Page 234 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 7 Gasification Theory 211

The second motivation for catalytic gasification is removal of methane
from the product gas. For this, we can use either catalytic steam reforming or
catalytic carbon dioxide reforming of methane. Reforming is very important
for the production of syngas, which cannot tolerate methane and requires a
precise ratio of CO and H 2 in the product gas. In steam reforming, methane
reacts with steam at a temperature of 700 1100 C in the presence of a metal-

based catalyst, and thus it is reformed into CO and H 2 (Li et al., 2007):
catalyst
CH 4 1 H 2 O ! CO 1 3H 2 1 206 kJ=mol steam reforming of methane
(7.22)

This reaction is widely used in hydrogen production from methane, for
which nickel-based catalysts are very effective.
The carbon dioxide reforming of methane is not as widely used commer-
cially as steam reforming, but it has the special attraction of reducing two
greenhouse gases (CO 2 and CH 4 ) in one reaction, and it can be a good option
for removal of carbon dioxide from the product gas. The reaction is highly
endothermic (Wang and Lu, 1996):
catalyst
CH 4 1 CO 2 ! 2CO 1 2H 2 1 247 kJ=mol dry reforming of methane
(7.23)
Nickel-based catalysts are also effective for the dry-reforming reaction
(Liu et al., 2008).

7.3.5.1 Catalyst Selection
Catalysts for reforming reactions are to be chosen keeping in view their
objective and practical use. Some important catalyst selection criteria for the
removal of tar are as follows:
Effectiveness
Resistance to deactivation by carbon fouling and sintering
Easily regenerated
Strong and resistant to attrition
Inexpensive
For methane removal, the following criteria are to be met in addition to
those in the previous list:
Capable of reforming methane
Must provide the required CO/H 2 ratio for the syngas process

Catalysts can work in both in situ and postgasification reactions. The
former may involve impregnating the catalyst in the biomass prior to gasifi-
cation. It can be added directly in the reactor, as in a fluidized bed. Such
application is effective in reducing the tar, but it is not effective in reducing