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Accumulation of greenhouse gases especially CO2 in the atmosphere leading to global warming with undesirable climate changes has been a serious global concern. Major power generation in the world is from coal based power plants. Carbon capture through pre- and post- combustion technologies with various technical options like adsorption, absorption, membrane separations, and chemical looping combustion with and without oxygen uncoupling have received considerable attention of researchers, environmentalists and the stake holders. Carbon capture from flue gases can be achieved with micro and meso porous adsorbents. This review covers carbonaceous (organic and metal organic frameworks) and noncarbonaceous (inorganic) porous adsorbents for CO2 adsorption at different process conditions and pore sizes. Focus is also given to noncarbonaceous micro and meso porous adsorbents in chemical looping combustion involving insitu CO2 capture at high temperature (>400 °C). Adsorption mechanisms, material characteristics, and synthesis methods are discussed. Attention is given to isosteric heats and characterization techniques. The options to enhance the techno-economic viability of carbon capture techniques by integrating with CO2 utilization to produce industrially important chemicals like ammonia and urea are analyzed. From the reader's perspective, for different classes of materials, each section has been summarized in the form of tables or figures to get a quick glance of the developments.

Carbon capture using various technical options, viz., adsorption, absorption, chemical looping combustion, membrane separation, and cryogenic separation in either pre-or post=combustion modes, has been found to be the effective solution to tackle a serious concern of global warming. Although adsorption has been widely employed in carbon capture as a result of its economically and environmentally benign nature, it could not be commercialized as a result of the highly energyintensive regeneration process involved. The major challenge in carbon capture is its sustainability at a high temperature, therefore enabling an easy integration with power generation to make it commercially viable, and also in the production of hydrogen using sorption-enhanced steam reforming. In this work, various combinations of sorbents based on CaO, MgO, zeolites H-Beta and H-ZSM 5, and Al 2 O 3 with and without doping of coal fly ash (C and F types) have been employed in carbon capture using a lab-scale fixed-bed reactor system. After initial screening of numerous sorbents, those based on CaO, MgO, and fly ash have been selected for rigorous standardization with reference to various critical process parameters, such as the sorbent combination, sorbent quantity, temperature, carbonation time, gas composition, and flow rate. It has been found that 50% CaO, 10% MgO, and 40% fly ash gave the highest capture besides exhibiting cyclic stability up to 15 cycles, and a positive influence of coal fly ash in stability and carbon capture enhancement has been reinforced.

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Carbon capture (CC) employing novel sorbents at high temperature is highly significant to address the serious concerns of global warming. In this work, thermodynamic and kinetic studies have been conducted on the carbonation using doped sorbents of CaO–MgO–CFA (coal fly ash). The thermodynamic estimations not only proved the feasibility and spontaneity of the reaction but also reinforced the positive role played by CFA in not only enhancing the CC but also reducing the regeneration temperatures. Regarding the kinetic studies, a model has been proposed for both the reaction and diffusion kinetic control regimes and has been validated with experimental data at optimal conditions. Various kinetic and Arrhenius parameters have been estimated and compared with the reported values. The rate constants at 650 °C and activation energies estimated for reaction and diffusion controlled regimes were 2.5 min−1, 23 kJ/mol and 0.8 min−1, 30 kJ/mol, respectively. Our values clearly indicate the enhanced rate achieved by doped sorbents along with thermal stability and also show that kinetics are strongly dependent on the nature of the sorbent along with process conditions.

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