So far, Huber has developed two generations of a reactor in the lab. In tests, the group starts with sawdust waste from a local mill. The ground-up biomass is fed into a fluidized bed reactor. Inside, a powdered solid catalyst swirls around in a mixture of gas heated to about 600 ºC. When wood enters the chamber, it rapidly breaks down, or pyrolyzes, into small unstable hydrocarbon molecules that diffuse into the pores of the catalyst particles. Inside the catalyst, the molecules are reformed to create a mixture of aromatic chemicals. The reaction process takes just under two minutes.
The company would not disclose details about the catalyst, but Huber says one of its most important properties is the size of its pores. “If the pores are too big, they get clogged with coke, and if they’re too small, the reactants can’t fit in,” says Huber. The company’s catalyst is a porous silicon and aluminum structure based on ZSM-5, a zeolite catalyst developed by Mobil Oil in 1975 and widely used in the petroleum refining industry. Sudolsky says that it can be made cheaply by contractors. Anellotech’s reactors are very similar to those used to refine petroleum. But the company’s reactors are designed to ensure rapid heat transfer and fluid dynamics that ensure that the reactants enter a catalyst before they turn into coke.
Stefan Czernik, a senior scientist at the National Renewable Energy Laboratory’s National Bioenergy Center in Golden, CO, cautions that the process has so far only been demonstrated on a small scale, and the complexity of these reactors could mean a long road ahead for scaling them up. “It is not easy to replicate at a large scale the relationship between the chemical reaction and heat transfer as it’s done in the laboratory,” he says.
After demonstrating the process at a pilot plant next year, Anellotech hopes to partner with a chemical company to build a commercial scale facility in 2014. Sudolsky says the company will either license the catalytic pyrolysis process to other companies or build plants distributed near biomass sources, since transporting biomass is not economically viable.