|Carbon Dioxide as a Polymer Feedstock
|Dated: 24 Sep 2008
|Sep 24, 2008
Carbon Dioxide as a Polymer Feedstock
This editorial takes a look at one of nature's most abundant materials and also one that is given environmentalists nightmares - carbon. What if we could use good old CO2 as a polymeric? Brilliant!
There are many efforts now underway by large, multinational companies such as General Electric on carbon dioxide capture or sequestration. These projects are aimed at developing processes by which the industrialized world can safely dispose of CO2, which is mainly generated at coal fired electricity plants. The alternative, of course, is to let it rise in the replica watches uk, contribute to a greenhouse effect, global warming and an environmental nightmare.
CO2 has been captured for uses in various commercial and industrial processes for decades. Limited markets exist for commercially produced CO2. It is used, for example, to make carbonated drinks and for a few processes at refineries and other industrial facilities. It is also injected into oil wells to increase production from declining fields. Once injected, the CO2 remains permanently sequestered from the atmosphere. 1
Wouldn't it be wonderful if polymer chemists could find a productive use for CO2? In fact, there are several efforts aimed at doing just that. CO2 is an interesting potential synthetic feedstock since it is abundant, inexpensive, non-flammable, and a waste product of many chemical processes.
It is estimated that nature uses CO2 to make over 200 billion tons of glucose by photosynthesis each year. However, chemists come in a poor second to mother nature. Synthetic chemists have had little success in developing efficient catalytic processes that can exploit this material.
The activation and application as a carbon source are rather limited. For example, in the organic materials area only urea, salicylic acid, and some cyclic carbonates can be viably produced from CO2. However, CO2 can be copolymerized with heterocycles (epoxides, aziridines, episulfides) to yield novel alternating copolymers.
Of these, polycarbonates represent a very promising class of material; they are thermoplastic and can be produced in reasonable efficiency from C02 and epoxies. Initial studies have also indicated that aliphatic polycarbonates can be recycled via hydrolysis reactions and in some cases biodegraded.
Way back in 1969, researchers found a way to make biodegradable plastics called aliphatic polycarbonate from CO2. Zinc catalyzed sequential copolymerization of CO2 and epoxide was reported as a route to producing polycarbonates. This discovery illuminated for the first time the potential of CO2 as a feedstock for large-scale polycarbonate systems. Alternating copolymerization of CO2 and propylene oxide has also been found to yield polypropylene carbonate (PPC), a thermoplastics material that can be processed by molding or extrusion.
Affordable, biodegradable plastics made from CO2 are moving closer to market. Novomer (Ithaca, NY, USA), a Cornell University spin-off is exploring a different catalyst technology to produce aliphatic polycarbonates. Novomer claims to be able to convert CO2 into everyday plastics such as packaging, cups, and forks. Currently, the plastic is being made on a pilot scale, and Novomer declines to give details of its commercial-scale manufacturing plants. 2
As any technology that promises such staggering paybacks, the conversion of CO2 to a polymer feedstock is not without mammoth hurdles. One is that CO2 is very stable, and it takes extra effort to activate the molecule so it will react. The processes are expensive, and only the most optimistic onlookers expect that CO2 can produce polymers that will eventually compete with petroleum-based products. Another problem is so much of the unwanted greenhouse gas is escaping into the atmosphere that even shunting millions of tons of it each year into making chemicals will not have much effect on global warming.
However, CO2 is also beginning to find use in several interesting processes that are not related to plastic feedstock:
It has been discovered that CO2 can be used widely as a solvent. For example, supercritical CO2 (the state existing at 31ฐC and 72.8 atm) offers advantages in product purifications and stereochemical control.
CO2 is also being explored for use in ponds filled with genetically modified algae that can convert CO2 from power plants into bio-diesel.
Frozen pellets of C02 at -73ฐC have also been used as an abrasive cleaning agent for surface preparation and removal of corrosion and old coatings from substrate surfaces. Not only does this provide an abrasive mechanism, but also certain inorganic salts and organic contaminants can be dissolved with the CO2.
Let's hope that scientists get ahead of the global warming curve. It's important to find something to do with CO2 before it finds something to do with us.
1. Ritter, S.K., What Can We Do with Carbon Dioxide?, Chemical & Engineering News, Vol. 85, No. 18, 2007.
2. Patel-Predd, P., Carbon Dioxide Plastic Gets Funding, MIT Technology Review, November 200
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Edward M Petrie