Global warming and climate change due to the excess release of CO2 from human activities has been one of the world’s problems for a number of years now. Many ideologies have been born in the quest to seek a solution to this global problem. One of the captivating solutions is to use right proportions of different sources of fuels together with a post combustion carbon capture technology to achieve net zero or negative CO2 emissions (Avor et al., 2022).

Post combustion carbon capture technology using solvent absorption has proven to be very reliable and efficient. However, some critical challenges faced by investors include solvent cost, solvent loss and cost of solvent regeneration. Monoethanolamine (MEA) being the most explored alkanolamine absorbent and the benchmark for all other absorbents is noted for high absorption rate, low solvent cost and low viscosity. Nevertheless, MEA has high rate of degradation which leads to high solvent loss.

Degradation in the context of CO2 capture process, refers to the loss of active sites of an absorbent. It is caused by the unsought side reaction between an absorbent and either oxygen, NOx, SOx or other flue gas impurities such as particulate matter and heavy metals. High temperatures are also known to aid degrade absorbents to form degradation products. Solvent degradation is an important parameter to consider during solvent selection for commercial use in CO2 capture process. Solvent degradation does not only lead to solvent loss but degradation products like carboxylic acids and heat stable salt (HSS) promotes corrosion. Also, nitrosamines emitted due to some absorbent reaction with NOx poses a threat to human health. There are chances of fouling and solvent foaming due to degradation. Least to mention is the increase in operational cost due to increase in heat duty required for regeneration because of the presence of degradation products.

This work seeks to evaluate the stability of a new amine blend which has better CO2 absorption and cyclic capacity compared to the benchmark, 5M MEA (Avor et., 2022). The degradation studies of the new amine blend will be fully characterised in terms of reaction kinetics and mechanisms. This will be done by running a simulated co-combustion flue gas of biomass and natural gas through the new amine blend at various absorption and desorption conditions for long hours. Also, gases emitted from the study will be analysed to ascertain how safe the process is to our environment.

Among the most developed CO2 capture processes is the amine-based chemical absorption process. Nevertheless, implementing the amine-based chemical absorption technology in industrial processes such as fossil fuel power plants, cement production, iron, and steel industries face the challenge of accelerated solvent degradation in the presence of trace components of particulate matter (PM), O2, NOx, and SOx.

Upon degradation, the concentration of the solvent is reduced hence the need to replace the degraded solvent. This increases the operating cost of the CO2 capture plant. In addition, nitrosamines and nitramines products resulting from the degradation of amines in the presence of NOx have been reported to be hazardous and carcinogenic, hence, poses a threat to human health and the environment (Vega et al., 2018; Selin, 2011). Also, beyond the associated health problems, PMs are responsible for causing clogging, fouling, erosion and corrosion of downstream process equipment (Acharya, 2018).

While O2 is almost impossible to be removed from flue gas streams, technologies such as electrostatic precipitators (ESPs) and cyclones have been employed over the years to get rid of particulate matters. However, due to the limited removal efficiencies achieved with the use of ESPs and cyclones, additional treatment processes are needed for the further removal of PMs from the flue gas.

This current work focuses on a laboratory exploration to develop a solvent to pre-treat the flue gas by selectively extracting the SOx and NOx prior to the CO2 absorption unit. Through this work, solvents will be screened for rigorous analysis upon which an optimum solvent will be formulated either as a blend or a newly developed solvent. Furthermore, empirical data collected during the research will be evaluated to study the performance and kinetics of the developed solvent.

As the world moves toward a more efficient and cleaner energy ecosystem, research in energy systems improvement and clean fuel technologies have taken the forefront of scientific studies within this domain. However, the development of innovative solutions from the laboratory to an industrial scale can be extremely costly, restricting the breadth of experimentation.

In addition, the world is currently on the precipice of a dramatic transition that requires a reduction in anthropogenic CO2 emissions in order to keep climatic conditions from tipping outside of our collaborative efforts. This in turn has prompted a slew of research in the field of Carbon Capture, Utilization and Storage. Amongst these solutions is the use of amine-based solvents as absorbent to extract CO2 from flue gas. This approach to dealing with the emission menace allows for the effective control of emissions and to preserve our industrial edge while reducing our impact/footprint on the natural environment.

