Introduction
The plate and frame filter is a widely used piece of filtration equipment in pharmaceutical processing, combining simple construction with effective solid-liquid separation. This guide explains the principle, construction, working, uses, merits and demerits of plate and frame filters, focusing on key concepts such as filter media, cake formation, filtrate flow and filter aids. B.Pharm students will gain practical insight into operation, maintenance, process variables, and troubleshooting relevant to API recovery, solvent filtration and product purification. Technical terms and operational parameters are clarified for exam preparation and lab work. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary principle behind the operation of a plate and frame filter?
- Adsorption of solute onto the plate surface
- Size-exclusion membrane ultrafiltration
- Solid-liquid separation by cake formation on filter media
- Centrifugal sedimentation of solids
Correct Answer: Solid-liquid separation by cake formation on filter media
Q2. Which component in a plate and frame filter supports the filter cloth and collects filtrate?
- Frame
- Plate
- Gasket
- Filter aid
Correct Answer: Plate
Q3. The filter medium commonly used in plate and frame filters is:
- Membrane sheet
- Filter cloth
- Activated carbon bed
- Rotary drum
Correct Answer: Filter cloth
Q4. What is the role of a frame in the plate and frame filter assembly?
- To apply pressure to close the filter press
- To hold the cake space and allow slurry distribution
- To pump filtrate to the receiver
- To heat the slurry during filtration
Correct Answer: To hold the cake space and allow slurry distribution
Q5. Which parameter most directly affects the rate of filtration in a plate and frame filter?
- Ambient humidity
- Filtrate colour
- Permeability of the filter cake and media
- Operator’s weight
Correct Answer: Permeability of the filter cake and media
Q6. What is a common filter aid used with plate and frame filters in pharmaceutical processes?
- Silica gel
- Diatomaceous earth (kieselguhr)
- Activated alumina
- Sand
Correct Answer: Diatomaceous earth (kieselguhr)
Q7. During operation, why is a precoat sometimes applied to the filter cloth?
- To increase filter plate weight
- To provide a uniform porous layer and protect the cloth
- To dissolve solids into the filtrate
- To cool the slurry
Correct Answer: To provide a uniform porous layer and protect the cloth
Q8. Which of the following is a major advantage (merit) of plate and frame filters?
- They are suitable for continuous large-scale centrifugal separation
- They provide easy cake washing and good cake dryness
- They require no maintenance
- They are ideal for gas filtration
Correct Answer: They provide easy cake washing and good cake dryness
Q9. A typical demerit of plate and frame filters is:
- Very low capital cost for all scales
- Limited ability to handle abrasive slurries and potential cloth blinding
- Uncontrolled particle breakthrough
- Inability to be cleaned
Correct Answer: Limited ability to handle abrasive slurries and potential cloth blinding
Q10. Which factor determines the cake thickness formed in a plate and frame filter?
- Filtrate colour only
- Solids concentration and volume of slurry filtered
- Ambient light intensity
- Filter cloth stitch pattern only
Correct Answer: Solids concentration and volume of slurry filtered
Q11. In plate and frame filters, washing of the cake is performed to:
- Increase cake porosity artificially
- Remove impurities and recover mother liquor from the cake
- Change the cake’s colour
- Reduce plate temperature
Correct Answer: Remove impurities and recover mother liquor from the cake
Q12. Which operational variable is adjusted to speed up filtration without damaging the cake?
- Increasing vacuum/pressure differential within safe limits
- Removing the filter cloth mid-run
- Heating plates to very high temperatures
- Shaking the frames violently
Correct Answer: Increasing vacuum/pressure differential within safe limits
Q13. What is cake resistance in the context of plate and frame filtration?
- Resistance due to electrical conductivity of cake
- Hydraulic resistance offered by the deposited solid cake to filtrate flow
- Thermal resistance of the filter plate
- Resistance to mechanical opening of the frame
Correct Answer: Hydraulic resistance offered by the deposited solid cake to filtrate flow
Q14. Which maintenance activity is crucial for sustaining filtration performance?
- Replacing the frame periodically with thicker frames
- Regular cleaning and inspection of filter cloths and plates
- Never lubricating moving parts
- Frequent replacement of gaskets with random sizes
Correct Answer: Regular cleaning and inspection of filter cloths and plates
Q15. Which modification can reduce cloth blinding and improve filtrate clarity?
- Removing precoat
- Using finer mesh cloth only
- Using filter aids or precoating and controlled cake formation
- Increasing cake thickness intentionally
Correct Answer: Using filter aids or precoating and controlled cake formation
Q16. The term “frame” in a plate and frame filter mainly refers to:
- The support plate for filtrate collection
- The space between two plates creating cake volume
- The hydraulic closure cylinder
- The motor driving the pumps
Correct Answer: The space between two plates creating cake volume
Q17. Which monitoring parameter indicates decreasing permeability during a run?
