K2CO3 Impregnation Research Articles

Copyrolysis of microalga Chlorella sp. and alkali lignin with potassium carbonate impregnation for synergistic Bisphenol A plasticizer adsorption

Composite functional materials offer promising opportunities for the development of tailored adsorbents with enhanced bioremediation potential towards toxic, carcinogenic endocrine disrupters such as Bisphenol A (BPA). Copyrolysis of microalga Chlorella sp. (CH) alkali lignin (L) with K2CO3 impregnation yielded a carbon-based composite (CHL-AC) with a micro–mesoporous structure of 0.643 cm3/g, surface area of 1414 m2/g, and BPA adsorption capacity of Qmax 316.858 mg/g. Enhanced BPA removal efficiency indicated a positive synergistic effect upon a combination of L and CH, resulting in a 73.24 % removal efficiency compared with the individual carbon components of 52.33 % for L-AC and 67.35 % for CH-AC. The kinetics and equilibrium results were described well by the pseudo second-order kinetic model and Freundlich isotherm, respectively. This paper elucidates the blending of microalgae and lignin into high-value carbon composite material, CHL-AC, with immense potential for the treatment of BPA-contaminated waters to contribute to Goal 6 (clean water and sanitation).

From aquatic biota to autogenous N-doping biochar—using a highly efficient nonradical dominant process for sulfamethoxazole degradation

Biochar has been considered as a promising environmental-friendly catalyst to activate peroxydisulfate (PDS) for contaminant degradation. In this study, a series of autogenous N-rich biochar derived from Spirulina were prepared by K2CO3 impregnation (NPSBs). The pyrolysis temperature and the rational design of morphology by K2CO3 had a significant influence on the performance of NPSBs to activate PDS. The NPSB-700 was capable of degrading 97.59% sulfamethoxazole (SMX) within 40 min because of the high surface area, high defect degree, and good electrical conductivity. The accelerated electron transfer and the generation of 1O2 were elucidated to be the dominant pathways for SMX degradation. It has been proven that this is a process of reducing toxicity. Furthermore, NPSB-700 also showed excellent degradation performance to various pollutants. This study provides a facile modification strategy of Spirulina-based catalysts and deepens the comprehension of persulfate activation via nonradical oxidation.

The investigation of activated carbon by K2CO3 activation: Micropores- and macropores-dominated structure

In this study, the K2CO3 activation of bamboo was investigated in detail, and the structure and properties of the prepared activated carbons were tested for the feasibility of CO2 capture application and the potential for both ion and bacteria adsorption for use in the field of hazardous wastewater treatment. Activated carbons were produced with different activator ratios, from 0.5 to 6 according to the sample mass ratio. The ratio of H or O to C (H/C or O/C) increased with the increasing amount of K2CO3 added for the activation. The samples had a highly-porous microporous structure, in which the micropore volume was calculated to be 0.6 cm3 g−1 by the DR method of the CO2 adsorption isotherm at 298 K. The BET surface area and total pore volume estimated from the N2 adsorption isotherms at 77 K of the activated materials increased according to the increase of the K2CO3 impregnation ratio to a maximum value of 1802 m2 g−1 and 0.91 cm3 g−1, respectively. Moreover, the K2CO3-activated samples had a specific morphology, that is, macropores which are presumed to be derived from bubbles. The X-ray-CT images showed that the bubble-like structure is not only on the surface but also inside the samples. The results of gas adsorption methods, mercury porosimetry, and SEM showed the co-existence of micropores (<2 nm) and macropores (100–10,000 nm). The results highlighted the unique pore structure, that is, the coexistence of micropores and macropores that would contribute to forming solutions for carbon sequestration in the atmosphere and wastewater treatment.

Preparation of Bamboo-Based Hierarchical Porous Carbon Modulated by FeCl3 towards Efficient Copper Adsorption.

