[Enthalpy]

Hello nice people!

Efficient rockets use presently liquid oxygen with hydrogen or a special kerosene.
http://en.wikipedia.org/wiki/RP-1
http://web.mit.edu/~bmich/Public/16.82/AIAA-6946-976.pdf

Hydrocarbons better than kerosene are difficult. Cyclopropane and methane are flammable. Syntin is abandoned, Boctane may emerge soon.
http://en.wikipedia.org/wiki/Syntin
http://www.chemicalforums.com/index.php?topic=50579

The engine's ejection speed improves with more hydrogen in the molecule to produce the lighter H2O, but also with the fuel's heat of combustion that favours less hydrogen (as does density), so no miracle is expected - though even modest gains are welcome.

Fuels serve to cool the combustion chamber's wall and shall not polymerize in the jacket, so multiple bonds are not desired. JP-10 and the future Farnesane (patent US7399323) hydrogenate the double bonds
http://www.boulder.nist.gov/div838/SelectedPubs/IR%206640%20ms.pdf
instead of hydrogenate, I propose here to cyclopropanate the double bonds of varied molecules.

Molecules with double bonds can be abundent and cheap, available for instance in turpentine from paper factories, from the cracking units of oil refineries, from pyrolysis, from natural triglycerides... More to come.

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About cyclopropanation:
http://www.thieme-chemistry.com/fileadmin/Thieme/HW-100/pdf/july/wm_E_17a_12121.pdf
http://discovery.ucl.ac.uk/17481/1/17481.pdf

First, is Simmons-Smith the best process (including its variants) to produce safely many tons?

And how dangerous are dihalo-methyls? As alkylating and methylating agents, they are to interfere with DNA. Would you consider them as risky as hydrazine, benzene, ethanol...? Is dihalo-ethyl or -butyl safer?

Thank you!
Marc Schaefer, aka Enthalpy

[Enthalpy]

Paper factories by-produce and process turpentine, cheap and more abundent that RP-1. Turpentine contains alpha-pinene, beta-pinene, a variable proportion of carene, sometimes phellandrene and others, separated by the factory.
http://www.nedlac.org.za/media/5937/turpentine.pdf
http://en.wikipedia.org/wiki/Pinene
http://en.wikipedia.org/wiki/Carene


Hydrogenation of pinene at the paper factory yields cis-pinane, the pine scent in detergents. As compared to RP-1 (806kg/m3), cis-pinane offers +13m/s ejection speed and 856kg/m3, flash point +48°C; for comparison, Boctane brings +49m/s and 828kg/m3, while Syntin brings +52m/s and 850kg/m3, and farnesane, a branched heavy alcane, +23m/s but 774kg/m3.

Carene is a frequent example of cyclopropanation. The terpenes here need only one cyclopropanation at the already strained C10H16; processed in successive batches, they can be blended to minimize the melting point. A C4 carbenoid leaving an n-propyl tail (not displayed) should widen here the liquid range and ease autoignition.

I won't try to predict the performance of these interfering rings; they must improve over cis-pinane.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Syntin is the ancestor (1960) and reference of strained rocket fuels.
Its synthesis is described at http://de.wikipedia.org/wiki/Syntin

Pyrolysis of natural rubber at 500°C produces 3-methyl-1,3,5-hexatriene whose full cyclopropanation should also bring Syntin. The paper about pyrolysis doesn't tell the amount... If this route works, maybe the too light pyrolysis fraction can be dimerized, the too heavy fraction cracked in hydrogen, and both reinjected in the oven. Or a co-dimer of propadiene with butadiene might give an acceptable isomer.




Paper factories pyrolyse pinene to make and sell cheap myrcene, which would just bear three -CH2- more than Syntin after full cyclopropanation. 30m/s gain over RG-1 while Syntin brings 44m/s, but this one should widen the liquid range.

A central cyclobutane is as good as Syntin's methylcyclopropane: 40m/s gain over RG-1 instead of 44m/s. The intermediate shall be a dimer of butadiene; catalysis by nickel makes the cis-1,2- dimer, or use UV to make the trans-1,2; the melting point may prefer the trans-1,3. Shall dicyclopropyl-cyclobutane be called Easyntin?

(Mono) cyclopropyl-cyclobutane with an n-propyl or butyl tail should improve the melting point over dicyclopropyl, more so if the tail can be brought to the flat side of the cyclobutane. The intermediate vinyl-cyclobutane is the codimer of ethylene and butadiene over titanium, so for instance trans-octadiene might bring the tail. We'd need some -100°C on Mars but a flash point over +55°C.

Marc Schaefer, aka Enthalpy

[Enthalpy]

These ones are (even) more speculative: too unstable for rockets? Synthesis don't go like I dare to figure them?

