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Name: Abigail
Status: Student
Grade: 9-12
Location: WI
Country: USA
Date: April 2005


Question:
Dear Sir or madam,

I am in debate, and this year's topic is "Resolved: That the United States should change its energy policy to substantially reduce its dependence on foreign oil." Each team argues for the resolution with a plan that they have written in one round, and in the next argues against another team's plan to change the energy policy. One popular plan that my partner and I have come against is thermodepolymerization. We are having trouble finding evidence that TDP has disadvantages, will not work on a large scale, etc. We have thought of several potential problems with it, but have not been able to back up our questions with evidence. Our Regional Tournament is coming up, and we still have very little evidence against TDP. Despite hours of research, I haven't been able to discover whether or not it costs more, whether or not only biodegradeable wastes can be used, what constitutes "organic wastes" and whether or not we have enough of them, if the private sector is widely willing to invest in TDP, what grade of oil it produces, what refining process it has to go through, if it has safety issues (especially in the production stage), and if it causes environmental damage, etc.

I really appreciate your taking time to answer questions for kids and teens--I really, really value your answers and advice. If you have any web sites or links that you could recommend, I would be quite grateful.



Replies:
Regarding "thermal depolymerization" [TDP]. There is a large literature "out there" on TDP. The problem in finding the literature is one of "jargon". TDP, in the jargon of polymer chemistry, is called "unzipping", so if you do a Google search on the terms "unzipping polymers" or "unzipping copolymers" you will enter the literature jungle on the subject. There are a number of considerations:

1. Ease of de-polymerization, i.e. how hot and under what conditions will a polymer "unzip". Styrene, alphamethyl styrene, and methacrylates are vinyl polymers that will thermally "unzip" and produce the starting monomers at a relatively low temperature. Other vinyl polymers are more or less difficult to "unzip". The issue is one of energy input / cost vs. monomer yield, purification, cost, and reprocessing for reuse. You will have to do some model calculations involving energy cost, product separation and purification for re-use. In general oxygen would have to be excluded, otherwise oxidation will occur.

2. Condensation polymers, such as polyesters, cellulose polymers, polyamides, and bio-polymers require a different set of conditions (hydrolysis or reaction with water) is required to unzip these polymers because you have to reverse the general reaction: A--H + B--OH ----> --A--B-- + H2O. These reactions produce monomers A--H and B--OH which then have to be separated and purified for re-use. There are also issues of other materials present that could be re-cycled on the one hand, or disposed of, on the other. Here high temperature and pressure, especially the steam pressure, are major issues. Biopolymers are readily depolymerized on an analytical scale -- this is the basis for DNA "fingerprinting". However, whether this can be done on a manufacturing scale is problematic.

In either case the point of vulnerability is whether, even at the present record cost of petroleum, does the cost of recycling compare favorably with the cost of virgin monomer. I suspect it does not, but I have no data to support that.

Vince Calder



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