Oxidative steam reforming of ethanol over Ru–Al2O3 catalyst in a dense Pd–Ag membrane reactor to produce hydrogen for PEM fuel cells

This study focuses on the influence of oxygen addition on ethanol steam reforming (ESR) reaction performed in a dense Pd–Ag membrane reactor (MR) for producing hydrogen directly available for feeding a polymer electrolyte membrane fuel cell (PEMFC). In particular, oxygen addition can prevent ethylene and ethane formation caused by dehydration of ethanol as well as carbon deposition. The MR is operated at 400 °C, H₂O:C₂H₅OH = 11:1 as feed molar ratio and space velocity (GHSV) ∼2000 h⁻¹. A commercial Ru-based catalyst was packed into the MR and a nitrogen stream of 8.4 × 10⁻² mol/h as sweep gas was flowed into the permeate side of the reactor. Both oxidative ethanol steam reforming (OESR) and ESR performances of the Pd–Ag MR were analyzed in terms of ethanol conversion to gas, hydrogen yield, gas selectivity and CO-free hydrogen recovery by varying O₂:C₂H₅OH feed molar ratio and reaction pressure. Moreover, the experimental results of the OESR and ESR reactions carried out in the same Pd–Ag MR are compared in order to point out the benefits due to the oxygen addition. Experimentally, this work points out that, overcoming O₂:C₂H₅OH = 1.3:1, ethanol conversion is lowered with a consequent drops of both hydrogen yield and hydrogen recovery. Vice versa, a complete ethanol conversion is achieved at 2.5 bar and O₂:C₂H₅OH = 1.3:1, whereas the maximum CO-free hydrogen recovery (∼30%) is obtained at O₂:C₂H₅OH = 0.6:1.     

Study on a catalytic membrane reactor for hydrogen production from ethanol steam reforming

Ethanol steam reforming in a membrane reactor with catalytic membranes was investigated to achieve important aims in one process, such as improvement in ethanol conversion and hydrogen yield, high hydrogen recovery and CO reduction. In order to confirm the efficiency of reaction and CO reduction, an ethanol reforming-catalytic membrane reactor with water–gas shift reaction (ECRW) in the permeate side was compared with a conventional reactor (CR) and an ethanol reforming-catalytic membrane reactor (ECR). In comparison with the CR, ethanol conversion improvement of 11.9–19% and high hydrogen recovery of 78–87% were observed in the temperature range of 300–600 °C in the ECRW. Compared with CR and ECR, the hydrogen yield of ECRW increased up to 38% and 30%, respectively. Particularly, the ECRW showed higher hydrogen yield at high temperature, because Pt/Degussa P25 loaded in the permeate side showed catalytic activity for the methane steam reforming as well as WGS reaction. Moreover, CO concentration was reduced under 1% by the WGS reaction in the permeate side in the temperature range of 300–500 °C.     

Thermodynamic analysis and heat integration for hydrogen production from bio-butanol for SOFC application: Steam reforming vs. autothermal reforming

Thermodynamic analysis of hydrogen production by steam reforming and autothermal reforming of bio-butanol was investigated for solid oxide fuel cell applications. The effects of reformer operating conditions, e.g., reformer temperature, steam to carbon molar ratio, and oxygen to carbon molar ratio, were investigated with the objective to maximize hydrogen production and to reduce utility requirements of the process and based on which favorable conditions of reformer were proposed. Process flow diagram for steam reforming and autothermal reforming integrated with solid oxide fuel cell was developed. Heat integration with pinch analysis method was carried out for both the processes at favorable reformer conditions. Power generation, electrical efficiency, useful energy for co-generation application, and utility requirements for both the processes were compared.     

Towards autothermal hydrogen production by sorption-enhanced water gas shift and methanol reforming: A thermodynamic analysis

Hydrogen production by the water gas shift reaction (WGS) is equilibrium limited. In the current study, we demonstrate that the overall efficiency of the WGS can be improved by co-feeding methanol and removing CO₂ in situ. The thermodynamics of the water gas shift and methanol reforming/WGS (methanol-to-shift, MtoS) reactions for H₂ production alone and with simultaneous CO₂ adsorption (sorption-enhanced, SEWGS and SEMtoS) were studied using a non-stoichiometric approach based on the minimisation of the Gibbs free energy. A typical composition of the effluent from a steam methane reformer was used for the shift section. The effects of temperature (450–750 K), pressure (5–30 barg), steam and methanol addition, fraction of CO₂ adsorption (0–95%) and energy efficiency of the shift systems have been investigated. Adding methanol to the feed facilitates autothermal operation of the shift unit, with and without CO₂ removal, and enhances significantly the amount of H₂ produced. For a set methanol and CO input, the MtoS and SEMtoS systems show a maximum productivity of H₂ between 523 and 593 K due to the increasing limitation of the exothermic shift reaction while the endothermic methanol steam reforming is no longer limited above 593 K. The heat of adsorption of CO₂ was found to make only a small difference to the H₂ production or the autothermal conditions.     

PTFE-nafion membrane reactor for hydrogen production

This paper presents an experimental and modelling study of the kinetics of hydrogen production through the methanol steam reforming (MSR) process using a membrane reactor with a self-made, porous PTFE-nafion membrane. The operating conditions were optimised through an analysis of the hydrogen recovery and the CO selectivity. The membrane reactor was modelled based on the hydrogen production rate, which was linked (chain) to the changes in the reactant concentrations. The analysis of the reaction kinetics provided an overview of the reaction process and the factors that affect the process. Moreover, the size of the membrane was estimated using the distribution of hydrogen concentrations along the reactor. The separation factors, particularly the separation of hydrogen from CO and CO₂, are some of the factors that can influence the performance of a membrane reactor.     

Start-up characteristics of commercial propane steam reformer for 200 We portable fuel cell system

Fuel processors in portable fuel cell systems require high efficiency, stable operation and rapid start-up time. External heating stabilizes operation of the conventional steam reforming system and allows higher hydrogen concentration in the reformate stream. In this study, we utilized a modified fuel processor that introduced a slip stream of air into the process line right before the water gas shift reactor. The air stream rapidly heated the water gas shift reactor to the desired temperature, eliminating initial CO concentration surges in the downstream. CO concentration quickly stabilized at the minimum concentration without surges by rapid preheating of the water gas shift reactor. The modified system reached a steady state within 10 min.     

Intensified bio-oil steam reforming for high-purity hydrogen production: Numerical simulation and sorption kinetics

This work proposes the production of high-purity hydrogen by an intensified non-isothermal sorption-enhanced bio-oil steam reforming (SEBOSR) process, by combining the bio-oil steam reforming over a Ni/La₂O₃-αAl₂O₃ catalyst and in-situ CO₂ adsorption over Li₂CuO₂. The kinetics of CO₂ adsorption on Li₂CuO₂ was studied experimentally and applied to assess the performance of SEBOSR in a fixed bed reactor via a non-isothermal mathematical model. Model simulations show that the prebreakthrough stage of the SEBOSR process, which corresponds to high purity H₂ production, can be extended by increasing the adsorbent loading and the S/C ratio, as well as by decreasing the inlet gas velocity. Increasing inlet temperature generates longer prebreakthrough step times but leads to a reduction in hydrogen purity. This intensified process allows to diminish the catalyst deactivation, which ultimately only occurs in the inlet region of the packed bed to some extent. In addition, SEBOSR indirectly uses sustainable CO₂-neutral biomass as a source of hydrogen; highly pure and renewable H₂ can be produced in one step (without the need of additional gas purification), via a process with enhanced thermal efficiency.