Japanese Chemists Report Catalysts for Supercritical Gasification of Wood.

[NNadir]

Gasification processes of wood biomass have received attention as an efficient technology for the conversion of biomass into energy. The gas obtained by biomass gasification has wide ranging applications, for example, in gas turbines, in fuel cells, and for the synthesis of chemicals. Generally, very high temperatures of over 1073 K are needed for steam reforming of lignin in the gasification process. However, low-temperature methods for lignin gasification are desirable, because waste heat available from high-temperature processes in industry can be utilized for
energy generation.1

Gasification in supercritical water (Tc ) 647.3 K, Pc ) 22.1 MPa) could be a potential technology to reduce the biomass gasification temperatures1-9 because of high solubility and hydrolysis rates of biomass in supercritical water, leading to minimized mass-transfer limitations of the reactant10-12 and its rinsing effect by washing coke precursors on the active catalyst sites.13 The decomposition behavior of lignin in supercritical water around 673 K was reported in which lignin was converted
to alkylphenols and formaldehyde via hydrolysis14-20 and then the decomposition of alkylphenols to gases...

...The gasification of biomass in supercritical water around 673 K is enhanced by metal catalysts.1-6,22-24 We have reported the order of activity of various catalysts for lignin gasification in supercritical water at 673 K as ruthenium > rhodium > platinum > palladium > nickel.23 Sato et al. conducted the gasification of alkylphenols as model compounds for lignin over several supported metal catalysts in supercritical water at 673 K and reported ruthenium as the most effective catalyst.24...

The report is from the scientific journal Energy and Fuels Energy & Fuels 2006, 20, 2337-2343

The article reports 100% gasification of lignin, giving a mixture of methane, ethane, propane, butane, hydrogen, carbon monoxide, and carbon dioxide. Carbon dioxide is often a major product, but carbon dioxide obtained from renewable sources can be a useful source of carbon based fuels suitable for use in motor fuels. The cleanest and most convenient of all possible motor fuels is dimethyl ether, DME, which is readily accessible by hydrogenation of carbon dioxide.

Lignin is a by-product of the paper pulping industry. The paper pulping industry is already the primary supplier of renewable electricity, providing a few percent of the world's electrical energy. What is different about this work is that it is gasification, which offers certain advantages, including the ability to manufacture motor fuels.

The most stable catalyst was ruthenium supported on titanium dioxide.

[mike_c]

1. how realistic is this for industrial scale implementation...?

Rare earth catalysis and all that. It would seem that reaction conditions would erode the catalyst fairly quickly, but I'm just guessing, of course-- this sort of engineering is not my field. The real problem in my mind is that there simply is nowhere near enough primary production on the entire planet to support the present human energy budget through biomass conversion, even if conversion efficiencies were to approach 100 percent-- an impossibility wrapped within an impossibility.

[NNadir]

2. These are not rare earth catalysts.

"Rare earths" are now generally referred to as "lanthanides." This is just a technical point though and not something you would generally know.

The catalyst used in this process is ruthenium, which is a precious metal, a transition metal that is found in the periodic table under iron. However many catalysts are precious metals and it is their catalytic nature that makes them affordable. Most catalytic converters on automobiles contain platinum, palladium and some ruthenium, for instance. They generally operate for the lifetime of the car, even though they must process many, many, many metric tons of automobile exhaust. That is, in fact, the focus of the work, to make the catalyst last for as many runs as is possible.

Ruthenium is thus far readily available from nickel ores mined in Canada, Russia and elsewhere.

In the next decade Japan will begin marketing ruthenium obtained from it's so called "nuclear waste." Ruthenium is fairly common fission product. (As an interesting side lite, the supply of the related and much more valuable catalytic metal rhodium from so called "nuclear waste" easily exceeds the world supply obtained from ores.) Ruthenium obtained from nuclear reactors typically contains the isotope Ru-106, which has a half-life of about a year. For this reason, ruthenium recovered from nuclear reactors can only be used after the fuel has aged for about 20 years, after which essentially all of the ruthenium-106 has decayed to the even more valuable metal palladium, which can also be recovered.

