e g e Posted about amazing new tech. called Sabatier reactors

[DEMVET-USMC]

These reactors apparently are be able to create methane from hydogen H2 and carbon dioxide. That and a very many other organic compounds, and things as diverse as producing Portland cement and ammonia ,splitting water into H2s and O2s and on and on using different reactants. The website is < http://www.angelfire.com/md/dmdventures/boot101.htm >. Once again it was: e g e who brought this up in another in another thread. ... Oscar

[Speck Tater]

1. Being a skeptic, this sounded too good to be true.

Follow up found this refernce. http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5087687

Apparently it's on the up and up.

"This paper presents the results of recent experimental and analytical studies of a Sabatier reactor where carbon dioxide and hydrogen in the presence of a catalyst react to form water, methane, and heat.^The work undertaken in this program was aimed at simplification of design and control concepts of Sabatier subsystems.^To this end, effort was expended to the development of UASC-151G, a highly active, physically durable catalyst composed of ruthenium on alumina.^UASC-151G is five times as active as that supplied for the SSP program.^The use of this improved catalyst has very significant effects on the Sabatier reaction subsystem design including: (1) lower temperature starting capability, (2) simiplification of active control and instrumentation requirements, (3) simplified reactor design, (4) improved reliability, and (5) high conversion efficiencies using only small amounts of catalyst.^Reasonable agreement between test and computer simulation has been obtained for temperature and lean component conversion efficiencies for both steady-state and cyclic operation. "

[NNadir]

2. This is simply hydrogenation.

The hydrogenation of carbon dioxide is not particularly new or exotic. As always, the question is where do you get the hydrogen. Hydrogen is NOT a form of energy; it is a form of energy storage. The Sabatier reactor is not an invention of a form of energy; it is merely a process improvement for a known chemical reaction.

Ruthenium, by the way is a very expensive and rare element. Almost all of it is obtained from Platinum ores, where it is an impurity.

Many hydrogenations are exothermic, but the heat generated is not enough to drive hydrogen making machines, since that would be a perpetual motion machine.

[papau]

3. I believe there is a paper claiming a 4% energy loss at the end of the day

which is not bad!

:-)

[NNadir]

5. 4% energy loss with respect to what state? What paper?

I suspect that the loss is with respect to the state of a mixture of hydrogen and carbon dioxide and not with respect to the hydrogen source (water? methane?) and carbon dioxide. It would be helpful if you can cite the paper.

Actually making methane from hydrogen is not particularly useful in mnay circumstances, since methane, like hydrogen, is not a liquifiable gas. It therefore has many of the same drawbacks as hydrogen itself, high transportation cost, low energy density and a relatively poor safety profile. The latter is ameliorated slightly in the case of methane when compared to hydrogen by increased viscosity and higher critical temperature.

Another exothermic reaction in which carbon dioxide is hydrogenated is the reaction in which carbon dioxide is reduced to dimethyl ether. This is done, as I recall, over cobalt catalysts, which are unquestionably cheaper than ruthenium catalysts. One problem with the latter reaction is catalyst lifetime. The catalyst must be constructed physically so that its temperature is moderated suitably to prevent catalyst breakdown.

I would expect this is also true of ruthenium catalysts. I would imagine that at high enough temperature, a water/methane/carbon dioxide/ruthenium system would be in equilibrium with ruthenium tetraoxide, which is a volatile compound that potentially would distill off, shortening catalytic lifetime. (Ruthenium tetraoxide distillation is a method of purifying ruthenium and its cogener osmium from mixtures of other platinum group metals.)

The world capacity for Ruthenium production is somewhere around 13 tons per year, which would easily fit into a single boxcar. All of it is consumed in existing industrial processes, many of which are catalytic: Ruthenium is the proposed catalyst in the fuel cells that are proposed to power cell phones and other portable devices.

