A day in the life of an Industrial Chemist – The AVGAS Affair

By Professor David Trimm.

Living with science is never dull and working with the applications of science can be quite exciting. Let me tell you of a funny thing that happened to me in February and you can perhaps begin to understand how all that information in the HSC syllabus can sometimes be useful!

I was quietly sitting in my office on a Friday waiting to go home when the phone rang – and I was up to me knees in alligators. It was Mick Toller, chairman of the Civil Aviation Safety Authority asking if I could help with a problem they were having with Avgas –aviation gasoline. Like an idiot I said yes – and next thing I knew I was in the middle of it.

Why me? I had been involved with all kinds of petroleum processing for a very long time. This is the process where crude oil is taken from the ground and converted into useful products. You will do some of this in your syllabus, but it is just worth outlining the basics.

The advertisement is right when it states that oils aint oils. They can be a variety of mixtures, ranging from black gunk you have to dig out with a shovel to sweet crudes that you can almost put straight in your car. These different raw materials are converted to something more useful in a refinery. There are about seven in Australia and they are all fairly small by world standards – but they do the job.

The basic processes are distillation and catalytic processing. Various boiling point fractions are separated from the crude, the amounts of which really depending on where the crude came from. Australian crude is light and makes lots of gasoline. The biggest reserves are in the Middle East and they are heavier – and make lots of diesel. Each fraction is useful for a different purpose, but there is never enough for the really popular products – like petrol. So other fractions have to be converted to make more of what people want.

A LINE DIAGRAM OF A REFINERY AND POSSIBLY A PICTURE

The biggest catalytic process in the world is called catalytic cracking. It breaks down heavier molecules into fragments, and one of the desired fragments is gasoline. The process is catalysed by a solid acid material called a zeolite and it is very unselective. Depending on operating conditions and on thermodynamics we can get a whole range of products varying from carbon to light olefins. However branched chain molecules and gasoline can be produced. This is great, because the efficiency of a gasoline is judged in terms of octane – either research octane number of motor octane number. It is the former (RON) that you usually see at the service station and the engine of a car is designed to work best with a given RON. Octane is improved by either branched chain molecules or aromatic molecules – remember the fuss over toluene in the fuel? Like Popeye, too much spinach and octane aint good for you!

Even so there is usually not enough octane even for gasoline, so some special processes were developed to improve octane. Engines in small planes are a particular problem because they need extra high octane – it is the way they are designed. Some of this octane is obtained by adding tetra ethyl lead to the fuel – a good octane improver. Some is generated by a process called alkylation.

One of the excellent octane additives is a class of compounds called alkyl aromatics. They consist of a benzene ring with one or more side chains attached. These could be methyl – toluene, xylene etc - or ethyl – but this is less likely because ethyl benzene is too useful to burn. So, in order to increase octane ,a process called alkylation is used to make these kinds of compounds. It is an acid catalysed process somewhat similar to cracking but carried out at different conditions. Since one is turning two molecules into one higher pressures help and since one is not breaking bonds one does not need as high temperature.

The reaction is welcome in a refinery because the profit margin is higher. We all tend to think of the cost of petrol as being very high – it really is not. The price of the gasoline that you buy is about 17 cents/litre. The rest is tax or service station running cost. And the processing of the petrol costs about 2 to 4 cents a litre of this 17 cents. So there is not much margin and refiners have been suffering for the last few years. When you can make more interest with a bank than a refinery, you know you are in trouble! So any product that can be made with a higher profit margin is very welcome.

There are several alkylation processes available, but one refiner (MOBIL) was using a process based on sulphuric acid catalyst. It is a process used all over the world but – in Australia – only with MOBIL The reactants are passed over the catalyst and the products washed with alkali and water. Any residual traces of acid are taken out with the addition of very small amounts of a strong base called ethylene diamine.

That tells you something about the process but not much about why they picked me. I was born in the UK and had worked in catalysis and petroleum for about 15 years. Like you, I used to think that the School syllabus stunk, but I was lucky enough to have a great chemistry teacher who made me think of something else but footie and girls. After a degree and a PhD I worked at Imperial College and then went to Norway as a Professor of Petrochemistry when the North Sea opened up. Imagine my surprise when I discovered that Norway was not covered in beautiful blondes, that it was very cold indeed and that income tax was 85% on the top dollar! So I came to civilisation in 1979 and have never regretted it since!

While in Europe and since coming to Australia I had kept in touch with what was going on in the oil world – both here and in places like the Middle East. So Mick Toller thought I could be useful in understanding what was going on. Certainly the process had been working and certainly it was definitely off the rails.

It was late in November 1999 that something went wrong. Nobody is saying too much because of potential legal problems, but it is rumoured that there was trouble with the pump adding caustic, and extra ethylene diamine was added to take care of the acidity. I do not know if this is true, but certainly extra diamine got into the fuel. Not a lot – of the order of 50ppm and the Avgas met all the required standards.

