Sodium and Potassium chlorate synthesis, the complete guide

Transcription

1 Sodium and Potassium chlorate synthesis, the complete guide Made by Plante1999 It is know that chlorates can be easily made. Much of the chlorate made by individual are used in pyrotechnic, but this thread will be mostly intended to use the chlorate as a general oxidizer in the laboratory. It is also know that there is many way to make chlorates, this document will be about electrolytic manufacture but other procedure are described as well. Warning! Chlorates are toxic to all life form and persistent in the environment use ''thermal'' disposition for chlorate. Never mix chlorate with sulphur and/or sulphide, such mixture can set off without apparent reason. Do not mix with ammonium compound, Ammonium chlorate could be formed and this compound is an explosive. Reference for everything in the text is on demand in contact my tab of this website. General use of the chlorate in the laboratory In the laboratory chlorate can be used as a general dry oxidizer, some of its property make it reassemble to a mixture of hydroxide and nitrate which is very useful to dissolve some transition metal element and bring them to high oxidation state. An example could be dichromate production using chlorate and chromium trioxide. 2KClO3 + Cr2O3 -) K2Cr2O7 + Cl2 + O2 Such reaction cannot be used to make permanganate since manganese dioxide decompose it, the second use of chlorate which is making oxygen in quantity without an oxygen gas cylinder, Manganese dioxide catalyze the decomposition of chlorate to make chloride and oxygen, this decomposition start at very low temperature and as such an alcohol burner give enough heat to make the reaction going. 2KClO3 -(MnO2)-) 2KCl + 3O2 The last general use is for pyrotechnics, I m not familiar with this use but It could be used as an oxidizer but usually perchlorate is preferred for safety reason. OTC chemical based synthesis. Sodium hypochlorite and calcium hypochlorite are very OTC and sold as disinfecting agent. There disproportion affords chlorate and chloride. Boiling 10% sodium hypochlorite in a glass vessel to decompose the hypochlorite and boil off water will make a concentred solution of sodium chlorate and

2 sodium chloride, adding saturated potassium chloride solution to it will add potassium ion which will separate out with the chlorate ion producing solid potassium chlorate by metathesis reaction.. Passing chlorine gas made from OTC calcium hypochlorite and hydrochloric acid in a boiling solution of potassium carbonate will make potassium chlorate and potassium chloride by chlorine disproportion, subsequent recrystallization will afford potassium chlorate. 3NaClO -) 2NaCl + NaClO3 3Cl2 + 3K2CO3 -) KClO3 + 5KCl + 3CO2 Electrochemical synthesis: The last common synthesis of chlorates is by electrochemical synthesis starting from a chloride salt. The mechanism of the reaction is not perfectly understood but the general idea is that chlorine form at the anode and dissolves in the water of the solution to make hypochlorous acid and hydrochloric acid in equilibrium. At the cathode hydrogen is formed which make OH- making alkali metal hydroxide. When the dissolved chlorine react with the hydroxide it form back alkali metal chloride plus alkali metal hypochlorite, as already know the hypochlorite disproportion in hot water to afford chloride and chlorate, The chloride Is re-oxidized at the anode to make chlorine gas and the cycle continue making more and more chlorate. This cycle is favored by a slightly acidic PH and hot temperature in the cell electrolyte. When the cell run small amount of chlorine escape making slowly the solution basic and stabilise at around PH 10 which is a lot less efficient since in acidic/neutral PH the hypochlorite disproportion in chlorate and chloride but in basic condition this hardly happen and only anode oxidation take place. This is hard to the anode and take 9 electron in place of the 6 in acidic PH. Cl2 + H2O -) HClO + HCl HClO + KOH -) KClO + H2O 3KClO -) 2KCl + KClO3 Do all synthesis outside! Chemical synthesis1: Reagents: Sodium hydroxide, NaOH Potassium hydroxide, KOH Calcium hypochlorite 70%, Ca(OCl)2 (Chlorine chock for pool) Hydrochloric acid 31%, HCl 31% (Muriatic acid, hardware store) can be substituted by Sodium chloride and sodium hydrogen sulphate, NaHSO4 (Pool Ph -)

3 Distilled water Material: PVC tubing ¼ inch Flask with a stopper with one hole (for the PVC tubing) 250ml beaker Funnel Filter paper Method to keep the solution in the beaker at degree Celsius Equation: KOH + 5NaOH + 3Cl2 -) 5NaCl + KClO3 + 3H2O Experimental: Dissolve 16g of potassium hydroxide and 44g of sodium hydroxide in 70 ml of distilled water. Fill the flask with 85g of calcium hypochlorite, secure the PVC tube in the stopper hole. Bring the hydroxide solution to 70 to 90 degree Celsius and depose the outlet of the tube in the solution, add 200g of hydrochloric acid to the flask in small increment and close it each time with the stopper. Chlorine gas will be produced in the flask and will react with the hot alkaline solution to make Chlorate and chloride anion. After a few minutes all the calcium hypochlorite will have reacted to make chlorine gas and the reaction will be considered as completed. Cool to 0 degree Celsius. On cooling Chlorate anion will condense with the potassium cation to make crystals of potassium chlorate. Filter the solution to get the crystals and Dry the potassium chlorate on a glass or polypropylene sheet. If the intended purpose is pyrotechnics there is no need for recrystallization. Purification is done by recrystallization with three times the weight of the crystals of distilled water. Yield: 14-15g

