57
Steam Gasification and Reforming Technologies
Generally, nickel and other noble metal catalysts, alone or composite bimetallic
or trimetallic form, work well. The literature has shown that coking and catalyst deactivation issue can be partially addressed by the use of pervoskite and
hydrotalcite (HT) catalyst supports with ABO 3 functionalities. Lanthanum- and
strontium-based supports were found to be more effective. These catalysts reduce
the degree of coking and the resulting catalyst deactivation. Dry reforming reaction produces H 2 /CO ratio of 1, which is lower than 2 for partial oxidation and 3 for
steam reforming.
Dry reforming gives good conversion generally at high temperature (around
850°C). Dry reforming is more endothermic than steam reforming and must be
carried out at high temperature and low pressure to achieve maximum conversion.
Besides noble metals, transition metal carbides (especially Mo) are also effective, but
these catalysts are stable only at high temperatures.
There are at least two examples of the commercial process for the dry reforming of methane [57–62]. The industrial caloric process (CALCOR), which has been
developed using nickel-based catalysts, is used for the production of CO-rich synthesis gas from natural gas or liquefied petroleum gas using a large excess of CO 2 .
Pure carbon monoxide is an important chemical feedstock, for example, in the production of acetic acid and phosgene, and it is important to produce on-site due to the
transportation risks caused by its toxicity. This multistage process was developed
by Caloric GmbH. In the first stage of the process, carbon dioxide and methane
are reacted together producing a mixture of carbon monoxide, hydrogen, carbon
dioxide, and water. The heat for the endothermic reaction is provided by the burning
of fuel in a similar manner to the steam reforming process. In the next stage, carbon
dioxide in the effluent stream is removed and recycled to the reformers. Carbon monoxide is separated from hydrogen (which can be used as a fuel and sold) and methane
leaving only a very small amount of methane remaining in the product stream and
giving purities up to 99.95%. The coking is prevented by packing the reactor with the
catalyst that has varying activities and shapes.
The dry reforming of methane has also been practiced by the SPARG (sulfurpassivated reforming) process created by Haldor Topsøe [57–62]. It was commercialized at Sterling Chemicals Inc., Houston, Texas, in 1987. The process produces
a variety of syngas compositions [57–62] and reduces H 2 /CO ratio from 2.7 to 1.8
without modification in steam reforming facility [38–43]. The process is operated at
915°C–945°C and coke deposition on Ni catalyst is reduced due to the treatment of
the catalyst by sulfur. The process uses mixtures of CO 2 and H 2 O, and thus, it is a
combined dry and steam reforming process. Impurities such as methane, hydrogen,
or other hydrocarbons in the feed stream decrease the mechanical strength of polycarbonates produced from syngas via phosgene reaction path. Higher hydrocarbons
are therefore removed in the pre-reforming step to reduce the product impurities as
well as coke deposition on the catalyst. Sulfur in the product may require additional
purification steps.
The literature indicates that the mechanism for dry reforming of C 1 –C 3 hydrocarbons is somewhat different from that of higher hydrocarbons [57]. The same
holds for steam reforming reaction. The general route in the cases of C 1 –C 3 alkanes
involves the dissociation of hydrocarbons and subsequent oxidation of carbon