DOE Providing Up To $7M for Research in Stabilizing Fast Pyrolysis Bio-Oils to Support Upgrading to Fuels
The US Department of Energy (DOE) issued a Funding Opportunity Announcement (FOA) for up to $7 million over two years (FY 2008 – 2009) to support advanced research and development in converting non-food based biomass to low-cost bio-oils. Combined with private minimum cost share of 20%, up to $8.75 million would be invested in this research effort.
Recent research has shown that upgrading bio-oils (pyrolysis oil) produced by fast pyrolysis to fungible hydrocarbon fuels—such as gasoline and diesel—by employing conventional petroleum refining techniques, such as hydrotreating and hydrocracking, is a promising pathway for alternate fuels. However, pyrolysis oil has long-term storage stability issues that need to be addressed for this upgrading technology to be commercially viable. In this FOA, DOE is specifically soliciting applications for the development of technology capable of stabilizing the bio-oils.
Under appropriate pyrolysis operating conditions, biomass can be converted to relatively high yields (~70 wt %) of liquids—a mixture of organic compounds (pyrolysis oil) and water. The liquid organics are oxygenated hydrocarbon compounds resulting from the thermal breakdown of lignin, cellulose, and hemicellulose.
Collectively, pyrolysis oil is comprised of a complex mixture of acids, alcohols, aldehydes, esters, ketones, sugars, phenols, furans, and multifunctional compounds such as hydroxyacetaldehyde. The relative amounts of each compound class can vary depending on the biomass feedstock used and the operating conditions employed during pyrolysis.
The specific stability issues relate to the characteristic of the pyrolysis oil viscosity to increase over time during storage. The rate of viscosity change is also exacerbated at elevated storage temperatures and can, under extreme conditions, result in the pyrolysis oil becoming a solid.
Because they contain a large number of oxygenated organic compounds many of which are organic acids (acetic and formic), pyrolysis oils have a relatively high total acid number (TAN) that require storage vessels and processing equipment to be fabricated from expensive corrosion resistant alloys.
Another compounding characteristic of pyrolysis oil is the presence of char particles in the condensed product, normally as a result of the thermal processing when cyclones are used to separate particles from the vapor stream.
During pyrolysis, the mineral matter present in the biomass feed ends up being sequestered in the char. Studies have shown this mineral matter to be uniformly distributed throughout the char particle including the surface. Prior research has also linked the presence of this char, and more importantly the mineral content, as potential catalysts for reactions between the various chemical compounds making up pyrolysis oil.
These characteristics present practical problems in the storage, transport, and processing of pyrolysis oils prior to and during their upgrading to hydrocarbon fuels.
DOE is seeking technical approaches to producing pyrolysis oil with a stability enabling the resulting pyrolysis oil to be transported and stored, in commercial scale tankage, for at least six months under ambient conditions. Specifically, it is looking for:
Reduction of oxygen content within the various organic compounds collectively comprising pyrolysis oil, with a preference toward rejecting the oxygen as an economically optimum balance between carbon oxides and water.
Removal of oxygen present as carboxylic acid groups such that the total acid number (TAN) of the pyrolysis oil is dramatically reduced, preferably below 5.
Reduction of char content with pyrolysis oil.
Conceptually, it is possible to approach the stability problem in two fundamentally different ways. One approach is to try to influence the chemistry of the molecular fragments de-polymerizing from the biomass substrate during the initial pyrolysis step. The other approach is to manipulate the chemistry of the pyrolysis oil post pyrolysis (except as noted above with reaction with alcohols). Either approach, or even a combination of the two, is acceptable within the parameters of this FOA.
Biomass Fast Pyrolysis Oil (Bio-oil) Stabilization FOA: DE-PS36-08GO98018