77
Steam Gasification and Reforming Technologies
While nickel on alumina is a workable catalyst for steam reforming of glycerol,
the effects of numerous promoters such as Ce, La, Mg, and Zr were examined at
600°C [143–155] (Cheng et al., 2012, pers. comm.). These results indicate that all
promoters improved the production of hydrogen with zirconium giving the best
results. The increase in hydrogen production can be due to an increased nickel concentration, an increased capacity to activate steam, and the stability of nickel phase.
Recent studies [143–155] (Cheng et al., 2012, pers. comm.) investigated various
noble metal catalysts on a variety of supports at 500°C–600°C, an atmospheric pressure, and a steam-to-carbon molar ratio of 3.3. The results indicated the activity order:
Ru = Rh > Ni > Ir > Co > Pt > Pd > Fe. Among Y 2 O 3 , ZrO 2 , CeO 2 , La 2 O 3 , SiO 2 , MgO,
and Al 2 O 3 supports, Y 2 O 3 (along with ZrO 2 and CeO 2 ) support gave the best glycerol
conversion and hydrogen production. These studies also demonstrated that at low conversion and low temperature (225°C–275°C), Pt/C and Pt–Re/C gave stable results. For
CeO 2 support, Zhang et al. [145] showed that at 400°C, Ir/CeO 2 gave the best glycerol
conversion with 85% hydrogen selectivity, whereas Co/CeO 2 and Ni/CeO 2 gave 88%
and 75% hydrogen selectivity at 425°C and 450°C, respectively. Glycerol has a higher
tendency for coke formation compared to methane and this coke formation can be significantly reduced by increasing the steam-to-glycerol ratio in the feed. The catalytic
steam reforming of glycerol (both conversion of glycerol and selectivity of hydrogen) is
affected by the operating parameters such as the reaction temperature, the pressure, the
steam-to-glycerol ratio, and the oxygen-to-glycerol ratio.
In a recent study, Maciel and Ishikura [144] have given an outstanding review
of steam reforming of renewable feedstock for the production of hydrogen. They
have considered methanol, ethanol, glycerol, glucose, and biomass as potential raw
materials for steam reforming. Their overall analysis led to the following conclusions: (1) reforming should be carried out at lower temperatures and an atmospheric
pressure to reduce the operating costs; (2) the catalyst should provide high selectivity
to hydrogen and inhibit CO and byproduct formation such as methane; and (3) the
catalyst must resist coke formation that reduces the number of active sites and hence
the reaction rates, and implies a regeneration process that is costly. Feedstock issues
such as supply, cost, logistics, and the value of byproducts are major factors in costeffectiveness of steam reforming process.
4.5.2.5 Biomass
Just like methane and other hydrocarbons, biomass can also undergo partial oxidation and steam reforming in the presence of oxygen and steam at temperatures above
around 725°C yielding gaseous products and chars [156–171]. The char can also be
converted to gaseous products such as hydrogen, carbon dioxide, carbon monoxide,
and methane under high-temperature conditions. The overall reaction is as follows:
C x H y O z + H 2 O + O 2 → H 2 + CO x + CH 4 + HCs + char
(4.67)
The hydrogen production for a variety of biomass under different operating conditions has been examined in the literature [156–171]. The literature data indicate that
in a fluidized bed reactor, under suitable operating conditions, as high as 60 vol%
hydrogen can be produced from biomass.
Steam Gasification and Reforming Technologies
While nickel on alumina is a workable catalyst for steam reforming of glycerol,
the effects of numerous promoters such as Ce, La, Mg, and Zr were examined at
600°C [143–155] (Cheng et al., 2012, pers. comm.). These results indicate that all
promoters improved the production of hydrogen with zirconium giving the best
results. The increase in hydrogen production can be due to an increased nickel concentration, an increased capacity to activate steam, and the stability of nickel phase.
Recent studies [143–155] (Cheng et al., 2012, pers. comm.) investigated various
noble metal catalysts on a variety of supports at 500°C–600°C, an atmospheric pressure, and a steam-to-carbon molar ratio of 3.3. The results indicated the activity order:
Ru = Rh > Ni > Ir > Co > Pt > Pd > Fe. Among Y 2 O 3 , ZrO 2 , CeO 2 , La 2 O 3 , SiO 2 , MgO,
and Al 2 O 3 supports, Y 2 O 3 (along with ZrO 2 and CeO 2 ) support gave the best glycerol
conversion and hydrogen production. These studies also demonstrated that at low conversion and low temperature (225°C–275°C), Pt/C and Pt–Re/C gave stable results. For
CeO 2 support, Zhang et al. [145] showed that at 400°C, Ir/CeO 2 gave the best glycerol
conversion with 85% hydrogen selectivity, whereas Co/CeO 2 and Ni/CeO 2 gave 88%
and 75% hydrogen selectivity at 425°C and 450°C, respectively. Glycerol has a higher
tendency for coke formation compared to methane and this coke formation can be significantly reduced by increasing the steam-to-glycerol ratio in the feed. The catalytic
steam reforming of glycerol (both conversion of glycerol and selectivity of hydrogen) is
affected by the operating parameters such as the reaction temperature, the pressure, the
steam-to-glycerol ratio, and the oxygen-to-glycerol ratio.
In a recent study, Maciel and Ishikura [144] have given an outstanding review
of steam reforming of renewable feedstock for the production of hydrogen. They
have considered methanol, ethanol, glycerol, glucose, and biomass as potential raw
materials for steam reforming. Their overall analysis led to the following conclusions: (1) reforming should be carried out at lower temperatures and an atmospheric
pressure to reduce the operating costs; (2) the catalyst should provide high selectivity
to hydrogen and inhibit CO and byproduct formation such as methane; and (3) the
catalyst must resist coke formation that reduces the number of active sites and hence
the reaction rates, and implies a regeneration process that is costly. Feedstock issues
such as supply, cost, logistics, and the value of byproducts are major factors in costeffectiveness of steam reforming process.
4.5.2.5 Biomass
Just like methane and other hydrocarbons, biomass can also undergo partial oxidation and steam reforming in the presence of oxygen and steam at temperatures above
around 725°C yielding gaseous products and chars [156–171]. The char can also be
converted to gaseous products such as hydrogen, carbon dioxide, carbon monoxide,
and methane under high-temperature conditions. The overall reaction is as follows:
C x H y O z + H 2 O + O 2 → H 2 + CO x + CH 4 + HCs + char
(4.67)
The hydrogen production for a variety of biomass under different operating conditions has been examined in the literature [156–171]. The literature data indicate that
in a fluidized bed reactor, under suitable operating conditions, as high as 60 vol%
hydrogen can be produced from biomass.