Obtaining sulfuric acid from battery electrolyte

[Marvin "Popcorn" Sutton]

Important: Observe safety procedures, when handling acids. Protect your respiratory organs and eyes!
If you have battery electrolyte, you can obtain high concentrations of sulfuric acid in a simple way. This is done by evaporating the electrolyte in a sand bath. To evaporate you will need: a stove, a sand bath and a heat-resistant flask, and the electrolyte. The electrolyte can usually be found in concentrations of <30%.
Pour the electrolyte into the flask, put it on the sand and start heating it slowly, it is better to use the lowest heat mode and do not let the solution boil too much. Once 2/3 of the solution has boiled out, and the gas from the flask has turned white, you have got sulfuric acid at a concentration of ~80%. To make it more concentrated, you need to boil it longer. But be careful, do all the work outdoors or in a ventilated room under a hood. The acid will also begin to evaporate, and you can get a burn.
The concentration of the acid obtained is very easy to determine by the density. To calculate the density, you must weigh a quantity and compare it with the table.

Table of density of sulfuric acid H2SO4.​

Density g/cm3 (25 °C)​ %​ g/L​ Mol/L​ 1,0051​ 1​ 10,05​ 0,103​ 1,0118​ 2​ 20,24​ 0,206​ 1,0184​ 3​ 30,55​ 0,312​ 1,0250​ 4​ 41,00​ 0,418​ 1,0317​ 5​ 51,59​ 0,526​ 1,0385​ 6​ 62,31​ 0,635​ 1,0453​ 7​ 73,17​ 0,746​ 1,0522​ 8​ 84,18​ 0,858​ 1,0591​ 9​ 95,32​ 0,972​ 1,0661​ 10​ 106,6​ 1,087​ 1,0731​ 11​ 118,0​ 1,203​ 1,0802​ 12​ 129,6​ 1,321​ 1,0874​ 13​ 141,4​ 1,442​ 1,0947​ 14​ 153,3​ 1,563​ 1,1020​ 15​ 165,3​ 1,685​ 1,1094​ 16​ 177,5​ 1,810​ 1,1168​ 17​ 189,9​ 1,936​ 1,1243​ 18​ 202,4​ 2,063​ 1,1318​ 19​ 215,0​ 2,192​ 1,1394​ 20​ 227,9​ 2,324​ 1,1471​ 21​ 240,9​ 2,456​ 1,1548​ 22​ 254,1​ 2,591​ 1,1626​ 23​ 267,4​ 2,726​ 1,1704​ 24​ 280,9​ 2,864​ 1,1783​ 25​ 294,6​ 3,004​ 1,1862​ 26​ 308,4​ 3,144​ 1,1942​ 27​ 322,4​ 3,287​ 1,2023​ 28​ 336,6​ 3,432​ 1,2104​ 29​ 351,0​ 3,579​ 1,2185​ 30​ 365,6​ 3,728​ 1,2267​ 31​ 380,3​ 3,878​ 1,2349​ 32​ 395,2​ 4,029​ 1,2432​ 33​ 410,3​ 4,183​ 1,2515​ 34​ 425,5​ 4,338​ 1,2599​ 35​ 441,0​ 4,496​ 1,2684​ 36​ 456,6​ 4,656​ 1,2769​ 37​ 472,5​ 4,818​ 1,2855​ 38​ 488,5​ 4,981​ 1,2941​ 39​ 504,7​ 5,146​ 1,3028​ 40​ 521,1​ 5,313​ 1,3116​ 41​ 537,8​ 5,483​ 1,3205​ 42​ 554,6​ 5,655​ 1,3294​ 43​ 571,6​ 5,828​ 1,3384​ 44​ 588,9​ 6,004​ 1,3476​ 45​ 606,4​ 6,183​ 1,3569​ 46​ 624,2​ 6,364​ 1,3663​ 47​ 642,2​ 6,548​ 1,3758​ 48​ 660,4​ 6,734​ 1,3854​ 49​ 678,8​ 6,921​ 1,3951​ 50​ 697,6​ 7,113​

