Sciencemadness Discussion Board

Synthesis of Sodium Hydroxide (NaOH) via the Caustification Process

NotBismuth - 28-2-2019 at 00:43

From where I come from, NaOH is nearly impossible to come by. I did manage to find a chemical supplier that sells NaOH, but quite frankly SGD$45 (USD$33.40) for 1kg is too much for a kiddo like me. I 'd prefer this method over the chloralkali process as the Cl₂ produced could react with NaOH to form NaClO & NaClO₃. Also, this process would honestly not be too hard for an amateur as the precursors are easily obtained. Na₂CO₃ can be easily purchased as washing soda. CaCO₃ can be obtained by reacting Na₂CO₃ with CaCl₂ (from dessicants). CaCO₃ can then be heated to >850°C to decompose it to CaO before reacting with water to yield Ca(OH)₂. The reaction is given, Na₂CO₃ (s) + Ca(OH)₂ (aq)→ 2NaOH (aq) + CaCO₃ (s). This reaction works on the principle that CaCO₃ is much less soluble that Ca(OH)₂

However, if I were to work with saturated sols. of Ca(OH)₂, that would take me forever to get NaOH efficiently. Theoretically as CaCO₃ ppts out, there would be a decrease in concentration of Ca²⁺ ions, allowing for more Ca(OH)₂ to dissolve in sol.? (ie. could I get away with using an aqeuous suspension of Ca(OH)₂) However, Ca(OH)₂'s solubility drops drastically in highly basicity conditions.

I have included in the attachment, some files that are of relevance. However, I don't really understand what is written. Could someone explain it to me? And is there a simplified table/graph I could follow to know the exact proportions of reactants to use? Thanks! :¶

Attachment: [Open Chemistry] The solubility of Ca(OH)2 in extremely concentrated NaOH solutions at 25C.pdf (646kB)
This file has been downloaded 374 times

Attachment: US5219541.pdf (783kB)
This file has been downloaded 352 times

[Edited on 28-2-2019 by NotBismuth]

XeonTheMGPony - 28-2-2019 at 03:44

electrochemical method much simpler, get some mercury and make a small cell. there after all you need is salt and water, and every now and then new graphite for the Anodes

Ubya - 28-2-2019 at 06:21

you could start by already buying Ca(OH)2, slaked lime is sold in garden stores and in the costruction aisle of hardware stores. i bought a 5kg bag for 4 euros.
this way you have already concentrated mixtures and you need much less work. if you don't need very pure NaOH just follow the stechiometry, do your calculations, if you want to decide where to stop adding the solutions just by looking at the ph it's not going to be easy, they are all really basic compounds, and universal ph paper is not sensitive enough to give you a definitive answer.

[Edited on 28-2-2019 by Ubya]

NotBismuth - 28-2-2019 at 06:52

Quote: Originally posted by Ubya  
you could start by already buying Ca(OH)2, slaked lime is sold in garden stores and in the costruction aisle of hardware stores. i bought a 5kg bag for 4 euros.
this way you have already concentrated mixtures and you need much less work. if you don't need very pure NaOH just follow the stechiometry, do your calculations, if you want to decide where to stop adding the solutions just by looking at the ph it's not going to be easy, they are all really basic compounds, and universal ph paper is not sensitive enough to give you a definitive answer.

[Edited on 28-2-2019 by Ubya]


Would it would work if I use an aqueous suspension of Calcium Hydroxide? It may take about an hour but it works I'd definitely not mind the wait. In the video, James used a saturated solution which would mean a less concentrated solution, and quite frankly having to carry out the experiment a dozen times just to obtain an appreciable amount would not be practical, judging by the amount of water I'd need to evaporate off :}

https://youtu.be/evMUa_HsztI

[Edited on 28-2-2019 by NotBismuth]

[Edited on 28-2-2019 by NotBismuth]

NotBismuth - 28-2-2019 at 06:57

Quote: Originally posted by XeonTheMGPony  
electrochemical method much simpler, get some mercury and make a small cell. there after all you need is salt and water, and every now and then new graphite for the Anodes


Yep, I'm aware of that method. Just wondered if there were other possibly better alternatives. Worst case, I'd use the cell electrolysis connect by a salt bridge

https://youtu.be/RjlfG1n2N2U

Ubya - 28-2-2019 at 07:10

a suspension will work, NaOH is much more soluble than calcium hydroxyde.

NotBismuth - 28-2-2019 at 07:40

I see, I will try it out in about a few weeks time and let you know the results :]

Alkoholvergiftung - 1-3-2019 at 02:14

You can use the first industrial Methode. They made it with Ferrit.
Heat NaCO3 with Fe2O3 it forms Sodiumferrit.When you Hydrolyse it. You have NaOH and Fe2O3 again. Small descripction in german from an chinese side i think ^^.

Ferritisch-Methode. Es besteht aus zwei Hauptphasen: das erste Sintern unter hoher Temperatur Natriumcarbonat und Eisenoxid (III). Dies erzeugt Natrium Ferrit (NaFeO 2). In der zweiten Stufe wird dem Wasser ausgesetzt und zersetzt sich mit Eisen (Fe 2 O 3 * H 2 O) vermischt , Natriumhydroxid und Wasser zu bilden. Die sich ergebende Natronlauge wird aus Kristallen oder weiße Flocken zu verdampfende. Seine Reinheit betrug etwa 92%.

Alucard - 1-3-2019 at 02:27

The most simple method as I assume is to react Ca(OH)2 with Na2CO3, so :

Na2CO3 + Ca(OH)2 = CaCO3 + 2NaOH

I tried it and it worked, but Ca(OH)2 actually absorbs some CO2 while storing it, or maybe is sold such impure, because it's sold as technical grade chemical, but anyway, reaction above goes under aquaeous conditions and yields NaOH water solution which absorbs CO2 from air while a whole reaction between Ca(OH)2 and Na2CO3 occurs, so it usually yields NaOH contaminated with an Na2CO3 impurity. After all, a CaCO3 suspension also absorbs a lot of aquaeous NaOH so it leads to losses of NaOH while filtering it from CaCO3.

Because all of these chemicals are cheap enough in my country, I simply prefer to buy solid NaOH for 4 EUR per 1 kg, despite Ca(OH)2 costs 5 EUR per 25 kg bag, and baking soda is about 1 EUR per 1 kg.

Alkoholvergiftung - 2-3-2019 at 01:32

Caustification only works to an NaOH concentration of 10%. Because no CaOH desolves in higher concentrations. They used SrOH for higher concentrations so they dont Need to boil to much water away.