In recent years, Carbon Capture and Storage (Sequestration) (CCS) has been proposed as a potential method to allow the continued use of fossil-fuelled power stations whilst preventing emissions of CO 2 from reaching the atmosphere. Gas, coal (and biomass)-fired power stations can respond to changes in demand more readily than many other sources of electricity production, hence the importance of retaining them as an option in the energy mix. Here, we review the leading CO 2 capture technologies, available in the short and long term, and their technological maturity, before discussing CO 2 transport and storage. Current pilot plants and demonstrations are highlighted, as is the importance of optimising the CCS system as a whole. Other topics briefly discussed include the viability of both the capture of CO 2 from the air and CO 2 reutilisation as climate change mitigation strategies. Finally, we discuss the economic and legal aspects of CCS.

a b s t r a c tIn 2005, the IPCC SRCCS recognized the large potential for developing and scaling up a wide range of emerging CO 2 capture technologies that promised to deliver lower energy penalties and cost. These included new energy conversion technologies such as chemical looping and novel capture systems based on the use of solid sorbents or membrane-based separation systems. In the last 10 years, a substantial body of scientific and technical literature on these topics has been produced from a large number of R&D projects worldwide, trying to demonstrate these concepts at increasing pilot scales, test and model the performance of key components at bench scale, investigate and develop improved functional materials, optimize the full process schemes with a view to a wide range of industrial applications, and to carry out more rigorous cost studies etc. This paper presents a general and critical review of the state of the art of these emerging CO 2 capture technologies paying special attention to specific process routes that have undergone a substantial increase in technical readiness level toward the large scales required by any CO 2 capture system.

A series of univalent cation forms of zeolite Rho (M(9.8)Al(9.8)Si(38.2)O(96), M = H, Li, Na, K, NH(4), Cs) and ultrastabilized zeolite Rho (US-Rho) have been prepared. Their CO(2) adsorption behavior has been measured at 298 K and up to 1 bar and related to the structures of the dehydrated forms determined by Rietveld refinement and, for H-Rho and US-Rho, by solid state NMR. Additionally, CO(2) adsorption properties of the H-form of the silicoalumino-phosphate with the RHO topology and univalent cation forms of the zeolite ZK-5 were measured for comparison. The highest uptakes at 0.1 bar, 298 K for both Rho and ZK-5 were obtained on the Li-forms (Li-Rho, 3.4 mmol g(-1); Li-ZK-5, 4.7 mmol g(-1)). H- and US-Rho had relatively low uptakes under these conditions: extra-framework Al species do not interact strongly with CO(2). Forms of zeolite Rho in which cations occupy window sites between α-cages show hysteresis in their CO(2) isotherms, the magnitude of which (Na(+),NH(4)(+) < K(+) < Cs(+)) correlates with the tendency for cations to occupy double eight-membered ring sites rather than single eight-membered ring sites. Hysteresis is not observed for zeolites where cations do not occupy the intercage windows. In situ synchrotron X-ray diffraction of the CO(2) adsorption on Na-Rho at 298 K identifies the adsorption sites. The framework structure of Na-Rho "breathes" as CO(2) is adsorbed and desorbed and its desorption kinetics from Na-Rho at 308 K have been quantified by the Zero Length Column chromatographic technique. Na-Rho shows much higher CO(2)/C(2)H(6) selectivity than Na-ZK-5, as determined by single component adsorption, indicating that whereas CO(2) can diffuse readily through windows containing Na(+) cations, ethane cannot.

Contents S1. Synthesis and Initial Characterisation S2. Crystallographic details of the refined hydrated Na-, (K-and K, Hand nd Cs-MER S3. Structural response to dehydration S4. Adsorption studies S5. In situ laboratory PXRD of M-MER with adsorbed CO2 S6. Crystallographic details of the refined dehydrated solids with adsorbed CO2 S7. CO2/CH4 separation and breakthrough curves S8. Kinetic measurements using the Zero Length Column technique S9. K,H-MER zeolite structural and adsorption results S2 S1. Synthesis and Initial Characterisation Synthesis Colloidal silica, Ludox HS-40 (12.5 g; 40%, suspension in water; Sigma-Aldrich) was added to 35% aqueous solution of tetraethylammonium hydroxide (3.15 g; 35% TEOAH, Sigma-Aldrich) and the resulting mixture was stirred for 1 h. To this mixture, a solution made by dissolving metal Al (0.8 g, 99%, Alfa Aesar) in 3 g TEAOH and KOH (0.6 g, 85%, Fisher Chemicals), which was also mixed for 1 h, was added. The gel formed was continuously stirred for 10 min, transferred to a PTFE-lined stainless-steel autoclave and hydrothermally treated at 423 K under slow rotation (60 rpm). The resultant solid product, collected after 96 h, was

