Deepak Tiwari

Novel nanostructured carbons derived from epoxy resin and their adsorption characteristics for CO2 capture

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.

Urea-formaldehyde derived porous carbons for adsorption of CO2

The aim of the research work is to develop high nitrogen content carbon adsorbents with high textural and surface properties using as a precursor urea-formaldehyde resin and as a template mesoporous-zeolite (MCM-41) through a nanocasting technique. The material undergoes carbonization followed by physical activation under a CO2 atmosphere to generate different carbon structure adsorbents. Different characterization techniques such as XRD, SEM, TEM, FTIR, CHN, TKN, nitrogen sorption, TGA, TPD and XPS were used for thorough characterization of the samples. XRD and TEM reveal the development of nanostructured carbon adsorbents. CO2 adsorption on adsorbents was investigated between temperatures of 30 and 100 °C and concentrations of 5 to 12.5% in a dynamic fixed bed column to overcome a gap in the literature. The carbon sample prepared at 700 °C through the nanocasting technique shows high basicity and exhibited a high CO2 uptake of 0.84 mmol g−1 with a nitrogen content of 17.18%. It shows higher values at a high adsorption temperature (100 °C) as compared to the literature, which fulfills the objective of this study. An adsorbent prepared at 800 °C shows the highest surface area (337.07 m2 g−1), but shows a lower adsorption capacity as compared to one prepared at 700 °C whose surface area was slightly lower (297.68 m2 g−1). This shows that besides textural and nitrogen content, adsorption capacity depends on nitrogen functionalities. The adsorbents exhibit stability and easy regenerability over four adsorption–desorption cycles with better selectivity for CO2. This was also confirmed from the lower value of Qst (kJ mol−1). The CO2 adsorption kinetics follow a fractional order model with less than 5% error. The equilibrium adsorption data fitted the Freundlich isothermal model well, demonstrating the heterogeneous nature of the adsorbent surface. Thermodynamics suggests a spontaneous, feasible and exothermic process.

Development of chemically activated N-enriched carbon adsorbents from urea-formaldehyde resin for CO2 adsorption: Kinetics, isotherm, and thermodynamics

Nitrogen enriched carbon adsorbents with high surface areas were successfully prepared by carbonizing the low-cost urea formaldehyde resin, followed by KOH activation. Different characterization techniques were used to determine the structure and surface functional groups. Maximum surface area and total pore volume of 4547 m2 g-1 and 4.50 cm3 g-1 were found by controlling activation conditions. The optimized sample denoted as UFA-3-973 possesses a remarkable surface area, which is found to be one of the best surface areas achieved so far. Nitrogen content of this sample was found to be 22.32%. Dynamic CO2 uptake capacity of the carbon adsorbents were determined thermogravimetrically at different CO2 concentrations (6-100%) and adsorption temperatures (303-373 K) which have a much more relevance for the flue gas application. Highest adsorption capacity of 2.43 mmol g-1 for this sample was obtained at 303 K under pure CO2 flow. Complete regenerability of the adsorbent over four adsorption-desorption cycles was obtained. Fractional order kinetic model provided best description of adsorption over all adsorption temperatures and CO2 concentrations. Heterogeneity of the adsorbent surface was confirmed from the Langmuir and Freundlich isotherms fits and isosteric heat of adsorption values. Exothermic, spontaneous and feasible nature of adsorption process was confirmed from thermodynamic parameter values. The combination of high surface area and large pore volume makes the adsorbent a new promising carbon material for CO2 capture from power plant flue gas and for other relevant applications.