# Glycerol Steam Reforming in a Pilot Plant: Effect of Temperature and Catalyst Load
## 1 Introduction
The use of catalysts (both homogeneous and heterogeneous [14] or acid and alkaline [15], which present their own advantages and challenges), for instance, sodium methylate, is required to make the process more efficient [16; 17]. Once fatty acid methyl esters (that is, biodiesel) are obtained, the purification process usually requires glycerol removal through decantation and washing treatments if homogeneous catalysts are used. Finally, a drying stage takes place, and the final product is obtained (normally biodiesel with at least 96.5% FAME content). Figure 1: Worldwide biodiesel production from 2010 and forecast for 2027. Source: [13]. In that sense, the latest trends in biodiesel production are devoted to innovative ways to improve the yield and efficiency of transesterification, mainly focused on machine-learning technology applied to biodiesel research [18] or the use of new dispositions such as bionic flow-induced peristaltic reactors [19]. As can be inferred from this figure, glycerol is obtained as a byproduct in transesterification, representing approximately 10% of biodiesel production. This process can present a high atom economy or efficiency depending on conversion and the use of byproducts [20; 21]. Traditionally, glycerol was obtained through several processes such as soap making or fatty alcohol, fatty acid methyl ester and fatty acid production, through synthetic methods or other methods such as microbial fermentation [22; 23]. A summary of the main properties of glycerol can be found in Table 1.  
Thus, glycerol is not toxic nor irritant, it is soluble in water and alcohols and stable at low pressure values and room temperature. Depending on the degree of purity of glycerol, it can be an interesting energy source (such as reforming or pyrolysis for energy [24]) or the starting point for the synthesis of other products such as C3 compounds (such as acrolein, propanediols or carboxylic acids) obtained from routes such as hydrogenation, oxidation or esterification or activated carbons through pyrolysis [21]. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{1}{c}{**Characteristics**} & \multicolumn{1}{c}{**Result**} \\ \hline Nomenclature and synonyms & 1,2,3-Propanetriol, glycerol, glycerine \\ Molecular formula & \(\text{C}_{3}\text{H}_{8}\text{O}_{3}\) \\ Molecular formula & \(\text{H}_{\text{}}\) \\ Molecular structure & \(\text{H}_{\text{}}\) \\ Molecular weight (g/mol) & 92.09 \\ Viscosity 1 at 20 \({}^{\circ}\)C (Poise) & 15.0 \\ Density 1, g/cm\({}^{3}\) & 1.261 \\ Melting point 1, \({}^{\circ}\)C & 18.2 \\ Boiling point 1, \({}^{\circ}\)C & 290 \\ Others & Liquid at room temperature, colorless and hygroscopic \\ \hline \hline \end{tabular} \({}^{1}\)Anhydroous and pure.  
\end{table} 
Table 1: Glycerol properties and characteristics. Figure 2: Transesterification of triglycerides with methanol to produce fatty acid methyl esters (FAMEs) and glycerol. Considering the future trend about biodiesel production, it is not surprising that glycerol generation has considerably increased in recent years, which can imply an opportunity for its reuse in industrial processes. A feasible possibility is the use of glycerol as an energy source to obtain synthesis gas (a mixture of hydrogen and carbon monoxide at different ratios) [25]. This synthesis gas, if it is suitably treated, can produce fuel in an environmentally friendly process, as glycerol is obtained from chemical routes by using renewable raw materials [26]. Glycerol steam reforming (GSR) is one of the most typical methods to produce hydrogen in industry, as it is efficient and profitable at an industrial level [21; 27]. This technique does not require excessively high pressures and higher hydrogen percentages are produced at high temperatures. Steam reforming consists of the conversion of hydrocarbons to hydrogen or synthesis gas, through a treatment at high temperatures with an oxidizing agent and a catalyst.