CO2 concentration in the atmosphere is increasing leading to global warming and thus, climate change. Moreover, current renewable technologies such as wind or solar energy only cover the electricity market. A big part of the global energy market is still based on fossil fuels and difficult to electrify. Hence, there is an urgent need to produce renewable liquid hydrocarbons to replace fossil fuels. Zero Emission Fuels (ZEF) is a start-up that aims to develop a small-scale chemical plant to convert carbon dioxide (CO2) and water (H2O) from the air into methanol (MeOH) using photovoltaic energy. In this work, the absorption of CO2 using bulk polyamines was characterized experimentally, as well as through numerical modelling. In addition to this, guidelines for the design of the absorber, part of the Direct Air Capture (DAC) unit of ZEF’s micro-plant, are given. The focus of the study is placed on the kinetics and loading of CO2. To be able to model the absorption process an experimental approach has been developed regarding the uptake of CO2 and H2O. Firstly, pure H2O absorption experiments were performed in a climate chamber in order to obtain the H2O loadings using polyamines for different H2O content in the air. Secondly, air capture experiments were performed at lab conditions in order to obtain both H2O and CO2 loadings for different process conditions. Thirdly, constants relevant for the modelling part (reaction rate constant and Henry constant) were obtained experimentally. An absorption model, developed in MATLAB, was used to estimate the diffusion coefficient of both H2O and CO2 using the experimental H2O and CO2 loadings.
Two main conclusions are obtained from the absorption model of CO2: the absorption of CO2 on polyamines is diffusion-limited and the diffusion coefficient of CO2 is two orders of magnitude lower than the diffusion coefficient of H2O. Based on the fact that the CO2 absorption process is diffusion-limited the mixing patterns should be introduced in the design of the continuous absorber. However, due to the fact that viscosity could influence the flowing behaviour of polyamines, more research is needed.