With the influx of the industrial revolution of the past centuries, the global energy demand has grown proportional to the global economical growth. Consequently, an enormous rise in greenhouse gas emissions has been observed, where the major contribution to global warming comes from the rising concentration of CO2. Therefore, the concept of capturing CO2 directly from the air (DAC) has gained world wide attention as it can reduce the carbon footprint of men kind.
Zero Emission Fuels (ZEF), an inspiring start-up based in Delft, aims to develop a micro plant that utilizes the DAC concept to produce methanol as a fuel, using only the sun as its energy source. CO2 and H2O is captured directly from the atmosphere by the DAC unit which operates continuously with the help of an amine sorbent that flows through an absorption and stripping column. Previous research shows pure tetraethylenepentamine (TEPA) having great potential as a CO2 capturing sorbent. However, it has some limitations regarding slow absorption and desorption kinetics due to a high sorbent viscosity, that prevent ZEF from reaching their goal of capturing 825 grams of CO2 per DAC unit in
eight hours of operation. The focus of this research is on the sorbent selection process of ZEF’s DAC system. Research has shown that adding a diluent to TEPA could potentially improve the performance of the ZEF DAC unit. Therefore, a total of nine diluents, DEG, PEG-200, PEG-400, PEG-600, selexol-250, selexol-500, glycerol, 1,4-butanediol, sulfolane, mixed in different ratio’s with TEPA, have been put to the test through the developed framework of sorbent selection.
In the framework of sorbent selection all the sorbents are tested through four different experiments, keeping efficiency and costs in consideration. The Airfarm experiments are used to evaluate absorption capacity and viscosity of the sorbent at specific ambient conditions. The Vapor-Liquid-Equilibrium (VLE) experiments are utilized to evaluate the desorption characteristics of the sorbent from where the regeneration energy demand can be calculated with the help of a mathematical model. The re-pumping experiments are used to evaluate the absorption kinetics of the sorbent and lastly, the degradation experiments
are used to evaluate the sorbent life time performance. After the experimental procedure the sorbents can be judged on the key performance indicators regarding the ZEF DAC unit operated in a specific climate. It was concluded through the literature research and proved by an extensive experimental research
that selexol, glycerol and sulfolane did not improve the characteristics of the sorbent. However, adding DEG, PEG or 1,4-butanediol to TEPA did have a profound positive effect on the overall performance of the DAC unit. Since the diluents reduce the sorbent viscosity, and therefore, increase the absorption
and desorption kinetics. Based on the experimental results and the design specifications set by ZEF, PEG-200 proved the most promising out of all diluents in the mixing ratio TEPA:PEG-200 2:5. This sorbent has been tested for two different climates; the dry Sahara climate and the more humid Mediterranean climate to see how the sorbent would have to be changed for different climates. It was concluded, for a more humid climate, it requires less diluent for the sorbent to stay within the 2 푃푎 ⋅ 푠 viscosity limit. The experimental results were included in a full DAC model to design the DAC unit utilizing the optimized sorbent for the two different climates considering the design specifications set by ZEF. Following
a sensitivity analysis an optimized conceptual DAC design was obtained for both climates. Where it was concluded that the optimized sorbent resulted in reduction in energy requirement for regeneration of the sorbent, where 1554 푘푊ℎ/푡표푛 of CO2 is needed for the Sahara climate and 1636 푘푊ℎ/푡표푛 of CO2 for the Mediterranean climate. Finally, a cost analysis has been performed regarding the operational and capital costs of the newly designed conceptual DAC units for both climates.

Over the past few decades, there has been an increased awareness and concern about the rising pollution, global warming, sudden climatic changes, and the accelerating CO2 emissions that have coerced people to shift to renewable resources and sustainable fuels. Zero Emission Fuels (ZEF) is a leading startup company that focuses on developing a sustainable methanol micro-plant that is powered by solar energy. CO2 and H2O are absorbed from the air (DAC system) and the extracted H2O is split into H2 (AEC system) in order to produce a methanol-water mixture where the mixture is then separated using a Distillation System (DS system). Each micro-plant operates for 7 hours per day and produces 600 g of methanol. with a distillate methanol purity of 99.8% (AA grade methanol) and in the future ZEF is planning to develop a ‘methanol farm’ with 13500 micro-plants.
