I am analyzing natural gas by gas chromatography technique. The main molecules to identify basically are light hydrocarbons such as methane, ethane, propane, butane (i- and n-), pentane (neo, i- and n-), however, natural gas also contains negligible amounts of hexane, heptane, and higher hydrocarbons, besides content of hydrogen sulfide and carbon dioxide are very important; density and liquefaction process are affected by such molecules and higher hydrocarbons.
For instance, during separation of methane using a PDMS column, it is possible that carbon dioxide can be adsorbed quickly to stationary phase affecting its chromatographic properties and producing a displacement of retention time. How can I correct this and improve separation?
Equipment and conditions: Agilent 7890A GC, injector (temp. 110ºC), column of PDMS phase (30m), chromatograph oven (temp. 150ºC), TCD detector (temp. 200ºC), and Argon gas as carrier. I will appreciate your comments and information.
Additionally, I would like to read your comments about advantages and disadvantages when a TCD or mass spectrometry detectors are used?
Thank you very much
I performed analysis of light hydrocarbons using a dual columns double FID gas chromatograph with a Porapak column, using a cryogenic technique to enhance the detection limit for methane, ethane, ethene, ethyne and propane. Separation was good with stable retention times?. I enhanced the detection limit for 15 accumulation times as low as 0.1 ppb for the low MW hydrocarbons. I was able to measure ethene emissions from plants using this approach. Moreover, I could on the second column of the chromatograph measure CO2, by first converting it catalytically to methane by hydrogenation on a Nickel catalyst and a hydrogen gas stream at 375 °C. I automized the whole analytical process using a pc and pneumatic actuators.
Worked quite well. I could measure hydrocarbon emissions and CO2 uptake and emission concomitantly in an open flow setup for plant species.
see more:
Article Importance of Time Constants in an Open Flow System: Mathema...
Yes. Porapak Q would be a good selection. Take a look for PLOT capillary columns.
Methanizer is also a good approach.
Probably you can detect CO2 in hydrocarbon matrix also by ECD.
Regards
GB
Thank you very much Prof. Frank Veroustraete, your recommendations about to use of Porapak Q column and cryogenic technique were very useful. At the present time, I'm working to define characteristics of cryogenic trapping system of analytes to improve resolution and detection limits. Thank you for additional information.
Dear Alejandro J. Cortés-López as a synthetic inorganic chemist I'm unfortunately not an expert enough to provide a qualified answer to your interesting question. All I can do is suggest to you some useful literature references which might help in your analysis. For example, the following relevant article is freely available as public full text on the internet:
Separation of light hydrocarbons by gas chromatography using serpentine as stationary phase
http://nopr.niscair.res.in/bitstream/123456789/9553/1/IJCT%2011%286%29%20793-796.pdf
(see attached pdf file)
Yet another potentially useful article is the following:
Separation of Light Hydrocarbons on Micropacked Bidentate Alkylsilane Silica Columns by Gas Chromatography
(also attached)
Good luck with your research and best wishes!
Dear Frank T. Edelmann thank you very much for your answer and related information. I appreciate your comments