# Glycerol Steam Reforming in a Pilot Plant: Effect of Temperature and Catalyst Load
## 1 Introduction
Thus, glycerol reacts with steam to produce H\({}_{2}\), CO\({}_{2}\) and CO, in a highly endothermal process (\(\Delta\)H\({}^{0}\) = 123 kJ/mol) represented in Equation (1), which is a combination of glycerol decomposition (\(\Delta\)H\({}^{0}\) = 251 kJ/mol, Equation (2)) and water-gas shift reaction (WGS, \(\Delta\)H\({}^{0}\) = \(-\)41 kJ/mol, Equation (3)) [28]:  
\[\mathrm{C_{3}H_{8}O_{3}+3H_{2}O}\leftrightarrow 3\mathrm{CO_{2}+7H_{2}} \tag{1}\]  
\[\mathrm{C_{3}H_{8}O_{3}}\leftrightarrow 3\mathrm{CO+4H_{2}} \tag{2}\]  
\[\mathrm{CO+H_{2}O}\leftrightarrow\mathrm{CO_{2}+H_{2}} \tag{3}\]  
Consequently, the H\({}_{2}\) and CO ratio depends on the reaction conditions, including the kind of catalyst used, as CO can be converted in the WGS reaction to produce carbon dioxide. Also, other secondary reactions can take place, such as methane generation through exothermal reactions like those included in Equations (4) and (5):  
\[\mathrm{CO+H_{2}}\leftrightarrow\mathrm{CH_{4}+H_{2}O} \tag{4}\]  
\[\mathrm{CO_{2}+4H_{2}}\leftrightarrow\mathrm{CH_{4}+2H_{2}O} \tag{5}\]  
As a consequence, the presence of these secondary reactions explains the difficulty in reaching 100% H\({}_{2}\) production during glycerol steam reforming. To increase H\({}_{2}\) production, through GSR, a suitable catalyst selection should be carried out to promote the cleavage of C-C, O-H and C-H bonds in the oxygenated hydrocarbon reactant and facilitate the WGS to remove adsorbed CO [28]. Other factors with a strong influence on glycerol steam reforming are the following:  
* Feed flow: Overfeeding could reduce the yield of conversion, whereas the contrary could imply a poor gas production. The optimum flow maximizes the energy efficiency of the process. * Temperature: This is one of the key factors, as it affects the yield of the process and gas composition. In general, high temperature values correspond to a higher gas production and higher H\({}_{2}\) percentage in the outlet gas. * Steam to carbon (S/C) ratio: As it increases, the gas produced is richer in hydrogen, whereas the gas flow decreases. * Catalyst use: The use of catalysts (normally transition metals belonging to group VIIIB) is essential in this kind of process to obtain high conversion values. Also, the use of a support (such as Al\({}_{2}\)O\({}_{3}\), ZrO\({}_{2}\), SiO\({}_{2}\) or TiO\({}_{2}\)) can promote conversion, and the particle size can play an important role in favoring mass transfer and contact among reagents within the reactor. Also, the use of additives or promoters can improve the activity or service life by avoiding problems such as poisoning or carbon deposition [29; 30]. Hydrogen production from renewable biomass has gained interest in recent years in the scientific community, international agencies and governments, promoting its implementation through international green chemistry policies [31]. Thus, biomass and glycerol reforming has been studied through gasification to improve glycerol conversion to hydro gen depending on the temperature, pressure and steam to carbon ratio, obtaining favorable results at high temperatures and low pressures. This study determined that the optimum condition to produce hydrogen was between 700 and 750 \({}^{\circ}\)C, at 0.1 MPa, concluding that glycerol and biomass steam reforming is feasible at practical operating temperatures, typical at an industrial level [32]. Similar studies tested glycerol valorization obtained from biodiesel synthesis to obtain a gas rich in H\({}_{2}\) through a sequential process where the first step consisted of glycerol purification to reduce impurities and, afterward, it underwent steam reforming. The theoretical and experimental studies showed that the temperature and glycerol concentration had a considerable influence on the thermodynamics, with an optimum point at 700 \({}^{\circ}\)C and a carbon conversion to gas of around 95%, with a gas composition of 67% H\({}_{2}\), 22% CO\({}_{2}\), 11% CO and 1% CH\({}_{4}\)[33].