1. Input + Generation = Output + Consumption
Process Calculations Supplementary Notes Material Balance with Chemical Reactions Dr. Maher Al-Jabari
Think of Environmental applications!
Think of related chemistry topics and Terminology?
Think of Form of material balance equation
Input + Generation = Output + Consumption

2. Review and Definitions
Stoichiometry
Stoichiometric Coefficient / Ratio
Stoichiometry proportions
Limiting Reactant
Excess Reactant
Fractional Excess
Fractional Conversion

3. Reaction Equilibrium Reversibility?
Reversible versus irreversible reactions
Equilibrium
Reaction Yield
Multiple Reactions
Reaction Selectivity

4. Chemical Equation-1 n1 A + n2 B  n3 C + n4 D
Contains qualitative and quantitative information
Stoichiometry: theory of proportions in reactions
What are the stoichiometric coefficients in the above equation?
Stoichiometric Ratio of A/B is n1 / n2
Example
C7H O2  7 CO2 + 8 H2O
Check number of atoms in both sides of the equation – reaction balance?
Stoichiometric Ratio of O2 / C7H16 is /1 = 11
With masses given– change to moles…

5. Chemical Equation-2
Same Example C7H O2  7 CO2 + 8 H2O If a feed contains 1 mole C7H16 of and 11 mole of O2 The reactant present: choose? a) with excess oxygen b) in Stoichiometry proportions c) none of the above  The reaction proceeds to completion = all reactants are consumed I f a feed contains 1 mole C7H16 of and 16 mole of O2 Which is the limiting reactant (run out)? Which is the excess reactant? What is the fractional excess (of the …………. Reactant)?

6. Fractional Excess Same Example C7H16 + 11 O2  7 CO2 + 8 H2O
Fractional Excess of …….. = (16-11)/11
Fractional Excess =
moles of excess reactant in the feed – moles of excess reactant needed to react with all moles of the limiting reactant
moles of excess reactant needed to react with all moles of the limiting reactant

7. Fractional Conversion
Same Example
C7H O2  7 CO2 + 8 H2O
Fractional Conversion f (for incomplete reaction)
f = moles reacted of A
moles fed of A
If the feed contains 10 moles of C7H16 and
if fractional conversion is 80%. What is
The amount of C7H16 reacted =
The amount of C7H16 leaving (unreacted) =

8. Reaction Extent (x) Starting with (moles): 20 + 50 50
Reacted (Known)
Reacted (calculated) / /2
At the end

9. Reaction Extent (x)

10. Try this question at home – Reaction Stoichiometry

16. Reaction Equilibrium
Distinguish between Chemical Equilibrium (final amounts / composition) Reaction Kinetics (Time needed) What is the difference between reversible and irreversible reactions. What is the Equilibrium Constant K = f (Temperature)

17. Equilibrium Calculations
For a sample reaction – extent analysis – x
Given Initial Moles of Reactants (and Products)
Suppose x for reaction
Determine Final (Equilibrium) moles of all– (reactants and products)
Estimate total number of moles
Determine Composition of each reactant and product
Substituting in expression for K
Solve for extent x – and choose the reasonable answer.
Determine number of moles of each reactant and product
Estimate other required variables e.g. fractional conversion
See example 4.6.2
Try this reaction on board

18. Example- Follow on Board in the class
CO is toxic, it can be converted to CH3OH by reaction with hydrogen
For a reactor containing initially equimolar amounts of CO and H2
but no CH3OH, the following reversible reaction occur:
CO + 2 H2 CH3OH
The reaction proceeds till reaching equilibrium, with K = 1.11
Calculate
the molar composition of the components in the final products
The fractional conversion of CO
Solve….
Answers:
X = (& 0.844?) and YCO= 0.5, YH2= …etch
f = 0.156

