192
aspect through their study on GDR process without presence of any catalyst under
various reaction temperatures to examine the non-catalytic glycerol conversion
routes. They have reported that without the presence of catalyst, the glycerol was
homogeneously broken down with the increase in temperature up to 750 °C. 7% of
glycerol conversion was obtained at 600 °C and increased to 31% at reaction temperature of 750 °C. Contrary with glycerol, no CO 2 conversion was observed in
reaction temperatures of 550–750 °C (Bulutoglu et al. 2018).
In practical reforming technologies, the production of syngas is significantly
increased with the increase in the reaction temperature. From the thermodynamic
analysis performed via MATLAB software using Lagrange’s undetermined method
focusing on the CO 2 reactant, Wang et al. (2009) reported that CO 2 possibly started
to breakdown at 677 °C. Similar observations by Bulutoglu et al. (2018) showed
that the CO 2 molecule starts to convert to syngas at 750 °C but the degree of conversion is also depending on the types of catalyst used. Different CO 2 conversions were
observed at 750 °C over the Rh − ZrO 2 and Rh − CeO 2 catalysts with 12.6% and
7.1%, respectively; however, within the range of 600–700 °C, negligible conversion
of CO 2 was obtained for both catalysts (Bulutoglu et al. 2018). Thus, it can be concluded that the process involved with CO 2 was favored at temperatures more than
650 °C due to thermodynamic limitation of CO 2 . However, at reforming temperatures above 500 °C with the presence of CO 2 , the reactant will favor the reverse
water-gas shift (RWGS), the reverse of Eq. (7.3). This side reaction gives a significant influence to the product distribution as the excess by-product of water will
inhibit the syngas production (Fernández et al. 2010; Bulutoglu et al. 2018).
As reported by Bulutoglu et al. (2018), glycerol possibly decomposes to various
species at temperatures as low as 600 °C although without the presence of catalyst.
This is apparently noticeable since the operation temperature itself could energize
the breakdown of glycerol molecule without any assisted active sites. Further investigation on GDR was conducted over Rh − ZrO 2 and Rh − CeO 2 catalysts, and the
result shows a similar increment in glycerol conversion up to ~82% in both catalysts
at temperature 700 and 750 °C, respectively (Bulutoglu et al. 2018).
Reaction temperature of GDR also affects the syngas yield or practically presented in H 2 /CO ratios. Hydrogen yield was reported to increase as the operating
temperature increased up to 700 °C, and the trend started to decline as the temperature increased (Wang et al. 2009; Freitas and Guirardello 2014). Wang et al. (2009)
found that at a reactant molar ratio CO 2 -to-glycerol ratio of 1:1, 727 °C was the
optimum temperature to achieve maximum hydrogen yield (Wang et al. 2009).
Meanwhile, the presence of intermediate species of methane during the GDR would
promote the formation of carbon monoxide and hydrogen (Bulutoglu et al. 2018).
The generation of methane during the glycerol decomposition will react with readily CO 2 and subsequently form carbon monoxide and hydrogen as shown in Eq.
(7.4). These gas products increase with the increase of temperature. Even though
high temperatures promoted the syngas yield, coke formation and active site sintering would also favor at extremely high temperatures (Bulutoglu et al. 2018).
S. Z. Abidin et al.
aspect through their study on GDR process without presence of any catalyst under
various reaction temperatures to examine the non-catalytic glycerol conversion
routes. They have reported that without the presence of catalyst, the glycerol was
homogeneously broken down with the increase in temperature up to 750 °C. 7% of
glycerol conversion was obtained at 600 °C and increased to 31% at reaction temperature of 750 °C. Contrary with glycerol, no CO 2 conversion was observed in
reaction temperatures of 550–750 °C (Bulutoglu et al. 2018).
In practical reforming technologies, the production of syngas is significantly
increased with the increase in the reaction temperature. From the thermodynamic
analysis performed via MATLAB software using Lagrange’s undetermined method
focusing on the CO 2 reactant, Wang et al. (2009) reported that CO 2 possibly started
to breakdown at 677 °C. Similar observations by Bulutoglu et al. (2018) showed
that the CO 2 molecule starts to convert to syngas at 750 °C but the degree of conversion is also depending on the types of catalyst used. Different CO 2 conversions were
observed at 750 °C over the Rh − ZrO 2 and Rh − CeO 2 catalysts with 12.6% and
7.1%, respectively; however, within the range of 600–700 °C, negligible conversion
of CO 2 was obtained for both catalysts (Bulutoglu et al. 2018). Thus, it can be concluded that the process involved with CO 2 was favored at temperatures more than
650 °C due to thermodynamic limitation of CO 2 . However, at reforming temperatures above 500 °C with the presence of CO 2 , the reactant will favor the reverse
water-gas shift (RWGS), the reverse of Eq. (7.3). This side reaction gives a significant influence to the product distribution as the excess by-product of water will
inhibit the syngas production (Fernández et al. 2010; Bulutoglu et al. 2018).
As reported by Bulutoglu et al. (2018), glycerol possibly decomposes to various
species at temperatures as low as 600 °C although without the presence of catalyst.
This is apparently noticeable since the operation temperature itself could energize
the breakdown of glycerol molecule without any assisted active sites. Further investigation on GDR was conducted over Rh − ZrO 2 and Rh − CeO 2 catalysts, and the
result shows a similar increment in glycerol conversion up to ~82% in both catalysts
at temperature 700 and 750 °C, respectively (Bulutoglu et al. 2018).
Reaction temperature of GDR also affects the syngas yield or practically presented in H 2 /CO ratios. Hydrogen yield was reported to increase as the operating
temperature increased up to 700 °C, and the trend started to decline as the temperature increased (Wang et al. 2009; Freitas and Guirardello 2014). Wang et al. (2009)
found that at a reactant molar ratio CO 2 -to-glycerol ratio of 1:1, 727 °C was the
optimum temperature to achieve maximum hydrogen yield (Wang et al. 2009).
Meanwhile, the presence of intermediate species of methane during the GDR would
promote the formation of carbon monoxide and hydrogen (Bulutoglu et al. 2018).
The generation of methane during the glycerol decomposition will react with readily CO 2 and subsequently form carbon monoxide and hydrogen as shown in Eq.
(7.4). These gas products increase with the increase of temperature. Even though
high temperatures promoted the syngas yield, coke formation and active site sintering would also favor at extremely high temperatures (Bulutoglu et al. 2018).
S. Z. Abidin et al.