ISRU Polymers

JoshNH4H · 2013-12-03 00:10:54

Polymers on Earth find a wide variety of applications. Some of the most important materials used in industry are polymers, and we see them everywhere. On Mars they will have very special uses because of the need to create and maintain pressure differentials between habitats and external areas. In addition to their many other uses, it will be necessary to find plastics and rubbers that can be synthesized and molded on Mars.

To be clear, I'm talking about a colony and not a first mission. This should be considered in the context of a self-propagating human presence, and not an initial prospecting mission.

On Earth, any discussion of polymers begins and nearly ends with Polyethylene. There are two polymerization processes that can be used to make polyethylene from ethene (common name ethylene) gas. The first synthesizes Low Density Polyethlylene, which has inferior properties but is presumably cheaper to make. This is the stuff that milk jugs are made of. LDPE is made by reacting ethene at high pressures (100-300 MPa) at somewhat elevated temperatures (80 C-300 C). Higher density Polyethylene is made by reacting the ethene gas at similar temperatures but much lower pressures (1-8 MPa). This process requires catalysts that would probably have to be imported from Earth for a while.

The process is relatively straightforward but fairly energy intensive; the pressure vessels required to synthesize LDPE are going to be expensive because of the huge pressures (If we're building out of Steel, assumed yield strength including safety factor 100 MPa, a cylinder would need to be 1-3 m thick per meter of internal radius. That's a lot of Steel, and more importantly represents a pressure vessel that may be dangerous and will probably be tough to design). The HDPE polyethylene process isn't as bad, although it does require that a small amount of catalyst be imported from Earth.

There is of course another issue in PE production in general: There are no fossil fuels on Mars. Unlike Earth, we would have to synthesize Ethene from the resources of Carbon Dioxide and Water. This is nontrivial. The synthesis route that comes to mind is dehydration of Ethanol. This can be done in the liquid phase with Sulfuric acid catalyst or in the gas phase with Aluminium Oxide as a catalyst.

Ethanol could be made inefficiently and expensively from fermentation of organic material. However, I wouldn't expect food production to have much "extra" when it comes to organics, and in energy and human labor terms plants are more expensive than chemicals (I think the issues that bioethanol have run into in the US suggest that we should be wary, even if we're not trying to use it as an energy source), so I would expect a chemical route to be more cost-effective.

Ethanol can be produced by hydrogenating Acetic Acid (I would guess at temperatures of a couple hundred C, perhaps with a Platinum or Palladium catalyst; it's not done because on Earth fermentation of organic material is cheaper); Acetic acid can be produced by carbonylation (Meaning Carbon Monoxide, produced from CO2 by reaction with Hydrogen) of Methane, with a metal carbonyl and Hydrogen Iodide as catalysts.

So, starting from CO2 and H2O:

(1) 2 H2O -> 2 H2 + O2 (electrical energy)
(2) CO2 + H2 -> CO + H2O (Reverse Water Gas Shift Reaction, must remove water)
(3) CO + 2 H2 -> CH3OH (5-10 MPa, ZnO Catalyst, 250 C)
(4) CH3OH + CO -> CH3COOH (Iridium, HI, and Metal Carbonyl catalyst)
(5) CH3COOH + 2 H2 -> CH3CH2OH + H2O (Hydrogenation Reaction)
(6) CH3CH2OH -> C2H4 +H2O (Sulfuric Acid catalyst in liquid phase; Alumina in gaseous)

Ultimately, to produce one molecule of ethylene you need to split 6 molecules of Water.

Some of these reactions can be performed in the same reaction vessel, perhaps downstream from one another. For example, the large stoichiometric excesses of Hydrogen required to make the reactions in later stages happen will also push the Reverse Water Gas Shift Reaction to go more quickly, and closer to completion.

Please note that this is very much a "brute force" method, which requires very significant energy inputs to produce the polymer through a fairly high number (7, plus recycling of various catalysts!) different chemical reactions. There are other ways to obtain polymers, which I will discuss in posts to come.

RobertDyck · 2013-12-03 01:22:13

LDPE is softer, more flexible. HDPE is harder. So there are other considerations than cost.

