Catalytic Methanation Hints updated 3/1/2005

1. Do not interrupt the gas chromatograph program in the middle. Wait until it says that it is completed. This avoids contaminating the two GC columns.
2. You may assume nth order kinetics for each reactant rather than the complicated rate expression.
3. You can assume a differential reactor for preliminary analyses, but it is better to integrate the packed bed reactor equations (i.e., plug flow) for final analysis.
4. Never use excess CO₂; this will cause carbon deposition in the catalyst bed andd mess up future experiments. A hydrogen to CO₂ ratio of 5:1 or higher is recommended to avoid catalyst poisoning.
5. Try to use dilute mixtures to avoid temperature excursions.
6. There are 2.0 grams of catalyst in this reactor.
7. It takes 45 minutes (at least) for the temperature to reach a steady value. Come in an hour early to start the temperature if you want to get enough data to be significant.
8. Try to get data as soon as possible. It takes 15 minutes for the GC to run. Try to get started on the first lab day if possible.
9. Do a “junk” run on the GC first (right when you start up). It does not work the first time, so do this while you are waiting for the temperature to reach steady state.
10. The CO₂ mass flow controller is not quite 10 times less than what you put into the Bailey. You will need to calibrate using the GC without reaction (bypass the reactor) in order to find out what the real flow rate of CO₂ is that enters the reactor.
11. Don’t forget to get the calibration curves for the GC.
12. Make sure that the method on the GC is ‘methane.’ Otherwise, tyou may have some odd peaks in your data that correspond to water, and this could cause problems with the GC over time.
13. When you calculate conversion, don’t use the hydrogen peak. Use the methane or CO₂ peak. Since the carrier gas is He, the hydrogen peak is not very reliable.
14. Make sure that you get a large enough range on your temperature. Do not go above 330°C.