Theories of filtration MCQs With Answer is an essential resource for B. Pharm students preparing for exams in unit operations and pharmaceutical process engineering. This concise, keyword-rich guide covers core filtration concepts—Darcy’s law, cake filtration equations, specific cake resistance, compressible vs incompressible cakes, Kozeny–Carman relationships, filter media and precoat techniques—presented as targeted multiple-choice questions with answers. Each question is crafted to deepen understanding of pharmaceutical filtration theory, practical factors affecting filtration rate, and selection of filtration equipment like filter presses, rotary vacuum filters, and Nutsche filters. Use these MCQs to strengthen theoretical knowledge and problem-solving skills. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What fundamental law relates the volumetric flow rate through a porous medium to pressure drop, viscosity, and medium permeability?
- Darcy’s law
- Fick’s law
- Henry’s law
- Kozeny–Carman equation
Correct Answer: Darcy’s law
Q2. In cake filtration, the cake resistance is directly proportional to which property of the cake?
- Cake porosity
- Specific cake resistance
- Surface tension
- Filter medium thickness
Correct Answer: Specific cake resistance
Q3. The cake filtration equation for constant pressure filtration predicts a relationship between filtration time t and filtrate volume V that is:
- Linear (t proportional to V)
- Quadratic (t proportional to V^2)
- Exponential (t proportional to e^V)
- Logarithmic (t proportional to ln V)
Correct Answer: Quadratic (t proportional to V^2)
Q4. Which term describes a cake whose porosity and resistance increase significantly under applied pressure?
- Incompressible cake
- Compressible cake
- Rigid cake
- Permeable cake
Correct Answer: Compressible cake
Q5. The Kozeny–Carman equation relates permeability to which set of parameters?
- Particle size, porosity, and specific surface area
- Temperature, pressure, and viscosity
- Filter area, cake thickness, and time
- Flow rate, Reynolds number, and density
Correct Answer: Particle size, porosity, and specific surface area
Q6. Specific cake resistance (α) has units typically expressed as:
- m^2
- m/kg
- m/kg·s
- m/g
Correct Answer: m/kg
Q7. Precoat filtration primarily serves to:
- Increase cake compressibility
- Protect and prevent blinding of the filter medium
- Reduce filtrate viscosity
- Decrease pressure drop across the cake
Correct Answer: Protect and prevent blinding of the filter medium
Q8. Which filter aid is commonly used in pharmaceutical filtration for clarification and precoat?
- Activated carbon
- Diatomaceous earth (kieselguhr)
- Sodium chloride
- Silicone oil
Correct Answer: Diatomaceous earth (kieselguhr)
Q9. In constant rate filtration, the applied pressure must be adjusted because:
- Filtrate viscosity increases with time
- Cake resistance increases so pressure must decrease
- Cake resistance increases so pressure must increase to maintain rate
- Permeability becomes infinite
Correct Answer: Cake resistance increases so pressure must increase to maintain rate
Q10. Which equipment is best described as a batch filtration vessel allowing washing and drying of the cake under controlled pressure?
- Rotary vacuum filter
- Filter press
- Nutsche filter
- Centrifuge
Correct Answer: Nutsche filter
Q11. The term “filter medium resistance” refers to resistance offered by:
- The solid cake only
- The liquid only
- The fabric or porous support through which filtrate passes
- The atmospheric pressure above the cake
Correct Answer: The fabric or porous support through which filtrate passes
Q12. Which of the following reduces cake resistance and improves filtrate flow when added as a filter aid?
- Fine clay particles that pack tightly
- Coarse, porous particles that create channels
- High molecular weight polymers
- Dense metal powder
Correct Answer: Coarse, porous particles that create channels
Q13. Darcy’s law assumes flow through the porous medium is:
- Turbulent and unsteady
- Laminar and proportional to pressure gradient
- Indifferent to fluid viscosity
- Controlled by surface tension alone
Correct Answer: Laminar and proportional to pressure gradient
Q14. Depth filtration differs from cake filtration in that depth filtration:
- Retains particles on the surface to form a cake
- Traps particles within the porous medium matrix
- Requires extremely high pressures only
- Is always reversible by backwashing
Correct Answer: Traps particles within the porous medium matrix
Q15. Specific cake resistance typically increases with:
- Increasing particle size
- Decreasing particle compressibility
- Increasing applied pressure for compressible cakes
- Decreasing solids concentration in feed
Correct Answer: Increasing applied pressure for compressible cakes
Q16. In the classic cake filtration equation for constant pressure, the slope of t/V versus V plot gives information about:
- Filter medium resistance only
- Specific cake resistance and solids concentration
- Fluid density and viscosity only
- Cake porosity directly
Correct Answer: Specific cake resistance and solids concentration
Q17. Which factor does NOT directly affect filtration rate in cake filtration?
