From Biomass to Chemicals in One Step
A startup's catalytic process converts biomass directly into components of gasoline.
By Katherine Bourzac, MIT Technology Review, March 29, 2010
An early-stage company spun out of the University of Massachusetts, Amherst, plans to commercialize a catalytic process for converting cellulosic biomass into five of the chemicals found in gasoline. These chemicals are also used to make industrial polymers and solvents. Anellotech, which is seeking venture funding, plans to build a pilot plant next year.
Anellotech's reactors perform a process called "catalytic pyrolysis," which converts three of the structural molecules found in plants--two forms of cellulose and the woody molecule lignin--into fuels. Ground-up biomass is fed into a high-temperature reactor and blended with a catalyst. The heat causes the cellulose, lignin, and other molecules in the biomass to chemically decompose through a process called pyrolysis; a catalyst helps control the chemical reactions, turning cellulose and lignin into a mix of carbon-ring-based molecules: benzene, toluene, and xylenes.
The global market for this group of chemicals is $80 billion a year and growing at a rate of 4 percent a year, says Anellotech CEO David Sudolsky. "We're targeting to compete with oil priced at $60 a barrel, assuming no tax credits or subsidies," he says. The company's founder, George Huber, says his catalytic pyrolysis process can create 50 gallons of the chemicals per metric ton of wood or other biomass, with a yield of 40 percent. The other products of the reaction include coke, used to fuel the reactor.
"The advantage of pyrolysis is that it uses whole biomass," says John Regalbuto, an advisor to the Catalysis and Biocatalysis Program at the National Science Foundation. On average, lignin accounts for 40 percent of the energy stored in whole biomass. But because it can't be converted into sugars the way cellulose can, lignin can't be used as a feedstock for fermentation processes such as those used by some biofuels companies to convert sugarcane into fuels.
Pyrolysis is also different from gasification, another process for using whole biomass. Gasification results in a mixture of carbon and hydrogen called syngas, which can then be used to make fuel. Pyrolysis, by contrast, turns biomass into liquid fuels in a single step. And while gasification can only be done economically at a very large scale, says Regalbuto, catalytic pyrolysis could be done at smaller refineries distributed near the supply of biomass.
Pyrolysis is an efficient way to use biomass, but it's difficult to control the products of the reaction, and it's difficult to get high yields. The keys to Anellotech's process, says Huber, are a specially tailored catalyst and a reactor that allows good control over reaction conditions. Huber's group at UMass, where he is a professor of chemical engineering, was the first to develop a catalytic process for converting biomass directly into gasoline, and Anellotech's processes are based on this work.
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.
Copyright Technology Review 2010.