Science Interviews


Sun, 15th Jul 2007

Kitchen Science - Making Fuel from Vegetable Oil

Prof. Matthew Davidson, Prof. Gary Hallway & Chris Chuck, University of Bath

Listen Now    Download as mp3 Part 1,2 from the show Fuels of the Future

Azi - Hello, welcome to Kitchen Science. This week, I’ve come to the historic city of Bath and I’, actually standing at the university of Bath’s Chemistry Department, I’m joined by Professor [Matthew] Davidson and also Christopher Chuck who is a PhD student here. The question I’ve come to you guys with, and I’m really hoping you can help me out here, is can you run your car on cooking vegetable oil?

Matthew - That’s an interesting question as to whether you can run your car on vegetable oil, what’s chemically called a triglyceride, a molecule with three long fatty arms on it. What happens is they all just get entangled together, and that means it has a very high melting point. The two most important problems are; firstly the stuff would freeze in your tank, so on a slightly cold morning you would have a solid mess and the second problem is that it simply doesn’t burn very well.

Azi - Okay, so what’s the solution?

Matthew - Well the solution is actually quite a simple chemical process, and I can show you exactly how we do it. Before we do, I want you to put on some goggles, just to make sure we’re safe.

Azi - Okay, I’ve got my goggles on.

Matthew - Right, well what we’re going to do is were just going to take some vegetable oil that we bought at the supermarket, and we’re going to take this mixture here, which is methanol and sodium hydroxide. We’re just going to mix it with vegetable oil, you can see that the vegetable oil is stirring away with a stirrer in it, it’s heated up to about 60 or 70 degrees centigrade.

Azi - Okay, so you’ve got the vegetable oil in a flask, and you’re putting sodium hydroxide which is mixed with methanol, in the measuring cylinder and you’re going to tip it in…

Matthew - Yeah, we need to wait about half an hour and what we will see is the separate components; the biodiesel will separate out from the by-product which is called glycerol, which is the other part of the fatty molecule that we started off with.

Azi - So what’s the chemical process that is happening inside that flask?Making Bio Diesel at Bath University

Matthew - Well the chemical process is something called transesterification, which is a bit of a complicated term for simply just changing the end of the long fatty molecule. So instead of just having 3 of the fatty molecules attached to one end, a bit like a piano stool with three legs, we’re changing the end, just capping off the fatty molecule with methanol. That give us individual fatty molecules, and that’s what is actually called biodiesel, that we could use in an engine; and another molecule called glycerol, which is just a waste product of the biodiesel process.

Azi - Well that sounds incredibly straightforward to me, is this something that you could perhaps do to any old oil?

Matthew - Well, yes, it is straightforward, but of course nothing is quite that simple. I’m going to hand you over to Chris now; he’s going to show you why it can’t work on just any old vegetable oil.

Chris - Yeah, that’s right, you have to use absolutely pure, virgin vegetable oil. If you use waste oils, the kind of oils you’ve cooked your chips in and things, because you’ve heated it up to high temperatures with food in you might have bits of chips, bits of organic matter and water. But most importantly, you’ll have free fatty acids which are the acid versions of those ‘arms’ [or stool legs]. As soon as the sodium catalyst comes in contact with those free fatty acid arms, it just makes soap, and no biodiesel whatsoever.

Azi - And you can’t really run a car on soap, can you?

Chris - No, you can’t run your car on soap! There are at least three of four different purification steps that you have to do first to get your waste oil ready to make biodiesel from, which is very expensive to do.

Azi - Alright, well we’ve got half an hour to wait before our vegetable oil is turned into biodiesel, so we will be back later on in the programme to show you what happens! Back to you guys…


[Half an hour later…]


Azi - Hello welcome back to kitchen science, I’m still at the Chemistry department at the University of Bath, with Chris and Matt and we have biodiesel being made in the fume hood here. The vegetable oil looks really clear, and it’s swirling around in the little flask. Chris, what’s going on?

Chris - Well, the vegetable oil has completely changed to biodiesel. We’re just going to work that out by pouring it into a conical flask and pouring water on top. That water will take away the glycerol, take away an excess methanol, and just leave us with our biodiesel on top, like if you poured oil into water.

Azi - Ok, so you just poured it into the flask, and here goes some water.

Chris - So we can tap off the biodiesel from the top.

Azi - Oh, right, well we’ve got our biodiesel, we are now going to run over to the engineering department and test it out!


Azi - Okay, so we’re now navigating the depths of the engineering department, and we’re about to test our biofuel…

Gary - My name is a Gary Hallway, professor of auto-engineering here in the department of mechanical engineering at the University of Bath.

Azi - You’ve got this huge white van in this lab…

Gary - What we have here is a vehicle research laboratory.

Azi - We’ve brought some biodiesel with us, so what are we going to do now.

Gary - Well, what we have here is pure biodiesel, 100%, but unfortunately the motor manufacturers in Europe will only guarantee the vehicle if it’s got a B5 blend. That means 5% of the fuel will be biodiesel, and 95% will be ordinary forecourt diesel. So we’re going to run the biodiesel in a B5 blend through the vehicle and see how it reacts.


Gary - Right, we’re going to start the test now. What’s happening now is the driver is driving the vehicle on a rolling road, so the wheels are going round, but the vehicle is not going anywhere because it’s strapped down.

Azi - That looks like the car is running in the gym.

Gary - That’s exactly what it is, it’s just like if you were on a running machine in a gym, you run on a conveyor belt. On this particular case, we have a roller going round so the wheels are turning the roller and the roller is absorbing the load. We’re measuring emissions, that’s oxides of nitrogen, carbon monoxide, CO2and unburned hydrocarbons. All together we’re measuring somewhere in the region of about 50 independent signals from the vehicle. What we’ll do now is we’ll go up into the control room and we’ll be able to see real time comparing what’s happening with this B5 blend, and what we did previously when it was just 100% forecourt diesel.


Azi - Alright so we’re just off to the control room now… Loads of computers in this room. Alright, so what did we get?

Gary - Well the first thing I’m going to do is to look at the vehicle performance. We can see here on the screen that there are no adverse effects on performance from using the actual biodiesel blend. So the next thing we’re going to have a look at is the fuel consumption. We can see that the fuel consumption is about the same, there’s a little bit of discrepancy in favour of the 100% forecourt diesel, but then again if we now look at the emissions we can see that the engine does appear to be running cleaner. That’s because of the clean properties of the biodiesel itself due to the fact that it does contain an amount of oxygen which helps to improve the cleanliness of the burn in the combustion chamber. So all in all, we’ve got no adverse effects on performance, fuel consumption is about the same and the emissions are fractionally improved.

Azi - But there doesn’t seem to be much difference between them, so where is the advantage of using this 5% blend?

Gary - Well the biodiesel it’s self has come from a renewable source, so you could actually say that, taking everything into account, the cultivation of the plants, turning the crops into oil and then turning the oil into a fuel, that 5% of it is approaching carbon neutrality.

Azi - Okay folks, so there you go; 5% biodiesel in your normal diesel is a little better for the environment and yes, you can make fuel out of vegetable oil.


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