3 Factors Affecting Carbon Filtration

Are you drinking something right now? Carbon filters might just play a part in what is in your cup. Despite the recent explosion of water filters and activated carbon in consumer products, carbon and charcoal have been used as a purification tool for thousands of years. Have you ever stopped to look at the filter on your fridge and wonder, "What does this thing do, anyway?"

Well, the fridge is only the beginning; carbon filters are not just used for purification of liquids but are also used to trap fumes and vapors as well. At AirClean Systems, our bonded carbon filters are designed and manufactured to meet your specific application needs. So how exactly does a carbon filter work and what factors impact how well it works?

What is activated carbon?

Carbon comes from a variety of sources, like trees, coal, and even coconut shells. Once you have identified your source, you need to activate it. Activation can be done in several ways, including the introduction of pressure, steam, or chemicals. Think of how heat changes a corn kernel to popcorn; activation expands and creates channels within carbon.

These pores and caverns add a key component: surface area. The increase in surface area in these pores and caverns offers more places for chemicals and vapors to bind. Just a single pound of activated carbon provides a surface area of 14,514,944 ft2, more than the area of 300 football fields!

These pores provide the perfect surface for adsorption, an electrostatic force at the molecular level. Like Velcro or tape, as chemicals pass through the carbon, the electrostatic or Van Der Waals forces pull the passing molecules to the structure.

Now that we have a grip on how these filters work, let's take a look at the factors impacting how well a carbon filter works. After all, we know our fridge mandates we must replace them, but why?

1. Molecular Size

While carbon filters can capture a wide variety of chemicals, it might come as a surprise they don't have the same capacity for every chemical. Molecular size plays a large role in how well something will be captured in a carbon filter. The larger the size of a chemical's molecular structure, the stronger the electrostatic forces are and the higher capacity a filter will have for it.

Think of walking through the mall with a group of friends. One person may want to stop by every store and spend hours bouncing from place to place while, if you're like me, you might go straight to the food court and then home! Larger chemicals act as the friend; they interact strongly with carbon and take their time moving through the filter. Smaller chemicals might act like me and pass by nearly every store, stopping only at the food court.

Ultimately this analogy means two things:

  1. I am frequently hungry and can't be bothered at the mall.
  2. Larger chemical structures are easily captured while smaller chemicals aren't captured as well.

If a chemical is poorly captured, one way to boost the efficiency of the filter is by offering an impregnate. An impregnate is a substance that helps facilitate and boost filter capacity, acting as an intermediate to transform the troubled chemical into a more capturable species.

At AirClean Systems, we can offer up to three layers of impregnates per filter, allowing a single carbon filter to be suitable for an array of chemicals being used. This allows one filter to accomplish the task of many even on acids vapors, amines, and chemicals like formaldehyde.

2. Environment - Temperature and Humidity

Carbon filtration efficiency can also be impacted by environmental factors like temperature and humidity. In cases where chemicals are being heated, kinetic energy is being added. As the chemicals spin and rotate through space, they might bounce from binding site to binding site, too excited to slow down.

Carbon filtration efficiency can also be impacted by environmental factors like temperature and humidity. In cases where chemicals are being heated, kinetic energy is being added. As the chemicals spin and rotate through space, they might bounce from binding site to binding site, too excited to slow down.

Heating also adds pressure to the system by pushing vapors upward. This pressure increases the speed at which they are traveling through the filter. By quickly being forced through, the retention time drops and the chemical is afforded less opportunity to interact.

Humidity is another environmental factor that plays a role in carbon filtration. The relative humidity of an environment a ductless hood is placed in can impact the performance of filtration. As chemical-containing vapors pass through the filter, so does water vapor. This water vapor in the air passes through the filter, the water bonds to the carbon as well, decreasing the available space for other chemicals to bond.

