Another CO2 roach motel?

As we all know the mystery is solved by tracking down the dog who did not bark in the night? Your challenge, dear anonymice, is to spot the dog in this story which is making its rounds.

UCLA chemists report a major advance in reducing heat-trapping carbon dioxide emissions in the Feb. 15 issue of the journal Science.

The scientists have demonstrated that they can successfully isolate and capture carbon dioxide, which contributes to global warming, rising sea levels and the increased acidity of oceans. Their findings could lead to power plants efficiently capturing carbon dioxide without using toxic materials.

"The technical challenge of selectively removing carbon dioxide has been overcome," said Omar M. Yaghi, UCLA's Christopher S. Foote Professor of Chemistry and co-author of the Science paper. "Now we have structures that can be tailored precisely to capture carbon dioxide and store it like a reservoir, as we have demonstrated. No carbon dioxide escapes. Nothing escapes -- unless you want it to do so. We believe this to be a turning point in capturing carbon dioxide before it reaches the atmosphere."

If you are of teh scientifical bent you can read more in Science

A high-throughput protocol was developed for the synthesis of zeolitic imidazolate frameworks (ZIFs). . . . Members of a selection of these ZIFs (termed ZIF-68, ZIF-69, and ZIF-70) have high thermal stability (up to 390°C) and chemical stability in refluxing organic and aqueous media. Their frameworks have high porosity (with surface areas up to 1970 square meters per gram), and they exhibit unusual selectivity for CO₂ capture from CO₂/CO mixtures and extraordinary capacity for storing CO₂: 1 liter of ZIF-69 can hold 83 liters of CO₂ at 273 kelvin under ambient pressure.

and Nature Materials. Investors can go to the USPTO and look up the patent application. The $64,000 question (Eli is old and cheap) is what's missing in all these write ups?


Bunnies and anonymice can get an idea from the perspective on this in Science by Robert Service

On page 939, Yaghi and colleagues report a new robotic high-throughput scheme for creating MOF relatives known as zeolitic imidazolate frameworks (ZIFs). And Mallouk and others say that the work is again an important blend of fundamental research and a critical application: materials that might help coal-fired power plants filter out carbon dioxide from their smokestacks. Mallouk calls the new work "very clever" because Yaghi and his colleagues have designed their hubs and linkers to mimic the construction of zeolites, a family of natural porous compounds widely used as catalysts and filters in industry. But because ZIFs are stable at high temperatures and are easier to tailor by adding desired chemical functional groups, they may prove even more useful in the long run.

One key race is to create a MOF that can store hydrogen for use in future fuel-cell cars. High-pressure gas tanks do the job fairly well. But pressurizing gases is a big energy drain and can create a hazard if the gas tank is punctured in a crash. By filling part of the tank with a MOF's cagelike network built with hydrogen-absorbent metal hubs and organic struts, however, it is possible-- at least in theory--to store more of the gas at a lower pressure. Slightly raising the temperature or releasing the pressure then liberates the gas. Yaghi's group and Jeffrey Long's group at UC Berkeley both recently created MOFs that can hold up to 7.5% of their weight in hydrogen, better than a benchmark for hydrogen storage set by the U.S. Department of Energy. Unfortunately, they only do so at 77 kelvin (-196°C), making them impractical for real-world use.

In July 2007, researchers led by William Goddard III of the California Institute of Technology in Pasadena reported in the Journal of the American Chemical Society that adding lithium to a MOF should make it possible to store 6% of its weight in hydrogen at room temperature. Long says many groups are working on it, but "it's not trivial." Lithium, he points out, tends to hold strongly to solvent molecules after synthesis, and removing the solvent requires so much energy that it typically blows apart the framework.

To put it bluntly, these things could be roach motels, the CO2 checks in but it can't check out, or the energy bill at check out makes the entire exercise academic. That makes them not very useful since the cost of synthesis and the mass of material needed requires that any capture method has to cycle tons of time. Yaghi says the ZIFs can be cycled, but what is the energy needed to cycle the system, how many times can it be cycled and what is the loss of the ZIF effectiveness per cycle. Eli has seen a lot of pretty chemistry founder on engineering issues and when something like this, a well known issue with respect to hydrogen storage, is not discussed his nose twitches.

UPDATE: A number of other important issues are raised in the comments below. Eli urges you to read them. Among them:

1. Tim McDermott- So 1 liter of ZIF-69 can capture 155 grams of CO2, which is 44 grams of C. Woot the problem is solved!
2. How will these things do in the presence of water vapor which screws up zeolites - Bocco
3. A good point is that the isotherms are constant implying they can handle changing pressure - Bocco
4. David Benson likes chilled ammonia (he must come from Jupiter!:)

and more. Read the comments.

Yaghi's lab has made a step forward, but much remains to do.