Activated Carbon Honeycomb Monolith Research Articles

Thermodynamic analysis on carbon dioxide capture by Electric Swing Adsorption (ESA) technology

This study explores the impacts of materials, such as adsorbents and electrodes, on the energy efficiency of a 4-step ESA cycle for CO2 capture. Three types of adsorbents including activated carbon honeycomb monolith (ACHM) and two hybrid adsorbents are compared, and two kinds of electrodes such as aluminum and brass are combined for comparative analysis. Process description of ESA cycle, including feed, electrification, electrification with purge and cooling, is presented via the adsorption isotherm diagram. By the theory of thermodynamic carbon pump, sensitivity analysis of cycle parameters is evaluated in terms of the second-law efficiency (Eff2nd) and the electrical heating efficiency (Effele). The results show that Eff2nd of the employed adsorbents is in the range of 1.17%–6.15%, and Effele of the selected electrodes is between 27.46% and 60.91%. Among the three adsorbents, Eff2nd of ACHM is the lowest one compared to the others. Similarly, Effele of the combination with brass is superior to that of the groups with aluminum. However, the actual efficiency of ESA cycle is the production of both Eff2nd and Effele, which is approximately 1.03%–3.66%. Typical measures are proposed to reduce the heat loss of the adsorbents and electrodes as well for future work.

Parametrical Study on CO2 Capture from Ambient Air Using Hydrated K2CO3 Supported on an Activated Carbon Honeycomb.

Potassium carbonate is a highly hygroscopic salt, and this aspect becomes important for CO2 capture from ambient air. Moreover, CO2 capture from ambient air requires adsorbents with a very low pressure drop. In the present work an activated carbon honeycomb monolith was coated with K2CO3, and it was treated with moist N2 to hydrate it. Its CO2 capture capacity was studied as a function of the temperature, the water content of the air, and the air flow rate, following a factorial design of experiments. It was found that the water vapor content in the air had the largest influence on the CO2 adsorption capacity. Moreover, the deliquescent character of K2CO3 led to the formation of an aqueous solution in the pores of the carrier, which regulated the temperature of the CO2 adsorption. The transition between the anhydrous and the hydrated forms of potassium carbonate was studied by means of FT-IR spectroscopy. It can be concluded that hydrated potassium carbonate is a promising and cheap alternative for CO2 capture from ambient air for the production of CO2-enriched air or for the synthesis of solar fuels, such as methanol.

Equilibrium and Dynamic CO2 Adsorption on Activated Carbon Honeycomb Monoliths

In this work, CO2 adsorption tests from simulated flue gas are carried out in a laboratory-scale fixed-bed reactor, at different temperatures (303 and 353 K) and CO2 concentrations (3–25%), in order to investigate both the kinetics and thermodynamics. To this purpose, two different activated carbon (AC) monoliths were synthesized starting from an African Palm stone (Elaeis guineensis), activated either with H3PO4 (48% w/v) or with a combination of H3PO4 (32% w/v) + CaCl2 (2% w/v), respectively. In order to increase the affinity toward CO2, the AC monoliths were subjected to the same surface modification postprocess, conducted with a 30% (w/w) aqueous ammonia solution. The textural characterization of the AC monoliths was carried out by N2 and pure CO2 adsorption at 77 and 273 K, respectively, allowing determination of the micro- and mesopore volumes as well as pore-size distributions. The adsorption tests show a maximum CO2 adsorption capacity for the sample with the greatest ultramicropore volume, while ...

