# Glycerol Steam Reforming in a Pilot Plant: Effect of Temperature and Catalyst Load
## 3 Results and Discussion
### Catalytic Glycerol Steam Reforming at Different Temperatures and Catalyst Concentrations  
In the case of catalytic studies, Table 6 shows the main parameters selected for each experiment, fixing the W/G ratio and inlet flow for all cases and varying the temperature (from 750 to 850 \({}^{\circ}\)C) and catalyst concentration (from 12 to 20% NiO). For these tests, nitrogen was used as the carrier gas in order to avoid air contact with the catalysts, implying the oxidation and, therefore, deactivation of the active phase. As in the case of non-catalytic experiments, a stabilization test was carried out, with gas sampling at every 15 min, to determine the gas composition and to establish the time at which the outlet gas presented constant composition. This experiment was carried out at the most unfavorable conditions, that is, at 750 \({}^{\circ}\)C. As a result, Figure 7 shows the results at different catalyst concentrations (12, 16 and 20% NiO). As can be observed, in the case of 12% NiO (Figure 7a), the reaction time required to stabilize the outlet gas composition was about 70 min (considering the starting point when the carrier gas was disconnected, and the oven reached 750 \({}^{\circ}\)C). In the case of 16% NiO (see Figure 7b), some fluctuations were observed, establishing a stabilization time at around 90 min, whereas regarding 20% NiO (Figure 7c), the outlet gas composition was practically constant from 70 min, which was the common sampling time for further analysis. It should be noted that the hydrogen yield was above 30% in all cases, pointing out the effectiveness of the selected catalysts, which was comparable to other Ni-based catalysts found in the literature with hydrogen yields between 32 to 45% [26]. The gas profile obtained was similar to those observed in the literature, where hydrogen was the majority gas, followed by CO and CO\({}_{2}\) and finally, hydrocarbons like methane or ethane were detected at very much lower concentrations [39] for Ni/Al\({}_{2}\)O\({}_{3}\) catalysts [30]. When the outlet gas flow and its hydrogen composition were compared at different temperatures and catalyst concentrations, Figure 8 shows the main results, with a considerable improvement in the gas flow and hydrogen yield when the temperature was increased (see Figure 8a), as observed in other studies [45]. However, an increase in the catalyst addition was not effective, obtaining better results with 12% NiO concentration (34.88 kW at 850 \({}^{\circ}\)C) compared to 20% NiO (26.55 kW at 850 \({}^{\circ}\)C). If these results in Figure 8a referred to the effective amount of catalysts for each catalyst load (that is, per gram of the active phase), the results would be the following: for 12%, 2.91 L-min\({}^{-1}\cdot\)g\({}^{-1}\); for 16%, 2.12 L-min\({}^{-1}\cdot\)g\({}^{-1}\); and for 20%, 1.32 L-min\({}^{-1}\cdot\)g\({}^{-1}\), proving the better efficiency of the catalyst at low concentrations. This fact could be due to a saturation effect when the alumina rings were impregnated, provoking an undesirable active-phase distribution on the support surface. The same effect could have a similar influence on the hydrogen percentage (see Figure 8b), with the best results observed for the lowest NiO concentration (41.35% for 12% NiO at 850 \({}^{\circ}\)C, whereas for 20% NiO, 34.42% of hydrogen was obtained). As in the case of non-catalytic tests, there was an increase in the hydrogen purity when the temperature increased. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**W/G Ratio** & **Inlet Flow, mL/min** & **Temperature, \({}^{\circ}\)C** & **NiO Concentration,** **\%** \\ \hline \multirow{6}{*}{0.7} & \multirow{6}{*}{40} & \multirow{6}{*}{750} & 12 \\  & & & 16 \\  & & & 20 \\ \cline{1-1} \cline{3-4}  & & & 12 \\ \cline{1-1} \cline{3-4}  & & 850 & 16 \\ \cline{1-1} \cline{3-4}  & & & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Experiments for catalytic GSR at different temperatures and catalyst concentrations.