Lignin is a byproduct of paper manufacture. It will be available for as long as paper is made from wood. Thus this is a niche source of energy. One shouldn't think of it as a generalized solution to our energy problems, but it is a useful approach that can ameliorate some of the fossil fuel burden that is now killing all of us.

Sweden has very large plans for the commercialization of wood gasification to make motor fuels, in particular the ultra-clean fuel DME, the cleanest diesel fuel possible. I think this is a practically achievable result. It will not eliminate all of Sweden's demand for oil, but it will eliminate a significant portion of it.

[mike_c]

3. LOL-- shows you how long it's been since I've had a chem course....

Oops. Bear in mind that when I took chemistry the only elements in the periodic table were fire, air, earth, and water. Transmuting rocks into gold was a big thing in the research community....

:rofl:

[NNadir]

4. Those were the good old days.

To be perfectly honest, when I first heard of the lanthanides, they were called the "rare earths." For me, though, "lanthanide" is a more beautiful and telling name, suggesting a fundemental truth about the periodic table.

Their chemistry, which proves to be interesting and unique, was very obscure not too long ago.

Although they have been known - with the exception of promethium - for more than a century, some of the lanthanides were isolated for the first time as ultra pure elements in my life time.

[Dead_Parrot]

5. What about scandium & ytrium?

These are (or were) rare earths, but not lanthanides. At least, as far as I know, but bear in mind I have the chemistry aptitude of a used tea-bag. :dunce:

[NNadir]

8. Scandium and yttrium are always found with the lanthanides.

Thus they are "rare earths" but they are not lanthanides.

All of these elements are dominated by a +3 oxidation state, although cerium has a well defined +4 oxidation state and Europium has a well defined +2 oxidation state that have been known since the discovery of these elements. (Oxidation states of these types have been found for a few other lanthanides in modern times - but they are not typically stable in water.) With the exception of these states - wherein cerium's chemistry is similar to that of thorium and europium to barium - the elements all behave similarly, including scandium and yttrium.

Scandium, if it were readily available and easy to purify, would be extremely valuable, since it is relatively light at melts at high temperatures. This suggests aircraft applications. A few minerals are known in which scandium exists without the other lanthanides, but these are very rare, and the scandium is very dilute.

The term "lanthanide" is a function of the filling of f orbitals in quantum mechanical terms. Considered in this way, scandium and yttrium are excluded, since they have no filled f orbitals. This was considered a triumph of the Bohr atomic model. It explained the heretofore inexplicable behavior of all of these metals which were the source of great confusion.

The great American Chemist Glenn Seaborg - who discovered plutonium and many other actinides - was the first to suggest that the actinides would be similar to the lanthanides and exhibit f orbital chemistry. This enabled him to suggest ways that the chemistry of plutonium would behave before a visible amount of plutonium had been prepared. Without his insight, the Manhattan project may have not been able to develop a plutonium bomb. In fact the chemistry of the actinides is considerably more complex than that of the lanthanides - many oxidation states exist for uranium, neptunium, plutonium and americium. Moreover thorium has no +3 oxidation state - it only exists in the +4 oxidation state, and protactinium shows a strong preference for the +5 oxidation state. However the the transamericium elements, curium and beyond, like the lanthanides, are dominated by the +3 oxidation state.

[eppur_se_muova]

6. Hmm ... can they extract Rhenium from nuclear fission products ?

On a practical scale, I mean ? Rhenium is the scarcest of the stable elements, so its chemistry has scarcely been explored. Someone once told me that Re has no stable isotopes, and when I checked the CRC Handbook, it appeared to be true! Must have been an error, though, the 76th ed. lists one stable isotope. The *major* isotope is radioactive, though, with a half-life of 44Gy. If Re is produced in reactors at all, this could enormously increase the amount available for study -- maybe there will turn out to be some interesting reactions catalyzed by Re, or organorhenium complexes.

[NNadir]

7. No. Rhenium is not a fission product.

There is a note in Cotton and Wilkenson - at least the edition I have - stating that the world supply of technetium could easily be made to outstrip the supply of Rhenium, even though technetium does not occur naturally on earth and rhenium does.

