Sweet Fuel from Fructose
And now to a story that should appeal to any would-be green with a sweet tooth and that is because scientists have sussed out how to turn fructose into a fuel that can rival the power of petrol. Chris spoke to Jim Dumesic...
Jim - The basic idea that we had was to try to convert carbohydrates into liquid transportation fuel and to compare what we could make by chemical catalysis with what is currently made by fermentation that is ethanol.
Chris - So, what is actually wrong with ethanol then Jim? Why cannot we use that?
Jim - Ethanol has certain disadvantages as a fuel. It has a relatively low energy density. So, the energy per litre of ethanol is about 30% lower than that of standard petroleum, gasoline or diesel. Also, ethanol has a bit of a high volatility and it tends to boil off in hotter weather. So, an ideal fuel will have a little bit lower volatility than ethanol, and finally ethanol loves water and therefore, it tends to be hygroscopic leading to absorption of water into your gasoline, which is undesirable. So, we were looking for routes to make other fuels that would alleviate these potential problems that ethanol has.
Chris - And what did you come up with?
Jim - Well, we came up with this compound called dimethylfuran, DMF. So, if you start with a molecule of a sugar like glucose, well in our case fructose, it has six carbons and six oxygen. It turns out if you remove five out of the six oxygen you end up with this dimethylfuran and it actually has all of the desirable properties you would look for in a fuel that is, it has the energy density that is very similar to petroleum. It has a volatility that is a little bit lower than ethanol, which is good and it also is hydrophobic meaning it does not like water, which is the same as petroleum.
Chris - Now how easy is it to actually do this though? Do you actually get more energy out than you have to put in, in the synthesis?
Jim - Well, we have a two-step process. In the first step, we remove three oxygen by removing three water molecules from the sugar, which leads to a chemical intermediate called hydroxymethyl-furfural, HMF. That process does not theoretically require energy and then in the second step, we pass hydrogen over this HMF and remove two of the oxygen which gives us dimethylfuran, which has one oxygen. Now, we do this all in a solvent and at the end of the process we have to evaporate the solvent to make the fuel; however, the solvent we use is an organic solvent and compared to the production of ethanol by fermentation, where water is the solvent, the energy required to evaporate the organic solvent is about one-third of the energy required to evaporate the water. So, potentially this is an energetically favourable process for making the fuel.
Chris - And I guess that because there is so much in the way of raw materials such as sugars, which are chucked out by plants such as the sugar industry, the chocolate industry, there must be no shortage of raw materials from which you can make this stuff?
Jim - Well, that is the hope. If you look at biomass, over 75% of biomass are sugars. I do point out though that the major sugar in biomass, for example, lignocellulosic, which is the main form, is glucose. Our process works primarily with fructose so that there is a biological step involved in converting the glucose in the fructose. Once we have the fructose, our process works pretty well to make the dimethylfuran.
Chris - Well, let us look at actually how you could use this. So, will it burn and behave in an analogous way to petrol, because that must be a key question?
Jim - Yeah, there was a discussion in the literature on this in the 1980s. People went through and measured the octane number of DMF and it turns out the octane number is something like around 120, which is a very, very good octane. So, dimethylfuran should be a very, very good burning fuel if you can make it efficiently from biomass.
Chris - And what about the cleanness of that burn, will it produce lots of nasty organic residues, which, you know, rather like diesel, it has a very poor press on this, are going to trigger respiratory problems or will it burn clean?
Jim - Combustion people I have talked to here at the engine centre at Wisconsin their suggestion is that it should burn cleanly, but there have not been many studies of this in the past because there has not been a lot of dimethylfuran available. I think now opening the possibility of DMF as a fuel - that would be interesting to study.
Chris - So, say you managed to pull that off and it does perform well as fuel engines will tolerate it; it would not corrode them and things like that, is the process to make it actually scaleable, can we get reasonable amounts of this that you could see then turning out of the petrol pump?
Jim - Yeah, the process should be scaleable because if you look at the steps that we use in our two-step process they are very similar to the kinds of processes that are currently used in the petrochemical industry. Therefore, they potentially should be scaleable.
Chris - And so, presumably you will be doing some tests on this to try and get this running into engines pretty soon and see how it behaves?
Jim - Yeah, that is the next step on our process, actually is to scale it up so that we can make amounts of DMF that are now suitable for engine test i.e., in fact, one of our short-term goals.