Using bamboo powder biochar as raw material, high-quality meso/microporous controlled hierarchical porous carbon was prepared—through the catalysis of Fe3+ ions loading, in addition to a chemical activation method—and then used to adsorb copper ions in an aqueous solution. The preparation process mainly included two steps: load-alkali leaching and chemical activation. The porosity characteristics (specific surface area and mesopore ratio) were controlled by changing the K2CO3 impregnation ratio, activation temperature, and Fe3+ ions loading during the activation process. Additionally, three FBPC samples with different pore structures and characteristics were studied for copper adsorption. The results indicate that the adsorption performance of the bamboo powder biochar FBPC material was greatly affected by the meso/micropore ratio. FBPC 2.5-900-2%, impregnated at a K2CO3: biochar ratio of 2.5 and a Fe3+: biochar mass ratio of 2%, and activated at 900 °C for 2 h in N2 atmosphere, has a very high specific surface area of 1996 m2 g−1 with a 58.1% mesoporous ratio. Moreover, it exhibits an excellent adsorption capacity of 256 mg g−1 and rapid adsorption kinetics for copper ions. The experimental results show that it is feasible to control the hierarchical pore structure of bamboo biochar-derived carbons as a high-performance adsorbent to remove copper ions from water.

Hydration kinetics of K2CO3, MgCl2 and vermiculite-based composites in view of low-temperature thermochemical energy storage

Thermochemical energy storage (TCES) may store heat for a theoretically indefinite amount of time at high energy storage density. It is an ideal means to achieve seasonal thermal energy storage (TES). Hydration at atmospheric pressure of inorganic hygroscopic salts has attracted much attention from the scientific community: TES in the range 30 °C-150 °C is achievable and suitable for domestic heating applications such a space-heating. While progress at both material and reactor scales have been made, there is still a lack of fundamental understanding of the relationships connecting the two, which is necessary in order to enable full TCES potential and develop technical solutions. We investigated inorganic salts K2CO3 and MgCl2, and composites consisting in these salts impregnated into vermiculite. Experimental measurements (dynamic vapour sorption) and numerical optimization of known solid-state kinetic models relevant for sorption were used to derive kinetic coefficients for different solid-state reaction kinetic models and to shed light on the possible rate-limiting mechanisms of the hydration of each material. Potassium carbonate (K2CO3) hydration was found to be kinetically hindered by what appears to be a diffusion barrier at the interparticle level. Impregnation of K2CO3 lead to a significantly improved hydration, controlled at 25 °C by nucleation and 40 °C by phase-boundary control according to the best fitting kinetic models. MgCl2 hydration was best modelled by first-order model and diffusion-type models, pointing towards intraparticle diffusion control. Finally, the hydration of MgCl2 impregnated into vermiculite was best modelled by phase-boundary control models, with no notable rate-limiting step change at different temperatures.

K2CO3-Impregnated Al/Si Aerogel Prepared by Ambient Pressure Drying for CO2 Capture: Synthesis, Characterization and Adsorption Characteristics.

