Chloralkali Process Safety: Can I Bubble Chlorine?

[The P-manator]

How dangerous really is the chloralkali process? I know chlorine is formed, but can I bubble it into a tube or something?

 

[Cesium]

Electrolyzing salt water? Its harmless if your amperage is low. With a 9-volt battery or something like that, you'll get very little product, but you'll be able to see bubbles form at the electrodes and smell the chlorine after a while. If you use something more powerful like a car battery, it would be wise to do it outside.

If your aim is the hydroxide, you'll want the anode at the surface of the cell so that little chlorine dissolves. If you want the (per)chlorate, you should try to keep the chlorine contained.

 

[The P-manator]

I'm trying to get the hydroxide. How do I keep the chlorine from reacting with the NaOH? When I was researching I saw that you can put a Nafion membrane to keep the two products separated.

 

[Cesium]

I'm not exactly sure how you would make a membrane using a home setup. If you only allow the anode to touch the surface of the salt water, then most of the chlorine produced will go into the atmosphere. I would suspend the electrode horizontally just above the level of the water. Also, high temperatures favor the formation of chlorate. Room temperature is probably ok for hydroxide.

Note: You can also make sodium hydroxide the old-fashion way with calcium hydroxide (slaked lime) and sodium carbonate (washing soda).

 

[The P-manator]

Yeah, I know, but I thought the electrolysis sounded kinda cool.

How does the Anode do anything if its not touching the water?

 

[Hootenanny]

How does the Anode do anything if its not touching the water?

It doesn't, for electrolysis to work both the anode and cathode must be in contact with the electrolyte.

 

[mrjeffy321]

In order for the electrolysis to work, both electrodes need to be in contact with the electrolyte.

I think what Cesium meant was that you should position the electrode so that it is just barely touching the water, so that very little of the electrolde material is submerged. By doing this, any Cl2 bubbles which form, form very near the surface and do not have much of an opportunity to dissolve in the water, they reach the surface and [hopefully] blow away. By contrast, if you submerged all of the electrode, the bubbles of Chlorine gas formed would need to travel all the way up through the solution in order to get to the surface, all the time, a little bit of Chlorine goes into solution.

However, with most[/all] electrode materials, current density is very important, especially on the anode.
Some materials (graphite is a great example) will erode away when used as an anode in an electrolytic cell. In order to slow this erosion process, it is a good idea to keep the "current density" (the current per unit surface area) as low as possible. By only submerging the end of the electrode, you are forcing a very high current denisty and the electrode will likely erode away much quicker than if you were to submerge the entire length.
This process of anode erosion becomes particular important when dealing with cells which need to be run for long periods of time (Chlorate cells) and/or when it becomes a hassel to replace electrodes.

 

[Cesium]

What mrjeffy clarified is what I meant. I suggested lying the anode horizontally (assuming it is rod-shaped) on top of the solution so that the current density would be lower.

 

[The P-manator]

So it is parralell to the water. I get it. I'll see when I have time. I need to get everything first, and the new MP3 player I bought has left me with 30 bucks.