I wrote a discussion about this on the original Mars Society forum. Before NewMars existed. When that one went down, I wrote most of my points as a page on the local chapter website. That page is dated 2002; my how time flies. But the method for making ethylene that I talk about is from Robert Zubrin's book "The Case for Mars": carbon monoxide and hydrogen over an iron catalyst. That book also stopped at polyethylene, but I went further to research reactions for: polypropylene, acrylic, polycarbonate, vinyl/PVC, polystyrene, Mylar/PET, polybutadiene rubber, ABS, phenolic, nylon, and melamine. Some intermediates are interesting: toluene, ethylene glycol, acetone, and terebinth also known as oil of turpentine or spirits of turpentine.

click here: Plastics

JoshNH4H · 2013-12-03 11:50:28

That's a great page you've got there, although I would like to see a bit more detail on the reactions and what conditions they occur under. Also just looking at your references it seems like the chemical processes you're suggesting aren't very well developed, or at least aren't common on Earth. I'm not suggesting that they're unworkable, just that it seems like they aren't used much here and I can't help but wonder what the reasons for this are.

RobertDyck · 2013-12-03 11:56:58

Reactions for Mars must start with CO2 and H2O. That requires a lot of energy. On Earth they start with oil or natural gas, because it requires a lot less energy. Mars doesn't have oil or natural gas.

Last edited by RobertDyck (2013-12-03 13:24:39)

JoshNH4H · 2013-12-03 12:17:33

No argument, but I would expect that these reactions would find some use, even if only in the lab. Alternatively, that method of synthesizing ethene is not one that I've ever heard of, and I'm suspicious that it would be difficult to catalyze to that particular reaction.

It looks like the papers you cite are using a Fisher-Tropsch synthesis process to get ethylene; However, it was my understanding that these processes are not selecting and you'll get a wide variety of different saturated and unsaturated hydrocarbons out.

RobertDyck · 2013-12-03 12:48:18

Yea, but the abstract of the paper from Zelinskii Institute of Organic Chemistry says "The olefin fraction contains only C2-C3 olefins, which amounts up to 76 wt.%." That's pretty good.

JoshNH4H · 2013-12-03 17:40:37

True. Do you know if they're unsaturated? If so, an ethylene-propylene copolymer should be just as good as a polyethylene for most purposes.

Having said that, the most ubiquitous (if not the largest volume) use of plastics on Earth is in disposable applications. This is highly unlikely to be a common application on Mars, since unlike on Earth polymers come at a significant energy cost.

Interestingly, polyethylene requires just about the same energy input, on a volumetric basis, as Steel: both are about 40 GJ/m^3 (to within 1%). However, because Steel has a much higher strength than Polyethylene it is likely to be preferable.

Aluminium requires slightly more energy (44 GJ/m^3), and is a somewhat more annoying and less efficient production process. However, the fact that all of these are pretty similar means that use of polymers on Mars will be lower, and Aluminium will be significantly higher.

Polymers will probably be useful in applications where a low Young's modulus is important, as well as high yield strains. This will be particularly true in things like seals. Indoor environments are more likely to use metals and especially ceramics and bricks wherever possible.

RobertDyck · 2013-12-03 18:58:47

I expect a lot of reusable containers; not disposable. They don't have to be steel. In fact glass jars make great containers for food. I wonder how much boron is in Mars soil? Pyrex is borosilicate glass: 14% boric acid. APXS results don't appear to go lower than sodium. For Curiosity, they improved sensitivity but never did fix the proton mode, so low atomic number elements just aren't measured.

SpaceNut · 2013-12-03 19:04:38

Maybe the starting point for what we would want to make should make use of the waste we would create just by living such as from this http://isru.nasa.gov/Propellant_Fuels_M … Waste.html

RobertDyck · 2013-12-03 21:57:05

Interesting link. However, they talk about converting waste to CO2 and CO. Here on Earth, some facilities use thermal decomposition. That converts plastic to oil and natural gas, with 15% mass lost during the process. That loss provides fuel to power the process. Video or articles I read about them say they sell the oil and natural gas for fuel. However, I would like to see a single facility process that oil and natural gas to become plastic pellets (nurdles). Use the exact same process to manufacture plastic from oil pumped from the ground. The facility may have to use some of the natural gas to power plastic fabrication. This would literally recycle old plastic to new. Remember old plastic has a limit: it can undergo polymer scission and cross-bonding, resulting in yellow plastic that's brittle. Once that happens, it can't be used again. Melting would just change shape; it would still be yellow and brittle. However, breaking it down to oil and re-building it would mean you literally have new plastic. Furthermore, the new plastic doesn't have to be the same as old. You could decompose high volume waste, and manufacture whatever plastic is currently in demand. This would probably be lower volume than most plastic manufacturers, so the fabrication plant would have limited options. What I suggest is actual recycling. Current practice of using the oil and natural gas as fuel is just a different way of disposal. Recycling plastic this way is something I would like to see all over Canada and the US.

