Chemical Engineering

1. FAQ on PROCESS CALCULATION
Prepared by- Mr. Vishal B. Thakare
(M.Tech Chemical, SVNIT Surat)
Assistant Professor, PARUL UNIVERSITY
Vadodara
vishalbt88@gmail.com

2. Gram mole-
It is the ratio of weight in gram of substance to molecular weight of
substance.
Weight in gram of substance B
Molecular weight of substance B
Normality-
It is defined as the number of gram equivalent of solute dissolved in
one liter of solution.
gram equivalent of solute
Volume of solution in liter
Mass in gram of substance
Equivalent weight of substance
Gram moles of compound B =
Normality (N) =
gram equivalent of solute =

3. Molarity-
It is defined as the number of gram moles of solute dissolved in one
liter of solution.
gram moles of solute
Volume of solution in liter
Molality-
It is defined as the number of gram moles of solute dissolved in one
kilogram of solvent.
gram moles of solute
mass of solvent in Kg
Molarity =
Molality =

4. Stoichiometric Equation-
It indicate theoretical moles of reactant and product.
Ex. CO + 2H2 CH3OH
From Stoichiometry of reaction
1 Kmol CO = 1Kmol CH3OH = 2Kmol H2
28 Kg CO = 32 Kg CH3OH = 2 Kg H2
Limiting Reactant-
It is reactant that disappear first during course of reaction. It is always
present in less than its stoichiometric proportion.

5. Excess Reactant-
It is defined as the reactant which present in excess of its theoretical or
stoichiometric requirement.
It is specified in terms of % excess.
Moles of B fed – Moles of B theoretically required
* 100
Moles of B theoretically required
Ex. Consider the reaction SO2 + O.5 O2 SO3
If 100 mol SO2/hr. and 75 mol O2/hr. are fed to reactor then
75-50
50
= 50
% excess of B =
% excess of O2 = *100

6. Conversion-
It is the ratio of amount of reactant reacted to the amount of reactant
charged or fed to the reactor.
moles of A reacted
moles of A charged or fed to reactor
Yield-
It is the ratio of moles of reactant reacted to produce desired product to
the total moles of reactant reacted.
Consider the reaction
A C (desired product)
A D (undesired product)
% conversion of A = *100

7. moles of A reacted to produce C
Total moles of A reacted
Selectivity –
Selectivity is the ratio of moles of desired product formed to the moles
of undesired product formed.
moles of desired product formed (C)
moles of undesired product formed (D)
* 100
Yield of C =
Selectivity =

8. Recycle Operation-
To obtain desired concentration product, product stream again recycled
to the feed stream.
Recycle ratio = R/F

9. Ex.
In distillation operations, a part of the distillate is fed back to column
to enrich the product, so that almost pure product can be obtained.
In drying operations, a major portion of the hot air leaving the dryer
is recirculated to conserve heat to utilize the heat being lost in the
exit air.

10. By Pass Operation-
To obtain desired concentration product, some of feed is directly
connect to product stream.
Purge Stream-
Presence of impurities in mixed feed beyond certain limit may lead to
decrease in conversion or may favor side reaction. In such cases
accumulation of inerts or impurities can be avoided by blending off/
purging fraction of recycle feed.
By pass stream
Process Unit Product
Feed

11. Recycle Feed R
Fresh
Feed F
Mixed
Feed M
Purge P
Product
SeparatorReactor
Purge ration = P/R
Purge ratio based on any component ‘A’ = ‘A’ in purge/ ‘A’ in recycle
feed

12. Combustion-
The rapid reaction of fuel with oxygen is called combustion.
When fuel burned, the carbon in the fuel reacts to form CO2 or CO,
hydrogen reacts to form H2O and Sulphur reacts to form SO2.
A combustion reaction in which CO is formed is referred as partial or
incomplete combustion.

13. EXERCISE
1) Define a) Heat capacity
b) Heat of formation
c) Heat of combustion
d) Proximate analysis of coal
e) Ultimate analysis of coal
2) State the Ideal gas law.