Catalysts marry many molecules.
  fantastic plastic lover

bride n groomMOLECULES. How to marry them? I figure you don't give it a second thought. Unless you're a chemist. Then you'd know that a ton of useful compounds are built by marrying long chains of simple molecules together.

You'd know that finding the best way to link up these simple molecules is a big deal, particularly in the plastics business. Plastic makers use plastic lovelots of catalysts (compounds that speed up reactions without getting consumed) to make these molecular marriages.

These days, plastics chemists are obsessing with catalysts called metallocenes. Metallocenes are made of one metal atom held between two rings of carbon atoms. There's some other jazz hooked up around the edges, and while one metallocene may look pretty much like another, details count. That's because the structure of a catalyst must hold small molecules together so they can quickly be linked up into chains of molecules.

On Oct. 1, University of Rochester chemist Guillermo Bazan announced a breakthrough in metallocene catalyst technology. His trick?

  Adding boron atoms to a standard metallocene structure. That sounds pretty, well, pedestrian.

Where's the so-what?
Here. Industrial observers are enthusiastic about the new catalyst. "This is a spectacularly interesting finding," says Rick Kemp, a senior research scientist at the Union Carbide Corporation and an expert on alpha-olefins. Alpha-olefins are a key chemical building block -- a raw material for innumerable chemicals that are made into plastic bags, soaps, detergents, oils and more plastics. In fact, Bazan says, alpha-olefin is a "very small plastic."

Could this new catalyst cut costs in the chemical industry? Baby blue = zirconium, gray = carbon, green = chlorine, pink = boron, and red = oxygen. Courtesy University of Rochester.   Chemical companies make billions of pounds of alpha-olefins each year. But Kemp says the new catalyst, described in the Oct. 1 Journal of the American Chemical Society, "appears to yield products that are virtually 100 percent pure, a trait that's increasingly desirable in industry."

Presently, alpha-olefins are made in reactors working at hundreds of times atmospheric pressure, and at hundreds of degrees Celsius. In contrast, Bazan's catalyst works at humdrum atmospheric pressure, and doesn't need much heat.

All that high-temperature, high-pressure stuff is not cheap to build and operate, so the new catalyst could make alpha-olefins safer, and presumably cheaper, than today's processes. Simply by varying the pressure and other conditions, the system also allows precise control over the structure of the product.

So where's the snag?
Here. Before Bazan's brainchild can enter production, it will have to pass a couple of hurdles. For one thing, he's only made a few grams of alpha-olefins. Since industry uses the stuff by the billions of pounds, a planned scale-up demonstration is needed to prove that the catalyst can work on a large scale.

The new catalyst might work in existing reactors, but any new reactors could be cheaper and simpler to build, A new catalyst could cut costs and boost safety in the plastics industry.

Bazan notes, since they would not need to handle extreme pressures and temperatures.

Also unknown is the price of the catalyst. Current plastic-industry catalysts are so cheap that they are not recovered (they're just entombed at tiny concentrations in the final product). An expensive catalyst might have to be recovered, implying a major change in equipment.

But why add boron instead of, say, silicon or seaborgium? Because Bazan knew boron would "lower the electron density" (remove electrons), thus altering how the catalyst interacts with the raw material. And since the catalyst must grab many small molecules, link them together, and repeat this process thousands of times, small alterations in the way it interacts can mean the difference between success and failure.

As Bazan plunges ahead with pilot tests, suffice it to say that his new catalyst has catalyzed considerable curiosity among chemical engineers. POSTED 16 OCT 1997.

-- Dave Tenenbaum

The Why Files


Credits | Search