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In the ongoing research campaign to reduce the global atmospheric CO2 concentration, technologies are being developed to enable the capture of CO2 from dilute sources and conversion into higher-value products. Amine and polyamine-based materials feature widely in the literature as solid CO2 sorbents and as catalyst modifiers for CO2 electrochemical reduction; however, advancing lab-scale research into a pilot or industrial-scale application is fraught with challenges, starting with the definition and identification of an effective adsorbent. This multidisciplinary review serves as an essential introduction to the role of amines in carbon capture and utilisation for scientists entering and advancing the field. The chemical and engineering principles of amine-based CO2 capture are considered to define the parameters required of an adsorbent, describe adsorption testing methods, and introduce the reader to a range of amine-based adsorbents and how they can be specialised to overcome specific issues. Finally, the application of electrocatalysts modified with nitrogen-containing compounds and polymers is reviewed in the context of CO2 utilisation.

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.

Vortex units are commonly considered for various single and multiphase applications due to their process intensification capabilities. The transition from gas‐only flow to gas–solid flow remains largely unexplored nonetheless. During this transition, primary flow phenomenon, jets, and secondary flow phenomena, counterflow and backflow, are substantially reduced, before a rotating solids bed is established. This transitional flow regime is referred to as the vortex suppression regime. In the present work, this flow transition is identified and validated through experimental and computational studies in two vortex units with a scale differing by a factor of 2, using spherical aluminum and alumina particles. This experimental data supports the proposed theoretical particle monolayer solids loading that allows estimation of vortex suppression regime solids capacity for any vortex unit. It is shown that the vortex suppression regime is established at a solids loading theoretically corresponding to a monolayer being formed in the unit for 1g‐Geldart D‐ and 1g‐Geldart B‐type particles. The model closely agrees with experimental vortex suppression range for both aluminum and alumina particles. The model, as well as the experimental data, shows that the flow suppression regime depends on unit dimensions, particle diameter, and particle density but is independent of gas flow rate. This combined study, based on experimental and computational data and on a theoretical model, reveals the vortex suppression to be one of the basic operational parameters to study flow in a vortex unit and that a simple monolayer model allows to estimate the needed solids loading for any vortex device to induce this flow transition.

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.

Nanostructured carbon adsorbents containing high nitrogen content were developed by templating melamine-formaldehyde resin in the pores of mesoporous silica by nanocasting technique. A series of adsorbents were prepared by altering the carbonization temperature from 400 to 700 °C and characterized in terms of their textural and morphological properties. CO 2 adsorption performance was investigated at various temperatures from 30 to 100 °C by using a thermogravimetric analyzer under varying CO 2 concentrations. Multiple adsorption–desorption experiments were also carried out to investigate the adsorbent regenerability. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the development of nanostructured materials. Fourier transform infrared spectroscopy (FTIR) and elemental analysis indicated the development of carbon adsorbents having high nitrogen content. The surface area and pore volume of the adsorbent carbonized at 700 °C were found to be 266 m 2 g −1 and 0.25 cm 3 g −1 respectively. CO 2 uptake profile for the developed adsorbents showed that the maximum CO 2 adsorption occurred within ca. 100 s. CO 2 uptake of 0.792 mmol g −1 at 30 °C was exhibited by carbon obtained at 700 °C with complete regenerability in three adsorption–desorption cycles. Furthermore, kinetics of CO 2 adsorption on the developed adsorbents was studied by fitting the experimental data of CO 2 uptake to three kinetic models with best fit being obtained by fractional order kinetic model with error% within range of 5%. Adsorbent surface was found to be energetically heterogeneous as suggested by Temkin isotherm model. Also the isosteric heat of adsorption for CO 2 was observed to increase from ca. 30–44 kJ mol −1 with increase in surface coverage.

