PES Membrane: Uses, Ratings & Selection

A PES membrane is not one standardized filter. PES means polyethersulfone, but products made from it differ in wettability, pore architecture, support layers, rating systems, formats, sterility claims, and operating limits. Start with the separation you need and the fluid you have. Then choose between a micron rating and molecular-weight cutoff (MWCO), select the appropriate format and membrane area, and verify the exact product’s compatibility, retention, sterilization, and integrity-test requirements.

This guide is a product-selection and supplier-documentation framework, not a complete sterile-process validation protocol. For critical or regulated work, use the applicable quality requirements and the manufacturer’s validated instructions for the exact filter assembly.

What a PES membrane is—and the first decision to make

Polyethersulfone is a membrane polymer used in microfiltration and ultrafiltration. The name identifies the base polymer, not a universal level of retention or performance.

Suppliers offer PES as flat discs, sheets, rolls, disposable devices, capsules, cartridges, centrifugal concentrators, and tangential-flow units. Construction varies as well. A membrane may be supported or unsupported, have different pore architecture or surface treatments, and sit inside a device whose housing, seals, drainage layers, and flow path impose additional limits.

Use this decision path before comparing catalog numbers:

1. Are you filtering liquid or gas?
2. Do you need microfiltration or ultrafiltration?
3. What must be removed, and what must remain?
4. Is clarification enough, or must the product carry a specific microbial-retention claim?
5. What volume must be processed, and within what time?
6. Will the system use pressure, vacuum, centrifugation, or tangential flow?
7. What chemicals, temperatures, and pressures will every wetted component encounter?

Wettability is one of the first distinctions to check. Hydrophilic PES grades are commonly offered for aqueous liquids. Hydrophobic PES grades are also available for air, gas, and venting duties. Do not assume every PES membrane is hydrophilic simply because many laboratory liquid filters are.

Descriptions such as “high flux,” “low protein binding,” “low fouling,” and “low extractables” are supplier claims tied to particular grades and test methods. They are useful for building a shortlist, but they are not universal properties guaranteed by the polymer name.

Micron rating versus MWCO: do not mix the two

The first technical split is between pore-rated microfiltration and MWCO-rated ultrafiltration.

A pore-rated PES microfilter is selected in micrometres, written as µm or “micron.” It is generally used to remove particles or microorganisms from a liquid or gas. Commercial PES microfilters include ratings such as 0.2, 0.22, and 0.45 µm, as well as finer and coarser grades.

An ultrafiltration membrane is usually selected by molecular-weight cutoff, expressed in daltons or kilodaltons. It is used to retain macromolecules while allowing much smaller species, including solvent and salts, to pass. Typical operations include protein concentration, desalting, and buffer exchange.

MWCO is not a direct measurement of a uniform physical pore diameter. It is an operational retention specification. Sartorius defines MWCO as the molecular weight at which 90% of a reference molecule, such as a globular protein, is retained. Its catalog also recommends starting with an MWCO around half the molecular weight of the solute to be retained when high recovery is the goal (Sartorius laboratory filtration catalog).

The two rating systems answer different questions:

Rating system	Main selection question	Typical uses
Micrometres (µm)	What particle or microorganism must be removed?	Clarification, bioburden reduction, product-specific sterile filtration, gas filtration
MWCO (Da or kDa)	What macromolecule must be retained while smaller material passes?	Concentration, desalting, buffer exchange

Treat the half-molecular-weight recommendation as a screening rule, not a final specification. Molecular shape, aggregation, concentration, membrane interaction, buffer composition, fouling, and operating conditions can all change observed retention. Test the actual molecule in the actual process fluid.

Decision table: match the membrane to the filtration goal

Choose the rating after defining the job—not the other way around.

Filtration goal	PES attribute and rating	Suitable format	What to verify
Aqueous clarification	Hydrophilic grade; micron rating based on the contaminant to remove	Disc, syringe device, capsule, cartridge	Clarity, area, solids capacity, pressure, and processing time
Sterile liquid filtration	Product carrying the required microbial-retention claim; 0.2 or 0.22 µm are common product ratings	Sterile device, capsule, cartridge, or validated disc-and-holder system	Challenge organism and level, validated process limits, sterility status, and integrity-test limits
Protein concentration or desalting	Hydrophilic ultrafiltration grade selected by MWCO	Centrifugal device, pressure cell, cassette, or tangential-flow unit	Retention, recovery, hold-up, fouling, and process time
Air, gas, or venting	Hydrophobic PES intended for gas service	Vent disc, capsule, or cartridge	Gas flow, liquid intrusion behavior, chemical exposure, and assembly integrity
High particulate load	Adequate final-filter area with possible prefiltration or staged reduction	Layered device, capsule, or cartridge train	Capacity and pressure rise with the real feed

For aqueous clarification, begin with the size and nature of what must be removed. Then consider effective membrane area, solids loading, acceptable filtrate quality, and available processing time. A smaller nominal pore size is not automatically better if it blocks prematurely or removes material that should remain.