- Fluid viscosity
- Filter area
- Atmospheric humidity
- Pressure drop across cake and medium
Correct Answer: Atmospheric humidity
Q18. Cake porosity is defined as:
- The fraction of cake volume occupied by solids
- The fraction of cake volume occupied by voids or pores
- The density of cake solids per unit area
- The thickness of the filter medium
Correct Answer: The fraction of cake volume occupied by voids or pores
Q19. Which phenomenon explains a decrease in filtration rate over time when solids compress and reduce permeability?
- Backflow
- Cake consolidation
- Brownian motion
- Osmotic flux
Correct Answer: Cake consolidation
Q20. In pressure vs vacuum filtration, vacuum filtration is typically limited by:
- Maximum achievable pressure differential equal to atmospheric pressure
- Ability to apply very high positive pressures
- Viscosity becoming zero
- Unlimited cake thickness
Correct Answer: Maximum achievable pressure differential equal to atmospheric pressure
Q21. Which parameter is most useful to compare cakes formed from different slurries under similar conditions?
- Filter area
- Specific cake resistance (α)
- Feed volume
- Atmospheric pressure
Correct Answer: Specific cake resistance (α)
Q22. Cake washing efficiency depends primarily on:
- Washing solvent color
- Diffusion and convection in the cake pores
- Filter cloth weave only
- Ambient room lighting
Correct Answer: Diffusion and convection in the cake pores
Q23. Which washing method applies a clean wash liquid from top to bottom through the cake to displace mother liquor?
- Immersion washing
- Displacement (percolation) washing
- Spray washing only
- Reverse osmosis washing
Correct Answer: Displacement (percolation) washing
Q24. The filter press primarily utilizes which principle for filtration?
- Continuous rotating action
- Intermittent batch pressing of filter plates to form cake
- Centrifugal acceleration for solids separation
- Membrane ultrafiltration
Correct Answer: Intermittent batch pressing of filter plates to form cake
Q25. In rotary vacuum filters, cake formation occurs during which segment of rotation?
- Only when submerged and then exposed to vacuum
- Only during drying in air
- When the drum is fully above the slurry surface
- Only during cake discharge
Correct Answer: Only when submerged and then exposed to vacuum
Q26. Which of the following increases filtration rate for a given system?
- Increasing filtrate viscosity
- Decreasing filter area
- Increasing applied pressure differential
- Decreasing cake porosity significantly
Correct Answer: Increasing applied pressure differential
Q27. The cake solidity (mass per unit cake volume) is inversely related to:
- Cake porosity
- Liquid viscosity
- Applied pressure
- Filter medium resistance
Correct Answer: Cake porosity
Q28. A high specific surface area of particles generally leads to:
- Lower cake resistance
- Higher cake resistance due to finer pores
- No change in filtration behavior
- Instantaneous clarification
Correct Answer: Higher cake resistance due to finer pores
Q29. Which practice helps prevent blinding of a filter cloth when filtering fine or gelatinous solids?
- Using a finer weave filter cloth
- Applying a precoat layer of filter aid
- Reducing slurry solids concentration to zero
- Operating at extremely low temperatures only
Correct Answer: Applying a precoat layer of filter aid
Q30. For compression filtration, the cake resistance α can be modeled as a function of pressure using:
- A constant independent of pressure
- An exponential relation α = α0·e^(mP)
- A logarithmic decrease with pressure
- Only linear decrease with solids concentration
Correct Answer: An exponential relation α = α0·e^(mP)
Q31. The term “breakthrough” in filtration refers to:
- The moment the cake reaches infinite thickness
- The first appearance of solids in the filtrate indicating filter medium failure
- Total drying of the filter cake
- Complete removal of all liquids from cake pores
Correct Answer: The first appearance of solids in the filtrate indicating filter medium failure
Q32. Which analytical curve is typically plotted to determine specific cake resistance and medium resistance experimentally?
- t versus V
- ln t versus V
- t/V versus V
- V/t versus ln V
Correct Answer: t/V versus V
Q33. When designing filtration for viscous pharmaceutical solvents, the most critical fluid property to consider is:
- Density
- Viscosity
- Surface tension only
- Color
Correct Answer: Viscosity
Q34. Membrane microfiltration differentiates from cake filtration primarily by:
- Operating at much higher pressures and relying on pore-size sieving rather than cake formation
- Always producing thicker cakes
- Never being used in pharma applications
- Having zero flux decline over time
Correct Answer: Operating at much higher pressures and relying on pore-size sieving rather than cake formation
Q35. In centrifugal filtration (centrifugation), the effective driving force is related to:
- Applied vacuum degree
- Gravitational acceleration multiplied by rotor speed squared (G-force)
- Atmospheric humidity
- Filter cloth permeability only
Correct Answer: Gravitational acceleration multiplied by rotor speed squared (G-force)
Q36. Which parameter describes how easily fluid can pass through the cake and is the reciprocal of resistance?
