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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Enthalpy on February 13, 2012, 04:35:06 PM

Title: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 13, 2012, 04:35:06 PM
Hello nice people!

As a rocket fuel operating on Mars, a chilly world, I consider branched alkanes freezing around -100°C, but with some 15 carbons so the flash point is safely above terrestrial temperature. 2,4,6-trimethyl-dodecane would be one such compound, but isn't available in tons nor easy to mass-produce.

(a) Do you agree?

My hope is to replace each side methyl at the previous compound by two geminal methyl groups (drawing), and shorten the alkyl tail a bit. This improves often the liquid range, and I imagine the compound could be produced by acid-catalysed alkylation, like isooctane is produced in oil refineries.
That is:
Isobutane and Isobutene give Isooctane (2,2,4-trimethyl-pentane)
Isooctane and Isobutene give 2,2,4,4,6-pentamethyl-heptane
pentamethyl-heptane and 1-Butene give 2,2,4,4,6,6-hexamethyl-decane

(b) What do you think?

In fact, I consider one could buy from a refinery the Isooctane, and even 2,2,4,4,6-pentamethyl-heptane, which must be a by-product contained in the refinery's alkylation output. Or buy the complete alkylate and separate the pentamethyl-heptane by distillation.

(c) Does this look sensible?

(d) In case 100t are needed, would a refinery de-tune briefly its alky unit to increase the C12 proportion?

So the rocket fuel would only need to append the straight alkyl tail to the C12 alkylate (this tail is to lower the melting point and the autoignition temperature).

(e) Feasible? Will the new bond target the only tertiary carbon?

(f) to (z) plus all the greek alphabet: other comments, flames, rants if needed.

Thank you!
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 14, 2012, 10:41:29 AM
Other broad liquid range compounds depicted below are Pristane, or 2,6,10,14-tetramethyl-pentadecane (induces autoimmune diseases in mice) and Phytane (one CH2 longer, no such reputation). They seem to be scarce in Nature and difficult to mass-produce, making them lab rarities.

(f) Do you agree?

As above, I imagine geminal methyl groups would keep a broad liquid range and enable massive synthesis by acid-catalysed alkylation, this time using Isohexene (4-methyl-1-pentene), in the hope that the new bond forms at the alkane's only tertiary carbon.

(g) Does this make sense?

Thanks!
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 14, 2012, 01:43:23 PM
(c) and (d) Meanwhile I've found more realistic literature about alkylation in refineries (terra incognita for me, sorry) and it differs from the only reaction given in encyclopaedia...

Refineries feed not just isobutene but as well propene, 1-butene, 2-butene, some pentenes... The alkylate may contain 28% of 2,2,4-trimethyl-pentane, and 16% of each 2,3,3- and 2,3,4-, plus a broad mix.

As the sought ultralow freezing point is very sensitive to the methyl groups location, the Martian rocket fuel would need more controlled synthesis conditions than a refinery - or a careful separation of the 2,2,4-trimethyl from the refinery alkylate.

More, refinery alkylate lacks iso-C12. I suppose C8 products leave the reaction zone quickly as they appear and condensate. Producing heavier isoparaffins would need a separate reactor in liquid phase or warmer.

Is that correct?
Title: Re: Produce a low-freezing rocket fuel
Post by: fledarmus on February 14, 2012, 03:33:12 PM
Pure iso-octane (2,2,4-trimethylpentane) is readily available. It is used as the standard for octane number in gasoline engines.
Title: Re: Produce a low-freezing rocket fuel
Post by: Honclbrif on February 14, 2012, 05:49:26 PM
Why not use a mixture of materials and let colligative properties do the heavy lifting?
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 14, 2012, 10:25:55 PM
Pure iso-octane (2,2,4-trimethylpentane) is readily available...
Yes. As a Martian module may need two tonnes of fuel, it won't disrupt the market, and that's the best solution.
I was still considering a production of hundreds of tonnes for lower stages, but with alkylate not being what I hoped, and refineries' alky unit unable to produce C12 compounds, rocket kerosene (Rp-1) should remain a better choice there.

As it is, iso-octane boils at +100°C hence is highly flammable, not nice. So I would like let the molecule grow beyond iso-octane, with more methyl groups and a straight tail.

Do the further steps I imagined make any sense? I'm very far away from anything I believe to understand here.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 14, 2012, 10:49:21 PM
Why not use a mixture of materials and let colligative properties do the heavy lifting?
Learnt a new English word, thanks. Nice to have Wiktionary.

If I get it properly, you suggest to stay at the complex mixture from the refinery, and go on with the process, since mixtures do a good job at keeping a low freezing point?

