gases by gc/tcd

[vestelshirley]

need a column (preferably packed) that will do an isothermal separation of
Ar, O2, N2, CO, CO2, CH4, H2, Ethane, Propane, Butane
Anything that will come off a sublimator unit (gasifier) running coal, straw, other biomass sources.

Will consider a cap column.

[chromatographer1]

Such a column does not exist at ambient temperatures. And to measure hydrogen accurately you will have to use Argon or Nitrogen as a carrier gas. The other gases can use hydrogen or helium as the carrier. If you use a HID then a single detector is possible, but not a TCD.

best wishes,

Rod

[Johnny Rod]

For the application I'm guessing you don't really want to quantify argon as it has no biological role and is in small quantities in the air compared to oxygen. Also columns that are good at separating the permanent gases might give you way too much retention for the HCs.

[mckrause]

GasChrom Q will give you an isothermal run (not at ambient, but you said isothermal). Use a PLOT column - the packed column efficiency is not sufficient to separate Ar and O2. You'll be able to get butane off, but that's it as far as the hydrocarbons go - the heavier HCs won't come off.

[chromatographer1]

Can you give more detail concerning the Gas Chrom Q PLOT column you mentioned. Who makes this column?

Gas Chrom Q is another name for Chromosorb 102, of the Century series of porous polymers. Are you running this column at 0 celsius? or 40 degrees below zero? If you want an accurate determination of oxygen you must separate argon. Is there separation using this column?

Most PLOT porous polymer columns should be able to elute hexane or even higher hydrocarbons. Why will this one only elute butane?

interested minds would like to learn.

Rod

[jdezeeuw]

This can only be done using column switching. You need a long Molsieve 5A to get the Ar/ O2 separation. Problem is that this column does not elute CO2.

All these type of analysis require porous polymer PLOT (like Rt Q-BOND), typically a 30m x 0.53mm, to get the CO2 , water , sulfurs and higher materials up to C10 retained, while the first eluting peak is led to a 30m a 0.53mm Molsieve 5A column. This one will do the perm gas separation + the CO.
All the peaks after the first composite(and eventually after methane) is switched straight to the detector.

You can do this also parallel, but then you have to regenerate the molsieve periodically at 300C as it gets poisoned by the CO2, sulfurs and water. In low levels this solution is interesting and works.

[AICMM]

vestelshirley,

A shincarbon might do most of this job, depending. I set one up for a very similar application, pyrolysis of sugar chaff. But it is not quite that simple.... At reasonable temperatures, it will not be possible to separate O2 and argon (which may not matter that much and which is probably better done with an oxygen meter anyway) and it will take a long time (and a temp program) to get the butane off the Shincarbon. The better way to do this is to run two channels, one for the fixed gases and the other for the hydrocarbons (perhaps a Shincarbon and a Q) in parallel. You will still inject heavies on the Shincarbon though, so ideally this is set up as a backflush to vent configuration.

The other problem, as Rodney noted, is that the hydrogen and the other fixed gases will probably require two TCD's or a single HID to analyze. Getting to be a bit hairer of an instrument, but still very doable.

Best regards,

AICMM