Novel Adsorption Process for Co-Production of Hydrogen and CO₂ from a Multicomponent Stream

The production of carbon-neutral H₂ is pivotal for reaching net-zero CO₂ in 2050. Undoubtedly, the time and scale of this transition call for the decarbonization of H₂ production from natural gas, where the separation processes account for a large share of the capital and operational expenditures. Energy- and cost-efficient processes are therefore highly sought after. With this contribution, we have developed, modeled, and optimized new vacuum pressure swing adsorption (VPSA) cycles for co-production of high-purity, high-recovery CO₂ and H₂ from a ternary feed stream with a significant amount of an impurity. We identified two cycles that can purify CO₂ up to 95% with recoveries greater 90% while co-producing hydrogen with the same specifications. Key cycle features include purge under vacuum with part of the hydrogen product and recycle of the hydrogen-rich outflow during the initial part of the blowdown. The latter should be carried out via a compressor for very high hydrogen purities and recoveries, or via a sequence of pressure equalization (PE) steps for the targeted separation, which also drastically reduces the energy consumption. The volumetric productivity ranges from 160 to 240 kg_CO2 /m³/h, which is significantly larger than the available open data for absorption-based CO₂ capture from hydrogen production plants (productivities in the range of 60-90 kg_CO2 /m³/h). The energy consumption, when evaluated via exergy to fairly compare heat and electricity, is in the range of state-of-the-art processes (0.5 MJ/kg CO₂). Finally, the developed VPSA cycles reduce the separation steps from two to one, which paves the way for further process intensification.