Sciencemadness Discussion Board

CO2 to CO

chemrox - 22-2-2007 at 20:08

As part of my ongoing effort to discover possible solutions to the end of cheap and easy petroleum, I've been re-reading the Fischer-Tropsche process. This Fischer was an amazing scientist. He devised methods for making petroleum by the carload in small plants. But he was starting with coal gassification and using CO as a precursor. Id like to read anything done on CO2 reduction and am having trouble finding sources or formulating the right search terms. If we could start with CO2 we'd at least have a CO2 balance. I need to find out what I'm up against. The change in entropy is about 30 kJ/mole. That doesn't seem an insurmountable barrier in itself.

Ozone - 22-2-2007 at 20:35

It is much easier to perform a "lean" oxidation than a reduction of any sort. Gasification tends to be a compromise between substrate reactivity and O2 applied at the given temperature.

So, where it is relatively simple to produce CO (and H2) from biomass, lignite, etc., it is not easy (or energy efficient, in *most* cases) to reduce CO2 to CO (unless you can invent a really efficient, stable catalyst operating under recycled H2).

Reformer gas might be an option, but I tend to go with the devil I know.

Cheers,

O3

not_important - 22-2-2007 at 20:43

But generating CO from carbon (coal) means using more fossil fuel, as does making it from natural gas.

A search turned up a recent conversation on this, with some numbers, and some alternative fuels as targets rather than petroleum-like fuels.

http://www.dailykos.com/story/2007/2/21/94023/9685

Ozone - 22-2-2007 at 21:04

True,

But making it from reactive agriwaste (bagasse, corn stover, etc.), with the exception to the loss of total high heat value (which is lost in the conversion) is feasible (see fluidized bed).

Too bad that the steam engine is not "in vogue"; conversion to more standardized fuels results in a net loss of fuel value.

Good night,

O3

12AX7 - 23-2-2007 at 00:03

CO2 + H2 = H2O + CO. I don't know if this is exothermic, check it.

Also, CO2 + C = 2CO. If you're talking about making petroleum, you'll be using up carbon anyway. This reaction is easily observed in a thick bed of ignited charcoal (or other carbon) with slow air blast.

Tim

not_important - 23-2-2007 at 01:45

Quote:
Originally posted by 12AX7
CO2 + H2 = H2O + CO. I don't know if this is exothermic, check it.

copied from the link I gave earlier:

Making carbon monoxide
CO2 + H2 <=> CO + H2O takes 41.2 kJ/mol
Quote:
Also, CO2 + C = 2CO. If you're talking about making petroleum, you'll be using up carbon anyway. This reaction is easily observed in a thick bed of ignited charcoal (or other carbon) with slow air blast.

Tim


The point is to not use fossil carbon, but either sequestered carbon dioxide or recent biologically fixed carbon.

12AX7 - 23-2-2007 at 09:14

Well, it's quite easy to convert "recently biologically fixed carbon" into carbon carbon. You even get workable distillates in the process of producing this carbon. (I even posted "charcoal", not specifically "coal" for instance.)

Tim

bereal511 - 23-2-2007 at 09:20

Why not work directly from biologically fixed carbon? It seems as though the energy usage to convert carboneceous compounds into petroleum is a bit wasteful, when you could probably thermolyse or pyrolyse the material.

12AX7 - 23-2-2007 at 09:58

Nobody wants to convert their car to a Stirling powered car that needs to be shovelled full of wood pellets and warmed up perhaps a whole minute before use.

Tim

bereal511 - 23-2-2007 at 11:01

Quote:

Originally posted by 12AX7
Nobody wants to convert their car to a Stirling powered car that needs to be shovelled full of wood pellets and warmed up perhaps a whole minute before use.


Well, not quite what I meant by working directly with fixed carbon. The actual conversion would be worked on an industrial of course. If one were to convert the wood components to distillates in a more direct fashion (i.e. pyrolysis) and collected/refined to petroleum-like compounds, would it not be less energy intensive? Pyrolysis occurs at around 500 degrees C and hydrothermolysis occurs around 200 degrees C, while biogasification would need up to 700 degres C to occur.

chemrox - 23-2-2007 at 14:13

Quote:
Originally posted by not_important
But generating CO from carbon (coal) means using more fossil fuel, as does making it from natural gas.


Yes, that's why I'm trying to develop a catalyst for the conversion of CO2 -> CO

chemrox - 23-2-2007 at 14:17

Quote:
Originally posted by 12AX7
Nobody wants to convert their car to a Stirling powered car that needs to be shovelled full of wood pellets and warmed up perhaps a whole minute before use.
Tim


Nobody will want to convert his car until there's no more petroleum.

The US is waging war on the middle east to get the last 100b barrels.. at least that's how I see it .. no wonder they're pissed off.

Levi - 24-2-2007 at 01:22

Quote:
Originally posted by 12AX7
Nobody wants to convert their car to a Stirling powered car that needs to be shovelled full of wood pellets and warmed up perhaps a whole minute before use.

Tim


Lol. I do! Where can i get one?

not_important - 24-2-2007 at 01:32

Quote:
Originally posted by chemrox
Quote:
Originally posted by not_important
But generating CO from carbon (coal) means using more fossil fuel, as does making it from natural gas.


Yes, that's why I'm trying to develop a catalyst for the conversion of CO2 -> CO


There are many known catalysts for the reaction, and some that take you to products further downstream. I think it mentions to Korean process for taking CO2 and H2 to dimethyl ether, an alternative fuel. Note that there are cleaner buring - less NOx and particulates - fuels than the conventional long chain hydrocarbons; most of these fuels are also better targets for production from CO2 or CO, better conversions, less byproducts.