Pd catalyst supported on activated carbon honeycomb monolith for CO oxidation and the application in air purification of vehicular tunnel

Different pretreatments (wet, oxidation and complex pretreatments) were used to modify activated carbon honeycomb monolith, and the role of surface properties of support in CO oxidation over Pd/ACHM catalysts was also investigated. Pretreatment was an efficient way to introduce oxygen groups, especially by complex pretreatment. Oxygen-containing groups increased 1.7 times as much as that of original ACHM, and 86% conversion was obtained at 30°C and 100% relative humidity on supported Pd catalyst prepared from modified ACHM. Oxygen-containing species on the support not only improved Pd dispersion but also affected Pd states. Compared with Pd dispersion, Pd states played a more important role in CO oxidation. The amount of low-valent Pd species (Pd0, Pd+1) on catalyst surface was consistent with CO oxidation activity. The presence of NO caused CO oxidation conversion to decrease by 15% which was attributed to the difference between NO and CO adsorption energy on Pd surfaces confirmed by density functional theory calculation. 90days' 1000m3/h pilot experiment results showed that the catalyst exhibited high activity and stability in the presence of moisture and NOx.

Activated carbon honeycomb monolith – Zeolite 13X hybrid system to capture CO2 from flue gases employing Electric Swing Adsorption

In this work, a preliminary study about the performance of a new hybrid adsorption bed, for CO2 capture from flue gases by Electric Swing Adsorption (ESA), was performed. The hybrid adsorption bed tested consists in an activated carbon honeycomb monolith with zeolite 13X particles packed inside its channels. The dynamic behaviour of the adsorption bed was evaluated by performing breakthrough experiments. The amount of CO2 adsorbed was the double when compared with employing the activated carbon monolith only, even when the content of zeolite is only 18%.ESA experimental cycles were tested. Purity of 46.6% was obtained while capturing 81.4% of the fed CO2 with a six-step ESA cycle. The obtained purity means an enrichment of the feed stream of 5.8 times. The experimental energy consumption is still high due to the mass transfer zone limitations. Solving this problem will allow decreasing the energy consumption more than five times which means that the process can present competitive energy consumption when compared with existing technology.

CO2 Adsorption on Activated Carbon Honeycomb-Monoliths: A Comparison of Langmuir and Tóth Models

Activated carbon honeycomb-monoliths with different textural properties were prepared by chemical activation of African palm shells with H3PO4, ZnCl2 and CaCl2 aqueous solutions of various concentrations. The adsorbents obtained were characterized by N2 adsorption at 77 K, and their carbon dioxide adsorption capacities were measured at 273 K and 1 Bar in volumetric adsorption equipment. The experimental adsorption isotherms were fitted to Langmuir and Tóth models, and a better fit was observed to Tóth equation with a correlation coefficient of 0.999. The maximum experimental values for adsorption capacity at the highest pressure (2.627–5.756 mmol·g−1) are between the calculated data in the two models.

Electrothermal performance of an activated carbon honeycomb monolith

The main advantage of Electric Swing Adsorption (ESA) process is related to the fast heating rates that can be achieved by Joule effect. Since this heating is done by passing electricity, its utilization should be efficient to reduce the overall losses of the system. This work discusses the heat transfer phenomena of an Electric Swing Adsorption (ESA) process in order to improve the overall energetic efficiency of the unit.Experiments were done with an activated carbon honeycomb monolith and testing different electrodes and column arrangements. The experimental set-up with lower electrical resistance has shown lower losses: faster heating rates can be achieved and less heat is lost by natural convection to the surroundings. Brass electrodes employed with a Teflon® support have resulted in lower energy losses. Results obtained in a laboratory-scale unit allowed a heating efficiency of 52% employing an average power of 293W. Most of the energy losses were to the electrodes and surroundings, reason why if the process is scaled-up, the efficiency of the unit should be better. Furthermore, the mass of adsorbent/mass of electrodes ratio can be reduced and then the overall efficiency can be increased up to 83%.

Synthesis of Activated Carbon Honeycomb Monoliths under Different Conditions for the Adsorption of Methane

Methane adsorption onto different types of carbon monoliths was studied at two temperatures (298.15 K and 303.15 K) and at pressures up to 35 atm in a volumetric adsorption apparatus. The mass basis results for methane adsorption indicated that the methane adsorption capacities of the carbon monoliths increased with increasing surface area, total pore volume and micropore volume. The maximum volumetric methane uptake of the carbon monoliths synthesized was 165 v/v at 298.15 K and 35 atm employing steam-activated monoliths derived from petroleum coal tar. The Clapeyron—Clausius equation was used to describe the interaction between the guest molecules and the adsorbent at low surface coverage and the energetic heterogeneous surface nature of the adsorbent, respectively. The methane storage capacity was found to be a function of the micropore volume and the developed superficial area.

