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### Topic: SO2 to SO3 conversion calculations  (Read 29031 times)

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#### maabdolat

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•   • Posts: 16
• Mole Snacks: +0/-4 ##### SO2 to SO3 conversion calculations
« on: July 21, 2012, 08:25:49 PM »
Hi…..
The conversion of SO2 to SO3 in Catalytic converter is based on equation below:
SO2  +  ½ O2 -------> SO3
I got problem in finding SO3 moles, kindly help me…
Details of reaction are following;

Temperature: 688 K
Pressure : 1 atm
Total Number of Moles : 408 Kmoles
Moles of SO2 : 46.97  Kmoles
Moles of O2: 38.39   Kmoles
Kp =  397
(value calculated from Bodenstein equation
Log Kp = 5186.5/T + 0.611 * log T – 6.75
Temperature is in K. The above calculated value was verified from book “Process industries by Norris Shrieve, page 333”

Kindly tell me in detail , how to calculate SO3 moles…..

Regards,

#### Bublik

• Regular Member
•   • Posts: 48
• Mole Snacks: +5/-1 ##### Re: SO2 to SO3 conversion calculations
« Reply #1 on: July 21, 2012, 09:00:09 PM »
Is this reaction assuming 100% yield? If so, I don't see why you need the temperature, pressure and all that. Just use simple stoichiometry (keep in mind that there may be a limiting factor).

#### maabdolat

• Regular Member
•   • Posts: 16
• Mole Snacks: +0/-4 ##### Re: SO2 to SO3 conversion calculations
« Reply #2 on: July 22, 2012, 06:31:15 AM »
let me explain dear....

i am working on Sulphuric acid plant, in which conversion of SO2 to SO3 takes place in a catalytic converter with 3 beds, each bed has its conversion efficiency...

1st bed. 56%
2nd bed. 28%
3rd bed. 9.5%

1st Bed                2nd Bed                        3rd Bed
IN            OUT              IN            OUT            IN            OUT
N2   304.231   304.231   304.231   304.231   304.231   304.231
SO2   46.159   20.310   20.310   7.386     7.386            3.000
SO3   0.000             ?                ?               ?               ?              ?
O2   34.712   21.787   21.787   15.325   15.325   13.132

Total 385.102   372.177   372.177   365.715   365.715   363.523
(KMoles)

---------------------------------------------------------------------

Temp.(K)       Kp
688         323
713         185
698         261

ref: Process industries by Norris Shrieve, page 333
-------------------------------------------------------

So, my question is how to find Number of Kmoles of SO3 in each bed? what equation should be used. kindly help me out..

regards,

#### discodermolide ##### Re: SO2 to SO3 conversion calculations
« Reply #3 on: July 22, 2012, 07:15:41 AM »
let me explain dear....

i am working on Sulphuric acid plant, in which conversion of SO2 to SO3 takes place in a catalytic converter with 3 beds, each bed has its conversion efficiency...

1st bed. 56%
2nd bed. 28%
3rd bed. 9.5%

1st Bed                2nd Bed                        3rd Bed
IN            OUT              IN            OUT            IN            OUT
N2   304.231   304.231   304.231   304.231   304.231   304.231
SO2   46.159   20.310   20.310   7.386     7.386            3.000
SO3   0.000             ?                ?               ?               ?              ?
O2   34.712   21.787   21.787   15.325   15.325   13.132

Total 385.102   372.177   372.177   365.715   365.715   363.523
(KMoles)

---------------------------------------------------------------------

Temp.(K)       Kp
688         323
713         185
698         261

ref: Process industries by Norris Shrieve, page 333
-------------------------------------------------------

So, my question is how to find Number of Kmoles of SO3 in each bed? what equation should be used. kindly help me out..

regards,

Surely you use the balanced reaction equation for each bed.
I assume the conversion efficiency = the yield.
Therefore you have, in the first bed a 56% yield of SO3, this gives you the Kmoles of SO3 and the Kmoles of SO2 going into the second bed, use the reaction equation again, with 28% yield, this gives you the Kmoles of SO2 and the Kmoles of SO3 produced going into the third bed. Work out the Kmoles of SO3 produced. Then add them all up and you have the total SO3.
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#### maabdolat

• Regular Member
•   • Posts: 16
• Mole Snacks: +0/-4 ##### Re: SO2 to SO3 conversion calculations
« Reply #4 on: July 22, 2012, 09:43:04 AM »
neglect conversion efficiencies, if dont have converter each bed efficiency then what will be method to find SO3 conversion in each bed....?