A new potassium-based adsorbent for CO2 capture with Al aerogel used as support is proposed in this work. The adsorbents with different surface modifiers (tetraethyl orthosilicate (TEOS) and trimethyl chlorosilane (TMCS)) and different K2CO3 loadings (10%, 20%, 30% and 40%) were prepared by sol-gel and iso-volume impregnation processes with ambient pressure drying. The CO2 adsorption performance of the adsorbents were tested by a fixed-bed reactor, and their adsorption mechanisms were studied by scanning electron microscopy (SEM), Brunauer Emmett Teller (BET), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and X-ray fluorescence spectrometry (XRF). Furthermore, the adsorption kinetics and the cycling performance were investigated. The results show that using TEOS to modify the wet gel can introduce SiO2 to increase the strength of the skeleton. On the basis of TEOS modification, TMCS can further modify –OH, thus effectively avoiding the destruction of aerogel structure during ambient drying and K2CO3 impregnation. In this work, the specific surface area and specific pore volume of Al aerogel modified by TEOS + TMCS are up to 635.32 cm2/g and 2.43 cm3/g, respectively. The aerogels without modification (Al-B), TEOS modification (Al/Si) and TEOS + TMCS modification (Al/Si-TMCS) showed the best CO2 adsorption performance at 20%, 30% and 30% K2CO3 loading, respectively. In particular, the CO2 adsorption capacity and K2CO3 utilization rate of Al/Si-TMCS-30K are as high as 2.36 mmol/g and 93.2% at 70 degrees Celsius (°C). Avrami’s fractional order kinetic model can well fit the CO2 adsorption process of potassium-based adsorbents. Al-B-20K has a higher apparent activation energy and a lower adsorption rate during the adsorption process. After 15 adsorption-regeneration cycles, Al/Si-TMCS-30K maintain a stable CO2 adsorption capacity and framework structure, while the microstructure of Al/Si-30K is destroyed, resulting in a decrease in its adsorption capacity by nearly 30%. This work provides key data for the application of Al aerogel in the field of potassium-based adsorbent for CO2 capture.

Transesterification of sunflower oil to biodiesel fuel utilizing a novel K2CO3/Talc catalyst: Process optimizations and kinetics investigations

A novel efficient and cost-effective heterogeneous catalyst for the production of biodiesel from transesterification of sunflower oil was prepared through the impregnation of K2CO3 upon the Talc material. The physicochemical features of the catalyst were studied through several characterization analyses. The effect of the K2CO3 loading was investigated by comparing the catalytic activity of various prepared catalysts. Moreover, the effect of the calcination temperature upon the catalytic activity was examined. To maximize the yield of the produced biodiesel fuel, reaction variables such as the reaction time and temperature, catalyst concentration, and methanol: oil molar ratio were optimized. Additionally, the kinetics of the reaction was understudied. Results revealed that the catalyst with 40 wt.% of K2CO3 calcined at 823 K possessed the highest catalytic activity. That is the biodiesel production yield of 98.4 %. Moreover, the kinetic parameters of the reaction rate constant of 0.01558 min−1, Eact of 62.4 kJ/mol, and Eyring-Polanyi’s ΔH and ΔS of 59.7 kJ/mol and -103.7 J/(mol K), respectively were obtained for this material. These were revealed under the optimum reaction condition of the catalyst reactor loading of 4 wt.% as well as the methanol: oil molar ratio of 6:1 operated at 338 K. Furthermore, the optimized catalyst was demonstrated to successfully withstand the aforementioned optimum criteria up to five consecutive reaction cycles while experiencing a negligible loss of about 8% of its activity.

Utilization of water hyacinth-based biomass as a potential heterogeneous catalyst for biodiesel production

With the aim to reduce the negative impacts caused by the widespread of water hyacinth to the environment, this paper reports the utilization of water hyacinth as a source of biomass to fabricate a heterogeneous catalyst. The catalyst was prepared by calcinating the grounded hyacinth biomass at 600°C, and K2CO3 was then introduced as a co-catalyst through impregnation method. The properties of biodiesel were also evaluated in terms of yield and density. To better understand the impregnation effects, surface topography, particle size, and atom composition of water hyacinth catalyst with K2CO3 impregnation were analysed. The performance of the synthesized catalyst was studied for the transesterification reaction of palm oil into biodiesel. The reaction was carried out in a batch mode for 3 hours with stirring at 65°C. The molar ratio of methanol to the oil of 12:1, and the catalyst loading was 15 wt. %. The highest yield (97.57%) was obtained from the process using 15% of the hyacinth-based catalyst which impregnated with 10% of K2CO3. The biodiesel produced was in the range of the SNI standard. The water hyacinth can be a promising heterogeneous catalyst for biodiesel production at an industrial scale.

