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Author Topic: Anyone know how to produce NaOH from salt water and electricity - or other means  (Read 6329 times)

Offline Tuprox

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Greetings,

I am in the process of researching various aspects of our industrial manufacturing and processing here in the US with hopes of maximizing our domestic energy resources and reserves while reaching the highest level of efficiencies by reclaiming heat from processes or use of other "waste" or unused sources of energy. 

I have come to examine the production of NaOH (specifically, I don't know how KOH is made).  It seems that a salt water solution is placed in a stainless steel tub and an annode is placed in the tube, electricity is applied and NaOH, CL2 and H2 are formed from the salt water.  I believe the balanced reaction looks somethign like this (take it easy on me it's been 17 years since my chem class in high school).
2H2O + 2NaCL  -> CL2 + H2 + 2NaOH   I'm guessing there will be some different charges on the resulting molecules but am not sure what they are or how to express them. 

Ok, so now that you know at what process I am considering for large scale NaOH production I have the following questions (Note, this is all theoretical for the paper/book which I am writing.  I am not planning on building a plant to do this or else I would hire someone who knows how this all works):
-Is there a specific type of salt that has to be used for this process? 
-Could sea water work for this?
-Would salt from the "Dead Sea" , mixed with river water work?
-How pure does the water have to be for this process?
-How pure does the salt have to be for this process?
-Would the salt from the Bonneville Salt Flats work?
-Would Salt water / Brine work from the Great Salt Lake?
-What % salinity should the salt water be?
-Does temperature of the salt water play any role in the electrolysis process?
-Is there a drying process needed after the NaOH is formed or any other process?
-What are the quantities of Chlorine gas and Hydrogen Gas produced in comparison to the quantities of NaOH.  Can these gases be easily seperated and collected?  What product could easily be made with Cl2 and H2?  I'm guessing that H2 could be burnt either in a tourch, engine, generator, fuel cell or other places. 

I guess I am basically in need of a description of the quality of the feed stocks, the quantities/ratios required, batch sizes (is continuous possible..  Etc.  I have read many Wiki pages on NaOH and it's production but it leaves much to be desired.  So, I'm humbling asking any of the brilliant people who visit this forum to hopefully shed some light on this process. 

If anyone has any questions about what I am doing here is my idea for publishing my research.  First of all I have always had a very deep interest in how industry works.  This could be anything from coal mining, oil pumping, aluminum manufacturing, steel production, home heating (anything with fire and combustion), any and all "green" energies or sustainable energies, geothermal, solar thermal, absorption cooling with heat, ground loop heat exchangers, on-site waste material conversion to fuel for inhouse heating/boiling/cooling etc, Biofuels, Green roofs for cities, synergistic energy practices, anaerobic digester, composting, humanure (municipal sludge & wood chips), sustainable ethanol/methanol production from cellulostic sources, Fuel Cells (HHO generators), BioDiesel, Green buildings such as rammed earth, straw bale, monolithic domes, organic farming, permaculture, etc. 

All the above, and more, are areas which I have been studying for 10+ years and have come to the conclusion that it would be great to pull much of the info together to show what is possible and how to structure your "setup" (house, business, land, etc) in the most efficient manner for synergistic effects for any and all of the above topics.   The NaOH production is going to be an example of how industry could produce a number of things from natural resources, like having a plant with electricity supplied from a geothermal source and the location is located with immediate access to vast amounts of salt and water and a major interstate and rail tracks.  So, finding out how to do this process will allow me to show what a plant COULD produce compared to what today's plants actually produce and the waste involved.


If anyone is interested in helping me with writing this publication/book I would love to have some technical assistance on some topics.  I am not published but I have a BSBA in MIS (Business Administration - Focus on Management Information Systems) and am an avid writer, tinkerer, builder and more.  I need people to help research and people who know how to put a book together.  Of course all credit will be given and I would be willing to share royalties or other form of payment should that happen.   I am also working on 2-3 other books which are very rough but have most research and writing already done.

Anyone interested can PM or email me at "book  at  tuprox   dot  cccoooommm"  obviously it is only com, but web spiders are too smart these days.


 

Offline Bill.D.Katt.

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I don't consider myself a brilliant person, and I am able to answer almost none of this. Here's the part I think I can answer though, The quantities of gas produced in comparison to NaOH is shown in your balanced equation, if you're considering volume you can probably use the 22.414 L/mol for a gas (this is an approximation for an ideal gas at STP). However, I'm not sure if it would yield H2, Cl2 and NaOH, or HCl (g), and NaOH. Cl2 is substantially heavier than H2, so it can probably be separated in that manner. If I am wrong, please someone correct me, just thinking out loud here.
 

Offline RD

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http://en.wikipedia.org/wiki/Brine#Electrolysis_of_Brine

http://en.wikipedia.org/wiki/Chlorine_production#Gas_extraction

The hydrogen produced would be explosive if mixed with air and ignited.

The chlorine gas produced is hazardous/lethal ... http://en.wikipedia.org/wiki/Poison_gas_in_World_War_I

NaOH a.k.a. "caustic soda" can cause chemical burns ... http://en.wikipedia.org/wiki/Caustic_soda#Safety
« Last Edit: 23/07/2010 01:58:17 by RD »
 

Offline Tuprox

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Thank you for the above replies as you have answered a good portion of my questions.

After reading the Wiki for Brine electolysis it seems clear that it is pretty standard for 3 products from the electrolysis of the brine solution.  This seems to be a pretty efficient means of production if you are in need of the three products. 

I am still curious about how pure the brine solutions must be for the process to work well.  Meaning if you were to take 1000 gallons of ocean water and evaporate it down to 60 gallons, this would raise the salt content from 3.5% in the 1000 gallons to about 56% but it would also concentrate the magnesium and sulfur to 2.1% and 1.44% respectively, along with .64% Potassium & Calcium and .11% Bromine as these elements are found in sea water.  Would these elements have an impact on the electrolysis?  I would think that these would make the resulting NaOH less pure to a degree.  Maybe the NaOH produced from sea water brine is a "technical grade" lye, used for applications such as drain cleaner or other such products where these impurites may not be as important, or maybe for the use of tanning leather or in paper mills.  IDK. 

Does anyone know if those impurities effect the resulting NaOH and if it does, by what degree or percentage? 

Thanks
 

Offline RD

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... it would also concentrate the magnesium and sulfur to 2.1% and 1.44% respectively, along with .64% Potassium & Calcium and .11% Bromine as these elements are found in sea water.  Would these elements have an impact on the electrolysis?

The potassium would form KOH, (similar reaction to to NaOH), the magnesium could be precipitated and filtered out ...

Quote
The Mg2+ cation  is the second most abundant cation in seawater (occurring at about 12% of the mass of sodium there), which makes seawater and sea-salt an attractive commercial source of Mg. To extract the magnesium, calcium hydroxide is added to seawater to form magnesium hydroxide precipitate.

    MgCl2 + Ca(OH)2 → Mg(OH)2 + CaCl2

Magnesium hydroxide (brucite) is insoluble in water so it can be filtered out
http://en.wikipedia.org/wiki/Magnesium#Occurrence
 

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