Thermally Stable Cross-linked P84 with Superior Membrane H₂/CO₂ Separation Properties at 100 °C

Polymers with a strong size-sieving ability and superior H₂/CO₂ selectivity are of great interests for pre-combustion CO capture at 100 °C or above. Polyimides (such as Matrimid^® and 6FDA-durene) have been cross-linked using diamines and show superior H₂/CO₂ selectivity. However, these cross-linked polymers cannot be used for the pre-combustion CO₂ capture because of the lack of thermal stability at 100 C. Herein we demonstrate that commercial P84™ can be chemically cross-linked using 1,4-butanediamine (BuDA) to achieve robust H₂/CO₂ separation properties at 100 °C to 150 °C. The cross-linked P84 were thoroughly evaluated using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The effects of the cross-linking time on the physical properties and H₂/CO₂ separation properties at various temperatures were determined and interpreted using a free volume model. An exemplary sample based on P84 crosslinked by BuDA for 6 h exhibits a H₂ permeability of 47 Barrers (1 Barrer = 3.35 × 10^-16 mol m/m²·s·Pa) and H₂/CO₂ selectivity of 14 at 100 °C, which is on the Robeson's upper bound, indicating their potential for practical applications.