Adsorbent from Rice Husk for CO2 Capture: Synthesis, Characterization, and Optimization of Parameters

In the present work, adsorbents were prepared from rice husk in order to capture CO2 from a flue gas stream. Various pretreatment processes such as desilicalization, chemical activation, and K2CO3 impregnation were followed to prepare the adsorbents. The physico-chemical characterization of the adsorbents was performed in detail in an elaborated way. A fixed-bed reactor was used to measure the CO2 capture capacity of the in-house developed adsorbents. The effect of various process parameters such as adsorption temperature, moisture content, and loading of active component on CO2 adsorption capacity was studied, and results were compared with a commercially available activated carbon. The maximum adsorption capacity observed for 20K-ARH adsorbent was as high as 67 g of CO2/kg sorbent. The effect of water on CO2 adsorption was critically examined, and formation of KHCO3 was observed in the presence of water during the adsorption process. The optimum operating conditions for the maximum removal of CO2 from a...

Comparative Study of Potassium Salt-Loaded MgAl Hydrotalcites for the Knoevenagel Condensation Reaction.

A series of potassium salt-loaded MgAl hydrotalcites were synthesized by wet impregnation of KNO3, KF, KOH, K2CO3, and KHCO3 salts over calcined MgAl hydrotalcite (Mg–Al = 3:1). The samples were characterized by X-ray diffraction, Fourier transform infrared, thermogravimetry–differential thermal analysis, scanning electron microscopy, and N2 absorption–desorption techniques to investigate their structural properties. The results showed formation of well-developed hydrotalcite phase and reconstruction of layered structure after impregnation. The prepared hydrotalcites possess mesopores and micropores having pore diameters in the range of 3.3–4.0 nm and Brunauer–Emmett–Teller surface area 90–207 m2 g–1. Base strengths calculated from Hammett indicator method were found increasing after loading salts, where KOH-loaded hydrotalcite showed base strength in the range of 12.7 < H– < 15, which was found to be the preferred catalyst. Subsequently, KOH loading was increased from 10 to 40% (w/w) and catalytic activity was evaluated for the Knoevenagel condensation reaction at room temperature. Density functional theory calculations show that among all of the oxygen atoms present in the hydrotalcite, the O atom attached to the K atom has the highest basic character. In this study, 10% KOH-loaded hydrotalcite showing 99% conversion and 100% selectivity was selected as the preferred catalyst in terms of base strength, stability, and catalytic efficiency.

Activated carbon–clay composite as an effective adsorbent from the spent bleaching sorbent of olive pomace oil: Process optimization and adsorption of acid blue 29 and methylene blue

An activated carbon–clay (ACC) composite was prepared using spent bleaching sorbent generated from refined olive pomace oil through carbonization followed by K2CO3 activation. The adsorption-removal efficiencies for acid blue 29 (AB 29) and methylene blue (MB) of the developed ACC were examined. The K2CO3 activation process was optimized using Box–Behnken design. The optimum conditions were a K2CO3 impregnation ratio of 1:1, an activation temperature of 800°C, and an activation time of 120min, under which the optimized ACC achieved 83.81% AB 29 and 96.20% MB removal. The surface properties of the optimized ACC were characterized by different physicochemical measures and techniques, including surface area, point of zero charge, scanning electron microscopy, and Fourier transform infrared spectroscopy. Pseudo-second-order and Langmuir models best fitted the adsorption kinetics and isotherm experimental data. The maximum monolayer adsorption capacity of the ACC was 104.83 and 178.64mg/g for AB 29 and MB, respectively, at 30°C. All these results indicated the potential application of ACC in dye adsorption.

