[HN Gopher] Solar Splitting of CO2 with 3D-Printed Hierarchicall...
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Solar Splitting of CO2 with 3D-Printed Hierarchically Channeled
Ceria Structures
Author : PaulHoule
Score : 38 points
Date : 2023-11-07 19:07 UTC (3 hours ago)
(HTM) web link (onlinelibrary.wiley.com)
(TXT) w3m dump (onlinelibrary.wiley.com)
| PaulHoule wrote:
| Note "Ceria" is https://en.wikipedia.org/wiki/Cerium(IV)_oxide
| mdorazio wrote:
| For those just reading the headline, this is for producing syngas
| / kerosene precursors, not for splitting to C + O2.
| PaulHoule wrote:
| Splitting to CO and O2. Not sure if you'd ever really want to
| split to C + O2 if you were interested in making something that
| wasn't graphene or some carbon compound like that.
| mdorazio wrote:
| If your goal is to get carbon out of the atmosphere instead
| of keeping it bound up in a fuel > CO2 > fuel cycle then
| splitting to C + O2 is exactly what you want to do. I.e., the
| same thing trees do; true carbon sequestration rather than
| repurposing.
| PaulHoule wrote:
| Well.. The trees are actually turning H2O and CO2 into
| carbohydrates which are a lot like hydrocarbons in that
| they can be an energy carrier (propane/sugars/starches) or
| a structural material (polyethylene/cellulose/lignin)
|
| It's been proposed that you could sequester carbon by
| making plastic pellets and burying them, for instance. (For
| that matter you can partially burn the trees to make a
| carbon-rich "biochar" which is one of the most powerful
| soil amendments known.)
|
| People who just want to take carbon waste from an
| industrial process or the atmosphere and just "make it
| disappear" are mostly happy to concentrate the CO2 and then
| pump it underground and not have to do the "work" of
| converting low energy CO2 into some other product. From a
| material handling perspective you can pipe the
| supercritical fuel 200 miles away without loaders and dump
| trucks and trains and similar hassles.
|
| I think though there is an "e-fuels" market in that someone
| is going to want to have fossil fuel independent chemistry:
| for instance the U.S. Navy would love to use nuclear
| electricity to make aircraft fuel on an aircraft carrier so
| that the carrier never needs to slow down to take on fuel.
| With a sufficiently high carbon tax, for instance, e-Fuels
| could be cheaper to end users than fossil fuels.
|
| I think it's an interesting technology for space
| exploitation in that the factory of a space colony has to
| produce all sort of carbon, hydrogen, oxygen, nitrogen and
| similar organic compounds to support biology _and_
| technology.
|
| Some asteroids contain huge amounts of "coal" and
| carbonates and also water and silicates and it would need
| some system to turn the coal into organic chemicals (like
| 20 billion kg of Kapton plastic film for solar sails, sun
| shades, stuff like that) They would never dispose of waste
| CO2 because it so precious and certainly they have a system
| that recycles the carbon... One of those solar reactors
| would be perfect for always shining sun out there.
| ZeroGravitas wrote:
| This is cool science but is it actually likely to be competitive
| with e-fuel approaches for practical purposes? This suggests in a
| couple of places it is, in a vague sort of way, but like almost
| everything I read in this space it seems to be avoiding a
| straight out comparison with e-fuels.
|
| Like this is a very weak claim:
|
| > For example, when compared to e-fuels, the solar thermochemical
| pathway bypasses the solar electricity generation, the water
| electrolysis, and the reverse-water gas shift steps, to directly
| produce solar syngas of desired composition for FT synthesis,
| i.e., three steps are replaced by one.
|
| Reducing the number of steps _might_ lead to some amazing
| efficiency breakthrough, but if you mention the step reduction
| and then stop, I 'm going to assume it doesn't.
| PaulHoule wrote:
| It has the disadvantage that the reactor is only going to run
| when there is very bright sunlight. Might be more desirable for
| applications in space where you have sunlight 24 hours.
