279
Fuel Production by Supercritical Water
10.7.2 BiomASS
A number of investigators have looked at glucose as a model for biomass reforming
under SCW. The pertinent reaction in this case is
C 6 H 12 O 6 + 6H 2 O → 6CO
12H
2 +
2
(10.8)
Generally, hydrogen yield is smaller than predicted from the above equation because
varying amounts of methane are produced depending on the reaction conditions.
Kruse ([132]; 2012, pers. comm.), Kruse and Gawlik [141], and Kruse and Henningsen
[142] gave a simplified reaction mechanism for cellulose reforming. Since glucose
(and fructose) is the main product of hydrolysis of cellulose, their reaction mechanism also applies to glucose. The reforming of glucose was accelerated by alkali
catalysts such as K 2 CO 3 and KHCO 3 . Both of these catalysts increased the hydrogen
production and decreased coke formation. For biomass with low salt content and
high protein content, these catalysts can increase the hydrogen yield.
Antal and xu (2012, pers. comm.) and Antal et al. [144] showed the effectiveness of SCW reforming for the production of hydrogen for numerous different types
of biomass such as wood sawdust, cornstarch gel, digested sewage sludge, glycerol,
glycerol/methanol mixture, poplar wood sawdust, potato starch gels, and potato waste.
Once again, higher temperature and catalysts gave better hydrogen productions. The
final product distribution did depend on the nature of the feedstock. Similar results
were obtained by Boukis et al. (2012, pers. comm.) for biomass slurries and sludges.
They also showed an improved heat exchange scheme in “VERENA” German pilot
plant for these processes. The VERENA pilot facility successfully demonstrated high
carbon and energy efficiency for the SCW reforming of ethanol and corn silage in
the temperature range of 540°C–600°C for at least 10 h. On average, the hydrogen
concentration in the product for these biomass was about 77 vol%. Zhang et al. [134]
examined the SCW reforming of glucose solution (50–200 g/l), a simulated aqueous
organic waste (composed of glucose, acetic acid, and guaiacol), and a real aqueous
organic waste stream generated from a sludge hydrothermal liquefaction process.
The experiments were performed using two different types of catalysts—0.1 RuNi/
gamma-Al 2 O 3 and 0.1 RuNi/activated carbon catalysts (10 wt% Ni with a Ru-to-Ni
molar ratio of 0.1). While the first catalyst was very effective with glucose solutions
and simulated aqueous organic waste giving hydrogen yield of 53.9 mol/kg dried
feedstock at 750°C, 24 MPa, and weight hourly space velocity (WHSV) of 6 h −1 , it
was not effective in resisting the alkali and nitrogen compounds in the real waste. The
second catalyst supported on active carbon exhibited higher stability.
10.7.3 glyCerol
Reforming of glycerol for hydrogen production can be summarized by the following
reactions [118,129,140,148,155,166].
First, the steam reforming of glycerol can be expressed as
C 3 H 8 O 3 → 3CO + 4H 2
(10.9)
Fuel Production by Supercritical Water
10.7.2 BiomASS
A number of investigators have looked at glucose as a model for biomass reforming
under SCW. The pertinent reaction in this case is
C 6 H 12 O 6 + 6H 2 O → 6CO
12H
2 +
2
(10.8)
Generally, hydrogen yield is smaller than predicted from the above equation because
varying amounts of methane are produced depending on the reaction conditions.
Kruse ([132]; 2012, pers. comm.), Kruse and Gawlik [141], and Kruse and Henningsen
[142] gave a simplified reaction mechanism for cellulose reforming. Since glucose
(and fructose) is the main product of hydrolysis of cellulose, their reaction mechanism also applies to glucose. The reforming of glucose was accelerated by alkali
catalysts such as K 2 CO 3 and KHCO 3 . Both of these catalysts increased the hydrogen
production and decreased coke formation. For biomass with low salt content and
high protein content, these catalysts can increase the hydrogen yield.
Antal and xu (2012, pers. comm.) and Antal et al. [144] showed the effectiveness of SCW reforming for the production of hydrogen for numerous different types
of biomass such as wood sawdust, cornstarch gel, digested sewage sludge, glycerol,
glycerol/methanol mixture, poplar wood sawdust, potato starch gels, and potato waste.
Once again, higher temperature and catalysts gave better hydrogen productions. The
final product distribution did depend on the nature of the feedstock. Similar results
were obtained by Boukis et al. (2012, pers. comm.) for biomass slurries and sludges.
They also showed an improved heat exchange scheme in “VERENA” German pilot
plant for these processes. The VERENA pilot facility successfully demonstrated high
carbon and energy efficiency for the SCW reforming of ethanol and corn silage in
the temperature range of 540°C–600°C for at least 10 h. On average, the hydrogen
concentration in the product for these biomass was about 77 vol%. Zhang et al. [134]
examined the SCW reforming of glucose solution (50–200 g/l), a simulated aqueous
organic waste (composed of glucose, acetic acid, and guaiacol), and a real aqueous
organic waste stream generated from a sludge hydrothermal liquefaction process.
The experiments were performed using two different types of catalysts—0.1 RuNi/
gamma-Al 2 O 3 and 0.1 RuNi/activated carbon catalysts (10 wt% Ni with a Ru-to-Ni
molar ratio of 0.1). While the first catalyst was very effective with glucose solutions
and simulated aqueous organic waste giving hydrogen yield of 53.9 mol/kg dried
feedstock at 750°C, 24 MPa, and weight hourly space velocity (WHSV) of 6 h −1 , it
was not effective in resisting the alkali and nitrogen compounds in the real waste. The
second catalyst supported on active carbon exhibited higher stability.
10.7.3 glyCerol
Reforming of glycerol for hydrogen production can be summarized by the following
reactions [118,129,140,148,155,166].
First, the steam reforming of glycerol can be expressed as
C 3 H 8 O 3 → 3CO + 4H 2
(10.9)