#### discodermolide ##### Re: SO2 to SO3 conversion calculations
« Reply #5 on: July 22, 2012, 09:50:57 AM »
neglect conversion efficiencies, if dont have converter each bed efficiency then what will be method to find SO3 conversion in each bed....?

You cannot neglect the conversion efficiency. If I am correct you will get the wrong answer if you do. Or do you want the theoretical yield.
In any case just use the reaction equation, if you neglect the conversion; in the first step all the SO2 will be converted to SO3 in that case the second and third bed don't matter for the calculation because there is no more SO2 available to react.
Development Chemists do it on Scale, Research Chemists just do it!
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#### maabdolat

• Regular Member
•   • Posts: 16
• Mole Snacks: +0/-4 ##### Re: SO2 to SO3 conversion calculations
« Reply #6 on: July 22, 2012, 01:59:41 PM »
ok... if i dont neglect conversion efficiencies, then tell me two things;

1). equation to find No. of moles of SO3 in each bed?

2). What is the equation to find conversion efficiency of SO3 with temperature?  (-- graph b/w %conversion & temperature is available in many sites, but equation is not available..

at page#12

at page# 3-4

at page#4
« Last Edit: July 23, 2012, 01:55:54 PM by Borek »

#### discodermolide ##### Re: SO2 to SO3 conversion calculations
« Reply #7 on: July 23, 2012, 12:41:35 AM »
ok... if i dont neglect conversion efficiencies, then tell me two things;

1). equation to find No. of moles of SO3 in each bed?

2). What is the equation to find conversion efficiency of SO3 with temperature?  (-- graph b/w %conversion & temperature is available in many sites, but equation is not available..

at page#12

at page# 3-4

at page#4

Don't know about any equation for conversion efficiency with temperature.
I get the following results which may be wrong, I assume the temperature in each bed is similar.
1 bed, SO2 in 46.159, at 56% conversion gives 25.849 SO3
2 bed 44% SO2 left = 20.310, at 28% conversion gives 5.687 SO3
3 bed 28% of bed two SO2 left = 5.686, at 9.5% conversion gives 0.50 SO3

Total SO3 = 32.076Kmoles

Development Chemists do it on Scale, Research Chemists just do it!
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#### maabdolat

• Regular Member
•   • Posts: 16
• Mole Snacks: +0/-4 ##### Re: SO2 to SO3 conversion calculations
« Reply #8 on: July 23, 2012, 03:30:58 AM »
what equation u used for calculation? tell me

#### discodermolide ##### Re: SO2 to SO3 conversion calculations
« Reply #9 on: July 23, 2012, 03:34:44 AM »
what equation u used for calculation? tell me

The reaction:
SO2 + 1/2O2 SO3
Development Chemists do it on Scale, Research Chemists just do it!
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#### maabdolat

• Regular Member
•   • Posts: 16
• Mole Snacks: +0/-4 ##### Re: SO2 to SO3 conversion calculations
« Reply #10 on: July 23, 2012, 08:45:32 PM »
hi...

i am not still getting clear picture....
again explaining my problem,

1.SO2 is converted to SO3 in Catalytic converter, in 4 stages....

SO2 + 1/2O2 SO3

According to reaction equation,

Kp = PSO3/(PSO2 x PO21/2)

---------------------------------------------------------------------

Temp.(K)       Kp
688             323
713             185
698             261

ref: Process industries by Norris Shrieve, page 333
-------------------------------------------------------

Inlet composition of reactor and efficiency of each stage is known, so no. of moles in each stage of SO2,O2 and SO3 can be calculated up to 3 stages.

