Bioasphalt developer Chris Williams and paving machine.Credit: Photo by Mike Krapfl/Iowa State University
Asphalt is usually made from the bottom of the barrel, the dregs of the oil refining process. But then along came the tar sands and better technologies for refining heavy oil into gasoline, and the price has climbed. John has noted that it has got so expensive that rural roads are going back to the stone age.
But Chris Williams of Iowa University has come up with an interesting alternative; he has cooked up a bio-oil from plants and trees that can replace the asphalt glue that holds our pavement together- Bioasphalt.
It's made by fast pyrolysis, "the rapid thermal decomposition of carbonaceous organic matter in the absence of oxygen", Science Daily explains:
Bio-oil is created by a thermochemical process called fast pyrolysis. Corn stalks, wood wastes or other types of biomass are quickly heated without oxygen. The process produces a liquid bio-oil that can be used to manufacture fuels, chemicals and asphalt plus a solid product called biochar that can be used to enrich soils and remove greenhouses gases from the atmosphere.
Robert C. Brown of Ohio State developed a process of fast pyrolysis, (perhaps this reactor shown in his patent 5711771) which was licenced to Avello Energy. Mr. Williams developed Bioasphalt using their product and is testing it on a bike path.
It is not the first bioasphalt; Shell Oil paved a road in Norway in 2007, and Vegecol, an asphalt made with vegetable oil binders was patented in France in 2004. In Australia, Ecopave is made from sugar cane and molasses. They also have trademarked the name Bioasphalt so Mr. Williams may be in for a bit of a fight over the name.
The stuff can be made from crop and mill residues, "woody biomass", AKA trees (the bike path was evidently made with oak) and since this is Iowa, what they discreetly call "energy crops", AKA corn. I am not too enthusiastic about paving our roads with food and trees, but there is enough other biomass around to probably pave much of America. They also note that the process works with switchgrass, reed canary grass, giant cane, miscanthus.