Recycler on a Mission
Christopher Bielawski | University
of Texas
Christopher Bielawski is a recycler on a mission. Some people
recycle water bottles (at 5 cents each). Dr. Bielawski’s
work could lead to a more efficient way to recycle metal catalysts like palladium
and rhodium (each about $5,000 a pound) and platinum (a whopping $18,000 a pound).
It could give such costly catalysts unlimited lifetimes by teaching them how
to change their size, depending on whether or not they are working.
Metal catalysts, reagents that help other chemical reactions proceed in an efficient
manner, are vital to such industries as plastics and pharmaceuticals.
A Modular Approach to Conjugated
Organic and Organometallic Polymers: We have recently discovered that difunctional
N-heterocyclic carbenes and their presursors are versatile and useful building
blocks in the construction of conjugated polymeric materials: they can
be homopolymerized or copolymerized with electrophiles including various
transition metals to form the respective organic and organometallic polymers.
We are currently exploring their use in electronic devices, as new drug
delivery systems, and as the foundation for self-healing materials.
In the past, one method to modify a catalyst was to tag it with some material
that enabled isolation. For example, with a water-soluble tag, you
could simply add water when your chemical reaction was over and extract
your catalyst. Unfortunately, such tags are often extremely large, which
ends up interfering which the basic operation of the catalyst.
“That’s the obvious way. We have come up with a novel idea for reusing
catalysts,” Dr. Bielawski said.
At his lab in Welch Hall at the University of Texas, his team is blending
many disciplines of the chemical sciences – organic chemistry, polymer
chemistry and inorganic chemistry – to devise a new and simple way
to recycle catalysts.
The goal is to design a system that works without the need for tags. His
approach is to develop very large, easily isolated materials that fall
apart into small catalysts and then come back together later on. Dr. Bielawski
offers this whimsical illustration:
“Imagine a group of people who represent a group of catalysts. If each
catalyst’s job was to carry wood from one end of a forest to another,
more work could be done if everyone ran and carried wood separately. But
it would be far easier to keep track of everyone if they held hands and
moved together.”
Catalyst recycling would work in a similar way.
“Since large molecules are generally easier to recover than small molecules,
we hope to teach each catalyst to join hands when all of them are done
doing what they do.”
“In the past, we’ve made very large molecules that can fall apart
into pieces under certain conditions, and come back together when we remove those
conditions,” he said. “Right now we are modifying these systems
so that they fall apart to form catalysts of interest to the chemical industry.”
Benefits might include big savings for industry and consumers – since the
field of catalysis represents up to 25 percent of the world’s gross
national product, which is now about $46 trillion. The findings might help
the environment by reducing waste as well as resources consumed.
In the pharmaceutical industry, the method could also help remove unwanted
toxic metals – which are often present because they are used as catalysts – from
the medicines supplied to consumers.
Ultimately, Dr. Bielawski and his research group hope to develop a general
strategy so that all catalysts, including those that have not yet been
developed, can be quickly and easily converted into recyclable variations.
“You could cycle between two states – maximum catalyst performance
and maximum recoverability,” he said. “In one state you would
have large molecules that are easy to recover and, in the other, you have
a bunch of little catalysts that rock and roll.”
Nov. 1, 2007
