(574g) CO2 Impurities Impact on Methanol and Methane Synthesis

For the application of carbon capture and utilization in emitting industries (e.g. iron and steel, cement, waste-to-energy, refineries etc.), the impact of CO₂ impurity components within the process chain is a critical issue which must be assessed for successful technology deployment. Flue- and off-gases targeted for capture comprise a range of components other than CO2, including contaminants at low concentrations in the parts per million or parts per billion region (e.g. SO_x, NO_x, Hg etc.). These have the potential to form impurity compounds in resulting CO₂ product streams that are amenable for use as feedstock to CO₂ utilization processes. The range and level of impurities in CO₂ streams captured from different industrial sources present differently depending on industry type, fuels and feedstocks, capture system employed, modes of operation, and additional pollution control systems used.

Selecting an appropriate CO₂ utilization route for a given emission source will also depend on a range of market factors including capacity and product value along with technical factors such as process scale and economics. Important amongst the technical considerations is the presence of impurities in the feedstock CO₂ stream for the conversion process. This is because impurities can have a range of potentially deleterious effects on CO₂ conversion. These effects include i) dilution, mainly from inert gases, ii) modification of catalyst properties, such as by adsorption on, or reaction with, a catalyst surface, iii) competition with CO₂ as reactant, and iv) contamination of products.

In this paper, we discuss how impurities that may exist in captured CO₂ can affect subsequent utilization processes and summarise the progress in this emerging research area. We begin by examining published works that investigate the influence of the interactions between impurity gases and the thermochemical CO₂ utilization processes of methanation and methanol production. These studies include several types of catalysts and involve various concentrations of impurities. We then use the information generated in the comprehensive review to define limits for CO₂ impurities for the CO₂ utilization processes. We next perform analysis using the data generated from the review and impurity limits definitions in order to match the most appropriate capture technologies and sources to specific CO₂ utilisation applications. Suitable technology matches are identified based on the tolerance levels for impurities of specific utilization technologies and estimated cost of CO₂ purification processes.