Self Assessment Quiz

Q1.1. Decomposition of acetaldehyde represented as CH3CHO = CH4 + CO. This is an irreversible second order reaction. The velocity constant at 5200 C is 0.33 m3/kmol-s. Pure acetaldehyde enters at 5200 C and 1 gmol/hr. The product is withdrawn at a rate sufficient to keep total pressure constant at 1 atm. Calculate the following for an exit conversion of 0.5.  Sourced from Denbigh

Reactor volume space time, in CSTR

Q1.1.2. Reactor volume, space time and actual residence time in PFR

Q1.1.3. Reaction time for a constant volume batch reactor

Q1.1.4. Reaction time for a constant pressure batch reactor


Q1.2. Pure liquid A is fed to a CSTR where it reacts in the liquid phase to form B (liquid) and C (gas). The reaction is elementary with activation energy of 50 kJ/mol. At the temperature of the reaction A has a vapor pressure of 0.1 atm, B is a liquid and C is gas. Gases A and C exit through the top CSTR while liquid A and B exit from bottom. We want 70% conversion of a feed stream 4.54 Kmol/hr of pure A. What is the liquid volume in the reactor?Sourced from Fogler

Hint : Data for Q1.2 :  k = 0.4/ hr, ρA= ρB = 800 kg/m3
P = 1.0 atm, MA = 200, MB = 175, MC = 25

Q1.3. An isothermal constant pressure plug flow reactor is designed to give a conversion of 63.2 percent of A to B for the first order gas phase decomposition A = B for a feed of pure A entering at a rate of 150 lit/hr. At the chosen operating temperature the first order rate constant is 5.0/hr.

After installation it was found that conversion of 92.7 percent is desired conversion was reached. This difference was brought to be due to a zone of intense back mixing. Assuming that this zone behaves like a perfectly mixed stirred tank in series and in between two plug reactors. What fraction of the total reactor volume is occupied by this zone?

Q1.4. You are designing a tubular reactor in which a reaction is taking place between a solid A and a liquid B to form a liquid product C.

A(s) +   B (liq)   =      C( liq)  ,     rB = - k CACB

The reaction takes place in the liquid phase. The solid keeps the liquid saturated with A. The solid particles are carried up the reactor at the same velocity as the liquid .

You do not want unreacted solids in the product. What minimum length of reactor would you specify?

DATA for Q1.4:
Diameter reactor: 30 cm ; Density of solid A : 1.6 g/mL ; Density of liquid: 0.8 g/mL
Solubility of A in liquid: 0.75 gmol / L ; Molecular weight: A = 200, B = 100
Velocity constant k = 0.062 lit/gmol s ;  Liquid flow rate = 280 lit/s  ; Solid rate = 226 kg/s

Q1.5. Bioreactors
Alcoholism is among the major causes of accidents on roads, railways, industries, air traffic etc. The removal of alcohol from the intestinal fluid (CB) into the blood stream (CA) can be modelled as series processes where the rate of absorption of the alcohol into  blood is given as :

r = k (CA – CB) with k = 10/ h

and the rate of physiological elimination of alcohol in blood is by a zero order process with rate of β gram alcohol per unit volume blood fluids per unit time.
Typically a bottle of alcohol contains 120g alcohol which is consumed quickly. Estimate the resting time required for person prior to resuming duty after consuming alcohol if the intestinal fluid   (CB) and blood fluid (CA) are not to contain concentration of alcohol more than 1.0 g/l as required by safety norms. DATA:Volume of blood fluids: 5.0 lit ; Volume of intestinal fluids: 5.0 lit ;Blood fluid β = 0.19 g/lit-hr.  Sourced from Fogler

Q1.6. Natural Bioreactors
The gut volume, gut residence time, body weight and digestion efficiency of two animals are estimated and given below. Study the data and comment on the underlying logic in the design of these natural bioreactors.


W, kg

Gut volume, lit

Residence time, hr












Q1.7. An irreversible first order gas phase reaction A = B is carried out in a packed plug flow reactor . The pressure gradient along the length of the packed bed is constant at
dP/dW = - 0.2 atm/kg
This system gives 86.5 percent conversion. The entering pressure is 20atm and catalyst weight is 60kg. Note as a guide the pressure drop in Metres could be typically 50-150 (v**2/2g). Sourced from Fogler.

Q1.7.1. If a CSTR in which there is no pressure drop is used, what is the conversion expected?

Q1.7.2. If packed bed pressure drop is neglected what is the conversion?