Steam Gasification and Reforming Technologies
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in nature, but literature has shown that too much basicity does not help the
reforming process. Along with Al 2 O 3 , lanthanum, cerium, and zirconium
oxides need to be examined. Just like mixed metals, mixed supports should
also be considered.
In more recent investigations on dry reforming, the overall objectives have been to
devise (1) a process that has less coke deposition on the catalyst such that the catalyst
is active and stable for a long period, (2) a process in which the catalyst ignites at as
low temperature as possible, (3) a process that is heat efficient, (4) a process in which
high conversion of CO 2 and hydrocarbons is achieved, and (5) a process in which
major products are carbon monoxide and hydrogen. As indicated earlier, the last
objective is a particular problem without deep dehydrogenation when the hydrocarbons contain two or more carbon numbers.
4.4 tri-reFOrminG
Fundamentally, there are three types of high temperature reforming processes:
stream reforming, dry reforming, and partial oxidation [57,63–65]. The term
“tri-reforming” is applied to the process in which all of these reforming processes
are combined in a single use. The three reforming processes are expressed by the
following set of chemical reactions for methane:
1. Steam reforming: CH 4  + H 2 O → CO + 3H 2
ΔH
0
298 K  = 206 kJ/mol
2. Dry reforming: CH  
H 2
ΔH
0
4 + CO 2  → 2CO + 2
298 K  = 247 kJ/mol
3. Partial oxidation: CH  
0
4 + O 2  → CO + 2H 2
ΔH 298 K  = −38 kJ/mol
The water–gas shift reaction always accompanies these three reactions. The major
technical problem of conducting steam reforming alone is carbon deposition on the
catalysts that can lead to rapid deactivation and breakup of the catalyst. Carbon
deposition can be substantially reduced by the use of an excess of water and a temperature of about 800°C. Other drawbacks of stream reforming are (1) the expensive
generation of superheated steam (in excess) at high temperature; (2) the production
of a significant amount of CO 2 in the product gas causing the onset of reverse water–
gas shift reaction (CO 2 + H 2 → CO + H 2 O) particularly at high temperature; and
(3) the H 2 -to-CO ratio is higher than the optimum required for the downstream synthesis gas conversion to methanol, acetic acid, or hydrocarbons.
Partial oxidation offers some advantages over steam reforming. The reaction produces extremely high yields of syngas by an exothermic reaction, and therefore, the
reactor would be more economical to heat. Oxygen is often used in steam reforming
to provide heat and high methane conversion. Partial oxidation also gives a better ratio
of hydrogen to carbon monoxide for subsequent conversion processes. The product
gases from the reaction are low in carbon dioxide that must often be removed before
the syngas can be used. Steam reforming and partial oxidation produce syngas of more
moderate H 2 /CO ratio (of about 2). This makes the direct use of syngas more versatile.
The dry reforming has the added advantage that it simultaneously consumes
two greenhouse gases: hydrocarbons and CO 2 . The best reducing agent for CO 2