Allene is said to produce spiropentane - which unfortunately decomposes over +200°C, and papers don't tell how quickly. The two propyl tails that raise the flash point may well cancel out spiropentane's density and performance advantage.
=>

Methylene cyclobutane is allegedly not very difficult to produce and would lead to spirohexane:
=>

Allene dimerizes to dimethylene cyclobutane which would give dispirooctane:
=> =>
similar to the dispiro[3,0,3,1]nonane or C1CCC12CC23CCC3 that was named soctane-2 (Соктан-2)

More realistic? Cyclopentadiene from refineries' cracking unit adds a moderate strain to cyclopropanes. Image here under, just log in.

Marc Schaefer, aka Enthalpy

[curiouscat]

How big is the world market for rocket fuels?

[Enthalpy]

Historically, only the Soviets had developed good (efficient and cheap) engines families for hydrocarbons, used on Zenit and others. After 1990, the RD-180 was acquired for Atlas V, and SpaceX developed the Merlin for its cheap Falcon:
http://en.wikipedia.org/wiki/Zenit_(rocket_family)
http://en.wikipedia.org/wiki/RD-180
http://en.wikipedia.org/wiki/Atlas_V
http://en.wikipedia.org/wiki/Merlin_(rocket_engine)
http://en.wikipedia.org/wiki/Falcon-9
companies and agencies (US, Europe) that have only solid boosters feel hydrocarbons would be better; all have plans, of varied probability, to develop or acquire hydrocarbon engines.

India develops a "semi-cryogenic engine" which suggests kerosene+oxygen, but I've proposed cis-pinane and pentamethyl-diethylene-triamine. OSC considers buying or producing the old good NK-33 engine. What will propel Ariane 6 is unclear.

Launchers that presently burn kerosene must sale ~1G$/yr worldwide. Let's imagine that a better hydrocarbon puts 4% more payload in orbit: the dumb ratio would mean 40M$/yr sales advantage, for which launchers might pay 10M$/yr to buy 2,000t/yr worldwide (1-2 trucks a week), or 5$/kg.

That is, one small company for the worldwide market, or a tiny department producing for one single launcher.

Alternately, launchers would run normally on RP-1 and buy the improved compatible hydrocarbon only if a heavier customer needs it, and then the amounts drop radically for nearly the same sales of improved hydrocarbon. This more probable scenario justifies maybe 20$/kg.

That's enough interest that a Russian company developed Boctane, and Atlas V plans to switch to it.

[Enthalpy]

Should dicyclopropyl-cyclobutane's (syntin isomer) production go the other way round? First cyclopropanate butadiene to vinyl-cyclopropane, which may be faster, then dimerize at the vinyl side to cyclobutane, which should require UV, alas?

If reactions were simple, this route would produce cis-1,3 plus trans-1,3 and some trans-1,2. Better aspect than cis-1,2 for the melting point.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Craking units in oil refineries by-produce huge amounts of di-cyclopentadiene.
http://en.wikipedia.org/wiki/Dicyclopentadiene
Among other uses, JP-10 is the hydrogenated endo- form. It's a missile fuel: it maximizes the combustion heat in air from a given fuel volume. Nice density (932kg/m³) but its unstrained cycles waste hydrogen, so the ejection speed at a rocket is worse than RP-1.

Cyclopropanation instead of hydrogenation would improve the ejection speed, and the density even further. The flash point should be well over +55°C but the melting point is a surprise, as usual.

It's mentioned in this report from Nasa about improved propellants
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770003210_1977003210.pdf
but beware its unfair comparison in Table 1 favours improved fuels a lot. It also considers unsaturated fuels which rockets wouldn't swallow, explosives like acetylene. Dispiro-octane is mentioned.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Bicyclo[1.1.1]pentane and variants were already considered as a rocket fuel:
http://www.dtic.mil/dtic/tr/fulltext/u2/a267508.pdf

The C₅H₈ itself is too volatile, but its dimer, possibly with one or two CH₂ in between, should have an acceptable liquid range.

It's said to be "very stable", and the dimer's strain brings 100m/s more exhaust speed than RP1 - let's say 80m/s rather, and it's better than Syntin.

Its production would involve things like SOCl₂ and methyllithium in multi-ton amounts, yuk... But it can also be isomerized optically from 1,4-pentadiene.

What price? Take the Zenit launcher as a favourable example - but Soyuz is nearly as favourable, and possibly Falcon-9. It has three kerosene-oxygen stages, each improving the payload by 5% if burning di-bicyclopentane, so the launcher could pay about 1M€ to get 4t for the third stage or 23t for the second stage. That's 250€/kg and 40€/kg.

Imagine the optical isomerization uses 3kW_e lamps, 10% power-efficient on 7.2eV photons, of which 10 are needed for one C5H8. Producing 4t in 50 days needs 1 million kWh <0.1M€ and 320 lamps plus some investments more, could fit. Making 23t for the same price would need to save electricity.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Assuming it changes little the strain in the big ring of pinene and carene, cyclopropanation brings about 20m/s more ejection speed than RG-1, as compared to 40m/s for Boctane or 30m/s for cyclopropanated myrcene - but pinene and carene have advantages:
- Just one cyclopropanation site per cheap C10H16, an accelerated process is documented
- Starting at 872kg/m³ for pinene and carene, the products must be denser than RG-1 and Boctane (832kg/m3)
- Existing rocket tanks carry more fuel. They fit the optimum oxygen-to-fuel ratio for cyclopropanated turpentine better than for Boctane.
- Would the three products make some eutectic?

