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 at 100 °C or above are of great interests for pre-combustion CO₂ capture. 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 100–150 °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 cross-linked 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.