|
| There's also the question of what kind of system it is embedded
| in. Typically people have made a CO + H2 syngas using pyrolysis
| of coal or rubber tires or municipal waste or something like
| that. You could make methane out of that or make gasoline or
| diesel compatible fuels, not to mention just about any chemical
| feedstock you need:
|
| https://en.wikipedia.org/wiki/C1_chemistry
|
| The "water shift" and "reverse water shift" reactions are about
| what to do if your ratio of CO and H2 are wrong for what you
| are trying to make so you can basically turn CO into H2 or vice
| versa. That reactor looks like it would make pure CO without
| any H2 so if you didn't have an H2 source you could use the
| energy in the CO to split water and make H2 ("water shift")
| Similarly an e-Fuel factory might primarily have an
| electrolizer that makes H2 and you would use the reverse water
| shift to turn some CO2 into CO.
| robocat wrote:
| Summary:
|
| Design a custom 3D printing process so you can build an optimally
| shaped structure for absorbing sunlight and converting CO2 to
| carbon monoxide.
|
| 1. Build a structure made of CeO2 (ceria = Cerium Oxide). The
| structure is shaped to absorb as much concentrated sunlight as
| possible to heat it to 1500degC, reducing to CeO and O2 at 0.1
| mbar
|
| 2. Pass a gas of CO2 and H2O over the structure at 900 degC and 1
| bar, oxidising the CeO back to CeO2, and producing CO and H2
| (syngas) in a ratio suitable for potential production of specific
| hydrocarbon fuels.
|
| Decide the structure should be layers of open grids with finer
| dimension of the grid from top to bottom. Sunlight is absorbed by
| sidewalls of the grid cells. Top layer grid might be a 1x1 cell,
| second layer 0.5x0.5, next 0.25x0.25 final layer 0.1x0.1. Light
| comes in at the top layer and light either hits cell wall or
| passes through cell void to reach the next layer.
|
| Previously investigated printing a scaffold and adding ceria to
| the outside of the structure - some problems.
|
| So decided to design a custom 3D extrusion printer that could
| print the ceria structure directly without any scaffold.
|
| Designed a custom fluid containing ceria with temperature
| dependent plasticity. Used that fluid to print 3D structures.
|
| Compared efficiency of syngas conversion process from sunlight
| energy depending on the 3D structure design.
| scythe wrote:
| >For operating conditions of the reduction at 1500 degC
|
| Unfortunately, this figure is fatal to any solar-thermal project.
| While the color temperature (hence theoretical limit) of sunlight
| is a blistering 5000 K, real concentrators achieve much less. For
| practical purposes they are divided into two categories:
|
| - _single-stage_ concentrators, which employ a single heliostat
| (array of mirrors) or parabolic trough to focus sunlight onto a
| collector;
|
| - _double-stage_ concentrators, which use a _second_ mirror to
| achieve very high temperatures.
|
| The largest double-stage concentrator ever built is the Odellio
| solar furnace operating at just one megawatt:
|
| https://en.wikipedia.org/wiki/Odeillo_solar_furnace
|
| For practical purposes in the foreseeable future, single-stage
| concentrators are _the_ technology of interest, currently
| representing around 7 GWp of installed capacity around the world
| and growing rapidly. These reach a maximum temperature of about
| 550 C, which is just barely enough to run the copper-chlorine
| cycle, but not many of the more fanciful solar fuel cycles. Some
| single-stage "dish" systems reach 750 C at much smaller sizes
| (the startup that was selling this pivoted to batteries [1]).
| Some research has proposed ways to boost power tower temperatures
| to as high as 800 C [2].
|
| But 1500 C? In a single-stage system? It would require a level of
| accuracy that just isn't available. Such a system requires a
| solar concentration ratio of around 2500 suns [3]. This is
| extraordinarily difficult, because the sun subtends a finite
| angle for an Earth observer and hence reflects off a mirror with
| a significant divergence; furthermore an ideal reflector is not
| planar but slightly curved, and every mirror on a flat field
| would be curved slightly differently, creating impossibly
| difficult manufacturing issues. Real-world systems hover around
| 500 suns, with 1000 suns being a commonly stated practical limit
| [4].
|
| 1: https://en.wikipedia.org/wiki/TEXEL
|
| 2:
| https://asmedigitalcollection.asme.org/solarenergyengineerin...
|
| 3:
| https://opg.optica.org/oe/fulltext.cfm?uri=oe-24-14-A985&id=...
| (See Figure 4)
|
| 4:
| https://www.sciencedirect.com/science/article/pii/S0038092X2...
| (Some thermal efficiencies in Figure 13; cost figures are, in my
| view, _highly_ optimistic)
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(page generated 2023-11-07 23:00 UTC)