- Increasing filtrate flow rate at constant pressure
- Decreasing filtrate flow rate at constant pressure
- No change in flow at all times
- Constant cake colour
Correct Answer: Decreasing filtrate flow rate at constant pressure
Q18. What is the usual method to discharge cake from a plate and frame filter?
- Melting the cake with heat
- Manually or mechanically opening the assembly and removing plates/frames
- Using ultrasonic vibrations only
- Flushing with alcohol to dissolve cake
Correct Answer: Manually or mechanically opening the assembly and removing plates/frames
Q19. In pharmaceutical applications, plate and frame filters are often used for:
- Gas purification only
- Separation of API crystals from mother liquor and washing cakes
- Sterilization of injectable solutions
- Final sterile filtration to 0.22 µm
Correct Answer: Separation of API crystals from mother liquor and washing cakes
Q20. Which safety consideration is important when operating a plate and frame filter with solvents?
- Ensuring adequate ventilation and explosion-proof equipment
- Running at maximum pressure without checking hoses
- Using open flames to speed solvent evaporation
- Ignoring solvent compatibility with filter aids
Correct Answer: Ensuring adequate ventilation and explosion-proof equipment
Q21. Which of the following affects the compressibility of the cake?
- Filter plate colour only
- Particle nature and applied pressure
- Ambient sound levels
- Cloth brand name
Correct Answer: Particle nature and applied pressure
Q22. What is the effect of increasing slurry solids concentration on filtration?
- Decreases cake formation rate
- Increases cake thickness and may reduce filtration rate
- Has no effect on filtration at all
- Makes the filtrate more volatile
Correct Answer: Increases cake thickness and may reduce filtration rate
Q23. A common troubleshooting step when filtrate is turbid is to:
- Change the color of plates
- Check for cloth damage/blinding and consider precoating or using filter aid
- Increase operating temperature drastically
- Reduce slurry particle size intentionally by adding water only
Correct Answer: Check for cloth damage/blinding and consider precoating or using filter aid
Q24. Which term describes a filter where the cake forms on a disposable support rather than the cloth?
- Leaf filter
- Precoat filtration
- Depth filtration
- Frame inversion
Correct Answer: Precoat filtration
Q25. Specific cake resistance is a measure of:
- Thermal conductivity of the cake
- Hydraulic resistance per unit mass or volume of cake
- Electrical resistance of filtrate
- Mechanical strength of plates
Correct Answer: Hydraulic resistance per unit mass or volume of cake
Q26. Which operational change helps achieve a drier cake?
- Reducing final wash volume to zero
- Applying a final wash and then vacuum or pressure blow to remove interstitial liquid
- Heating the cake above solvent boiling point without control
- Removing the cloth before discharge
Correct Answer: Applying a final wash and then vacuum or pressure blow to remove interstitial liquid
Q27. In scale-up of plate and frame filtration, which parameter is most critical to preserve?
- Plate colour
- Superficial filtrate velocity and pressure drop per unit thickness
- Operator shift timing
- Brand of filter aid
Correct Answer: Superficial filtrate velocity and pressure drop per unit thickness
Q28. Which cleaning method is commonly used for filter cloths?
- Chemical cleaning with compatible solvents or detergents and mechanical scrubbing
- Leaving them to dry and never cleaning
- Burning the cloth after each run
- Soaking in strong acids regardless of material
Correct Answer: Chemical cleaning with compatible solvents or detergents and mechanical scrubbing
Q29. What is the purpose of gaskets in plate and frame filters?
- To filter fine particles
- To seal between plates and prevent slurry bypass
- To heat the assembly
- To act as a filter aid
Correct Answer: To seal between plates and prevent slurry bypass
Q30. Which of the following best distinguishes a plate and frame filter from a filter press?
- Plate and frame filters are always operated continuously; filter presses are batch only
- Plate and frame filters use alternating plates and frames creating a removable frame space; filter presses often use recessed plates forming chambers
- Filter presses cannot wash cake
- Plate and frame filters always have larger throughput than filter presses
Correct Answer: Plate and frame filters use alternating plates and frames creating a removable frame space; filter presses often use recessed plates forming chambers
Q31. Which measurement indicates filtrate clarity during operation?
- pH only
- Turbidity or particulate count in the filtrate
- Plate temperature exclusively
- Color of the filter cloth
Correct Answer: Turbidity or particulate count in the filtrate
Q32. Why is controlled feeding of slurry important?
- To cause sudden cake collapse
- To ensure even cake formation and avoid channeling or uneven deposits
- To reduce operator duties only
- To change filter cloth weave randomly
Correct Answer: To ensure even cake formation and avoid channeling or uneven deposits
Q33. The hydraulic closing system in some plate and frame filters is used to:
- Open the plates during discharge only
- Apply uniform pressure to the stack to prevent leakage
- Spray cleaning solution externally
- Measure filtrate conductivity
Correct Answer: Apply uniform pressure to the stack to prevent leakage
Q34. Which of these is a typical pharmaceutical use of plate and frame filters?
