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I am interested in implications of using various gasses that are commonly packaged in small containers for household use, such as propane, butane and so forth. It is mostly for awareness purposes, and understanding. I am not particularly interested in lecture on unsustainability of using petroleum by-products (it is understood), just practical consideration of the energy source we are going to be using in the foreseeable future.

I want to see which kind is more energy dense: I am not too good with chemistry, and I am not sure if simple measure of energy content in J/kg is sufficient enough to make a comparison. There might be differences in efficiency of combustion processes (some reactions are simple, others are extremely complex multi-stepped affairs), and in efficiency of the actual methods by which we use them. Also different processes produce different amounts of pollutants of various degrees of toxicity which need to be considered.

There are other considerations. For instance, as far as I know (anecdotally), butane is more efficient for cooking than propane, but as butane used industrially to produce synthetic rubber, is it better to curb other, non-industrial uses for butane? On the other hand, propane with some butane and other gasses mixed in, is used as a cleaner alternative to petrol in the form of LPG. How do we balance these various uses?

Which fuels are better for cooking, and which are more efficient in small engines (such as Lehr)? Which fuels are better for refilling reusable containers (e.g. I know that propane is refillable, but I had only seen butane in small aerosol cans)? Which kinds of fuels can be more sustainably generated via capture of septic, agricultural by-products and so forth?

I hope I did not throw too much in one question, I just wanted a sort of overview, to set a starting point. I focused on propane and butane, because I often use both, and I am not aware if methane and other gasses are readily used in small-scale portable applications.

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    That is a big sprawly question. The energy-density question is probably best asked on Chemistry, and bear in mind that it's not just J/kg: there will also be a question of compressibility and J/l. Can you narrow this one down to a single use? As I think you recognise, as far as sustainability is concerned, the simple answer to the question "propane or butane?" is "neither". – 410 gone Feb 27 '13 at 9:10
  • @EnergyNumbers, I noted unsustainability in the question (first paragraph). Also, it was propane v. butane v. other (possibly less unsustainable) alternatives of which I would be interested to find out. I do see how this question came out to big, and still struggling with it. – theUg Feb 27 '13 at 9:14
  • Maybe pick just one application to start with. We already have a question on cooking. Maybe synthetic generation of liquid/gas hydrocarbons makes a good standalone question, and would address part of what you're interested in? – 410 gone Feb 27 '13 at 9:18
  • Note also you may have trouble burning butane in cold conditions. – Highly Irregular Feb 27 '13 at 21:41
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    You really need to break this up into questions that can be answered directly. What you are asking for here is a discussion of environmental impact. That's outside SE's Q&A format. – OCDtech Mar 7 '13 at 16:25
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A couple of factors.

Methane is a greenhouse gas but can be produced in some ways sustainably (methane digesters, etc). It has the lowest energy density per volume or weight. It is also lighter than air. Nitrogen has a molecular weight of 14, while methane is at 10.

Ethane, Propane, and so forth are going to be heavier than air. Ethane has a molecular weight of 18, and propane has one of 26. Butane is even heavier. As the molecular weight of a hydrocarbon increases two things happen:

  1. It produces more heat when burned per weight or volume but

  2. It produces more CO2 when burned per unit weight (and less water).

Both of these are because the hydrogen to carbon ratio goes up when the chains become smaller and down when they become larger. Polyethylene has a ratio of 2 for example, while methane has a ratio of 4, and ethane has a ratio of 3.

The environmental profile of these gasses is just different. I don't know that they can be directly compared on a single scale. Sustainability-wise, though, methane is the only one I can think of that is particularly sustainable.

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