How could we make fossil fuels?
September 28, 2016 2:28 PM   Subscribe

So, fossil fuels were formed over about 300 million years from dead biomass. Could a far-future society make its own over, ideally, somewhat less time?

I'm not asking about synthetic fuels made today from corn, sugarcane, etc., or really anything we could do in the next century. I want the old-fashioned method of laying down dead plants and animals, burying it under sediment, and waiting for eons. But I'd be interested if we can improve it so it takes, say, a million years instead of 300 million. Would it help if we buried it deeper? Did it on a bigger planet? Mushed up the biomass first?

Although I'm mostly just curious, this might go into a science fiction universe. Think of it as a project for really patient aliens.
posted by zompist to Science & Nature (14 answers total) 1 user marked this as a favorite
 
So, biomass + pressure + heat + bacteria + time = fossil fuels. Yeah, it could probably be sped up substantially by altering those; perhaps higher pressure, or genetically engineered more efficient bacteria, or other modifications to the conditions. Mushing up the biomass might let bacteria work on it faster.

I think the real question, though, is whether that would be any more efficient than just burning the biomass directly. You've got a conservation of energy issue there: the energy you get from burning one oak tree's worth of coal isn't likely to be much more than the energy you just get from burning the oak tree directly. Other types of plants that don't burn as well as trees, well they might have to be dehydrated first so they burn well, but after doing so I suspect the same still applies. And I imagine our "far future" society would be substantially better at capturing the energy from burning wood, or whatever.
posted by DevilsAdvocate at 2:51 PM on September 28, 2016 [3 favorites]


Sadly I'd be willing to bet that the most efficient way to do this would be to just get a nice rainforest going and then do some strategic bombing upwind hard enough to coat the whole area in silt.
posted by aspersioncast at 2:53 PM on September 28, 2016


But yeah, you've got an issue of energy inputs here; it would be more efficient to just breed better firewood than to figure out how to recreate fossil fuels.
posted by aspersioncast at 2:55 PM on September 28, 2016 [1 favorite]


It's been a bit of a background question in my mind, just how did all that biomass get to the bottom of the deep wells, below oceans? The only thing I can think of is having a bunch of ice ages push dirt on top of a big layer of stuff. So planned ice ages would certainly accelerate the process. Easy to trigger if you can control the phases of the local sun. Research project!
posted by sammyo at 3:20 PM on September 28, 2016


I think you are missing the point by eliminating biofuels. There are methods to go from dead plant matter to fuel without fermentation. They are not so very different from fossil fuel, just faster.
posted by SemiSalt at 4:20 PM on September 28, 2016 [2 favorites]


I'm sure the process we currently use to make biofuels could be slowed down so it takes a million years via some esoteric but straightforward long-now/pitch-drop type mechanism. The "why" then becomes the problem.
posted by ftm at 4:33 PM on September 28, 2016


There are a lot of (especially industrial) researchers working on mimicking this process synthetically, but the energy inputs required to mimic and accelerate a passive geological process are prohibitively high (for now). It's definitely on the table, though (I saw a presentation about this a couple years ago that was fascinating).
posted by late afternoon dreaming hotel at 4:40 PM on September 28, 2016


Thermodynamics basically says that you store less energy in fuel that you use to create it and that you get less energy out of fuel than exists as potential energy.

The energy input for fossil fuels comes from carbon sequestration via photosynthesis of those long-dead plants and from reactions catalyzed by heat in the earth's core which is free but basically comes from gravitational stress and pressure. In theory energy captured in fossil fuels cools down the earth's core every so slightly. Luckily there are only an estimated 3.3e13 kg of oil left in the earth - let's say we've used half of it and there was 6.6e13 kg of oil initially, compared to the 6e24 kg mass of the earth. So presumably the heat energy used to create the oil didn't cool the earth's core down too much.

Anyway the trouble is that anything you do to speed up the process like digging holes or moving things around uses up energy and probably more energy than it generates in the end.

For stuff like coal at least much of it depends on the rate of carbon sequestration which is basically how fast do the plants grow. If you had a primordial plant-covered animal-less planet like the earth once was you could get a higher throughput by using faster-growing crops that have C4 carbon fixation vs crummy ancient ferns of whatever. It wouldn't be faster per se but at the end you'd have more carbon in the ground.

I suppose the best thing you could do would be to get rid of animals as they're useless and ensure the whole planet stayed in the perfect climate to grow whatever plants you're growing. Or that you have the perfect plants for each region. Clearly deserts are useless as are tundra areas where things barely grow at all.
posted by GuyZero at 5:22 PM on September 28, 2016 [2 favorites]


I'm not sure where you'd draw the distinction between processed biomass and fossil fuels. Peat is a fossil fuel which starts at a few hundred years old, and merges smoothly into lignite, bituminous coal and anthracite the older and more lithified it gets.

With oil and gas, there's not really the same amount of residue, but bogs have gas and oils floating up as things decompose. How long do things have to have been there before that's fossil fuel rather than biomass?

Drawing the line between accelerating fossil fuel formation and creating fuels from pyrolysis of biomass is similar. The reason that there's no bright line is that there's basically no energy that gets put into the fuel during the geological processes that cause the creation of fossil fuels.
posted by ambrosen at 10:24 AM on September 29, 2016


Take the plants, let them decompose to methane and use that in the Fischer-Tropsch process.
posted by KevCed at 7:54 PM on September 29, 2016


Thanks for the interesting answers. As a refinement or follow-up question: Suppose we want to make sure a civilization a million years hence has some cheap energy available. I figured creating some fossil fuels might be an efficient way to do it, since other forms of storage (batteries...?) would degrade. Is there a better way?

(We could just leave barrels of oil and let them seep back into the rocks, but why not let the million years work to our advantage and start with raw biomass?)
posted by zompist at 5:10 PM on September 30, 2016


Hrm, if we're picturing some sort of scifi scenario and not too worried about ethics, you could still go with using thermonuclear explosions to intentionally cover a bunch of existing biomass with dust. You'd get rid of a bunch of pesky carbon and methane emitting mammals at the same time as packing away a whole bunch of organic matter underground.
posted by aspersioncast at 12:25 PM on October 3, 2016


So you would make a solar-powered system that turns simpler materials into more complex materials that have stored energy. The limiting factors are the amount of sunlight and the amount of raw materials available to convert to fuel. Again you have to take into account that doing anything results in energy expenditure and thermodynamics may suggest that you're better off doing nothing. Which makes for a pretty boring plot. And you can't build anything because things fall apart.

So: move a planet from a non-habitable-zone orbit to a habitable zone orbit and terraform it to the extent it can grow carbon-sequestering plants. Bombard it with comets to get free volatiles. Come back in a million years to free biomass. In our solar system letting Venus cool off a bit or letting Mars warm up would be good. All you need to do is figure out how to move a planet.
posted by GuyZero at 12:43 PM on October 3, 2016


Also you could try to convince a star to create uranium for you faster than normal which is arguably a better energy source than carbon-based biomass. That's kinda up there with moving a planet though.
posted by GuyZero at 12:44 PM on October 3, 2016


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