CaCl2 + H2SO4

Mixell: HSO₄ has a charge of -1. Ca(HSO₄₂.

The reason for using dry salts and conc. sulfuric acid is because it produces HCl gas, meaning it can be bubbled into water as hissingnoise and others have mentioned, free of sulfate or cationic impurities.

Quote: Originally posted by bbartlog

If your goal is to produce an aqueous *solution* of HCl, especially a dilute one as you initially indicated, then an insoluble salt as a product is obviously an advantage. Just make sure you don't try to produce an aqueous solution of 70% HCl or something.

Quote: Originally posted by bbartlog

If your goal is to produce moderately dry HCl *gas*, then what you want is a salt that will react fairly completely with concentrated H2SO4. In this context, the relative solubility of NaHSO4 is an asset because it allows new NaCl to be exposed to attack by H2SO4. CaCl2 is likely to become covered with CaSO4 before it finishes reacting, though I have to think that it could still be used (fine powder, heating, agitation and so on). If your goal is to produce an aqueous *solution* of HCl, especially a dilute one as you initially indicated, then an insoluble salt as a product is obviously an advantage. Just make sure you don't try to produce an aqueous solution of 70% HCl or something.

Quote: Originally posted by entropy51

Obviously you've never tried to filter CaSO4!

Quote: Originally posted by blogfast25

and never had any filtering problems, quite the contrary: it filters like a dream!

Quote: Originally posted by blogfast25

I also disagree somewhat where you wrote: ”You can't produce pure (or strong) HCl by this method.” Hmmm… much of the world’s hydrochloric acid sloshing around is still produced by heating conc. H2SO4 and NaCl in cast iron pans, hence the Fe contamination that’s still so common in ‘hardware store muriatic acid’.

Quote: Originally posted by madscientist

The reason for using dry salts and conc. sulfuric acid is because it produces HCl gas, meaning it can be bubbled into water as hissingnoise and others have mentioned, free of sulfate or cationic impurities.

Quote: Originally posted by blogfast25

Bbart, there’s no need to put asterisks around the words gas and solution. HCl gas really exists and it’s called hydrogen chloride, similarly HCl solutions are very real too and are called hydrochloric acid. [Edited on 24-1-2011 by blogfast25]

I'm sure he's using the asterisks to show he's talking about gas production, as opposed to using dilute acids and wet salts to have the gas captured in the original solution and present as hydrochloric, not to mock us.

If you're trying to produce the sulphate and don't want the hydrogen chloride around, bubbling it into water is one method. Add some base to encourage it to stay put.

Calcium Chloride will yield twice as much of the gas per unit of salt volume - which is useful if you don't have big flasks to hand as you shouldn't really be opening the generator mid work to refill it - it will stink, ruin the finish on every metallic fitting in the room, moisture will start running in and the gas stream is then contaminated with atmosphere; some of which may or may not be problem depending on what you're doing.

The three most common methods I know of to hydrogen chloride are table salt / calcium chloride + sulphuric and hydrochloric onto calcium chloride. Which you choose and how you do it depends largely on what you're doing with the resulting hydrogen chloride.

If the goal is making hydrochloric, that rules out the latter of the three, since you need hydrochloric to run it - but it can be used to purify shitty hydrochloric.

If it's making hydrochloric very easily with bits you'll readily find on the shelf, it's going to be sulphuric onto table salt, as you can pick up kilos of it at the cheapo stores like Aldi and Lidl for about 30p a bag and sulphuric is easier to find than surfactant free hydrochloric.

If you want clean hydrochloric, I'd go with bubbling the resulting gas into some distilled water.

The benefit of bubbling is that it will separate all the rest of the rubbish in your impure reagents out of the product; with a very high ratio of separation for next to no effort.

If you want a very well known gas stream, for anhydrous work and such, you'll want the hydrochloric onto calcium and to blow it through carbon or some more anhydrous salt; this way you know the acid in the generator is the same species as the gas you're producing and it doesn't have mist coming over with it.

You have to be careful assuming gas generators are truly anhydrous and pure if they're just a flask with a funnel and some tubing. I have watched reactions fail from what appears to be damp and / or acid coming over - probably as a result of the mechanical fizzing going on picking it up.

