China-US team concludes duckweed biorefineries can be cost-competitive with petroleum-based processes

Researchers from the US and China have determined that a duckweed biorefinery producing a range of gasoline, diesel and kerosene products can be economically competitive with petroleum-based processes, even in some cases without environmental legislation that penalizes greenhouse gas emissions. A paper describing their analysis of four different scenarios for duckweed biorefineries is published in the ACS journal Industrial & Engineering Chemistry Research.

Duckweed, an aquatic plant that floats on or near the surface of still or slow-moving freshwater, is attractive as a raw material for biofuel production. It grows fast, thrives in wastewater that has no other use, does not impact the food supply and can be harvested more easily than algae and other aquatic plants. However, few studies have been done on the use of duckweed as a raw material for biofuel production.

The team, comprising researchers from Princeton University; Peking University; Institute of Process Engineering, Chinese Academy of Sciences; and PetroChina company, investigated four different thermochemical pathways for the production of gasoline, diesel, and kerosene from gasified duckweed synthesis gas as the intermediate:

• Low-temperature and high-temperature Fischer‚àíTropsch processes (LTFT and HTFT) using both iron and cobalt based catalysts. Clean syngas is converted to hydrocarbons via cobalt or iron-based catalysts operating at either low or high temperature. The residue/wax produced from FT synthesis is directed to a hydrocracker, and the vapor phase C3‚àíC22 hydrocarbons are sent for further upgrading.

• Methanol to hydrocarbons via the methanol-to-gasoline (MTG) or methanol-to-olefins (MTO) processes. The hydrocarbons are refined into the final liquid products using ZSM-5 catalytic conversion, oligomerization, alkylation, isomerization, hydrotreating, reforming, and hydrocracking.

Fischer‚àíTropsch (FT) synthesis flowsheet. Credit: ACS, Baliban et al. Click to enlarge.	Methanol synthesis and upgrading flowsheet. Credit: ACS, Baliban et al. Click to enlarge.

The team developed a process synthesis framework to select the refining pathway that will produce the liquid fuels at the lowest possible cost. The used the synthesis framework to determine the effect of refinery capacity and liquid fuel composition on the overall system cost, the refinery topological design, the process material/energy balances, and the lifecycle greenhouse gas emissions.

The researchers used four case studies focused on two target capacities (i.e., 1,000 and 5,000 bpd) and two product compositions (i.e., unrestricted and US demand ratios of gasoline, diesel, and kerosene) to demonstrate the capability of the process synthesis framework and determine the process design that has the lowest overall cost.

The price of crude oil for which the duckweed BTL refineries will be competitive is $100/bbl for the 1 kBD unrestricted study, $69/bbl for the 5 kBD unrestricted study, $105/bbl for the 1 kBD US ratio study, and $72/bbl for the 5 kBD US ratio study. An important highlight for these four studies is the strong use of methanol synthesis opposed to FT synthesis. The lack of inert production during methanol synthesis allows for the use of a large internal synthesis gas loop and less complex synthesis gas conversion design within the refinery. The methanol can be readily converted to gasoline, diesel, and kerosene using a ZSM- 5 catalyst.

A parametric analysis on the duckweed purchase price indicates that there exists a threshold price of duckweed above which the refinery will no longer be economically competitive with crude oil refining. This threshold level for duckweed purchase depends on the desired refinery capacity and will decrease as the capacity decreases.

If crude oil was priced around $105/bbl, then the 1 kBD refineries would be economically competitive with a duckweed purchase price of $50/dry metric ton. A reduction in the duckweed purchase price to $30/dry metric ton will make the 1 kBD duckweed refineries competitive at crude prices above $95/bbl. For the 5 kBD refineries, the process synthesis framework demonstrates the economic viability at a crude price above $72/bbl for duckweed purchase prices at $50/dry metric ton. If this purchase price was raised to $70/dry metric ton, the refineries would remain competitive at crude priced above $82/bbl.

-Baliban et al.

The US National Science Foundation and the Chinese Academy of Sciences provided funding for the research.

Resources

• Richard C. Baliban, Josephine A. Elia, Christodoulos A. Floudas, Xin Xiao, Zhijian Zhang, Jie Li, Hongbin Cao, Jiong Ma, Yong Qiao, and Xuteng Hu (2013) Thermochemical Conversion of Duckweed Biomass to Gasoline, Diesel, and Jet Fuel: Process Synthesis and Global Optimization. Industrial & Engineering Chemistry Research doi: 10.1021/ie3034703

http://www.greencarcongress.com/2013/03/arpa-e-to-issue-new-funding-op

http://www.greencarcongress.com/2013/03/duckweed-20130307.htm

Researchers develop new Fischer-Tropsch catalyst and production method; Total patents both

A team of researchers led by University of Amsterdam (UvA) chemists has developed new Fischer-Tropsch catalysts-consisting of ultra-thin cobalt shells surrounding inexpensive iron oxide cores-that can be used to produce synthetic fuels from natural gas and biomass. The method used to produce the catalysts is based on an approach previously optimized for preparing magnetic tape for audio cassettes in the 1960s.

France-based energy major Total, which was part of the research team, has patented the new catalysts and the method for their preparation, naming the UvA researchers as co-inventors. The research has just been published online as a VIP (very important paper) communication in the journal Angewandte Chemie.

The Fischer-Tropsch process is used for producing fuels from synthesis gas, which in turn is made from natural gas, biomass or coal. Large reserves of shale gas and natural gas currently changing the world energy market have increased interest in F-T technology. However, F-T reactors are huge, and typically use hundreds of tons of catalyst.

Cobalt-based catalysts are the optimal choice for synthesizing middle distillate fuels such as diesel and kerosene with F-T technology. But cobalt is also expensive. In 2009 the Total Gaz & Power company contacted the Heterogeneous Catalysis and Sustainable Chemistry group (Van 't Hoff Institute for Molecular Sciences) at UvA to develop a new F-T catalyst together.

Roberto Calderone, Raveendran Shiju and Gadi Rothenberg from the group took up the challenge to design a less-expensive catalyst that can be prepared on a very large scale, yet performs at least as well as pure cobalt.

To gain an economic advantage would require engineering of the particles at single-nanometer resolution, yet in a manner that can be scaled up to multi-ton scale. This rules out all chemical procedures that require high sophistication, extreme temperatures, or expensive chemicals.

The UvA team sought to meet these restraints with the surface nucleation of a cobalt phase onto iron oxide colloids. They were inspired by the method that companies such as TDK used in the 1960s for producing magnetic tapes for audio cassettes. The standard recording materials in these cassettes were polymer-based tapes containing cigar-shaped cobalt-doped iron oxide particles.

After two years of hard work they achieved a cheap, reliable, efficient and, most importantly, scalable method for synthesizing spherical core-shell catalyst particles. The particles have an average diameter of 10 nanometer (nm) and consist of a 8 nm magnetite (iron oxide) core with a cobalt oxide shell of only 1 nm.

The new catalysts were then tested in collaboration with research groups in Lille. The catalysts proved to be excellent Fischer-Tropsch catalysts, giving good diesel fractions.

Resources

• V.R. Calderone, N.R. Shiju, D. Curulla Ferr√©, S. Chambrey, A. Khodakov, A. Rose, J. Thiessen, A. Jess and G. Rothenberg. (2013) De novo design of nanostructured iron-cobalt Fischer-Tropsch catalysts. Angew. Chem. Int. Ed. doi: 10.1002/anie.201209799

http://www.greencarcongress.com/2013/03/ft-20130305.htm