Constructed from pieces of PVC pipe, the chlorine generator was a simple electrolytic cell with gas collection capability. It consisted of two compartments, for the anolyte and catholyte separated by fibreglass matting. The volumes above the anolyte and catholyte were isolated to prevent mixing of the gases evolved at each electrode. All joints in direct contact with electrolyte were glued using PVC adhesive (PVC dissolved in MEK) whilst the temporary seals were made with hot glue. The gas collection tubes were made from cheap 6mm flexible vinyl hose, however they become rigid and cloudy on exposure to chlorine gas.
Components (shown on the table is the steel cathode)
Generator after a run ~5-10min
The jar later that evening (when the temperature had dropped to about 10*C)
The electrolyte used was saturated sodium chloride solution & the anolyte was slightly acidified before use. It was found that if the cell was operated for some time and then allowed to sit it would not longer produce any gas at the anode. I assume this to be due to a diffusion of OH- across the diaphragm raising the pH of the anolyte and thus allowing the formation of ClO3- in preference to Cl2 .
No erosion was noticed from the anode when the cell was operated continuously, however severe erosion of the cathode (iron) resulted when the cell was allowed to stand after a run. Corrosion of the iron in the electrolyte is most likely due to OCl- attack formed when the cell is operating. Restarting the cell after a run additionally saw some erosion of the anode, again probably due to the increased concentration of OCl- & OH-. This might be avoided by acidifying the anolyte before restarting.
The photos show the collection jar immediately after the production of the gas and the the same jar a few hours later. Over the time span shown the temperature dropped from the daytime ~22*C, to night ~10*C and clearly a significant amount of the gas dissolved in the some 2.5L of water. The colour of the water changed quite visibly from near colourless just after the run to a pale green a few hours later. I believe the undissolved gas in the picture to in fact be oxygen - as it only had a faint chlorine smell to it when the jar was overturned. The dissolved chorine may be easily recovered by heating the solution.
Now that you know how to build a chlorine generator, you might be wondering what to do with all that chlorine? I've included this scanned page from a book on the industrial uses of chlorine - it lists many interesting reactions:
As a side note, this generator was later tried as a chlorate cell - rigged to pass any chlorine generated at the anode thru the catholyte. The idea was to maintain a low pH in the anolyte in an attempt to prevent anode erosion, however it was found that the anode eroded just as fast - if not faster than before. The advantage of this arrangement, however was the gas output of the cell contained almost no chlorine, beneficial in a chlorate cell as the pH will thus be maintained.
Later the cell was emptied - the carbon anode replaced with a length of steel pipe and the electrolyte replaced with concentrated sodium hydroxide solution. It was then used quite satisfactorily as a hydrogen generator:
