Hydrogen production by thermal partial oxidation of ethanol: Thermodynamics and kinetics study

In this study thermodynamics and kinetics analysis of the thermal partial oxidation (TPOX) of ethanol for producing hydrogen is performed. Equilibrium and kinetics calculations are performed in order to find the limiting parameters for the thermal partial oxidation. The effects of air ratio λ (the ratio of the oxidizer -to- fuel ratio to the stoichiometric oxidizer -to- fuel ratio) and mixture inlet temperatures (Tmix-in) on the reforming efficiency, the H2 mole number, the reaction progress, the equilibrium time and the ignition delay time are investigated. Furthermore, the analysis is performed using different kinetics schemes and the results are compared. The optimum practical operating conditions of the partial oxidation process of ethanol are identified. In this way, the results of this work can be useful as a guideline in experimental work.It is found that the reforming efficiency increases with increasing the process temperature for λ < 0.3 and remains nearly constant elsewhere. The efficiency reaches a maximum value of 90% at λ = 0.20 and Tmix-in ≥ 1000 K. The kinetics simulations suggest that three different regions exist during the partial oxidation process of ethanol: the oxidation region, the water gas shift reaction- reforming region and the reforming region. The reforming reactions in the 3rd region are the reaction process limiting step. Additionally, it is found that the equilibrium concentration of a given species is not affected by the pressure when the process temperature lies outside the range of 500 K < Tprocess < 1700 K. However, the minimum time required for a given species to reach the equilibrium is affected when pressures higher than 1 atm are employed. Pressures higher than 1 atm shift this minimum time towards lower values. Due to preheating limitations (self ignition and reactor material stability) and the kinetics behavior of the TPOX process of ethanol, practical operating conditions could be bounded in λ range of 0.4 to 0.45 and Tmix-in range of 650 K to 850 K.