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Pure component (CO2 and N2) adsorption isotherms of oxygen enriched nanostructured carbon (RF-700) were evaluated using a static volumetric analyzer at four different adsorption temperatures ranging from 30 to 100 °C. Langmuir, Sips, and dual-site Langmuir (DSL) models were used to correlate pure component adsorption isotherms and it was found that Sips and DSL isotherm model fitted well with the experimental data, indicating the heterogeneous nature of the adsorbent surface. Fixed-bed column was used to obtain dynamic breakthrough data for binary system CO2–N2 at different adsorption temperatures (30–100 °C) and CO2 feed concentrations (5–12.5% by volume). Extended Sips, extended DSL, and IAST (ideal adsorbed solution theory) models using pure component adsorption isotherm data were used for the prediction of adsorption of binary system (CO2–N2). Predicted equilibria data was compared with experimental breakthrough curve data, and it was found that extended forms of the isotherm models (Sips and DSL) und...

In this work, we report carbon adsorbents obtained from high nitrogen content melamine-formaldehyde resin as starting material and mesoporous zeolite MCM-41 as template through nanocasting technique. To synthesize different carbon structure adsorbents with improved textural and surface properties, the material undergo carbonization followed by physical activation under CO2 atmosphere at different temperatures. Characterizations of the adsorbents using SEM, TEM, XPS, nitrogen sorption, CHN, TKN, and TPD have been carried out. Characterization results reveal the development of nanostructured carbon adsorbents with better texture and surface properties as compared to the sample prepared by direct carbonization. Sample prepared at carbonization-activation temperature of 700 °C shows highest basicity, surface area (193.28 m2 g-1) and pore volume (0.32 cm3 g-1). Performance evaluation of adsorbent was performed thermo gravimetrically at different temperatures and concentrations and was found that the adsorbent synthesized at 700 °C exhibit highest CO2 uptake of 0.93 mmol g-1 with nitrogen content of 22.73%. It was found that both surface area and nitrogen functional group have a major impact on adsorption capacity. Physiosorption process was confirmed by a decrease in adsorption capacity with increase in temperature. Three kinetic models and isotherms were used in this study and found that fractional order kinetic model and Freundlich isotherm best fitted with the experimental data. Isotherm study depicts the heterogeneous nature of adsorbent surface. Adsorbent exhibited complete regenerability and was stable over four adsorption-desorption cycles. Low value of isosteric heat of adsorption of 15.75 kJ mol-1, indicates physiosorption process. Negative value of ΔG0 and ΔH0 confirms spontaneous, feasible and exothermic nature of adsorption process.

In this work, we report carbon adsorbents prepared using MCM-41 (mesoporous zeolite) template and high nitrogen content, melamine-formaldehyde resin as starting material by using nanocasting technique. The material was carbonized and physically activated with CO2 at different temperatures to obtain different carbon adsorbents. Synthesized adsorbents were characterized using various techniques for their elemental, surface and textural properties. Effect of nanocasting technique was seen by the improvement in textural property e.g. the surface area and pore volume of the adsorbent prepared at 700 °C were found to be maximum, i.e. 193.28 m2 g−1 and 0.32 cm3 g−1, respectively. This was not seen for the sample prepared by direct carbonization (MF-700). Also, development of nanostructured carbon adsorbents was confirmed from XRD and TEM results. Adsorption of CO2 on carbon adsorbents was evaluated at different temperatures (30–100 °C) and concentrations (5–12.5%) in a dynamic fixed bed column. Adsorbent prepared at 700 °C exhibited highest CO2 uptake of 0.64 mmol g−1 due to high basicity as confirmed from X-ray photoelectron spectroscopy. Both surface and texture chemistry have a strong influence on the CO2 adsorption performance. The CO2 adsorption kinetic study was performed by using three kinetic models and was found that a fractional order fits well with the experimental data with maximum error% of 3.68%. Regeneration study of the adsorbent was carried out by using multiple adsorption-desorption cycles and found that the adsorbent exhibited easy regenerability and stability over multiple cycles. The Temkin isothermal model fitted best among three isotherm models indicating the heterogeneous surface of adsorbent surface. The isosteric heat of adsorption is found to be 15.05 kJ mol−1, which indicates physiosorption process and also supports easy regenerability of the adsorbent. Thermodynamic parameters such as ΔH0 and ΔS0 were found to be −5.7 kJ mol−1 and 0.033 kJ mol−1 K−1. The thermal energy estimated for CO2 desorption is 2.15 MJ per kg CO2.

Pure component adsorption isotherms for CO2 and N2 on the prepared nitrogen enriched carbon were evaluated using a static volumetric analyzer at four different adsorption temperatures ranging from 30–100 °C and were then correlated with three pure component adsorption isotherm models, namely, Langmuir, Sips, and dual-site Langmuir (DSL) models. Adsorption equilibria of binary CO2–N2 adsorption was then predicted by extending Sips and DSL equations empirically along with the usage of ideal adsorbed solution theory and was compared with experimental data obtained from the breakthrough curves through various phase diagrams. Breakthrough data for binary system were obtained at four different CO2 feed concentrations (5–12.5% by volume) and four adsorption temperatures (30–100 °C) using a fixed-bed reactor. Among three adsorption isotherms models used to investigate the equilibrium data of pure component system, Sips and DSL adsorption isotherm models fitted well, indicating energetically heterogeneous adsorben...

