**1. Introduction**

Carbon dioxide (CO2 ) is a stable and relatively inert triatomic molecule that exists as a gas at ambient temperature and pressure. A CO2 molecule exhibits a linear structure in which the carbon is bonded to each oxygen atom *via* a sigma and pi bond forming two C=O bonds. Each C=O bond has a length of 116.3 pm and 750 kJ.mol−1 bonding energy, considerably higher than the bonding energy of C=C, C–O, and C–H bonds [1]. Carbon dioxide is generated naturally from various sources such as forest fires, volcanic eruptions, and respiration of living organisms. The photosyntheses of plants and other autotrophs play an indispensable role in balancing the carbon/oxygen cycle and consequently in maintaining the earth life. The global concentration of CO2 in the atmosphere was approximately 270 ppm by volume prior to industrial revolution. Nowadays, the carbon dioxide level has reached up to 405 ppm, approximately a 50% increase. This steady increase in CO2 emissions stems from the large consumption of fossil fuels and anthropogenic activity (power plants, oil refineries, cement, iron, and steel industries, biogas sweetening, and chemical industry and processing) in addition to the wide deforestation for land usage [2].

Pollution is regarded as the issue of our era, since dominant industries deem its control as an expense that overwhelms the domains that are beneficial to the advances of science. Finding alternatives to indispensable fields such as providing energy, food, drugs, and dyes for medicinal probes, among others, seems to conflict the innovative progress reported every day in academia and industry. The greenhouse effect is one of the utmost contemporary issues in this regard. Carbon dioxide is currently the most abundant greenhouse gas (GHG). Greenhouse gases such as ozone, nitrous oxide, methane, chlorofluorocarbons (CFCs), and CO2 has a detrimental role in preventing the heat loss and protecting

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

the life on earth during nighttime. However, the increased concentrations of GHGs, particularly CO2 , are believed to cause drastic changes such as global warming and ocean acidification [3].

emissions. The future trends, however, should be directed to reduce energy consumption and dependence on fossil fuels and to develop and employ renewable and less carbon-intensive

This introductory chapter discusses the *basic properties* and the *major technologies of carbon* 

nologies will be introduced in the next sections of this preview and will be further detailed in

Carbon dioxide capture technologies involve the processes of producing relatively high purity

in principle by compression to a pressure typically higher than 10 MPa, thus requiring a huge amount of energy aside from the large volumes produced that can rapidly fill the storage reservoirs. Therefore, carbon capture and storage (CCS) technologies represent an economic

the carbon source is known as postconversion process. Different technologies are developed for this capture process such as adsorption by solid sorbents, vacuum swing adsorption, absorption by solvents, and cryogenic separation. These methods are still considered energy demanding. Solvent absorption is elaborated here as an example of the capture. In particular,

this application. In contrast, chemical absorption depends on the chemical reaction between

in ammonia synthesis. It is commonly achieved using absorption by solvents or adsorption

(at low partial pressure) and the used solvent forming weak bonds. The latter is more

capture, storage (**CCS**), and utilization (**CCU**). The most important tech-

Introductory Chapter: An Outline of Carbon Dioxide Chemistry, Uses and Technology

from waste gas streams after the conversion (mainly combustion) of

relies on its solubility based on Henry's Law without inducing a

emissions in industrial processes given the flue gas conditions of

produced by an intermediate step in some conversions such as

), biofuels, geothermal, and

5

http://dx.doi.org/10.5772/intechopen.79461

emissions and the various methods used or

emissions from electricity generation

in combustion systems of fossil fuels, namely

). Storage of flue gas is possible

partial pressures are needed for

, which might be low

sources of energy on large scale, such as nuclear energy (e.g., H2

for transport and storage, since most CO2

*postconversion capture*, *preconversion capture*, and *oxy-fuel combustion* (**Figure 1**).

and industries are released as flue gas (4–14% by volume CO<sup>2</sup>

chemical reaction. Thus, low temperatures and elevated CO2

ambient pressure and large volumes with varied concentrations of CO2

processes. This capture also suffers from the high energy demands.

*dioxide*. **Figure 1** outlines the main sources of CO2

the separate chapters of this "*Book* project."

**2. Carbon dioxide capture**

solution for storage of flue gases [4, 8].

**2.1. Postconversion capture**

physical absorption of CO2

adjusted to capture CO2

**2.2. Preconversion capture**

It involves the capture of CO2

in some processes.

CO2

The separation of CO2

Three methods are known for capturing CO2

tidal energy [4, 6, 7].

envisioned for CO2

stream of CO2

Global warming refers to the increase in the average global temperatures, mostly noticeable in the melting of ice caps in polar regions and the rising of sea levels. Specifically, the greenhouse effect of CO<sup>2</sup> relies on its asymmetric stretching and bending vibrational modes, which allow this gas to absorb and emit infrared radiation at wavelengths of 4.26 and 14.99 μm, respectively [1, 4]. On the other hand, ocean acidification refers to the ongoing decrease in the pH of water in seas and oceans. About 30–40% of the anthropogenic CO2 are dissolved in oceans and seas forming carbonic acids to achieve chemical equilibrium. Consequently, the formed H+ ions are leading to decrease the pH of earth water from slightly basic conditions toward neutrality or even acidity in the long term, hence affecting the life cycles of marine organisms and the subsequent food chains [5].

Several international conventions and governmental protocols have been formulated to reduce the CO2 emissions such as *The Kyoto Protocol*, *the UN Framework Convention on Climate Change*, and *the Intergovernmental Panel on Climate Change*. To date, there is no universal agreement on these laws, and many countries and industries do not abide by these conventions. Therefore, immediate actions and solutions are demanded to circumvent the potential influence of the yet high CO2 emissions on the climate. In general, the total CO2 emission can be controlled by reducing the energy intensity, limiting the carbon intensity, or by improving the CO2 sequestration. In the short term, carbon-based fossil fuels will persist to be the main source of energy. Thus, there is an urgent need to develop economically feasible and efficient processes for capturing, separating, storing, sequestering, and utilizing the continuous CO2

**Figure 1.** Major sources of CO2 emissions and technologies used in CCS and CCU.

emissions. The future trends, however, should be directed to reduce energy consumption and dependence on fossil fuels and to develop and employ renewable and less carbon-intensive sources of energy on large scale, such as nuclear energy (e.g., H2 ), biofuels, geothermal, and tidal energy [4, 6, 7].

This introductory chapter discusses the *basic properties* and the *major technologies of carbon dioxide*. **Figure 1** outlines the main sources of CO2 emissions and the various methods used or envisioned for CO2 capture, storage (**CCS**), and utilization (**CCU**). The most important technologies will be introduced in the next sections of this preview and will be further detailed in the separate chapters of this "*Book* project."