I don't know for sure if the mix' -100°C melting point will be kept when growing the molecules from C8 to about C15 to raise the flash point. My fear is that some of the resulting compounds will have a very high melting point, thus freezing within the mix at Martian cold.

(Which uses to happen at the injectors, in order to produce the biggest unwanted effect. That's why kerosene refined for high-flying aeroplanes is cleaned of components that freeze easily like moisture, heavy paraffins... Additionally, kerosene for rockets must make no bubbles nor polymers when flowing in an engine's cooling jacket).

Uncomfortably, very similar compounds can have very different freezing points:
-112°C for 2,2,3-trimethyl-pentane, but
+101°C for 2,2,3,3-tetramethyl-pentane (just one methyl more)
and since C15 compounds, desired for their high flash point, use to melt around room temperature, and only the fewest stay liquid at -100°C, I'd like to be selective about the composition of the fuel.

But if several compounds are liquid between -100°C and +220°C, blending them would certainly improve, with great pleasure.
Title: Re: Produce a low-freezing rocket fuel
Post by: Wastrel on February 16, 2012, 06:18:04 AM
I'm a little confused by the initial premise.  Why should a rocket fuel for use on Mars be designed to have a flash point greater than room temperature on earth?  Is flash point even relevant on a planet with too little oxygen to support combustion?

Wouldn't specific impulse be of greater importance?  Would it be better to pick an oxidiser first and determine performance properties when used in combination?

I applaud the molecular tinkering and given the cost of getting the material to another planet it's certainly worth getting it right.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 16, 2012, 11:10:44 AM
...Why should a rocket fuel for use on Mars be designed to have a flash point greater than room temperature on earth?...

Wouldn't specific impulse be of greater importance?  Would it be better to pick an oxidiser first and determine performance properties when used in combination?

Thanks for your interest!

The flash point is useful for safety on Earth. It's unimportant once on Mars, sure. But rocketry is already dangerous enough that single hazard sources should be prevented where possible.

The choice to my eyes, after progress among other options, boiled down to
- Liquid oxygen and a small hydrocarbon, both pressure-fed;
- Or Mon-33, preferably with a storable hydrocarbon, used in my original pumping cycle
http://www.scienceforums.net/topic/60205-pumping-cycles-for-rocket-engines/page__gopid__629135#entry629135
corresponding to the third drawing there.

Presently, I've concluded that I prefer Mon-33 (33%wt NO dissolved in 67% N2O4). It's toxic and the cycle needs a pump, but
- Being storable, it needs neither a permanent active cooling nor a fragile vacuum thermal insulation in the Martian atmosphere;
- Isp is 30s better than pressure-fed oxygen-methane;
- Tanks are lighter.

The Isp combined with lighter tanks lifts Martian samples or a crew from Mars to low Martian orbit in a single stage which previously de-orbits and lands the full craft (aided by parachutes). This is much harder with pressure-fed oxygen-methane.

The pumping cycle promises to start easily, and an igniter for Mon-33 looks reliable as well
http://forum.nasaspaceflight.com/index.php?topic=27308.msg849905#msg849905

Both solutions, Mon-33 and LOx, combine well with the attitude thrusters.

Putting all arguments together, I believe the cycle with Mon-33 is a more reliable global solution despite toxicity.

-----

Several fuels combine well with Mon-33 and my pumping cycle. Some of them more efficient:
+3s, mp=-100°C Tetramethyldiaminobutane
+5s diazaspiroheptane with N,N' methyl or cyclopropyl
+5z azetidine with N-methyl or cyclopropyl
+6s, mp=-83°C Azetidine
+7s 1,3-diazetidine with N,N' methyl or cyclopropyl

All are amines likely to ignite upon contact with Mon-33 but too slowly for a thruster. Only dangerous.
Azetidine is a volatile flammable amine; hazards for most others are little known, liquid range neither.

The limited performance improvement would optimize masses a little bit but not the number of stages at a Martian descent-ascent module, making the alkane a clear choice.

-----

The rest of the trip shall use hydrogen-oxygen everywhere possible, clear. Including the return leg, since tanks are easy to insulate in vacuum, and I describe a permanent cooler there
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2051
moving part on Tue Jan 12, 2010 - cycle on Sun May 16, 2010 - fabrication of the heat exchanger on Wed May 19, 2010
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 16, 2012, 11:31:25 AM
So, what about the synthesis at the first drawing? If starting from bought iso-octane:

Iso-octane and iso-butene give 2,2,4,4,6-pentamethyl-heptane
pentamethyl-heptane and 1-butene give 2,2,4,4,6,6-hexamethyl-decane

Is that realistic?
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 16, 2012, 04:14:24 PM
I applaud the molecular tinkering...
Lego forever !

--------

Latex, Gutta-Percha and synthetic polyisoprene have already the pattern with one methyl branch every fourth backbone carbon (drawing).

(h) Can a tri- or tetramer of Isoprene be obtained, instead of a polymer? Or a reasonable mix!

After just a hydrogenation, I'd get Phytane or some other nice fuel!
(Nice as well as laboratory solvent, apparently)

Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 22, 2012, 02:44:33 PM
Myrcene is dirt-cheap, as a by-product from paper production: pinene is extracted from turpentine and pyrolysed to Myrcene. Myrcene is also a dimer from Isoprene.

Various documents about turpentine tell that Myrcene is stabilized with butylhydroxytoluene or with vitamin-E for shipment or storage, or it will dimerize at moderate temperature.

The dimer of Myrcene is an isomer of Geranylgeranene, with all double bonds shifted a bit. It gives Phytane through hydrogenation. Please see the drawing.

Now, Myrcene is much more volatile (2Pa@+20°C) than its dimer and than both stabilizers.

Hence the process I imagine:
- Buy Myrcene with its stabilizer;
- At moderate temperature, evaporate Myrcene a low pressure, freed of its stabilizer;
- Pass the gas through a catalyst or a zone at higher temperature to dimerize it;
- The dimer condensates, harvest it and cool it to stop polymerisation;
- Saturate all double bonds with hydrogen to get Phytane.  :D

Nice : Phytane here is free of the seemingly unhealthy Pristane.  :D

In a variation, Myrcene would react with Isoprene to produce the trimer of Isoprene, which gives Farnesane  :D by full hydrogenation - also a potential fuel.

Instead of buying Myrcene from the paper industry, it can be dimerized from Isoprene, also a dirt-cheap by-product from ethylene at refineries. Phytane and Farnesane obtained this way are probably too expensive to replace jet fuel  ::) but cheap enough for rockets, and are up to now expensive laboratory products.

(i) Does this look reasonable to you?
Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 23, 2012, 09:15:40 AM
My mistake, sorry: the Isoprene dimer isn't Myrcene. Which ruins the attempt to make Phytane and Farnesane from turpentine. Hence I can answer by myself:

(i) is nonsense.

And if you use the software Mpbpvp included in Episuite, be more careful than I was: it identifies wrong compounds from the Smiles description.

--------------

Some people want to produce jet fuel from biomass and one compound is the already depicted Farnesane.

Their patents are US7589243 and US7399323, available for instance through Freepatentsonline.

They "mass-produce" (kilograms in the patent, already an achievement) Farnesene Diphosphate from Isoprene Diphosphate and hydrogenate it.

Their AMD-200 fuel is pure Farnesane, with fp=+109°C bp=+243°C d=773,7kg/m3@+15°C. They indicate only mp<-71°C, but I have good hope it's <-100°C, so even if they can't fly all airliners, they could supply a Martian module.

--------------

What about the Isoprene tri- or tetramer? Do you believe it can be obtained from the cheap Isoprene by reasonable means? Quenching the Ziegler-Natta mechanism early, well before the polyisoprene is obtained?

I still like the two-steps process where the dimer is isolated then itself dimerized, as this should produce selectively the tetramer, and also allows different reaction conditions for the different compounds.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on February 25, 2012, 01:05:01 PM
What I wrongly called Myrcene, the head-to-tail isoprene dimer, is (little) known as
Hymentherene, Menthrene, Isomyocorene and
2,6-Dimethyl-1,3,7-octatriene
Alpha-menthrene has even the cas=6876-07-9

Dimerization and oligomerization of Isoprene was studied in the 70's. Some papers:

- Synthesis of 2,6-Dimethyl-1,3-trans,7-octatriene (Head-to-tail Isoprene Dimer) by a Temperature-Controlled Two-Stage Reaction

- Oligomerization of Isoprene by Vanadium Catalysts

- Isoprene Oligomerization with Lithiated Diethylenetriamine Catalyst

which doesn't tell me if ton amounts are any reasonable.

Still interested in your comments and inputs!
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on March 02, 2012, 10:05:34 AM
The production of iso-octane by alkylation (points c and d) differs even more from the
Isobutane+Isobutene -> 2,2,4-Trimethylpentane
given is encyclopaedia and some textbooks...

Found more detailed descriptions, and it's a huge mess - a possible reason why Fox&Whitesell don't even mention it under alkylation nor addition...

