Tuesday, September 22, 2009

Symbiotic Industries: Chevron and Mascoma

Lignin is the sticky, gunky material that holds the cellulose and hemicellulose of plant stalks together. Mascoma wants the cellulose for making ethanol, but the lignin is just an annoying waste product. But now, Chevron is developing a process for turning the lignin into liquid transportation fuel. So Chevron and Mascoma have a deal, where Chevron provides biomass feedstock to Mascoma, and Mascoma returns the discarded lignin byproduct back to Chevron. Mascoma makes ethanol from the cellulose. Chevron makes hydrocarbon fuels from the ligning. Win - win.
* 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 recycling.
* 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.
If this relationship works out, Mascoma will be relieved of the headache of constantly searching for biomass feedstock, and Chevron will be spared the work and expense of discarding the cellulose from biomass to get at the lignin.

It all comes down to economics. Biomass is not very dense, energy-wise. It must be compressed and densified before transport and processing. This need opens up a huge niche for companies capable of gathering and pre-processing biomass for transport and refinement.

At this point in time, the downstream demand for pre-processed biomass is insufficient to support the farmers, loggers, and pre-processors who will eventually make a very good living providing biomass to the soon-to-be kingpins of bioenergy. But the demand will grow -- because liquid fuels are not going away for a while. And as the huge megacorporations discover ways to make biofuels competitive with petrofuels, an interlocking set of industries will grow up where now there is nothing.

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