Stirred Cells
Sterlitech offers a variety of stirred cells that utilize a cross/tangential flow design for the filtration of small volumes of feed solution. The compact design and capacity is also ideal for membrane studies and characterization.
Stirred Cell Features and Benefits:
- Tangential flow stirred cell design increases membrane life and sample throughout
- Test small areas of membrane or small volumes of feed solution
- Filter small volumes ranging from 10 mL to 2L
- Options operable up to 2500 psi
- Solvent resistant options available
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Frequently Asked Questions
Q: Can I use microfiltration membrane disk filters in the stirred cells?
Yes, you can use almost all microfiltration membrane disk filters in the stirred cells. The only exception are the ceramic membrane disk filters; these are too thick to fit in the stirred cells.
Q: What do I need to operate a stirred cell?
You can find a diagram for a typical stirred cell system at https://www.sterlitech.com/media/wysiwyg/Manual/HP4750_Flow_Diagram.png. In addition to the stirred cell itself, the user will require a pressure source consisting of a regulated supply of compressed inert gas or air, a bleed valve for releasing the air pressure, an appropriately sized magnetic stirring plate, and a permeate collection vessel (e.g. flask or beaker) to collect the filtrate.
Q: Do I need to precondition the membrane disk used in a stirred cell?
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.
To pre-condition the membrane disk, install it in the stirred cell and then fill the stirred cell with purified deionized water. Initiate operation of the stirred cell at the pressure and temperature expected for the separation experiments. Allow the cell to operate until the permeate flux has stabilized at an expected value. Then release the pressure, discard any water remaining in the stirred cell, and discard the water from the permeate collection vessel. You may now proceed with your experiments by refilling the cell with the desired feed sample. At no time should the wetted membrane disk be allowed to dry.
Q: Do you have operating manuals for the stirred cells?
Yes, we offer operating manuals for the HP4750, HP4750X, UHP polymeric stirred cells. You can find links to the operating manuals for the stirred cells by clicking on the “Documention/Media” tab on the stirred cell product pages.
Q: Why am I not achieving the membrane manufacturer’s published rejection and/or permeate flux while using my stirred cell?
It is important to note that membrane manufacturer’s specifications for rejection and permeate flux are usually based on testing of large area spiral wound membrane elements operating in crossflow mode using standardized feed streams and pressures. It is normal, and to be expected, that rejection and permeate flux will be different for feed streams and pressures that are not similar to the standardized test conditions. It is also normal, and to be expected, that rejection and permeate flux will have greater variability from published specifications for devices with membrane active areas that are very much smaller than spiral wound elements, such as stirred cells. Some amount of concentration buildup in the feed for stirred cells is inevitable and this may affect rejection and permeate flux.
There are some tactics that can be used to optimize rejection and permeate flow while using stirred cells. First, the membrane should be pre-conditioned using purified deionized water. Please refer to the operating manual for the pre-conditioning procedure. Second, make sure that the stir bar is turning properly and at an appropriate rate. Third, the operating pressure should correspond to the membrane manufacturer’s recommended pressure. Finally, you may want to stop your experiments while there is still some feed liquid remaining in the stirred cell to mitigate effects associated with increasing concentrations.
Q: Can I attach the stirred cell permeate line directly to an HPLC analyzer or other laboratory instruments?
Yes, you may connect the permeate line directly to an instrument. However, it is important to understand that if the membrane fails or is allowed to dry, then the full feed pressure may be applied to the permeate line. If the instrument cannot withstand the feed pressure, then directly connecting the permeate line is not recommended. Alternatively, if the membrane becomes prematurely fouled (due to a high TDS or particulate loading), permeate levels may drop below detection in the HPLC inlet port.
Q: What is the maximum membrane thickness for the stirred cells?
The stirred cells are designed to accept flat sheet membranes with thickness of 350 microns or less.
Q: What is the pore size rating for the porous support disc (SKU 1114910)?
The porous support disk has a nominal pore size of 20µm.
Q: What are the materials of construction for the polymeric stirred cells?
All of the wetted surfaces are non-metallic. The UHP stirred cells have polycarbonate or acrylic barrels, polyacetal endcaps and stir rod, PTFE stir bar, polypropylene support screen, and silicone o-rings. The UHP-K stirred cells have polysulfone wetted components and silicone o-rings.
Q: What is the maximum operating pressure for the polymeric stirred cells?
The maximum operating pressure for the UHP stirred cells is 73psi (5.0bar). However, the nominal safety relief pressure for the vent valve is 63psi (4.3bar).
The maximum operating pressure for the UHP-K polysulfone stirred cells is 71psi (4.9bar). However, the nominal safety relief pressure for the vent valve is 57psi (3.9bar).
Q: Why is the flat sheet membrane I'm using measuring a flux value less than the published flux value?
Flow characteristics for a spiral element and flat sheet membrane are significantly different and are really only comparable on a qualitative basis. Variability in the membrane manufacturing process, differences in water composition, test procedures, and test equipment, used in a factory, laboratory, or elsewhere, will impact water flux results.