## 6 Identification of MS-Driven Processes of Renewable Gas Production
Furthermore, MSs can be used to supply heat to the hydride acid decomposition (endothermic stage at 300-450 \({}^{\circ}\)C): 2 HI (aq, g) \(\rightarrow\) I\({}_{2}\) (g) + H\({}_{2}\) (g). Figure 12: A conceptual diagram of the integration of an RES and an MS-TES system to provide heat and electricity to processes for hydrogen and syngas production. **Non-volatile metal oxide cycles**: Due to the very high temperatures of the high-temperature step, no MS mixtures are available for direct heat supply. Currently, only direct irradiation is considered to supply these processes with solar energy. MSs could be considered for heat recovery/thermal buffering/reactant pre-heating in some parts of the plant. **Mixed ferrites**: Some processes, like mixed ferrites, may require CO\({}_{2}\)-separation processes, which require heat at \(\sim\)100-200 \({}^{\circ}\)C and could be served with MSs. **Cu-Cl cycle**: This is a 4-step hybrid cycle. The highest-temperature thermochemical step is carried out at 530 \({}^{\circ}\)C and can be served with solar salt:  
\[\text{CuOCuCl}_{2}\text{ (s)}\to 2\text{ CuCl (molten)}+0.5\text{ O}_{2}\text{ (g)}\text{, Thermolysis (endothermic)} \tag{4}\]  
**Steam reforming**: This conventional high-temperature (700-1000 \({}^{\circ}\)C) process is operated by using gas-fired furnaces to produce hydrogen and carbon monoxide, according to the overall reaction. \[\text{CH}_{4}+2\text{ H}_{2}\text{O}\to\text{CO}_{2}+4\text{ H}_{2}, \tag{5}\]  
Consequently, no MS mixture is employable. In order to enable its integration, the steam reforming process can be modified. [PERSON] et al. [146] presented a case study considering a methane steam reformer followed by a water-gas shift section fed with molten nitrates (namely, the solar salt mixture). A methane inlet of 3 kmol/hour is introduced at 20 bars into a tubular reactor, where the molten salt flows counter-currently into an external shell. With a nitrate inlet temperature of 550 \({}^{\circ}\)C and an outlet value of 460 \({}^{\circ}\)C, a conversion of up to 21% can be obtained for methane into CO\({}_{2}\) and H\({}_{2}\). Very interestingly, as the heat necessary for the endothermic reaction is obtained by the nitrates' sensible heat, which is in turn provided by a parabolic solar trough plant, the produced carbon dioxide drops from 8.3-10.1 kgCO\({}_{2}\)/kgH\({}_{2}\) (where fossil fuels are employed) to 5.5 kgCO\({}_{2}\)/kgH\({}_{2}\). Methane conversion can be still improved by using hydrogen permselective modules, which also makes CO\({}_{2}\) capture easier once separated from H\({}_{2}\)[108; 147]. **Gasification**: In a down-draft reactor, the drying, pyrolysis, and gasification zones are well separated. In this case, the reactions in the pyrolysis step can be powered by MSs up to a temperature of 500 \({}^{\circ}\)C.  
**Supercritical water gasification:** In this process, the operating conditions (higher than 374 \({}^{\circ}\)C, usually up to 500 \({}^{\circ}\)C or above) are compatible with the use of binary solar salt. **Pyrolysis**: MS mixtures can be used to supply heat in the slow and intermediate pyrolysis process. Biomass can generically be chemically represented by C\({}_{x}\)H\({}_{y}\)O\({}_{z}\), where the components \(x,y,\) and \(z\) can be determined by the Total C/H/O (%/m/m) divided by the respective MW_C/H/O (g/mol). Slow pyrolysis is characterized by the relatively low operational temperature and longer heating rate values. In intermediate pyrolysis, more C-C connections are broken, and, therefore, there is a tendency to have more bio-oil and syngas. **Hydrothermal liquefaction**: In this process, temperatures are moderate (typically 200-400 \({}^{\circ}\)C), compatible with the operating temperatures of some MS mixtures. For electrolysis, after a thorough review of the literature, including studies from previous analyses and based on various works conducted by ENEA, heat is required almost exclusively for this process of steam generation.