Clean & Green: A Comprehensive Review of "Syngas" Cleanup for Biomass Gasification

July 7, 2015

Synthesis gas production model.
Contrasting with ethanol production with microorganisms to ferment raw material into liquid fuel, biomass materials can be directly “gasified” through controlled burning (called pyrolysis, literally “fire splitting”). Gasification releases energy stored in complex plant structures like cellulose, just like a campfire or fireplace does. The difference is that “gasification” is designed to capture the byproducts of combustion including gaseous carbon monoxide, methane, plus carbon dioxide and water vapor. This gaseous mix, called “synthesis gas,” forms the building blocks of “engineered” liquid fuels.

In an idealized model of combustion, the sole byproducts of combustion are water and carbon dioxide. But, in the "real world," biomass feedstocks introduce contaminants to the combustion equation including tars, sulfur-based molecules, hydrogen halides, and trace metals like Potassium and Sodium-- chemicals originally contained in living plant tissue, then freed during combustion (in the case of metals), or generated during the combustion process (tars, for example).

To safeguard both the environment and the purity of engineered liquid fuel products, un-wanted particles and molecules must be removed from synthesis gas produced during gasification of biomass.

This review builds on recent work covering hot gas catalytic and sorbent removal of tar, along with conditioning of hydrogen sulfide, ammonia, and syngas, to encompass a specific subset of synthesis gas cleanup: halides and trace metals, topics which the authors note have received “limited attention.”

The authors discuss “cold gas” cleanup, “hot gas” cleanup, and technical barriers in synthesis gas cleanup. It provides data on wet scrubbing technologies for tar removal including absorption efficiencies. It discusses nitrogen containing contaminants as well as those containing sulfur, with information detailing conventional sulfur removal solvents and methods. Hydrogen halides and metals are discussed with reference to water-based and caustic-based scrubbing, and gas cooling / condensation.

For “hot gas” cleanup, catalysts are reviewed, along with tar reforming studies. Catalysts include alkaline compounds and transition metals including Iron, Nickel, and Zeolites (crystalline structures of aluminum and silica). Catalysts for nigrogen contaminant removal are also reviewed in the same context, with the addition of Iron, Ruthenium, and other transitional metal-oxide catalysts. Studies detailing sorbent materials and catalysts for de-sulfurization are reviewed, along with Zinc-based, Copper-based, and other transition-metal oxides.

The review concludes that major focus areas for syngas cleanup should center on 1) developing multi-material gas cleanup strategies that enhance efficiency and reduce costs, and 2) exploration of catalyst resistance to deactivation that investigate material lifetime and activity levels.

The online version of this review is available in the June 2015 edition of the journal Applied Energy < http://www.journals.elsevier.com/applied-energy/>. It will appear in print in the October, 2015 edition of the journal.

Check out the publication online or download the citation with metadata from the IBSS Zotero Account.

Nourredine Abdoulmoumine, Sushil Adhikari, Avanti Kulkarni, Shyamsundar Chattanathan, A review on biomass gasification syngas cleanup, Applied Energy, Volume 155, 1 October 2015, Pages 294-307, ISSN 0306-2619, http://dx.doi.org/10.1016/j.apenergy.2015.05.095.

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