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Frequently Asked Questions

Learn more on what Sterlitech Corporation has to offer. Find answers to your questions about our filtration products here!

Flat Sheet Membranes FAQ

Rinsing the membrane on both sides with a stream of clean water is sufficient to remove the preservative solution. There is no need to pre-condition.
Membranes should be stored in the fridge. Do not allow to freeze. Membranes should be stored away from sunlight. 
Post use, the membrane should be rinsed with water after testing and stored in clean water if the storage duration will be less than 24 hours.  If the membrane is rinsed with water and expected to be stored for longer than 48 hours, it is recommended to use a 1% sodium metabisulfite (SMB, chemical formula Na2S2O5) to prevent bacterial growth from occurring. Periodically inspect the membranes for biological growth. If the preservative solution is cloudy you need to replace it.  Renew the preservative solution every month.
Some manufacturers supply their membrane in wet to prevent the membrane from going dry. There is always moisture in these sealed bags and it is not uncommon for some condensation (droplets) to form.

We offer both BN and V3 Ultrafiltration Flat Sheet Membranes from Synder. The BN is composed of a standard polyvinylidene fluoride material (PVDF), while V3 iscomposed of material designated as PVDF+. This membrane has been treated to create a positive surface charge, optimizing it for alkaline cleaner and industrial waste water treatment applications.

Yes, for flat sheet membranes that will be used with water or aqueous solutions, we recommend that you pre-condition the membranes prior to conducting your separation experiments. Pre-conditioning helps ensure that the membranes perform as expected. Also, pre-conditioning removes preservatives and other residuals from the membranes. Purified deionized water is used to pre-condition the membranes. For all flat sheet membranes except the forward osmosis (FO) membranes, install the membrane in the test cell and apply the purified deionized water feed at the normal operating rate and pressure for the membrane. Allow the system to operate with the purified deionized water feed until the permeate flux stabilizes at an expected value. You can now replace the purified deionized water feed with your feed solution and begin your experiments.

The Evonick PuraMem flat sheet membranes are expected to be stable when used with apolar hydrocarbon-type solvents such as: alcohols (including ethanol, methanol, and 2propanol), aliphatic hydrocarbons (including hexane and heptane), aromatic hydrocarbons (including Toluene and Xylene), butyl acetate, ethyl acetate, methyl ethyl ketone (MEK), and Methyl tert-butyl ether (MTBE). The membranes are not recommended for use with water-solvent mixtures.

Please contact us if you desire to use the PuraMem flat sheet membranes with other solvents. We would be glad to assist with evaluating the compatibility of the membranes with your application. 

The Evonick Duramem flat sheet membranes are expected to be stable when used with most polar and polar aprotic solvents such as: acetone, butyl acetate, ethanol, ethyl acetate, methanol, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl tert-butyl ether (MTBE), and tetrahydrofuran (THF). The membranes are generally stable in water-solvent mixtures that have neutral pH.

Please contact us if you desire to use the Duramem flat sheet membranes with other solvents. We would be glad to assist with evaluating the compatibility of the membranes with your application.

The active side of the membrane (as indicated by the packaging) should be facing the feed solution.

You can estimate the rejection of forward osmosis membranes by using the following formula, where Cp is the concentration of solute in the permeate and Cf is the concentration of solute in the feed:
R= 1-(Cp/Cf)

Both the Microdyne Nadir PES UF membranes and the PESH UF membranes are composed of polyethersulfone and are hydrophilic. The PESH UF membranes have been modified for enhanced hydrophilic properties and, consequently, may be more easily preconditioned and may have better resistance to fouling in some applications.

In general, retention of large molecules is not only influence by the molecular weight of the molecule, but also by the shape of the molecule and the physiochemical interactions between the molecule and the membrane. For greatest retention, you should select a UF membrane that has a molecular weight cut-off (MWCO) rating equal to or smaller than the molecular weight of the target molecule.

You may also want to evaluate a UF membrane with a MWCO rating that is one step larger than the target molecule. You may find that this selection offers advantages of lower operating pressure and/or higher permeate flux while still exhibiting acceptable retention of the target molecule.

You can find Sterlitech’s offering of flat sheet UF membranes at https://www.sterlitech.com/ultrafiltration-uf-membrane.html. Please click on the “Application/Specification” tab near the middle of the page, and scroll down as necessary, to review the MWCO ratings.

Currently we do not offer cellulose acetate UF flat sheet membranes. However, we do offer a wide variety of hydrophilic flat sheet UF membranes that may be considered as alternatives.

For a feed solution of 2,000 ppm sodium chloride (NaCl) at 70 psi (0.5 MPa) and 77°F (25°C), the NF90 membrane has sodium chloride rejection of between 90-96% while the NF270 membrane has approximately 50% rejection.

