Unraveling the Role of Water in Microwave/Electromagnetic-Assisted Catalytic Heating for Hydrogen Production from Gas Reservoirs

Abstract To cope with the increasing pressures of decarbonization that the petroleum industry is facing, a novel approach, entitled in-situ microwave/electromagnetic-assisted catalytic heating technology, is recently proposed for hydrogen (H2) production directly from petroleum reservoirs. This work investigates H2 generation from methane (CH4) cracking in the presence of sandstone rock powders under microwave irradiation through a purpose-designed lab-scale microwave reactor system. The role of water and rock minerals during reactions is also examined. The real-time variations of measured temperature of rock samples, gas flow rate, and concentration of hydrogen and other generated gases are monitored. Deuterium oxide, or the so-called heavy water (D2O), is used to track the sources of hydrogen from methene and water. A rapid temperature increase is identified for the sandstone samples during microwave heating, which is referred to as the "temperature soaring" (TS) phenomenon. The TS phenomenon happens at 560-590 ℃ under microwave irradiation at a relatively higher power. Once TS phenomenon occurs, the sample can be easily re-heated up to 700 ℃ using a low microwave power at less than 0.3 kW. The experimental results show that Fe-based and other metal minerals in the sandstone rocks have an evident natural catalytic effect for promoting CH4 conversion to H2. The H2 production with 1.0 mol.% concentration starts at a measured temperature of 392 ℃, followed by a maximum H2 concentration and CH4 conversion at 91 mol.% and 79% respectively as the temperature reaches 668 ℃. Furthermore, in the presence of D2O, a peak concentration of 4.9 mol.% D2 gas and 18.2 mol.% HD gas are generated during methane conversion to hydrogen experiments. Further, water can enhance H2 generation via coke gasification in a temperature range from 330-580 ℃. Additionally, negligible CO2 and minor CO are generated in the experiments when methane continuously flows through the sandstone samples and converted to hydrogen under microwave irradiation. The proposed technology potentially opens a new pathway for clean H2 production directly from natural gas reservoirs.