Valorisation of biodiesel byproduct glycerol for hydrogen production via self-catalytic nickel membrane reactor

As a plentiful byproduct of biodiesel production, crude glycerol is difficult to purify and utilise efficiently. Its conversion to hydrogen represents an effective approach toward sustainable energy cycles but remains a formidable challenge. Here, we present an asymmetric nickel hollow fiber membrane (ANHFM) reactor that simultaneously enables glycerol steam/oxidative-steam reforming (GSR/GOSR) and selective H 2 separation in a single unit operation. Capitalising on in-situ H 2 separation, this system delivers two proven advantages: (i) shifting the reaction equilibrium to enhance H 2 yield through an apparent equilibrium shift due to in-situ H 2 extraction, and (ii) eliminating downstream H 2 purification requirements. Additionally, this continuous H 2 removal may inherently mitigate competitive H 2 oxidation pathways. The asymmetric architecture integrates an ultrathin dense separation layer with a porous catalytic support, demonstrating intrinsic self-catalytic activity and superior H 2 flux. Under optimal GSR conditions (900 °C, S/G=18), the system achieves exceptional performance, with 93.76% glycerol conversion, 87.71% H 2 yield, and a H 2 flux of 16.60 ×10 -3 molm -2 s -1 . Introducing oxygen (GOSR at 850°C, O/G=0.4) effectively suppressed coke formation, resulting in only a marginal reduction in hydrogen flux of approximately 6.04%, while simultaneously reducing the performance decay rate by about 70.11%. This design demonstrates the potential for distributed H 2 production from crude glycerol, balancing high conversion efficiency with operational stability across both GSR and GOSR modes.