- Number 362 |
- May 7, 2012
NREL Catalyst Brings Drop-In Fuels Closer
NREL Engineer Whitney Jablonski
places a quartz reactor tube with
a nickel-based catalyst into a
reactor at NREL's Thermochemical
Credit: Dennis Schroeder.
Researchers at DOE's National Renewable Energy Laboratory are looking for ways to thermochemically treat biomass to arrive at an end product that is similar to oil. NREL has patented a catalyst that cleans up biomass gas, making it ready to convert into fuels compatible with today's infrastructure.
"In the end you want to create something that's going to look just like gasoline, with a cost similar to gasoline, but that is derived from biomass," NREL Principal Scientist Kim Magrini said. "There is an added benefit to this process because you are taking biomass, which has carbon in it, and putting it into your fuel, which gets combusted into carbon dioxide — which is food for future biomass. If you look at the life-cycle analysis, it has a greater than 90 percent closure on the carbon loop."
In fact, thermochemically derived fuels have a number of benefits. The flexibility of thermochemical processes, such as gasification and pyrolysis, provides cost-effective options for manufacturing cellulosic ethanol and advanced biofuels. Often called "drop-in" fuels, these advanced biofuels are compatible with the existing fuel infrastructure, which will speed commercial adoption. And, as Magrini noted, advanced biofuels produced via thermochemical conversion could significantly reduce greenhouse gas emissions.
Work on the fluidizable tar reforming catalyst started in NREL's Hydrogen Program, where researchers were looking to produce hydrogen from the aqueous hydrocarbon fractions of pyrolysis oil, also thermochemically produced from biomass, Magrini said.
"Pyrolysis oil is analogous to petroleum oil, although it is chemically different," Magrini said. "Once you form the pyrolysis oil, you can do a variety of things with it, like upgrade it into fuel-like intermediates that can go into the existing fuel structure. Or, you can reform the aqueous phases and get hydrogen. When you do this, you need a catalyst that breaks down the components into hydrogen and carbon monoxide. The problem was that the catalyst that can do this reaction gets fouled in the process.
"Commercial catalysts wouldn't work; they are made for use in a fixed bed, which is a packed bed of catalysts that you run the materials through. We had to find a fluidizable material that moves around in the reactor and provides more efficient contact of the liquid with the catalyst."
The NREL team was successful in creating a catalyst that worked. The next idea was to take this reforming catalyst, designed for getting hydrogen, and see if it could be used to reform the tars that result from biomass gasification.
"The answer was, yes, we could," Magrini said. "It worked quite well. But the problem with this process was that when you gasify biomass, sulfur compounds from proteins are produced from the biomass. Those compounds deteriorated the catalyst because it is nickel on aluminum, and nickel readily reacts with sulfur."
Magrini's team, including NREL's Yves Parent, Steve Landin, and Marc Ritland, identified the need for the catalyst to reside on a better support. The commercially available materials NREL tried simply fell apart in the reactor — so NREL staff enlisted the help of a Colorado neighbor, CoorsTek, to further refine the catalyst support so it would work in the fluidized bed of a gasification reactor.
The resulting catalyst support is made by taking all the raw materials and grinding them in water to form a high-solids solution. The particles in the solution are approximately one micron in diameter. The solution is spray-dried by atomizing the liquid in really hot air, forming droplets. The tiny droplets are little round pellets of ceramic; each one is formed when numerous particles from the solution adhere together. Then the material is fired, giving it strength, but the porous surface of the ceramic is not totally sealed, so the catalyst components — nickel, magnesium and potassium — can "soak in."
Once the support structure was identified, NREL created the catalyst by mixing a nickel, magnesium, and potassium salt solution with the support. When this is heated, a chemical reaction occurs and the catalyst components of the solution stick onto the surface of the support.
"So when you take the CoorsTek support and add our patented formulation, we can efficiently clean up the syngas for downstream fuel synthesis," Magrini said. "All that work comprised NREL's material patent because it didn't exist anywhere else in industry."
NREL's decade of work on this process will culminate in the summer of 2012 when a biomass-to-ethanol process will be demonstrated at pilot scale to show that the catalyst is ready for industry.Just patented last year, NREL's unique solution for a fluidizable tar reforming catalyst has already caught the attention of industry and has been licensed by Rentech, Inc., for use in the Rentech-ClearFuel biomass gasifier in Commerce City, Colorado.
[Heather Lammers, 303.275.4084,