Thermal decomposition can also be done with organic matter. One company specializes in offal from turkeys. They get high volume from the Butter Ball factory around Thanksgiving. But the thermal decomposition facility has to be "tuned" to organic vs plastic. The process is very sensitive to moisture content, so you can't mix food with plastic.

This is something we can do on Mars. But the linked article mentions dry solid human waste? Eww! Is there any fuel energy in it after it's dry? Mars Society member Terry Kok has done experimental work with a recycling toilet. He built one on his home/farm. After composting, the material is fertilizer for his vegetable garden. He argues the process is better than grey water recycling. There are others who argue for grey water recycling; I won't take sides, but the point is to produce fertilizer. Either way takes a lot of time to break down so it's safe for food crops, but definitely something you want for a permanent Mars settlement.

But again, the NASA web page talks about decomposing to CO2 and CO, then using a Sabatier to build it up again. That's wasteful. Thermal decomposition to directly produce oil and natural gas is more efficient.

Last edited by RobertDyck (2013-12-03 22:13:24)

Glandu · 2014-02-22 11:39:30

All this is nice chemical reactions, but that's just the first part. I lost(in the big crash) a comprehensive post I made here on the topic of polymer transformation, so I will make a summary(in my crappy english, sorry for that, I'm just an illiterate frenchman...with a degree in plastics transformation).

(1)Thermosets are doable "by hand", as long as you have an oven big enough. It is labor intensive(for most of them, you neet to make a composite with a fiberglass clothing), but low-tech in terms of machinery.

(2)Thermoplastics are much, much more demanding in terms of machinery, as they need huge pressure for being pout as they need. They are quite a few different methods here on earth to make something useful of thermoplastic pellets, but most of them are useful only for big number of identical pieces(injection is my target here, molds are prohibitive).

3D printing is a false friend, here. You can do any shape with it. Cool. But as you put layers on layers, the sutff itself lacks cohesion. Therefore, mechanical properties are bad.

IMHO, possible low-quantity processes usable in a low-population settlement are :
(1)Rotational molding
(2)Thermoforming
(3)Extrusion

Each one has a few drawbacks. Rotational molding needs a light, but mechanically complex, mold. Sealing is the key here. Thermoforming uses a lot of air, & you need a big, big room full of air. Plus you need a primary material that comes from extrusion, you don't directly thermoform from pellets. Finally, extrusion requires an extrusion screw, which is a masterwork of steel machining.

RobertDyck · 2014-02-22 11:46:56

I started a list of materials we could make on Mars. On the Mars Society's original forum, before NewMars. When that one came down, I put much of my work on the local chapter website. You can find my list of plastics here.

GW Johnson · 2014-02-22 16:02:48

Hi Glandu:

No such thing as an "illiterate Frenchman". The original language of science was French, about 2 centuries ago. A lot of folks seem to have forgotten that.

All:

Making plastics on Mars will require inherently different chemical engineering processes than here, simply because both the resources, and the environment, are so different. But, it must be done. Period. Not being a Chem-E, I cannot contribute much to that discussion.

I will say this: plastics are very unlikely to be on Mars the throwaway material that they are here on Earth. Steel will more likely be closer to that throwaway material, simply because there is a lot of iron in surface rocks on Mars, than there is organic material. Yet, even steel will be made differently there, and for exactly the same reasons as I cited for plastics.

Because it is (currently) so hostile there on Mars. I personally rather doubt that anything will be a "throwaway" material there. That's my hunch. No reasons to back that up, other than engineering intuition.

GW

RobertDyck · 2014-02-22 18:42:27

We can make all the plastics we do on Earth. The catch is it's expensive: lots of energy. Instead of starting with oil, you start with water and CO2. Electrolysis of water to make hydrogen.
CO2 + H2 → CO + H2O
2 CO + 4 H2 → C2H4 + 2 H2O
C2H4 is ethylene. Polymerize that to make polyethylene.

Many reactions produce water as a waste product. You have to keep breaking up water via electrolysis. For other plastics, click the link.

louis · 2014-02-22 20:16:47

RobertDyck wrote:

We can make all the plastics we do on Earth. The catch is it's expensive: lots of energy. Instead of starting with oil, you start with water and CO2. Electrolysis of water to make hydrogen.
CO2 + H2 → CO + H2O
2 CO + 4 H2 → C2H4 + 2 H2O
C2H4 is ethylene. Polymerize that to make polyethylene.
Many reactions produce water as a waste product. You have to keep breaking up water via electrolysis. For other plastics, click the link.