The available technetium probably now does outstrip the supply of rhenium.

A lot of people talk about transmuting technetium into ruthenium to eliminate the activity of technetium. I'm not sure this is a particularly good idea. Technetium, it seems to me, has value in its own right. Among other things, it has a very high melting point. Some technetium steels are among the most oxidation resistant known. I'm sure that there are many other alloys of technetium that have interesting properties, although the radioactivity (which is not all that intense because of the long half life) probably limits this to closed systems.

For most of the common isotopes used as nuclear fuel, U-233, U-235, Pu-239 and Pu-241 fission is asymmetric, leading a distribution of fragments that looks like a pair of camel humps when yield is graphed vs atomic weight. One hump peaks between the atomic weight of 90 and 100 and the other between 135 and 145. This means that the elements between Zr and Pd are well represented on one hand, and the elements Iodine through Promethium are present in significant quantities on the other. Other elements like silver, cadmium, and samarium are also represented but in much lower yields. The accumulation of one samarium isotope, Sm-149, a strong neutron absorber, has important consequences in nuclear engineering and accounts for the shutdown of reactors before all of the fissionable isotopes have been consumed.

In naval reactors, hafnium, which is very similar to zirconium, but has a high neutron capture cross section, is sometimes used in control rods. (The separation of hafnium and zirconium was first developed industrially for the Manhattan Project because the presence of hafnium, which is always found in zirconium in nature, tended to keep the reactors from running properly. Until that time there was no good reason for the expensive task of removing hafnium.) When a hafnium control rod remains in the reactor for a long time, very small traces of rhenium (along with tantalum and tungsten) are formed, but not enough to have any industrial significance.

[eppur_se_muova]

9. Thanks. I knew there was some asymmetry but am not as into the details as I know you are.

Oh, and I'm not interested in destroying Tc -- I am not only aware that is useful in steels, but I know at least one friend who had a tumor removed by Tc therapy. IIRC, the major isotope of Tc has a halflife of ~40ky and low-energy beta decay only, makiing it one of the least dangerous sources of radiation around.

[NNadir]

10. The Tc used in medical applications is Tc-99m.

This is a nuclear isomer of Tc-99. The Tc-99m has a very short half-life, about six hours, and decays to Tc-99 by gamma emmission which is then eliminated by peeing.

The Tc-99m is not obtained from so called "nuclear waste," but is made in medical facilities using portable accelerators that bombard Mo-98 with protons.

The Tc-99 that results from these procedures, ending up in toilet bowls around the world, is a trace.

Tc-99 has a half-life of 211,100 years. This is the isotope formed in nuclear reactors.

Technetium is regarded a problematic fission product, since it is one of the few that is known to be soluble and mobile. This is because of the pertechnate ion which corresponds to the permanganate ion.

But you are right. The long half-life makes the specific activity fairly low. Also the element is a pure beta emitter, and is thus relatively easy to shield.

Traces of technetium can be found in the North Sea and the Irish sea because of operations at Sellafield and at La Hague. These releases always make a lot of noise - and cause Greenpeace types to declare that the world is about to end - but there is zero evidence that they have ever actually involved any ill health effects. More recently technetium is being recovered. I think it should be recovered and reserved. It has some very useful properties. I would estimate that the yield of Tc-99 around the world is about 3 to 4 tons per year. One could do some interesting things with this much metal.

Here is an interesting fact that I read in Chemical and Engineering news some time ago - I don't recall the exact reference, so I'm working off the top of my head. In 1925 the Noddacks - who were the discoverers of rhenium - announced the discovery of "Masurium" that filled the place now occupied by technetium. After the true nature of technetium became known the Masurium claim was discarded and subject to some ridicule. However the Noddacks it seems, were very careful chemists, and it has been suggested that they may have in fact isolated a trace amount of technetium. Very small amounts of technetium do occur in nature in uranium ores owing to spontaneous fission events and the low neutron fluxes that occur as a result in all natural uranium and from interactions with cosmic rays. I don't know how anyone could prove this, but this was what the article suggested, that the Noddacks did in fact discover "Masurium."