- Final sterilizing filtration to 0.22 µm
- Isolation and washing of crystalline APIs from mother liquor
- Gas chromatography sample injection
- Autoclaving parenteral products
Correct Answer: Isolation and washing of crystalline APIs from mother liquor
Q35. Excessive cake compression can lead to:
- Higher cake porosity and faster filtration
- Lower permeability and reduced filtrate flow
- Immediate dissolution of solids
- No measurable effect
Correct Answer: Lower permeability and reduced filtrate flow
Q36. What is the effect of using a finer filter cloth mesh?
- Increases filtrate turbidity
- Reduces particle passage but may increase resistance and slow filtration
- Eliminates the need for washing
- Causes automatic cake release
Correct Answer: Reduces particle passage but may increase resistance and slow filtration
Q37. Which operational sequence is correct for a typical plate and frame filtration batch?
- Open stack, wash, feed slurry, close stack
- Close stack, feed slurry, wash cake, drain filtrate, open and discharge cake
- Wash cake, feed slurry, open stack, close stack
- Discharge cake, close stack, wash plate, feed slurry
Correct Answer: Close stack, feed slurry, wash cake, drain filtrate, open and discharge cake
Q38. Which maintenance check helps prevent slurry bypass during filtration?
- Checking bolt torque or hydraulic pressure for uniform closure and gasket integrity
- Painting the plates yearly
- Removing all gaskets to increase flow
- Using thinner plates exclusively
Correct Answer: Checking bolt torque or hydraulic pressure for uniform closure and gasket integrity
Q39. What is the purpose of a filtrate collection channel in plate design?
- To mix the cake unevenly
- To collect and direct clear filtrate away from the plate area
- To store the filter aid permanently
- To provide a place for operators to stand
Correct Answer: To collect and direct clear filtrate away from the plate area
Q40. Which cake property is critical for effective washing?
- Cake elasticity only
- Cake porosity and permeability to washing solvent
- Cake colour uniformity
- Number of plates in the filter only
Correct Answer: Cake porosity and permeability to washing solvent
Q41. Which filter aid property is important to improve cake permeability?
- High density to compact the cake
- Porous, inert, and high surface area to form a permeable structure
- High solubility in mother liquor
- Reactive chemistry with API
Correct Answer: Porous, inert, and high surface area to form a permeable structure
Q42. When designing a filtration cycle, which objective is typically balanced?
- Maximizing cake thickness regardless of wash efficiency
- Balancing filtration time, cake dryness, and product recovery
- Minimizing filtrate clarity at all costs
- Eliminating operator involvement entirely
Correct Answer: Balancing filtration time, cake dryness, and product recovery
Q43. Which is a sign that the filter cloth needs replacement?
- Improved filtrate clarity over time
- Persistent filtrate turbidity, frequent blinding, or damage to the weave
- Decreased cake thickness only
- Lowered ambient temperature
Correct Answer: Persistent filtrate turbidity, frequent blinding, or damage to the weave
Q44. Precoating helps mainly to:
- Remove all solids from the slurry instantly
- Protect the cloth and provide a uniform filtration layer for fine or sticky solids
- Make the cake dissolve in water
- Increase the filter’s mechanical strength only
Correct Answer: Protect the cloth and provide a uniform filtration layer for fine or sticky solids
Q45. What is the likely effect of high slurry viscosity on filtration?
- Improved filtrate flow due to lubrication
- Reduced filtrate flow rate and potential difficulty in cake formation
- No impact at all
- Instant cake drying
Correct Answer: Reduced filtrate flow rate and potential difficulty in cake formation
Q46. In batch operations, how can throughput be increased without changing filter area?
- Shortening cycle times by optimizing feeding, washing and drying steps
- Skipping washing steps entirely
- Using fewer plates
- Reducing slurry concentration to zero
Correct Answer: Shortening cycle times by optimizing feeding, washing and drying steps
Q47. Which analytical test would you perform to evaluate residual solvent in a washed cake?
- Particle size distribution only
- Gas chromatography or suitable solvent residue assay
- Turbidity measurement
- Filter cloth tensile strength
Correct Answer: Gas chromatography or suitable solvent residue assay
Q48. Which operational practice reduces the risk of particle breakthrough during filtration?
- Using a coarser cloth than required
- Maintaining appropriate cloth selection, precoating and controlled feed rates
- Feeding slurry at extremely high velocities
- Never washing the cake
Correct Answer: Maintaining appropriate cloth selection, precoating and controlled feed rates
Q49. Which design change can help handle corrosive process fluids?
- Using plates and frames made of compatible corrosion-resistant materials or appropriate coatings
- Using wooden frames
- Removing gaskets to avoid chemical interaction
- Increasing cloth weave density only
Correct Answer: Using plates and frames made of compatible corrosion-resistant materials or appropriate coatings
Q50. What is a typical reason for performing a final pressure blow after washing?
- To dissolve the cake into filtrate
- To remove residual wash liquid from cake pores and improve dryness
- To compact the cake to immovable density
- To break the filter cloth intentionally
Correct Answer: To remove residual wash liquid from cake pores and improve dryness
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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