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Author: Subject: Calcium Carbide CaC2 - Acquisition, Uses and Synthesis
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[*] posted on 30-8-2004 at 13:43
Calcium Carbide CaC2 - Acquisition, Uses and Synthesis


Hallo to all,

I'm looking for CaC2 in Italy, but I haven't find anything. Is it today used?
I don't know, because acetylene lamps aren't used today.
Where and under what name I can buy it (except scientifical suppliers)?

Thanx for help.

[Edited on 3-9-2004 by chemoleo]
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[*] posted on 30-8-2004 at 15:05


CaC2 is used in the steel industry for desulfurization. I'm not sure on availibility. You might check ebay. I know there was some for sale in the past. I haven't checked in a while.
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[*] posted on 30-8-2004 at 16:32


United Nuclear sells it, but as usual at shitty prices.

Anyone know of a way to make it that doesn't involve 2000C and an arc funace?




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[*] posted on 1-9-2004 at 15:48


If you have powdered or granulated Ca metal - which has been offered elsewhere on this forum, usually made by electrolysis of a fused Ca halide salt - and powdered carbon (e.g. lampblack/soot, graphite, coke, anthracite coal), you can stoichiometrically mix them together in a steel pressure vessel in the absence of air (preferably under argon), and heat the mixture to the melting-point of Ca, 810ºC (but below its boiling point, 1,200ºC), you would get the carbide, CaC2, which is an ionic acetylide. The reaction is fairly exothermic, so no further heating should be required to keep the Ca molten except when it is near completion.

It reacts rapidly with water to produce C2H2 and Ca(OH)2. C2H2 is used in the gas cutting of steel, and (at lower heat) gas welding of bronzes and brasses, due to its very hot flame.

It has other uses, in industrial organic syntheses, e.g. ethylene glycol, and especially to make, by partial catalytic hydrogenation, C2H4, which is widely polymerized to make polyethylene and other plastics. However, most ethylene now comes as a byproduct of catalytic cracking in petroleum refining.

Acetylene adds water readily in the presence of H2SO4 and Hg++ ions as catalysts, producing vinyl alcohol which can be polymerized to polyvinyl alcohol (used as PVA glue), although the alcohol tends to rearrange to acetaldehyde.
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[*] posted on 1-9-2004 at 16:14


As far as I know, there is no easy way.
However, it is entirely possible to make it with an arc furnace.... that is, because I made it myself!
Quite simple really, miix the correct amounts of CaO and C, and subject them right into the arc.
You willl get chunks of solid stuff - and these chunks, when put into water, produce a flammable gas, that burn with a small pop and a yellow flame.
If you want I can tell u more.
I did this a long time ago, and I always meant to take pictures (this was before the digital age) just to document the process. It seriously isnt that hard. I got about 2 g worth, in a matter of 15 seconds (I stopped, or got stopped because of the power failing.... seemed like I took more than 16 Amp/230 V out of the power grid. Basically, the automatic power fuse shut down, for the whole house. and 230V * 16Amp = ~ 4kW is about the max it seems.




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[*] posted on 1-9-2004 at 16:32


Shops which sell stuff for cave-exploring sell also calcium carbide. The cave explorers still use acetylene lamps for several reasons.
Cave exploring has become a widespread hobby in the last years, it shouldnt be so hard to find a supplier in Italy - Google.

Here were live CaC2 is sold OTC in every Drugstore - dont even know what for exactly.




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[*] posted on 1-9-2004 at 18:51


http://www.calcium-carbide.com/

not much help to you but if your from the states you can order from there. I bought a pound and it is fun to play around with in small quantities
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[*] posted on 2-9-2004 at 11:11


Starting from CaO (burnt lime) mixed with powered carbon is rather less efficient energetically than using electrolytically-produced Ca metal with C, because of the much higher temperature needed (CaO melts at 2,570ºC, above the melting-point of steel), it may be an endothermic reaction because of the much higher enthalpy of formation of CaO compared to that of CaC2, and the CO2 gas produced in the closed container which adds to the pressure. But, if you have plenty of cheap anthracite coal, and a refractory-lined furnace, it may not matter.

