Author Topic: 30% H2SO4  (Read 3288 times)

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timsong

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30% H2SO4
« on: January 05, 2002, 05:51:00 PM »
A couple of years ago the company that I was working for was having a clear out, and a barrel of 30% battery top up H2SO4 was intercepted by myself before it was disposed of.

Of course 30% was not much use to me so I started trying to concentrate it. I done this by boing it in a pyrex beaker on the hob until white fumes started to be evoled.
Problem was that this is still not as concentrated as I would like (does not char sugar) and the acid turned a slight brown colour.
So next I tryed to distill it, but I just could not keep the apparatus hot enough and even when it did get it hot enough, clouds of dense white fumes were all that came over to the receiver.

Reading up on H2SO4 it says that a constant boiling acid (98.3%) distills at 338c, but it also says that the 95% acid boils at 295c emitting dense white fumes (what I had).

So how do I get pass the 95% concentration to rid these fumes (they don't condense easily). Will I have to distill under reduced pressure ? do I need to distill in an inert atmosphere ?

Or will I be able to get pass the 95% by continuing to boil in a beaker until the fumes disapear, then transfering to the distill aparatus ?

Also, these impurities in the acid (that made it turn slightly brown when concentrated) can these be rid of by filtering the 30% acid though activated charcoal or something ?

Hampstead Incident - Donovan 1967

halfapint

  • Guest
Re: 30% H2SO4
« Reply #1 on: January 05, 2002, 08:51:00 PM »
The brown color you are getting may bee from iron discoloration. Having metal ions in your conc. sulfuric acid can give real problems in some reactions. For other uses, it may turn out OK. As far as purifying sulfuric acid, you have to do all that work while it's dilute. After it's concentrated, what you see is what you get.

The charcoal cleaning is also best done at the dilute stage. Float your charcoal in water, and use only the bigger stuff that settles first --- you've got to filter that. Sometimes you may have luck in filtering cold battery acid thru paper, if you do it FAST before it eats the paper. Generally, though, you filter sulfuric acid thru glass.

You used a beaker, I would use a casserole for more exposure to the air. Working always outside, I'd heat it (below boiling) down to ~1/3 volume. My rule of thumb was to heat it until it stopped steaming and started smoking. You can see the difference. 93-95% should serve for most applications, at that strength it will char sugar or paper. To get 98%, you'll need to use a water aspirator. Just heat to get the water out, don't try to raise a boil. Don't sacrifice your vac pump for this. And no, you won't distill sulfuric acid. Just forget that notion.

A beaker down, and a barrel to go? Gives you lots of incentive to get that brown stain out. Assuming it's in your acid source, and not a result of processing. There must bee something, acid insoluble, which can be added to flocculate your impurity out of the 30% acid. Can't think of it right now. You can try Ca(OH)2, to precipitate out calcium sulfate, but I doubt you could hook much of your impurity that way. Good luck anyway.

turning science fact into <<science fiction>>

timsong

  • Guest
Re: 30% H2SO4
« Reply #2 on: January 05, 2002, 09:10:00 PM »
Thanks for the advice.

There does not seem to be any colouration in the 30% acid, this colouration only appears on concentration.

I guess the activated charcoal would only get rid of any organic impurities, but if the colouration was from organic impurities (say from the HDPE barrel, does smell plastic when concentrating) most of these would be de-hydrated on concentration/heating and just fall the the bottom as carbon. But unfortunatly there is no precipitation after the concentrated acid is left standing, so you may be right that this slight brown colouring is cause by metal salts. If i had some SO3 I guess I could just concentrate the acid so much that these salts would precipitate, but SO3 or phosphorus pentoxide just aint handy to me !

Hampstead Incident - Donovan 1967

timsong

  • Guest
Re: 30% H2SO4
« Reply #3 on: January 05, 2002, 09:19:00 PM »
What about if I saturated the acid with HCL gas, would this cause the impurities to precipitate ?

Then I could just gently heat the acid to remove the HCL

Hampstead Incident - Donovan 1967

halfapint

  • Guest
Re: 30% H2SO4
« Reply #4 on: January 05, 2002, 10:11:00 PM »
Nah, chlorides are more soluble than sulfates. Phosphates less so, but getting phosphoric acid out of sulfuric is another thing that just ain't happening.

turning science fact into <<science fiction>>

timsong

  • Guest
Re: 30% H2SO4
« Reply #5 on: January 05, 2002, 10:21:00 PM »
Yes more soluble in H2O, but I meant in the (95%appx)concentrated H2SO4 not the 30% H2SO4.
If the concentrated H2SO4 what saturated with HCL there would be no free H2O for the salts to dissolve in, so maybe they would precipitate ?

(maybe I'm talking shit ?)

Hampstead Incident - Donovan 1967

cheeseboy

  • Guest
Re: 30% H2SO4
« Reply #6 on: January 06, 2002, 08:12:00 AM »
Either bees love breathing in sulphuric acid fumes or else they are too lazy to have a "friend" pick them up a litre or two at the nearest supply house. Cheese never had a problem finding 95-98% H2SO4.

May The Source Bee With You....Always.

Osmium

  • Guest
Re: 30% H2SO4
« Reply #7 on: January 07, 2002, 02:40:00 AM »
Just forget about cleaning up your acid and make it colourless. Won't work.
One little piece of dust and it will turn that colour. Live with it, it doesn't matter anyway.

cheeseboy

  • Guest
Re: 30% H2SO4
« Reply #8 on: February 17, 2002, 08:55:00 PM »
Sulphuric acid is almost like an oily liquid, how do they make it?

May The Source Bee With You....Always.

Elementary

  • Guest
Re: 30% H2SO4
« Reply #9 on: February 17, 2002, 09:10:00 PM »
Either by the "Contact Process" or the "Chamber Process"

The most concentrated commercial acid (97-98%) is made by heating the 93-95% acid in pans by a direct fire. The 98% acid does not attack cast iron, whilst 93-95% acid dissolves it. The acid is run in a thin stream on the surface of 98% acid boiling in a large cast-iron pot with a siphon ("Swan neck") from which the concentrated acid runs continuosly. The acid is more easily brought to the required strenth by adding oleum. (General & Inorganic Chemistry For University Students - J.R Partington 1954)

"Either bees love breathing in sulphuric acid fumes or else they are too lazy to have a "friend" pick them up a litre or two at the nearest supply house. Cheese never had a problem finding 95-98% H2SO4."

Maybe easy where you are, but where I am it will only be supplied to companies !

Some people would rather ruin a thread than answer the question !

PrimoPyro

  • Guest
Re: 30% H2SO4
« Reply #10 on: February 17, 2002, 09:10:00 PM »
If you mean "they" as in industry, then they make it by catalytic oxidation of sulfur dioxide to sulfur trioxide, followed by reaction with water.

2SO2 + O2 <---> 2SO3
SO3 + H2O ---> H2SO4

EDIT: Damnit, Elementary was faster.  :P

                                                  PrimoPyro

The Water Will Be Your Only Mirror

Elementary

  • Guest
Re: 30% H2SO4
« Reply #11 on: February 17, 2002, 11:31:00 PM »
For any nutty bees thinking of setting up a nano "Contact Process", I noticed the other day that Vanadium Pentoxide is available as a colouring oxide for potters !!!

(Vanadium Pentoxide is one of a choice of catalysts used for making SO3 from air and SO2)

Don't try this at home kids !!! (all theory)

Some people would rather ruin a thread than answer the question !

Flip

  • Guest
Re: 30% H2SO4
« Reply #12 on: February 18, 2002, 12:09:00 AM »
halfapint or anyone,


Having metal ions in your conc. sulfuric acid can give real problems in some reactions.




What kind of problems? Would this cause problems with hydrolisis using 15% h2so4(epoxide->mdp2p)?



Mountain_Girl

  • Guest
Re: 30% H2SO4
« Reply #13 on: February 18, 2002, 11:42:00 AM »
The question is do you really need 98% H2SO4 ?
If it is only required for something like drying gas, then such a high conc. may not be necessary. A useful thing about dilute H2SO4 is that if it is boiled, the vapor is almost entirely water up until it reaches about 170°C and only then does some H2SO4 start to appear in the vapor. At this point the conc. is about 75% H2SO4. Therefore it is not too difficult to remove a major portion of the water, rendering the acid sufficiently hygroscopic for some, if not most drying purposes. This strength may also be high enough for this acid to be used for some syntheses.
Also, a good method to estimate the strength of the acid is to measure its density. Someone has already posted a conc. vs density table here. It is easy info to find in any case.

Elementary

  • Guest
Re: 30% H2SO4
« Reply #14 on: February 18, 2002, 01:27:00 PM »
H2SO4%  Density@15°c

1       1.0061
5       1.0332
10      1.1045
20      1.1424
25      1.1816
30      1.2220
35      1.2636
40      1.3065
45      1.3514
50      1.3990
55      1.4494
60      1.5024
65      1.5578
70      1.6151
75      1.6740
80      1.7324
85      1.7841
90      1.8198
95      1.8388
97      1.8414
98      1.8411
99      1.8393
100     1.8384

Some people would rather ruin a thread than answer the question !

Archaeoptrix

  • Guest
Re: 30% H2SO4
« Reply #15 on: March 07, 2002, 09:16:00 PM »
Just wondering if this table is correct.
From 97% to 100% the density goes down.
Maybe H2SO4 density is like a h2o at 4 degC type thing?

circlesnort

Elementary

  • Guest
Re: 30% H2SO4
« Reply #16 on: March 07, 2002, 10:05:00 PM »
Maybe it was a typing error in the book ? I really don't know !!! (help bees)

If you look at Oleum in the book is gives this:

OLEUM

Free SO3%   Density

10          1.888
20          1.920
30          1.957
40          1.979
50          2.009
60          2.020
70          2.018
80          2.008
90          1.990
100         1.984


Umm, how interesting !!

MTM

  • Guest
Re: 30% H2SO4
« Reply #17 on: March 07, 2002, 10:24:00 PM »
According to BASF product specifications for sulfuric acid the table must be wrong:

Sulfuric acid content 95.5 - 98.5 wt.%
Density (20 °C) 1.835 g/cm3
 
Sulfuric acid content 99-101 wt.%
Density (20 °C) 1.840 g/cm3


Maybe H2SO4 density is like a h2o at 4 degC type thing?



As far as I know ONLY H2O has this density anomaly at 4 °C. Somebody correct me, in case that´s wrong, please.


M T M

Elementary

  • Guest
Re: 30% H2SO4
« Reply #18 on: March 07, 2002, 10:59:00 PM »
Your densities are measured at a higher temperature, so it is not conclusive.

Come on bees, get your chemistry books out !!

Umm, how interesting !!

MTM

  • Guest
Re: 30% H2SO4
« Reply #19 on: March 07, 2002, 11:06:00 PM »
The density of 100 % H2SO4 is HIGHER than the density of 96 % H2SO4 at 20 °C. At 15 °C it will be very likely the same. I´d really be very, very very surprised if H2SO4 had a density anomaly at 15 °C. But Elementary is right, get your chem. and phys. books out, bees.

M T M

Elementary

  • Guest
Re: 30% H2SO4
« Reply #20 on: March 07, 2002, 11:49:00 PM »
I agree with you, it does not seem logical for the density to go down as the concentration goes up at the end of the scale.

Unfortunately it is the only ref I can find, searching with webferret brought nothing up but single densities on datasheets that don't even state the temperature it was measured at.

I just find it strange that there is this oddity with the oleum densities as well. Maybe they had SO3 bubbles clinging the the hydrometer, the book was printed in 1954.



Umm, how interesting !!

Mountain_Girl

  • Guest
Re: 30% H2SO4
« Reply #21 on: March 08, 2002, 08:53:00 AM »
Unfortunately I can't explain why it happens (chemistry resembles voodoo sometimes) , but the density peak is for real.
Ullman's Encyc. of Ind. Chem. says:

'At constant temperature, the density of sulfuric acid increases steeply with rising H2SO4 concentration, reaching a maximum at about 98 %. From there up to a concentration of 100 % the density decreases slightly, but it rises again in the oleum range up to a concentration of ca. 60 % free SO3.'

Also I have table of densities at 20°C issued by a company which shows the same trend.

I neglected to mention in my previous post that using density as an indicator of composition is only useful up to about 95% H2SO4 for this reason. That is, if you measure a density of 1.838 say, then it could be either 100% or about 94% H2SO4 - you wouldn't know.

[That was nicely spotted Archaeoptrix.]

Elementary

  • Guest
Re: 30% H2SO4
« Reply #22 on: March 08, 2002, 09:06:00 PM »
Thanks for that Mountain_Girl !!  :)

Umm, how interesting !!