Limitation of K2CO3 as a Chemical Agent for Upgrading Activated Carbon

Abstract

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.

CO2 Capture and Direct Air CO2 Capture Followed by Integrated Conversion to Methane Assisted by Metal Hydroxides and a Ru/Al2O3 Catalyst

“…It is important to note that the reaction temperature of 250 °C is well below the temperature at which any of these carbonate salts generally start decomposing to CO 2 , the lowest of which is calcium carbonate starting to decompose above about 600 °C (Figure S21). [60][61][62][63][64] To determine the stability of the catalyst and base, the recyclability of both of these components was tested over several cycles of reactivity. The results are presented in Table 3.…”

KNO3-Loaded Coffee Husk Ash as a Heterogeneous Alkali Catalyst for Waste Frying Oil Valorization into Biodiesel

“…The increase in leachable basicity with the calcination temperature was due to carbonate decomposition to their corresponding highly water-soluble alkali oxides such as CaO and K 2 O . The carbonate decomposition at lower calcination temperature was may be facilitated due to the presence of carbon for K 2 CO 3 and K 2 CO 3 for CaCO 3 in the CCM. , The KNO 3 modification may boost the catalyst basicity in two ways: that is, by facilitating the K 2 CO 3 and CaCO 3 decomposition and by acting as a source of K 2 O during its decomposition.…”

“…64 The carbonate decomposition at lower calcination temperature was may be facilitated due to the presence of carbon for K 2 CO 3 and K 2 CO 3 for CaCO 3 in the CCM. 64,76 The KNO 3 modification may boost the catalyst basicity in two ways: that is, by facilitating the K 2 CO 3 and CaCO 3 decomposition and by acting as a source of K 2 O during its decomposition. Catalyst Morphology Analysis.…”

Review on Coal-Based Activated Carbon: Preparation, Modification, Application, Regeneration, and Perspectives

“…The reaction path is shown in Figure . The activation mechanism of K 2 CO 3 is shown in eqs and . In addition, K 2 CO 3 has a strong catalytic effect on coal gasification, in which it can catalyze coal to release more gas, thus promoting the formation of pore structure. − Mochizuki et al studied the influence of different mixing ratios of lignite, melamine, and K 2 CO 3 , activation temperatures and activation times on the CO 2 adsorption performance, and pore structure of CAC prepared using lignite as the raw material.…”

“…K 2 CO 3 melts at 891 °C and decomposes at >1200 °C, so it has high thermal stability and low activity during activation. 72 K 2 CO 3 activation can also effectively limit the expansion behavior of coal-based materials and expand the applicability of these materials. 73 During the activation process, K 2 CO 3 reacts with carbon to produce CO gas to form a porous structure.…”