Syngas analysis

[AICMM]

The chromatograms above are actually in response to a post by buxbaum. Thank you for being patient while I figure out how to post images (I love learning something new!)

The first image is a chromatogram of a MTG mix containing O2, CO, CH4 and CO2 in balance Nitrogen on a ShinCarbon column. The configuration for all of these chromatograms is a single valve, 25 uL loop, split injection, to a DBD-HID detector (standard disclaimers apply to the DBD-HID.) Data was collected on an HP5890A series GC using an external data system (0-1V limited) at a range setting of 6. You will notice the separation for the O2/N2 is not fantastic but not unreasonable either (in my opinion.) This chromatogram, as well as the last, were run with a temperature program in order to elute the CO2 in a reasonable amount of time which explains the hump at the end.

The second chromatogram is a hydrogen in balance air mix (~20% H2, balance air) that I made in my own lab. This chromatogram was done with a parallel assembly of mol-sieve and porous polymer. In this chromatogram the first cluster of peaks is the H2/air on the porous polymer while the three latter peaks are the H2, O2, and N2 on the mol-sieve with good resolution.

The third chromatogram is the same MTG mix (above) on the parallel configuration. The neat thing about the first cluster is the CO2 peak from the porous polymer followed by the separation of the other components (less the CO2) on the mol-sieve.

The fourth chromatogram is the H2 in air mix again on the ShinCarbon column to show the hydrogen separation from air and to show the relatively decent separation of oxygen from nitrogen at high concentrations on the ShinCarbon.

The bad news is..... When using a ShinCarbon for something like SynGas analysis, the water and the other components (ethane, ethylene, etc...) will eventually elute in all their glory. A proper bake out regime will resolve this but it does add some spice to this configuration. It is probably better (if you can) to use a porous polymer in front of the ShinCarbon to keep the water and more off your ShinCarbon. The bad news for the parallel configuration is ... the water and CO2 don't come off the sieve and do come off the Q. Baking the sieve in this configuration is about a 5 minute maintenance step to pull the Q before baking the sieve, but the Q will eventually have to spit up the water so that has to be taken into account as well.

So, depending on what you need to do, a relatively simple system can get you good data if you pay attention to the limitations of the system.

Sorry for the long post, sorry for butchering the images, thanks to buxbaum for presenting the challenge.

Best regards,

AICMM

[chromatographer1]

Err.. Mathew,

Could you describe the chromatograms: ppm or uL or % details, and columns etc.

It would add so much to your postings.

Thanks,

ROd

[AICMM]

Rod,

The MTG mix chromatograms are a pre-made mix consisting of % levels of O2, CO, CH4, and CO2 (amounts on the very first chromatogram.) The H2 mix was an in-house mix (exact concentration unknown but ~ 20% H2 balance air.) The injection was done with a 25uL loop on a 6-port valve with a split inside the oven of the GC. In the case of the parallel chromatograms it was split to two columns as well as a split vent and in the case of the ShinCarbon split to the split vent and column. Columns were 1/8" Shincarbon for the single column analysis and for the parallel configuration I used a 1/16" Hayesep Q in parallel with a 1/16" MolSieve 13X in series with a 30 m PLOT molsieve (a strange combination I admit but what I had on hand....)

The parallel configuration was run at 85 C isothermal. The Shincarbon was run at 38/6min/14 C min(-1)/110 C for 2.75 min.
Helium carrier in all cases, helium reaction gas to the detector (~50 mL/min.) Detector temp = 220 C.

Let me know if I missed something.

Best regards,

AICMM