Yes, we can supply the flat sheet membranes in the correct disk size for your stirred cell. Please contact us at [email protected] for pricing and availability.
We do not offer complimentary samples of the flat sheet crossflow membranes. However, most customers find the standard pack quantities to be quite reasonable for initial evaluations. For customers that want to evaluate several different membranes, we do offer custom variety packs. And, in some instances, we may be able to offer custom packs containing smaller sheet quantities. Please contact us to inquire about pricing and availability.
These membrane sizes are intended for use in the bench-scale crossflow test cells offered by Sterlitech. Please see the list of flat sheet membranes we offer and their dimensions: HP4750 Stirred Cell: 47 mm (1.85") discs, CF016 cell: 58 x 75 mm (2.26 x 2.95") coupons, CF042 cell: 56 x 115 mm (2.20 x 4.53") coupons, Sepa CF cell: 140 x 190 mm (5.51 x 7.48") coupons, CF047 circular cell: 47 mm discs, CF090 circular cell: 90 mm discs
Yes, we are able to offer some of the flat sheet membranes as roll stock. Please contact us at [email protected] to inquire about pricing and availability.
The recommended TMP will depend on the type of flat sheet membrane and on the application. Typically, a reasonable TMP will be the same as that noted for the permeate flux specification of the membrane. The specifications for any of the flat sheet membranes can be easily found on our website by clicking the “application/specification” tab on the product web page and scrolling down as necessary. Please contact us at [email protected] if you need additional assistance.
Cross flow velocity (CFV) is the linear velocity of the feed flow tangential to the membrane surface and is typically reported in m/sec or ft/sec. It is calculated by dividing the volumetric flow rate through the feed channel by the cross-sectional area of the feed channel. Please refer to the CFV article at <a href="https://www.sterlitech.com/blog/post/tech-tips-cross-flow-velocity-cfv">Tech Tips</a> for more information.
Most membrane manufacturers recommend CFVs of 5 to 35cm/s for their spiral wound membrane elements. The flat sheet membranes can be operated in this range to simulate use in such elements. Additionally, the flat sheet membranes may be operated outside of this range by users that want to examine the relationship between CVF and fouling and membrane performance in their applications.
Unfortunately, allowing a previously wetted crossflow membrane to dry usually results in permanent reduction of water permeability. Nevertheless, you can attempt to re-wet the membrane and use it. First, soak the membrane in a 50% alcohol solution for at least 15min (ethanol, methanol, or IPA would be acceptable). Next, install the membrane in the test cell and operate the cell with purified deionized water as though you were pre-conditioning the membrane. After about 30min, the permeate flux should stabilize to whatever rate the membrane is now capable of.
Yes, you need to pre-wet the membranes. The best procedure is to place them in a dry holder and allow them to wet from the inlet side first. It may be best to perform this operation with water or a buffer, then dispose of the first rinse, and introduce the process fluid. This prevents any wetting agents or preservatives from mixing with the process solution.

Slight change in color towards yellow/brown is completely harmless and caused by the chemicals used in the production process of the Aquaporin Inside FO membranes . This change in the color does not affect Aquaporin Inside membrane's characteristics or performance.

Determining which solution to use to clean a flat sheet membrane depends on the substance it is fouled with. As a general rule, you can use a caustic or oxidant solution for organic fouling and an acidic solution for inorganic causes. Please remember that different membranes polymers have different pH tolerances.

Yes, you need to pre-wet the membranes. The best procedure is to place them in a dry holder and allow them to wet from the inlet side first. It may be best to perform this operation with water or a buffer, then dispose of the first rinse, and introduce the process fluid. This prevents any wetting agents or preservatives from mixing with the process solution.

Used flat sheet crossflow membranes must be stored wet at all times. If a membrane is allowed to dry out, it can irreversibly lose water permeability and performance.

For storage, place the membrane fully submerged in one of the following solutions:
0.5% formaldehyde solution (helps prevent microbial growth)
1.0% sodium metabisulfite (SMBS) solution -- Replace the SMBS solution monthly to maintain effectiveness

UPDI water (ultrapure deionized water)--Replace the water weekly to reduce contamination and biofouling

Sterlitech flat sheet crossflow membranes should be stored sealed in the original packaging in a climate-controlled environment, protected from direct light, heat, and temperature extremes. While we recommend using membranes as soon as practical after receipt, most flat sheet membranes can typically be stored for up to one (1) year without affecting performance when stored properly.

Yes, you may attempt to reuse flat sheet membranes. However, you may find it difficult to achieve a leak free seal. The cell body o-rings necessarily compress the membrane during installation and the physical action of separating the membrane from the o-rings during removal may cause damage. This damage can impede that ability to achieve a leak free seal when the membrane is reused.
Prior to use, the FTSH2O™ flat sheet membranes should be rinsed with DI water. Keep membranes moist at all times, the membranes should not be allowed to dry.
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