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| Chemboy |
 Posted: Wed Jun 11, 2008 10:22 am Post subject: Propane, octane emissions |
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Forum Ph.D.
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Location: NY
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I was examining the CO2 emissions of propane compared to those of octane, and came to this question: when comparing the CO2 emissions of each, is it more appropriate to consider those from the complete combustion of each hydrocarbon, or from one mole of each hydrocarbon?
When the combustion reactions are balanced, you end up with 1 C3H8 and 2 C8H18, so the CO2 emissions of propane are 18.75% those of octane based on the complete combustions, and 37.5% based on an equal number of moles of each hydrocarbon. Which way, if either, is the more appropriate or correct or accurate way to look at it?
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| Bunbury |
| Posted: Wed Jun 11, 2008 10:27 am Post subject: |
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| I think the right way to look at the emissions would be on the basis of energy released per mole of CO2 produced. Take the moles of CO2 divided by the energy released and the fuel with the smaller number has the lower carbon footprint. |
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| Chemboy |
| Posted: Wed Jun 11, 2008 10:29 am Post subject: |
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Forum Ph.D.
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| Bunbury wrote: |
| I think the right way to look at the emissions would be on the basis of energy released per mole of CO2 produced. Take the moles of CO2 divided by the energy released and the fuel with the smaller number has the lower carbon footprint. |
Ok, but if what if I'm looking strictly at emissions and not so much energy efficiency or environmental impact? Thanks for the reply though, it was good to learn that.
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| Bunbury |
| Posted: Wed Jun 11, 2008 12:39 pm Post subject: |
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Forum Ph.D.
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| If you completely burn one mole of propane you get 3 moles of CO2 and if you completely burn one mole of octane you get 8 moles of CO2. The fact that you need 12.5 moles of oxygen for a mole of octane is irrelevant. There's no law against fractional moles. |
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| SteveF |
| Posted: Wed Jun 11, 2008 1:34 pm Post subject: |
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Forum Bachelors Degree
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Location: NC USA
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None of the above suggestions are universally appropriate. Apples and oranges. Use equal pounds (gms, kgs, tons) of each fuel and you should find equal weights of CO2 product. Doesn't this make more sense?
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| KALSTER |
| Posted: Wed Jun 11, 2008 1:55 pm Post subject: |
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Forum Cosmic Wizard
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| Quote: |
| I think the right way to look at the emissions would be on the basis of energy released per mole of CO2 produced. |
This makes more sense to me as well, since practically speaking one would have to look at the application of each gas, i.e. for cooking or internal combustion engines IMHO. How much CO2 produced per Joule in other words.
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| Bunbury |
| Posted: Wed Jun 11, 2008 2:15 pm Post subject: |
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Forum Ph.D.
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| Quote: |
| Use equal pounds (gms, kgs, tons) of each fuel and you should find equal weights of CO2 product. Doesn't this make more sense? |
Not exactly. The H/C ratio of the fuels progressively diminishes as the MW increases so the weight of CO2 per unit weight of fuel increases. The difference for propane and octane is only about 3%, but still... |
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| William McCormick |
| Posted: Tue Jun 24, 2008 5:37 pm Post subject: |
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Forum Professor
Joined: 03 Apr 2008
Posts: 1111
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| Bunbury wrote: |
| Quote: |
| Use equal pounds (gms, kgs, tons) of each fuel and you should find equal weights of CO2 product. Doesn't this make more sense? |
Not exactly. The H/C ratio of the fuels progressively diminishes as the MW increases so the weight of CO2 per unit weight of fuel increases. The difference for propane and octane is only about 3%, but still... |
It all depends on how much you burn the fuel. In the case of the propane and natural gas, there is very little CO produced. Most goes out as water and CO2
With gasoline, you have a good portion of the fuel leaving as water and CO, unless you put it through a catalytic converter and high temp incinerate it. Who would have thought of such a device? Ha-ha.
In oil burners when we set them up, we can adjust them to burn in a wide range of either CO output or CO2 output. Years ago most burners would melt the chamber, if you raised the CO2 output to high. Although you were throwing out a ton of unused fuel, you could not create a lean burn. It was for safety reasons.
Today many systems have high temperature fuel efficient, ceramic chambers that allow for super high combustion temperatures. Allowing for super high CO2 output. We are taught not to set them for high CO2 output though.
You are supposed to use a Bacharach gauge, whenever you setup a burner.
https://www.trane.com/Commercial/Uploads/PDF/573/RSP-PRC034-EN.pdf
Sincerely,
William McCormick
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