Pyrolysis Oil Challenges and Solutions
Traditionally, biomass was converted to charcoal or biogas for generation of energy. Currently, due to environmental concerns and the high price of fuel, the approach has shifted to the conversion of biomass into pyrolysis oil for use as fuel.
What is pyrolysis oil? It’s a complex mixture of chemicals resulting from the thermal decomposition of biomass. The types and amounts of each chemical may vary widely depending on the thermal process used. Pyrolysis oil is also known as biocrude, bio-oil or bioleum. There are a number of technologies that convert biomass into pyrolysis oil and all of them involve high temperature (between 400 and 650 degrees Celsius). Pyrolysis oil has the potential to become a viable alternative to fossil fuel. The U.S. DOE estimates that there are more than 1.3 billion tons of recoverable biomass today. Using current technologies, this biomass could be converted to 130 billion gallons per year of fuel per year, or 65 percent of the total U.S. consumption. Some energy crops such as switchgrass and Miscanthus, as well as algae, can also be used as feedstock for pyrolysis oil, which can then be further processed into transportation fuels.
There is a catch, however: pyrolysis oil is highly acidic and corrosive. As a result, it is difficult to store and transport, and can damage engines, boilers and refinery processing equipment. Upgrading pyrolysis oil in a cost-effective manner to remove the high acid content is a challenge that must be overcome.
What are the options for upgrading bio-oil? Technologies like hydrogenation, hydro-deoxygenation and other similar conventional processes address the high acidity problem; however, they require large-scale plants and capital, and exhibit substantial yield losses (up to 50 percent sometimes) mainly due to the use of hydrogen.
Some next-generation technologies attempt to use existing infrastructure and eliminate the use of hydrogen to reduce the high capital and operating costs of upgrading pyrolysis oil. My company, the Houston-based Enhanced Biofuels, has developed such a technology. We use a proprietary reactor system that bolts onto existing facilities, to share infrastructure, and it uses a readily available and relatively inexpensive alternative to hydrogen for reducing or eliminating the acidity of pyrolysis oil in a cost-effective manner.
Once upgraded, the pyrolysis oil can be used many different ways. It could be fed directly into a conventional refinery to make green transportation fuels while using existing infrastructure, becoming a domestic green feedstock for the U.S. refining infrastructure. It could also be a blend-stock for bunker or marine fuel. Bio-oil has lower heating value than bunker fuel, but it also has lower viscosity, essentially no sulfur, and high oxygen content. These properties will likely make a bunker fuel/pyrolysis oil mix easier to handle, and will improve the burning characteristics of bunker fuel. Pyrolysis oil is also a domestic, green low-cost alternative to heating oil and boiler fuel, which are fossil-fuel based. Upgraded bio-oil can also be used for power generation in diesel and sterling engines. This application supports distributed green power efforts, because the fuel’s easier to transport and handle, and has higher energy density than biomass. Finally it can be a chemical feedstock. Pyrolysis oil contains carboxylic acids, and phenolic and nitrogen compounds, which can be converted into resins, adhesives, solvents, fertilizers, flavors and more. In addition to these valuable building blocks, pyrolysis oil can be processed into traditional petrochemicals and plastic intermediates through refining and processing.
Pyrolysis oil has the potential to be available in large amounts and competitively priced. Upgrading bio-oil in a cost-effective fashion to reduce its high acid content is essential. Next-generation technologies that attempt to address this challenge will give pyrolysis oil great promise as a domestically grown, green feedstock for production of fuels and chemicals using the current refining and transportation infrastructure.
Author: Roman Wolff
President, Enhanced Biofuels