Calcium chloride generators using sulphuric do work when the salt is present as granules, but grinding it up will encourage it to go quicker. Going quickly is usually not the objective with gas generators. If anything, I find I want them running slower to be sure that the gas has a chance to be absorbed where it's going; not bubbling through it and out the exhaust.

You can bake NaCl generators to drive more hydrogen chloride out, but it's more mess to think about for what amounts to very little extra money. I'd also recommend you're careful when it comes to cleaning out calcium / sulphuric generators, as I've found big lumps of it that have been difficult to remove, and actually seen a flask pop when trying to rinse one out.

Because of this, I started looking into using plastics instead. From what I remember, HDPE isn't stunningly resistant to sulphuric according to the tables, yet I have bought sulphuric, many times, in HDPE bottles. Neither is it excellent against hydrogen chloride. But when a HDPE bottle costs less than a pound, and a boro flask costs tens of pounds, I don't really see it as a big problem if the plastic one goes in the bin after a while.

Theoretically, you should have 98% sulphuric and freshly baked salt to ensure you get the absolute maximum out of the generator, and none of it is left behind dissolved in the moisture present. In practice, the amount of effort and risk involved in redistilling sulphuric is no where near the cost of loosing a small amount of hydrogen chloride.

Incidentally, the cost for a lecture bottle of dry hydrogen chloride is over £100, and the Monel regulators / manifolds are £500->£2k for corrosive gases.

Generating the same amount using these methods costs about £5->10 from memory. So super duper efficiency isn't really essential when comparing it with the alternative.

You can buy dirty grade hydrogen chloride at about £140 for 5 kilos, but the damages you'll pay when 5kg of it goes wrong will swamp that with the first letter to the lawyer.

You also can't easily rent cylinders of the reactive gases as they can be used as chemical weapons.

To bubble gas a length of tubing will work. As hydrogen chloride has such a high solubility in water, if you're running the generator slowly, you may see few or no bubbles, as the gas dissolves into solution before escaping as a bubble.

[Edited on 24-1-2011 by peach]

Quote: Originally posted by peach

To bubble gas a length of tubing will work. As hydrogen chloride has such a high solubility in water, if you're running the generator slowly, you may see few or no bubbles, as the gas dissolves into solution before escaping as a bubble. [Edited on 24-1-2011 by peach]

Quote: Originally posted by blogfast25

... Hmmm… much of the world’s hydrochloric acid sloshing around is still produced by heating conc. H2SO4 and NaCl in cast iron pans, hence the Fe contamination that’s still so common in ‘hardware store muriatic acid’....

As far as making clean hydrochloric cheaply and easily goes, it's drain cleaning sulphuric onto table salt bubbled into distilled water.

Using a gas to water method (with a state change involved) avoids the possibility of insoluble products and soluble contaminants in the reagents getting through filter papers - you are effectively 'distilling' the acid.

Use CaCl2 if you can find it cheaply, since you'll get more gas per flask of salt you use. Bearing in mind CaCl2 will only give you twice as much, it can't cost much more than double a bag of NaCl or it's questionable whether or not it's worth it.

Job done!


[Edited on 25-1-2011 by peach]

Quote: Originally posted by peach

To bubble gas a length of tubing will work. As hydrogen chloride has such a high solubility in water, if you're running the generator slowly, you may see few or no bubbles, as the gas dissolves into solution before escaping as a bubble.

Hmmmm

Quote: Originally posted by not_important

I'd like to see references for that. From what I've read the main sources are byproduct HCl from chlorination of organics (which contains iron from attack on the pipes and so on), from burning H2 and Cl2 from electrolytic production of NaOH, from controlled incineration of chlorine-containing organic waste.

I don’t have any, not_important, I was merely going by the fact that nearly all HCl I’ve ever bought is yellow coloured (demonstably by Fe3+), I didn’t realise they carried on that tradition with by product HCl!

Quote: Originally posted by peach

You could try a silicone stopper instead, or painting silicone caulk over the whetted surface of the natural rubber. You could even bed PTFE tape over the silicone before it cures.

Quote: Originally posted by Arthur Dent

What would be the best tubing material for HCl gas and/or Cl ?

Teflon tubing is not only expensive, it is not easy to make connections with due to it being a rigid polymer, as opposed to an elastometer, and not particularly flexible by comparison. This problem is only made worse by the fact it won't thermoform (that is such a bitch!), so you can't easily melt connections together - as they do with the underground mains pipes in the road.