Beds Efficiencies are given below;
1st bed. 56%
2nd bed. 28%
3rd bed. 9.5%
4th bed. 6%

Beds Inlet Temperature are given below;
1st bed. 688k
2nd bed. 713K
3rd bed. 713K
4th bed. 698K

Composition of 1-3 beds are given below;

1st Bed                       2nd Bed                      3rd Bed
IN          OUT              IN          OUT              IN            OUT
-----------------------------------------------------------------------
N2     304.231   304.231      304.231     304.231        304.231      304.231
SO2   46.159     20.310       20.310       7.386           7.386         3.000
SO3   0.000      25.849   25.849       38.774     38.774     43.159
O2     34.712     21.787       21.787       15.325          15.325      13.132
------------------------------------------------------------------------

Total 385.102   372.177      372.177     365.715          365.715   363.523
(KMoles)

4th bed composition can not calculated by me, because after 3rd pass there is an Inter-Absorber which absorbs SO3 formed upto 3rd stage,as equilibrium is achieved.

so, to convert remaining SO2 to SO3 , an absorber is placed to disturb equilibrium, and convert remaining SO2 to SO3.

Here i have two question;

1. How to calculate no. of moles of SO3 absorbed in absorber?
2. How to calculate no. of moles of SO3 in 3rd stage, where equilibrium is established using Kp equation ?

These are my two problems , hop u understand for any confusion, plz ask.... but help me in these two problems....

regards,

#### discodermolide ##### Re: SO2 to SO3 conversion calculations
« Reply #11 on: July 24, 2012, 12:34:30 AM »
Composition of 1-3 beds are given below;

1st Bed                       2nd Bed                      3rd Bed
IN          OUT              IN          OUT              IN            OUT
-----------------------------------------------------------------------
N2     304.231   304.231      304.231     304.231        304.231      304.231
SO2   46.159     20.310       20.310       7.386           7.386         3.000
SO3   0.000      25.849   25.849       38.774     38.774     43.159
O2     34.712     21.787       21.787       15.325          15.325      13.132
------------------------------------------------------------------------

Total 385.102   372.177      372.177     365.715          365.715   363.523
(KMoles)

4th bed composition can not calculated by me, because after 3rd pass there is an Inter-Absorber which absorbs SO3 formed upto 3rd stage,as equilibrium is achieved.

so, to convert remaining SO2 to SO3 , an absorber is placed to disturb equilibrium, and convert remaining SO2 to SO3.

Here i have two question;

1. How to calculate no. of moles of SO3 absorbed in absorber?
2. How to calculate no. of moles of SO3 in 3rd stage, where equilibrium is established using Kp equation ?

These are my two problems , hop u understand for any confusion, plz ask.... but help me in these two problems....

regards,

[/quote]

I don't get this,surely the number of moles SO3 going into the absorber is 43.159.
and the number of moles in the third stage is what? The amount formed in the reaction or the total?
I'm not a chemical engineer but this makes no sense at all!
Development Chemists do it on Scale, Research Chemists just do it!
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#### maabdolat

• Regular Member
•   • Posts: 16
• Mole Snacks: +0/-4 ##### Re: SO2 to SO3 conversion calculations
« Reply #12 on: July 24, 2012, 03:51:56 AM »
hi....

how did you calculated no. of moles of SO3 absorbed? show me calculation steps?

and second question is regarding Kp equation , see equation and tell me where this equation is used to find no. of moles?
regards,

#### discodermolide ##### Re: SO2 to SO3 conversion calculations
« Reply #13 on: July 24, 2012, 05:16:45 AM »

1st Bed                       2nd Bed                      3rd Bed
IN          OUT              IN          OUT              IN            OUT
-----------------------------------------------------------------------
N2     304.231   304.231      304.231     304.231        304.231      304.231
SO2   46.159     20.310       20.310       7.386           7.386         3.000
SO3   0.000      25.849   25.849       38.774     38.774     43.159
O2     34.712     21.787       21.787       15.325          15.325      13.132
------------------------------------------------------------------------

I don't get this,surely the number of moles SO3 going into the absorber is 43.159.
and the number of moles in the third stage is what? The amount formed in the reaction or the total?
I'm not a chemical engineer but this makes no sense at all!

[/quote]

The amount going into the absorber is in your table, 43.259 Kmoles.
I do not see that the Kp equation has anything to do with it.
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

#### maabdolat

• Regular Member
•   • Posts: 16
• Mole Snacks: +0/-4 ##### Re: SO2 to SO3 conversion calculations
« Reply #14 on: July 24, 2012, 02:02:11 PM »
hi....

i want to calculate no. of moles absorbed in absorber which is after 3rd bed..