This set of Bioseparation Technology Multiple Choice Questions & Answers (MCQs) focuses on “Equilibrium, Rate Processes & Mass Transfer”.

1. The equilibrium established by the transfer of species from one zone to another across the interface can be defined in terms of ____________

a) Chemical potential, concentration

b) Temperature, electric potential

c) Temperature, concentration

d) Concentration, electric potential

View Answer

Explanation: The chemical potential and the concentration define the equilibrium which is established by the transfer of species from one zone to another across the interface. At equilibrium many separation processes ends and these type of process are called equilibrium processes.

2. Which separation processes are referred to as equilibrium processes?

a) Filtration

b) Liquid-liquid extraction

c) Sedimentation

d) Adsorption

View Answer

Explanation: Bioseparation processes like liquid-liquid extraction of penicillin G from the fermentation broth to methyl isobutyl ketone are referred to as equilibrium processes as it stops once equilibrium is achieved. The reaction stops at equilibrium because it is the state at which the reactants and the products reaches same concentration and it will not change with time therefore, there will be no observable change in the properties of the system.

3. What is referred to as a rate processes?

a) Rate processes and equilibrium processes are same

b) Delayed equilibrium is observed in rate processes

c) Rate processes are the non-equilibrium process

d) There is no concept of rate processes

View Answer

Explanation: The rate processes are the non-equilibrium processes in which no identifiable equilibrium is reached in a specific chemical reaction and the concentration of the reactant and product is maintained throughout the process.

4. Which bioseparation process is referred to as rate processes?

a) Filtration

b) Liquid-liquid extraction

c) Reverse osmosis

d) Haemodialysis

View Answer

Explanation: Haemodialysis is the process which is referred as an example of rate process in which the concentration of the reactants and the products is maintained throughout the reaction process. It is a rate determining process in which the rate of change of concentration of the reactants and products are maintained without the equilibrium state.

5. Which coefficient can be determined using numerical correlations on the basis of heat-mass transfer analogy?

a) Mass transfer coefficient

b) Heat transfer coefficient

c) Diffusivity coefficient

d) Phase change coefficient

View Answer

Explanation: Mass transfer coefficient can be determined using the numerical correlations on the basis of heat-mass transfer analogy. It includes dimensionless group of correlations. It is a rate constant of diffusion which relates the rate of mass transfer with area of mass transfer as well as the rate of change of concentration of the reactants.

6. Which dimensionless numbers are correlated to the mass transfer coefficient?

a) Marangoni number, Sherwood number, Schmidt number

b) Reynolds number, Sherwood number, Schmidt number

c) Nusselt number, Sherwood number, Schmidt number

d) Reynolds number, Marangoni number, Nusselt number

View Answer

Explanation: Reynolds number, Sherwood number, Schmidt number are the group of dimensionless quantities which are involved in the estimation of mass transfer coefficient. Schmidt number is the ratio of momentum diffusivity and mass diffusivity which is used in characterization of flow of liquid involving mass diffusion process. Reynolds number is the ratio of inertial forces and viscous force which is used to estimate the type of fluid flow involving mass transfer.

7. What is the equation for mass transfer coefficient depending on the dimensionless numbers?

a) N_{sh} = a N_{Re}^{b} N_{Sc}^{c}

b) N_{Re} = a N_{Sh}^{b} N_{Sc}^{c}

c) N_{Sc} = a N_{Re}^{b} N_{Sh}^{c}

d) N_{sh} = a N_{Sc}^{b} N_{Re}^{c}

View Answer

Explanation: The equation for mass transfer coefficient depending on the dimensionless number is N

_{sh}= a N

_{Re}

^{b}N

_{Sc}

^{c}where, N

_{sh}is Sherwood number and N

_{sh}= \(\frac{k_A d}{D}\) d is the diameter of tube, k

_{A}is the mass transfer coefficient, D is the solute diffusivity. N

_{Re}is the Reynolds number and N

_{Re}= \(\frac{du\rho}{\mu}\) u is the velocity of flowing liquid, μ is the viscosity of the solution and ρ is the density. N

_{Sc}is the Schmidt number and N

_{Sc}= \(\frac{\mu}{\rho D}\), a, b, c are the constants.