For sterile filtration, a 0.2 or 0.22 µm label does not by itself prove sterilizing-grade performance. Sartorius states that its specified 0.22 µm PES membranes are classified as sterile filters based on retention of a challenge of 10^7 Brevundimonas diminuta per cm² of filter area (Sartorius membrane selection guidance). Cytiva separately identifies its 0.2 µm Supor Prime PES products as sterilizing-grade filters (Supor Prime product datasheet). Those statements apply to the named products and documented conditions, not to every membrane with the same nominal rating.

For high-solids feeds, do not assume that simply increasing pressure will solve premature blockage. Compare a coarse prefilter, depth stage, larger final-filter area, or staged pore-size reduction using the real process fluid.

Choose the format and membrane area for your scale

Membrane chemistry and rating determine what a filter may separate. Format determines how it fits the workflow.

• Flat discs fit reusable holders for pressure- or vacuum-driven laboratory filtration. They work well for small batches, analytical tasks, and method development because the holder and membrane can be selected separately.
• Centrifugal ultrafilters suit small-volume concentration and buffer exchange. Check starting volume, MWCO, rotor compatibility, active area, hold-up volume, and maximum centrifugal force.
• Capsules and cartridges suit closed processing and larger liquid volumes. Capsules are self-contained; cartridges require a compatible housing.
• Cassettes and self-contained tangential-flow units suit larger ultrafiltration and diafiltration processes in which feed moves across the membrane surface.
• Sheets and rolls support custom conversion, equipment integration, and nonstandard dimensions.

Do not transfer recovery figures from one centrifugal device to another. Sartorius reports recoveries of 95% to 98% for selected Vivaspin 2 PES tests and 96% for specified Vivaspin 500 tests, but those results are tied to named proteins, sample volumes, MWCO configurations, temperatures, centrifugal forces, and concentration factors (Sartorius laboratory filtration catalog).

Processing time depends on more than filter diameter. Important variables include:

• Effective membrane area
• Pressure differential or centrifugal force
• Fluid viscosity and temperature
• Membrane thickness and porosity
• Pore architecture and support structure
• Device geometry and downstream resistance
• Particulate loading and prefiltration

When throughput matters, size the filter using the real feed. Water-flux measurements can help compare controlled tests within a product family, but they should not be treated as predictions for viscous, sugary, saline, protein-rich, or particle-loaded liquids.

Check product-specific chemistry and operating limits

There is no universal PES compatibility range. The polymer name alone cannot establish whether a filter will tolerate a particular acid, solvent, cleaning agent, temperature, pressure, or exposure time.

Published specifications demonstrate the variation:

Product family	Published pH range	Important qualification
Cobetter hydrophilic PES laboratory discs	3–14	Unsupported, nonsterile discs; vendor warns against ketones, esters, and similar compounds (Cobetter product page)
Sartorius Sartocon Slice and Sartocube PES units	1–14	Range applies to the specified self-contained ultrafiltration units (Sartorius SCU datasheet)

Neither range should be transferred to an unrelated PES grade or assembly. A membrane disc and a complete capsule may contain different supports, seals, connectors, and housing materials even when both use PES as the filtering layer.

Broad compatibility charts are useful for screening candidates, but qualitative labels such as “good” or “fair” do not qualify a process. Review the exact product documentation against:

• Every liquid component and its concentration
• pH and ionic strength
• Operating, cleaning, and storage temperatures
• Exposure time
• Differential and absolute pressure
• Membrane supports and drainage materials
• Seals, adhesives, connectors, and housings
• Sterilization method and permitted cycle count

Incompatibility does not always appear as obvious structural failure. Solvent absorption may swell a polymer and alter effective pore behavior. Chemical degradation may weaken materials or release extractables. Adsorption may remove the target molecule even when the filter remains physically intact.

For a demanding fluid—or whenever the documentation does not match the intended concentrations and conditions—run a small-scale compatibility and performance trial before committing to a full batch.

How to evaluate flow, binding, and recovery claims

PES is frequently marketed as high-flow, low-binding, low-fouling, and low in extractables. Treat those descriptions as product-specific supplier claims rather than automatic consequences of choosing polyethersulfone.

Two PES filters with the same nominal rating may behave differently because of differences in:

• Thickness and porosity
• Pore-size distribution and architecture
• Surface treatment
• Support and drainage construction
• Effective membrane area
• Device flow path
• Test pressure and temperature

The fluid can widen those differences. Higher viscosity generally reduces flow under otherwise comparable conditions, while particles and proteins may block pores or form a surface deposit. Temperature can affect viscosity and integrity-test results.

“Low binding” also does not mean “no product loss.” Separate three mechanisms:

1. Adsorption: the target binds to the membrane or another wetted material.
2. Hold-up: product remains in pores, supports, tubing, connectors, or housings.
3. Fouling or concentration effects: product becomes trapped, aggregated, or retained in deposits.

The Vivaspin results cited earlier show what selected PES device-and-protein combinations achieved under specified test conditions. They do not predict recovery for a different protein, buffer, concentration, or operating procedure. The same Sartorius catalog identifies cellulose triacetate as an option when very low nonspecific binding and filtrate recovery are priorities, illustrating why PES should not automatically be ranked above every alternative chemistry.