Interestingly, I would note that the accumulated so called "nuclear waste" in the United States contains about 100 MT of Ruthenium, almost eight times the annual consumption of this precious metal. The Ruthenium that exists in a nuclear reactor when the fuel is removed is radioactive since it contains two radioactive isotopes, 103 and 106. However both isotopes are relatively short lived. Ruthenium 103 has a half-life of 39.26 days and decays to give isotopically pure and (extremely, extremely) valuable nonradioactive Rhodium metal. Ruthenium-106 has a half-life of 373.59 days and decays to give isotopically pure Palladium 106. Palladium of course is also a valuable metal. Thus, if one wishes to recover Ruthenium, Rhodium and Palladium, one will have to wait around 15 years after removal from the reactor to allow the radioactivity of Ruthenium to fall below background radiation levels. (If one however finds that the radioactivity improves catalytical performance - which is easy to imagine, one might wish to recover the Ruthenium while it's still "hot".)

You might ask why, if these metals are so valuable, why they are not recovered from "nuclear waste?" Well the answer would depend on where you live. In the United States, the plan is simply to bury these metals in Yucca Mountain on the grounds that we are extremely stupid people and oppose nuclear reprocessing because we can't stand the word "radioactive." Therefore we have rendered such recovery politically unpalatable. The Japanese on the other hand, do plan to recover these metals from their "nuclear waste," and sell them on the open market. This will probably ameliorate the long term supply shortages of Ruthenium and Rhodium, especially if Japan builds lots more nuclear reactors.

The situation with respect to Ruthenium supply can be further improved by transmuting the radioactive element Technetium into Ruthenium, which can be accomplished by getting Technetium-99 to absorb one neutron, where upon it decays (in 17 seconds) into nonradioactive Ruthenium-100. I would guess we have about 100 MT of Technetium in our "waste." I am somewhat ambivalent about proposals to transmute Technetium, since I regard Technetium, which does not occur naturally on earth, as a valuable metal in its own right. I suppose that a decision on whether or not transmute this valuable metal will depend on the long term demand for both metals. Again this will not be an issue in the United States, where we plan to "dump" our Technetium as well as our Ruthenium, Rhodium and Palladium formed in nuclear reactors in Yucca Mountain.

[phantom power]

6. Propane would be even easier to work with, and I bet

you could modify the process to produce propane.

[phantom power]

8. methane can be liquified

LNG is essentially liquid methane.

Here is one discussion
http://catf.vizonscitec.com/Index/83C82D16418C1E2988256976006C2FA4!OpenDocument

(on edit)
Hydrogen can be liquified too. It's just much more difficult than liquifying a larger molecule such as propane.

[NNadir]

10. Helium can be liquified. Any gas can be liquified but...

The question is more properly, "Is it economic to do so?"

The answer for most of history for methane has been "no." Most methane in oil fields has been flared, burned off at the site. The reason is that it is too expensive to liquify and ship it.

For hydrogen the situation is worse.

To have an economically liquifiable gas, it is much more economic if the critical temperature (the highest temperature at which a gas can be liquified by the application of pressure) is near room temperature. Dimethyl ether, propane, and butane all have this property. Most LPG is in fact propane.

Methane is now being liquified commercially because the price has risen, but it must be refrigerated during shipment, adding to expense and energy loss, and therefore greenhouse gas generation. This liquification scheme is also very dangerous, and people are routinely killed in these types of operations.

The critical temperature of hydrogen is about 33 K (or -240C). This means that if you don't keep hydrogen colder than the boiling point of liquid nitrogen (-195C), you cannot liquify it. The critical temperature of methane is -82.7C, colder than the temperature of dry ice. It wastes quite a bit of energy running refrigeration systems to get the gas that cold. The critical temperature of propane is 96C, or near the boiling point of water. The critical temperature of dimethyl ether is 127 C, which is higher than the boiling point of water. This means that for dimethyl ether or propane, one need merely to pressurize it. You don't need any refrigeration at all.

Therefore it is probably not a good idea to hydrogenate carbon dioxide in such a way to get methane. There are far better choices.

Sometimes natural gas that was formerly flared is reformed and made into higher molecular weight gases. This is one avenue of liquification, but it isn't free or cheap either.

[phantom power]

11. If propane is more economical, then I'm for it.

My main goal in bringing methane up was that there are alternatives to hydrogen that are easier, safer and more economical.

Whatever energy-storage fuel we choose, we need some kind of reaction for manufacturing that fuel, and it will require some kind of energy source to drive the cycle. If that fuel is carbon-based, then we will want our cycle to remove CO2 from the atmosphere.

