Capturing Carbon Dioxide directly from the air: A theoretical modeling approach

Direct Air Capture processes capture carbon dioxide directly from the air and aim to utilize the captured carbon dioxide; this would allow CO2 capture independent of source and location and can therefore address all CO2 emissions. Although already quite some processes and materials exist that are capable of this, it is still not yet widely applied in industry. The aim of this thesis is to first select a suitable material and then provide the tools to start designing such a process. The present work focuses on a solid (primary) amine-based sorbent and models the CO2 capture process on both a molecular scale, using quantum chemical calculations, as well as on a macroscopic scale, using a numerical representation of a fixed bed adsorption column. The quantum chemical calculations in the present work show that in order for this specific sorbent to capture CO2 the reaction needs a catalyst. It was found that functional amine groups are close enough to each other to catalyze CO2 capture. Besides that it was found that H2O can also catalyze the CO2 capture. The CO2 reacts with these molecules to either form a carbamic acid complex or a bicarbonate complex with the other (protonated) amine. The H2O catalyzed CO2 capture, where it reacts to form carbamic acid, was somewhat unexpected; no reports of this mechanism were encountered in literature during the study. The results of the quantum chemical calculations were successfully implemented in the numerical model and were able to describe the sorbent’s CO2 capacity as a function of temperature. The numerical model can be used as a design tool to estimate parameters such as speed of adsorption and can serve as an input for design calculations. Processes using solid sorbents seem to be highly scalable. They can be applied everywhere and can be designed as a modular system. Once a single DAC unit has been designed that captures 1 kg of CO2 a day it can used in a modular system of several units, eventually scaling up to tonnes of CO2 per day. The sorbent in this study regenerates the CO2 at a temperature of approximately 80 ⁰C which could be supplied in the form of waste heat. Using this technology, CO2 becomes available everywhere, makes further use of waste heat and is able to address CO2 emissions from every source (vehicles, industry, residential).Mechanical, Maritime and Materials EngineeringProcess and Energ