Sciencemadness Discussion Board

Carbon removal from glass.

Jhavenga - 21-7-2015 at 03:43

Hi all. Just registered.

We're testing total organic carbon of soils using the walkley-black method. For those who don't know, it involves a soil sample being treated with K2Cr2O7 and H2SO4. Finally the solution is titrated with Fe(NH4)2SO4 with a Ferroin indicator.

I have a feeling that some of the carbon is attaching to the bottom of the Erlenmeyer flasks, becuase with each blank titration we do, we get a different value (1-3ml difference). This means that my samples are being influenced as well - by whatever it is!

Has anyone had problems with the above method, and also, how can one remove carbon from glass?

aga - 21-7-2015 at 06:04

Pihraña Fluid works a treat !

H2SO4 + H2O2

https://en.wikipedia.org/wiki/Piranha_solution

AJKOER - 22-7-2015 at 20:36

Strong heating of the carbon in a current of air may work.

As a fuel consider CH4, H2, alcohol,...

Cheap, safer than working with strong acids and no residue with a clean burning fuel.

Texium - 22-7-2015 at 21:10

Dissolving it in chromic acid (which appears to be what the first step of your procedure is) works very well, as does piranha solution. I don't feel like what AJKOER is describing would work too well in practice. Normally I consider chromic acid to be a sort of last resort, but since you're already using it in your procedure, it probably wouldn't be that big of a deal to clean the flask with a small volume of a hot solution of it in between runs.

chemrox - 22-7-2015 at 22:47

For black C on glass I've been applying wet NaOH or saturated NaOH solution. Works in all but the most resistant cases e.g. where access with a brush or spatula is not available.

BromicAcid - 23-7-2015 at 03:22

As aga said, Piranha should work but it is pretty slow with anything that might be considered a large deposit. AJKOER suggested strong heating in a current of air but might I suggest putting a small amount of NaNO<sub>3</sub> into the flask and heat the deposit and flask from the outside, once the sodium nitrate is molten it should oxidize your carbon vigorously then it can be rinsed out when cool. Note that the melting point of sodium nitrate is just outside the extreme service temperature of borosilicate but it is also far below the annealing point (although you might reach it in hot spots), point being you will likely start to reduce the lifetime of your glassware if you perform this trick on a regular basis.

AJKOER - 23-7-2015 at 08:47

A novel dea (and, besides, Blogfast wouldn't be happy unless I tried to inject a hypochlorite somehow), would be to attack the Carbon residue via Cl2O/Cl2, which could be prepared in situ.The logic is based on my expectation of a chemical reaction between carbon and dichlorine monoxide, the acidic anhydride of HOCl, which is generally cited as the main reactant in chlorination of micropollutants (see, for example, https://www.google.com/url?sa=t&source=web&rct=j&... and this source noting a bulk attack of activated carbon by HOCl, https://books.google.com/books?id=5oIO2hzQD6wC&pg=PA172&... and this patent reference discussing commercial chlorination applications with Cl2O in CCl4 and also HOCl http://www.google.com/patents/EP0084254A2?cl=en ).

Possible embodiments include adding Ca(ClO)2 and CO2 to the vessel, or a Cl2 source and either Baking or Washing Soda with varying requirements of generally low to modest heat, and just let the reaction sit.

Here is a quote from Wikipedia on Cl2O with respect to possible preparations (link: https://en.m.wikipedia.org/wiki/Dichlorine_monoxide ):

"A safer and more convenient method of production is the reaction of chlorine gas with hydrated sodium carbonate, at 20-30°C.

2 Cl2 + 2 Na2CO3 + H2O → Cl2O + 2 NaHCO3 + 2 NaCl
2 Cl2 + 2 NaHCO3 → Cl2O + 2 CO2 + 2 NaCl + H2O

This reaction can be performed in the absence of water but requires heating to 150-250°C; as dichlorine monoxide is unstable at these temperatures[3] it must therefore be continuously removed to prevent thermal decomposition.

2 Cl2 + Na2CO3 → Cl2O + CO2 + 2 NaCl

Dichlorine monoxide can also be formed by the reaction of calcium hypochlorite with carbon dioxide

Ca(ClO)2 + CO2 → CaCO3 + Cl2O "

Also, one may consider more simply just using concentrated HCl/H2O2, if available.

Note, if even a significant amount of unreacted gaseous Cl2 is still presence, with more heat, also still a possible chemical assault. See, for example, Chemosphere, 2003, Jul;52(4):709-16., Article: "Formation of chlorinated hydrocarbons from the reaction of chlorine atoms and activated carbon" by Khachatryan and Dellinger. To quote the abstract:

"The reactions of chlorine atoms and activated carbon have been studied over the temperature range of 200-400 degrees C using an isothermal flow reactor in conjunction with 337 nm laser photolysis of Cl2. These studies have shown that carbon tetrachloride is the major product, with chloroform, methylene chloride, and methyl chloride being formed in progressively decreasing yields. Trace quantities of methane, ethane, and dichloroethylenes were also observed. Mechanisms of carbon fragmentation by successive addition of chlorine atoms are proposed. The formation of small chlorinated hydrocarbons by the direct reaction of chlorine with carbon may be a key link in both the de novo and precursor pathways.."

