Thermodynamic analysis of hydrogen production from methane via autothermal reforming and partial oxidation followed by water gas shift reaction

Reaction characteristics of hydrogen production from a one-stage reaction and a two-stage reaction are studied and compared with each other in the present study, by means of thermodynamic analyses. In the one-stage reaction, the autothermal reforming (ATR) of methane is considered. In the two-stage reaction, it is featured by the partial oxidation of methane (POM) followed by a water gas shift reaction (WGSR) where the temperatures of POM and WGSR are individually controlled. The results indicate that the reaction temperature of ATR plays an important role in determining H2 yield. Meanwhile, the conditions of higher steam/methane (S/C) ratio and lower oxygen/methane (O/C) ratio in association with a higher reaction temperature have a trend to increase H2 yield. When O/C ≤ 0.125, the coking behavior may be exhibited. In regard to the two-stage reaction, it is found that the methane conversion is always high in POM, regardless of what the reaction temperature is. When the O/C ratio is smaller than 0.5, H2 is generated from the partial oxidation and thermal decomposition of methane, causing solid carbon deposition. Following the performance of WGSR, it suggests that the H2 yield of the two-stage reaction is significantly affected by the reaction temperature of WGSR. This reflects that the temperature of WGSR is the key factor in producing H2. When methane, oxygen and steam are in the stoichiometric ratio (i.e. 1:0.5:1), the maximum H2 yield from ATR is 2.25 which occurs at 800 °C. In contrast, the maximum H2 yield of the two-stage reaction is 2.89 with the WGSR temperature of 200 °C. Accordingly, it reveals that the two-stage reaction is a recommended fuel processing method for hydrogen production because of its higher H2 yield and flexible operation.