August 8, 2004

        This was my big experimental day with vacuum distillation and it was quite the learning experience.  First off was distillation of drain cleaner, the dye and such apparent in drain cleaner can be removed by distillation but the temperatures involved usually prohibit this course of action, so I figured I would give it a try.  Roughly 100 ml black drain cleaner was poured into a 250 ml Erlenmeyer flask and this was in turn sat into a metal pan to help diffuse the heat from a range type heating element.  The flask was attached to a full 24/40 distillation apparatus with condenser, vacuum adaptor, etc. with the exit gasses being run through sodium hydroxide/calcium chloride before running into the vacuum pump which was salvaged from an air conditioner.  

        I later learned that using flat bottom flasks like the Erlenmeyer shown above is a big no-no in a vacuum setup but I didn't know it at the time, also I learned that using boiling stones under a vacuum really doesn't do anything, another thing I later learned.  Regardless, vacuum was applied and heating was begun.  Immediately the NaOH and the CaCl2 in the trap reacted with on another heating up greatly in the process and making a gunk that partially blocked the vacuum.

        I ended up with a small amount of distillate, but usually just white fumes like shown above came over.  The pump was inconsistent and occasionally lead to flash boiling, and whenever water that condensed in the neck of the flask dripped back it resulted in terrible bumping that threatened to break the flask.  The temperature at the still head remained low throughout (~60C) but when I was done and measured the temperature of the liquid it was above 180C.  The thick H2SO4 constantly jumped and bumped and scared the crap out of me, the boiling stones floated to the top and bubbled so they did something but they were for the most part ineffective.  Also I had to turn off the vacuum pump which started to die, but I continued heating while it was off, when I turned it back on flash boiling drew the H2SO4 through the whole setup and filled everything with the befouled H2SO4 so I started over, I ended up with a small distillate of clear H2SO4 of unknown purity.

        A more constant pump and magnetic stirring would have done wonders to make this experiment pay off.  A round bottomed flask would have decreased my worries as well and for the trap next time I would run the gasses through calcium oxide to take out water and acid gasses before it hits the pump.

        After the little excursion with the H2SO4 I decided to try vacuum distilling some nitric acid from a mixture of H2SO4 with NaNO3.  ~50% H2SO4 about 150 ml was added to a 500 ml round bottom and 70 g NaNO3 was also added. The mixture was heated without stirring under maximum vacuum and product started coming over readily without apparent NO2 evolution from decomposition.  A constant temperature at the still head of 58C was observed and the bath temperature was 82C although it constantly rose.  I obtained in a short time nearly 50 ml of HNO3 in the receiving flask, it did not react as vigorously as my 72% HNO3 but it reacted with copper producing NO2 in a sealed container so it was somewhat concentrated.  The azeotrope should have come over but I think I heated too quickly and simply drove off the HNO3 as it was formed.  In the end there was a cake of NaNO3/Na2SO4 in the bottom of the flask, magnetic stirring would have helped this reaction but the boiling was much more manageable then with my attempt at distilling H2SO4 above.

        One of my many methods of bromine production.  The Erlenmeyer flask contained H2O2/NaBr and the sepretory funnel contained concentrated sulfuric acid.  The flask was under magnetic stirring.  As the sulfuric acid was added the following reaction took place:

H2O2(l) + 2NaBr(aq) + H2SO4(l) ---> Br2(g) + 2H2O(l) + Na2SO4(aq)

        This picture was taken after the addition of a small amount of the H2SO4 resulting in a red solution.  A picture of the distillation further along is available on the main page.  The heat from the dissolution of the sulfuric acid and from the reaction itself was enough to drive off the bromine as vapor, the water running through the condenser had to be ice cooled to condense most of the bromine and the receiving flask had to be kept in ice.  The scrubbing bottle on the end was filled with Na2CO3, however this only reacted with a small portion of the bromine that was escaping, I had to add another bottle after it where the bromine was bubbled through a NaOH solution, this is the best choice to scrub away bromine vapors, they were gone before they hit the surface.  Yield by this method approached 60% however bromine was lost through the lack of ability to condense it and by reaction with H2SO4 to produce HBr.  I will probably try this again in the winter when I have lots of snow laying around to keep things cool.

