Apple pulp promises better and cheaper capacitors

Licensing opportunity

A collaboration between the Université de Neuchâtel in Switzerland and the National Carbon Institute of Oviedo (INCAR) in Spain is about to license a process to transform apple pulp into highly efficient activated carbon.

Unlike batteries, ultra capacitors store directly an external charge of electricity. They can deliver it the same way, within a second if needed. For that reason ultra capacitors have been applied in electronics whenever a circuit needs electricity on demand to compensate any current drop, in trains, telecom routers or wind turbines for example.

Recently, the market for ultra capacitors has also been pulled by the new demand for hybrid vehicles, which also instant delivery of electricity to start the engine before running on batteries. The market for ultra capacitors was estimated at around $100 million worldwide in 2005 and has been growing fast since.

Ultra capacitors use the remarkable properties of activated carbon. Because one gramme of this sponge-like material has a surface area of 500 square metres (about twice the size of a tennis court) it can store large amounts of electricity in relatively small devices.

Currently, activated carbons are produced from materials such as wood and coal. “The problem is that with wood you have deforestation and coal may be rather expensive”, explained Fritz Stoeckli from the Université de Neuchâtel. “With my colleague Teresa Centeno at INCAR, we tested various sources and activation processes to find the best cost/efficiency combination.”

That turned out to be apple pulp, a waste product of cider production. The surface of activated carbon from apple pulp source reaches 1200 square metres per gramme. And the raw material is cheap because to get rid of pulp wastes, cider producers have actually to pay a tax in Spain. Stoeckli adds: “Our activation process is also based on steam, which avoids the cost and pollution issues associated with chemical activation processes.”

With two patents, shared 50:50 by the Spanish and Swiss institutions, Stoeckli and Centeno hope now investors are going to build factories to industrialise their process. The government of the Asturias region, where the cider industry produces around 12,000 tonnes of apple pulp waste a year, is currently considering a project.