This is an important moment for us at Mascoma. The upgrading of our byproduct lignin to high value transportation fuels is an important step in our effort to prove the effectiveness of integrated biorefineries. It has been our goal all along to make our process as integrated and sustainable as possible.

—Dr. Jim Flatt, President of Mascoma

Lignin is a complex chemical compound (a cross-linked amorphous phenolic polymer) and is the biomass component with highest energy content (9,000 - 11,000 Btu/lb compared to 7,300 - 7,500 for cellulose, Johnson 2002). After biomass has been converted through Mascoma’s proprietary Consolidated Bio Processing method (earlier post), which breaks down the sugars in the cellulose and turns it into ethanol, the energy-rich lignin is left.

Lignin is not directly useful as a refinery feedstock for biofuels synthesis, however. The high oxidation state of lignin (by virtue of its phenolic characteristics) means it has a low energy content compared to common refinery fuels, and it is so highly oxygenated that it is not generally compatible with hydrocarbon streams.

Chevron and lignin for fuels. In February 2008, Chevron Corporation and Weyerhaeuser Company created a 50-50 joint venture company—Catchlight Energy LLC— focused on developing the next generation of renewable transportation fuels from nonfood sources. (Earlier post.) Catchlight’s initial focus is developing and demonstrating novel technologies for converting cellulose and lignin into biofuels. There are two main thrusts to its current research efforts: a near-term focus on early commercialization opportunities for producing ethanol and a longer-term focus on direct conversion of biomass to hydrocarbons.

Also in February 2008, Chevron filed applications for two patents on refinery-based processes for converting lignin to hydrocarbon fuel components. In one embodiment, the lignin is first separated from the black liquor at a paper mill and then the lignin is transported from the paper mill to the refinery for hydroprocessing. In an alternative embodiment, the entire black liquor solution may be transported from the paper mill to the refinery for hydroprocessing. The Mascoma agreement opens up the potential for an alternative source of lignin.

The processes described in the patent applications significantly increase the energy content of the lignin and reduce the oxygen content. The basic steps are:

• Lignin is introduced into a hydroprocessor. Hydroprocessing includes hydrocracking and hydrotreating—cracking the larger lignin molecules into smaller molecules—using a reductant and a catalyst at high temperature and pressure. Examples of hydroprocessing catalysts include molybdenum, cobalt, nickel, tungsten, iron and/or platinum on an amorphous or crystalline oxide matrix. Optionally a hydrocarbon solvent can also be added as a slurry for the catalyst.

• After the introduction of the lignin and the catalyst into the hydroprocessor, the reductant is pressurized into the hydroprocessor. One example of a reductant for the hydroprocessor is hydrogen, which can be obtained from the same source providing hydrogen for other refinery processes. In addition, the reductant for the hydroprocessor could also be syngas. The presence of carbon monoxide in the syngas can assist with the conversion of lignin, and the observed effect is similar to that seen for coal hydroprocessing with syngas compared to hydrogen alone.

• Unlike coal or heavy crude oil hydroprocessing, significant amounts of water are produced as a result of lignin hydroprocessing, due to the fact that lignin is oxygenated to a much greater degree than coal or heavy crude oil. Chevron says tests have shown that this produced water does not inhibit the lignin conversion. At the end of the reaction the water will condense and phase separate from the biofuels feedstock. The water extracts any residual salts that may be present in the lignin thereby preventing fouling or deactivation of the catalyst. After the separation from the water the biofuels feedstock will also be separated and filtered to remove the catalyst for recycle.

• In an exemplary embodiment cited in the patent application, the hydroprocessing comprises activated slurry hydrocracking with a molybdenum sulfide heterogeneous catalyst at approximately 2000 psi with hydrogen for about six hours.

• At the end of the reaction, the product is introduced into the refinery processes to produce a biofuel. The particular location of the introduction of the biofuels feedstock within the refinery processes will depend on the composition of the biofuels feedstock. The biofuels feedstock will be primarily a diesel-like stream.

In December 2008, Mascoma began creating ethanol from cellulosic biomass with positive results at its demonstration facility in Rome, New York. The company, in collaboration with its commercialization subsidiary Frontier Renewable Resources, is in the process of financing its first full-scale ethanol facility in Kinross, Michigan. The company plans to break ground on that facility during the first half of 2010.

Resources

• US Patent application 20090218062 Process for Generating a Hydrocarbon Feedstock from Lignin

• US Patent application 20090218061 Process for Generating a Hydrocarbon Feedstock from Lignin

• David K. Johnson, Esteban Chornet, Wlodzimierz Zmierczak and Joseph Shabtai (2002) Conversion of Lignin into a Hydrocarbon Product for Blending with Gasoline. ACS Fuel Chemistry Division Preprints 47(1), 381