Sciencemadness Discussion Board - A safer procedure of mineral acid synthesis

A safer procedure of mineral acid synthesis

ave369 - 30-8-2015 at 09:47

This post is mostly addressed towards beginners, not experienced independent chemists who already know all that.

Everyone knows that all mineral acids start with sulfuric acid. Everyone knows that the more concentrated the acid is, the better. Everyone also knows that concentrated sulfuric acid is made by boiling battery acid.

However, what also many people know is that highly concentrated sulfuric acid has a boiling point above 300 degrees C. This is already enough to ruin some glassware by thermal cracking, and more than enough to burn holes through hapless independent chemists that happened to be nearby.

It is generally safe to concentrate battery acid up to 70-80%, until the white mist appears (the temperature here is around 200 C, which is easier for glassware to handle). And here is the idea: stop here! Do not boil any more! There is a better method to get conc. sulfuric acid and even oleum, and you will also receive nitric and hydrochloric acids as a nice bonus!

The idea is to use the "tower grade" sulfuric acid that was boiled until the mist appears for Glauber's classic mineral acid syntheses. This concentration is enough to get both azeotropic nitric and fuming hydrochloric acids. And the side products...

Ta-dam! They are bisulfates!

These bisulfates can be used to convert your leftover tower sulfuric acid to oleum. Calcine the bisulfates to convert them to pyrosulfates. These pyrosulfates you put into your worst test tube, the one which it won't be a shame to lose, stopper the tube with a PTFE stopper with a Gamma-shaped glass tube, with the glass tube's other end in a flask with 80% sulfuric acid, and...

FFFFFF--IIIIII--RRRRRR-EEEEEE! at the test tube. The pyrosulfate releases sulfur trioxide which goes into your tower acid and converts it to oleum. There is no need to boil the acid itself.

What's next? You've got tower sulfuric acid, oleum, azeotropic nitric acid and fuming hydrochloric acid. You now have to make 98% sulfuric and red fuming nitric.

To make 98% sulfuric, carefully dilute oleum with 70% sulfuric until the oleum no longer fumes.

To make RFNA re-run your Glauber's nitric acid synthesis with 98% sulfuric.

aga - 30-8-2015 at 10:12

Wow !

Just Wow.

papaya - 30-8-2015 at 14:04

I like how you describe the process Ave, of course it will be more complex than presented, and as you are an russian, I think you've already seen this before: http://chemistry-chemists.com/N1_2009/ChemistryAndChemists_1...

Metacelsus - 30-8-2015 at 15:14

In my view, making oleum won't be a "safer procedure." However, the other ideas (only concentrating acid to 80%, etc.) are good. In fact, my stock of sodium bisulfate comes from nitric acid synthesis, and I can personally say that the method works quite well.

Of course, here in the USA I can just buy 98% sulfuric and 31% hydrochloric acids as cleaning products. (In the same country that restricts iodine!)

byko3y - 30-8-2015 at 15:56

I described a good procedure for concentration and distillation of sulfuric acid up to 92-96% in an appropriate thread about sulfuric acid. Also there's thread about preparation of oleum from bisulfates and pyrosulfates.
http://chemistry-chemists.com/N1_2009/ChemistryAndChemists_1... - this one is actually a translation of procedure made by len1 in his book "Small-Scale Synthesis of Laboratory Reagents with Reaction Modeling"
Cheddite Cheese, it's not that big problem once you actually know how to dehydrate sulfuric and hydrochloric acid, which is actually a really easy process (HCl can be concentrated with CaCl2). But also I realize I've missed the time when a lot of reagents like acetone, sulfuric, hydrochloric acid, phosphorus were perfectly legal. So I try to catch up for the lost time.
Good news are: the guys who became accustomed to usage of nowadays banned reagents, today they have the same problems as me

ave369 - 31-8-2015 at 00:35

byko3y, phosphorus is no longer in the FSKN lists. AntrazoXrom sells it by mail order with no fuss. Technical grade acetone is everywhere in the hardware stores of my town.

byko3y - 31-8-2015 at 01:01

So sad I don't live in russia. No phosphorus and acetone here. Well, except matches and nail polish remover.

kecskesajt - 31-8-2015 at 01:19

Niiiiceee. What about the thermal decomposition of Fe or Cu sulphates?Much cheaper for me.

byko3y - 31-8-2015 at 02:17

Iron sulfate decomposition is a relatively expensive process because you need to heat the compound to red glow. Either porcelain retort or quartz vessel needed for that. And a furnace, of course.