CO2 adsorption over modified AC samples: A new methodology for determining selectivity

Activated carbon (AC) based adsorbents having high and stable CO2 adsorption capacity with enhanced CO2 selectivity in presence of CH4 were developed. Alkali modified AC samples were prepared, their CO2 adsorption capacities were measured, a new methodology for selective adsorption capacity determination under multicomponent gas mixture flow was developed, and the results were analyzed to determine the preparation procedure yielding optimum adsorbent design. Two groups of adsorbents were prepared by K2CO3 impregnation on air and HNO3 oxidized forms of a commercial AC followed by calcination at various temperatures. The resulting adsorbents were named according to calcination temperatures as ACxK-calT. The highest CO2 adsorption capacity was measured on AC3K-300 sample as 110mg/g adsorbent at 1000mbar CO2 and 25°C. CO2 adsorption was confirmed reversible, whereas CH4 adsorption was found partially irreversible. The highest mass based CO2:CH4 selectivity, ca. 3.7, was achieved over AC2K-200 at 25°C for the 50%CO2-50%CH4 mixture. AC2K-200 was further tested at higher total pressures, for 0–5000mbar pressure range, at 25°C. CO2 adsorption capacity was measured as 197mg/g adsorbent at 5000mbar CO2. Among Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models, D-R was found to be the most successful one explaining CO2 adsorption behavior of AC samples.

Influence of Potassium Carbonate on the Swelling Propensity of South African Large Coal Particles

The swelling propensity of some coals may restrict their use in fixed- and fluidized-bed gasification operations, and effective reduction of swelling can widen the applicability of these coals. Extensive research has been published on the influence of additives on the swelling of pulverized coal (<500 μm), but limited knowledge exists on the influence of additives on large coal particle swelling behavior. This paper presents an investigation on the influence of K2CO3 on the extent of swelling of 5, 10, and 20 mm particles, which are suitable sizes for fixed- and fluidized-bed operations. Three South African coals were selected: TSH coal (FSI 9), GG coal (FSI 5.5–6.5), and TWD coal (FSI 0). Large coal particles (5, 10, and 20 mm) were impregnated with a 5.0 M K2CO3 solution, and the K-loading increased by a factor 9–33. Maximum K-loadings of 3.3, 3.0, and 1.4 wt % K (coal basis) were obtained for the 5, 10, and 20 mm particles, respectively. The volumetric swelling ratio (SRV) of the 20 mm GG particles was reduced from 3.0 to 1.8, and for the TSH particles from 3.1 to 2.1. The TWD coal particles showed SRV values up to 1.7, in contrast to the nonswelling behavior of the pulverized (−212 μm) coal, and were not influenced by the K2CO3 addition. It was concluded that K2CO3 only influences the volumetric transformation of coals that undergo significant plastic deformation, such as GG and TSH. Comparison of the maximum swelling coefficients showed that K2CO3 impregnation reduces the kA from 0.025 to 0.015 °C–1 for GG and from 0.013 to 0.009 °C–1 for TSH. The results show the viability of using an additive for swelling reduction of large coal particles, and together with further development, may be a suitable method for reducing unwanted swelling in relevant coal utilization processes.

CO2 Sorption-Enhanced Processes by Hydrotalcite-Like Compounds at Different Temperature Levels

Abstract The aim of this work is to identify solid sorbents for CO2 capture for coal and biomass syngas conditioning and cleaning by means of a sorption-enhanced reaction process. Hydrotalcite-like compounds (HTlcs) were synthesized with and without K2CO3 impregnation. Samples were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) porosimetry after synthesis and after capture tests, respectively. Sorption and desorption tests were performed in a fluidized bed reactor, under cyclic conditions, at two different temperature levels: 350/450°C and 600/700°C. At low temperature only the Mg–Al HTlcs K promoted samples showed stability and sorption capacity comparable with literature values. On the other hand, results at high temperature indicate that the mixed Mg-Ca-Al HTlcs samples exhibit the best behavior with the highest sorption capacity (1.7 mmolCO2/g) almost stable over 5 sorption/regeneration cycles; furthermore, addition of steam allowed increasing their reactivity by 70% compared to the dry value. This type of sorbent could be a promising candidate to prepare a bifunctional sorbent–catalyst for sorption-enhanced processes, taking place directly in the fluidized bed gasifier, or downstream the reactor for adjustment of gas composition before further conversion in gaseous energy carriers.