Density g/cm3 (25 °C)​ %​ g/L​ Mol/L​ 1,4049​ 51​ 716,5​ 7,306​ 1,4148​ 52​ 735,7​ 7,501​ 1,4248​ 53​ 755,1​ 7,699​ 1,4350​ 54​ 774,9​ 7,901​ 1,4453​ 55​ 794,9​ 8,105​ 1,4557​ 56​ 815,2​ 8,312​ 1,4662​ 57​ 835,7​ 8,521​ 1,4768​ 58​ 856,5​ 8,733​ 1,4875​ 59​ 877,6​ 8,948​ 1,4983​ 60​ 899,0​ 9,166​ 1,5091​ 61​ 920,6​ 9,386​ 1,5200​ 62​ 942,4​ 9,609​ 1,5310​ 63​ 964,5​ 9,834​ 1,5421​ 64​ 986,9​ 10,060​ 1,5533​ 65​ 1010​ 10,300​ 1,5646​ 66​ 1033​ 10,530​ 1,5760​ 67​ 1056​ 10,770​ 1,5874​ 68​ 1079​ 11,000​ 1,5989​ 69​ 1103​ 11,250​ 1,6105​ 70​ 1127​ 11,490​ 1,6221​ 71​ 1152​ 11,750​ 1,6338​ 72​ 1176​ 11,990​ 1,6456​ 73​ 1201​ 12,250​ 1,6574​ 74​ 1226​ 12,500​ 1,6692​ 75​ 1252​ 12,770​ 1,6810​ 76​ 1278​ 13,030​ 1,6927​ 77​ 1303​ 13,290​ 1,7043​ 78​ 1329​ 13,550​ 1,7158​ 79​ 1355​ 13,820​ 1,7272​ 80​ 1382​ 14,090​ 1,7383​ 81​ 1408​ 14,360​ 1,7491​ 82​ 1434​ 14,620​ 1,7594​ 83​ 1460​ 14,890​ 1,7693​ 84​ 1486​ 15,150​ 1,7786​ 85​ 1512​ 15,420​ 1,7872​ 86​ 1537​ 15,670​ 1,7951​ 87​ 1562,00​ 15,930​ 1,8022​ 88​ 1586,00​ 16,170​ 1,8087​ 89​ 1610,00​ 16,420​ 1,8144​ 90​ 1633,00​ 16,650​ 1,8195​ 91​ 1656,00​ 16,880​ 1,8240​ 92​ 1678,00​ 17,110​ 1,8279​ 93​ 1700,00​ 17,330​ 1,8312​ 94​ 1721,00​ 17,550​ 1,8337​ 95​ 1742,00​ 17,760​ 1,8355​ 96​ 1762,00​ 17,970​ 1,8364​ 97​ 1781,00​ 18,160​ 1,8361​ 98​ 1799,00​ 18,340​ 1,8342​ 99​ 1816,00​ 18,520​ 1,8305​ 100​ 1831,00​ 18,670​

 

[ASheSChem]

is it really feasible to obtain an acid that we can use in our syntheses with this method?

 

[MadHatter]

Sure. I've done it. Thing is, the electrolyte in old batteries is dirty, full of lead particles and other impurities. So I needed to distill it, and distillation of sulphuric acid is demanding.
The boiling point of aceotropic sulphuric acid is above 300 C, so you need a good heat source. Superheated SA is really really corrosive, so you need good PPE also: thick rubber gloves, apron, good, thick glasses, splash protection visir, the works.
It also tends to bump like crazy when boiled, so much sometimes that the one risks damage to the glassware. And you dont want the boiling beaker to crack, cause then your heting mantle is fucked forever, and your fume hood, and so on. Sometimes boiling chips help, sometimes sand, and sometimes nothing.
But there's a TON of videos on this on youtube. You'll find at least one per chemtuber out there.

 

[MadHatter]

Oh, and my top tips for distilling sulphuric acid is:

1. Grease all the glass joints with sulphuric acid. Anything else will boil off at the high temperatures used.
2. Connect all your joints with METAL claps, or the bumping will separate them. Plastic ones will melt.
3. Have boiling chips in the boiling flask, and clean sand ready for use. If none of them helps and the bumping gets too violent, be ready to lower the temperature quickly by having your heating mantle set up so you can lower it from the flask. You don't want to move the glassware.
4. Work with quality borosilicate glassware, make sure you're not using knockoffs or they can very well crack.

 

[ASheSChem]

thank you for your feedback, it's already a little reassuring..
but I admit... I will still continue to look for some to sell

I saw a lot of videos but it seemed to me quite dangerous (for me) and hazardous with uncertain quality

but if I try one day, I will carefully follow your instructions!

 

[ASheSChem]

a last question...
you speak about dirty electrolyte acid, but if we buy clean one like this

do we need to distill it ? or just evaporate is ok ?
distilling acid afraid me a little bit

 

[MadHatter]

Well, if you succeed, the quality is pretty guaranteed. Sulphuric acid is sulphuric acid. And sure, it's a bit dangerous, but not too much. It was one of the first distillations I did, actually. And it worked out fine.
But if you manage to get clean battery electrolyte it usually has a concentration of about 30%, and then you only have to boil off water. But do it outside, because when you start to hit the 90%-mark, a lot of corrosive vapor will be produced.

 

[MadHatter]

Haha, yes, you see the answer above. You need to boil it in a big, open glassware. Outside. Once it start giving off thick white vapor (that you DONT want to inhale or get near anything made of metal), check the concentration by determining density. After it has cooled down.

 

[ASheSChem]

thanks a lot