Highly Cross-Linked Polymers for Membrane H2/CO2 Separation at Elevated Temperatures

Highly Cross-linked Polymers for Membrane H₂/CO₂ Separation at Elevated Temperatures

Maryam Omidvar, Mark Swihart, and Haiqing Lin

 

Department of Chemical and Biological Engineering

University at Buffalo, The State University of New York)

 

Membrane technology has attracted significant interest for pre-combustion H₂ purification and CO₂ capture. The key to the success of this technology is membrane materials with high H₂ permeability and H₂/CO₂ selectivity at elevated temperatures of syngas processing (>100 °C). Polyimides such as P84 have been explored for H₂/CO₂ separation due to their strong size-sieving ability and resulting high H₂/CO₂ diffusivity selectivity. In this study, we demonstrate that these polymers can be cross-linked chemically to further improve H₂/CO₂ selectivity. We systematically evaluate the effect of cross-linking P84 using amines such as propane diamines, butane diamines and p-xylene diamine on the H₂/CO₂ separation properties. The cross-linking can significantly increase H₂/CO₂ selectivity while retaining moderate H₂ permeability. For example, cross-linking of P84 with butane diamine with 42% conversion increases H₂/CO₂ selectivity from 2.4 to 8.0, while decreasing H₂ permeability from 40 to 24 Barrers at 100 ^oC. The combination of 24 Barrers for H₂ permeability and 8.0 for H₂/CO₂ selectivity is very close to the Robeson’s upper bound for H₂/CO₂ separation, demonstrating the potential of this approach for membrane development. These cross-linked polymers are thoroughly evaluated using FTIR, DSC, TGA, WAXD, and XPS. The effect of cross-linking degree on the physical properties will be discussed, including glass transition temperature, fractional free volume and pure- and mixed-gas H₂/CO₂ separation properties at various temperatures. This presentation will also discuss the fundamental structure/property relationship in these highly cross-linked polymers with promising H₂/CO₂ separation properties.