High Polymer Content m/p-Polybenzimidazole Copolymer Membranes for Electrochemical Hydrogen Separation under Differential Pressures

Abstract

High polymer content phosphoric acid (PA)-doped meta-para (m/p) polybenzimidazole (PBI) copolymer membrane was prepared via the poly(phosphoric acid) (PPA) process. This m/p-PBI copolymer membrane exhibited a much higher polymer solids content of 17 wt%, leading to the significantly improved creep resistance (1.9 × 10−6 Pa−1) compared to the homopolymer para-PBI (only 5.6 wt% and 10.3 × 10−6 Pa−1). The performance of an electrochemical hydrogen separation (EHS) device based on the m/p-PBI membrane was investigated and showed the expected operational trends according to the Nernst equation and excellent recoverability over a wide range of operating temperatures (160 °C to 200 °C) and differential pressures (10 psi to 30 psi). Utilizing the EHS technique, the hydrogen products with a purity of 99.7%–99.96% were efficiently separated from diluted reformate feed streams containing 1%–3% CO with a very high power efficiency up to 77%. The long-term durability test under 30 psi differential pressure over ∼3500 h without any signs of failure indicated that the durable m/p-PBI membranes with excellent creep resistance could be a more favorable candidate than para-PBI membranes (only ∼130 h) under challenging EHS operating conditions.