What's the difference between natural gas & LP?

[Jackpine Radical]

I know that natural gas is delivered via pipeline & LP is trucked around. Also, the 2 are different enough to require different aperture sizes in appliances such as stoves & water heaters. But do they ultimately come from different sources? Do their prices track each other closely? Does a shortage in one imply a shortage in the other? etc.

[hatrack]

1. Propane (butane, pentane, etc.) are "associated liquids"

They're part of what comes up when natural natural gas formations are tapped, but have different chemical structures, weights, freezing/boiling points, etc.

[ProfessorGAC]

7. Chemically, They're The Same

They're all low boiling alkanes. The structure is the same in that is CnH(2n+2). IOW, methane has one carbon, so H(2n+2) would be 4 hydrogens. Propane has 3 carbons, so 8 hydrogens. The bond energies drop a little as the molecule gets larger, so the absolute heat release per mole falls slightly for propane, as opposed to methane.

The rest of your description is exactly correct. As the molecular weight rises, so do the boiling points, while vapor pressure falls.

Just picking a minor technical nit on the first one.
The Professor

[hatrack]

8. Always appreciate correction - how else would I learn?

:hi:

[ProfessorGAC]

9. Very Minor Correction

But, i was originally trained as a chemist. It's just not my nature to ignore that nor is it my nature to be able to resist the tendency to be pedantic!

The Professor

[htuttle]

2. Natural gas is found 'in the wild' with separate wells...

...whereas propane is usually made as a byproduct of refining crude oil (and can also be made during the natural gas purification process).

I do not think propane is found separately in nature.

[Kali]

3. Yes you need different settings on appliances

my guess is lp is delivered at a lower pressure than Nat. gas. I once rented an apt that had a stove set for lp - and had to be reset. It would not light correctly and the gas would pool around the burners and then light in strange places - kind of scary. Not sure of the rest of your questions.

Just reread your post and you already know this, and weren't actually asking about appliances - will leave it as an annecdote anyway. Sorry.

[Tesha]

10. The stochiometry is different as well.

> my guess is lp is delivered at a lower pressure than Nat. gas.

No, the owrking pressures (after all the regulators) are pretty similar
but the "stochiometry" differs between the gases.

If we take Natural Gas to be pure Methane (not quite true, but pretty
close), then for every molecule of Methane that you burn, you need
two molecules of oxygen. (The one carbon atom combines with two
oxygen atoms to form a CO2 molecule and the four hydrogen atoms
combine with two oxygen atoms to form two H2O (water vapor) molecules.

By comparison, if we take LP Gas to be pure Propane (also not quite
true, but pretty close) then for every molecule of Propane that you
burn, you need five molecules of oxygen. (The three carbon
atoms combine with six oxygen atoms to form three CO2 molecules while
the eight hydrogen atoms combine with four oxygen atoms to form
four H2O molecules.)

So Propane needs more air (oxygen) in proportion to each volume
of gas burned.

Tesha

[Kali]

13. AHA. Man that takes me back a few years

- been a while since organic chem, or any chem other than the daily/recreational types. Interesting.

We recently acquired an old 5th wheel and were just talking about whether using the propane heater would be cheaper/more/the same as the house heaters that are nat. gas.

[HereSince1628]

4. Natural gas is predominately methane, LP is propane

Methane is CH4
Propane is C3H8

[Mr_Spock]

5. NG is a gas, LP is a liquid at very low positive pressures...

LP is stored under pressure as a liquid. As soon as it is exposed to atmospheric pressure (lower pressure) it turns to a gas. LP smells bad so you know when it's leaking, NG has to have a smell added to it since it has no smell. That's about all I know...

[jmowreader]

11. Propane has the smell added to it, too

For some strange reason I'm not completely aware of (probably because of the different chemical reactions that go on when you burn the two gases--natural gas creates one molecule of CO2 plus two of water when reacted in the presence of enough air, and propane creates three CO2 plus four H2O, once again if you've got enough air. So what? Every CO2 that's created, and every H2O that's created, creates heat when it happens--and the reason you're burning the gas in the first place is to get heat!) propane will give you more power than natural gas.

I know this because we sell these propane/natural gas powered generators that list their output as 15,000w if run on propane or 12,000w if run on natural gas.

In reality if you want to get rid of the CO production that REALLY happens when you react methane or propane with oxygen, you need to put a turbocharger on the engine. If you blow in an abundance of air, you get nice clean reactions without a lot of CO.

[Mr_Spock]

12. I wasn't sure if Propane had a highre BTU content - Guess it does..

I wonder why someone said at work yesterday that Propane naturally smelled and didn't need a smell added :shrug:

[BlueEyedSon]

6. Natural gas is a mixture, mostly methane (see link)

http://www.uniongas.com/aboutus/aboutng/composition.asp
http://en.wikipedia.org/wiki/Natural_gas

LP has some trace other stuff too...
http://en.wikipedia.org/wiki/Propane