I have used fluoroelastomer tubing with HCl(g) before. When combined with halogenated solvents, it too can turn opaque, but the mechanical properties of the tubing don't change.

I have been playing around the last few days building a generator out of HDPE bottles, hydroponic fittings and, what I suspect to be neoprene, tubing - using concentrated sulphuric onto table salt.

Test number one was a failure in terms of getting clean hydrogen chloride out of it.

I drilled the holes for the little barbs dead on - they were 5.3mm in size according to the micrometer, so I chose a 5mm bit for a push fit. I then siliconed the barbs as they went in, to try and get a gas tight seal around them - letting it cure overnight.

All seemed to be going to plan, until fixing the tubing and filling it came to fruition. For a start, the silicon bond to the smooth caps on the bottles was not great. Trying to push on the, now fairly rigid, tubing (having been out in the garage at 4C) caused the seal on the top bottle to start peeling away as I wiggled it. I thought... oh well, it's probably still plugged well enough inside the hole. And, it didn't matter anyway, given what happened next.

On filling the top bottle with the sulphuric, the silicone seal utterly failed - within seconds it was peeling apart.

In addition to that, I was trying to think of an easy way to control the flow rate, and had tried bending the tubing over on it's self and clamping it with one of the free arms on the retort. Again, with the tubing being so dense and cold, it obviously hadn't cut it off anywhere near well enough, as the acid drained far too quickly into the salt. With the bottles being tall and thin, the salt foamed and went over into the water I was using to collect the gas.

Rather than simply hose the entire thing down and bin it, I am leaving it alone to finish, as it can still provide useful feedback on how compatible the other components are given that they're now exposed to the salt, concentrated acid and hydrogen chloride.

I seem to recall sauron saying PVC will ignite in the presence of hydrogen chloride. I'm not sure about that, as I've never seen it do it and the cole parmer resistance guide actually rates it A for compatibility - maybe that was a joke that passed me by. It rates it as A, excellent, for all sulphuric acid up to 75%, then D, severe, for anything above. As with everything science and engineering related - TEST IT YOURSELF

In terms of neoprene, again, a D for concentrated sulphuric. I've just been dipping a length of it (or what I assume to be a length of it) in sulphuric and not seen any problems. There is no data available for hydrogen chloride. I have used it with hydrogen chloride a number of times before and not seen any immediate problems - it did have a major problem when it was also in contact with DCM.

You can only buy into the resistance guides so much. They are VERY broadly speaking and heavily application dependant. For example, a piece of tubing that is constantly being flexed in an aeroplane's wings and that needs to last for a decade supplying fuel to the engines is much more of a problem than a piece that's going be exposed for a few hours, not manipulated and then rinsed - or possibly binned after ten or so goes doing an experiment in the garden. You will also note that every single resistance guide you find will say "These are approximations and our experiences, we assume no responsibility, check it yourself, lazy"

Whilst this attempt has entirely died on it's arse, I'm not all that bothered as there are things I can note about this that could lead to being able to do a lot better with another go. I also don't need the resulting gas or hydrochloric.

The goal was to see if the far harder to break and cheaper plastics could be used over glass. If a compatible setup is found, you could scale this up and run it in 1/ 2 / 5 / 25l HDPE containers. That would be useful for producing larger quantities of anhydrous salt or for drying such salts.

I need to have another look at the plastics once it's had time to sit out there and stew, I'll leave it overnight I expect.

But, the observations thus far!

1.) The HDPE doesn't seem to care. I have so many chemicals turn up in HDPE - including 34% hydrochloric and concentrated sulphuric. Before I check the bottles outside, I can be almost certain the HDPE will be fine, as it's fine when it turns up in bottles made of the same polymer. This in line with Cole Parmer's guide, listing even LDPE as fine for the sulphuric and hydrogen chloride.

2.) Crimping the tubing is not an excellent method of controlling it, unless you're using a fine control clamp, and one that's light enough it's not going to pull on the tubing

3.) Coloured drain acid is good because the HDPE is opaque, making the bright pink / red stand out well

4.) DO NOT bother with silicone anywhere that it will come into contact with the sulphuric. Silicone tubing will likely go the same way. I would go further and suggest you don't use it at all, as you'll probably end up with the acid on it at some point and then be wondering why the generator isn't working, but everything around you is rusting.