Marc Schaefer, aka Enthalpy

[Enthalpy]

Fatty acids are cheap and can contain double bonds:
http://en.wikipedia.org/wiki/Fatty_acid
For a rocket fuel, fatty acids must be decarboxylated, which is reputedly difficult - but I naively imagine on could first cyclopropanate (the methyl ester) everywhere, then decarboxylate at +200°C instead of +500°C over a ThO2 catalyst. I may be horribly wrong.

Fatty acids have methylene-interrupted double bonds, leaving a -CH₂- between the cyclopropanes, which eases bond rotations. The orientation of the cyclopropanes makes also many isomers. Both shall lower the melting point.

Some candidates:

Gamma-linolenic 18:3 is banal, the resulting CCCCC1CC1CC2CC2CC3CC3CCCCC would bring hand-estimated 21m/s more ejection speed than RG-1.
Stearidonic 18:4 looks less abundent.
Eicosapentanoic 20:5(n-3) or EPA comes from fish oil. CCC1CC1CC2CC2CC3CC3CC4CC4CC5CC5CCC would improve by 26m/s over RG-1.
Docosahexanoic 22:6(n-3) or DHA, same sources, for CCC1CC1CC2CC2CC3CC3CC4CC4CC5CC5CC6CC6CC.

Performance is marginally better than cyclopropanated turpentine (20m/s and dense), but the liquid range may be better. For instance, Eicosapentanoic acid melts at -54°C despite the 20 carbons and before removing the acid end. Consider a eutectic mix.

Marc Schaefer, aka Enthalpy

[discodermolide]

Have a look at your boctane thread

[Enthalpy]

Farnesane, or 2,6,10-trimethyl-dodecane, has three (hydrogenated) isoprene patterns. It melts at atypical -100°C and boils at +252°C so its flash point is +109°C. Patents US7589243 and US7399323 call it AMD-200 to power aeroplanes; their combustion heat looks wrong, but assimilating to 2,4,6-trimethyl-dodecane, the exhaust speed at a rocket would improve by 8m/s over RG-1, with fair 773kg/m3.

Phytane, or 2,6,10,14-tetramethyl-hexadecane, has one isoprene pattern more. It melts at -99°C as well and boils at +296°C. The exhaust speed is kept, density improves to 791kg/m3.

That's the kind of freezing point, safety and performance I'd pick for a Martian descent-ascent module, including manned. Could cyclopropanation keep the liquid range and improve performance?

I imagine to trimerize or tetramerize butadiene (log in to see the drawing). Maybe some butene can adjust the oligomer's length; a mix is good, a eutectic welcome. At the polymer, lithium catalyst produces 20...60% of the 1,4-trans, while neodymium, cobalt and nickel make the 1,4-cis.
http://es.wikipedia.org/wiki/Polibutadieno
http://de.wikipedia.org/wiki/Polybutadien
If only the cyclopropanated 1,4-trans has the low melting point (just an intuition) the oligomers should be separated, say by cold. Eutectics welcome.

The cyclopropanated 1,4-trans oligomer has all features I suppose make the outstanding melting point of farnesane and phytane:
- Many position isomers, as each methyl can be at right or left, and so do the cycles.
- The molecules stack badly. Asymmetric ends (0 and 2 carbons beyond the cycles) would improve.
- The bonds next to the branches or cycles rotate more easily than in a straight alkane. Or at least, AM1 alleges it...

Cyclopropanes improve the density over the alkane, and gain 30m/s exhaust speed over RG-1.
(The fuels derived from fatty acids must be better than that, exceeding my previous estimates - but what is their freezing point?)

Marc Schaefer, aka Enthalpy

[Enthalpy]

Cyclooctatetraene or COT, C1=CC=CC=CC=C1, is a non-aromatic annulene easily obtained from acetylene. Not very healthy nor stable, but once cyclopropaned to C12CC2C3CC3C4CC4C5CC51, a seducing candidate as a rocket fuel. Log in to see the image.

It would improve the ejection speed by 37m/s over RG-1 (Boctane: 40m/s) and its flash point could be around +70°C. It increases by 16% the proportion of fuel over RG-1 and its density may increase about as much, since COT weighs 925kg/m3 - advantage over Boctane.

As cyclopropanes can be polar or equatorial, there must be 4 isomers - but if the too symmetric all-equatorial freezes easily, it should be removed, say by cold. Some (10%?) random methylcyclopropanes would achieve more isomers and make them asymmetric.

If the acetylene is made at the plant, the amounts of dangerous compounds is reduced there and on the ways.

Marc Schaefer, aka Enthalpy