Nitrogen doped mesoporous carbons were prepared by nanocasting method at varying carbonization temperatures followed by characterization in terms of their structural, textural and chemical properties. Melamine-formaldehyde resin and mesoporous silica were used as the polymeric precursor and hard template respectively. Meso-structural ordering of the template was retained by the prepared carbons as suggested by the structural analysis. Evolution of nitrogen and oxygen functionalities along with textural properties of nitrogen doped carbons were regulated by the carbonization temperature. The prepared carbons obtained by carbonization at 700 °C exhibited a maximum surface area of 266 m2 g−1 along with a nitrogen content up to 21 weight%. CO2 adsorption was studied in a fixed-bed column at several temperatures (30 to 100 °C) and CO2 concentrations (5 to 12.5%). Adsorbent reusability was examined by carrying out multiple adsorption–desorption cycles. MF-700 showed the highest CO2 adsorption capacity of 0.83 mmol g−1 at 30 °C. CO2 adsorption kinetics were investigated by fitting experimental CO2 uptake data to different adsorption kinetic models, out of which the fractional order model was found to fit over the complete adsorption range with the error% between experimental and model predicted data within the range of 5%. In addition, the isosteric heat of adsorption was estimated to be around 17 kJ mol−1, confirming the occurrence of the physiosorption process.

Silica templated nanostructured carbons were developed from a resorcinol–formaldehyde polymeric precursor by varying the carbonization temperature from 400 °C to 800 °C. The prepared carbons were characterized thoroughly for their textural, surface and chemical properties followed by dynamic CO2 capture performance at various adsorption temperatures from 30 °C to 100 °C under simulated flue gas conditions. Among the prepared carbons, carbonization at 700 °C resulted in the nanostructured carbon material, as indicated by XRD and TEM results, having the best textural properties i.e. specific surface area and total pore volume around 435 m2 g−1 and 0.22 cm3 g−1, respectively. The sample obtained by carbonization at the most severe conditions (≥800 °C) exhibited textural properties comparable to that of RF-700 but showed lower CO2 adsorption capacity on account of reduction in surface basicity at higher temperatures. On the other hand, preparation of the carbon material by direct carbonization of the polymeric precursor, i.e. without using a template, resulted in a completely non-porous material with very low CO2 adsorption capacity. Moreover, both the textural properties and the surface chemistry had an effect on the CO2 adsorption performance of the prepared carbons. RF-700 exhibited the highest dynamic CO2 adsorption capacity of 0.761 mmol g−1 at 30 °C in a binary mixture of 12.5% CO2 in N2 attributed to a well-developed porous structure and high surface basicity of 1.93 meq g−1. It also demonstrated high selectivity towards CO2 over N2 and stable adsorption capacity over multiple adsorption–desorption cycles. CO2 adsorption on the prepared carbons was well described by a fractional order kinetic model. Fitting of equilibrium data of CO2 adsorption by Temkin isotherm model and variation in isosteric heat of adsorption with surface coverage indicated an energetically heterogeneous adsorbent surface. Thermodynamics of CO2 adsorption on the carbon material suggested an exothermic, random and spontaneous nature of the process. The thermal energy required for desorption of CO2 was also estimated to be around 1.9 MJ per kg CO2.

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 CO

Mesoporous carbon adsorbents, having high nitrogen content, were synthesized via nanocasting technique with melamine–formaldehyde resin as precursor and mesoporous silica as template. A series of adsorbents were prepared by varying the carbonization temperature from 400 to 700°C. Adsorbents were characterized thoroughly by nitrogen sorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), elemental (CHN) analysis, Fourier transform infrared (FTIR) spectroscopy and Boehm titration. Carbonization temperature controlled the properties of the synthesized adsorbents ranging from surface area to their nitrogen content, which play major role in their application as adsorbents for CO 2 capture. The nanostructure of these materials was confirmed by XRD and TEM. Their nitrogen content decreased with an increase in carbonization temperature while other properties like surface area, pore volume, thermal stability and surface basicity increased with the carbonization temperature. These materials were evaluated for CO 2 adsorption by fixed-bed column adsorption experiments. Adsorbent synthesized at 700°C was found to have the highest surface area and surface basicity along with maximum CO 2 adsorption capacity among the synthesized adsorbents. Breakthrough time and CO 2 equilibrium adsorption capacity were investigated from the breakthrough curves and were found to decrease with increase in adsorption temperature. Adsorption process for carbon adsorbent–CO 2 system was found to be reversible with stable adsorption capacity over four consecutive adsorption–desorption cycles. From three isotherm models used to analyze the equilibrium data, Temkin isotherm model presented a nearly perfect fit implying the heterogeneous adsorbent surface.