Meetings Briefs

The American Institute of Chemical Engineers annual meeting, held on Nov. 12-17 in San Francisco, attracted some 4,500 chemical engineers. Among the many presentations that they could opt to attend, here are three of special interest.

The Midwest has a huge abundance of waste corncobs. Peter Pfeifer, Parag S. Shah, and Galen J. Suppes of the University of Missouri, Columbia, have found a way to use this resource to make nanoporous activated carbon that could become a valuable material for mass storage of methane, natural gas, and hydrogen.

The researchers "carbonize" dried and crushed corncobs at 450 ^oC and chemically activate it in a multistep process, Shah reported. The resulting nanoporous carbon is crisscrossed by a nearly space-filling network of 1-nm channels. This type of material initially was discovered by Pfeifer and his colleagues.

Normal activated carbon, typically made from more costly anthracite, coconut shells, or polymeric materials, has a surface area as large as about 900 m²/g. The corncob carbon made by Pfeifer's method, on the other hand, has a surface area in excess of 3,500 m²/g, which meets the Department of Energy's target for a gas-storage material. The activated carbon can be formed into hockey-puck-sized monoliths in a hydraulic press and absorbs large amounts of gases under high pressure.

This carbon is "some pretty special stuff," Suppes told C&EN. It appears to have the highest methane uptake and storage of any material reported so far, and it appears to absorb hydrogen very well, he added. The material has potential applications not only in gas storage but also in electronics and catalysis, Suppes said. It is being further developed by the Alliance for Collaborative Research in Alternative Fuel Technology (All-Craft) based at the university.

Cationic lipids form complexes with DNA, and these so-called lipoplexes facilitate the transfer of the DNA across cell membranes, a process that is potentially useful for developing gene-based therapies. Christopher M. Jewell, David M. Lynn, Nicholas L. Abbott, and their coworkers at the University of Wisconsin, Madison, have been working to improve this process by developing lipoplexes containing redox-active groups that permit reversible electrochemical control over cell transfection.

The researchers reported last year that the known electrochemically controllable surfactant bis (11-ferrocenylundecyl) dimethylammonium bromide (BFDMA, shown) was a plausible lipid candidate, and they have been investigating the range of conditions over which it can work for cell transfection.

Using the standard COS-7 cell line, the team carried out transfection experiments with plasmid DNA constructs that encode fluorescent or bioluminescent proteins, which enables monitoring the extent of transfection by microscopy. They found a window of BFDMA concentration near 10 µM in which reduced BFDMA (with Fe²⁺) is nontoxic to the cells and yields high levels of transfection and gene expression of the proteins, whereas oxidized BFDMA (with Fe³⁺) yields very low levels of transfection. Dynamic light-scattering and neutron-scattering experiments showed that changes in the oxidation state of ferrocene lead to structural changes in the lipid-DNA aggregates, and the researchers surmise that these differences allow for the control.

The results demonstrate that ferrocene-containing cationic lipids could be used as a type of on-off switch to control DNA delivery to cells, Jewell said.

Microchannel flow-through chemical reactors have potential to replace bulk reactors for more efficient and environmentally friendlier production of industrial chemicals. They also are turning out to be valuable research tools to study catalytic reactions, according to Katie Barillas, Götz Veser, and their colleagues at the University of Pittsburgh.

The high surface-to-volume ratio in the reactors allows very precise control of reaction conditions, Barillas reported. The team's "simple and flexible" design involves etching submillimeter channels into silicon chips and coating the channels with platinum metal catalyst.

The researchers have been using the microreactors in a combination of simulations and experiments to investigate high-temperature air oxidation of hydrogen or methane. They are focusing on the interplay between heterogeneous reactions taking place on the catalyst-lined reactor walls and homogeneous gas-phase reactions taking place in the channels.

One of their key findings is that purely kinetic radical scavenging by the walls can completely suppress gas-phase side reactions, in particular NO_x formation during simulations of methane oxidation to make synthesis gas. These side reactions can degrade process selectivities and also trigger runaway reactions that can lead to explosions under the high-temperature, high-pressure conditions in larger reactors, Barillas noted.

The simulation studies further indicated that careful control of the amount of catalyst coverage on the microchannel walls can delay the start of a desired oxidation reaction along the length of the channels while still quenching the gas-phase reactions. "Quite surprisingly, under the right conditions, a catalyst could be turned from a reaction promoter to a reaction inhibitor," Veser told C&EN. This phenomenon could lead to "novel possibilities for tuning heterogeneous-homogeneous interactions," he said.

Overall, microchannel reactors could be important for developing efficient and safe processes for large-scale production of hydrogen or synthesis gas or for safer and low-polluting burning of hydrogen or natural gas to generate electricity, Veser noted.