How can I increase the concentration of H2SO4 using electrolysis?

[derekmohammed]

Electrolysis Of Water Help Please...

Hi,

I have been trying to raise the Concentration of H2SO4 by using electrolysis. I figure that since the overall reaction will yeild H2 gas and O2 gas (therefore no sulfur is lost) the concentration of the Acid will rise. (If I am correct up to here continue reading)...

I have tried this:
1) Using a car battery (400Amps) and Carbon Electrodes, but the one carbon stick is getting oxidized! And leaves a mess in the solution. I was under the assumption that Carbon was relitivly inert?

2) I heard that Nichrome wire will work for this becuase it too is supposibly inert. Can anyone conform this?

Thank you

Derek Mohammed

 

[mrjeffy321]

I don't think the carbon is actually getting oxidized, but I do know from experience that the carbon will tend to crumble away when using it as your electrodes, at a rate that depends on (amoungs other things) the amount of amps you use, and 400 amps is extreamly high my goodness how are you getting 400 amps for vey long out of a car battery!
soaking the carbon rods in linseed oil and using a smaller current will cut down on the break down of the rods, as well as using the densist piece of carbon you can find (ie. not pensil "lead"), I like to use artificial graphite blocks that i saw into a rod, but welding "gauring" (i think that is what it is called) works very well too. In the end, no matter what you do, the electrodes will eventually erode away no matte what, all you can do is try to slow it down.

I have no experience using Nichrome wire, but I would expect that they too will eventually erode away too, i expect, but I am not sure. if they dont, I really ought to get me some.

 

[Josef Tapper]

Have you gotten it working ? You might try Stainless steel rods.

 

[mrjeffy321]

I don't think stainless steel would work.
For one, the acid in the water that the electrode is in would eat away at it, and also, I think the the metal would still dissolve away due to the electric current.

I have heard that gold/silver or even more ideally, platinum, electrodes are best, but I have not heard any conclusive accounts on the part of others who have used them, and I have not used them myself, so I cannot speak for or against it. This uncertainty is keeping me from investing the money into a pair of platinum electrodes, platinum anything doesn't come cheap.

 

[so-crates]

If money is no object, I'm sure platinum of gold would work great!

 

[google]

iridium...lol the most inert metal I know of.

 

[Waters2]

Iridium?Can be use in electrode?? Can u tell me more? Normally platinum and carbon used in electrode...

 

[Gokul43201]

...that depends on (amoungs other things) the amount of amps you use, and 400 amps is extreamly high my goodness how are you getting 400 amps for vey long out of a car battery!

The battery is rated for 400 CCAs. This does not mean he is putting 400amps through the cell. This would simply boil off everything in the cell. The current through the cell is determined by its intrinsic impedance.

In any case, all this discussion of electrodes has sidetracked the first obvious concern with the experiment : will it even work in theory ?

I would imagine you could easily go from 0.01% H2SO4 to 0.1% H2SO4 this way (even though it would take a while). I'm not anywhere nearly as convinced that you could go from 90% H2SO4 to 99% H2SO4.

What are the concentrations you are dealing with ? Does the principle behind the electrolysis of water hold for concentrated solutions too ?

 

[redwraith94]

It will work, but it will take an ungodly amount of time to get rid of all of the excess water. A much faster, and still VERY unsafe way is to boil the solution in an enameled pot out doors, until dense white fumes (sulfuric acid clouds) appear. At that point it is aboot ~99% pure acid, assuming the starting solution was only acid, and water, no dyes etc.

Platinum clad electrodes are the cheapest way to go, for longevity. Even then they still have a limited amount of use before the break down (unless the platinum is more pure than can be feasibly manufactured right now...less than .01% impurities) Solid platinum wouldn't suffer at all, but it is way to expensive to consider, and not very conductive compared to copper for high current densities.

Nichrome wire will not work. It will be better than stainless though.

 

[seattle_rust]

Gold actually works better, it resists H2SO4 better than platinum.

For concentration it would be better to use selective permeability membranes, one to pass H+ and block SO4(2-) and the other to pass the SO4 and block the H+. The acid then concentrates in the area betwen the two membranes. This take a lot less energy than vconverting all that H2O to H2 and O2 (unless you're going to use the gases to rn a fuel cell to produce electricity), and generally less than boiling off a lot of water.

Distilling off the water is better than electrolysis. Use glass or ceramic containers, until you get past about 10% H2SO4 open pans are just fine. The boiling point of the mix starts noticeably rising past that, and you want some sort of reflux for getting a bit of fractionation to prevent the loss of too much acid.

 

[Josef Tapper]

Tantalum is available cheaply on ebay. Conducts electricity and is about as inert as it comes. Cheaper alternative is Niobium.

 

[Josef Tapper]

P.S. doesn't boiling give H2SO3 ... something about sulfer trioxide which needs to be recombined to H2SO4.