5.) Rather than crimping and clamping the tubing, one could use a PE or PP stop cock, as is used on garden watering system, wine siphons, jerry cans and so on

6.) Do away with barbs and use screw in fittings

7.) You could consider using either HDPE or Polypropylene tubing in place of PVC and neoprene, as both the formers are more resistant to what's happening. Like Teflon, however, they tend to be rigid. Unlike Teflon, they are thermoformable; you can melt connections together.

About as successful as my attempts to woo Kelly Brook by hiding in her garden every night

I removed the equalising tube and stuck that in the water as well, after realising this wasn't going to work and watching the salt bottle foam up. Even with that tube gone and the barb being a tight fit, there was sulphuric dripping out around the fitting on the top bottle where the silicone had previously been. You can see the acid on the green plastic bin it's sat on; look between the front right of the clamp stands base and the volumetric flask


The main offender - silicone, sliding off like an egg on a greased up frying pan


Does anyone remember the kid's TV show called "It'll never work". Well, that's never going to work. But the bottle and plastic barb don't seem to mind, or the (probably) neoprene tubing. The place I bought the tubing from didn't say what it was, but that spongy, shiny surface looks familiar


Crimping over the tubing didn't block the tubing off anywhere close to how well it should be. I don't think this is a stellar method, using any form of clamp, crimp, adjustable pliers and so on, as they tend to be for on / off control and struggle to do it finely; more so when the tubing is tough (they can get significantly more rigid with changes in the weather). It would be better with an actual stop cock there (check online garden / pet / fishy stores)


The silicone on the lower bottle is a liar. Because it wasn't subject to much movement and wasn't in direct contact with the sulphuric, it's pretending it'll be okay.


Even though the pile of salt in the bottom isn't taking up much room, you can see the water in the collection flask is pink, from it foaming. The foaming would be less of a problem if most of the acid hadn't drained through in a minute or two. I would also suggestion caution if you're going to have a go at doing this without any previous experience making the gases in glassware, and dealing with them, as something at these early stages of testing fittings could potentially clog and then pop - blowing the acid all over you and the inside of your house, along with releasing a decent quantity of hydrogen chloride. You certainly wouldn't want to start testing your ideas by generating ten moles of something very toxic or flammable - e.g. hydrogen sulphide, acetylene, monoxide, hydrogen cyanide...


Concluderoodo

I was quite pleased with it personally. I think there's potential there.

I'm sure I saw a plastic stop tap in the house that was PP.

Plumbing fittings are PEX and PB. PEX is cross linked HDPE. And you can also get pushfit PEX pipe. The only problem could be the rubber seals in them.

The only way to find out is to try breaking one.

Hmmmmm^2

---> Opens catalogues

[Edited on 27-1-2011 by peach]

Submitted to Barclays PLC for consideration of loan approval to Mr John

S2 = You'll want a hole in the top of the upper bottle to equalise the pressure between the two. Having a hole in both the top and bottom makes filling it with concentrated acid, not easy. Hence, a stop tap here to close it off when filling.

S1 = Start the acid flowing

T = Rather than drill yet more holes into the bottles, I'd prefer to keep all of the connections in the caps, with those being thick and rigid. There is only so much space on the caps, fewer holes means not only means fewer sealing problems on the bottles but more chance of being able to fit the fitting on there in the first place. I am, therefore, considering taking the gas off from the same connection that equalises the bottle pressures. Tubing to floating plastic fittings is usually a lot more durable than tubing to rigid plastic to wonky, thin plastic

G = I also considered not making any holes anywhere other than the caps, by having the pressure equalising tube go up through the top bottle cap. Problem! 1.) needs a double sided connection 2.) will 100% ruin your work if the connection comes loose inside or the tube gets sulphuric in it

W = An optional dry bottle. Would also serve to catch and mistakes if option G was used. However, even with W in place, if G failed, you would still have to refill the generator. Decisions, decisions!



Addendum

I am thinking it may be best to avoid using plastic plumbing fittings.