Nitrogen enriched porous carbons were prepared by nanocasting method using hexamethoxymethylmelamine (HMMM) as precursor and MCM-41 silica as template. Carbonization temperature was varied from 500 °C to 800 °C and was followed by physical activation with CO 2 at the same temperature. These materials were evaluated as adsorbents for CO 2 capture. Textural and morphological properties of these carbons show that they have mesoporosity derived from template removal. Carbonization and activation at 700 °C produced carbon with highest surface area of 463 m 2 /g and total pore volume of 0.48 cm 3 /g with nitrogen content of 9.2 wt%. Both of these properties account for the highest CO 2 uptake of 0.80 mmol/g at 30 °C using pure CO 2 . CO 2 uptake decreased with increase in temperature suggesting occurrence of physiosorption process. Additionally, these prepared carbons exhibited stable cyclic adsorption capacity. CO 2 adsorption kinetics on these adsorbents follow pseudo-first order model with maximum error of ca. 5.4%. The adsorbent surface was found to be energetically heterogeneous as suggested by Temkin isotherm model. Thermodynamics suggested exothermic, random and spontaneous nature of the process.

A range of novel nitrogen enriched porous carbons were obtained by varying carbonization temperature from 500 to 800 °C using nanocasting technique. Hexamethoxymethylmelamine (HMMM) and mesoporous silica were used as carbon precursor and template respectively. Prepared porous carbons were evaluated for their textural and chemical properties followed by CO 2 adsorption–desorption performance by conducting breakthrough experiments. Evolution of nitrogen functionalities in carbon materials during the carbonization process was investigated by X-ray photoelectron spectroscopy. Porous carbons obtained at 700 °C showed the best textural properties among the prepared carbons. It exhibited the specific surface area of 463 m 2 /g and total pore volume of 0.48 cm 3 /g and showed equilibrium adsorption capacity of 0.676 mmol/g at 30 °C and 12.5% CO 2 concentration. The adsorption capacity of C-700 was found to decrease with increase in adsorption temperature while it increased with increase in inlet CO 2 concentration. CO 2 adsorption kinetics on the prepared carbons was explained by pseudo-first order adsorption model. Three isotherm models were used to investigate the CO 2 adsorption equilibrium data and among the studied models Temkin isotherm model was found to explain the equilibrium data suggesting the heterogeneous nature of carbon surface.

Processes requiring intensive interfacial momentum, mass and heat exchange between gases and particulate solids can be greatly enhanced by operating in a centrifugal field. This is realized in the Gas-Solid Vortex Reactor (GSVR) with centrifugal accelerations up to two orders of magnitude higher than the Earth's gravitational acceleration. Here, the flow patterns of two 1g-Geldart B-type particles are experimentally assessed, over the gas inlet velocity range 82–126 m s−1, in an 80 mm diameter and 15 mm height GSVR. The particles are monosized aluminum spheres of 0.5 mm diameter, and walnut shell in the sieve fraction 0.50–0.56 mm and aspect ratio 1.3 ± 0.2. Two dimensional Particle Image Velocimetry combined with Digital Image Analysis and pressure measurements revealed that periodic fluctuations in solids azimuthal and radial velocity between gas inlet slots are strongly related to the average solids azimuthal velocity and bed uniformity. Aluminum particles feature steeper changes in azimuthal velocity and more attenuated changes in radial velocity than walnut shell particles. Within the assessed gas inlet velocity range the solids bed of aluminum exhibits average azimuthal velocities and bed voidages 40–50% and ≈10% lower than those of walnut shell. The aerodynamic response time of the particles, i.e. ρsdp2/18μg, emerged as an important parameter to assess the influence of the carrier gas jet on the radial deflection of the particles and the interaction solids bed-outer wall. Too low aerodynamic response time relates to nonuniformity in bed voidage due to solids radial velocity fluctuations. Excessive aerodynamic response time indicates low solids azimuthal velocities due to solids bed-outer wall friction.

In this work, a nanocasting technique has been used to synthesize oxygen enriched carbon adsorbents with epoxy resin as the precursor and mesoporous zeolite as a template. Carbonization and physical activation with CO2 was carried out to prepare different carbon adsorbents. Characterization of the synthesized adsorbents was done using N2 sorption, XRD, SEM, TEM, TGA, FTIR spectroscopy, CHN analysis, and XPS. The surface area and pore volume of the synthesized adsorbent prepared at 600 °C were found to be a maximum of 686.37 m2 g−1 and 0.60 cm3 g−1, respectively, but showed a lower adsorption capacity due to lesser oxygen content as compared to the sample prepared at 700 °C. The sample prepared at 700 °C exhibited the highest CO2 uptake, approximately 0.65 mmol g−1, at 30 °C due to the high oxygen content, which was estimated to be about 53.98% determined using CHN analysis and also due to high surface basicity confirmed by XPS. The sample prepared by direct carbonization of the polymeric precursor shows a completely non-porous and highly acidic material having the least adsorption capacity. It was found that an increase in concentration of CO2 increases adsorption capacity and an increase in adsorption temperature decreases adsorption capacity. CO2 adsorption kinetics were performed by using three kinetic models and from the correlation coefficient, adsorption kinetics were found to obey fractional order with error% within the range of 4.24%. For checking the regenerability, four adsorption–desorption cycles were examined. It was found that the adsorbents exhibit easy regenerability, stable adsorption capacity and good selectivity for CO2–N2 separation. The experimental data are well fitted with the Freundlich isotherm, showing a heterogeneous adsorbent surface. The isosteric heat Qst of CO2 is 9.09 kJ mol−1, which indicates the presence of the physisorption process. The negative value of Gibbs free energy suggests the spontaneous nature of the process. The values of ΔH° and ΔS° were found to be −2.562 kJ mol−1 and 0.033 kJ mol−1 K−1, respectively. The negative value of ΔH° suggests the exothermic nature of the adsorption process.