280
Water for Energy and Fuel Production
followed by the water–gas shift reaction
CO + H 2 O → CO 2 + H 2
(10.10)
The desired overall reaction is then summarized as
C 3 H 8 O 3 + 3H 2 O → 7H 2 + 3CO 2
(10.11)
Some hydrogen is also lost via the methanation of CO and CO 2 :
CO + 3H 2 → CH 4 + H 2 O
(10.12)
CO 2 + 4H 2 → CH 4 + 2H 2 O
(10.13)
As a result, the product stream is a mixture of the above gases. Furthermore, the
yield of hydrogen depends on several process variables such as system pressure,
temperature, and water-to-glycerol feed ratio.
Most recently, Knoef [140] studied the reforming of glycerol over Ru/Al 2 O 3 catalyst in SCW conditions at a temperature range of 700°C–800°C, feed concentration up to 40 wt%, and reaction time less than 5 s. Under these conditions, glycerol
was completely gasified to hydrogen, carbon dioxide, and methane along with a
small amount of carbon monoxide. xu and Antal [21,22], Antal and xu (2012, pers.
comm.), xu et al. [129], and Antal et al. [144] showed that even in the absence of a
catalyst glycerol decomposes in SCW to a hydrogen-rich gas, with almost no CO
after 44 s at 600°C and 34.5 MPa. Higher temperature, more active reforming catalyst, and longer residence time result in higher gas and hydrogen productions.
10.7.4 eThylene glyCol
de Vlieger et al. [164] studied catalytic reforming of ethylene glycol (5 and 15 wt%)
in SCW at 450°C and 250 atm pressure. The results were obtained for Pt, Ir, and Ni
containing mono- and bimetallic catalysts. The best catalyst was found to be Pt–
Ni/Al 2 O 3 having a metal loading of 1.5 wt% (Pt:Ni molar ratio of 1:1). With this
catalyst, high hydrogen and carbon dioxide yields (selectivity of around 80%) were
obtained by suppressing methanation reaction. The addition of Ni prevented sintering of Pt particles, thereby providing a stable performance by bimetallic catalysts.
Ethylene glycol also produced more CH 4 and CO than what was produced in methanol reforming.
10.7.5 meThAnol
Numerous studies have reported methanol reforming in SCW to produce hydrogen
[158–160,170]. Compared to water that has a critical pressure of 22.1 MPa, a critical temperature of 374°C, and a critical density of 320 kg/m 3 , methanol has a lower
critical temperature of 239°C, a critical pressure of 8.1 MPa, and a critical density
of 270 kg/m 3 . Thus, reaction of methanol in SCW also implied that methanol is
also under supercritical conditions. Methanol reforming can be described by five
chemical reactions:
Water for Energy and Fuel Production
followed by the water–gas shift reaction
CO + H 2 O → CO 2 + H 2
(10.10)
The desired overall reaction is then summarized as
C 3 H 8 O 3 + 3H 2 O → 7H 2 + 3CO 2
(10.11)
Some hydrogen is also lost via the methanation of CO and CO 2 :
CO + 3H 2 → CH 4 + H 2 O
(10.12)
CO 2 + 4H 2 → CH 4 + 2H 2 O
(10.13)
As a result, the product stream is a mixture of the above gases. Furthermore, the
yield of hydrogen depends on several process variables such as system pressure,
temperature, and water-to-glycerol feed ratio.
Most recently, Knoef [140] studied the reforming of glycerol over Ru/Al 2 O 3 catalyst in SCW conditions at a temperature range of 700°C–800°C, feed concentration up to 40 wt%, and reaction time less than 5 s. Under these conditions, glycerol
was completely gasified to hydrogen, carbon dioxide, and methane along with a
small amount of carbon monoxide. xu and Antal [21,22], Antal and xu (2012, pers.
comm.), xu et al. [129], and Antal et al. [144] showed that even in the absence of a
catalyst glycerol decomposes in SCW to a hydrogen-rich gas, with almost no CO
after 44 s at 600°C and 34.5 MPa. Higher temperature, more active reforming catalyst, and longer residence time result in higher gas and hydrogen productions.
10.7.4 eThylene glyCol
de Vlieger et al. [164] studied catalytic reforming of ethylene glycol (5 and 15 wt%)
in SCW at 450°C and 250 atm pressure. The results were obtained for Pt, Ir, and Ni
containing mono- and bimetallic catalysts. The best catalyst was found to be Pt–
Ni/Al 2 O 3 having a metal loading of 1.5 wt% (Pt:Ni molar ratio of 1:1). With this
catalyst, high hydrogen and carbon dioxide yields (selectivity of around 80%) were
obtained by suppressing methanation reaction. The addition of Ni prevented sintering of Pt particles, thereby providing a stable performance by bimetallic catalysts.
Ethylene glycol also produced more CH 4 and CO than what was produced in methanol reforming.
10.7.5 meThAnol
Numerous studies have reported methanol reforming in SCW to produce hydrogen
[158–160,170]. Compared to water that has a critical pressure of 22.1 MPa, a critical temperature of 374°C, and a critical density of 320 kg/m 3 , methanol has a lower
critical temperature of 239°C, a critical pressure of 8.1 MPa, and a critical density
of 270 kg/m 3 . Thus, reaction of methanol in SCW also implied that methanol is
also under supercritical conditions. Methanol reforming can be described by five
chemical reactions: