Warning: Copper salts are toxic.
Sulfur dioxide is a toxic gas.
Sulfuric acid and hydrochloric acids are corrosive.
Wear gloves and work outside or in a fume hood.
Greetings fellow nerds.
In this video we're going to demonstrate yet another way to make sulfuric acid.
Our key ingredient this time is going to be copper chloride.
As usual i need to crush your expectations.
This is far more labor intensive and costly than just buying sulfuric acid directly.
In fact for the amount of work put into this you can probably get a better return
by getting a minimum wage job and then buying the acid with your earnings.
As usual our objective is to explore the science.
So let's get started wasting valuable hours of our life.
First we need a solution of copper (II) chloride.
I have about 150g in 400mL of water.
This was made in a previous video using copper metal and hydrochloric acid and used as a printed circuit board etchant.
Now the mixture for printed circuit board etchant tends to have a lot of excess hydrochloric acid.
It can still be used in this video but to help see the chemistry i distilled off the acid first and then added clean water back in.
I'll explain further why i did this as the video progresses.
Anyway, now we need a source of sulfur dioxide gas.
The most efficient way to make it is to burn sulfur and pump the sulfur dioxide gas into the reaction.
I'm going to instead use a sulfur dioxide generator that uses a solution of sodium metabisulfite and drips in hydrochloric acid.
This is overall a more expensive way of making sulfur dioxide but i'm using it because it's more convenient.
You can burn elemental sulfur instead.
Now we simply lead the gas into the solution of copper (II) chloride with vigorous stirring.
I placed the tube slightly above the surface of the solution to prevent backflow.
Anyway, Copper (II) chloride is an oxidant and reacts with the sulfur dioxide to form a mixture of sulfuric acid, hydrochloric acid, and copper (I) chloride.
The copper (I) chloride precipitates out as this white powder you see suspended in the solution.
Now the reason why i removed the excess hydrochloric acid from the copper chloride solution earlier
is because in concentrated solutions of hydrochloric acid the copper (I) chloride actually redissolves again
as it complexes with hydrochloric acid.
There is little visual indication of the reaction progressing.
While there is some color change the solution is too dark to notice.
At this point you might be wondering if other copper salts will work.
Copper bromide works but the resulting hydrobromic acid will reduce the sulfuric acid in the later steps.
Copper iodide doesn't form stable copper (II) salts so that can't be used.
Copper sulfate by itself doesn't react in this way so you have to have add halide ions for this to work.
Overall copper chloride is the best copper salt for this process.
Although you may substitute it with a mixture of copper sulfate
and a molar equivalent of hydrochloric acid since it'll form copper chloride in solution.
Anyway back to our reaction.
Now we can't add unlimited amounts of sulfur dioxide.
The copper (II) chloride can only absorb a half molar equivalent before it's depleted.
At this point we can separate our sulfuric acid
but we can instead regenerate our solution by changing our gas tube and this time bubbling in air.
The oxygen in the air slowly reoxidizes the copper (I) chloride into copper (II) chloride.
It helps to heat up the solution to between 60 and 90 celsius.
As the reaction progresses the copper (I) chloride will dissolve and the solution will become homogenous.
Unfortunately this oxidation step seems to be the achilles heel of this process.
It's incredibly slow.
I needed to bubble air for a full day before it all dissolved.
This makes the process very impractical for actual amateur synthesis of sulfuric acid
unless you start with kilograms of copper chloride and are very patient.
The main advantage of this process is that it's fully catalytic.
Once you regenerate the copper chloride solution you can bubble in additional sulfur dioxide to make more sulfuric acid.
Afterward you can repeat the cycle with more air.
Eventually though there will be so much sulfuric acid that it interferes with the absorption of gases and slows down the process.
I ran about 3 cycles before i decided i had enough.
For the last cycle don't regenerate the copper chloride.
Instead, let it precipitate and cool to room temperature.
Then filter the mixture to remove as much of the copper (I) chloride as possible.
This another reason why i removed the excess hydrochloric acid at the beginning.
If the copper (I) chloride remained dissolved it would make our sulfuric acid recovery much harder.
Now we have a solution of sulfuric acid, hydrochloric acid and small amounts of copper salts.
To separate our sulfuric acid distill off the remaining hydrochloric acid
and boil down with the maximum hotplate temperature until nothing distills over.
With the hydrochloric acid completely removed the sulfuric acid solution will precipitate out copper sulfate
and copper chloride salts that have very low solubility in high concentrations of sulfuric acid.
Now filter our sulfuric acid to remove the nearly insoluble copper chloride and copper sulfate salts.
And there we have it, sulfuric acid made by the copper chloride process.
It's slightly blue due to some to some minor copper contamination.
If you want you can distill the sulfuric acid using the high temperature heating mantle i showed an earlier video
to get pure concentrated sulfuric acid.
As for the copper salts and the bulk copper chloride from earlier,
now that we have removed the sulfuric acid we can regenerate it again.
Copper (I) chloride will oxidize on air somewhat so don't be surprised when it changes from white to a green, blue or even brown color.
Anyway, mix all the copper residues in a flask.
The copper sulfate in the distillation residue will feed forward to help make more sulfuric acid in the next run
so you don't need to worry about it building up.
Anyway, now once you've gathered all your copper chloride, add the hydrochloric acid that was distilled earlier.
You may need to top up extra water as the sulfuric acid carries away a small amount in its formation.
Now bubble air through the mixture to regenerate the copper (II) chloride.
Once it's dissolved, you are now ready to reuse the copper chloride to make more sulfuric acid.
Overall, the process does work and is catalytic.
The only consumed reactants are sulfur dioxide, water and air,
and the output is sulfuric acid, with everything else being recycled back in.
The catalyst, copper chloride, is very easy to make.
And as long as you're careful the process is much safer
and less toxic than some of my other processes like the electrobromine process.
In the end though i only got about 96 grams of sulfuric acid out of the three cycles i ran.
I'm not sure it's worth it for the labor involved.
The slowest part, the air oxidation, really hampers the utility of this process.
In theory you could bubble in air while simultaneously bubbling in sulfur dioxide for a continuous process.
But since the air oxidation is so slow you'll still be waiting long periods of time.
Now i know some of you would suggest using hydrogen peroxide.
I actually already showed in a previous video that hydrogen peroxide can oxidize sulfur dioxide and produce sulfuric acid directly.
No need for copper chloride catalyst in that case.
The drawback of hydrogen peroxide of course is that it's more expensive than air.
Nonetheless, there may be improvements to the copper chloride process with different concentrations of reactants,
hydrochloric acid and different temperatures.
I'll leave the optimizations up to anyone that wants to explore this process.
I have enough sulfuric acid as is.
So that is how you make sulfuric acid by the catalytic copper chloride process.
Thanks for watching.
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