(497g) Hybrid DDR Zeolite Membranes for Advanced CO2 Separation and Biogas Upgrading

Membrane-based separation and purification methods offer more efficient and less energy-demanding alternatives compared to traditional, energy-intensive processes such as distillation and re-crystallization. These methods are also favored for their lower environmental impact, especially critical as the global temperature and sea level continue to rise steadily, and local climates change unpredictably due to CO₂ emissions from fossil fuel usage. Consequently, membranes find significant applications in the petrochemical and refining industries, carbon capture and storage, and the enhancement of biogas and natural gas, providing both economic and environmental benefits. Specifically, for biogas, recognized as a sustainable and environmentally friendly energy source, to reach the required purity levels of approximately 90-95% methane, an effective separation of CO₂ from CH₄ is essential.

The deca-dodecasil 3 rhombohedral (DDR) zeolite, which has a pore size of 0.36 × 0.44 nm², excel in selectively separating CO₂ (kinetic diameter of 0.33 nm) from CH₄ (0.38 nm) and N₂ (0.364 nm), a property that facilitates both biogas upgrading and post-combustion carbon capture. Despite DDR zeolites' potential, producing high-performance DDR zeolite membranes remains a complex challenge. A recent breakthrough was the development of hybrid zeolite membranes using a heteroepitaxial approach. In this research, we utilized heteroepitaxial growth to form a DDR zeolite from a CHA zeolite seed layer, using the conventional structure-directing agent 1-adamantylamine. We then assessed the membranes' efficiency in separating CO₂ and CH₄ under both dry and wet conditions, a critical factor for biogas upgrading. The study also examines the membranes' permeance and selectivity factors, comparing these properties from both membrane and module perspectives. We established a direct relationship between the selectivity required for CO₂ purity and the permeance necessary for CO₂ recovery, noting that recovery and purity levels of CH₄ on the retentate side correlate directly to the CO₂ processing outcomes on the permeate side. By analyzing the performance based on module properties, we provided insights into optimizing operating conditions, underlining the balance between selectivity for purity and permeance for recovery in membrane applications.