Advancements in mixed amine atmospheric kinetic models (Flexible Funding 2021)

We’re pleased to share the blog report as an output of ‘Advancements in mixed amine atmospheric kinetic models‘, one of our Flexible Funding 2021 projects from Dr Kevin Hughes and Prof Mohammed Pourkashanian, and their Research Associate Dr Christopher Parks, at the University of Sheffield.

Context

Modern civilisation is built on the exploitation of the world’s natural resources, chief amongst these being the burning of fossil fuels – coal, oil and gas to provide energy. A byproduct is the release into the atmosphere of carbon dioxide, thus pushing up the atmospheric carbon dioxide concentration approximately 50% since the beginning of the industrial age. It has been known for many years that carbon dioxide acts as a “greenhouse gas” leading to a warming of the lower atmosphere that could impact the world’s climate, and climate change in the context of global warming arising from these carbon dioxide emissions and the problems it leads to – ever more extreme weather events, sea level rise and potential disruption to world food production is an issue taking on ever more urgency in the world’s consciousness, as exemplified by the ongoing series of the “conference of the parties” (COP) meetings under the auspices of the United Nations,  first held in the 1990s and most recently culminating in COP26 held in Glasgow in 2021 leading to a range of commitments designed to limit the average rise in world temperature to within 1.5 °C of pre-industrial levels. In the context of the UK, this has led to legislation being introduced to require the country to reach a “net zero” level of greenhouse gas emissions by 2050.

Implications – why is this research needed?

A net-zero target of greenhouse gas emissions implies that the major sources of carbon dioxide emissions will need to be eliminated. While efforts are underway to increase renewable power sources such as wind and solar, there is still a role for gas-fired power generation for the foreseeable future as a flexible backup to when wind or solar is insufficient. The carbon dioxide emitted will thus need to be captured, and similarly from large single point industrial sources such as steel and cement production. The capture technology most likely to be deployed involves retrofitting existing plant to capture the carbon dioxide from the flue gas using an amine-based solvent. This solvent is continually recirculated through a stage of carbon dioxide capture, then stripping of the captured carbon dioxide to storage, regenerating the solvent to be reused in the capture stage. It is unavoidable that some of this solvent escapes the capture plant and is emitted into the atmosphere where the question arises at to what happens to it, and especially in terms of any potentially harmful products it may produce. This project aims to address that question by developing models to predict what happens to this solvent, based on a fundamental understanding of the chemistry of the processes that occur, and thus increase our understanding of both existing solvents used in this process, and possible alternatives, or even mixtures of solvents that might be used in the future.

Modelling Details

A commercial software package, Gaussian 09, was used to predict the properties of the chemical species that compose the solvent or solvent mixture, and to predict the outcome of their reaction with other chemical species that might be released in the flue gas or already present in the atmosphere. This gives details on the structure of both the reacting species, their products, and any intermediate species that connect the reacting species to the products allowing a ”potential energy surface” for the system. Two specific amine solvents that may in future be used in carbon dioxide capture were investigated, namely AMP and piperazine. Reaction networks for the atmospheric degradation of each are illustrated in figures 1 and 2.

Figure 1: Schematic reaction network for atmospheric degradation of AMP

Figure 2: Schematic reaction network for atmospheric degradation of piperazine

Analysis of the species properties calculated by the Gaussian 09 software allows the prediction of how fast the individual reactions represented in figures 1 and 2 occur. In ongoing work these will be used to adapt the atmospheric dispersion model, known as ADMS, to be able to predict the real-world outcome of the release of these solvents into the atmospheric conditions prevalent in the locations where these capture plants are likely to be constructed in future.