Catalytic effect of Ca and K on CO2 gasification of spruce wood char

Gasification is one route to produce chemicals and liquid fuels from biomass. The gasification of the char is catalyzed by alkali and alkaline earth metals in the biomass. In this work the catalytic effect of calcium (Ca) and potassium (K) on CO2 gasification of spruce wood was studied using a thermo gravimetric analyzer (TGA). The ash-forming elements were first removed from the wood using an acid leaching method. Then, various concentrations of K and Ca were absorbed to the wood by ion-exchange to carboxylic and phenolic groups, impregnation of K2CO3 or physically mixing of CaC2O4. The prepared spruce samples were placed in a mesh holder and gasified in the TGA at 850°C in 100% CO2.The results demonstrate that the gasification rate of the char increased linearly with an increase in the concentration of Ca or K. Crystalline CaC2O4 distributed only at the surface of the wood particles resulted in low catalytic activity. The catalytic activity of Ca was higher than K in the beginning of char gasification but the catalytic effect of Ca decreased earlier than the catalytic effect of potassium. Further, the char structure was investigated by SEM–EDX. The SEM analysis from interrupted gasification experiments showed the formation of CaCO3 and K2CO3 layer on the char surface. By adding corresponding levels of Ca and K as the original spruce to the acid washed sample, a similar gasification reactivity was obtained at 850°C.

Thermogravimetric analysis of carbonation behaviors of several potassium-based sorbents in low concentration CO2

Thermogravimetric analysis is finding increasing utility in investigations of reaction paths and carbonation behaviors of CO2 sorbent. Potassium-based sorbents are currently suggested as new options for capturing CO2 from flue gas after combustion or removing CO2 from confined space, such as submarines, space crafts, and aircrafts. In this paper, K2CO3/AC, K2CO3/Al2O3, K2CO3/5A, K2CO3/13X, and K2CO3/SG were prepared with the impregnation of K2CO3 on activated carbon (AC), Al2O3, zeolite 5A, zeolite 13X, and silica aerogels (SG), respectively. The carbonation paths and behaviors of these sorbents in low temperature and CO2 concentration were revealed with TG. The carbonation conversions and average reaction rates were measured under different conditions by changing support material, temperature, CO2 concentration, and H2O concentration. The carbonation conversions for K2CO3/AC, K2CO3/Al2O3, K2CO3/5A, K2CO3/13X, and K2CO3/SG are 93.3, 67.3, 34.5, 60.0, and 10.1 %, respectively. The reaction paths of K2CO3/AC and K2CO3/SG are found out that the hydration reaction occurs first to form K2CO3·1.5H2O and K4H2(CO3)3·1.5H2O, then KHCO3 is produced rapidly. In the case of K2CO3/Al2O3, K2CO3/5A, and K2CO3/13X, a new phase of KAl(CO3)2(OH)2 is formed which requires a higher temperature of 350 °C to be decomposed. The carbonation conversions increase with the increase of the CO2 concentration and H2O concentration, but decrease with the increase of temperature. The average reaction rate increases when the aforementioned variables increase to a high value. The support material is the key factor that affects the carbonation conversion and average reaction rate. Choosing a proper support material is most important for obtaining enhanced CO2 capture capacity of potassium-based sorbent.

Biochar production by sewage sludge pyrolysis

Sewage sludge was pyrolyzed in order to assess the effect of pyrolysis temperature, residence time and biomass chemical impregnation on the yield of biochar production. The pyrolysis temperature was a key factor affecting biochar yield, while the highest yield was obtained at a temperature of 300°C. Biochar surface area increased with increasing pyrolysis temperature and was maximized (90m2/g) by impregnating biochar with K2CO3. Raw sewage sludge, as well as biochar samples, were subjected to leaching tests in order to investigate the potential release of heavy metals. Pyrolysis suppressed heavy metal release for the non-impregnated biochars, indicating that there is no environmental risk using sludge-derived biochars as soil amendments. Although K2CO3 and H3PO4 impregnation enhanced the solubility of specific heavy metals, the concentrations in the leachates were low. Biochar impregnated with K2CO3 released 85.7% of its potassium content, whereas orthophosphates were bound strongly in the biochar matrix impregnated with H3PO4. The non impregnated biochar was subjected to batch kinetic experiments in order to examine its ability to adsorb As(V) and Cr(III). Biochar removed approximately 70% of Cr(III) at equilibrium time, whereas only 30% of As(V) was adsorbed onto biochar surface, implying that biochar is more efficient in removing cations than anions from aqueous solutions.