8. How can you determine the mass transfer coefficient of a solute in flowing liquid?

a) Unsteady state experiments based on N_{A} = k_{A} Δc_{A}

b) Steady state experiments based on N_{A} = k_{A} Δc_{A}

c) Steady state experiments

d) Unsteady experiments

View Answer

Explanation: The mass transfer coefficients of a solute in a flowing liquid can be estimated by performing steady state experiments based on N

_{A}= k

_{A}Δc

_{A}. It will help in maintaining the equilibrium of reaction so that the rate of reactions will be same and the values when used in the equation will help in determination of the mass transfer coefficient.

9. Why the general approach is used in the experiments of mass transfer coefficient?

a) To measure the solubility

b) To measure the diffusivity

c) To measure the transferred amount of solutes

d) To measure the mass transfer area

View Answer

Explanation: The general approach is used in the experiments of mass transfer coefficient to estimate the transferred amount of solutes which are transferred across the surface area at a given time for a specific concentration difference across the transfer zone.

10. Solute mass transfer coefficient in a liquid which is flowing in a tube cannot be estimated by coating the solute over the inner wall of the tube.

a) True

b) False

View Answer

Explanation: Solute mass transfer coefficient in a liquid which is flowing in a tube can be estimated by coating the solute over the inner wall of the tube. It should be followed by measuring the amount of solute removed, so that exact amount of solute transfer can be determined without any loss of solute concentration.

11. How will you calculate the average flux across the mass transfer zone?

a) N_{A} = \(\frac{am}{t}\)

b) N_{A} = \(\frac{m}{at}\)

c) N_{A} = \(\frac{m}{a \Delta t}\)

d) N_{A} = \(\frac{\Delta tm}{a}\)

View Answer

Explanation: The average flux across the mass transfer zone can be calculated using N

_{A}= \(\frac{m}{a \Delta t}\) where, Δt is the time taken by the solute to transfer from one are to another, m is the amount of solute being transferred during the mass transfer process, a is the area covered during the mass transfer. By combining this equation with the equation used in estimation of mass transfer coefficient, the equation obtained is k

_{A}= \(\frac{m}{a\Delta t \Delta c_A}\).

12. Calculate its average molar flux and the mass transfer coefficient of the benzoic acid when a liquid is flowing past one of the rectangular sides of a slab containing benzoic acid and the surface area which is exposed to liquid is 0.01 m^{2} the estimated time required for the transfer is 600 seconds, the amount of benzoic acid lost by dissolution is 5 x 10^{-4} kg. (Given: molecular weight of benzoic acid is 121.1 kg/kg-mol and the solubility of benzoic acid in water are 0.2 kg/m^{3}.

a) 4.17 × 10^{-4} kg-moles/m^{2} s and 6.9 × 10^{-7} m/s

b) 4.17 × 10^{-7} kg-moles/m^{2} s and 6.9 × 10^{-4} m/s

c) 6.9 × 10^{-4} kg-moles/m^{2} s and 4.17 × 10^{-7} m/s

d) 6.9 × 10^{-7} kg-moles/m^{2} s and 4.17 × 10^{-4} m/s

View Answer

Explanation: For the calculation of average molecular flux – m = \(\frac{5 × 10^{-4}}{121.1}\) kg-moles = 4.13 × 10

^{-6}kg-moles, since N

_{A}= \(\frac{m}{a\Delta t}\) ∴ N

_{A}= 6.9 × 10

^{-7}kg-moles/m

^{2}s. The concentration difference across the transfer zone is Δc = \(\frac{0.2}{121.1}\) kg – \(\frac{moles}{m^3}\) = 1.65 × 10

^{-3}kg – \(\frac{moles}{m^3}\) and the mass transfer coefficient is k

_{A}= \(\frac{m}{a\Delta t \Delta c_A}\) = \(\frac{4.13 × 10^{-6}}{0.01 × 600 × 1.65 × 10^{-3}} \frac{m}{s}\) ∴ k

_{A}= 4.17 × 10

^{-4}m/s.

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