Fuel Production by Supercritical Water
277
catalyst gave the best hydrogen production. Titania-supported catalysts gave lower
hydrogen conversions but did not plug the reactor over time. All support materials
suffered surface area loss due to sintering.
Glycerol (HOCH 2 –CHOH–CH 2 OH) is obtained as a by-product from biodiesel
manufacturing by transesterification of vegetable oils. Nine grams of biodiesel generates approximately 1 g of glycerol. With increasing production of biodiesel, glycerol production will rise, and it can be used for food, oral and personal care, tobacco,
polymers, pharmaceuticals, and replacements of petroleum feedstock. Kersten et al.
[153] have reported gasification results for glycerol and other model compounds in
a variety of catalytic and noncatalytic reactors in SCW and found that without addition of a catalyst, only very dilute concentrations of model biomass feeds could be
completely gasified. The density of SCW is higher than that of steam, resulting in a
higher space time yield. Higher thermal conductivity and specific heat were helpful
in carrying out the endothermic reforming reactions. The formation of char and tar
was also minimized because of the solubility of hydrocarbons in SCW. Importantly,
hydrogen produced from SCW reforming was produced at high pressure, which can
be stored directly, thus avoiding large expenses associated with compression.
The above-described studies and many others lead to some general conclusions
[83,84,119–153] (Antal and xu, 2012, pers. comm.; Boukis, 2012, pers. comm.;
Kruse, 2012, pers. comm.; Veriansyah et al., 2012, pers. comm.). As the temperature
increases above the critical temperature, more gases are generally produced from
most carbonaceous materials. At lower temperatures, for higher feedstock concentration, and in the absence of a catalyst, the gas production rate tends to be lower and
contain more methane. At high temperature, for lower feedstock concentration, and
in the presence of an effective catalyst, hydrogen production rate rapidly increases.
Higher temperature and the presence of a catalyst promote reforming of gas and
favor reverse water–gas shift reaction, thus producing more hydrogen and carbon
dioxide. Pressure also affects the equilibrium of water–gas shift reaction. Higher
pressure favors methane formation as opposed to hydrogen production.
10.7 reFOrminG in sCW
SCW is an ideal medium to carry out reforming reactions for both single components
and complex materials [154–176] (Barendregt 2012, pers. comm.; Cremers et al.,
2012, pers. comm.; Veriansyah et al., 2012, pers. comm.). Besides all the positive
features of the supercritical medium outlined earlier, SCW provides possibilities of
lower temperature, lesser coking issues, and more active and stable catalytic reforming process. In Sections 10.7.1 through 10.7.7, we briefly assess important reported
literature on the subject.
10.7.1 liquid FuelS
Lee et al. [154] showed that reforming of JP-8 fuel and diesel fuel can be carried out
in SCW in the absence of a catalyst. High enthalpy level of SCW and high solubilities
of fuel in SCW allowed the reforming reactions to occur in the temperature range
of 650°C–825°C and 220–330 atm pressure. The study examined the productions
277
catalyst gave the best hydrogen production. Titania-supported catalysts gave lower
hydrogen conversions but did not plug the reactor over time. All support materials
suffered surface area loss due to sintering.
Glycerol (HOCH 2 –CHOH–CH 2 OH) is obtained as a by-product from biodiesel
manufacturing by transesterification of vegetable oils. Nine grams of biodiesel generates approximately 1 g of glycerol. With increasing production of biodiesel, glycerol production will rise, and it can be used for food, oral and personal care, tobacco,
polymers, pharmaceuticals, and replacements of petroleum feedstock. Kersten et al.
[153] have reported gasification results for glycerol and other model compounds in
a variety of catalytic and noncatalytic reactors in SCW and found that without addition of a catalyst, only very dilute concentrations of model biomass feeds could be
completely gasified. The density of SCW is higher than that of steam, resulting in a
higher space time yield. Higher thermal conductivity and specific heat were helpful
in carrying out the endothermic reforming reactions. The formation of char and tar
was also minimized because of the solubility of hydrocarbons in SCW. Importantly,
hydrogen produced from SCW reforming was produced at high pressure, which can
be stored directly, thus avoiding large expenses associated with compression.
The above-described studies and many others lead to some general conclusions
[83,84,119–153] (Antal and xu, 2012, pers. comm.; Boukis, 2012, pers. comm.;
Kruse, 2012, pers. comm.; Veriansyah et al., 2012, pers. comm.). As the temperature
increases above the critical temperature, more gases are generally produced from
most carbonaceous materials. At lower temperatures, for higher feedstock concentration, and in the absence of a catalyst, the gas production rate tends to be lower and
contain more methane. At high temperature, for lower feedstock concentration, and
in the presence of an effective catalyst, hydrogen production rate rapidly increases.
Higher temperature and the presence of a catalyst promote reforming of gas and
favor reverse water–gas shift reaction, thus producing more hydrogen and carbon
dioxide. Pressure also affects the equilibrium of water–gas shift reaction. Higher
pressure favors methane formation as opposed to hydrogen production.
10.7 reFOrminG in sCW
SCW is an ideal medium to carry out reforming reactions for both single components
and complex materials [154–176] (Barendregt 2012, pers. comm.; Cremers et al.,
2012, pers. comm.; Veriansyah et al., 2012, pers. comm.). Besides all the positive
features of the supercritical medium outlined earlier, SCW provides possibilities of
lower temperature, lesser coking issues, and more active and stable catalytic reforming process. In Sections 10.7.1 through 10.7.7, we briefly assess important reported
literature on the subject.
10.7.1 liquid FuelS
Lee et al. [154] showed that reforming of JP-8 fuel and diesel fuel can be carried out
in SCW in the absence of a catalyst. High enthalpy level of SCW and high solubilities
of fuel in SCW allowed the reforming reactions to occur in the temperature range
of 650°C–825°C and 220–330 atm pressure. The study examined the productions