An Intensified H2 Production Process from Biogas Via Chemical Looping Water Splitting

H₂ is a clean and efficient secondary energy source. Although the combustion of H₂ does not emit CO₂, the production of H₂ can result in significant CO₂ emissions. Globally, more than 96% H₂ is produced from non-renewable fossil fuels including coal, oil and natural gas, which raises great concerns not only in CO₂ emissions, but also in the long-term sustainability of those processes. Biogas, a mixture primarily containing CH₄ and CO₂, is a promising alternative feedstock for H₂ production. Unlike traditional fossil fuels, biogas is both renewable and carbon-neutral. However, CO₂ removal is usually an indispensable step for H₂ production from biogas using conventional CH₄ reforming processes, lowering the energy efficiency and increasing the capital cost of the overall process.

The chemical looping water-splitting (CLWS) concept offers an alternative pathway to bypass the CO₂ removal step associated with H₂ production from biogas, resulting in significant process intensification by eliminating not only the CO₂ separation unit, but also the water gas shift unit, the H₂ purification unit, the biogas compressor and the combustion furnace. The CLWS process performs the CH₄ reforming reaction in three reactors, namely a reducer (fuel reactor), an oxidizer (steam reactor), and a combustor (air reactor). In the reducer, biogas is fully oxidized into CO₂ and H₂O by metal oxide particles. In the oxidizer, reduced metal oxide particles react with steam to produce pure H₂. In the combustor, the metal oxide particles are fully regenerated by air.

In this work, the CLWS process is simulated in ASPEN Plus to quantify its benefits compared to conventional reforming systems. The material, heat and power balances of the CLWS system are established in the process model. Sensitivity analysis on the influence of feedstock CO₂ concentration on the system performance is studied in ASPEN Plus, which shows that the CLWS system can directly process biogas feedstock with up to 50% CO₂ concentration without compromising the system performance. These significant improvements in thermal efficiency are a result of the high level of process intensification achieved by the CLWS process, which is even more remarkable when CO₂ capture is performed.