Poisoning of Ammonia Synthesis Catalyst Considering Off-Design Feed Compositions

Alireza Attari Moghaddam,Ulrike Krewer

doi:10.3390/catal10111225

Abstract

Activity of ammonia synthesis catalyst in the Haber-Bosch process is studied for the case of feeding the process with intermittent and impurity containing hydrogen stream from water electrolysis. Hydrogen deficiency due to low availability of renewable energy is offset by increased flow rate of nitrogen, argon, or ammonia, leading to off-design operation of the Haber-Bosch process. Catalyst poisoning by ppm levels of water and oxygen is considered as the main deactivation mechanism and is evaluated with a microkinetic model. Simulation results show that catalyst activity changes considerably with feed gas composition, even at exceptionally low water contents below 10ppm. A decreased hydrogen content always leads to lower poisoning of the catalyst. It is shown that ammonia offers less flexibility to the operation of Haber-Bosch process under fluctuating hydrogen production compared to nitrogen and argon. Transient and significant changes of catalyst activity are expected in electrolysis coupled Haber-Bosch process.

Highlights

Use of intermittent renewable energy (RE) sources, like solar and wind power, causes an imbalance between electricity supply and demand
In the temperature range between 673–773 K, which is mostly practiced in industrial applications, an almost linear dependency can be seen with a similar slope for different water concentrations
Activity of an iron-based catalyst for the synthesis of ammonia in variant conditions of the electrolysis coupled HB process was studied. It was shown for all gas compositions that, increasing the water content by only few ppm’s changes the activity of the catalyst significantly

Summary

Introduction

Use of intermittent renewable energy (RE) sources, like solar and wind power, causes an imbalance between electricity supply and demand. One way to deal with this, is to convert surplus electrical energy produced from renewable sources into chemical energy for energy storage. The molecules should be preferably carbon-free liquid fuels, and their chemical energy should be convertible back into electricity on demand (power-to-x-to-power) [1]. This would enable better geographical accessibility to power through the transport of RE in the form of liquid fuels or through decentralized power-to-x-to-power units. Among energy-dense carbon-neutral liquid fuels, ammonia and its production from renewable resources, known as power-to-ammonia, has gained special attention [2,3].

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