Bio buzzword

Sept. 15, 2009

Sustainability, climate change, job creation, energy independence and infrastructure investment are issues being discussed nationally as the U.S. economy looks to recover from the current recession.

Sustainability, climate change, job creation, energy independence and infrastructure investment are issues being discussed nationally as the U.S. economy looks to recover from the current recession.

Other issues in the transportation community such as transportation reauthorization and funding exist and are further complicated with the recently released new Corporate Average Fuel Efficiency (CAFE) standards increasing gasoline mileage from 27.5 mpg to 35.5 mpg by the year 2016, which represents an increase of nearly 30% in fuel efficiency as funding for transportation is generated by the 18.3-cent-a-gallon federal gas tax. Without an increase in the federal gas tax, the increase in fuel economy will represent a corresponding decrease in annual highway revenues of at least 20% in the long term. If this is coupled with the fact that average vehicle-miles driven have decreased about 12 billion miles monthly in the past year and a half, this results in about an additional billion dollars less in tax revenue for highways.

Clearly there is a need for policy makers to address the substantial shortfall in revenues for transportation funding; however, technological advances can assist by improving the efficiencies and longevity of the transportation infrastructure as it is being rehabilitated and reconstructed. Technological advances developing binders to supplement and replace asphalt binders with those derived from nonpetroleum crude sources are being developed.

Breaking into fractions

Substantial advancements have been made in fast pyrolysis, a thermal-chemical conversion process that converts biomass into three fractions consisting of gases, solids and liquids. What happens is that researchers can readily use plant life that has harvested the sun’s energy—essentially plant life represents natural solar collectors—and compress the time it takes to produce crude petroleum, which is thousands of years, down to a few seconds with fast pyrolysis.

The gases are similar to natural gas and can be used to fuel the fast pyrolysis process, and the solid fraction primarily consists of char, which sequesters carbon and has a lot of potential as a fertilizer for agricultural uses. The liquid phase is called “bio-oil,” and Iowa State University has developed technology that fractionates bio-oil into multiple fractions similar to the distillation of crude petroleum, which produces transportation fuels to the heavier fractions including asphalt. The fractionation of bio-oil utilizes a condenser train and produces varying fractions consisting of ones that are lighter to ones that are heavier and have similar properties to that of asphalt. Other products that can be derived from upgraded bio-oil fractions include bio-diesel and levoglucosan, which is used in the pharmaceutical industry.

Binder finder?

Asphalt prices in the 2008 construction season saw substantial increases in many markets across the U.S., topping at $700 per liquid ton—and in some instances asphalt shortages were encountered. Asphalt prices have subsided in the current 2009 construction season, with prices commonly in the $450-per-liquid-ton range. However, this is higher than historical pricing of $180 per liquid ton, which was experienced as recently as the 2003 construction season.

The U.S. is moving more toward energy independence and thus an impetus toward a reduction in importing foreign crude petroleum. Several energy alternatives are being expanded, including wind and solar energies, as well as the expansion of natural gas and coal, but these processes do not provide asphalt-like materials for use in roadway construction.

The research work under way at Iowa State University has identified bio-oil fractions that can be used to supplement and possibly fully replace asphalt binders. The asphalt grade range of the unmodified binder is XX whereas the grade range of the bio-oil modified binder ranges from XX to YY. Commonly used binders such as a performance-grade 58-28 or 64-22 have a grade range of 86°C. It is clear that the use of bio-oil in asphalt binders will need to be engineered as various biomass sources have varied effects on asphalt binders similar to other additives and modifiers that are used in the asphalt community.

Advanced notice

More advanced work on developing bio-asphalt consisting of upgraded bio-oil fractions is under way, with more recent research showing promise for developing noncrude petroleum asphalt. Bio-oil primarily consist of lignin, which is a nondescript chemical reference to a complex family of phenols whose chemistry can vary. Lignin has been used for many years in asphalt emulsion technology and has been proven to be an antioxidant in other fields.

The challenges associated with developing bio-asphalt from bio-oil fractions is the stabilization of the upgraded bio-oil fractions. This has been achieved, yet the results illustrate that the effect of temperature on the viscosity of bio-asphalt is more sensitive than standard asphalts. The mixing and compaction temperatures for the developed bio-asphalt are XX and YY, respectively, and tend to be on the lower range of warm-mix asphalt technologies. Lower asphalt mixture production temperatures results in lower energy inputs per ton of mix produced as well as reduced air emissions.

The bio-asphalts are undergoing mix design and performance testing to ensure performance expectations are being met and to find out how the bio-asphalt can be used with production and construction technologies used in the asphalt industry. Demonstration projects utilizing bio-oil modified asphalt are anticipated within a year, with projects using a bio binder to ensue soon after.

Plenty of greenery

The fast pyrolysis of biomass materials represents the use of non-food source materials for a range of products including bio-diesel, bio-asphalt, levoglucosan, char for use as a fertilizer and other materials yet to be identified. Moving forward, installation of fast-pyrolysis production facilities represents development of a new industry and jobs in rural communities across the U.S. and supports the movement toward energy independence while sequestering carbon, providing for enhanced environmental stewardship.

For the asphalt industry, fractionated bio-oil represents the emergence of a source material that is not derived from crude petroleum and will have lower production temperatures similar to warm-mix asphalt and thus will lower greenhouse-gas emissions at asphalt plants and reduce production costs through lower energy inputs.

About The Author: Williams is an associate professor with Iowa State University, Ames, Iowa.

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