- Permeability
- Porosity
- Compressibility index
- Specific gravity
Correct Answer: Permeability
Q37. Cake washing by “intermittent displacement” improves washing efficiency by:
- Allowing diffusion to equilibrate between wash pulses and improving displacement
- Removing the need for any wash solvent
- Compressing the cake to trap mother liquor
- Decreasing cake porosity permanently
Correct Answer: Allowing diffusion to equilibrate between wash pulses and improving displacement
Q38. In the Kozeny–Carman model, tortuosity affects:
- Chemical composition of solids
- Flow path length and therefore permeability
- Ambient temperature directly
- Particle melting point
Correct Answer: Flow path length and therefore permeability
Q39. Which of the following reduces the tendency of fines to pass through the filter medium into filtrate?
- Using a coarser filter medium
- Applying a precoat or using finer medium pores
- Increasing slurry temperature drastically
- Reducing applied pressure to zero
Correct Answer: Applying a precoat or using finer medium pores
Q40. Filtration flux decline over time is commonly caused by all EXCEPT:
- Cake buildup increasing resistance
- Clogging or blinding of filter medium
- Decreasing filtrate viscosity with time
- Compression of cake reducing permeability
Correct Answer: Decreasing filtrate viscosity with time
Q41. Which practice is used to measure residual moisture in a filtered cake?
- Gravimetric drying to constant weight
- Visual inspection only
- Measuring cake thickness alone
- Monitoring filtrate turbidity only
Correct Answer: Gravimetric drying to constant weight
Q42. The filter medium pore size selection for sterile filtration typically targets removal of:
- Macro solids >100 μm
- Bacteria around 0.2 μm
- Viruses >10 μm
- Only dissolved organics
Correct Answer: Bacteria around 0.2 μm
Q43. Which is a correct statement about filtration of flocculated vs deflocculated suspensions?
- Deflocculated suspensions form porous, easily washed cakes
- Flocculated suspensions often form more permeable cakes with larger pores
- Flocculation has no effect on cake properties
- Deflocculation always reduces filtration rate
Correct Answer: Flocculated suspensions often form more permeable cakes with larger pores
Q44. The washing principle that relies on replacing pore liquid by a less soluble wash liquid is called:
- Diffusion washing
- Displacement washing
- Solubilization washing
- Evaporative washing
Correct Answer: Displacement washing
Q45. In batch filtration using a filter press, cake washing is typically performed after:
- Complete cake formation and initial drainage
- Full cake drying only
- Removing the cake from the plates
- Excessive blinding of the medium
Correct Answer: Complete cake formation and initial drainage
Q46. Filtrate clarity (absence of solids) is most directly assessed by:
- Measuring filtrate turbidity or solids content
- Weighing the cake only
- Observing the color of the cake
- Measuring the filtration time alone
Correct Answer: Measuring filtrate turbidity or solids content
Q47. Which adjustment would you make to improve washing penetration into a dense cake?
- Decrease wash pressure
- Apply intermittent pressure pulses or reduce cake compaction
- Use a more viscous wash solvent
- Increase cake thickness further
Correct Answer: Apply intermittent pressure pulses or reduce cake compaction
Q48. The concept of “superficial velocity” in filtration refers to:
- The actual velocity through the pores only
- Volumetric flow rate divided by total cross-sectional area as if no solids occupied volume
- The velocity of particles in the cake exclusively
- Velocity measured at the filter medium surface only
Correct Answer: Volumetric flow rate divided by total cross-sectional area as if no solids occupied volume
Q49. Which filtration mode would you select to minimize product loss from sensitive solids and allow closed handling and washing?
- Open tray vacuum filtration
- Nutsche filter (closed vessel)
- Simple cloth bag filtration
- Gravity decantation only
Correct Answer: Nutsche filter (closed vessel)
Q50. When scaling up a filtration process, it is most important to maintain similarity in which dimensionless parameter related to flow through porous media?
- Peclet number only
- Reynolds number and relative pressure gradients ensuring similar flow regimes
- Biot number only
- Froude number only
Correct Answer: Reynolds number and relative pressure gradients ensuring similar flow regimes
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