Energy will be the least of the problems facing the first Mars colonists.

But what about plants to make plastic substitutes? There are certainly plastic substitutes based on corn and other plants - might it not be easier to grow the plants than try to replicate in miniature the whole of a complex oil refining industry?

Also - why do we need all these polymers? For the first colonists glass and basalt will provide plenty of containers. We might make use of fast growing bamboo as well which can be deployed in a very wide range of application including construction, flooring, piping, and so on. There will be no shortage of metal which is a ready alternative to plastic in many applications e.g. food preservation.

RobertDyck · 2014-02-22 22:58:59

Iron requires a lot of energy itself. The direct iron method is the most efficient. You can only use it with high grade ore, but hematite concretions are that high grade ore. It still requires 900°C and both CO and H2. They extract oxygen from iron oxide ore, becoming CO2 and H2O. You make CO and H2 the same as you do for plastic.

You can smelt iron with pure CO, but that absorbs too much carbon, making steel so high in carbon that it's brittle. A Bassemer Converter uses oxygen to burn off excess carbon, but that requires melting steel. It's far more efficient to use a lot of hydrogen in the smelting process so you don't add to much carbon in the first place.

You would make a smaller number of polymers, not them all. But helmet visors currently are made with polycarbonate. You could use PCTFE instead, it's not quite as strong but handles cold better. Astronaut Chris Hadfield had a problem outside ISS: the anti-fogging spray they apply to the inside had gotten into his eye. He teared up, couldn't see. Polycarbonate can't handle the cold of space so they use a single layer, warmed by the same air inside the helmet. PCTFE can handle the cold of space, so you could use one thick layer for micrometeoroid protection, then several layers of stiff film. This would form a multi-pane window. No fogging, and no need for any spray. But PCTFE is a fluoropolymer, requiring fluorine. The outermost layer of spacesuit fabric (the white stuff) is PTFE, another fluoropolymer. Do you want to use that instead? Just don't make polycarbonate?

SpaceNut · 2014-02-23 12:00:51

The key to energy and materials is taking a stance that any process that is started has no end waste output since the enrgy cost to start as well as to continue processing is so high, even when we use nuclear.

So we need to look to biology as well to create other sources of methane, biofuels and such as these are taking advantage of waste recovery.

We also have talked about acids as another means to start some of the chemistry to free up what we need from the surface.

Iron and plastic was also a thread that we had here for a source of carbon.

We are diffenitely going around in circles due to the crash as these have all been worked through before.

Glandu · 2014-02-25 14:40:38

Ah, I forgot a little detail : polymers do not recycle well. In fact, they lose 20/30% of their mechanical properties upon recycling(i.e. heating them again & transforming them again into some useful shape).

Reason is the following one : polymers are veryyy long molecules. Like 3 meters-long spaghettis, scaled down. Each tile you heat up & transform the stuff, spaghettis get broken. Get shorter. Lose mechanical qualities.

And it is worse for thermosets : you just don't recycle them at all. Once the molecules are "cooked", they get 3D structures, which simply gets destroyed by heat long before melting.

The only solution for having back proper molecules is pyrolysis. 800°C for PET(the plastics you make water bottles from), IIRC. Energy costly, again.

Last but not least : radiations of all kinds cut the molecules, and therefor also degrade the qualities of the polymer. That's why lifespan of plastics outside is limited, to a few dozen of years. That's not really a problem for interiors, but for outdoors, plastics will not last long.

RobertDyck · 2014-02-25 16:44:54

Glandu wrote:

Ah, I forgot a little detail : polymers do not recycle well. In fact, they lose 20/30% of their mechanical properties upon recycling.

Not if you use thermal depolymerization. That decomposes polymers to oil and natural gas. It loses 15% mass in the process, that's the energy that drives the process. Of course that consumes oxygen, but on Earth that's just air. You can then convert that oil and natural gas into polymers using the exact same process as oil and natural gas pumped out the ground. Oil is oil, it doesn't matter where it comes from. By decomposing them completely, reconstituting monomers, then rebuilding polymers, that means they are literally new. Of course it will take more energy to rebuild polymers from oil and natural gas; that's better than nothing. On Earth that's far better than throwing them in a land fill. Recovering much of the energy is better than recovering nothing. On Mars we just can't afford to be wasteful.

