Carbon Capture

The scope of carbon capture is the carbon isolation and its storage in such a way as to allow its further treatment. The technologies utilized depend on the carbon source and form, and its compatibility with the sequestration method. The known carbon capture techniques are the following:

• Chemical absorption utilizing solvents

• Physical absorption on solids

• Low-temperature distillation

• Gas separation films

• Mineralization and biomineralization

• Germination-vegetation

These techniques are mentioned due to their simplicity, their low environmental burden, and their relative low cost.

16.2.1 Chemical absorption through solvents

Carbon can be captured from a gas flow, with physical or chemical absorption techniques, utilizing solvents. This process can easily be modeled using Henry's law. CO2 is an acidic gas, thus its chemical absorption is depending on neutralization reaction using base solvent. The most common solvents utilized are as follows: alcaloamines, such as monoethalomine (MEA), dietheloamine (DEA), and methyldietheloamine (MDEA). Additionally, ammonia and superheated potassium carbonate can be used. The exhaust gases also contain SOX, NOX, O2, hydrocarbons, and molecules that affect the operation and the efficiency of the chemical absorption. There has to be a pretreatment stage of the exhaust gas, to minimize the content of these gases, which in turn will lead to an increase in the cost of the overall process.

Carbon capture through chemical absorption is a technique that is widely used commercially, especially in the hydrogen production industry, where the carbon is continuously emitted to the atmosphere. This technique is also used to capture CO2 from biogas. It is important to take into consideration the fact that the absorption rate is not steady and it is strongly depended on the solvents, the CO2 pressure, the temperature of the exhaust gas, etc. Chemical absorption technique needs further development.

16.2.2 Physical absorption on solids

Carbon capture can be done through physical absorption on large surface solids. Zeolites, for instance, are able to absorb efficiently gases such as steam, oxygen, and carbon. There are two dominant processes of physical absorption: the pressure swear absorption (PSA) and the thermal swear absorption (TSA). Both processes have high energy usage and high operational cost. Notwithstanding, the processes are commercially used in the hydrogen production industry.

16.2.3 Low-temperature distillation

Low-temperature distillation is commercially used for the liquefaction and capture of carbon from exhaust gases with high carbon content, over 90%. Low-temperature distillation is economically feasible for large-scale plants. The advantage of this process is that it produces liquid CO2 that can be easily stored and transported. Among the disadvantages are the high energy use and the fact that the other gaseous components of the exhaust flow must have their cooling point above the operational temperature.

16.2.4 Gas separation films

Gas separation films are of many types. There are polymer films, palladium films, and inorganic porosity films, metal or ceramic. Their future potential is considered to be acceptable, although their total effectiveness is not proven. The diffusion mechanism that takes place is not unique and varies with the film type. The most efficient gas separation films are the inorganic films, which usually have great permeance and they can be able to operate in high pressure and temperature and in acidic environments. Additionally, they have a long life cycle and construction "flexibility," as they can be produced by a large number of materials and of different porosities. On the other hand, they are extremely costly and some of them are vulnerable due to the fact that they react with sulfur.

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