Based on a previous study at ZEF, fractional distillation was seen as a potential system for separating methanol and water mixture with desired purity. On the other hand, it was also suspected that implementing multiple decentralized separation units could be expensive with higher energy consumption and therefore alternative methods of implementing the DS system were analyzed. For this purpose, 3 different schemes namely Decentralized (1 DS per micro-plant), semi-centralized (1DS per 1000 micro-plant) and centralized (1 DS per 13500 micro-plant) were analyzed. Furthermore, heat integrations were introduced as various literature pointed out that a significant improvement in the total cost and energy consumption was observed and hence they were adapted to ZEF requirements. Therefore, six different systems namely conventional distillation (base case), Feed pre-heating, Vapour recompression, Bottom flashing, External heat integrated distillation and Vapour compression systems were suggested. The primary focus of this research will be to analyze these different distillation designs for all the three schemes and recommend a feasible design for the DS sub-system that is both energy-efficient and economically viable along with analyzing the impact of varying ambient conditions on the DS system.
For this purpose, each of these systems was modelled in COCO and the modelling results obtained were used in analyzing the overall energy consumption and the total cost of each design. Different scenarios were analyzed, preliminary equipment designs were estimated. Each system was compared and evaluated in terms of energy and cost-saving and a quantitative and qualitative analysis was performed. Based on this analysis a centralized VRC and base case systems powered by solar PV operating for 7 hours were recommended. In order to understand the impact of fluctuating solar radiation and ambient temperature on the DS system, a MATLAB model was developed. From the results, it was evident that the fluctuating ambient conditions affected the product purities and the startup and shutdown of the DS system. A feed mass flow-temperature control was implemented for Centralized base case system, where the feed mass flow rate into the DS system was adjusted depending on the fluctuating power input. The control structure was able to effectively control the distillate and bottom purities by varying the feed mass flow rate.

The world is currently in the middle of an energy crisis, with a growing demand for energy playing catch up with an increasing population. The problem stems from the fact that we rely heavily on fossil fuels to meet our energy needs, and the combustion of these fuels are the primary source of greenhouse gas emissions. An accelerated rate of emissions of greenhouse gases has led and continues to lead to an increase in the average temperature of the planet, stated: Global Warming.
Shifting the balance in our favour requires arresting and lowering our emissions. Direct air capture of Carbon dioxide is one solution that has garnered massive traction in the global scientific community. Zero Emission Fuels is a visionary start-up operating out of Delft that aims to build a micro-plant capable of producing methanol using energy derived from the sun and raw material (CO2and H2O)harnessed from the atmosphere. The heart of their concept is liquid amine-based direct air capture. ZEF has pioneered the continuous process that involves the simultaneous absorption and desorption of CO2and water as the amine circulates from the absorber to the desorption column. The raw material and the energy to drive the process is harnessed from the environment. Thus these inputs remain outside the control of the ZEF system and are treated as external disturbances. This research aims to analyse the impact of the varying environmental conditions, i.e. the ambient temperature, absolute humidity and incident solar radiation, on the performance of the desorption column. Following which a control scheme is developed to ensure the system meets the requirements of ZEF, i.e. production of CO2and water in a 3:1 molar ratio and an energy consumption limit of 450 kJ/mole of CO2desorbed.Firstly, a set of experiments with a trayed stripping column were performed to understand the start-up and shut-down behaviour of the column. Based on the observations, a simplistic model of the reboiler was developed to predict the transient behaviour of the column during start-up. A sensitivity analysis was carried out to gain insights into the parameters influencing start-up time and energy demand. Furthermore, different scenarios to start up a column were identified and based on the results, the batch mode is adopted as the efficient way to start up a column. The model predicts that start-up and shut-down account for less than 10% of the total operating time available. Moreover, start-up accounts for a maximum of 6% of the total available energy for production.
Secondly, a set of single-stage kinetic experiments were performed at different temperatures to understand the limitations of the desorption process inside the column. A vapour-liquid equilibrium based stage-by-stage model of a desorption column integrated with a varying space-time yield based absorber model. Design parameters of the integrated DAC model were tweaked, and a base case was developed, to understand the impact of a varying sorbent composition and PV panel output on the performance of the DAC subsystem. It was clear the open model was not capable of meeting the 3:1top ratio specifications of ZEF. Which prompted the implementation of control structures. Single loop mass-flow control, pressure control and cascade mass flow-temperature control schemes were individually tested with the aid of the integrated DAC model. Finally, based on the performance of the individual control schemes, a final parallel control scheme was developed. Wherein the temperature and the pressure of the system adjusts according to the varying power input and the absolute humidity conditions that impact the top ratio of products. The parallel control scheme was found to be adequate in maintaining the top ratio at desired levels.