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[*] posted on 2-9-2004 at 19:20
THIS CAN'T BE TRUE!?!?


Well maybe there is an easy way to the synthesis of CaC2!!!

Check this US patent 4,301,133

To quote the method:
Quote:

Into a stainless steel cylinder is placed a uniformly blended mixture of 56 grams of calcium oxide (60 mesh) and charcoal (60 mesh). To the mixture is added 25 grams of pyrophosphoric acid with stirring to form a pasty mass which is then compressed with a rod piston adapted to fit the inside of the reaction cylinder.

The exothermix reaction is allowed to run its course and after cooling (about 15-20 minutes) the piston is removed from the cylinder together with the hard cake of calcium carbide.

The calcium carbide so produced, after crushing to a uniform particle size of 0.25 inch mesh and placing in water, reacts to generate an acetylene base fuel gas.


Now, what is going on here?
The pyrophoric acid reacts with the CaO, to form the phosphate and water... and how does this WATER not interfere with the putative resultant CaC2?
What's the mechanism of this?
Or does this guy just produce methanes and such?
Very strange, the whole thing... ideas?

Wow, if I don't misread this or something, and if this is truly possible - then I know my next project!

Two neatly-fitting steel parts, and a bench press --> bingo! THat is, if the pressure required isn't super high... which is what I suspect. THis guy shamelessly didn't bother remarking on the pressure required :(

[Edited on 3-9-2004 by chemoleo]




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[*] posted on 2-9-2004 at 19:32


That patent 4,301,133 does not sound plausible - the patentor must have fooled the US Patent Office somehow, especially as no (at least initial) heating is specified. Even allowing for the fact that the pyrophosphoric acid would take up the water produced to become phosphoric acid, this would not stop the immediate acid hydrolysis of any CaC2 produced to Ca3(PO4)2 and acetylene. And as I said before, the reaction is unlikely to be exothermic.

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[*] posted on 2-9-2004 at 20:30


Hummm, you missed the key word in the patent, 'Compressed' the patent author could have compressed this mix with a pressure that could have equivalently have made diamonds. This could have resulted in a branching type reaction where new bonds are formed by pressure alone.

Besides, there may have been no fooling involved, you don't have to prove a reaction works to patent it, there are plenty out there that just may have showed some possibility of working that some scientist was quick to patent out of worry before extensive testing proved them wrong.

Edit:
Quote:
It thus will be seen that the objects and advantages of this invention have been fully and effectively achieved. It will be realized, however, that the foregoing specific embodiments have been disclosed only for the purpose of illustrating the principles of this invention and are susceptible of modification without departing from such principles. Accordingly, the invention includes all embodiments encompassed within the spirit and scope of the following claims.

They always get you with that don't they, saying that this might not be how we do it, this is just enough information so that we can sue you if you attempt :(

Is it 56 g of CaO and 56 g of charcoal of is it 56g total? I was trying to figure out the molar ratios and 56 g is about the atomic weight of 1 mol of CaO which could be coincidental. Still the description is odd in that the rection mixture immediately starts to exotherm with the production of water vapor, why would you immediately try to seal it if the water vapor was being trapped within?

[Edited on 9/3/2004 by BromicAcid]




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[*] posted on 3-9-2004 at 03:29
Thats how it looks like:






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[*] posted on 14-3-2005 at 19:26


Some on aquisition, some on preparation, but nothing in this thread on uses really. I recently came to own 500 g or so of calcium carbide and I found that my intentions to make dichloroethane may have been mislead and that it is most likely unsuitable for this purpose. As such I need something to do with it. No energetics though. There is a thread around here about reacting it with alcohols but it really doesn't have any conclusion. Any suggestions would be honestly appreciated.



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[*] posted on 14-3-2005 at 19:55


Well, I think I mentioned it before, any acid stronger (in theory) than acetylene should produce the respective Ca-salt and acetylene.
Acetylene has a pKa of 26, and NH3 36. So acetylene is a stronger acid than ammonia. But ethanol has a pK of 16, butanol is at 19, primary amides RCONH2 at 17, etc, so this should react with the CaC2, producing the respective derivatives.
So yes, this seems a route to calcium ethanolate! Make sure you use 100% EtOH though.

