The chemical activation of a carbon precursor with KOH generally results in an activated carbon (AC) with a high specific surface area. However, this process generates a large volume of wastewater that includes dissolved alkali metals, existing mainly as K₂CO₃. Thus, wastewaters with a high concentration of dissolved K₂CO₃ can potentially be used in place of KOH as a chemical agent. In the present study, to reduce the thermal stability of K₂CO₃, which decomposes at temperatures greater than 891 °C, K₂CO₃ was chemically impregnated into carbon precursors prior to activation of the precursors. The thermochemical properties and activation efficiency of the carbon precursors treated with K₂CO₃ were compared with those of carbon precursors treated with KOH. Analysis by XPS indicated that C–O–K complexes formed on the surface of the carbon precursors; in addition, their peak intensities were approximately the same irrespective of the chemical agent used. However, the specific surface area of the K₂CO₃-impregnated AC was 2162 m²/g, which was ~70% of that of the KOH-impregnated AC (3047 m²/g) prepared using the same K/C molar ratio of 0.5. XRD results confirmed that both K₂CO₃ and KOH transformed into KHCO₃ and K₄H₂(CO₃)₃·1.5H₂O during the impregnation. The peak intensities of these compounds in the XRD pattern of the K₂CO₃-impregnated carbon precursors were two times greater than those in the pattern of the KOH-impregnated carbon precursors. These compounds eventually transformed into K₂CO₃, which hardly participated as a chemical agent at the temperature used in the present study (850 °C). Therefore, recrystallisation of K₂CO₃, even during the impregnation, appeared to adversely affect the degree of activation. Nevertheless, the specific surface area of the K₂CO₃-activated AC was still ~1.6 times greater than that of the untreated carbon precursor (1378 m²/g), suggesting that the use of wastewater as a chemical agent is feasible for resource recycling.

Activated carbon (AC) is used in commercial electric double-layer capacitors (EDLC) as electrode active material owing to its favorable properties. However, oxygen functional groups (OFGs) present in AC reduce the lifespan of EDLCs. Thus, we investigated the correlation between the OFGs in AC and their electrochemical characteristics. Samples were prepared by heat-treating commercial AC at 300 °C–900 °C for 1 h under two gas atmospheres (N₂ and 4% H₂/N₂ mixed gas). The textural properties were studied, and the reduction characteristics of AC under Ar and H₂/Ar mixed gas atmospheres were investigated. Additionally, changes in the OFGs with respect to the heat-treatment conditions were examined via X-ray photoelectron spectroscopy. The specific surface areas of AC-N and AC-H were 2220–2040 and 2220–2090 m²/g, respectively. Importantly, the samples treated in hydrogen gas exhibited a higher yield than those treated in nitrogen while maintaining their pore characteristics. Additionally, the electrochemical performance of the AC was significantly enhanced after the reduction process; the specific capacitance increased from 62.1 F/g to 81.6 F/g (at 0.1 A/g). Thus, heat treatment in hydrogen gas improves the electrochemical performance of EDLCs without destroying the pore characteristics of AC.

In this study, a feasible experiment on adsorbed natural gas (ANG) was performed using activated carbons (ACs) with high surface areas. Upgraded ACs were prepared using chemical activation with potassium hydroxide, and were then applied as adsorbents for methane (CH₄) storage. This study had three principal objectives: (i) upgrade ACs with high surface areas; (ii) evaluate the factors regulating CH₄ adsorption capacity; and (iii) assess discharge conditions for the delivery of CH₄. The results showed that upgraded ACs with surface areas of 3052 m²/g had the highest CH₄ storage capacity (0.32 g-CH₄/g-ACs at 3.5 MPa), which was over two times higher than the surface area and storage capacity of low-grade ACs (surface area = 1152 m²/g, 0.10 g-CH₄/g-ACs). Among the factors such as surface area, packing density, and heat of adsorption in the ANG system, the heat of adsorption played an important role in controlling CH₄ adsorption. The released heat also affected the CH₄ storage and enhanced available applications. During the discharge of gas from the ANG system, the residual amount of CH₄ increased as the temperature decreased. The amount of delivered gas was confirmed using different evacuation flow rates at 0.4 MPa, and the highest efficiency of delivery was 98% at 0.1 L/min. The results of this research strongly suggested that the heat of adsorption should be controlled by both recharging and discharging processes to prevent rapid temperature change in the adsorbent bed.

Anthracite stands as a valuable precursor for carbon materials, owing to its high carbon content. However, producing activated carbon from anthracite presents significant challenges due to its elevated ash content (23–40 wt%) and crystalline nature. The high ash content not only fails to contribute to the activation process but also obstructs pore formation on the carbon surface. To address these challenges, this study explores the preparation of activated carbon from anthracite using KOH activation. This method demonstrates remarkable efficacy in enhancing reactivity beyond the inherent physical properties of anthracite. In contrast to physical activation, the utilization of KOH as a chemical agent substantially enhances the specific surface area, resulting in a production yield of 62% and a specific surface area that reaches up to 1596 m²/g at a KOH/anthracite weight ratio of 4.0. Moreover, rinsing the activated sample with tap water achieves an ash removal rate of about 37.9%, surpassing twice the rate achieved through acid pretreatment (67.0%). A noteworthy observation from this study is the substantial reduction in the content of major ash components, such as silicon (Si) and aluminum (Al), both of which are prominent constituents in anthracite ash. Following KOH activation, their levels decrease by approximately 54% to 65%, respectively. These findings highlight the potential of utilizing available anthracite, even with elevated ash content, as a superior carbon material. Fundamentally, the KOH activation method serves a dual purpose: it effectively reduces ash content and promotes pore creation within a highly alkaline environment. This dual advantage positions the method as a promising approach for the production of top-tier activated carbon.

Chemical activation consumes copious quantities of chemicals is therefore hampered by its low economic feasibility. However, this issue can be overcome through the recovery and reuse of alkali compounds leached into wastewater. Because the leached potassium compounds exist as the relatively less reactive K₂CO₃, we explored three different approaches to remove carbonate ions (CO₃ ²⁻) from the wastewater: (i) CO₂ stripping after acidification, (ii) exchanging CO₃²⁻ for OH⁻ using strong basic anion exchange resins, and (iii) inducing a phase transition via a reaction with Ca(OH)₂ to precipitate CaCO₃. Both ion exchange and phase transition convert K₂CO₃ into highly reactive potassium compounds such as KOH. The phase transition effectively enhanced the specific surface area of the activated carbon and thus had implications for pore development in carbon precursors, while offering a viable recovery strategy for alkali compounds that reduces costs by approximately 20% compared to traditional methods. These findings suggest that the in-situ recycling of wastewater for the production of activated carbon can improve the economic viability of manufacturing processes.

Mass flow meters (MFMs) are widely used to secure reliable flow rates based on the mass value of the gas being measured. However, chemical reactions produce various kinds of gases, and their composition also changes in real time. Thus, there may be a large deviation in the gas flow if the gases’ composition and its mixing ratio are not known. In this study, we derived a gas flow rate measurement method using a chemically stable chemical specie and verified the precision of the proposed method through comparative analysis with an MFM. The flow rate by this method showed reliable results in both single and mixed gases. Notably, the results were within ±2.74% of the injected flowrate values in the gas mixtures. This method is expected to be able to fundamentally overcome the limitations of the mechanical flowmeter because it is not affected by changes in gas composition or mixing ratio during the reaction.