[Edited on 31-8-2015 by byko3y]

ave369 - 31-8-2015 at 10:21

As far as I know, copper sulfate has the same rate of decomposition and the same required temperatures as sodium bisulfate. But sodium bisulfate you get for free as a side product, and blue vitriol you have to buy in the gardening store.

aga - 31-8-2015 at 11:43

Quote: Originally posted by byko3y

except matches and nail polish remover.

(acetone was replaced with ethyl acetate in NPR years ago)

ave369 - 31-8-2015 at 12:16

Forgot to add an important caveat for the main text: to get bisulfate, pour sulfuric acid in excess. This morning I've forgot about it and poured too little acid when making HCl. The resulting cake in my retort wasn't NaHSO4, it was a crazy mixture of NaHSO4, Na2SO4, unreacted NaCl, and to boot NaI and elemental iodine (the salt was iodinated. Damn health nuts!)

aga - 31-8-2015 at 13:45

How much excess sulphuric acid ?

Сколько еще, и кто пил всю свою бензин?

ave369 - 31-8-2015 at 23:31

As my experience tells me, in a 250ml retort the proper amount of 70-80% sulfuric acid is a layer the thickness of my pinky finger above the layer of the acid-permeated salt.

And it's not "кто пил всю свою бензин", it's "кто выпил весь свой бензин". And thank you very much, we do not drink hydrocarbons. Medical grade ethanol, yes. Gasoline (or Coleman fuel, or naphtha, or even maybe pet ether, they are all бензин), thank you very much but no.

[Edited on 1-9-2015 by ave369]

papaya - 1-9-2015 at 05:25

Quote: Originally posted by ave369

is a layer the thickness of my pinky finger above
[Edited on 1-9-2015 by ave369]

I fear to comment

I know only about pinky noses after vodka, not gasoline!

[Edited on 1-9-2015 by papaya]

Marvin - 1-9-2015 at 05:38

I've read that oleum can be made by dissolving the pyrosulphate in ordinary concentrated acid and cooling to precipitate the neutral sulphate. Might be a lot easier than heating the pyrosulphate, what sort of temperature is needed for that?

ave369 - 1-9-2015 at 06:45

I'll try to do this, if nobody refutes this method. I've just got a royal yield of bisulfate while making fuming HCl, when I dry and calcine it, I'll check.

[Edited on 1-9-2015 by ave369]

aga - 1-9-2015 at 12:14

It sounds like a great experiment.

Please take photos.

We like photos of the outside world.

[Edited on 1-9-2015 by aga]

Camroc37 - 1-9-2015 at 19:24

Quote: Originally posted by aga

Quote: Originally posted by byko3y

except matches and nail polish remover.

(acetone was replaced with ethyl acetate in NPR years ago)

Good thing China doesn't really care; Dollar-store nail polish remover still has it!

j_sum1 - 1-9-2015 at 21:19

Let's see if I have this right.
I have easy OTC access to sodium bisulfate. I have some H2SO4 that I made by myself via electrolysis. So, with these, I can produce as much H2SO4 as I want -- for the price of a little bit of sacrificial glassware. (I break stuff anyway!)

Produce SO3. Concentrate half my acid to oleum. Dilute back with the remaining acid to get high conc sulfuric. Dilute further by adding to water. Lather, rinse repeat.

Is that right?

ave369 - 2-9-2015 at 05:06

j_sum, if you have an unlimited supply of dilute sulfuric acid, then yes, you can concentrate it in large amounts. That's what I'm doing now: buying cheap battery acid in a spare car parts shop and making real, hardcore sulfuric acid from it. Getting other mineral acids by the way (I don't have access to OTC bisulfate, so I have to make my own from chlorides and nitrates).

