Technologies and Materials for Carbon Dioxide Capture

Article History Received: 06 September 2019 Revised: 15 September 2019 Published: 30 September 2019 This paper was aims to review the technologies and materials for CO2 capture. Carbon dioxide is one of the triggers for the greenhouse effect and global warming. Some methods to reduce CO2 are separation technologies include air capture, CO2 Capture Utilization and Storage (CCUS) and CO2 Capture and Storage (CCS) technology. CCS technology have several systems namely postcombution, pre-combustion and oxy-fuel combustion. Post-combution systems can be done in various systems including absorption, adsorption, membrane, and cryogenic. Adsorption proses for CO2 capture applied with porous material such us mesopore silica, zeolite, carbon, MOF dan COF. This review was described the advantages and disadvantages of each technology for CO2 capture. Materials for CO2 adsorption also descibed in this review.

Based on Table 1, CCS technology was chosen and reviewed for carbon dioxide gas separation because this technology has low risk of danger and cost. The three systems derived from CCS technology are pre-combustion, post combustion and oxy fuel combustion was described in Table 2.
In pre-combustion capture, carbon and carbon dioxide in fossil fuels are separated before combustion. This fuel source is chemically converted into a stream of two gases, carbon dioxide and CO2. The process of Pre-combustion Capture [9] is shown in Figure 1.  In Oxy-fuel Combustion is simpler than pre-combustion capture because the oxidation process uses oxygen so it only produces CO2 and H2O. Because the fuel used in the combustion process only produces CO2 and H2O, there is no need to separate the exhaust gas anymore, so that the CO2 gas produced from this process can be directly captured. The process of Oxy-fuel Combustion [9] is shown in Figure 2. The last process is the post-combustion capture process. In this process, separating CO2 is easier because it uses methods such as adsorption, membrane, cryogenic, and adsorption. The process of Post-combustion Capture (Miller, 2011) is shown in Figure 3. The use of post-combustion capture technology has been more developed because CO2 separation methods are simpler and more efficient than the two processes above. The use of cryogenic and membrane methods requires high energy, but this can be avoided by choosing absorbs or adsorption methods to reduce operating costs. At present, the most commonly used carbon dioxide (CO2) separation method in the post-combustion capture technology includes absorption, cryogenic, membranes, and adsorption. A comparison of the four carbon dioxide separation methods can be seen in Table 3. The absorption and adsorption methods require lower operational costs compared to cryogenic or membrane methods. In the membrane method, selectivity to CO2 is still very low compared to adsorption, whereas the cryogenic method requires high energy to convert CO2(g) to CO2(l) (Miller, 2011). Absorption methods generally use chemical solvents such as fluorinated solvents, ammonia solutions and ionic liquids  and require high energy because of the interaction between adsorbents (chemical solvents) and adsorbate (CO 2 gas) in the form of chemical bonds, making it very difficult to separate when adsorbent regeneration. While the adsorption method uses materials such as porous silica, carbon and zeolites (Li, Table 3, the adsorption method has a lower pure limit than the absorption and cryogenic methods, but has a faster time to reach the pure limit that is in units of minutes. The pure limit is the maximum purity limit obtained by using the CO2 separation method. In addition, the adsorption method only requires lower energy when capturing CO2 than all methods, so it is more profitable.

HASIL DAN PEMBAHASAN (RESULT AND DISCUSSION) I. Materials for Carbon Dioxide Adsorption
Some materials which have been developed for carbon dioxide adsorption are porous materials such as mesopore silica, zeolites, carbon, MOF (metal organic framework), and COF (covalent organic framework). Several studies showing the effect of adsorption type and pore diameter on the carbon dioxide adsorption capacity can be seen in Table 4.  Mesopore silica material, MOF, and COF have a type of chemical adsorption, while carbon and zeolites are physical adsorption. Chemical adsorption requires relatively high pressure to adsorp CO2 gas in MOF and COF materials. However, when chemical adsorption uses relatively low pressures in mesopore silica material, the adsorption ability will decrease. In addition, chemical adsorption requires high energy during desorption because there is a chemical bond between carbon dioxide and material sorbent, it could difficult to release from CO2 capture material (Miller, 2011). In the physical adsorption on carbon and zeolite materials, the temperature and pressure used are relatively low and the carbon dioxide adsorbed is also more abundant than mesopore silica. Physical adsorption is reversible and tends to require low energy during desorption.
Besides the type of adsorption, another parameter that affects the adsorption of carbon dioxide is the pore diameter. Based on Table 4, mesopore silica has a larger pore diameter than zeolite, carbon, MOF and COF material. Carbon dioxide has a kinetic diameter of 3.3 Å (0.33 nm) [21] . The materials which suitable for CO 2 adsorption are those that have a diameter between 0.4 nm -2 nm, and will be optimal if adsorbed by a material with a pore diameter of 0.4-0.6 nm. For this reason, zeolite, carbon, MOF and COF materials have a pore diameter suitable for CO2 adsorption.
Another thing of affects CO2 adsorption is the adsorption capacity. Materials that have a large adsorption capacity for CO2 are carbon, zeolite, MOF, and COF. CO2 adsorption capacity on the MOF and COF greater than on the carbon and zeolites, nevertheless COF and MOF are chemical adsorption where the adsorption conditions require high pressure between 30 -50 bar. While carbon and zeolite only require 1 bar of pressure and room temperature. It causes zeolite and carbon more to be developed as CO2 capture material. Several studies using zeolite and carbon for CO2 Adsorption are shown in Table 5 and Table 6.

KESIMPULAN (CONCLUSION)
Based on the description of technology and material for CO2 adsorption above, it can be concluded that CO2 adsorption can be carried out through absorption, adsorption, membrane and cryogenic technologies. From these techniques, the adsorption method is considered more efficient and can be applied with various porous materials such as mesoporous silica, zeolite, carbon, MOF and COF. Porous material has each advantages and disadvantages. Zeolites and carbon are more interesting to develop due to zeolites have good porosity but a small surface area and carbon has a large surface area but irregular porosity. There have been several studies that have combined carbon and zeolite materials into zeolite-templated carbon with synthetic zeolite and resulted in increased adsorption capacity.

SARAN (SUGGESTIONS)
One proposal that can be done on further research in the development of adsoption materials is combine zeolite and carbon into zeolite/carbon composite. Zeolite/carbon composite materials can be synthesized with basic materials from nature, such as rice husks, bagasse and others. By utilizing natural waste as a basic material for making composites material, the cost of making zeolite/carbon composites material becomes cheaper and the waste of natural materials can be increased in value.

UCAPAN TERIMA KASIH (ACKNOWLEDGMENT)
Author would like to Universitas Islam Lamongan, East Java, Indonesia for providing research facility and help for this paper