# Silicon Based Fuels? **URL:** \ **Category:** Factual Questions\ **Created:** [February 26, 2007, 6:59am UTC](https://boards.straightdope.com/t/silicon-based-fuels/393697 "2007-02-26T06:59:19Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [February 26, 2007, 6:59am UTC](https://boards.straightdope.com/t/silicon-based-fuels/393697/1 "2007-02-26T06:59:19Z")
'Kay, lots of science fiction writers have postulated that there might be silicon based lifeforms out there, instead of carbon based like us. I’m wondering if it would be _possible_ ( **not** practical) to swap the carbon atoms in gasolene with silicon. Certainly if it were practical/cost effective folks would be selling the stuff (assuming it had similar characteristics to gasolene), so I’m certain that the practicality of the matter has been answered. ---
**Author:** ![Crescend](https://avatars.discourse-cdn.com/v4/letter/c/b9bd4f/32.png) [@Crescend](https://boards.straightdope.com/u/Crescend)\ **Post date:** [February 26, 2007, 8:31am UTC](https://boards.straightdope.com/t/silicon-based-fuels/393697/2 "2007-02-26T08:31:58Z")
Gasoline is a mixture of hydrocarbons. It is certainly possible to manufacture a silicon-based mixture analogous to it - its constituents would obey the formula SinH2n+2. This wouldn’t be “swapping”, but rather a ground-up chemical synthesis. The hydrocarbons in gasoline have 5 to 12 carbons in them. Assuming they’re unbranched, a 5-carbon hydrocarbon would look like this: ```auto H H H H H | | | | | H--C--C--C--C--C--H | | | | | H H H H H ``` The analogous silicon-based molecule would look like this: ```auto H H H H H | | | | | H--Si--Si--Si--Si--Si--H | | | | | H H H H H ``` Because silicon is in the same group as carbon on the periodic table, it behaves similarly in chemical reactions. But as you can see, it’s not a matter of just “swapping” out the carbons. Let’s say you have a magic catalyst that will in a single reaction break a carbon-carbon bond and instead put a hydrogen atom on the carbons, with perfect efficiency (If you have such a catalyst, the oil industry will ensure that you live like a king for the rest of your days.). If you do this to a 2-carbon hydrocarbon (ethane), you will produce two one-carbon hydrocarbons (two molecules of methane). To truly “swap” a carbon for a silicon, you’d have to break the four carbon-hydrogen bonds and make each hydrogen form a bond with a silicon atom. I guess you could sorta-kinda do something like this, but it would require one hell of a catalyst, a nanomachine that would pass for biological in dim light. You can definitely synthesize silanes. The longer they are, the less stable they are (silicon-silicon bonds are a bit weaker than carbon-carbon bonds), but you can synthesize pentasilane (the analog for pentane, the carbon molecule I drew above). I am not sure if a process exists for reliably producing arbitrary-length silanes, but assuming one exists, I see no reason why you can’t make 12-silicon silanes. Practicality-wise, you’re better off literally pounding sand. ---
**Author:** ![Dervorin](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Dervorin](https://boards.straightdope.com/u/Dervorin)\ **Post date:** [February 26, 2007, 9:36am UTC](https://boards.straightdope.com/t/silicon-based-fuels/393697/3 "2007-02-26T09:36:22Z")
Wouldn’t the fact that the residue after burning is a solid rather than a gas put rather a crimp in the design of this engine? SiO2 isn’t a particularly nice thing to have in moving parts - made particularly apt by the pounding sand comment up there. ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [February 26, 2007, 9:57am UTC](https://boards.straightdope.com/t/silicon-based-fuels/393697/4 "2007-02-26T09:57:46Z")
Silanes will burn, but (as above post) residue is a solid They are not as volatile more importantly they are moisture sensitive - releasing hydrogen and polymerising. They also cost a fortune. Totally impractical ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [February 26, 2007, 8:06pm UTC](https://boards.straightdope.com/t/silicon-based-fuels/393697/5 "2007-02-26T20:06:35Z")
There’s some speculation that silane (SiH4) might be produced on the Moon as a rocket fuel. The justification is that by weight it would be mostly silicon, which is exremely plentiful on the Moon’s surface. I have no idea how practical this would be however. ---
**Author:** ![Crescend](https://avatars.discourse-cdn.com/v4/letter/c/b9bd4f/32.png) [@Crescend](https://boards.straightdope.com/u/Crescend)\ **Post date:** [February 26, 2007, 11:53pm UTC](https://boards.straightdope.com/t/silicon-based-fuels/393697/6 "2007-02-26T23:53:19Z")
It would be practical in cases where you have lots of cheap energy, and very little access to useful reaction mass. If you’re stuck on the moon with a nuclear reactor and no fuel, you can cook the soil and produce silane and oxygen. I haven’t run the numbers, but assuming sufficiently efficient energy sources, you could get away with the inherent inefficiency of producing the fuel in-situ. Basically, given cheap enough energy, lots of things become feasible. It’s like hydrogen fuel cells for cars. The hydrogen is just a way of moving energy from the power plant to your car’s wheels. The power plant produced energy, which was used by the cracking plant to produce hydrogen (let’s say H2 for simplicity’s sake). This hydrogen (high-energy state relative to what it was before - H2O) is then used to produce power in your car and drive the wheels. The hydrogen is a means of chemically storing the energy produced by the power plant. Likewise, the silane is a means of chemically storing the energy produced by the power plant.