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Nasty oil ? Transformer oil in dummy loads

Some time ago I needed to use a dummy load, while talking to one of my fellow radio operator he both reminded me of the existance of PCBs (polychloro biphenyls) and he showed me a leaking dummy load in the bottom of a bucket. I looked into the bucket at the “paint tin” load which had an oily coating and at the golden brown liquid which was in the bucket. 


After we made a point of placing a warning label on the bucket, I sat back and thought about the question of “is the oil simple mineral oil or is it contaminated with polychlorobiphenyls ?”. For those of you who do not know, the polychloro biphenyls are another of those “wonder chemicals” from yesteryear which has been a great source of trouble to humanity. 

Before we go any further let us take the chance to look at the vile offender, it is important to bear in mind that no one substance is in PCB oil. The PCBs were always made in a process which formed a complex mixture. The most obvious method of making PCBs would be to treat biphenyl with chlorine and a lewis acid such as iron(III) chloride (do not try that at home, or even in the comfort of your highschool or university lab). The reaction would be an example of electrophilic aromatic substitution which is a reaction which I teach in my freshman organic chemistry lessons. 

The PCBs were used in power factor correction capacitors and in some transformers. One reason to use PCBs in transformers was to reduce the chance of a fire, the PCBs are non flammable. Sadly they are very toxic and then to make things even worse they can form hydrochloric acid if they are partly degraded. The acid then makes the transformer leak. While walking in a rural location I noticed the casing of an old oil filled transformer on the ground near an old substation. 


I discovered that the two liquid samples were less dense than water which instantly suggested that the liquids were not pure PCB liquid. 

While a normal person is unlikely to have access to GCMS I choose to run all three samples with a GCMS. I knew that gas chromatography was one method for detecting PCBs but as I knew that the average radio ham does not have a GC fitted with either a ECD, MS or even a FID I thought about the alternatives. But sadly I can not think of one which is as good as GC for detecting PCBs. I mixed my liquid samples with light petroleum and I examined them with thin layer chromatography, it was interesting that neither oil sample contained any substance which absorbs short wave ultraviolet light (circa 250 nm). As PCBs are aromatic they would absorb UV light this result coupled with the low density of the oils suggested to me that either PCBs were absent or only present at low concentrations. 

My next test was to use GCMS, I found that both oils were chemically similar and appeared to be hydrocarbons. The oils were complex mixtures of compounds. Was able to get a reasonable match to a tetraalkyl cyclohexane and an alkylated perhydro naphthalene. No peaks for chlorine containing compounds could be found, which suggested to me that PCBs were absent from the oil samples. 

I tried a sodium fusion test with the oil samples, like the synthesis of PCBs this is another thing which I would suggest that you do not try doing in the comfort of your home. Using a small bit of sodium I did the Lassaigne test for sulphur and halogens. When I treated a sample of the aqueous extract with nitric acid and silver nitrate I obtained a black solid which is a sign of sulphur, so I boiled a sample of the extracts with nitric acid to drive out any sulphur as hydrogen sulphide. This time the aqueous extracts from the transformer oil did not form any solid when treated with silver nitrate. However when I did the test with an aqueous solution made by digesting ortho-dichlorobenzene a nice white solid was formed. The sodium nitroprusside test on the extract suggested that a small amount of sulphur was present. This sulphur brings me onto the topic of another post which will be about the joy of hydrodesulfurization. 

The Beilstein test to me seems a very bad idea for most people to use as a method of testing for PCBs, this test involves heating copper wire with the unknown substance using a flame. In short with PCBs it seems like a close to perfect dioxin synthesis, as a result I quickly abandoned this test method as a screening test from my mind. But just in case you want to see what a positive Beilstein test looks like, I took a photo of what happens when you treat copper wire with hydrochloric acid and then place it in a propane / butane  flame. 


A simulated positive Beilstain test. Do not try doing this with transformer oil, chlorine containing weedkillers or other aromatic chlorine compounds. 

As I have access to fumehoods suitable for plutonium work (lamena flow hoods with two stages of HEPA filters) I choose to try the beilstein test with the oil samples and ortho-dichlorobenzene. No green colour was seen for either oil sample, while the dichlorobenzene did cause the copper from the wire to become volatile. With the dichlorobenzene treated copper wire was heated in the flame the flame became green in colour proving that the beilstein test is valid. 

As all the tests I did on the oil samples suggested that chlorine compounds are absent I was glad to conclude that PCBs are either absent or are at very low concentrations in the oil.


One Response

  1. […] Nasty lubricator ? Transformer lubricator in dummy loads […]

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