Sciencemadness Discussion Board

H2/O2 from electrolysis of water

wireshark - 21-1-2013 at 16:21

There are many catalytic hydrogenation procedures I would like to do in my garage. There are also numerous applications of oxygen (e.g., making ozone).

Although it's possible to buy tanks of hydrogen and oxygen, it seems pretty dangerous, inconvenient (I don't have a truck), and inaccessible (I'm not a welder and have no commercial use for these gases). I thought a convenient and accessible source would be electrolysis of tap water (more electrolytes). Something like a Hofman voltameter could be made to obtain pure gases; H2 from the cathode and O2 from the anode. So what about putting the hydrogen into a pressure vessel? Low throughput of gas shouldn't be a problem if there are absolutely no leaks. The movement of gas would of course require higher pressure in the output tube than the pressure vessel. Maybe one could substitute glass in the electrolysis device for heavy duty steel pipes coated with something inert?

Any advice at all would be appreciated.

[Edited on 22-1-2013 by wireshark]

[Edited on 22-1-2013 by wireshark]

99chemicals - 21-1-2013 at 18:00

It may be simpler to make the gasses separate.
H2O2 --> (2)H20 + O2
HCl + (Fe Al Zn Mg) --> H2 + metal chloride.

You would have to dry the gases but that would be required with any setup. If you have ground glass it would not be difficult to set up the generators and dryers.

Do you want to compress the gas or use it immediately? If your reactions are sensitive to nitrogen at all i would recommend a purer source then DIY gasses(Bleeding the system would be a bi*ch) You can buy O2 at home improvement stores in small bottles.

wireshark - 21-1-2013 at 18:21

I prefer the water electrolysis route over other reagents, if it is possible. Electricity is cheaper, and besides, I've wanted to do some electrochemistry.

You brought up compressing the gas. That I did not immediately consider. It would solve the pressurization problem in the electrolysis device, although introducing the need for a gas compressor and storage tank.

What do you mean by "bleeding the system"?

elementcollector1 - 21-1-2013 at 21:13

I assume "bleeding the system" means making the gas as absolutely dry and pure as it can be.

99chemicals - 22-1-2013 at 03:03

By bleeding the system I meant generating enough gas to "push" all of the air out of you gas generators.

Would you be using something like a Hoffman aperatus?
http://unitednuclear.com/index.php?main_page=product_info&am...

watson.fawkes - 22-1-2013 at 06:13

Quote: Originally posted by wireshark  
Although it's possible to buy tanks of hydrogen and oxygen, it seems pretty dangerous, inconvenient (I don't have a truck), and inaccessible (I'm not a welder and have no commercial use for these gases). [...] So what about putting the hydrogen into a pressure vessel?
So you want to substitute a pump capable of compressing hydrogen and expect that to be cheaper for you than commercial compressed gas? Please. And "pretty dangerous"? The whole reason there's a compressed gas industry is because the safety concerns have been long-ago satisfied, that is, as long as you don't do anything stupid.

Commercial gas suppliers should be considered as a form of specialized retail. Just walk in and bring money. You can easily buy 10 lb and 20 lb gas bottles. In fact, Harbor Freight is stocking 10 lb bottles in their retail stores nowadays. Since your gas supplier won't have such small bottles already pre-filled with hydrogen, you'll need to drop off your tank and come back in a few days after they've filled it. Oxygen is likely already in stock because of the number of small oxy-acetylene kits out there. Now you pay a lot more per unit mass for small bottles rather than large, but it's still cheaper that most other ways of getting equivalent amounts of gas.

One thing to know about hydrogen: It uses a different series of CGA (350) connectors than argon (580), CO2 (320), and oxygen (540). If you get an oxygen or argon tank retail, you'll need to swap out the main valve. You'll also need to swap out the inlet adapter on the tank regulator to match.

wireshark - 22-1-2013 at 15:02

Okay, I did some more research. The absolute easiest way to do tabletop hydrogenations is to first fill a balloon with hydrogen. React Al and NaOH in a flask with the balloon over it. First evacuate the flask somehow with an inert gas so you don't get oxygen contamination (haven't found an easy way to do this). Then take a clean, evacuated flask with your reactants + catalyst + magnetic stir bar and put the balloon over it. Set the temperature or other conditions according to the reduction you're doing.

I suppose you could just as easily use electrolysis to fill the balloon.

If I were doing a larger scale hydrogenation, I would buy cylinders of hydrogen (it's actually cheaper to buy cylinders than make it yourself with electrolysis because steam cracking of methane is dirt cheap), buy a Parr shaker or a big stirred reactor.

wireshark - 22-1-2013 at 15:22

Quote: Originally posted by watson.fawkes  

Commercial gas suppliers should be considered as a form of specialized retail. Just walk in and bring money. You can easily buy 10 lb and 20 lb gas bottles. In fact, Harbor Freight is stocking 10 lb bottles in their retail stores nowadays. Since your gas supplier won't have such small bottles already pre-filled with hydrogen, you'll need to drop off your tank and come back in a few days after they've filled it. Oxygen is likely already in stock because of the number of small oxy-acetylene kits out there. Now you pay a lot more per unit mass for small bottles rather than large, but it's still cheaper that most other ways of getting equivalent amounts of gas.


Is that so? Just anyone can buy hydrogen? If so, I'll look into doing this. Thanks.

watson.fawkes - 22-1-2013 at 19:45

Quote: Originally posted by wireshark  
Is that so? Just anyone can buy hydrogen? If so, I'll look into doing this.
It's not there's a permit or anything, not anywhere in the USA I've heard of. Remember, though, it's specialized retail, which means most of the customer know what they're doing there. Since you don't, give the folks there the opportunity to educate you. I find most people working in jobs like that are just ordinary blokes and respond well to respect, respect that they know what they are doing and that their advice is valuable to you. So exercise a bit of humility with them and let it carry you far.

The biggest issue will be availability. Not every place will have hydrogen available. Some that have it available won't have it on-site. If you're lucky enough to be close to a place with a hydrogen filling station, they may not be able to fill your tank immediately. Be accommodating. Call around first. Sellers that don't have it will likely be able to refer you to one that does.

There might be some unwarranted and unwanted attention if you're buying hydrogen gas for chemistry. Another application that bottle hydrogen gets used for is as fuel for an oxy-hydrogen torch, used in jewelry to work platinum and in glassblowing to work quartz.

wireshark - 26-1-2013 at 19:23

For anyone reading this, here's a gem I found on the topic of generating DIY hydrogen:

http://www.instructables.com/id/Hoffman-Apparatus-for-pure-h...

He says his apparatus can output 1L/minute, which is competitive with commercial electrolyzers that cost thousands of USD.

zed - 30-1-2013 at 19:58

Yup! Or, you could buy yourself a Hydrogen generator on Ebay. Sometimes a few hundred buck will do the trick.

At the University, they like to have the latest equipment. Sometimes, an infrequently used machine will be liquidated, to make way for a newer model.

Patience is required. Eventually, your dream machine will appear. Have some money on hand, and it will become yours.

Houngan - 18-2-2013 at 07:05

I found this a while ago and I'm considering making one myself.
http://www.dangerouslaboratories.org/h2_generator.doc

elementcollector1 - 17-3-2013 at 21:23

So, is hydrogen miscible with air? If not, wouldn't it float up to the top of any airtight chamber?

DraconicAcid - 17-3-2013 at 21:49

All gases are miscible with all other gases.