The definitions of absolute, excess and net adsorption in microporous materials are used to identify the correct limits at zero and infinite pressure. Absolute adsorption is shown to be the fundamental thermodynamic property and methods to determine the solid density that includes the micropore volume are discussed. A simple means to define when it is necessary to distinguish between the three definitions at low pressure is presented. To highlight the practical implications of the analysis the case of adsorption of helium is considered in detail and a combination of experiments and molecular simulations is used to clarify how to interpret adsorption measurements for weakly adsorbed components. List of symbolsGibbs energy of the solid without the adsorbate (J) DH Adsorption enthalpy (J mol -1 )Dimensionless (absolute) Henry law constant K ex Dimensionless excess Henry law constant K net Dimensionless net Henry law constant K P Henry law constant (absolute) (mol m -3 kPa) L Length of adsorption column (m) M Bu Mass of bucket (kg) M S Mass of solid (kg) Mw A Molecular weight of adsorbate (kg mol -1 ) n A Moles of adsorbate (mol) n abs Absolute adsorbed amount (mol) n ex Excess adsorbed amount (mol) n net Net adsorbed amount (mol) n S Moles of solid (mol) n TotTotal moles in the system (mol) PPressure (kPa) P 0 d Pressure in dosing cell before valve is opened (kPa) P 1 d Pressure in dosing cell after valve is opened (kPa) P 0 u Pressure in uptake cell before valve is opened (kPa) P 1 u Pressure in uptake cell after valve is opened (kPa) q A Adsorbed phase concentration (mol m -3 ) q abs Absolute adsorbed phase concentration (mol m -3 ) q ex Excess adsorbed phase concentration (mol m -3 ) q net Net adsorbed phase concentration (mol m -3 ) r Position (m) R Ideal gas constant (J mol -1 K -1 ) s A Molar entropy of adsorbed phase (J mol -1 K -1 ) s G Molar entropy of gas phase (J mol -1 K -1 ) T Temperature (K) U Interaction energy of atom (J atom -1 ) DU Adsorption energy (J mol -1 ) v G Molar volume of gas phase (m 3 mol -1 ) V Bu Volume of bucket (m 3 ) V d Volume of dosing cell (m 3 ) Volume of fluid phase (m 3 ) V NA Volume not accessible (m 3 ) V P Volume of pellet (m 3 ) V S Volume of solid, including micropores (m 3 ) V u Volume of uptake cell (m 3 ) z Compressibility factorGreek letters e m Porosity of microporous material e P Macroporosity of pellet / C Fraction of active material in a pellet l A Chemical potential of adsorbate (J mol -1 ) l S Chemical potential of solid (volume basis) (J m -3 ) l 0 S Chemical potential of solid without adsorbate (J m -3 ) g CP Reduced density at close packing g A CP Reduced density of adsorbed phase at close packing q Gas Density of gas phase (kg m -3 ) q S Solid density including micropores (kg m -3 ) q C S Density of active material (kg m -3 ) q SkSkeletal density (kg m -3 ) wGrand potential (J m -3 ) XSignal from microbalance (force) (N)

Multiscale material screening strategies combine molecular simulations and process modeling to identify the best performing adsorbents for a particular application, such as carbon capture. The idea to go from the properties of a single crystal to the prediction of material performance in a real process is both powerful and appealing; however, it is yet to be established how to implement it consistently. In this article, we focus on the challenges associated with the interface between molecular and process levels of description. We explore how predictions of the material performance in the actual process depend on the accuracy of molecular simulations, on the procedures to feed the equilibrium adsorption data into the process simulator, and on the structural characteristics of the pellets, which are not available from molecular simulations and should be treated as optimization parameters. The presented analysis paves the way for more consistent and robust multiscale material screening strategies.

This study reports the detailed evaluation of ten different configurations of amine capture processes using 30 wt% aqueous monoethanolamine (MEA) solvent to capture 90% CO 2 from an exemplary sub-critical PC-fired boiler power plant. The process configurations are compared with respect to total energy consumption, including thermal and electrical energy used. The comparison includes known configurations available in the literature and in patents. Additional configurations which lead to improved amine capture processes are presented, which result in further reduction in the reboiler heat duty. The use of detailed process flowsheet simulations enables the quantification of the effect of using multiple strategies in achieving greater reduction in the energy required for the integrated carbon capture and compression units. The simulations are also constrained to limit temperatures below conditions that lead to amine thermal degradation. Compared to the simple absorber/stripper configuration, which reduced the efficiency of the power plant by 9-12%, the multiple alteration system proposed in this study achieves the same capture rate with a 0.9% gain of net plant efficiency only by an advanced amine process configuration and a reduction in steam consumption of up to 37%.

Computational screening methods have changed the way new materials and processes are discovered and designed. For adsorption-based gas separations and carbon capture, recent efforts have been directed toward the development of multiscale and performance-based screening workflows where we can go from the atomistic structure of an adsorbent to its equilibrium and transport properties at different scales, and eventually to its separation performance at the process level. The objective of this work is to review the current status of this new approach, discuss its potential and impact on the field of materials screening, and highlight the challenges that limit its application. We compile and introduce all the elements required for the development, implementation, and operation of multiscale workflows, hence providing a useful practical guide and a comprehensive source of reference to the scientific communities who work in this area. Our review includes information about available materials databases, state-of-the-art molecular simulation and process modeling tools, and a complete catalogue of data and parameters that are required at each stage of the multiscale screening. We thoroughly discuss the challenges associated with data availability, consistency of the models, and reproducibility of the data and, finally, propose new directions for the future of the field.