Glandu · 2014-02-26 05:52:29

That's what they used to call pyrolysis; ful decompozition & recomposition(can even be a different polymer). But energy cost is far worse than first polymerization. Can be done, but you need loads of solar panels.

RobertDyck · 2014-02-26 07:02:44

Thermal depolymerization works at a lower temperature than pyrolysis. Similar idea, but pyrolysis will leave nothing but CO2 and H2O. Technically thermal depolymerization is hydrous pyrolysis. One company tuned his device to produce diesel fuel. If I had the money to set up a company, I would build a single facility that takes recycled plastic in one end, plastic nurdles out the other. And pyrolysis typically requires a lot of energy, while thermal depolymerization is self-fueling. Once you get it going, 15% of the mass of plastic input is lost as CO2 and H2O. Again, that's the energy source. Output is oil and natural gas. Typically "oil" is light crude oil. Why would that take more energy to convert into plastic than oil pumped out the ground?

It can be tuned for other organic matter. Another company has tuned his for turkey offal from the Butter Ball factory. There's a lot more water in offal than plastic. But I'm interested in plastic. Oil is a non-renewable resource. Well, it could be considered renewable if you're willing to wait millions of years.

GW Johnson · 2014-02-26 15:24:20

The only real problem with manufacturing and reusing plastics on Mars is the energy. You'll need a significant nuke power plant or else one whopping lot of PV panels. Same for steel. Same for aluminum. Same for making water, oxygen, and hydrogen out of local ice, especially if you have to desalinate the water. Etc.

That kind of setup is not something you land in one or two small landers. The capable your ISRU is to be, the more mass you had better be prepared to land. (Sorry, that's just a restatement of Murphy's Law, I suppose, but then we engineers are paid to be professional pessimists.)

GW

SpaceNut · 2014-02-27 19:58:01

it has to with what is use as the catalyst.... zinc-based catalyst used to react CO2 and epoxide molecules to produce a class of materials called polycarbonates.
polypropylene carbonate (PPC) polymer
http://www.technologyreview.com/news/40 … s-funding/
http://www.eurekalert.org/pub_releases/ … 280399.php
http://energy.gov/fe/articles/recycling … e-plastics

SpaceNut · 2015-04-16 17:02:19

bump from ISS thoughts

Terraformer wrote:

How about a plastics recycler for the ISS? Or even better, a waste reprocessing module. Especially if we can scoop Nitrogen and Oxygen from the upper atmosphere...

RobertDyck wrote:

Do you want to start manufacturing on ISS? If not, then recycling raw materials isn't useful. Current practice is to send up finished equipment; if it breaks then send up replacement parts. They aren't mounding or machining on ISS. So there's no purpose to recycle raw material.
Although LEO has a thin wisp of atmosphere, enough to slow ISS or any satellite enough to fall out of orbit, it's not enough to collect. Not for any practical use. If you created a large enough collector to produce a practical amount, then that collector would act as aerobrake to slow ISS out of orbit. That would create a need for more propellant to stay in orbit, so defeat the point of reducing consumables.
What I think we need:
fix the urine processing assembly
replace the toilet with one that recovers moisture from solid human waste (thermal or vacuum desiccator)
shower (like Skylab) and sink (like a glove box, but for washing hands)
direct carbon dioxide electrolysis, based on NASA's ISPP Precursor designed for the Mars 2001 Lander (oxygen to cabin for breathing)
methane pyrolysis (recover hydrogen for use in Sabatier reactor)
clothes washer/dryer designed for operation in zero-G
Your suggestion of recycling raises another issue: reuse. The slogan on Earth is "reduce/reuse/recycle", where recycle is the last resort. So we could replace plastic spoons and plastic knives for eating with normal cutlery that can be washed. That could be hard, durable plastic, or metal. That means a dishwasher. You could wash dishes by hand in the sink (see above), but want to free as much astronaut time as possible. So a small dishwasher, designed for zero-G.

Plastic could be recycled into its raw chemical for reuse but lets continue this in the plastics topic. The other thing about manufacturing should be a science as to how to produce what we need from raw materials or from recycled materials. The items that we could make from them could be an inflateable module, radiational coating for the modules, fuels as well as carbon for use in the sabatier reactor.

More later...

SpaceNut · 2015-04-16 17:28:08

You may have seen the plastic resin chart, but what do those numbers actually mean, and why should they be important to you?

The industry calls it the "resin identification coding system." It indicates the type of plastic your product is made from and is ultimately your guide to recycling that plastic.

This is what the codes help to identify for there properties:

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ISRU Polymers

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