SelfInflicted
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Production of Sodium Hypochlorite %5.25
Hello.
I am a new member and not a trained/experienced chemist but I have been studying.
The price of Bleach in my area has been over $3USD per Gallon and I use about 2 to 3 gallons a week. So I thought set out to see how I could produce
my own via electrolysis.
I not sure but I am assuming that %5.25 sodium hypochlorite refers to available chlorine. Based on that assumption to produce one liter of bleach I
would require 86.5 grams of NaCl per liter of H2O to get 52.5 grams of chlorine.
I would assume that the process is not exact, meaning that not all the NaCl is going to be converted into NaClO. Some Cl will escape into the air and
would assume that excess salt would normally be in the commercial household bleach along with excess sodium hydroxide. I can not make a guess to
amount of excess NaCl the process would require but I would guess that an excess would improve the efficiency/time of the process.
Then there is the loss of hydrogen so would excess of water be needed or would the escape of Cl and H offset each other?
My test apparatus is a quart size canning jar , carbon electrodes from zinc carbon batteries and a DC bench power supply. I rather use graphite but I
do not have any at this time. Wires are wrapped around the carbon rods and sealed with wax to help prevent electrolysis of Cu.
69 grams ( ~ 7 teaspoons ) NaCl and water to make up 800ml in the vessel.
I have adjusted the power supply to 1 amp and measured ~ 11 volts at the electrodes.
I calculated 31.75 hours at this rate.
My calculations:
%5.25 of 800ml = 42g of Cl
69.2g NaCl = 42g Cl
42b Cl = 1.18 mole Cl
1.18 x 96485.46 = 114303 Coulombs
114303 Coulombs at 1 Amp = 31.75 hours.
1 amp at 11 volts = 11 watts
11 watts x 31.75 hours = .3492 kw/hours
I pay about $0.10usd per kw hour and $4usd for 18kg Nacl so 1 gallon of bleach should cost me about $0.20 usd plus water and electrode wear.
Are my assumptions and calculations correct?
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chief
National Hazard
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It seems your'e making chlorate: No diaphragma ... . My favourite question: How to easily turn chlorate-solution into hypochlorite-soluition (which is
really useful !)
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garage chemist
chemical wizard
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Commercial hypochlorite bleach is made by bubbling Cl2 gas into NaOH solution. It is important that a small excess of NaOH be left over in the
reaction, since NaOCl is only stable in strongly alkaline solution (the HOCl, present in equilibrium if too little NaOH is present, rapidly undergoes
disproportionation with hypochlorite to chlorate), and the solution kept cold thoughout the reaction.
Direct electrolysis of NaCl solution without diaphragma can produce a few tenths of percents of NaOCl in solution, but not more- chlorate production
is strongly favored at higher hypochlorite concentrations, by oxidation of OCl- at the anode.
So you need to find a cheap way to make Cl2 gas.
Check out the price of TCCA tabs and of HCl.
Making pure Cl2 from chlorate and HCl is possible, though.
Under normal conditions, combining solutions of the two produces mostly the explosive gas ClO2 together with some Cl2, but I recently found a
preparation in an old chemistry book where it is explained that if:
1. the HCl (24% w/w) is put in the gas generator flask and heated to 100°C
2. the NaClO3 solution is intruduced deep below the surface of the HCl by means of a dropping funnel with attached long inlet tube
and 3. the HCl always kept in excess and not depleted below 5-6% at the end of the NaClO3 addition,
the evolving gas is pure chlorine, free of ClO2.
The high temperature, good contact of ClO2 with the hot HCl and excess of HCl ensure that any ClO2 initially produced further reacts with HCl to Cl2
and the reaction
6 HCl + NaClO3 ---> NaCl + 3 Cl2 + 3 H2O
can be used for chlorine generation.
If wanted, I can give the reference for this (an old german book from google books).
BTW, to save yourself the cost of NaOH for your bleach, you can simply use chlorine water for bleaching, it works just as well. It just has to be
prepared fresh.
[Edited on 28-12-2008 by garage chemist]
[Edited on 28-12-2008 by garage chemist]
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SelfInflicted
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So what you are saying that after a certain percentage of Chlorite is formed then chlorate is produced. I read somewhere that chlorate was produced in
excess of 40 C.
So then a two stage process would be use a divided cell to produce sodium hydroxide and free chlorine. Then on the next run bubble the Cl into the
last batch of NaOH and so forth. ?
From http://en.wikipedia.org/wiki/Sodium_hypochlorite
qoute ---
Sodium chlorate (NaClO3) may be prepared by absorbing chlorine gas in hot and concentrated sodium hydroxide solution:
3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O
Whereas, sodium hypochlorite NaOCl and sodium chloride NaCl is formed when chlorine is passed into cold and dilute sodium hydroxide solution. It is
prepared industrially by electrolysis minimal separation between the anode and the cathode. The solution must be kept below 40 °C (by cooling coils)
to prevent the formation of sodium chlorate.
Sodium hydroxide and chlorine are commercially produced by the chloralkali process, and there is no need to isolate them to prepare sodium
hypochlorite.
--- end wiki
This would be describing producing sodium hypochlorite in an undivided cell.
By the way, my test cell appears to be producing bleach. The solution is slippery indicating sodium hydroxide and has the smell of diluted bleach. The
anode is eroding as expected with carbon settling to the bottom.
Now I am wondering how can one test for and differentiate between NaClO NaClO2 NaClO3.
[Edited on 28-12-2008 by SelfInflicted]
Last night the temperature of the solution reached 38.5 C. I cooled the solution with 2 ice cubes and lowered the current to .5 amps.
This morning my anode was almost completly gone. I think I got about 18 hours total electrolysis time.
The project is on standby until my graphite electrodes arrive.
I just ordered 6 12"x 4" x 1" graphite pieces from ebay for $2.50usd each.
[Edited on 28-12-2008 by SelfInflicted]
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SelfInflicted
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I drilled an tapped my graphite anodes and mounted them to the lid of a 5 gallon paint bucket.
I also mounted a small computer fan to the lid and drilled a hole on the opposite side
to expel gasses.
I was reading the "Thoughts on Anodes" thread here http://www.sciencemadness.org/talk/viewthread.php?tid=5050&a... and found dann2's post about PH controlled cells and the graph he posted showing
Distrbution of Cl2 in electrolysis of 1M Chloride solution.
Now if the production of ClO is 100% at a ph of 10 and greater in 1M solution why wouldn't it be similar in other strength solutions. So I tought I
should adjust the ph to 10 before attemping to make bleach again.
I added 15g NaOH to my softened water in my bucket and I tought Na2CO3 should buffer the ph so I added 15g Na2CO3 ( this could be a mistake ).
Then I dissolved the NaCl and made up water the the 4.5gallon mark 17 Liters.
The ph measured just over 10.
The garage is -1C and after 20 hours the cell temp is 5C at about 2.75 amps.
The cell is runing at about 4.42 volts and the fan is wired direct to the cell and runs slow which is just enough to keep the gasses diluted.
At 100% eff. the cell should run just under 5 days. after 2-3 days I should check the concentration and make time adjustment.
I don't understand why the temp has to be under low except to keep decomposition down and I should not be able to form ClO3 at such a high PH. unless
the secondary anodic chlorate formation occurs at the anode but my graphte anode is not cathylitic, or is it?
The cost for energy salt and lye is 0.325usd for 17L at 50% effeciency it jumps up to a whopping 0.47usd.
[Edited on 1-8-2009 by SelfInflicted]
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