Melamine-formaldehyde derived porous carbons for adsorption of CO2 capture.

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.

Development of nitrogen enriched nanostructured carbon adsorbents for CO2 capture.

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. CO2 adsorption performance was investigated at various temperatures from 30 to 100 °C by using a thermogravimetric analyzer under varying CO2 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. CO2 uptake profile for the developed adsorbents showed that the maximum CO2 adsorption occurred within ca. 100 s. CO2 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 CO2 adsorption on the developed adsorbents was studied by fitting the experimental data of CO2 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 CO2 was observed to increase from ca. 30-44 kJ mol(-1) with increase in surface coverage.

Mesoporous carbon adsorbents from melamine-formaldehyde resin using nanocasting technique for CO2 adsorption.

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 CO2 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 CO2 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 CO2 adsorption capacity among the synthesized adsorbents. Breakthrough time and CO2 equilibrium adsorption capacity were investigated from the breakthrough curves and were found to decrease with increase in adsorption temperature. Adsorption process for carbon adsorbent-CO2 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.