Despite the fact that the most significant challenges to the amine absorption-regeneration approach to capture CO2 from flue gas has to do with solvent management and a higher cost of regeneration energy, research has been done to develop ionic solvents that mimic the performance of these amine-based solutions but with a better stability.

A newly developed ionic solvent, is to be tested in order to understand its performance and utilization on an industrial scale. Thus, necessitating the development of a mathematical model as a first point of system assessment, to adequately predict the performance and reliability of the solvent in both its catalyzed and uncatalyzed states, based on physicochemical properties, empirical data, reaction kinetics and thermodynamic behaviors, while also serving as a quick and easily accessible aid to system diagnostics and troubleshooting.

Application of CO2 Loaded Ionic Solvent in Concrete

The increase in CO2 emissions, as a major greenhouse gas, has led to increase in average global temperature. At present CO2 levels in the atmosphere are more than 412 ppm and rising. To succeed in limiting the increase in global temperature to 1.5˚ C above pre-industrial levels, CO2 emissions worldwide must be reduced substantially in all sectors of the economy. Carbon capture utilization and storage (CCUS) provides a means of producing low-carbon electricity from fossil fuels and of reducing CO2 emissions from industrial processes such as gas processing, cement and steel making, where other decarbonization options are limited. However, there is urgent need for research and development to deliver even more cost-effective CCUS technologies for the capture, conversion, utilization, transportation, and storage of CO2 (Zhang et al., 2020; Zhu, 2019). Studies on various means of reducing CO2 emission or on the capture, storage and sequestration of emitted CO2 have been conducted to provide mitigation measures for greenhouse-induced temperature increases from a medium-and long-term perspective. Geologic sequestration, among others offered as a substitute for the sequestration of captured CO2, was until recently thought of as the main method of CO2 sequestration.

Although the geologic sequestration method has the capacity to sequester a significant amount of CO2, recent reports of its high cost, little economic added value, and occasionally unfavourable environmental effects indicate a need for a more developed technology. Henceforth, utilizing captured CO2 in a process that yields valuable materials has consequently recently attracted a lot of attention. One of the prime examples is the sequestration of CO2 by mineral carbonation and transformation into an industrially useful product using similar processes. Cement-based substances, such as unhardened cement paste, mortar, concrete, and waste from these cement-based products, can be carbonated in order to absorb CO2 more effectively. Due to their tremendous strength, exceptional durability, and financial advantages, cement and concrete are the most often used construction materials worldwide (Jang et al., 2016).  Despite the fact that the cement sector is responsible for 27% of all direct industrial CO2 emissions and 8% of worldwide CO2 emissions, CO2 is still necessary for the curing (carbonation) of concrete and other cement-based materials which is as a result of a reaction between the CO2 and the cement hydrate. (Zhaurova et al., 2021).  Among the benefits of carbonation of cement-based material are early strength, reduction in shrinkage, reduction in water permeability and efflorescence in the cement-based material (Monkman & Shao, 2010).The methods under investigation for the utilisation of CO2 in cement-based material include dissolving recovered CO2 in water and adding it to the cement-based material as well as injecting recovered CO2 from exhaust gases into a precast cement-based material in a closed chamber. However, this technology has not been successful in achieving the efficiency of CO2 uptake by cement-based material due to the poor solubility of CO2 in water (Han et al., 2022; Monkman & Shao, 2010). On the other hand, recovering CO2 from exhaust gas and injecting it into a precast cement-based material is seen to have many drawbacks. Despite the equipment cost and energy requirement cost involved in capturing the CO2, precipitation of the calcium carbonate decreases the porosity, inhibiting CO2 diffusivity in the cement-based material (Jang et al., 2016; Monkman & Shao, 2010).