August 15, 2004

        One of my more grandiose experiments, a somewhat large Castner cell.  The pan shown was cast iron, my experiments showed cast iron was attacked by NaOH somewhat slowly.  In the bottom of the pan I drilled a hole and inserted a length of pipe into it.  In the middle of this pipe was a nickel electrode, held in place by pouring molten NaOH into it and allowing it to cool.  I drilled a hole in the bottom of the range hotplate shown here so the electrode went through the bottom of that and the cable could be connected from the bottom.  The nickel bell shown hanging above it was to collect the sodium underneath it.  The anode is to the right of the bell, hanging within the wood cover.

        The cell itself was filled with 2 kg of NaOH and heated initially covered with a propane torch until there was a small pool of molten NaOH at the bottom.  From there the pan was lowered into its hole in the hot plate and high heat applied.  The anode was lowered into the molten NaOH at the bottom and electrolysis commenced.  It took over an hour for everything in the middle to become molten and the coating on the pan turned the hydroxide red.  Hydrogen started becoming a problem so I got a torch and positioned it right above the bell that dipped into the solution that the hydrogen was coming up from, hereafter it was burned and occasionally flashed back into the bell popping the lid off.  The underside of the lid became heavily charred but whenever I checked for sodium I found none.  I moved off the top of the lid and a massive fire resulted, the bell was too low and sodium had been formed somewhere and burned vigorously.  

        This cell was a failure, it was too large and took too much energy to remain molten, it was a definite safety hazard, that became especially apparent when it started raining and drops of water would fall into it and explode, and the electrodes were too far apart, the current density was too low to allow sodium production at any rate close to reasonable.  Keep it small.

August 22, 2004

        Taking what I learned from the previous Castner cell version I made this one which was significantly smaller.  The electrodes both ran up from the bottom and right above the electrodes the cell was divided with a sheet of nickel to keep the product side separate from the reactant side.  It was just a simple reducing adaptor with a brushing screwed into the bottom and a plug screwed into that.  The electrodes were set before hand by drilling holes in the plug and inserting them, cementing them in place with epoxy which actually held up, however in later reaction when more surface area of the epoxy was exposed to the molten NaOH a massive reaction occurred which greatly endangered me.  The cathode entered the cell slightly less then the anode to allow for greater current density at it which should increase the sodium production.

        Molten NaOH,  a small volume of the cell was first poured in on its own to allow electrolysis to begin, but the electrodes were too close and small explosions propelled the NaOH form between the electrodes where it solidified on the sides and prevented electrolysis.  More molten NaOH was added and after a few tries sustained electrolysis was obtained.  However it could hardly keep what I had in there, roughly 1/2 the volume molten, hence my second attempt with this cell later and my third attempt.  Some sodium was produced though, I scooped it out with a nickel wire, this cell seemed to show some promise, modifications for the next one, further separation of the electrodes and insulation would have been a good idea.

Current Comments

4 comments so far (post your own)

Where can I buy NaBr or other bromides? I will like to make some bromine too!

Posted by ... on Saturday, 10.8.05 @ 09:59am | #24

You can buy them for use in the pool and spa. Sodium bromide can be bought as such from some places for use in the spa, additionally organo-bromine compounds are widely avalible for the bromination of spas and jacuzzi's and such, just keep an eye out.

Posted by BromicAcid on Monday, 10.10.05 @ 20:20pm | #26

Have you tried using hydrochloric acid to generate the bromine instead of sulphuric acid. Maybe this would keep most bromine from escaping.

Posted by chochu3 on Wednesday, 12.28.05 @ 08:34am | #27

Yeah, I've used hydrochloric acid, the reaction is slightly more manageable, but since I was distilling simultaneouslly with production of the bromine I didn't see a need to use HCl as the H2SO4 allowed for the reaction to heat on its own. Also the H2SO4 helped to tie up some water, distilled bromine contains about 2% water, not an azeotrope, just something that carries over, although I could just have easily shaken the obtained bromine with conc. H2SO4 afterward.

Posted by BromicAcid on Thursday, 12.29.05 @ 20:20pm | #28

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