a flow rate of 100 mol/h. The products are nitrogen monoxide and water, and the unused reactants, ammonia and oxygen. The attempt at a solution is to do a mass balance on molecular species.
Mangoes

Homework Statement

The following chemical reaction takes place inside a reactor where 80% conversion is obtained with an equimolar mixture of NH3 and O2 fed at the flow rate of 100 mol/h.

4NH3 + 5O2 ⇔ 4NO + 6H2O

What are the output rates of all species?

There's a diagram shown where ammonia and oxygen are pictured as feed, output are the products, nitrogen monoxide and water, and the unused reactants, ammonia and oxygen.

The Attempt at a Solution

The problem wants me to do a mass balance on molecular species.

I've just recently started looking at processes involving reactions however and I'm not too sure on how to write balances when reactions are present. If we looked at NH3 for example,

input = consumption + output

I can denote different variables to represent input and ouput for NH3, but I'm not sure how I'd quantify the consumption of NH3 per unit time. Previously, I would be given the flow rate of one of the outputs of a species and then from stoichiometry I'd be able to get the consumption/generation of any of the species, but I'm not being given it this time.

I assume I have to use the 80% conversion somewhere, but that's for equimolar mixtures and I'm not sure how I'd account limiting reactants into the equation to get the appropriate consumption term.

Mangoes said:

Homework Statement

The following chemical reaction takes place inside a reactor where 80% conversion is obtained with an equimolar mixture of NH3 and O2 fed at the flow rate of 100 mol/h.

4NH3 + 5O2 ⇔ 4NO + 6H2O

What are the output rates of all species?

There's a diagram shown where ammonia and oxygen are pictured as feed, output are the products, nitrogen monoxide and water, and the unused reactants, ammonia and oxygen.

The Attempt at a Solution

The problem wants me to do a mass balance on molecular species.

I've just recently started looking at processes involving reactions however and I'm not too sure on how to write balances when reactions are present. If we looked at NH3 for example,

input = consumption + output

I can denote different variables to represent input and ouput for NH3, but I'm not sure how I'd quantify the consumption of NH3 per unit time. Previously, I would be given the flow rate of one of the outputs of a species and then from stoichiometry I'd be able to get the consumption/generation of any of the species, but I'm not being given it this time.

I assume I have to use the 80% conversion somewhere, but that's for equimolar mixtures and I'm not sure how I'd account limiting reactants into the equation to get the appropriate consumption term.

For a few seconds I asked myself 80% conversion of what? - but if you look at the products it is clear they will be interested in the % conversion of the ammonia into NO.

Start with the NH3 conversion into NO. One mole of one converts into how many moles of the other?

And 80% conversion of anything converts a mole into how many?

The answer for two of the substances needs very little chemistry just some common sense.
For the other two a very little chemistry as well is also required.

Last edited:
Take as a basis 100 moles of reactants entering the reactor.

How many moles of NH3 enter?
How many moles of O2 enter?
For 80% conversion, how many moles of NH3 react?
How many moles of NH3 are left?
How many moles of O2 react?
How many moles of O2 are left?
How many moles of NO are produced?
How many moles of H2O are produced?
How many moles of each species exit the reactor?

Chet

1. What is the purpose of mass balance in the oxidation of ammonia for nitric acid production?

The purpose of mass balance is to ensure that the amount of each component involved in the reaction remains constant throughout the process. This helps in calculating the theoretical yield and determining the efficiency of the reaction.

2. What are the main inputs and outputs in the mass balance of ammonia oxidation?

The main inputs in the mass balance of ammonia oxidation are ammonia (NH3), oxygen (O2), and water (H2O). The main output is nitric acid (HNO3).

3. How is the mass balance equation for ammonia oxidation derived?

The mass balance equation for ammonia oxidation is derived based on the law of conservation of mass, which states that the total mass of the reactants must be equal to the total mass of the products. This equation is then balanced by adjusting the coefficients to represent the stoichiometric ratio between the reactants and products.

4. What factors can affect the accuracy of mass balance in ammonia oxidation?

The accuracy of mass balance in ammonia oxidation can be affected by factors such as impurities in the reactants, incomplete conversion of reactants, and side reactions that may occur during the process. It is important to use pure reactants and carefully control the reaction conditions to ensure an accurate mass balance.

5. How can the mass balance on ammonia oxidation be used to optimize the production of nitric acid?

The mass balance on ammonia oxidation can be used to optimize the production of nitric acid by identifying the limiting reactant and adjusting the reactant ratios to achieve the maximum theoretical yield. It can also help in identifying any inefficiencies in the process and finding ways to improve the reaction conditions for better yield and efficiency.

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