Adsorption of CO2, CH4, and N2in Activated Carbon Honeycomb Monolith

Biomethane generated from renewable sources can be used as a renewable fuel to achieve ambitious targets for biofuels. The development of adsorption-based technologies for purification of biogas requires knowledge of adsorption equilibria and kinetics of pure gases on a specific adsorbent material. In this work, we have measured adsorption equilibria of CO2, CH4, and N2 at (299, 323, 348, 373, and 423) K over a pressure range between (0 and 700) kPa on a carbon honeycomb monolith. The adsorption capacity of the activated carbon honeycomb monolith was CO2 > CH4 > N2. The multisite Langmuir model was employed to fit the data of the pure gases offering the possibility of direct prediction of multicomponent adsorption equilibria. The diffusion of single gases in the microporous structure of the activated carbon honeycomb monolith was studied by diluted breakthrough experiments. The experiments were performed over the same temperature range [(303 to 423) K]. A simplified 1D mathematical model was employed in t...

Electric Swing Adsorption for CO 2 removal from flue gases

One of the most important sources of CO 2 emissions are the fossil-fuel fired plants for production of electricity. Removal of CO 2 from flue gas streams for further sequestration has been proposed by the International Panel on Climate Change experts as one of the most reliable solutions to mitigate anthropogenic greenhouse emissions. When natural gas is employed as fuel, the molar fraction of CO 2 in the flue gas is lower than 5% causing serious problems for capture. The purpose of this work is to present experimental validation of an Electric Swing Adsorption (ESA) technology that may be employed for carbon capture for low molar fractions of CO 2 in the flue gas streams. To improve energy utilization, an activated carbon honeycomb monolith with low electrical resistivity was employed as selective adsorbent. A mathematical model for this honeycomb is proposed as well as different ESA cycles for CO 2 capture.

Effect of preparation conditions on the properties of a coal-derived activated carbon honeycomb monolith

Activated carbon honeycomb (ACH) monoliths were prepared by extruding of a mixture of bituminous coal and organic additives and subsequent carbonization and steam activation. Preparation parameters that were varied were carbonization temperature and activation time. The carbonization conditions were 500, 650 and 800 °C for 1 h and the steam activation conditions were 850 °C for 2, 4 and 6 h. The monoliths at various states were characterized by SEM, XRD, nitrogen adsorption and compression test. It was found that carbonization temperature has significant effects on pore size distribution and mechanical strength of ACH monoliths. The ACH monoliths prepared from high carbonization temperatures exhibited lower values of the BET surface area and total pore volume and higher value of the mechanical strength than those of the ACH monoliths prepared from low carbonization temperatures. This was attributed to the effect of high temperature carbonization that results in the formation of relatively less defective structures.

Effect of coal rank on the properties of coal-based activated carbon honeycomb monoliths

Activated carbon honeycombs (ACHs) were prepared by extrusion of honeycombs from a mixture of coal, coal tar, bean oil, methylcellulose and water, followed by carbonization and steam activation. Three Chinese coals, Qujing, Shenfu and Datong, were used as carbon precursors. The ACH monoliths obtained were characterized by N2 adsorption,thermo-gravimetry and compression tests. Results show that both coal rank and activation time have great a impact on the pore size distribution and mechanical strength. The ACHs from Datong obtained under optimum conditions have the highest BET surface area(884m2/g), the highest ignition temperature (535℃) and the highest mechanical strength(13MPa) among the three coals. The mechanical strength of the ACH monoliths decreases with increasing macro-pore volume. The ignition temperature is hardly affected by ash content but decreases with increasing volatile content.