1.) They have rubber seals, as mentioned above - possibly not a problem
2.) The smallest bore they come in is 10mm, and the 10mm range doesn't usually have many components available for it. The next up is 15mm, which is starting to get big
3.) The pipe is so rigid it's annoying to bend. If the generator wasn't fixed rigidly together, any knock or misalignment would stress the connections to the bottles, and likely open them

Why not get that HDPE Kipp's Generator Mossydie linked to?

That is an AWESOME deal. The whole thing is HDPE and done for you.

However, it also has a fixed volume, and you will tend to be using dilute acids with one given the large volumes needed.

This method would allow you to use both concentrated acids - for maximum space saving - and very large containers, if you like it so phat it needs spelling with a p.

Given the massive solubility of hydrogen chloride in water, using water in the generator is likely going to reduce the yield by a decent amount. I thought I was being Ghetto by not suggesting people redistill the acid to 98% and then bake their salt in the oven.

Quote: Originally posted by peach

A better option is to forget the glues and either melt the plastics together or use screw together fittings with sealing washers.

The hot method is perfect in terms of keeping the number of materials down. I was hoping to find a 'squeeze it out the tube' solution for others to repeat, but I'd be perfectly willing to try melting it. I wonder how a hot glue gun likes having HDPE rods stuffed into it.

In terms of the mixing, when you generated it, could you actually see white salt left in the generator?

Quote: Originally posted by peach

The hot method is perfect in terms of keeping the number of materials down. I was hoping to find a 'squeeze it out the tube' solution for others to repeat, but I'd be perfectly willing to try melting it. I wonder how a hot glue gun likes having HDPE rods stuffed into it. In terms of the mixing, when you generated it, could you actually see white salt left in the generator?

Attempt, two

This time I'll be using some PVC tubing and these little HDPE taps


Leaving a sample of the tubing in some concentrated sulphuric overnight


The tubing was tan / brown / amber by the morning, and would later go opaque when rinsed. However, the tubing has not become brittle to my hands


Neither has it's wall thickness changed by any sizeable quantity. I decided to try PVC since it's so easily available and transparent, so I can see what's going on as I test this


This is the last generator, which has been sat outside since I posted the pictures of it above. You can see unreacted salt, despite there being an excess of sulphuric. Likely as a result of so much of the acid ending up outside the bottles. There are still faint fumes licking out of the opening. I tried to photograph them, but they weren't playing


The resulting cake, not budging after three rinses with cold water and me squeezing the bottle. It is from a NaCl generator. The cake did later break up when I filled the bottle with some hot tap water and gave it another squeeze


Mmmmmmm, cake


Washing the first generator out, I see no signs of wear and tear on the bottles, tubing, cap liners or fittings


I'm going to try melting the fittings into place with a hot pin first, practising on the first generators caps and fittings. I have been using arc and gas welders since I was 13 or 14, and soldering things since before my teens. But plastic ain't metal


The first attempt, I only did the edges of the fitting and it broke away with little effort. I then put more effort into blending the fitting into the base material of the cap and got a better result


I purposefully set about trying to snap the fittings, to see how well they'd bonded 8^o


The hot pin method wasn't exactly great, so I tried the soldering iron and hey presto, it works beautifully. Despite having zero temperature control and costing about £3. I've stuck a bit of copper wire in the end but later switched it to an old tip instead. This is a 40w iron. The temperature is just high enough to get the plastic flowing, not high enough to instantly cut through it and not high enough to easily burn it


The third ever intentional plastic weld I've made in my life


Bingo! The fitting has snapped before the bond. Mission complete!


The finished bit of tubing. I decided to have the equalising tube come up through the cap and a bit of tubing inside the bottle because I wasn't at all happy with the bond it was making onto the base of the top bottle. I was worried a lot of sulphuric would end up in the equalising tube as I turned the top bottle upside down to drain, and so put a tap on there. I found this worked perfectly well, there was no sign of acid in the gas line once the bottle was flipped


Not pretty, but not presently the point


I've removed the cap liners so I could melt the fittings and caps together on the inside as well. Which means I will need to wrap the threads in PTFE. Good job I remembered that seconds before turning the bottle upside down.


Everything is looking good! Been for dinner, no leaks!