Methane + sabatier process is one example of such a system, but I'm sure that there's some variation that uses propane instead of methane.

[NNadir]

12. You are right. There are many possible options for hydrogen equivalent

fuels. It is largely a function of reaction conditions and choice of catalyst.

The chief impediment to building infrastructure for these types of systems is hardly technological; it is economic.

It's a matter of capital investment. Because we do not care about external cost, only direct cost, and do not charge (through taxation) for external costs, the most sustainable solutions are not embraced.

Still when the price of oil (either from internal or external cost) rises high enough, the impetus for such investment rises. This is why OPEC in anxious to keep the oil price below a certain threshold, and why those who give a shit about the environment should be thrilled whenever the price of oil rises (the temporary pain aside). If the price of oil had stayed high enough in the 1970's, and had President Carter been re-elected rather than the potted plant that's dying now in California, we would certainly be enjoying the benefits of such an infrastructure now.

[papau]

9. Reaction yields of 96% have been achieved in the Lockheed-Martin machine

Sabatier Reactors (Methane Production up to 96% efficiency)
(CFM p155)
36cm x 5cm dia filled with Ru Ruthenium or Ni Nickel
Nichrome heating wires
Condensing system to separate H2O from CH4 and CO
Condensing system to separate CH4 from CO
Exothermic reaction starts and sustains at 400 degrees Celsius
3CO2 + 6H2 => CH4 + 2CO + 4H2O
Condense out 4H2O
Condense out CH4
When the H2O is electrolyzed and the H2 is cycled back into the reactor while the O2 is trapped in it’s tank, this yields a 4:1 CH4 to O2 ratio and an over all 18:1 for CH4 to H2 (seed quantity brought from earth).
The remaining CO is available for other uses.


http://advlifesupport.jsc.nasa.gov/documents/simaDocs/MSAD-01-0221.pdf

4H2 + CO2 = CH4 + 2H2O DH= -40 kcal/mole (1)


Reaction (1), known for over a century as the "Sabatier reaction," is highly exothermic and has a large equilibrium constant (~109) driving it to the right. It occurs spontaneously in the presence of either a nickel or ruthenium catalyst (nickel is cheaper, ruthenium is better) at temperatures above 250 C. (Typical reactors operate with peak temperatures around 400 C in the forward reaction zone, declining to 200 C at the exit.) Because of the high equilibrium constant and high reaction rate when properly catalyzed, yields over 90% are readily obtained even with very small reactors. Reaction yields of 96% have been achieved in the Lockheed-Martin machine at stoichiometric mixture ratios, and 99.9% conversion rates of lean reagents have been achieved at non-stoichiometric mixture ratios17.


The methane and water produced by reaction (1) are easily separated in a condenser. The methane is then liquefied and stored, while the water is electrolyzed in accord with:


2H2O = 2H2 + O2 DH= +57 kcal/mole (2)


The oxygen so produced is liquefied and stored, while the hydrogen is recycled back into the Sabatier reactor to produce more methane and water, and so forth.


It will be noted that reaction (2) only produces two hydrogen molecules to recycle back to reaction (1), which requires an input of four hydrogens. Thus a net input of hydrogen is required to make the system run. This could, in principal, be acquired on Mars at large energy cost by condensing it out of the atmosphere1,18 in a relatively simple automated system, or mined from Martian permafrost with the aid of human explorers or a very advanced type of automated mining system. Alternatively, (and more practically for early missions) the hydrogen can simply be brought from Earth. In this case, the combination of reactions (1) and (2) will produce 12 kg of CH4/O2 bipropellant on Mars for every 1 kg of hydrogen imported.


