Hydrogen production and geometry optimization of ethanol steam reforming combining water gas shift reaction in a crossflow membrane tube reactor

Abstract

Crossflow tube reactors are a novel design showing excellent H2 production and separation potential. A membrane reactor enables H2 production and separation in the same unit and helps the reaction overcome the equilibrium conversion limitations. This work investigates the performance of ethanol steam reforming (ESR) followed by a water gas shift reaction (WGSR) for H2 production and separation. Crossflow catalytic tubes are designed in ESR and WGSR, and Pd-based membrane tubes are installed behind the WGSR to permeate H2 and enhance the chemical reaction. The effects of inlet temperature, steam-to-ethanol molar (S/E) ratio, and reaction pressure on the system performance are investigated. The results showed that a higher inlet temperature lowers H2 yield, and 600 °C is the most suitable temperature for this system. The S/E ratio at 3 leads to the highest H2 recovery. Higher S/E ratios may increase ethanol conversion but result in more steam in the reactor, lowering the H2 partial pressure and recovery. Two-stage design optimization is performed for the WGSR catalytic membrane tubes. In the first stage with parametric sweep, the H2 yield and recovery are improved by 1.25% and 22.27%, respectively. In the second stage via the Nelder-Mead method, the H2 yield and recovery are further improved by 6.79% and 18.76%, respectively. The two-stage optimization in total intensifies 8.8% H2 yield and 45.22% H2 recovery. A comparison between ESR + WGSR/without membrane and ESR + WGSR + membrane with optimization suggests the H2 yield is substantially lifted by 22.26%, and only 0.34 times catalyst is applied in the system. The results show that an optimized crossflow membrane reactor has excellent prospects for effective hydrogen generation and separation.