Need help selecting gas filters/traps?

Selecting the most appropriate gas filter/trap for your specific needs can be a daunting task because there are often many choices.  Hopefully after reading this post, the selection process will be easier.

Before beginning the selection process, I suggest asking yourself the questions below.

1. What is the gas which needs to be cleaned?
2. What impurities need to be removed from the gas?
3. What are the levels (concentration) of the impurities?
4. What is the gas line pressure?
5. What will be the maximum flow rate of the gas?
6. What is the tubing material and the outside diameter (OD) of the tubing that you will be using?

Several more questions you may want to think about (I would consider these as personal preferences).

1. Do you prefer an inline filter or a baseplate-type filter?
2. Do you prefer an indicating filter or a non-indicating filter?
3. What is/are the most important factors when selecting a filter? Is it cost, capacity, ease of replacement, maximum gas flow rate/line pressure, or something else?

Since there are many choices available, I highly recommend that you begin your search/selection by reviewing the following literature "Gas Management: Supplies for GC Labs (restek.com)".  This document will provide you an overall visual summary of all the gas filters/traps available from Restek.  When combined with the Excel spreadsheet (which can be downloaded below), your gas filter selection should (hopefully) be quick and easy.

In addition to the information contained in the link above and spreadsheet, below are several general guidelines to keep in mind while shopping for a filter/trap.  Also included is information on best plumbing practices which were found in various resources, including manufacturers of tubing and fittings, and from instrument manufacturers via webinars and/or installation guides.  Finally, please review the Restek website product page for a complete/detailed listing of all available specifications.

1. For inert gases like nitrogen, helium and argon, copper tubing and brass fittings are fine to use. For reactive gases like hydrogen, stainless steel tubing and fittings are often recommended (and may even be required in certain locations).
   
   
2. A trap/filter will not remove 100% of any contaminant. Generally speaking, unless stated otherwise, a gas/trap filter can be expected to remove an order of magnitude of a targeted impurity from a gas, when used below the maximum line pressure and below the maximum flow rate, over the lifetime of the filter.  For example, if the concentration of an impurity in a gas is 10ppm, and the line pressure and flow rate are below the maximum suggested limits, the concentration of the impurity exiting the filter can be expected to be 1ppm over the lifetime of the filter.  In other words, the purity of the exiting gas will (almost always) be higher when the filter is new and the exiting gas purity will decrease over the lifetime of the filter.   Please see the product page for a particular gas filter/trap for a complete listing of specifications.
   
   
3. The traps/filters Restek sells are designed to take a very clean gas and make it cleaner. They are not designed to take a low quality/grade of gas and turn it into a high quality/grade of gas.  If you only have access to a low grade of gas and need to increase the purity, consider purchasing a gas generator (if one is available) or install multiple traps/filters, including several high-capacity filters followed by an indicating filter.
   
   
4. Install inline traps/filters vertically with the gas inlet at the bottom of the filter and the outlet at the top of the filter. This should prevent any channeling of the gas stream.
   
   
5. Reactive gases like hydrogen are often filtered to remove moisture, and sometimes hydrocarbons, but not oxygen (unless the hydrogen has very low levels of impurities). This is because removing oxygen from a gas stream is often accomplished via a heat-generating catalytic reaction while moisture removal and hydrocarbon removal are from absorption.  If using a filter to remove hydrocarbons and moisture from hydrogen, I recommend installing an indicating moisture filter first, followed by a hydrocarbon filter (these filters are not indicating).  The reason is that if moisture is allowed into the hydrocarbon filter, it may displace the contaminates trapped by the hydrocarbon filter and cause chromatographic issues (like ghost peaks) with the analysis.
   
   
6. Hydrocarbon removal filters are only for C4’s (butanes) and larger/heavier hydrocarbons. Smaller molecules (methane, C2’s and C3’s) often break through the filter medium.
   
   
7. Carefully review the published maximum flow rate. Did you know that (in some cases) the maximum published flow rate may not mean what you think it does?  One filter’s maximum flow rate may actually be for the expected flow rate though the filter at the maximum published pressure limit, and that another filter’s maximum flow rate may be the maximum gas flow through the filter which it can operate properly (remove the impurities). 

Click here for a downloadable Excel spreadsheet showing many of the specifications of each filter available from Restek.  Once you have narrowed down your selection, review the product page for additional information which may be available.  Please note: H2O = water/moisture, O2 = oxygen, HC’s = hydrocarbons, CO = carbon monoxide, CO2 = carbon dioxide, Sulfur = sulfur gases.

If you still need help, Contact Us.