A short comparison test is usually more useful than comparing catalog adjectives:

1. Select two or three candidate filters in the intended format.
2. Process equal portions of the real feed under matched conditions.
3. Measure filtrate or retentate recovery, as appropriate.
4. Record time, pressure or centrifugal conditions, and final volume.
5. Note pressure rise, flow decay, visible fouling, and handling problems.
6. Keep each result tied to the exact membrane, device, lot, area, and procedure tested.

Installation, wetting, and integrity-test troubleshooting

The manufacturer’s procedure and acceptance limits take precedence over general guidance. Membrane orientation, support, wetting liquid, test pressure, flush volume, contact time, and allowable temperature may all be product-specific.

A general pre-check sequence is:

1. Confirm the membrane identity, rating, and supply condition.
2. Check whether the product specifies feed and filtrate sides.
3. Provide the required holder support for an unsupported disc.
4. Inspect seals, O-rings, clamps, and contact surfaces.
5. Install the assembly so trapped air can be vented.
6. Introduce the approved wetting fluid slowly.
7. Vent the assembly until trapped air is removed.
8. Apply the specified contact time and flush volume.
9. Perform any required test using the product-specific fluid, temperature, procedure, and acceptance limit.

Cobetter instructs users to install its identified unsupported PES discs with the indicated feed side facing upward (Cobetter PES disc instructions). Do not generalize that orientation to supported discs or another manufacturer’s product.

Complete wetting is necessary for meaningful bubble-point or forward-flow testing. Remaining air pathways can increase gas flow and produce an apparent integrity-test failure. Residual process material can also elevate gas flow during post-use testing. Cytiva’s technical guidance emphasizes slow initial filling, effective venting, adequate contact time, and removal of product residues where the approved procedure permits it (Cytiva filter-wetting guidance).

If the bubble point is unexpectedly low or forward flow is high:

• Confirm the correct test fluid and composition.
• Verify the fluid and assembly temperature.
• Repeat wetting slowly and vent trapped air.
• Check membrane orientation where specified.
• Inspect seals, clamps, housings, and connections.
• Remove process residues using the approved flush procedure.
• Confirm that the installed membrane is the intended grade and rating.
• Inspect the membrane, support, and assembly for damage.

Do not substitute a generic “PES bubble point.” Use the acceptance limit specified for the exact product, rating, device format, wetting fluid, and test temperature.

PES membrane buyer and validation checklist

Use this as a supplier-question and product-screening checklist. It does not replace a process-specific validation plan.

Membrane and device

• [ ] Exact manufacturer and catalog number
• [ ] Pure PES, modified PES, or PES-containing hybrid
• [ ] Hydrophilic or hydrophobic grade
• [ ] Micron pore rating or MWCO
• [ ] Diameter, nominal area, and effective filtration area
• [ ] Supported or unsupported construction
• [ ] Disc, sheet, roll, centrifugal device, capsule, cartridge, or cassette
• [ ] Sterile or nonsterile supply condition
• [ ] Holder, housing, tubing, and connector compatibility
• [ ] Required orientation and installation procedure

Process conditions

• [ ] Complete fluid composition and component concentrations
• [ ] pH, temperature, and exposure time
• [ ] Maximum operating, inlet, and differential pressure
• [ ] Fluid viscosity
• [ ] Expected particulate or bioburden load
• [ ] Batch volume and required processing time
• [ ] Required filtrate or retentate recovery
• [ ] Need for a prefilter or staged filtration
• [ ] Approved flushing and wetting fluids
• [ ] Intended sterilization method and permitted cycle count

Sterile-filtration documentation

• [ ] Product-specific microbial challenge data
• [ ] Challenge organism and challenge level
• [ ] Validated fluid and operating conditions
• [ ] Maximum pressure, flow, time, and throughput covered
• [ ] Required pre-use or post-use integrity-test method
• [ ] Product-specific bubble-point or forward-flow limits
• [ ] Test-fluid and temperature requirements
• [ ] Manufacturer documentation connecting the integrity test to the product’s microbial-retention claim

Regulated or sensitive applications

• [ ] Extractables and leachables information
• [ ] Flushing recommendations
• [ ] Sterilization documentation
• [ ] Lot traceability
• [ ] Certificate of analysis or conformity
• [ ] Shelf life and storage conditions
• [ ] Change-notification policy
• [ ] Material declarations for membrane, supports, seals, and housing

Treat sterilization attributes separately. Sterile supply, gamma compatibility, autoclave tolerance, and steam-in-place capability are not interchangeable. Each applies to the complete filter assembly under specified conditions, not to PES as a polymer.

The final selection rule is simple: choose the exact PES product, not the polymer name alone. Start with the separation target and fluid, decide between a micron rating and MWCO, select the required wettability, area, and format, and then verify compatibility, retention evidence, sterilization limits, and integrity-test requirements. If the supplier cannot document those points for the intended process, test another grade or another membrane chemistry rather than relying on the PES label.