A Georgia company says it has overcome a major roadblock in turning agricultural waste into vehicle fuel and other useful chemicals by experimenting with a technology that treats the waste with compressed water heated to very high temperatures.
If it works, the technology could reduce the nation’s reliance on oil imports for gasoline in favor of a cleaner-burning and less expensive source of energy. A company with a workable technology would have a guaranteed market, given that Congress has set quotas for the consumption of cellulosic fuel but so far, hardly any is being produced.
What is more, the supply of cellulosic biomass is far larger than the amount of corn available for making ethanol, and it does not involve diverting many resources from food production.
Cellulose is made up mostly of sugars that can be fed to microorganisms to make ethanol or be chemically processed into other fuels or chemical feedstocks. Yet those sugars are locked up in a form that makes them mostly useless to anything but grazing cows and termites.
The process developed by Renmatix involves putting hardwoods into a small pressurized chamber. One class of sugars, the type with five carbon atoms, is broken off and harvested. The remaining material is pumped into a second pressurized vessel for a longer period to release the remaining sugars.
A solid component of woody biomass called lignin remains and is burned to provide energy for the process.
In both phases, the cellulosic material is treated by water at a pressure and temperature that is so high that the water is neither steam nor an ordinary liquid but in a form known as “supercritical.”
Competitors use various combinations of steam, acid and enzymes to convert the woody waste into fuel. But the enzymes are far more expensive than water, and the acid residue must be removed from the resulting product. Some companies have tried to blast the cellulose into very small molecules and then recombine them as alcohols or other chemicals, but they have had trouble controlling the mix that results.
Renmatix uses only pressurized water. When the water is in the so-called supercritical phase, the company says, its pH level can be adjusted to turn it into an acid. When it is depressurized, it reverts to pure water with a neutral pH level.
Renmatix began its lab-scale process in late 2008. A year later, it began operating a pilot-scale plant in Kennesaw, Ga., that processes three tons a day of mixed wood chips.
“We use no significant consumables, like enzymes or acids,” said Fred Moesler, a company engineer who is in charge of scaling up the process.
But scaling up and reaching competitive prices have tripped up several competitors in the field.
“It’s not unimaginable that it would work,” said Thomas L. Richard, a professor of agricultural and biological engineering at Penn State University and the director of itsInstitutes for Energy and the Environment. Yet he cautioned, “I’m quite confident that they will face some challenges moving from a lab success to a tens-of-millions-of-gallons commercial refinery.”
Renmatix’s process stops at the point that the wood waste is transformed into useful sugars. Other companies would convert the sugars into feedstock chemicals or motor fuels.