To detect how the environmental factors affect the carbon filtration, AirClean Systems incorporates both a temperature and humidity sensor package into our Endeavour and Independence ductless fume hoods. These sensors are designed to measure the relative humidity and temperature inside the hood and will alarm if values exceed the preset maximum.

3. Volume of Evaporation

The volume of evaporation can be difficult to quantify. For a ductless fume hood to provide proper protection, understanding the chemical volume moving through the filter is important in predicting how long filters will last.

The volume of evaporation represents how much of a chemical is getting into the air and passing through the filter. This value varies based on the application being performed in the unit. Applications like slide staining and solvent mixing are going to release different volumes of vapors compared to epoxy coating.

Each carbon filter offers a finite number of binding sites and, as these sites become occupied, the filter runs out of space to capture chemicals. Like a hotel running out of rooms, the molecules run out of options and breakthroughs can occur.

We understand the volume of evaporation isn't always something on the mind of a scientist. When considering a ductless option, we suggest asking questions about your application like:

  1. What is the difference in chemical volumes from the start of your procedure to the end of your procedure?
  2. Are you using any heat in the application that could increase the volume of vapors produced?
  3. Are you using a condenser or rotary evaporator?

Calculating the volume of evaporation can be difficult, but ultimately the types of chemicals, environment the unit is placed in, and the volume of chemical evaporating is key to ensuring the right filters and unit are selected to ensure end-user safety.

AirClean Systems' Solutions

At AirClean Systems, we have over 25 years of industry experience for ductless solutions and are a proud member of the Scientific Equipment and Furniture Association (SEFA). As a member of SEFA, we have pushed to establish safety requirements and best practices for ductless fume hoods. Foremost, we believe safety should be a priority and not an option. This philosophy can be seen in our application worksheets and our units' features.

For every ductless application, we require a completed application worksheet, so as to ensure a ductless hood will serve as a safe and cost-effective solution. Our filter specialists review every application worksheet to ensure that the proper filters, for both the chemicals being used and the volume of evaporation, are recommended.

In addition to analyzing the application to ensure it is a suitable fit for ductless, every ductless fume hood offers uncompromised safety features. From our AC600 Series Ductless Chemical Workstation to our Independence Ductless Fume Hood, each unit includes an airflow sensor to ensure proper face velocity at the front of the unit. If there is a drop-in airflow or a clogged filter, the unit will alarm notifying the user of unsafe operating conditions. This sensor also adjusts the face velocity of the unit to always ensure proper containment.

One key to filtration efficiency is the size or bed depth of the filter. Other factors do play into the overall performance and filter life but AirClean Systems filters are bonded, making the bed depth constant, unlike traditional granulated filters. Our bonded carbon filters offer unmatched capacity while also preventing potential off dusting or dead spots seen in granular carbon filters.

In the event of saturation, every unit includes a gas sensor that will alarm if breakthrough occurs. This safety sensor comes calibrated and tested for sensitivity to volatile organic compounds including things like alcohols, alkanes, and aromatics commonly seen in most laboratories. In event of filter saturation, our unit will alarm with an audible and visible alarm to notify of required filter replacement.

While these features come standard on every ductless solution, our Independence offers protection through revolutionary sensors to ensure your safety. Offerings our TriAnalyze 3x3 Gas Detection Technology, the Independence offers a metal oxide safety sensor, an acid sensor, and a photoionization detector. These sensors provide the added ability to sample three points; Interfilter, filter exhaust, and room air to ensure zero breakthroughs occurs. These features are easily observed on our AirSafe TOUCH Controller. Independence also has an onboard chemical library, complete with application verification, to make sure that the filters installed will protect you, even if your application changes.

AirClean Systems strives to provide safe and environmentally friendly solutions. By treating each application as unique, we aim to offer a solution for the problems of each individual lab by providing tailored solutions. For additional information on our ductless fume hoods, contact our technical sales specialists at +1 (800) 849-0472 or email us at sales@aircleansystems.com.