absorption and adsorption engineer Interview Questions and Answers

1. What is the difference between absorption and adsorption?

   • Answer: Absorption is the process where one substance is taken into the bulk of another substance. Adsorption is the process where a substance adheres to the surface of another substance.

2. Explain the different types of adsorption isotherms.

   • Answer: Common isotherms include Langmuir, Freundlich, and BET isotherms. Langmuir assumes monolayer adsorption, Freundlich describes multilayer adsorption with heterogeneous surfaces, and BET extends Langmuir to multilayer adsorption on homogeneous surfaces. Each isotherm has a specific mathematical equation describing the relationship between adsorbate concentration and adsorption amount.

3. Describe the factors affecting adsorption.

   • Answer: Factors include temperature, pressure (or concentration for liquid-phase adsorption), surface area of the adsorbent, adsorbate-adsorbent interactions (e.g., van der Waals forces, chemical bonding), and the presence of other substances in the system (competitive adsorption).

4. What are some common adsorbents used in industrial processes?

   • Answer: Activated carbon, zeolites, silica gel, alumina, and various polymeric resins are frequently used.

5. Explain the concept of adsorption equilibrium.

   • Answer: Adsorption equilibrium is the state where the rate of adsorption equals the rate of desorption. At equilibrium, the amount of adsorbate on the surface remains constant unless conditions (temperature, pressure, concentration) change.

6. How is the surface area of an adsorbent determined?

   • Answer: Methods include BET (Brunauer-Emmett-Teller) analysis, which uses gas adsorption data to calculate the surface area.

7. What is the role of pore size distribution in adsorption?

   • Answer: Pore size distribution determines which size molecules can access the interior surface of the adsorbent. Microporous materials adsorb smaller molecules preferentially.

8. Explain different types of adsorption processes (e.g., fixed bed, fluidized bed).

   • Answer: Fixed bed adsorption involves a stationary bed of adsorbent through which the fluid flows. Fluidized bed adsorption uses a fluid flow strong enough to suspend the adsorbent particles. Moving bed and simulated moving bed systems are also used for continuous operation.

9. How is adsorption capacity determined experimentally?

   • Answer: Batch or column experiments are conducted where a known amount of adsorbent is contacted with a solution (or gas) of known concentration. The change in concentration after equilibrium is reached determines the adsorption capacity.

10. Describe the process of regeneration of adsorbents.

    • Answer: Regeneration methods include temperature swing adsorption (TSA), pressure swing adsorption (PSA), and purge with steam or other solvents. The goal is to remove the adsorbed material and restore the adsorbent's capacity.

11. What are some industrial applications of absorption?

    • Answer: Absorption is used in gas purification (e.g., scrubbing of SO2 from flue gases), solvent extraction, and various chemical processes.

12. What are some industrial applications of adsorption?

    • Answer: Adsorption is widely used in water purification, air purification, separation of gases, catalysis, and drug delivery.

13. What is Henry's Law and its significance in absorption?

    • Answer: Henry's Law states that the amount of gas dissolved in a liquid is proportional to the partial pressure of the gas above the liquid. It's crucial for predicting gas solubility in absorption processes.

14. Explain the concept of mass transfer in absorption and adsorption.

    • Answer: Mass transfer involves the movement of the adsorbate or solute from the bulk phase to the surface of the adsorbent or into the bulk of the absorbent. This process is influenced by factors like diffusion, convection, and the driving force (concentration or pressure gradient).

15. How do you design an adsorption column for a specific application?

    • Answer: Design involves considering factors like the adsorbate, adsorbent type and properties, flow rate, desired purification level, and regeneration strategy. Modeling and simulation are often used to optimize the column design.

16. What are the challenges in scaling up adsorption processes?

    • Answer: Challenges include maintaining uniform flow distribution, ensuring adequate heat and mass transfer in larger columns, and handling the increased adsorbent volume and regeneration requirements.

17. Discuss the role of thermodynamics in adsorption.

    • Answer: Thermodynamics helps predict the equilibrium conditions for adsorption, determines the feasibility of a process, and helps analyze the energy changes involved.

18. Discuss the role of kinetics in adsorption.

    • Answer: Kinetics describes the rate of adsorption and desorption processes. Understanding kinetics is crucial for optimizing process design and determining the time required to reach equilibrium.

19. What software or tools are commonly used for simulating adsorption processes?

    • Answer: Aspen Adsorption, COMSOL Multiphysics, and various custom codes are commonly used.

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