Here's a good summary of pKa's of various (in)org. compounds, this should give us some ideas as to what can be done... in theory :)

Acetylene gas can be used to prepare alkynes, too; acetylene reacts with NaNH2 to form HCCNa, this can react onwards with i.e. 1 bromo propane to form NaBr and 1-butyne.

This can of course be reacted onwards, i.e. again with sodium amide, to form the Na derivative, which can be reacted with any arbitrary bromo alkane. Looks like with NaNH2, synthesis of simple alkynes is easy.
I don't know however how this synth route fares with substituted bromo derivatives. This route only works with primary bromo derivatives, secondary/teritiary ones undergo elimination.

[Edited on 15-3-2005 by chemoleo]




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[*] posted on 14-3-2005 at 20:54


Maybe crush it up some more and pull dried air though it to make cyanimide. There shouldn't be a reaction with oxygen would there, just the nitrogen?



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[*] posted on 14-3-2005 at 22:32
home arc furnace


I think the O has to be taken out.

Brauer's:
A large porcelain crucible, at least 80 mm. in diameter on top
and 60 mm. high, is filled with a well-blended, dry mixture of
equal parts of quicklime and wood charcoal to a level 10 cm. below
the rim. The ingredients are not too finely powdered to prevent
elutriation losses during later gas evolution. The crucible is
placed on top of a brick. Two carbon rods (carbon welding
electrodes, or rods made of electrolytic graphite), at least 15
mm. in diameter and 200 mm. long, are tapered to a point at
their lower ends, while slotted (and thus flexible) brass caps are
affixed on their upper ends. Each cap has a clamp screw, which
serves as an electric terminal. A horizontal hole is drilled through
each carbon rod and cap combination, and a 1-2 mm. connective
copper wire is fitted snugly into the hole and bent back at both
ends so that the cap is securely attached to the electrode. The
electrodes are attached to a stand in such a way that they reach
down to the center of the crucible, and their points are about 10
mm. apart. The asbestos insulated clamps connecting the electrodes
to the stand are attached just below the brass caps. The lime-charcoal
mixture is piled up in the center of the crucible and the
latter is then covered with an asbestos sheet. Insulated copper
wires (cross section 16 mm.) connect the electrodes to the power
supply. The electrodes are in series with 0-50 amp. ammeter, a
40 amp. rheostat (6 ohms at 220 v., 3 ohms with a line voltage of
110 v.) and a double-pole knife switch. Where a suitable rectifier
is available the use of direct current is preferred since a D. C.
arc is far smoother than an A.C. arc. The potential across the
electrodes is measured with a voltmeter.

The current is switched on with the rheostat set at maximum.
It takes some time before the electric arc is initiated. The current
is then set at 30-40 amp. The voltmeter should register a
potential of 50-70 v. If the reading is much higher, the carbons
are too far apart (and vice versa). The current must be shut off
before any adjustment is made. When the operation is properly
conducted, long tongues of burning CO escape from the crucible
together with occasional puffs of dust from the charge. The current
is shut off after 5-10 min. and the crucible is left to cool. A
few grams of sintered or lump calcium carbide will be found under
the electrode ends.

Mellor's:

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[*] posted on 15-3-2005 at 15:43


I tried reacting a test tube full of methanol with calcium carbide today. If there was a reaction it was incredibly slow, there were some tiny clinging bubbles on the surface of the pieces I put in there, but they didn't grow and I suspect there were just adhering there due to the rough surface texture. The reactants were cold but still nothing noticeable. Going to let it sit overnight with a watch glass on top and check tommorow to see if the piece of calcium carbide is anywhere near dissolved.



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[*] posted on 15-3-2005 at 17:28


Just as a suggestion, it does sound like a case of the product not being soluble in the reactant (methanol).
I wonder what happens if you actually crush the CaC2, and THEN react it with methanol while stirring continuously?
Alternatively, maybe we ought to look into solvents in which the PRODUCT is soluble in. I.e. Ca-methanoate, is it soluble in methanol? if not, we know why it doesnt dissolve (and therefore inhibits the reaction despite favorable pKas.).
So using other solvents might solve the problem.