Isobutene protonated by the acid is to react with an other Isobutene or olefin, like the beginning of an oligomerization, and Isobutane quenches the polymerization at the dimer by providing an H-. The reaction happens in the liquid, with Isobutene and Isobutane in solution or emulsion in the acid.

The thesis dissertations by Wei Shen and by Thi Le Thuy Bui confirm that significant amounts of C12 isoparaffins are obtained unless the conditions are actively tuned for C8.

All authors tell that the molecules isomerize during the process, and more so the carbocations, which only need to move an electron pair. Even if reacting pure Isobutene and Isobutane, a wide range of Isooctanes and isoparaffins is obtained. A serious obstacle on the way to one precise molecule.

If carbocations react with olefins rather than paraffins, the desired alkyl tail won't be any easier to obtain, as this should be done before H- addition. React only Isobutene first, then add the straight alkene and Isobutane?

Now oligomerization or Propylene or Isoprene seems a better way than alkylation to obtain a precise product.
Title: Re: Produce a low-freezing rocket fuel
Post by: opsomath on March 02, 2012, 01:42:20 PM
This problem has been extensively studied. Read the following glorious memoir for a ton of possibilities, and some hilarious stories. I like the one about the glove.

library.sciencemadness.org/library/books/ignition.pdf
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on March 02, 2012, 06:21:16 PM
Excellent reading indeed. I had appreciated the experiment with a rat tail in a barrel of peroxide, and a few more.

I wish readers would not only remember the fun, but as well the thousands of attempted propellants rejected for being too dangerous. These times, people come again with N2O, H2O2, Propyne and the like, while older chemists had already ruled them out.

A rocket fuel for Mars, freezing below -100°C and preferably with a flash point well over terrestrial temperatures, is not in use nor investigated as far as I know, hence the present thread.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on May 28, 2013, 08:47:26 PM
Phytane-like branched alkanes must be excellent as transformer oil:
The first three points need only a strict alkane, while the fourth accepts Phytane (four-pattern chain) be blended with a little Farnesane (three-pattern) and much of longer chains.

They can also be good as lubricants and vacuum seal grease for their wide liquid range and low vapour pressure.

These two uses are an easier market than aeroplane kerosene which is extremely cheap to obtain from petroleum. All products must be free from unhealthy Pristane.

I suppose the diphosphate path that mimicks Nature, as described in the patents from Amyris Biotechnologies Inc, can produce Phytane and longer chains, not just Farnesane whose density matches kerosene. Oligomerization of Isoprene (dimer then tetramer?) is an other way if scalable and may qualify as ecological as well, if Isoprene is obtained from hevea, gutta-percha or waste tyres.

Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on September 04, 2013, 07:56:35 PM
Aza compounds are easier to produce than the hydrocarbon homologue. As rocket fuels, they are a tad more efficient and denser. Tertiary amines have melting and boiling points close to their hydrocarbon homologue. The following amines are not volatile, so their main drawback is the risk of ignition of leaks by contact if N2O4 is present in the launcher.

Propyleneamines are industrial products with liquid ranges better than ethylene amines, just like homologue hydrocarbons do; according to Huntsman, the permethylated dipropylene triamine offers excellent mp=-78°C, fp=+92°C, bp=+227°C. Polyethyleneamines are often synthesized from dichloroethane and ammonia, followed by an easy permethylation, making them cheap mass-products. Methylamine may be an alternative and avoids uncontrolled branching.

With just one ethyl instead a methyl, we get the aza versions of farnesane and phytane. The ethyl reduces the molecule's symmetry and increases the number of isomers, two properties that depress the melting point from already -78°C, possibly attaining -100°C as farnesane and phytane do.

A second ethyl at the opposite end would ease the synthesis, especially after a methylamine route. The asymmetry is lost, but the increased number of isomers is kept.

A mix of aza-farnesane and -phytane would be easier to produce and acceptable as a fuel; even better, they may form a eutectic.

Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on December 02, 2013, 08:02:26 PM
As a cooling liquid, phytane-like branched alkanes have advantages:
Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on May 06, 2014, 12:08:20 PM
Compounds similar to farnesane (mp -100°C) and phytane (mp -100°C as well) but even longer should retain a reasonably low freezing point and provide a tiny vapour pressure; if liquid enough, they could make a vacuum oil, and if thicker, a vacuum grease - as an alternative to silicone and fluorosilicone oils and greases used presently.

Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on May 11, 2014, 12:03:31 PM
Pentamethyl-dipropylene-triamine is already seducing as a propellant, among others to return from chilly Mars, but:
- The price of this mass product (Jeffcat ZR-40, Polycat 77) may not be exorbitant enough for space activities;
- I hope ethyls at the ends lower the freezing point further by making more isomers (4 vs 1 ?), just like the heavier phytane melts as easily (-100°C) as the lighter farnesane. Ethyls will also ease the ignition.

I naively imagine one can produce 100t/month as on the joined pictures:
Does this sound any reasonable to you?
Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on August 10, 2014, 07:03:47 PM
The low melting point (like -100°C) and high flash point (+100°C) of properly branched alkanes like Phytane look interesting for aeroplanes, which use to operate in air at -70°C, and appreciate materials hard to light.

These alkanes could find uses as hydraulic fluid, lubricant, cooling liquid... They lubricate better than other compounds do, are noncorrosive and protect better against water.

Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on August 18, 2015, 06:49:04 PM
Is it possible to get a halogen only at primary carbons?

From what I've read:
BUT with myrcene (appended sketch) I have a branched conjugated diene. I imagine the most stable carbocation is at the tertiary carbon, so where would the halogen go: to the central carbon?

Also: is a Grignard reactant any reasonable in bigger amounts?
I meant zinc vapour as an alternative, but this is speculative.
http://www.chemicalforums.com/index.php?topic=72951.msg287717#msg287717

Possibly a path from myrcene to phytane (and from myrcene and isoprene to farnesane) but I suppose there are flaws in it.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on August 24, 2015, 05:56:35 PM
Finally I've found some papers that oligomerize isoprene to farnesene.

One with Va and Zr catalyst produces much dimer, and the trimer's structure isn't elucidated. But that one
http://yamamotogroup.uchicago.edu/yamamoto.pdf (565kB)
gets farnesene from prenyllithium on page 49, sketch appended here.
Prenylbromide synthesis is known, example with PBr3 / SiO2
http://www.scielo.br/pdf/jbchs/v12n5/a13v12n5.pdf (66kB)
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on May 05, 2017, 09:58:32 AM
I've just stumbled at Wiki on an example of Suzuki-Miyaura coupling
https://en.wikipedia.org/wiki/Suzuki_reaction
starting from citronellal and others to obtain capparatriene (Wiki's picture is appended) which, after hydrogenation, is farnesane, an alkane with wide liquid range. A mix of left or right placed methyl groups is desired.

Do you see advantages to this route as compared with Yamamoto's one here above?

Can it potentially reach the $/kg range in 100t/month? If not, other uses must pay more for smaller amounts.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on June 10, 2017, 03:14:57 PM
Some silicon atoms in alkanes widen much the liquid range, at least in neopentane (-17°C to +10°C becomes -99°C to +27°C) and others, possibly by easing the rotations of the attached groups. Si-H are pyrophoric but quaternary silicons apparently not.

Such silanes would be bad rocket or jet fuels, but may excel as aeroplane hydraulic fluid, transformer oil, coolant fluid for electronic equipment, vacuum oil and grease, and all uses needing a high flash or boiling point combined with a low melting point.

Synthesis seems easier (at least to me!) with silicon, as Si-H add to multiple bonds with anti-Markovnikov orientation.
(thanks Wildfyr, that was the missing bit! http://www.chemicalforums.com/index.php?topic=91666.msg327437#msg327437)
Appended is an example of silane inspired by farnesane, keeping three carbons between the branchings and unsymmetric groups that permit isomers.


Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on July 12, 2017, 03:57:12 PM
Compounds with a wide liquid range could also protect steel against corrosion, especially in mechanical workshops. Many steel tools can't accept a paint or protective layer, which would be inaccurate or too soft, so their functional surfaces remain blank and get covered with oil. Though, these petrol cuts evaporate within weeks or are unpleasantly viscous to the fingers. Compounds with a lower melting point shall remain mobile but not evaporate.

Candidates must be non-toxic, water repellant, excellent at wetting steel, with low odour, preferably good lubricants at low speed and high pressure,  and non-flammable. 500g might retail at 10€, so production should cost under 2€/kg.

Wind music instruments need lubricants too, which are already special productions. Slide trombones, rotary and slide valves need very pure mobile lubricants that don't evaporate, while sealant corks need half-thick greases.

These must be totally innocuous, absolutely water-repellant, benign to wood and varnishes and Cu-Ni-Zn-Ag alloys over decades, resist carbonic and some hydrochloric acid, with low pleasant odour or rather none, good lubricants at low speed and low pressure, excellent at wetting metals. 50g can retail for 20€, so production should cost under 20€/kg.

Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: wildfyr on July 12, 2017, 04:18:06 PM
Don't poly- or oligosiloxanes already fulfill the roles of these last two posts?
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on July 17, 2017, 09:33:08 AM
Hi Wildfyr and the others, thanks for your interest!

For some reason (beyond the price), silicones are not used against corrosion on workshop tools nor as lubricant for music instruments. The drawbacks I see:
- They are horrible lubricants. As a thin film (or rather at high "shear number") their viscosity vanishes, so they build no gliding wedge. The parts go in contact and wear quickly.
- They don't wet metals as well as hydrocarbons do - but that's only my impression.

Silicone oils do have a remarkable liquid range, which I suppose (with big doubts) results from their ease of rotation at the Si-O bonds. While hydrogen atoms hinder the C-C rotations of alkanes, methyls are out of the way for dimethylsiloxanes. The resulting irregular and changing shape must favour the liquid.

This explanation, if correct, would apply to SiCH too, telling why tetramethylsilane melts at -99°C versus -17°C for neopentane. That's why I suggest such SiCH. Since silane looks cheaper to obtain than siloxanes, and addition of alkenes too, maybe such SiCH are affordable for many uses.

From estimations I got from Am1 (beware software), methyl branches help the C-C rotations of alkanes too, by making the easiest conformation less favourable. This can be an element of explanation too, in addition to the unfavourable stacking.
Title: Re: Produce a low-freezing rocket fuel
Post by: wildfyr on July 17, 2017, 09:53:24 AM
https://en.wikipedia.org/wiki/Polysilane#Properties

It appears they are sensitive to UV as a small caveat, and while the wikipedia article isnt explicit, they seem to be solids. Are you thinking more towards the small molecule angle for this? I'm a polymer chemist so my mind goes straight to polymers due to their processability and generally superior mechanical properties.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on July 17, 2017, 09:55:33 AM
If the low melting point of siloxanes, tetramethylsilane and hopefully silicon-containing alkanes results from the ease of rotation at Si-O and Si-C bonds, making the deformed molecules hard to stack orderly, then much void must remain between the molecules and disappear at high pressure.

This would give silicon-containing alkanes a bulk modulus as low as, or maybe lower than, silicones - the reference materials for low bulk modulus (big volume compressibility).

A low bulk modulus would be a drawback as a (aeroplane) hydraulic fluid, but an advantage in volumic springs, where a piston compresses a liquid or solid which is often silicone oil up to now, or in windows and lenses for underwater acoustics which use polymethylpentene (PMP) presently.

A solid silicon-containing alkane could hopefully result from disubstituted silane and a diene.

Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on July 17, 2017, 10:53:02 AM
https://en.wikipedia.org/wiki/Polysilane#Properties
It appears they are sensitive to UV as a small caveat, and while the wikipedia article isnt explicit, they seem to be solids. Are you thinking more towards the small molecule angle for this? I'm a polymer chemist so my mind goes straight to polymers due to their processability and generally superior mechanical properties.

I have obviously nothing against polymers nor polysilane. Wiki tells implicitly that the polymers are solids: crystalline to amorphous, and so on.

My initial thoughts were about a few silicon atoms where the alkane is branched, but if a polysilane has good properties, it's just fine. UV are present in some applications only.

Dimethyldichlorosilane is widely available as the precursor to polydimethylsiloxane but it said to cost a bit. Silane is hopefully cheaper. That said, some uses accept more expensive compounds: vacuum grease, computer coolant, underwater acoustics, volumic springs and others.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on May 16, 2018, 05:56:28 PM
Easy precursors of farnesane make most of the oil of Ocotea caparrapi.

Citing Palomino et al
http://www.academia.edu/11238744/Caparratriene_an_Active_Sesquiterpene_Hydrocarbon_from_Ocotea_caparrapi
incisions in the large Colombian tree secrete oil comprising mostly nerolidol, together with caparrapi oxide, and the diol and triol analogues of nerolidol, plus a bit of caparratriene.

It is my hope that indistinct dehydration of the mixture provides hydrocarbons with the proper skeleton, whose hydrogenation gives mainly farnesane with a nice mix of stereoisomers - or hydrogenate first or in several steps. The intermediate alkene may also grow longer chains easily, preferred for flash point and lubrification. Beware caparratriene is a cell growth inhibitor.

Palomino et al got their >100g sample from the market in Caparrapi. Incisions in trees make latex for cheap, Ocotea caparrapi oil hopefully too. Competing against Kerosene and Diesel oil is presently uncertain, but hydraulic fluid, transformer oil, cooling oil seem easy markets, Mars and Moon landers obviously.

Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on May 17, 2018, 11:50:26 AM
Trying to compare the production of Ocotea caparrapi oil with latex, without reliable sources...