Link: http://www.ncbi.nlm.nih.gov/pubmed/12738284

[Edited on 23-7-2015 by AJKOER]

chemrox - 23-7-2015 at 13:23

I've read several versions of Cl2 generation at lab scale. One is sodium bisulfate and bleach; another is permanganate and HCl.. what were you thinking of for the Cl2?

Wow what a toxic mess the method you propose would make. Worse than pirhana

AJKOER - 23-7-2015 at 13:46

Chemrox:

One of my paths via concentrated HCl/H2O2 is, in effect, a known acid piranha. I think it would be interesting if it happen to work, albeit slowly, on carbon using say strong HCl and just dilute H2O2.

The other methods are possibly more accessible in terms of starting reactants, but are obviously more difficult when it comes to implementation (but there are always inventive chemists out there).

[Edited on 24-7-2015 by AJKOER]

aga - 23-7-2015 at 14:55

The fatal flaw is that it's not Activated Carbon the OP wants to dissolve/remove.

The difference between 'Carbon' and 'Activated Carbon' is a million-fold increase in surface area.

aga - 23-7-2015 at 15:00

Quote: Originally posted by chemrox  
what a toxic mess the method you propose would make

Hasn't stopped any chemist so far ...

To be fair to AJ, he was not asked for a full environmentally safe way to get the reaction products into a safe disposal form, and he probably did not provide any info on that as he'd probably expect any sane chemist to be able to do that for themselves.

I suspect AJ would be more than able to oblige, if asked.

AJKOER - 24-7-2015 at 06:12

Quote: Originally posted by aga  
The fatal flaw is that it's not Activated Carbon the OP wants to dissolve/remove.

The difference between 'Carbon' and 'Activated Carbon' is a million-fold increase in surface area.


Aga:

You may wish to change your opinion to the opposite extreme based on this report of the properties of, I suspect, undiluted Cl2O (for which a dilute solution in CCl4, for example, are employed commercially as per my prior patent reference ), to quote:

"The liquid at 2 °C is an unstable spark- and touch-sensitive explosive. The gas may explode when heated above 42 °C. A powerful oxidizing agent. Explodes on contact with alcohols, ammonia, antimony, antimony sulfide, arsenic, barium sulfide, calcium phosphide, carbon, carbon disulfide vapor, charcoal, cork, dicyanogen, ethers, hydrogen sulfide, mercury sulfide, nitrogen oxide, paper, phosphine, phosphorus, potassium, rubber, sulfur, tin sulfide, turpentine, and other oxidizable materials. Self-explodes. Incompatible with carbon, dicyanogen, diphenylmercury, nitrogen oxide, oxidizable materials, and potassium. Explosive reaction when heated above 50 °C with many hydrocarbons (e.g., butadiene, ethane, ethylene, methane, propane)."

Link: http://www.guidechem.com/dictionary/en/7791-21-1.html

So the new possible point of contention is whether the characteristically low yield Cl2/Na2CO3 path (under 10% Cl2O as I recall, which may be advisable for safety reasons as well), for example, is possibly too reactive with the seemingly inert carbon deposit at the bottom of the flask. I suspect not, but safety concerns argue for first appropriately small scale testing with safety measures in place.

I would contend not too concentrated aqueous solutions (basically HOCl related paths) are probably less reactive but safer.

[Edit] It just occurred to me that a possible product between a working dilute Cl2O gas mix (which I will define as under 5% Cl2O and 95% CO2, as 30% or more Cl2O can be detonated with a spark per an article on Cl2O preparation available at http://www.sciencemadness.org/talk/viewthread.php?tid=23152 ) and carbon could include CO, Cl2 and even possibly COCl2, a highly toxic gas (which can be neutralized by shaking with water). As such, be especially mindful of exposure to fumes and neutralize as recommended.

[Edited on 24-7-2015 by AJKOER]

ave369 - 25-7-2015 at 06:34

You can try the secret superweapon of Russian chemists: the nitrochromium mixture. Mix CrO3 and concentrated HNO3.

zed - 25-7-2015 at 14:45

Gettin' invisible layers of clingy stuff, out of the insides of glass ware, is a tough business.

How about, you just use something to scour the insides of you flasks.

Like....fill 'em half full with Fine Sand/Ice cubes...or Ice cubes and Comet Cleanser, and swirl/shake em, until they are scoured clean.

Then, clean 'em in the usual way.

This is the secret superweapon of American Diner Personnel.

aga - 25-7-2015 at 14:55

Quote: Originally posted by AJKOER  
You may wish to change your opinion to the opposite extreme

I will do so at the drop of a hat when faced with undeniable Evidence that the carbon deposits are in fact 'Activated'.

Given the enormous increase in surface area of AC, i would expect it to react faster, or am i missing something ?

I will spend some time on Activated Carbon shortly, and will have some experimental data to report.

Possibly a good idea to hold those thoughts until the data is in.

BromicAcid - 25-7-2015 at 15:01

Quote: Originally posted by zed  
Gettin' invisible layers of clingy stuff, out of the insides of glass ware, is a tough business.

How about, you just use something to scour the insides of you flasks.

Like....fill 'em half full with Fine Sand/Ice cubes...or Ice cubes and Comet Cleanser, and swirl/shake em, until they are scoured clean.

Then, clean 'em in the usual way.

This is the secret superweapon of American Diner Personnel.



Always been a fan of rock salt and methanol for the same effect.