Hydrogen production by methanol reforming in supercritical water: Suppression of methane formation

The reforming of methanol is carried out in supercritical water at 276 bar and 700 degrees C to produce H-2 along with CO, CH4, and CO2. The reactions are catalyzed by the wall of the tubular reactor made of Inconel 600, which is an alloy of Ni, Cr, and Fe. Experiments are conducted to study the effects of the pressure, residence time, and steam-to-carbon ratio on the H2 yield. The residence time is varied by changing the length of the reactor as well as the feed flow rate. Both the experimental results and equilibrium calculations show that, as the pressure is increased, methanation of CO and CO2 takes place, resulting in a loss of H-2. In addition, the methane formation is favored at a high residence time and low steam-to-carbon ratio. In this study, the following three strategies are proposed for the suppression of methane formation during the production of H2 from methanol in supercritical water: (1) operation at a low residence time by having a small reactor length or a high feed flow rate; (2) addition of a small amount of K2CO3 or KOH in the feed; (3) utilization of the surface catalytic activity of the reactor made of Ni-Cu alloy. All three of these strategies resulted in a significant reduction in the methane formation and corresponding enhancement in the H2 production.