Some of the ingredients in many common household products, from laundry soap to plastic toys, are made by an industrial process called hydroformylation.
The process requires a material called a catalyst to speed up the reaction. Currently, the chemical industry uses inexpensive cobalt catalysts to do the job. But they require high temperatures and pressures and produce unwanted by-products. And toxic solvents are used to recycle the catalyst.
The Center for Environmentally Beneficial Catalysis, or CEBC, is developing a new hydroformylation process to save energy, prevent waste, and reduce toxicity. It operates at milder conditions and uses a rhodium catalyst, which significantly out-performs the conventional cobalt catalyst.
But rhodium is not cheap. It is the most expensive precious metal, with current prices around $26,500/lb! For the greener CEBC method to be adopted by industry, it must be made economical. To do this, no more than 0.2% of the rhodium can be lost during the process. This translates to a rhodium loss of about 1.3 cents per pound of product.
A recent economic analysis of the CEBC process predicts that about 0.4 cents of rhodium would be lost per pound of product – significantly less expensive than the economic criterion. This means that the process has promising commercial viability.
Jon Tunge, associate professor of chemistry at the University of Kansas, leads the CEBC effort to invent a method to prevent loss of the rhodium catalyst. The tiny catalyst is attached to a bulky side group, called a polymer. This “polymer-bound catalyst” can be separated just as coffee grounds are filtered from a pot of coffee, except that in this case the bulky material remains dissolved and does not clog the filter.
“Two recent discoveries have significantly improved this process and strengthened the economic viability,” said Darryl Fahey, CEBC Industry Liaison Director.
First, Ranjan Jana, postdoctoral researcher at CEBC (above), has improved the method for making the bulky polymer. In the old method, a wide range of different sized polymers was produced. Now, fewer of the small-sized polymers are made. This means that a much smaller fraction of the rhodium is lost through the filter. Once stable operation is reached, only ultra-low quantities of rhodium are detected in the product. “Our studies show less than 1 part-per-million of rhodium is lost into the product mixture,” said Jing Fang, another CEBC postdoctoral researcher working on the project.
Second, the reactor has been modified to enable improved stirring. The process combines syngas (a mixture of carbon monoxide and hydrogen gas) with a liquid called 1-octene. Better stirring helps dissolve the syngas in the liquid. This has resulted in faster conversion rates and improved selectivity (over 95%) to the desired product (1-nonanal).
Ongoing research is expected to further improve the process and lower the costs even more.
CEBC was established at KU in 2004. Its purpose is to speed up the development of greener, more efficient industrial processes for chemical and fuel production.
--Story by Claudia Bode