methanol analysis

[chromatographer0001]

hi, i need your help
i want to analyze methanol content at methanol reactor outlet in GC. it is about 6%. plz suggest suitable column, detector conditions and proper way for sampling because it is a mixture of permanent gases and methanol condensate.

[rb6banjo]

Are you restricted in the detector(s) available to you? If not, I'd use a flame ionization detector as the permanent gases will be essentially invisible. If your sample contains a bunch of water, the flame might be a problem. Wax phases (pick the one you like) are very good for alcohols like methanol.

If the methanol is 6%, what's the rest (air, water, etc.)? You might have to split your sample pretty dramatically when you inject it. Will you use a rotary injection valve? If yes, you'll have to dilute it (with carrier gas or some other inert gas) before you fill the loop.

Sounds like an interesting sampling problem. The analysis will probably be pretty easy if you can nail down a good sampling protocol.

[chromatographer1]

Keep the sample warm after it leaves the reactor and as you transfer it to a small injector valve.

You don't want the methanol to drop out of phase as a liquid.

best wishes,

Rod

[chromatographer0001]

Tanks for response,
the sample contains methanol condensate +(H2,CH4,CO2,CO)% + water condensate.
pls suggest proper sampling way.
can i use TCD detector?
How can i calculate % of methanol?
How can i calculate gas components on dry basis?
thanking you,

[rb6banjo]

Those are some pretty loaded questions. What is the true nature of the sample? Are you merely analyzing the condensate (liquid) or is it a predominantly gas-phase sample and you're trying to get all of those other things as well?

[chromatographer1]

You have to keep the sample completely volatilized as a vapor to properly analyze it. This is not impossible, and the temperature required depends upon the composition of the matrix from the reactor.

Keeping this sample a vapor allows you to inject a representative portion into the chromatograph. You can then calibrate the results by using prepared standards. Since such components as you have described do not follow ideal gas laws a single standard to calibrate with is not likely a practical result but multiple standards will be necessary.

Even so the only reason to have such accurate results is for the paper you will write describing the performance of the reactor. It is not necessary to be that precise or accurate when doing research to optimize the output of the reactor.

Doing a description of the sample in liquid volume percent is highly problematic when part of the composition is H2 and CO, much less CO2 or methane.

You can use a TCD but remember that H2 response will be small and HIGHLY inaccurate (non-linear) in comparison to the other components.

In other words, calculating mole percent of dry? gases is a fool's errand or the topic of a paper required for a college course in engineering.

May I assume your question is theoretical and not real world?

best wishes,

Rod