(10g) Preparation of FAU Zeolite Membranes on Polydopamine Modified Al2O3 Tubes for Dewatering of Amine-Based Post-Combustion CO2 Capture Solutions

Amine scrubbing is currently regarded as among the most economical technology for post-combustion CO₂ capture. In this process, aqueous amine solvent is circulated between an absorber column for CO₂ absorption and a stripping column for solvent regeneration. To reduce the energy required in the stripping column per mole of CO₂ captured, a selective ceramic membrane is proposed here to dewater and enrich the carbon loading in the amine solution prior to the stripper [1]. In this work, FAU zeolite membranes installed after the lean-rich heat exchanger were investigated as part of a dewatering unit for implementation into the carbon capture process. The concentrated CO₂-rich solution is sent to the top of stripper while the water-rich permeate is joined with the lean amine solvent exiting the bottom of the stripper and is sent back to the absorber. Based on polydopamine (PDA) modified Al₂O₃ substrates, a simple and facile synthesis strategy was developed to prepare highly reproducible FAU zeolite membranes. In this approach, polydopamine was deposited on Al₂O₃ tubes (coated with a 30-μm thick α-alumina layer with an average pore size of 0.05 μm) under varying time periods between 1-20 h for the fabrication of cross-linked polymer layer. The optimized modification time was 4 h to achieve uniform dopamine polymerization on the Al₂O₃ surface. Attributing to its bio-adhesive ability through non-covalent self-assembly and covalent polymerization [2], PDA functioned as a “molecular seed” for the attachment of zeolite onto the Al₂O₃ substrate surface for the formation of a dense and selective membrane layer with a thickness of approximately 3 μm. The physicochemical properties of these zeolite membranes were characterized to understand the hydrothermal synthesis temperature and time on membrane formation by techniques including X-ray diffractometer (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The effects of dewatering test operation temperature (353-413 K) and pressure (0-150 psi) on the membrane dewatering performance were comprehensively investigated in a 5 M monoethanolamine (MEA) solution to work towards an optimized condition. Membranes synthesized at 85 °C for 11 h exhibited fluxes as high as 6.5 kg m^-2 h^-1 with rejection rates of 95% at 403 K and 75 psi. In addition, FAU zeolite membrane batches were prepared with a high reproducibility of >90%.

References

[1] X. Li, J. E. Remias, J. K. Neathery, K. Liu, J. Membr. Sci., 2011 (366), 220-228.

[2] C. Zhou, C. Yuan, Y. Zhu, J. Caro, A. Huang, J. Membr. Sci., 2015 (494), 174-181.