PS good to see someone is trying at least!

[Edited on 16-3-2005 by chemoleo]




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[*] posted on 15-3-2005 at 17:41


Looking up calcium methoxide online I found no physical data except that when it is purchased it still has a high methonol precentage, maybe if it toally dries out it decomposes or maybe it holds it somehow. Maybe it's one of those many "Thermodynamically favorable but Kenetically Slow reactions". I'll have to just throw CaC2 at everything I have to see how it reacts, isopropyl alcohol, chloroform, phenol (which should definatley react) and other things.



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[*] posted on 16-3-2005 at 19:33


The calcium carbide I put into the methanol has crumbled to dust. There is a white powder in the bottom of the test tube. It was loosely covered with a watch glass to allow any acetylene generated to escape. There is still a very small piece of calcium carbide at the bottom but mostly it turned to the dust. Water could have gotten in, but for that quantity to have come in with the watch glass in place seems a little unlikely along with the constant vapor pressure exterted by the methanol vapor. Next step, strain it and heat it, if it is calcium methoxide I would think that it would decompose quickly at heat, or maybe attempt to react with water.



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[*] posted on 19-3-2005 at 09:41


It took roughly 4 days for the ~1g piece of calcium carbide in 7 ml of methanol to turn to a white powder. I decided that there was a simple way to test if there was caclium ions in solution and a hard way. I took a few drops of water and added them. Immediately a precipiate of white powder (calcium hydroxide I would assum) another drop, more white powder, another, more powder, this layer of white powder I created settling on top of the layer beneath it, showing they look somewhat different. The test tube heated slightly. Not 100% conclusive but it shows that there was atleast some calcium in solution and it wasn't in the form of hydroxide to begin with.



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[*] posted on 19-3-2005 at 09:55


Shouldn't dry calcium methoxide burn?
I guess the fact it's turned into dust suggests that it is insoluble, and thus makes the reaction slow (albeit it being a favourable one).
Anyway, to test for the methanol, I guess you could take the dry powder, add some boric acid to it, and a bit of dil. H2SO4. THe resulting boric acid methyl ester should burn green.




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[*] posted on 3-7-2005 at 05:02
CaC2 problems


Ok so I weighed out 130 grams +8 mesh hardwood charcoal and 200g +8 mesh limestone (hrm... I forgot to account for the CO3...doh, excess of C), toasted it a bit with some gouging rods and 80 amperes, obtaining some fused lumps with a pretty high melting point (not as high as CaO; definetly a different material). So I let the bits cool, crushed and added to water. And. No bubbles. HCl doesn't even do anything.

Too much SiO2 in my rock or something? (It's only Wisconsin yellow limestone/dolomite.)

Hrm, lesse... CaCO3 + 4C = CaC2 + 3CO, so I should've used 270, not 200, grams of limestone. Oh well, it's not like it forms a higher carbide (though C3(-2) is known), even if it did, it would still hydrolyze...

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[*] posted on 24-8-2005 at 11:24


I am currently trying to dry Ethanol (94 - 96%) with Calcium carbide. I added a few spoons of the small CaC2 rocks to 250ml Ethanol.
There is a bit of bubbling, the rocks seem to get smaller and lots of white/grey powder is produced.
Does anyone know if CaC2 reacts with absolute Ethanol?

Another problem is the produced acetylene gas. I am trying to make some 99% ethanol for production of Chloral hydrate, and dissolved acetylene would be very inconvenient here due to formation of tetrachloroethane, a very toxic and carcinogenic compound.

Will a distillation get rid of the dissolved acetylene?
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[*] posted on 24-8-2005 at 12:34


I think the patent 4,301,133 has to be right. It would answer a question I always had, i.e. why does the gas have a garlic odor created by a phosphine impurity in the gas. This is very common in every batch of carbide I have ever had. Where else could the phosphine impurity be coming from other than the fact that it is likely most commercial carbide is made by this patent?

I have 2 pounds of carbide I bought for 10 bucks from a guy on ebay in canada, and the Acetylene also has the phosphine odor, telling me that they also must use this same process to make it.


[Edited on 24-8-2005 by IrC]
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