9 replies to this topic

[A mukherjee]

Hello everybody,
I need help urgently.
There is a catalytic fixed bed reactor in CO2 plant.

The reactor is for converting methane (present in CO2 feed) to CO2 & H2O.The operating pressure & temperature of the reactor is 17 barg & 450 degc respectively.Actually I am bit confused about the step of reaction.There may be two ways:
1.Methane cracks at 450 degc to form Carbon & H2.Then they react with O2 to form CO2 & H2O respectively.
OR
2.Methane reacts directly with O2 to form CO2 & H2O.

Can any one suggest me the correct path of reaction?Is 450 degc sufficient for cracking of methane at 17 barg?

Regards,
Arpan

[A mukherjee]

????????????

[engg]

????????????

i guess if there is O2 (or air being blowed) in the reactor then we might say there is combustion Ch4 + O2....otherwise not and also i have never heard of a catalyst for combustion.
What is the bed material, catalyst? this might give a hint.

[A mukherjee]

Reactor bed catalyst is palladium.

[ankur2061]

Arpan,

Refer the following link. It is a good presentation on methane reforming:

http://shgr.unlv.edu...arch_5_2004.pdf

Regards,
Ankur.

[A mukherjee]

I have already gone through it. Any way thnaxx...

[engg]

Reactor bed catalyst is palladium.

what is % methane in gas and why is methane required to be converted? so basically what is the process

Edited by engg, 15 September 2011 - 06:04 AM.

[A mukherjee]

The feed stream entering the reactor mainly consists of CO2 (More than 99%).The rest consists of N2,O2 & Other hydrocarbons.CH4 is present at around 900 ppm.
The reactor has been provided to oxidise the hydrocarbons to CO2 & H2O.
Hope it will clear your doubt.

[kkala]

Cracking of hydrocarbons heated in tubes (not specifically CH4) starts at about 360 oC but gets severe above 438 oC, according to http://www.cheresour...h__1#entry35152. CH4 looks more heat resistant, according to http://www.fischer-t..._10ch4crack.pdf. Cracking temperatures are about same, but in the presence of Fe-Mo catalysts (1st diagram of Web reference), while cracking without catalyst would start at temperatures above 600 oC (non oxidative environment).
Catalyst plays an important role in reaction mechanism and it is now Pd in an oxidative environment. Cracking of methane at 450 oC as controlling step of the reaction cannot be excluded, seeing that even a very small amount of cracked CH4 can be immediately oxidized, thus promoting more and more cracking to sustain equilibrium.
Reaction mechanism can be revealed either by catalyst supplier, or by litterature dedicated to this catalyst, unless some member has got the specific experience.

[kkala]

Further googling "Pd catalyst methane oxidation", "palladium oxidation methane", "Pd catalyst hydrocarbon oxidation", etc, reveals info giving the impression that CH4 oxidation in question follows way (2) of A mukherjee's post (14 Sep 2011), that is direct oxidation:
Pd + 1/2O2 <---> PdO (200-700 oC) and CH4+4PdO --->4Pd+CO2+2H2O
http://www.rsc.org/e...42142-00001.pdf, http://scienzechimic...t/dbb2.file.pdf,
also other free references (some articles, not approached, require payment).
Controlling step may be diffusion of combustion products out of catalyst pores.
It is noted that conditions similar to 99+% CO2, 0.09% CH4 + a bit other HC,etc, were not found, pressure (17 barg) was ignored, my understanding is limited on these matters. One aware of the subject can understand / evaluate Web data critically, answer without ambiguity can be there.

Edited by kkala, 17 September 2011 - 12:16 AM.