Preparation of high-surface-area activated carbon from Zizania latifolia leaves by one-step activation with K2CO3/rarefied air

An activated carbon (AC) with high-porosity was prepared from Zizania latifolia leaves by a one-step method combining chemical and physical activation. K2CO3 was employed as a chemical reagent, and air as a physical agent. During the activation, several key parameters were discussed, including the effects of activation temperature, K2CO3 impregnation ratio, amount of introduced air on the surface area and pore volumes evolution of the ACs derived from the Zizania latifolia leaves. The synergistic effect between the chemical agent and the physical agent was also investigated. Under optimal activation conditions, the as-synthesized AC attained a maximum surface area up to 2481 m2/g, with 1.21 cm3/g pore volume, and it had a micro/meso porosity developed by the combining activation. The crystal sizes of the as-synthesized AC along the a- and c-axes were about 5 nm and 1–2 nm, respectively. The average thickness of the crystallites is 3–4 layers with about 0.37 nm interlayer spacing.

Carbonation and Active-Component-Distribution Behaviors of Several Potassium-Based Sorbents

To investigate active-component-distribution and carbonation behaviors, potassium-based sorbents were prepared by impregnation of K2CO3, K2CO3·1.5H2O, and KHCO3 on supports such as activated carbon (AC) and Al2O3. The CO2 capture capacity is significantly increased for K2CO3 and K2CO3 dehydrated from K2CO3·1.5H2O after they have been loaded on AC and Al2O3. For the sorbents with AC as their support, the active components keep their original phase in the impregnation process. Under an atmosphere of CO2 and H2O, the hydration reaction occurs first, and then KHCO3 is produced rapidly. The active components are held in macropore spaces without blocking micropores, and the rest is nonuniformly distributed on the surface of AC in the form of large aggregates. For the sorbents with Al2O3 as their support, all of the active components change into K2CO3 during the impregnation process. Under the same reaction atmosphere, K2CO3·1.5H2O is not produced. H2O is adsorbed at first, and then CO2 reacts with the adsorbed H2O and K2CO3 to produce KHCO3. Most of the active components are distributed in the mesopores and macropores of the support, and the rest is uniformly distributed on the surface of Al2O3 in the form of many small aggregates.

Hydrotalcites for adsorption of CO2 at high temperature

Adsorption of carbon dioxide by hydrotalcites was investigated by using a gravimetric method at 450 ‡C. Hydrotalcites possessed higher adsorption capacity of CO2 than other basic materials such as MgO and Al2O3. Two different preparation methods of hydrotalcite with varying Mg/Al ratio were employed to determine their effects on the adsorption capacity of CO2. In addition, varying amounts of K2CO3 were impregnated on the hydrotalcite to further increase its adsorption capacity of CO2. The hydrotalcite prepared by the high supersaturation method with Mg/Al=2 showed the most favorable adsorption-desorption pattern with high adsorption capacity of CO2. K2CO3 impregnation on the hydrotalcite increased the adsorption capacity of CO2 because it changed both the chemical and the physical properties of the hydrotalcite. The optimum amount of K2CO3 impregnation was 20 wt%. The hydrotalcite prepared by the high supersaturation method with Mg/Al=2 and 20 wt% K2CO3 impregnation has the highest adsorption capacity of CO2 with 0.77 mmol CO2/g at 450 ‡C and 800 mmHg.