Put a shrimp in your tank

You've heard of putting a tiger in your tank, but now how about putting a shrimp in your tank? Doesn't sound quite so impressive does it? But, that's exactly what scientists in China have been doing in an attempt to make biodiesel production more efficient.

XinshengZheng and colleagues from HuaZhong Agriculture University in Wuhan have discovered that shrimp shells could be a great improvement on the catalysts currently used to convert natural oils - from crops like soya,sunflowersand rapeseed - into diesel fuels for vehicles.

The use of biofuels is fraught with controversy. One possible way to get closer to a sustainable source of renewable fuel is to improve the yield of fuel per acre of crop.

Making biodiesel involves a process known as transesterification, which is essentially changes the chemical makeup of fatty acids in seed oils to convert them into a useable fuel. The reaction normally takes place very slowly, if at all, with the addition of a simple alcohol like methanol.

Traditionally it is speeded up and made more efficient by adding a catalyst in the form of a strong acid or base. The problem with these acid and base catalysts is they can't be reused and they involve the use of lots of water, another limited resource.

Now it seems shrimp shells could provide an alternative, more efficient catalyst that can be reused and doesn't need masses of water. Shrimp shell is made up mostly of chitin, the same stuff that our nails and hair are made of. By carbonizing - or burning - the shells and adding potassium fluoride,Zheng and the team made a catalyst which, after 3 hours, converted 89% of samples canola oil into biodiesel.

Shrimp shell make aparticularly good catalyst because is it's complex porous structure with dense honeycomblayers. With such a large internal surface area to the shell fragments there are lots of sites the oils come into contact with and where theesterification reaction will be speeded up, making the conversion to alcohol quicker and more complete.

The authors of the study, which appears in the journal Energy and Fuels, point out that shrimp shell is biodegradable and cheap, being a bi-product of the seafood industry. And while no-doubt the diofueldebate will rage on, they think this new finding could prove to be an important breakthrough in making biofuels more efficient and perhaps a bit less controversial.

Paper: Yang, L, Zhang, A., Zheng, X. 2009. Shrimp shell catalyst for biodiesel production. Energy & Fuels.