19. Try this question at home - Reaction Equilibrium
For the reaction At T = 1300 K, K = 0.55

25. Reaction Design aims at
Maximizing rate of desired reaction (1)
Minimizing rate of undesired reactions (2 and 3)
Maximize Profit
Thus, define Yield and Selectivity

26. Yield Definitions may vary:
Moles of desired product / moles of reacted (Fed or consumed)

27. Example- Follow on Board in the class
Given
Fractional conversion of CH4 = 95%
Fractional yield of HCHO = 90%
Determine
Output Compositions
Selectivity of HCHO relative to CO2

28. HW 3 – Mass balance with Reactions

29. Try this question at home -

35. Balance on Atomic and Molecular Species
What are the types of Balances you can make?
Balance on total masses: input = output
Balances on any of the molecules – Form for each?
Input + Generation? = Output + Consumption?
What about balances for H-atoms and C-atoms?
input = output
Atoms can neither be created no destroyed? In a …. Reaction
Hydrogen Balance – H versus H2 balance
Follow example-text in the book
How many moles of C in C2H6?
How many moles of H in C2H6?

36. What about this balance?
Atomic Balances – Simple?

37. What is the type of this balance - Molecular or Atomic Balances?

38. No. of Equations = No. of independent Species?
For non-reactive systems
No. of Equations = No. of independent Species?
Are Oxygen and Nitrogen in air independent species?
Read

39. Analyze Independent Species
The process is
Physical-chemical?

40. Analysis Techniques Mass Balance Problems with Reactions
Three methods
Molecular species balances (approach with no reactions)
Atomic species
Extent of Reaction
Do they lead to SAME results?
Choose the most convenient - which for which?
Based on problem type (or your convenience?)
Cases: one reaction, equilibrium, multiple reactions
See example 4.7.1
Read Sections 4.7 c, d and e – and practice methods

41. Independent Reactions/Equations
Are these 2 equations independent
For Reactive systems:
the degree of freedom analysis must count only independent reactions

42. Molecular Species Balances
Read p.128

43. Atomic Species Balances
Read p.129

44. Extent of Reaction - Balance
Read p.130

45. Follow the book – in three methods
- Notice the common starting steps (for methane and nitrogen)
- Compare simplicity.

46. Combustion Reactions-1
Fuel + O  CO2, CO, H2O & SO2 (NOx at High T) + Heat
Comment on Environment – Energy
Types of Fuel
- Coal - C (with H and S content)
- Fuel Oil
- Natural Gas (mainly CH4)
- Liquefied petroleum gas (e.g. C3H12)
Types of Combustion reactions:
complete versus incomplete (partial) combustion

47. Combustion Reactions-2
Oxygen Supply From air 79% N2 and 21% O2 N2/O2 = 3.76 (dependent species?) Also contains humidity (water vapor). The product gas – Flue gases- Stack gases Dry basis: without including water vapor in calculations Wet basis: with including water vapor in calculations How you convert from given basis to another – Recall conversion between mass and molar composition! See example – can be a quiz See example on combustion

48. Combustion Process Fuel - Expensive Flue gases Combustion Chamber
Limiting air (free) CO2
excess CO
H2O
Theoretical air? N2
%excess air? Unreacted Fuel
NOx (at High T)
SO2 (from sulfur)
Use wet or dry basis
Example – Methane Combustion

49. Combustion Process – Air Supply
Chamber
Fuel Flue gases
air
C  CO and H  H2O

50. Combustion Calculations
Given Find
Fuel and entering air Composition of Flue gases
Composition of Flue gases Find Fuel and air rate, excess ratio
Similar Mass Balance Calculations
Use Molecular Species Balance
Use Atomic Species Balance (more convenient with multiple reactions)

51. Example – Combustion of Ethane – Follow on the board
Find Composition of Flue gases
In class using molecular species balance
At home using atomic species balance

53. If nitrogen is not withdrawn from the system (purged)
At the same rate it enters the process
Where shall it go?

54. HW 4 – Mass balance with Reactions
Read section 4.9 P