How to convert CO2 to CH4 or C2H6??? 1

[nong]

Our offshore natural gas plant have 50MMscfd of CO2 which we burn out everyday. I heard about CO2 can be converted back to CH4 or C2H6 by using H2, heat and some catalyst.
I wonder that is it practical or economical? I know H2 is much expensive, so can we obtain H2 from H2O electrolysis or else?
If it's acceptable,this would reduce CO2 at flare, save environment, save the world!!

 

[vsvenkat7]

It is possible to convert CO2 to CH4 using H2 over a NiO catalyst as in the purification step of ammonia synthesis gas. However, we are talking about CO2 concentration in ppm level and that too the process involves operating the system above a minimum temperature of 250 degC.

However, for the quantity of CO2 you are talking about, it is better to scrub the gas with a solution of lime or look for a commercial process like soda ash preparation to use this CO2 gas - which might be commercially attractive.

 

[nong]

vsvenkat7,
I don't understand what you said. We have membrane process to scrub CO2 from nat gas. Gas to flase contain about 80% CO2 and 20%CH4.

 

[TD2K]

No, it's not economical Nong.

You burn CH4 to make CO2 and H20. Now, you essentially want to take H2 (which you can make from splitting H20 or steam reforming methane) and convert the CO2 back to methane. What you are essentially proposing is to go around and around in a loop and with inefficiencies in each step, you will lose money in the end.

CO2 rich streams are sometimes reinjected for enhanced oil production or to maintain reservoir pressure but that takes some expensive compression also. I would assume your company went through some sort of technical analyses when they decided on membranes so recovering the CH4 out of the waste gas stream with, for example, an amine system, likely isn't going to be cost efficient either.

 

[nong]

TD2K,
CO2 is from reservoir(38% of nat gas). I don't think that we burn CH4 to get CO2. We have membrane unit to separate CO2 to comply with GSA(23%). Then we burn separated CO2 (75%) with little bit CH4(25%) 50 MMscfd because of membrane efficiency. I just think that we could use this CO2 to make benefits also save environment or not. Many thanks to share idea.

 

[DeltaCascade]

Burn CO2? It is already a combustion product and will not be oxidized further. Make CH4 from CO2 without using energy? It seems that you could "save the world" with a perpetual motion machine...if only we lived in such a fantasy world! As TD2K said, it's not economical, neither is it energy efficient. This appears to be basic high school chemistry.

On the other hand, if you mean, getting that 20% of CH4 out of the flare stream ... well that would make sense ... sell it instead of flaring it, if recovery is economical! Is that what you mean?

Best wishes ...