October 19, 2019, 06:24:01 AM
Forum Rules: Read This Before Posting


Topic: Chemical process calculations  (Read 446 times)

0 Members and 1 Guest are viewing this topic.

Offline Seeeker

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +0/-0
Chemical process calculations
« on: August 07, 2019, 07:52:48 AM »
Q4.40, what's bothering me is what's the contribution and relation of NO in the reaction and how to take it into consideration in calculations, also is air is supplied separately also besides NH3-Air mixture?
I have submitted my attempt also and the answer is wrong!
Ans of problem is a) 1511.9 kg/h
b) 20086.5kg/h

Offline chenbeier

  • Full Member
  • ****
  • Posts: 608
  • Mole Snacks: +56/-14
  • Gender: Male
Re: Chemical process calculations
« Reply #1 on: August 07, 2019, 08:58:22 AM »
First: If you post pictures here take care they are not up side down. Not everybody has a tablet.

You have to create two equations:

1. NH3 get oxidiesed to NO with yield I
2. NO get  converted to HNO3 with yield II

Also in your calculation I think you use wrong molar weight for HNO3. It is 63 g/mol and not 36 g/mol.

Offline Seeeker

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +0/-0
Re: Chemical process calculations
« Reply #2 on: August 08, 2019, 03:33:45 AM »
Thank you for your reply and sorry for the upside down image!
I have written down the two reactions and got the answer but in the formula of yield% in the denominator the main component(NH3) totally reacted should have been the same but to get the answer I got two NH3 totally reacted is there another formula of yield, that should be written here please,let me know if any.

Offline chenbeier

  • Full Member
  • ****
  • Posts: 608
  • Mole Snacks: +56/-14
  • Gender: Male
Re: Chemical process calculations
« Reply #3 on: August 08, 2019, 04:02:27 AM »
The calculation looks good.

One hint you can also calculate how you started. But you have to use both yields.

5000 kg *17/63 = 1350 kg. Then 1350 kg/(0.92*0.97) =1511,9 kg NH3

Your question I don't understand where you get 2 NH3?

In the last line I also dont understand  21598 *57 *0,93 = 20086,5

Probably you have also to calculate the oxygen consumption and from this the air consumption. Air contain 21% Oxygen.
« Last Edit: August 08, 2019, 04:14:34 AM by chenbeier »

Offline Seeeker

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +0/-0
Re: Chemical process calculations
« Reply #4 on: August 08, 2019, 05:02:30 AM »
1) I meant as you know the formula of yield% for this problem will be
Yield of NO= kg of NH3 reacted to
                        produce NO/ kg NH3
                        totally reacted
Yield of HNO3= kg of NH3 reacted to
                            produce HNO3/kg of NH3
                             totally reacted
So in the solution you notice I have calculated "NH3 totally reacted" two times but isn't it should be the same for both reactions? Since it's total reacted quantity. So I was asking what formula do you use for calculation of yield?
2) And I see that shortcut method but how am I suppose to know I have to divide theoretical quantity of NH3 by both of the yield?
3)In the last line I have calculated the air consumption so, first I calculated total mixture of air and ammonia( by diving the ammonia consumed by mass fraction of ammonia) then multiplied it by mass fraction of air( given in the problem).
And I was wondering is it possible to calculate the oxygen consumption from the reactions I calculated it from the reactions  but it was wrong maybe I wasn't doing correctly or it is not possible since we don't know amount of ammonia supplied?

Offline chenbeier

  • Full Member
  • ****
  • Posts: 608
  • Mole Snacks: +56/-14
  • Gender: Male
Re: Chemical process calculations
« Reply #5 on: August 08, 2019, 05:09:38 AM »
Quote
Yield of HNO3= kg of NH3 reacted to
                            produce HNO3/kg of NH3
                             totally reacted

No this is Yield of HNO3= kg of NO reacted to
                            produce HNO3/kg of NO
                             totally reacted
Check
https://en.wikipedia.org/wiki/Ostwald_process

By the way your chemical equations have also still some calculation error.
« Last Edit: August 08, 2019, 05:24:17 AM by chenbeier »

Offline Seeeker

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +0/-0
Re: Chemical process calculations
« Reply #6 on: August 18, 2019, 01:09:57 PM »
Yes, the reaction I wrote was not correct exactly for the calculation and I was writing the wrong formula of yield for HNO3 since the reaction was not correct! So I rewrote the equations and solved it. But this time it's quite lengthy. I hope the procedure I followed is correct as my answer is matched with the textbook.
Thank you for the reference and pointing out the mistakes. You helped a lot. And please check if my procedure is correct.

Sponsored Links