This study seeks to investigate the utilization of CO2 in cement-based material by using a CO2 loaded ionic solvent. In this case, the CO2 captured from industrial exhaust gas is absorbed using a catalyst aided solvent which is being worked on by fellow research students.  After the absorption of the CO2, the CO2 rich solvent will then be utilized directly in a cement-based material without desorption to accelerate curing and also improve on the strength and other beneficial properties of the cement-based material. Despite the efficiency and permanent utilization of CO2 by this method as reported in similar work done by (Yu et al., 2019) by using CO2 loaded solvent in CaO rich industrial waste, the cost of desorption column and other ancillary equipment as well as cost of energy requirement for CO2 desorption is also eliminated.  For quality assurance of the concrete cured by this method, analysis or tests such as compressive strength, tensile strength, modulus of elasticity, permeability test, density, thaw resistance, resistance to chemicals, resistance to abrasion will be run on the cured concrete. The results of these tests will be compared with that of concrete cured by the conventional method as a benchmark. Moreover, in order to ensure that the captured CO2 is retained in the concrete, CO2 leakage test is also carried out on the cured concrete samples.

In the pre-industrial era, the amount of CO2 released into the atmosphere due to the natural geological processes was almost equal to that of sinking back to the land, vegetation, and ocean. It can be said that the carbon cycle was balanced. Due to human evolution especially in the industrial era, human activities create CO2 much faster than natural geological processes, leading to an imbalance of the carbon cycle that directly affects global warming and climate change. Previously, scientists argued that the global temperature rise must be kept below 2°C by the end of this century to avoid the worst impacts. However, with heavy emissions of CO2, the temperature rise should rather be kept below 1.5°C (Paris Agreement) which is now considered as a far safer temperature limit for the earth.

As shown from the top part of our graphical abstract, the carbon budget term is used to quantify the amount of additional carbon we can add to the atmosphere before the global temperature reaches +1.5°C. According to the latest annual update of the global carbon budget for 2021, the concentration of CO2 in the atmosphere has already reached 414.7 ppm or 50% above pre-industrial levels, which gives rise to about 1.2°C warmer temperature than that observed in the late 19th century. With the current rise rate of temperature, the carbon budget remained before the 1.5°C rise reached is only 360 Gt CO2. This would mean if CO2 emissions are allowed to still occur at the current rate we have, it will only take 10 years for the global temperature to rise by 1.5°C. This scenario is undesirable and must be prevented. Also, having carbon budget of 360 Gt CO2 does not mean that it is ok to still keep emitting the CO2 to the environment as long as the threshold limit is kept. CO2 will always give adverse effect to human and the environment regardless of its amount being released.

Our graphical abstract also shows the averaged global carbon cycle perturbing by anthropogenic activities for the decade 2011–2020 (GtCO2/yr) (Friedlingstein et al., 2022).  The amount of CO2 emitted from fossil fuel and industry is enormously high (33-37 GtCO2) compared to those from deforestation and land-used change (2-7 GtCO2), while the ability of nature able to sink the CO2 into land and vegetation (9-13 GtCO2) and ocean (9-12 GtCO2) is not sufficient to balance the cycle. Therefore, approximately 19 Gt of CO2 still remains in the atmosphere whose amount then reduces the global carbon budget year by year. To prevent the CO2-induced climate change effect from being further aggravated, the amount of CO2 released into the atmosphere should be minimized as much as possible or even cut down to zero. This will surely get us to become a true carbon neutral or net-zero carbon society which is regarded as the best effective scenario to fight against global warming and climate change.

As noticed in the article of Global Carbon Budget 2021 (Friedlingstein et al., 2022) a large quantity of CO2 is emitted from fossil fuel combustion. Thus, one best option used to effectively cut down the CO2 is to stop producing electricity from fossil fuel burning. However, this option is quite difficult to achieve on a global scale because a constant increase in demand for power and electricity for human living still relies heavily on fossil fuels (e.g. coal, oil, and natural gas) as the main source of energy (i.e. more than 80% of the world’s energy). Due to this, the next best option must be considered which is done by integrating the CO2 capture process as part of the fossil fuel-based power generation.

This can also be done in conjunction with cutting down the consumption of heavy emitter sources like oil and gas but increasing lighter emitter like natural gas in the power production process. Incorporation of renewable biomass to the power production must also be done to reduce the amounts of fossil fuel used to minimum possible. Combination of all these will surely help us move more quickly towards becoming a carbon neutral or net-zero society mandated for safety for human and environment.

Though the post – combustion capture process by absorption – regeneration is the more mature technology in Carbon Capture Utilization and Storage (CCUS), its cost reduction is still necessary and requires immediate attention. The high cost in the capture process relates principally to infrastructure, energy and disposal of the CO2 captured.