4 Chemical synthesis2: Reagents: Sodium hypochlorite 10-12%, NaOCl (liquid chlorine for pool) Potassium chloride, KCl (No salt substitute) Distilled water Material: 2x500ml beaker Funnel Filter paper Method to boil the solution which will be in one of the beaker Equation: 3NaOCl -) 2NaCl + NaClO3 NaClO3 + KCl -) KClO3 + NaCl Experimental: 250g of 10-12% sodium hypochlorite solution is boiled to 1/9 of its starting volume and cooled. Dissolve 9g of potassium chloride in the minimum amount of cold distilled water. Filter the boiled sodium hypochlorite solution in the potassium chloride solution. Cool to 0 degree Celsius and filter the crystalline precipitate. Purify using the same method as the first chemical synthesis. Small scale electrochemical synthesis: Reagents: Saturated sodium chloride, NaCl solution (can be found as salt) Saturated potassium chloride solution, KCl (can be found as no salt substitute) Optional: Sodium or potassium (di)chromate (cannot be found OTC)

5 Material: Anode: Carbon or graphite rod are the best since they are easy to find and cheap, you can get some at your local hardware store in the lantern battery, tutorial can be found on internet. They can also be found as gouging rod in a welder shop. These anodes will erode and it is recommended to use dichromate additive. Carbon was the industrial choice before MMO (DSA) anode was invented. Cathode: Carbon will do the job very well and is cheap. If you can easily find titanium rod this is even better than carbon but it will need to be cleaned after each run to remove titanium dioxide crust. In industry iron is used but the solution need to have 7g/L of sodium dichromate which is carcinogenic, also iron which is not in solution will need to be protected with rubber, epoxy will do the job for some time but it will eventually flake of. Iron have a great advantage, it is very common and cheap. You might have heard of stainless steel but from my own experimentation normal grade stainless steel will not do a better job than iron but will cost much more. If iron ore stainless steel is used without dichromate a suspension of iron hydroxide will form making necessary to filter your solution before precipitating your chlorate. Cell body (container): A glass beaker will do a great job but if PH control is not used the beaker will be corroded. If PH control is not one of your priorities use a polypropylene container (recycling number 5). 100ml volume minimum per amp for overheating protection. Power supply: You need a 3.3 to 6 volt power supply which can deliver at least 1ampere. This can be found in electronic store. Funnel Filter paper Running/processing: First you need to know the maximum amperage your anode can take. For graphite/carbon this is ampere per square centimeter. Don t pass more amperage than you r anode can take or it will shred into pieces. 3.3 volt is the best to protect erosion at your anode but up to 6volt is manageable. Put the positive wire on the anode and the negative on the cathode. Fill you Cell body with the sodium chloride solution and turn the power supply on. Keep your cell solution below 40 degree Celsius, if it go to high place the cell in a water bath. Adding (di)chromates will increase your yield very much, in this type of cell it is highly recommended, from 0.25 to 7g per L is a right proportion the yield goes up as the (di)chromate concentration goes up. PH control is also highly recommendable to protect anode erosion. To make PH control simply add 31% HCl in your cell solution time to time. It is much more easy to add the right amount of HCl using dichromate additive, when the solution turn yellow add HCl30% until the

6 solution turn orange, repeat this every time the solution turn yellow. Dichromate also serve as a PH buffer, When the PH is basic it will decompose to chromate increasing the acidity and when the PH is acid the chromate will turn into dichromate removing excess acidity (Equation will be added in V 1.1). To calculate how much time it will need to electrolyse do this equation, The %100 represent the efficiency of your cell so for an amateur cell 35% is considered normal. The saltm is the number of mole of salt in your cell electrolyte (For a rough idea use 0.5mole. per 100ml solution). Amp is the amperage that goes in your cell. Time(H)= ((171.6/amp)x saltm)x %100 This will give you the number of hour you need to lets The chloride convert in chlorate, Do not forget PH control if you use it. After this run time filter the solution and add the same molar equivalent of potassium chloride in the form of saturated solution. Cool the mixed solution to O degree Celsius and filter the crystalline potassium chlorate precipitate. Purify it using the same procedure as the chemical synthesis 1. Add few ml of methanol to your mixed solution if you were using (di)chromate additive and add metabisulphite to reduce chlorate, then poor it down the drain. Larger scale electrochemical synthesis: Material: Anode: If you are planning to make chlorate on a larger scale buying an MMO anode sheet on ebay is a very good idea. It won t erode and will stop working after thousands of hour. They can run at 80 degree Celsius nd at 0.200ampere per scare centimeter. Cathode: The same as small scale electrosynthesis Cell body (container): Same as small scale electrosynthesis. Power supply: Same as small scale electrosynthesis Running/processing: Very similar as the small scale synthesis but because of the MMO the cell solution is keep very hot (70-80 degree Celsius) and you can directly run with saturated potassium chloride solution and purify the precipitate (which will form in the cell) to get potassium chlorate. This type of production gives also the

7 chance to make sodium chlorate. When the cell is runned at 80 degree Celsius it will evaporation a lot. For potassium chloride solution tap of is made with distilled water, but for sodium chloride the tap of is done with saturated sodium chloride solution, after a few days of running a precipitate will form. This is the sodium chlorate. Filter to get the sodium chlorate but do not purify. Do not use sodium chlorate for pyrotechnics, use sodium chlorate for chemistry only. This is the version 1.0 and is only a part of the complete guide. Sources: Dan2 website (link does not work) Synthetic inorganic chemistry 5em, Blanchard 1937 Electrochemical process in chemical industry, Albert Regner