The tree is banal in a part of Colombia. Producing its oil resembles more an individual and occasional activity exploiting isolated uncultivated trees.

One Ocotea caparrapi seems to produce as much per year as one hevea, need more area but far less work. Selection and optimization would improve the yield. Automation looks feasible.

Latex sells for 1.5usd/kg presently. Prior to heavy investments, farnesane a few times more expensive would not replace aeroplane and car fuels, but address easily all other markets.

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As an early alternative to start an activity, farnesol sells for some 30usd/kg on Alibaba. It's nearly nerolidol, with one double bond and the hydroxyl elsewhere. Cheap enough for Mars landers and others.

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Looks like Amyris, who initially wanted to fly aeroplanes with farnesane produced by bacteria, have good readings
https://www.energy.gov/sites/prod/files/2014/11/f19/x_velasco_biomass_2014.pdf
page 6: lubricants, transformer oil, hydraulic oil.

Together with partners, they flew airliners with farnesane, kudos. As a costly demonstration, but this is already admirable.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on March 21, 2019, 05:10:50 PM
Since Juul has a nice application for low-freezing heavy alkanes
https://www.chemicalforums.com/index.php?topic=99108.0
maybe you chemists could give opinions, comments, remarks about farnesane obtained from caparrapi oil?

The tree, Ocotea caparrapi or Nates Dugand Lauraceae, is an endangered species. Apparently no restriction on its oil, or rather resin. I hope a commercial use of living trees would help the species rather than threaten it.

The resin comprises mainly nerolidol and caparrapi oxide, plus a bit of diol and triol whose loss wouldn't be bad, plus a zillion minor compounds, and traces of caparratriene that can be lost. Image appended.

Caparrapi oxide might allegedly result from the cyclisation of nerolidol. Unless someone sees how to de-cyclise it to the proper skeleton, I'd remove it by distillation at low pressure. It may serve as a hydrogen source or a perfume.

1atm boiling points estimated (!) by Mpbpvp:
+256°C Caparratriene
+256°C Caparrapi oxide
+292°C Nerolidol (measured +276°C)
+319°C Caparrapidiol
+344°C Caparrapitriol

I haven't seen how to remove the alcohols and saturate the double bonds at once. Two steps hence.

To remove the alcohols, I've found only dehydrations. They create a double bond whose random location is unimportant here. Tertiary alcohols are said not to make ethers. At least three usual ways:
Nerolidol, diol and triol would provide caparratriene and isomers with the same skeleton. I suppose they are too difficult to separate from caparrapi oxide, which is hence distilled away before. Though, if for instance polymerisation of the allenes is likely during the dehydration, maybe the hydrogenation can be done first, and Caparrapi oxide or its products removed by cold and filtration? Or should the dehydration proceed with added hydrogen?

Hydrogenation of all double bonds is usually made by H2 and Pd/C, unless someone knows a better way. The resulting broad mix of right-left isomers contributes to the low melting point.

Thank you!
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on March 27, 2019, 10:49:44 AM
Will the diene polymerise spontaneously during the dehydration attempt?
Title: Re: Produce a low-freezing rocket fuel
Post by: wildfyr on March 27, 2019, 11:20:27 AM
Temperature dependant.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on March 28, 2019, 06:49:45 AM
Ouch... With sulphuric acid, dehydration temperatures are like 140°C, and with alumina (which is a catalyst, not a water absorbing reactant as I had imagined) rather 300°C. But the pressure can be lowered, ah.

Sulphuric acid is a catalyst in alkylation reactions, and fine alumina powder catalyses many reactions.

Dehydration of nerolidol would create ramified dienes, probably conjugated.

Any chance that the dienes don't dimerize immediately?
Title: Re: Produce a low-freezing rocket fuel
Post by: wildfyr on March 28, 2019, 09:33:07 AM
The conjugated ones are the most worrisome. It's like butadiene to make rubber.

Let me look in on how butadiene polymerization is done to see if my hunch is right.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on March 29, 2019, 07:20:59 AM
Ahum. Alkylation units operate at +16°C with alkenes, less prone to polymerization than conjugated dienes, using sulphuric acid as the only catalyst
http://www2.dupont.com/Clean_Technologies/en_US/assets/downloads/AlkyUnitDesign2001.pdf

Can I forget the sulphuric route?

On the other hand, the similar myrcene has a measured boiling point of +167°C
https://en.wikipedia.org/wiki/Myrcene
so it doesn't polymerize immediately at that temperature, and it's obtained by pyrolysis of β-pinene at +400°C, so at this temperature it has some stability. Alumina route then?
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on April 02, 2019, 07:23:22 AM
Can a single step reduce the alcohols and the double bonds at once?