If some of the infrastructure with its ancillaries could be removed from the capture process, then the cost involved in the capture process could be drastically reduced and the only problem would be how to dispose of the CO2 captured without re-introducing it back into the atmosphere. This work seeks to solve both the issues of cost reduction and the disposal of CO2 captured in an environmentally friendly manner.

In this work, a catalyst is being developed to accelerate CO2 absorption to boost CO2 loading in a novel solvent that is also being developed by the group. This catalyst, which is alkaline, would generate a catalytic pathway where a lower activation energy is required for the absorption process and provide a large inter-facial area for mass transfer. This would help the system to approach equilibrium faster than the non-catalyzed reaction, which would enable the use of a much smaller absorber vessel and a higher CO2 uptake level in the solvent.

The rich solvent would be utilized in the making of concrete, mortar and grout after it has chemically absorbed CO2 from the exhaust gas of major industries and power plants. In the concrete-based industry, the rich solvent would replace the water component used during the concrete or mortar making process. Using CO2-loaded solvent facilitates CO2 utilization in the concrete-based industries. This would help to accelerate the curing process leading to the complete curing of the concrete.

By this approach, CO2 will be captured using a smaller absorber vessel, the regeneration (desorption) section of the capture process will be eliminated as well as its ancillaries and energy requirements, and CO2 will be utilized and permanently stored in the concrete, mortar and grout.

Effect of Intermolecular Interaction of Amine on Specific Heat Capacity and Heat Vaporization

The knowledge of intermolecular forces and their strength between molecules of amines is a very important piece of information that one can use to determine the behavior of amines used for capture of carbon dioxide from industrial exhaust gases. In today’s what’s cooking post, we discuss on how the intermolecular forces that hold molecules of the amine together affect its specific heat capacity (Cp) and heat of vaporization (ΔHvap) which in turn, can affect the heat consumption of the amine process.

Intermolecular forces stem from the attraction of opposite charges that exist between molecules of a compound. Strength of these forces are highly dependent on the atomic and molecular arrangement of the compound’s molecule. Two major factors that have a direct impact on the strength of the forces are;

1. The molecule’s size of electron cloud and
2. The extent to which it can distort to form opposite charges on the molecule.

In general, an increase in the electron cloud size which commonly can be estimated by the number of electrons of that compound, increases the force strength. The same trend is also applied to the ability to distort the molecular electrons, which if increased, the strength of the intermolecular attraction will also increase. Our graphical abstract shows a side-by side comparison of 2 amines whose intermolecular forces are weak and strong, respectively. The amine molecules with weaker intermolecular interactions (e.g. smaller electron cloud and smaller electron cloud distortion) experience less attractive forces between them. As a result, the molecules are only held together loosely.

Such a situation provides the molecules with more freedom of movement which further facilitates the amine in the process of gaining kinetic energy upon the absorption of heat and allows the amine temperature to rise easily. This phenomenon is reflected in the amine’s lower Cp, an intrinsic property of amine that shows the amount of energy needed to raise the temperature of one gram of the amine by one degree of temperature. The heat of vaporisation, ΔHvap typically dependent on the connectivity strength of molecules also increases with an increase of the intermolecular force strength.

In comparison to an amine with stronger intermolecular forces (e.g. larger electron cloud and larger electron cloud distortion), the molecules are more attracted and more tightly bound to one another. The gaining of kinetic energy induced by the same amount of heat supply to the former amine to raise the amine temperature will therefore occur to a lesser extent in this case. So, a smaller rise in temperature is observed with a reflection of higher Cp and ΔHvap values.

The heat duty of an amine comprises sensible heat (required for temperature rise), latent heat (required for a phase change from liquid to vapor), and desorption heat. At least the first 2 heat components of amine heat duty will be affected by the strength of the intermolecular forces of the amine molecules. The stronger interactions in an amine will require more sensible and latent heats in the desorption process as compared to the weaker interaction in an amine. If heats of desorption of the 2 amines are approximately close, the stronger interaction amine will likely have a higher heat duty than the weaker amine.

Having a fundamental knowledge of an amine at the atomic level, for example, understanding the concept of intermolecular forces that exist between amine molecules, can definitely help one to pre-screen amines with the least energy requirement before further testing them to finally select the best amine.