The primary advantages of the SE system are simplicity, robustness, scalability, and energy efficiency. The Sabatier reactor is basically a simple steel pipe containing a catalyst bed, which can easily be scaled to support a mission of any size. For example, the Lockheed Martin unit demonstrated that a small Sabatier reactor 0.1 liter in volume would be sufficient to support the MSR mission propellant requirement of ~1 kg/day. Based on these results the entire Mars Direct manned mission propellant production could be done in three 10 liter pipe reactors. Operating at ~400 C with a filter to preclude catalyst poisoning by Martian dust, such reactors are basically bulletproof, especially since their small size makes it practical to support virtually any desired level of subsystem redundancy. Available water electrolysis units using solid polymer electrolytes are highly efficient (>90%) and extremely rugged, as they have been designed for nuclear submarine use with specifications that include resistance to depth charge attack. The power advantage of the SE system is illustrated in Table 1, which compares the achieved performance to date of the SE unit at Lockheed Martin with the best results from zirconia-electrolysis units at the University of Arizona. The results shown are for chemical process requirements only, since that is the only issue the University of Arizona machine addresses. It should be noted, however, that the power requirements for the gas acquisition to service the zirconia based system would be about 4 times greater than the SE system, because the zirconia system only removes one oxygen atom from each CO2 reacted, and only reacts about 46% of input CO2, while the SE system removes both oxygens from each CO2 and is more than 95% efficient.


The primary disadvantage of the SE system is the need to import hydrogen. This requirement is especially painful on the MSR mission, where the relatively small tank sizes employed increases the tank surface area/volume ratio, increasing heat-leak and thus boiloff, making transport of the required hydrogen to Mars difficult. The SE process, operating alone, produces 2 kg of oxygen for every one kg of methane. But the optimal mixture ratio to burn O2/CH4 in a rocket engine is not 2/1 but about 3.5/1, where an engine specific impulse as high as 380 s can be achieved. If the SE process is acting alone, the only way to achieve this mixture ratio is to throw away some of the methane produced. This drops the net propellant leverage actually achieved by the system from the theoretical 12/1 (propellant produced to hydrogen imported ratio) to an actual 10.3/1. Since the hydrogen required to produce 10.3 times its weight in CH4/O2 propellant actually occupies a volume equivalent to about 14 times its weight in CH4/O2 propellant, and at least 20% extra hydrogen will be needed at launch to allow for boil-off losses during flight to Mars, such limited leverage requires that the CH4/O2 tanks be drastically oversized if they are to be used to transport the required hydrogen feed stock. Oversizing the tanks to meet this requirement causes tank weights to increase, thereby increasing net propellant requirements, etc., with the net result being a severe negative impact on overall mission performance.


Thus we see that a simple SE system incorporating only reactions (1) and (2) cannot provide a really attractive Mars in-situ propellant production system. This situation changes, however, if a third reaction is introduced which allows the 3.5/1 mixture ratio to be achieved not by throwing away methane, but by adding oxygen. In this case, instead of the propellant production leverage falling from the theoretical SE 12/1 to 10.3/1, it rises to 18/1. Since this leverage is significantly greater than the density ratios of CH4/O2 bipropellant to H2 feed stock, this means that the hydrogen feed stock can be transported to Mars in the ascent vehicles propellant tanks, without any oversizing required. Put more simply, having a third, oxygen producing reaction available nearly doubles the propellant leverage of the SE system, and this doubling of performance is the difference between an attractive system and an inadequate one.


So, in short, what we need is an oxygen machine. The zirconia electrolysis nominally fits the bill, but as we have seen it is inadequate from a practical point of view, with power requirements greatly in excess of anything likely to be available on an MSR mission (a zirconia-electrolysis based MSR mission would need at least 5 RTG's, which are not to be had), and scalability problems that preclude use as a central technology for supporting a piloted Mars mission. What we need is a in-situ propellant production system that combines the simple steel-pipe reactor and high energy efficiency advantages of the SE system with the "infinite leverage oxygen machine" talking points of the zirconia-electrolysis approach. The only system that potentially meets these requirements is the reverse water gas shift (RWGS). In fact, as we shall see, a RWGS system may offer much more.

[phantom power]

7. Yes. In this case, the energy input occurs when you produce

the hydrogen. The advantage I see here, is that the hydrogen does not have to be transported around the country, or stored in fuel tanks for vehicles, etc. It can be produced on-site, and then used at the same site to produce methane.

Or, propane could probably be produced with a modified process.

[DEMVET-USMC]

4. Right ,and the catalyst is five times as active according to that report

from the: American Society of Mechanical Engineers. These are there investigative results. ...Oscar