The $SnO2/Sn$ Carbothermic Cycle for Splitting Water and Production of Hydrogen

The carboreduction in $SnO2$ to produce Sn and its hydrolysis with steam to generate hydrogen were studied. The $SnO2/C/Sn$ system has several advantages compared with the most advanced cycle considered so far, which is the ZnO/C/Zn system. The most significant one is the lower reduction temperatures (⁠$850–900°C$ for the $SnO2$ versus $1100–1150°C$ for the ZnO). The rate of carbothermal reduction was studied experimentally. $SnO2$ powder (300 mesh, 99.9% purity) was reduced with beech charcoal and graphite using a thermogravimetric analysis apparatus and fixed bed flow reactor at a temperature range of $800–1000°C$⁠. Optimal temperature range for the reduction with beech charcoal is $875–900°C$⁠. The reaction time needed to reach conversion of $SnO2$ close to 100% is 5–10 min in this temperature range. The transmission electron microscopy results show that after cooling, the product of carboreduction contains mainly metallic Sn with a particle size of $1–3μm$⁠. The hydrolysis step is crucial to the success of the entire cycle. Reactions between the steam and solid tin having as powder structure similar to the reduced one were performed at a temperature range of $350–600°C$⁠. Results of both the reduction and hydrolysis reactions are presented in addition to thermodynamic analysis of this cycle.