However, it's the "heating the pyrosulfate" bit that requires sacrificial glassware. So you should only rely on it for the last step: from 80% sulfuric acid to over 100%. If you try to SO3-nate dilute sulfuric acid without boiling it down first, you will need too much sacrificial glassware. You will end up sacrificing your entire lab. Liters of boiled down battery acid should be the main source of H2SO4 in my method, and the decomposition of pyrosulfate just the final kicker to increase the oomph of the product. Just to replace boiling down over 80% and producing Cytherean clouds of that same SO3 in your kitchen.

So you don't buy tons of NaHSO4, calcine and decompose it to turn your one liter of dilute H2SO4 to oleum. Kicking the required SO3 out of "tons" of NaHSO4 requires more than just sacrificial test tubes, maybe a big retort made of platinum-unobtainium alloy, and those kilograms of SO3 are insanely dangerous themselves. If you want to follow my method, you take your electrolysis machine, make more liters of dilute acid, boil it down to produce maybe 200 grams of tower grade acid, and then fire at the pyrosulfate in the sacrificial test tubes.

[Edited on 2-9-2015 by ave369]

kecskesajt - 2-9-2015 at 05:47

Here,battery acid is more expensie than cc. H2SO4. And be aware that battery acid contains a lot of lead.

careysub - 2-9-2015 at 06:32

Quote: Originally posted by ave369

Just to replace boiling down over 80% and producing Cytherean clouds of that same SO3 in your kitchen.

"Cytherean" - I like it!

ave369 - 2-9-2015 at 07:21

Quote: Originally posted by kecskesajt

Here,battery acid is more expensie than cc. H2SO4. And be aware that battery acid contains a lot of lead.

Here in old Mother Russia it isn't. And brand new, rather than used, battery acid here has no contaminants.

careysub - 2-9-2015 at 10:51

Quote: Originally posted by ave369

However, it's the "heating the pyrosulfate" bit that requires sacrificial glassware.

If doing this on a substantial scale (test tubes are pretty cheap, flasks - not so much) I would think using iron pipe as the sacrificial reaction vessel might be a good idea. Drill a hole in the cap, and run in stainless steel tubing (you might need to torch heat the tubing to keep the SO3 flowing).

papaya - 2-9-2015 at 11:57

I want to ask you ave, what do you think regarding the following purely theoretical plan: First boil down dilute acid to 80% , then put 2 lead electrodes into it and electrolyze that until all the remaining water is decomposed to it's elements. Though, I don't know how stable Pb electrodes will behave in concentrated H2SO4, will they survive?(at least they do fine in batteries)

ave369 - 3-9-2015 at 00:49

I'm no Copenhagen in questions of electrolysis. Not my field, sorry, and no experience of dealing with high currents and voltages. The biggest electrolysis I've done was making chlorine with a flashlight cell and two graphite sticks from pencils, and this was when I was ten years old.

j_sum1 - 3-9-2015 at 01:29

papaya, I don't see any reason why it wouldn't work. But a couple if things to consider.
1. You would want to calculate how long it would take to remove that much water. It is always longer than you think.
2. You are going to build up lead dioxide on your electrode. In other words, your electrode life will be finite. You could minimise this by keeping the voltage down but that would lower your current and see point 1.

It is worthy of an experiment however.

[edit: typo]

[Edited on 4-9-2015 by j_sum1]

papaya - 3-9-2015 at 14:04

Lead electrodes stay well in acid batteries for many years, both under anodic and cathodic conditions, that's why I supposed to use lead, not graphite for example. The idea about electrolysis is very simple here - when you electrolyze sulphuric acid solutions in water, only water breaks apart forming H2 and O2, thus if electrode materials hold up conditions you can reach higher and higher concentrations of acid in solution as you continue the process! I only fear that at higher concentrations of acid (compared to battery 30-40%) lead will start to dissolve (does any acid sulfate of lead exist?), however one should find this out practically. On the other hand one can start only with CuSO4 solution - first all copper will be plated out on the cathode leaving dilute acid in solution, then water (hopefully all what is left) breaks apart leaving only sulfuric acid behind. And calculations.. faraday's laws will do.

aga - 3-9-2015 at 14:24

Lead Sulphate somehow leaps to mind ...