Unit Operation: Filtration theory – pressure, vacuum and centrifugal methods MCQs With Answer

Unit Operation: Filtration theory – pressure, vacuum and centrifugal methods MCQs With Answer

This collection of 20 multiple-choice questions is designed for M.Pharm students studying MPC 204T Pharmaceutical Process Chemistry. The questions explore filtration theory in depth, covering cake and medium resistance, Darcy’s law, compressible vs incompressible cakes, constant-rate and constant-pressure filtration, selection criteria for vacuum and pressure filtration, filter aids, washing and cake handling, and centrifugal separation types and design considerations. Each item tests conceptual understanding, mathematical relationships, equipment selection, and practical operational parameters encountered in pharmaceutical production. Use these MCQs for self-assessment, exam preparation, and deeper insight into filtration processes used in drug manufacture.

Q1. Which equation fundamentally describes the flow of liquid through a porous cake and filter medium under laminar conditions?

• Stokes’ law
• Darcy’s law
• Navier–Stokes equations
• Hagen–Poiseuille equation

Correct Answer: Darcy’s law

Q2. In cake filtration, the total resistance to flow is the sum of which two resistances?

• Viscous resistance and inertial resistance
• Filter medium resistance and interfacial resistance
• Filter medium resistance and cake resistance
• Pore resistance and membrane resistance

Correct Answer: Filter medium resistance and cake resistance

Q3. Specific cake resistance (α) depends primarily on which properties of the cake?

• Permeability and cake porosity
• Solubility and density of the filtrate
• Surface tension and contact angle
• Electrical charge and zeta potential

Correct Answer: Permeability and cake porosity

Q4. For incompressible cakes under constant pressure filtration, the filtration volume V varies with time t according to which relationship?

• V ∝ t^2
• t/V = At + B (linear in t/V versus t)
• V ∝ ln(t)
• t ∝ V^2

Correct Answer: t/V = At + B (linear in t/V versus t)

Q5. A compressible cake typically shows what behavior when differential pressure is increased?

• Cake permeability increases due to pore expansion
• Cake compresses, decreasing porosity and permeability
• Specific resistance remains constant
• Filtrate viscosity decreases

Correct Answer: Cake compresses, decreasing porosity and permeability

Q6. Which filter aid is commonly used in pharmaceuticals to improve filtrate clarity and prevent blinding?

• Sodium chloride
• Activated carbon
• Diatomaceous earth (celite)
• Cellulose acetate

Correct Answer: Diatomaceous earth (celite)

Q7. In vacuum filtration compared to pressure filtration, what is a primary limitation that often reduces filtration rate?

• Higher allowable differential pressure across the cake
• Lower achievable differential pressure due to absolute vacuum limits
• Excessive heating of the cake
• Inability to use filter aids

Correct Answer: Lower achievable differential pressure due to absolute vacuum limits

Q8. Which of the following is a characteristic advantage of pressure (pressure-driven) filters in pharmaceutical production?

• Suitable only for low-viscosity fluids
• Limited to batch operation
• Can achieve higher differential pressures and faster filtration
• Always produces higher micron-level clarity than vacuum filters

Correct Answer: Can achieve higher differential pressures and faster filtration

Q9. In centrifugation, which device is best suited for continuous separation of relatively large solids from liquids in slurry with moderate solids concentration?

• Batch Nutsche filter
• Decanter centrifuge
• Plate and frame filter press
• Rotary drum vacuum filter

Correct Answer: Decanter centrifuge

Q10. The Kozeny–Carman equation relates permeability to which combination of parameters?

• Particle size, porosity, and specific surface area
• Temperature, viscosity, and density
• Filtrate conductivity and ionic strength
• Filter medium tensile strength and thickness

Correct Answer: Particle size, porosity, and specific surface area

Q11. In a plate-and-frame filter press, an effective practice to improve cake washing is to:

• Increase feed solids concentration without changing wash volume
• Use counter-current washing or staged washes
• Reduce wash solvent volume to minimize dissolution
• Apply only vacuum during washing

Correct Answer: Use counter-current washing or staged washes

Q12. Which parameter is most directly improved by adding a filter aid like diatomaceous earth to a slurry before filtration?

• Solubility of the active ingredient
• Electrical conductivity of the filtrate
• Permeability of the precoat and cake, preventing blinding
• Thermal stability of the slurry

Correct Answer: Permeability of the precoat and cake, preventing blinding

Q13. For a rotary vacuum drum filter, which factor does NOT directly influence filtrate flow through the cake?

• Drum rotational speed
• Cake thickness
• Ambient humidity
• Vacuum level inside the drum

Correct Answer: Ambient humidity

Q14. Which of the following best describes the principle behind a basket centrifuge used in pharmaceuticals?

• Filtrate passes through a membrane under transmembrane pressure
• Rotational centrifugal force separates solids which form a cake on the basket wall
• Gas flow moves solids against a porous cloth for separation
• Filtrate flows radially by gravitational settling

Correct Answer: Rotational centrifugal force separates solids which form a cake on the basket wall

Q15. When designing filtration for a high-viscosity slurry, which change will most improve filtration rate?

• Decrease differential pressure
• Increase filtrate viscosity further
• Raise temperature to reduce viscosity
• Reduce particle size to submicron uniformly

Correct Answer: Raise temperature to reduce viscosity

Q16. The term “blinding” in filtration refers to:

• Cake collapse under excessive pressure
• Clogging of filter medium pores by fine particles or precipitates
• Spontaneous filtration of air through the cake
• Complete removal of all solids from the slurry

Correct Answer: Clogging of filter medium pores by fine particles or precipitates

Q17. In a constant-rate filtration test, what is held constant to permit determination of cake resistance and medium resistance?

• Filtrate flow rate (Q)
• Differential pressure (ΔP)
• Temperature
• Filtrate viscosity

Correct Answer: Filtrate flow rate (Q)

Q18. Which centrifuge type provides efficient washing of cake with minimal re-suspension and is often used for pharmaceuticals requiring sterile or contained operation?

• Decanter centrifuge
• Hydrocyclone
• Peeler (discharge) basket centrifuge
• Rotary vacuum drum

Correct Answer: Peeler (discharge) basket centrifuge

Q19. Which statement about filter medium selection in pharmaceutical processes is TRUE?

• One material fits all: stainless steel is always best
• Selection depends on chemical compatibility, particle size, cake release, and cleaning requirements
• Porosity is irrelevant if a filter aid is used
• Only non-woven fabrics are permitted in production

Correct Answer: Selection depends on chemical compatibility, particle size, cake release, and cleaning requirements

Q20. During pressure filtration, what is the main effect of increasing feed solids concentration while keeping other parameters constant?

• Filtration time per unit mass decreases due to thinner cakes
• Specific cake resistance always decreases
• Volume of filtrate per batch decreases, and cake thickness increases, often slowing filtration
• Viscosity of filtrate becomes negligible

Correct Answer: Volume of filtrate per batch decreases, and cake thickness increases, often slowing filtration

Download