Filtration Resources
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December 07, 2016
Sterlitech Corporation is proud to announce the launch of gold-sputtered polycarbonate membrane filters. “Why gold? What is sputtered?” you may ask. Well, some particles are just too small to see with an ordinary light microscope, for these things we need get down to details not seen by traditional microscopy. Scanning Electron Microscopy (SEM) is a powerful tool that uses a focused beam of electrons to resolve some of the smallest objects. But in order to see anything at this level, the sample must be prepared correctly. Gold is very conductive and won’t corrode (NASA wraps many of their satellite probes in gold-coated blankets to protect them) and polycarbonate filters have a smooth focal plane for keeping everything in view under a microscope; gold-sputtered polycarbonate filters bring these two attributes together
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November 02, 2016
A large part of extracting commercially important compounds from plants involves passing a type of solvent over plant material, then filtering out any plant debris and undesirable by-products. This latter filtering process can be difficult to optimize if too many undesirable compounds inadvertently come along for the ride; so how can you speed things up?
In several states, cannabis sativa (AKA: marijuana) is being processed in this way to extract the active compounds THC and CBDs for medicinal use; four of these states have already passed legislation permitting recreational use, and more states are expected to do the same in the next few years. The process to extract THC and CBDs from cannabis is usually done by passing liquefied butane, supercritical CO2, or cold ethanol over the plant material. These processes are very efficient at extracting the compounds, but also need a secondary filtering process (often called “winterizing’ in butane extraction methods) to remove
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October 05, 2016
Numerous industries have a necessity to keep things clean and sanitary. Filters are an efficient and cost effective way to keep dirt, dust, bacteria, viruses and other small particulates out. The variety of applications are endless, and hundreds of product manufacturers employ filtration to keep things clean: from medication, to automobiles, to even your home.
Within the life sciences, it is often critical for researchers to keep the growth environments of key cells sterile for production of significant compounds. Contamination could mean the loss of hundreds of thousands of dollars’ worth of product. At university labs, cell biologists and clinical researchers alike utilize small vent filters and devices to keep their cell growth devices and growth media free of any bacteria or molds that could damage their cell lines in their ongoing research. Sterlitech offers standard
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September 13, 2016
What is silt density index (SDI)?
Silt density index (SDI) estimates the quantity of suspended solids and colloids inside of water. SDI is measured following the ASTM D19.08 Standard Test Method for Silt Density Index (SDI) of Water, using a 0.45 micron membrane. SDI provides information about the fouling potential of water treatment equipment, including membrane filtration systems, and therefore is commonly used in their design and choice.Is SDI a reliable fouling propensity parameter? How is it used?
SDI is a simple and helpful tool extensively used in pilot or large-scale treatment plants as a standard test to verify the fouling potential of RO and NF membranes. However, using SDI to estimate the fouling intensity of water treatment equipment has some limitations. Even though SDI is measured using a dead-end filtration unit, hydrodynamic conditions in dead-end filtration units are not representative of the hydrodynamic conditions -
September 13, 2016
When particles of a known and defined size are removed via filtration, it is fairly easy to choose the right filter by simply selecting a pore size smaller than the particle. But what happens when you need to filter a very dirty solution that contains an innumerable amount of particle sizes? If a pore size too small is chosen, a cake layer of debris will form on the membrane surface and foul it completely. If too big of a pore size is selected, then a large portion of the solids will pass right through the filter. Because it could be easily overdone, it’s usually not a good idea to stack multiple filters in the same filter holder and process it all at once. So what is an effective solution to this problem?
Enter the world of pressure drop! Back in 1856, French hydrogeologist Henry Darcy figured out the physics behind fluid flow in a filter medium while he was working in Dijon, France (yes, also the little town that gave us great mustard). Henry figured out that in order to
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September 13, 2016
In 2015, the US Food and Drug Administration (FDA) signed off on new legislation to finalize the Food Safety Modernization Act (FSMA), which requires food and beverage manufacturers to be more proactive to minimizing food-borne contamination from microorganisms. The FDA now places more effort on the individual companies to test food products according to the new guidelines in various parts of the production process. These processes can be ideal places to draw fluid samples for bacterial capture and subsequent analysis. The use of membrane filters to evaluate bioburden in these types of liquids is the standard means of recovering and quantifying potentially harmful microorganisms. Does this sound like it makes for more work for the food processors in our communities? It might, but Sterlitech Corporation can help!
According to the new regulations, high-risk food producers will be inspected more frequently, will have to maintain more detailed records, and establish clear food safety
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July 13, 2016
Q: What is Cross Flow Velocity?
A: Cross flow velocity (CFV) is the linear velocity of the flow tangential to the membrane surface and is reported in [m/sec] or [ft/sec]. CFV affects the hydrodynamic conditions in the cell, and as a result affects the fouling rate and formation of concentration polarization at membrane surface and is calculated by dividing the volumetric flow rate [lpm or gpm] in the flow channel by the cross sectional area [m2 or ft2] of the flow channel.
Q: How is CFV calculated in Sterlitech’s bench-scale test cells?
A: Example: Calculate CFV in the CF042 cell
- Flow channel cross sectional area: Channel depth x Channel width* = 0.23 x 3.92 cm
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July 12, 2016
Water, oils, and solvents sometimes need to be filtered. But when you see filters labeled as hydrophilic, hydrophobic, and now oleophobic; what does all this mean? Sterlitech currently offers membrane disc and sheet filters in 10 different polymer types and 4 inorganic filters. 2 of the polymer types are subdivided into 4 subgroups based on surface chemistry alone.
Filters listed as hydrophilic, which has its origins in the Greek language and means water (hydro) loving (philos), love to get wet! Hydrophilic filters will easily pass water or water-based solutions such as dairy, river water, seawater, cell culture solutions, buffers, beverages, and many more. The filters best suited to handle these solutions are silver, ceramic
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June 08, 2016
Sterlitech’s polycarbonate and polyester track-etch membrane filters are a unique product that find use in numerous applications. They possess clean cylindrical pores that transverse the membrane surface from one side to the other. As a result of this unique feature, the pore density must be much lower compared to almost all other standard thin-film membranes such as Nylon, PTFE, PVDF, and more. Particulates either pass through the pores in track-etch filters, or remain on the surface. Almost never do they become embedded within the pore’s interior. But what happens when these filters are needed for your project and the particles being filtered occlude the opening of the pores? This effect is called pore blinding; and you may ask “But what can be done?”
Fear not brave scientist! In most applications, the track-etch filters will work fine on their own. But if a difficult particulate is clogging up your filter too soon, consider use of our Polyester
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May 09, 2016
Filtering difficult biological solutions? Normally, using a thin membrane filter can pose serious questions:
- “How much liquid can I get through the filter?”
- “When will it clog?”
- “What if my solution is very critical to the project?"
Sterlitech Polyethersulfone (PES) membrane filters have a unique asymmetric pore structure that allows the user to take advantage of this feature; PES can be its own pre-filter and dynamically increase throughput!
Hold a sample piece of this material up to the light at an oblique angle, and you will see a glossy/shiny side, and a more matte/dull side. This sided-ness feature (see Figure 1) is helpful in that the more open area (matte side) has larger entry pores compared to the glossy side; and it should face into the incoming liquid stream for the best results with particulate-heavy liquids. If you were to view an SEM image of the matte side, you may quickly notice the pores seem much larger