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
Do you need a Chemical Compatibility Chart?
We have a Chemical Compatibility Chart that you can use for reference.
How should I remove the preservative solution from the membrane and is there any specific recommendations before use?
Q. How should I remove the preservative solution from the membrane and is there any specific recommendations before use?
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.
How do I store new forward osmosis (FO) flat sheet membranes?
Q. How do I store new forward osmosis (FO) flat sheet membranes?
Membranes should be stored in the fridge. Do not allow to freeze. Also membranes should be stored away from sunlight.
How do I store used forward osmosis (FO) flat sheet membranes?
Q. How do i store used forward osmosis (FO) flat sheet membranes?
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 recommend 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.
We noticed that there are water drops in the flat sheet membrane sealed bag. Is that a quality issue?
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.
What's the difference between Synder PVDF and PVDF+ Membranes?
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.
Do I need to pre-condition the flat sheet membranes? And, if so, what is the recommended procedure?
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.
What solvents are compatible with Evonik PuraMem flat sheet membranes?
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.
What solvents are compatible with Evonik DuraMem flat sheet membranes?
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.
What is the proper orientation of the forward osmosis membrane?
The active side of the membrane (as indicated by the packaging) should be facing the feed solution.
How do I calculate the rejection of forward osmosis (FO) membranes?
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)
What is the difference between Microdyne Nadir polyethersulfone (PES) ultrafiltration (UF) membranes and hydrophilic polyethersulfone (PESH) UF membranes?
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.
I want to separate a large molecule of known molecular weight from an aqueous solution. Which ultrafiltration (UF) membrane would I select?
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.
Do you offer cellulose acetate ultrafiltration (UF) flat sheet membranes?
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.
What is the sodium chloride rejection for the Dow nanofiltration (NF) membranes?
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.
I have a polymeric stirred cell and discovered that my disk size is not listed in the ordering information for the flat sheet membranes. Can I purchase the flat sheet membranes in the correct disk size for my stirred cell?
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.
Do you offer samples of the flat sheet cross flow membranes?
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.
I have noticed that the flat sheet membranes come in sizes described as CF016, CF042, and Sepa CF. What are these sizes?
These membrane sizes are intended for use in the bench-scale crossflow test cells offered by Sterlitech. Please see list of flat sheet membranes we offer and their dimensions:
- HP4750 Stirred Cell: 47 mm (1.85") discs
- CF016 cell: 58 x 75mm (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: 47mm discs
- CF090 circular cell: 90 mm discs
Are the flat sheet membranes available as roll stock?
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.
What is the recommended transmembrane pressure (TMP) for the flat sheet membranes?
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.
How do I calculate the cross flow velocity (CFV) for flat sheet membranes?
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 https://www.sterlitech.com/blog/post/tech-tips-cross-flow-velocity-cfv/ for more information.
What is the recommended cross flow velocity (CFV) for the flat sheet membranes?
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.
I accidentally allowed my flat sheet crossflow membrane to dry out. Can I still use it?
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.
The Flat Sheet Membranes appear dry in their packaging. How do I pre-wet them? Do I need to do this?
Q. The Flat Sheet Membranes appear dry in their packaging. How do I pre-wet them? Do I need to do this?
A. 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.
Aquaporin Inside FO membranes are changing color from neutral to yellow/brown. Does this affect the membrane's characteristics or performance?
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.
How do I clean the flat sheet membranes?
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.
The flat sheet membranes appear dry in their packaging. Do they need to be pre-wetted before use?
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.
How do I store used flat sheet crossflow membranes?
Q. How do I store used flat sheet crossflow membranes?
A. Used flat sheet membranes must always remain wet, including during storage. Membranes that are allowed to dry will irreversibly lose water permeability. To prevent microbial growth, the membranes can be stored in a 0.5% solution of formaldehyde. Alternatively, the membranes can be stored in a 1.0% solution of sodium metabisulfite (SMBS). To maintain efficacy, the SMBS solution should be replaced monthly. Or the membranes can be stored in UPDI water that is replaced weekly.
What is the shelf life for the flat sheet crossflow membranes?
Prior to use, the membranes should be stored in a climate controlled environment, away from sunlight and heat, while sealed in the original packaging. We recommend using the membranes as soon as practical after receiving them. However, most of the flat sheet membranes may be stored for up to one year without affecting performance. The exceptions are the GE cellulose acetate membranes (CE and CK) and the Aquaporin FO membrane which should be used within 6 months.
Can I reuse flat sheet membranes after they have been removed from a test cell?
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.
Do I need to pre-condition the forward osmosis (FO) flat sheet membranes? And, if so, what is the recommended procedure?
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.