I have only found subtle reactions intending to preserve the functions of alkenes, enantiomers and so on, but what is needed here is a brutal reduction that keeps the C-C bonds, nothing more.

Heat and hydrogen must be available from the discarded caparrapi oxide.
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on April 12, 2019, 07:06:09 PM
From reading and partial understanding of reduction and hydrogenation reactions, comments welcome:
So, better one easy step more in the process than synthesizing a fancy reactant. Unless someone has a better idea, the process from caparrapi resin to farnesane would look like:
Simply by partial oxidation of only the caparrapi oxide with air
C15H26O + 7×O2 :rarrow: 15×CO + 13×H2
while the conversion of nerolidol, diol, triol consumes 4×H2, so most resin compositions need no steam reforming and waste no alcohol.

CO burners heat the process. Heat exchangers can save caparrapi oxide if it has a market value (perfume).

The process seems to consume only caparrapi resin ("oil"), labour, air, fuel only at start, little electricity, no water. Waste are vapour and carbon dioxide, by-products are caparrapi oxide and little caparratriene, a cell growth inhibitor.

The plant can operate in the middle of an Ocotea caparrapi plantation if desired.

Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: wildfyr on April 12, 2019, 09:47:19 PM
Let's find 50 million in start up funds and get cranking!
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on April 14, 2019, 07:30:08 PM
 ;D and in a nice country. Choose the altitude for the temperature, it's constant all the year under the equator
https://es.wikipedia.org/wiki/Caparrap%C3%AD
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on April 15, 2019, 11:09:27 AM
The usual process to separate H2 from CO, N2 and others after partial oxidation seems to be pressure swing adsorption (PSA). Looks simple and efficient. It can separate CO from N2 too, or maybe it's better to remove N2 from O2 prior to partial oxidation.

I've not found how quickly Ocotea caparrapi grows. Just "large tree (25m)" or "20m de altura". "Humid area surrounding the town of Caparrapi" suggests a fast growth under the equator.
https://es.wikipedia.org/wiki/Ocotea_caparrapi
https://www.academia.edu/15574491/Bandoni_LOS_RECURSOS_VEGETALES_AROM%C3%81TICOS_EN_LATINOAM%C3%89RICA_
https://pubs.acs.org/doi/pdf/10.1021/np960012r
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on May 30, 2019, 06:44:56 PM
Turpentine and other paper by-products make decent fuels, possibly separated as beta-pinene, alpha-pinene, carene, optionally saturated. But their big ring brings no or little heat of formation, loses two hydrogen atoms, and makes a stiffer molecule more prone to freeze. Due to C10, the flash point could be higher.

Maybe metathesis affords better molecules. Ethylene would make a C12, uneasily flammable. The flexible, open and very unsymmetric backbone should be harder to freeze. As is, it might be a (component of) jet fuel, or a Diesel fuel since the C3 chain eases autoignition. After saturation with hydrogen, it could be a rocket fuel, not magic but easily produced.

Beta-pinene, which has other uses, wouldn't fit as its double bond isn't in the ring. Carene I suppose neither because its big ring is unstrained. But alpha-pinene, otherwise little useful, has a double bond in its strained ring, which should help the metathesis.

The product has one very accessible double bond and may readily dimerize. I hope the strain in alpha-pinene lets the useful reaction outpace the unwanted one.

Comments please?
Marc Schaefer, aka Enthalpy
Title: Re: Produce a low-freezing rocket fuel
Post by: Enthalpy on June 02, 2019, 06:30:39 PM
It goes without saying, but maybe better if I say it: longer alkenes can react with alpha-pinene to produce bigger molecules.

Symmetric alkenes like 2-butene would remain identical if reacting among themselves, but I suppose the double bond of alpha-pinene is too crowded for them.

Longer straight 1-alkenes (cheap propene, butene...) would increase the boiling and flash points of the product and ease its autoignition, while branched ones make autoignition harder if any useful. In a jet engine, a broader spectrum of boiling points stabilizes the flame, while in a Diesel engine, more uniform properties reduce sooting. This holds for metathesis products alone (synthetic fuels are a known solution to Diesel sooting), which can already be a mix, and holds also for mixes with biofuels or fossil fuels.

The longer metathesis products, having no fully exposed double bond, should be less prone to further metathesis.

Saturating the double bonds would improve the energy per mass unit of a jet fuel. If the alkene is obtained from methane of from C3 and C4 fractions, hydrogen is available.