The taps are controlling the acid brilliantly. It's held it at that position for the fifteen or twenty minutes I've been away


Oooooooo! Close, but not yet! Everything is fine, but it looks like that tap had a rubber seal in it, which is now toast. I've again set the generator outside and, once it's calmed down, I'll snap open that tap and have a look. Again, I should point out, the rest of the fittings are absolutely sound. The only leak is from the seat of the tap it's self. The tubing isn't going to fall off those connections easily, it's ID is about 2mm smaller than the barbs and I had to force it on after a dunk in boiling water


[Edited on 31-1-2011 by peach]

Quote: Originally posted by blogfast25

Hmmm… much of the world’s hydrochloric acid sloshing around is still produced by heating conc. H2SO4 and NaCl in cast iron pans, hence the Fe contamination that’s still so common in ‘hardware store muriatic acid’.

Someone else has asked about the taps as well, for an entirely different purpose to what they're being put to here.

They're Hozelocks, the micro-irrigation things you find at B&Q in the garden section. They're £4 or so for two. But they are very nice when they're not full of acid, they open and close very smoothly and, even in the example above, they provided a positive on and off, and fine control in between. You can find them cheaper on eBay, no name brands, where they're about £1.50 but, by the time you pay the pound or more of postage, it's the same price and you may as well get the Hozelocks at B&Q. Unless you're doing the entire garden as well.

You may also run into Gardena brand micro taps in the shops.

I have thought about using a Hoffmann clamp yes. I wanted to try the little taps because I thought they'd give better control, particularly if the tubing is cold, which makes it quite a lot more rigid. As is clearly evident, even though they're designed to work on about 15psi for the garden irrigation from memory, these rubber sealed taps are not suitable around strong acids; and not just a bit, but entirely.

I also thought about using glass taps, but thought I'd try the plastic ones first as they're cheaper and easier to come by and, provided they don't melt, not so brittle.

I have seen plastic taps that don't use washers, as you'd find them on lab glass, but finding them is a bit more effort - which is why I haven't tried it again yet (I'll need to find some). If all else fails, I will use glass ones yes.

The second tap is there because I needed to make the connection to the top bottle (to equalise the pressure) through the cap, as melting the plastic of the walls and bases doesn't work very well at all - it's too flexible. Because of that, the equalising tube has to be dunked into the acid as the cap gets screwed back on. I was worried that a decent amount of acid would then run straight into the lower bottle (through the equalising tube) as I turned the top one upside down. That extra tap there prevents that.

What is likely to happen if you forget to open it is that pressure will build up in the bottom bottle, and then stop any more acid coming down. Provided the bottom bottle is open to the experiment, pressure shouldn't build up in the top bottle; a vacuum will, which will also prevent more acid coming down. But you are right, you'd be best making sure it was open before starting.

The WORST thing to do would be to put a tap on the exit of the generator. That would allow the acid to come down to the salt, and it'd sealed, so pressure would most certainly build up; in both bottles.

Here are two things I thought might also interest you;

Chemglass, and others, make addition funnels with a tap on the equalising arm for isolating the sample from the atmosphere in the glass at specific points in the work. You imagine the fun that involves if you forget to open or close one at the right time!


QuickFit, and others, make these variants on the Hoffman clamps which feature a little roller on steps, so tubing can be proportionally clamped off. I'm sure you can find these from RC model stores cheaper than QuickFit will sell you one for.


[Edited on 6-2-2011 by peach]

Does the bubbles still disappear before leaving the catcher water when it is already nearing 37%?
HCl might be useful for:

precipitation of the common ion> for example bubbling through FeCl3 until it precipitates out as a solid

replenishing dissolving baths.

Halp

This way you can accomplish usefulness of the compost other that trying to creat a 90% solution out of it


[Edited on 3-26-2012 by Poppy]

I remember the source

Quote: Originally posted by elementcollector1

Another method (cannot remember source, think it's on YouTube) is to take the impure stuff from the hardware store, and place it in a sort of dessicator-box setup, with distilled water in another beaker. Then you'll have a pure solution of half the concentration of HCl.

Quote: Originally posted by soma

Came across this after doing a search on google. If anyone has access to the Journal of Chemical Education (A Convenient Way to Generate Hydrogen Chloride in the Freshman Lab, Francisco J. Arnáiz, Journal of Chemical Education, 1995, 72 (16), 1139.) I'd appreciate a copy of the article. http://curlyarrow.blogspot.com/2009/03/how-to-make-dry-hcl-g... How to make dry HCl gas