[Paleopsych] depolymerization doubts (energy future)

[Lynn D. Johnson, Ph.D.]

My smart brother (prof, chem engineering, expert in mathematical 
modeling of chemical processes) says the following about thermal 
depolymerization in regards to the Discover article:

Dear Lynn, 

Sorry for the slow reply. I've been busy trying to finish sections of the 
book I'm working on. 

I just read the article you attached and read some (not all) the comments 
on the web pages. 

Random thoughts:
Depolymerization is indeed possible and has been performed on different 
materials for a long time.

Breaking chemical bonds takes a fixed amount of energy. You can't cheat 
thermodynamics (at least you can't and get an A in my class). Therefore, I 
doubt the claim of 85% efficiency. I do not see how that can possibly be 
close to the correct number. The process they describe requires a good 
deal of mechanical and thermal energy. Even if you put water in (as they 
claim about making water your friend) then you still have to provide about 
350 kJ/mol of energy to break a carbon-carbon bond. Hence, I can't see how 
you could get 85% efficiency. Maybe I'm wrong, but it would mean that you 
are only breaking about 15% of the bonds in the material that you are 
depolymerizing. That seems unlikely to produce "pure oil" as claimed. 

Could it work? Yes. Does it work as advertised? I doubt it. Maybe I'm 
wrong. There's really not enough information there to analyze the process. 

Water at high temperature and high pressure has been used to degrade 
organics before, but typically they use supercritical or near-critical 
water. This does not mean water that nags you to pick up your socks, but 
water that is near 650 K = 377 C = 710 F and 220 bar = 3200 PSI. Their 
process is at 500 F and 600 PSI. Still, I think you could do some fairly 
aggressive chemistry at those conditions that would require higher 
temperatures otherwise. 

The other thing that bothers me is this claim:
Dehydration via depressurization is far cheaper in terms of energy 
consumed than is heating and boiling off the water, particularly because 
no heat is wasted.

The fact is that it still costs energy to vaporize water. If you have to 
vaporize 1 kg of water it will take you about 2000 kJ, no matter how you 
do it. The heat of vaporization changes as a function of temperature, 
decreasing at higher temperatures. However, I don't see any way to cheat 
thermodynamics. 

If you don't vaporize the water, but instead separate it in a two-phase 
separator then you can do the separation for much less energy. I.e., you 
rely on the fact that oil and water don't mix and take the oil off the top 
of a gravitational separator or cyclone separator. 

End random thoughts.