Paving with Wood

Almost everywhere on the planet, people are taking a hard look at fuel and other products made from petroleum, and some are coming up with exciting renewable alternatives. One of these is Bioasphalt, made from wood-based, fractionated pyrolysis oil and currently being tested on a bike trail near Iowa State University (ISU).

Grimes Asphalt and Paving Corp. of Grimes, Iowa, uses an asphalt-pyrolysis oil formulation to test-pave a bike trail near Iowa State University. Photo: Anthony Pollard, Avello BioEnergy

“I was down at the trail last week with other people and we couldn’t discern any difference between Bioasphalt and the petroleum-based material,” says Dr. Christopher Williams, associate ISU professor of civil, construction, and environmental engineering, who created Bioasphalt. “It was placed October 6 and has made it through the winter with no low-temperature cracking. We’re also doing lab test comparisons and have so far found that moisture sensitivity is better with the Bioasphalt.”

The idea came from Williams’ thinking on the plastics industry. “In plastics, they use lignin as an antioxidant; it prevents materials from losing their pliability and elasticity,” he says. “This is the same thing we want to have with asphalt. We want to protect it from temperature-related cracking and oxidative aging cracking, and so testing a wood-based bio-oil to replace the crude petroleum component of asphalt was a logical first step.”

The pyrolysis oil used by Williams to make the Bioasphalt was produced at the fast pyrolysis pilot plant at ISU’s BioCentury Research Farm. The research and development of the technologies used at this facility were led by Dr. Robert C. Brown, an Anson Marston Distinguished Professor of Engineering, the Gary and Donna Hoover Chair in Mechanical Engineering, and director of ISU’s Bioeconomy Institute. Three of Brown’s former graduate students, Jared Brown, Cody Ellens, and Anthony Pollard, have created a startup company called Avello Bioenergy Inc., which is currently leasing ISU’s pyrolysis pilot plant (see sidebar on page 22).

The Avello team includes (front, left to right) Cody Ellens, Jared Brown, (back, left to right) AJ Pollard, and Dennis Banasiak. The fast pyrolysis plant is behind them. Photos: Iowa State University

Fast pyrolysis is a thermochemical process in which some type of biomass is quickly heated without oxygen, resulting in liquid pyrolysis oil, solid biochar, and other products. “Avello fractionates this in a process analogous to petroleum refining,” notes Williams. “With the bio-oil used in Bioasphalt, the heavy fractions with low moisture content are taken, and all the water is removed. At the same time, a polymer matrix is created.”

The bike trail Bioasphalt contains 3% Avello pyrolysis oil and 97% crude petroleum. These proportions were mainly due to the small size of the pilot plant. “It took two weeks to produce the 600 pounds (272 kilograms) of bio-oil we needed,” says Williams. “If we had wanted to use 25%, it would have taken two to three months with our pilot plant. Avello is in the process of planning and building a demonstration-scale facility capable of producing much larger quantities for additional demonstration projects.” He believes a little more tweaking of low-temperature performance is needed before 100% Bioasphalt could be used throughout the United States and Canada.

Williams sees the product as providing many important benefits. “It could create a new market for crop residues and provide jobs in rural areas,” he says. “Bioasphalt can be mixed and paved at lower temperatures than conventional asphalt, and once you get above 10%, the cost savings really start to become realized.” Bioasphalt costs $400 a ton, and petroleum asphalt is $550 a ton.

Scott Schram, a bituminous engineer with the Iowa Department of Transportation, adds, “Any state department of transportation is going to be looking for alternative sources for binders, whether that’s from non-petroleum or recycled sources. This is because the more petroleum-based binder you use, the more the cost of asphalt is tied to the price of oil.” Price fluctuations will not be as dramatic if other sources are used, Schram observes, and using less petroleum-based asphalt therefore allows a state better financial stability and planning with regard to transportation.

Avello Bioenergy Avello Bioenergy Inc. is one of several players in the North American pyrolysis game.  Avello has exclusive rights to the pyrolysis oil separation technology developed by Brown and the Bioasphalt developed by Williams. “We currently operate a pilot plant at Iowa State University,” says Avello president Dr. Dennis Banasiak.  “The facility can process up to a quarter ton of biomass per day.”  The company has also been approved by the Iowa Power Fund for a $2.5-million grant to begin building a 2.5 ton/day (2.3 tonne/day) demonstration unit early in 2012.  Avello is focused on using feedstocks with “near-term commercial potential,” says Banasiak.  These are mainly woody biomass and corn stover.  Pyrolysis oil can also be made from dedicated energy crops. Banasiak says that the pyrolysis oil they made using different feedstock categories (hardwood, softwood, herbaceous crops, agricultural residues) varies only slightly in terms of chemical and physical properties.  It is also very similar for different types of biomass within each category.  Yields of pyrolysis oil and biochar, however, vary to a larger degree with biomass type.  “This feedstock flexibility is an important benefit provided by our process and fast pyrolysis processing in general,” Banasiak notes.  “Being able to produce a similar end-product from different feedstock types means it is possible for us to provide customers with a consistent product.” In addition to producing pyrolysis oil that can be used to make asphalt, Avello is producing “biofuel oil” (a stable, low carbon liquid fuel oil for direct fossil fuel replacement or blending), biochar (a soil amendment, renewable heat and power fuel, and potential carbon sequestration agent), and various chemicals for specialty markets.