What are these? Australia has standards but not too many for fuel. Gasoline and diesel are well described. Everything else is referenced to the American Standards (ASTM) – a normal practice all over the world. Refiners make sure they meet these standards – or they are really in the poo. So the Avgas with the extra diamine met all standards. I would have been surprised if it had not.

What was happening demanded a knowledge of inorganic chemistry – another focus of your syllabus. The ethylene diamine was forming a complex with brass in the fuel delivery system and both attacking the

FORMULA OF CuEN COMPLEX

brass and blocking brass filters. Why was the brass there? People who fly airplanes do not like fire, and brass is used because it minimises sparking. How did the brass react? Through formation of the complex with the copper component of the brass. What was the net result? Attack on brass which – in items like bellows and springs – can be very unwelcome and build up of deposits whıch can block fılters. One of the first filters blocked with a learner pilot who managed to land the plane. It took two hours to clean the filter and six hours to clean the cockpit!

The problem was then that not all planes had been refuelled with contaminated fuel, so how do you know which ones have? That is where I came in.

MOBIL had acted very responsibly and had flown a team in from the States to sort things out. They came up with a test that worked – but nobody really trusted them after the first error and it was my job to check the test. I suspected that everything was fine – MOBIL were certainly not going to do anything counter productive, but I was asked to be suspicious and that is what I did.

The first problem was to find out how much diamine was in the fuel, and that is not easy when there is two-fifths of nothing there! An outfit called PROBE had developed a test based on Nuclear Magnetic Resonance (NMR) – an expensive technique, but one that is very sensitive for these kinds of amines. After a struggle we found that we could detect down to less than 1ppm if it was there. So at least we knew how much was in a solution and now we had to find out how much the test could detect. Why not use NMR anyway? Two reasons. The main one was that planes were grounded all over the bush and there was no way of getting an NMR machine to the planes. Secondly, the technique is good but it sure is not cheap!

On to the test. It is based on a spot test using an indicator called fluorescamine. What one does is to add water to an aircraft tank and shake it all about. Easier than you think – these are hardly Jumbos. You then extract the water and make a couple of dots on a filter paper. A solution of fluorescamine is then used to make a combined dot with one of the previous dots and to make a third dot. One then waits for everything to dry and shines a UV light at the dots. If the mixed dot flouresces you have amines.

Sounds easy does it not? But you do not know the half of it. The first problem was that the water had to be in a certain pH range. Easy – use bottled water. Would you believe that the pH of the same brand of bottled water can change significantly? I did not dare to ask whether this was due to a sheep standing up stream! So we had to worry about pH control. The second problem was the filter paper. Would you believe that different kinds of porous paper do show the presence of amines after a while? Something to do with their processing but a pain in the rear end! So we had to specify the brand! Needless to say, if someone left some cleaning fluid containing ammonia, you were in real trouble!

Then of course the efficiency of extraction of diamine from fuel by the water had to be checked. Not very efficient – and certainly less than you would expect from the material you have studied – but good enough.

A main problem was where to find a dark place on an aerodrome to look at the fluorescence. Thank God nobody recorded five men and a fluorescent light disappearing into a ladies lavatory!! I would never have lived it down!

Well, finally I was about to OK the test, when someone mentioned a white gooey material. MOBIL had identified a substance called carbamate which was produced from reacting amine with carbon dioxide. It was white. It was gooey. The only thing it turned out not to be was the white material in the fuel tanks. So the poo hit the fan.

A major problem was that nobody was flying, so how could we get a sample? I made the mistake of referring to it as seagull poo – did I get my leg pulled. But nobody could find a sample. If you leave Avgas in the sun the lead salts will decompose and a white/pale yellow deposit of lead oxide is formed. We got lots of that but it was not the right stuff. To be honest we still do not know exactly what the material is, but we believe it is a mix of aluminium oxides and hydroxides .They may be formed through old age and moisture in the tanks. They may be formed because there are some bugs that can live in Avgas and slowly chomp the fuel tank. Everyone to their taste – me I prefer BurgerKing!

As a result we are keeping a gentle eye on things and making sure planes get washed and no more white junk appears. Some planes are passing. Some planes are failing and it has been suggested the test is too sensitive. Perhaps it is, but I am grateful that it is every time I fly in those beautiful little planes.

When I was your age I had no idea what I wanted to do for a living and my Dad suggested a chemist. He meant a pharmacist, but being more stupid than most I have finished up with a mix of Industrial Chemistry and Chemical Engineering. The best thing about the whole job is that it is fun. It does not pay as well as some but I have enjoyed my working life tremendously. Much of the syllabus that you are struggling with I thought I would never use. I was right – but I did not know which bits – and I still do not. I hope my tale of one particular adventure can help show all the bits and pieces of knowledge that you need to do something really to help the community and – incidentally – to have fun.