Production of high purity H2 through chemical-looping water–gas shift at reforming temperatures – The importance of non-stoichiometric oxygen carriers

Wenting Hu,Christopher De Leeuwe,John Evans,Ian S Metcalfe,Moritz Von Stosch

doi:10.1016/j.cej.2021.130174

Wenting Hu, Christopher De Leeuwe + Show 3 more

Open Access

https://doi.org/10.1016/j.cej.2021.130174

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Abstract

H2 is an important feedstock for many industrial processes and could be used as an energy carrier in a low carbon economy. This means that carbon neutral methods for H2 production are of vital importance. Chemical looping allows for H2 production with inherent carbon separation, making it an ideal system to produce low carbon H2. This work generates insights into the production of high purity H2 using a chemical looping packed bed reactor system containing an oxygen carrier of variable oxygen non-stoichiometry. Such a system has been shown to achieve 95% conversion of H2O to H2 at 1073 K outperforming the maximum theoretical conversions of 50% achieved by a conventional water gas shift reactor at that temperature. A numerical model was developed from theoretical consideration, with no fitted parameters and used to simulate the working reactor.Operando measurement of gas conversions and changes in solid oxygen capacity, through synchrotron X-ray diffraction, were used to validate the numerical model and confirmed that the reaction was thermodynamically limited. The model the model was shown to reproduce the conversion of the oxygen carrier, the reactant conversion and the product evolution.Sensitivity analysis showed that the relationship between the oxygen carrier material oxygen content and the chemical potential of oxygen in the carrier was the key consideration for the design and operation of a packed bed chemical looping reactor using an oxygen carrier of variable non-stoichiometry.

Highlights

H2 is an important feed stock for many industrial processes as well as a potential energy carrier for transportation [1]
Previous work has shown that chemical looping H2 production in such systems using oxides with variable nonstoichiometry can produce high purity H2 and CO2 (H2:H2O and CO: CO2 > 19:1 at the reactor outlets, on a molar basis) at temperatures around 1100 K [15]
For the first half cycle the oxygen carrier material (OCM) was assumed to be in equilibrium withPO2 = 9.38 × 10− 8 bar

Summary

Introduction

H2 is an important feed stock for many industrial processes as well as a potential energy carrier for transportation [1]. The product stream from these processes normally consists of a mixture of H2 and carbon-containing species, mostly CO2, and requires further separation before use [3,4]. Conventional water gas shift reactors are a mature, efficient and well developed technology and can achieve high conversion of H2 but require low temperatures (~473 K) where the thermodynamics allow for higher conversion, but the kinetics are less favourable. This requires large catalytic reactors, highly optimised catalysts and, for H2 production from methane reforming, requires the gas stream to be cooled from around 1073 K. If pure H2 via carbon capture, is required expensive and energy-intensive separation processes such as pres sure swing adsorption are needed

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