The escalating level of atmospheric carbon dioxide is one of the most pressing environmental concerns of our age. Carbon capture and storage (CCS) from large point sources such as power plants is one option for reducing anthropogenic CO(2) emissions; however, currently the capture alone will increase the energy requirements of a plant by 25-40%. This Review highlights the challenges for capture technologies which have the greatest likelihood of reducing CO(2) emissions to the atmosphere, namely postcombustion (predominantly CO(2)/N(2) separation), precombustion (CO(2)/H(2)) capture, and natural gas sweetening (CO(2)/CH(4)). The key factor which underlies significant advancements lies in improved materials that perform the separations. In this regard, the most recent developments and emerging concepts in CO(2) separations by solvent absorption, chemical and physical adsorption, and membranes, amongst others, will be discussed, with particular attention on progress in the burgeoning field of metal-organic frameworks.

Carbon Dioxide Capture: Prospects for New Materials

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 CO2 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 CO2 capture technologies, available in the short and long term, and their technological maturity, before discussing CO2 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 CO2 from the air and CO2 reutilisation as climate change mitigation strategies. Finally, we discuss the economic and legal aspects of CCS.

Carbon capture and storage update

Structure and nanostructure in ionic liquids.

This review gives a survey on the latest most representative developments and progress concerning ionic liquids, from their fundamental properties to their applications in catalytic processes. It also highlights their emerging use for biomass treatment and transformation.

Ionic liquids and catalysis: Recent progress from knowledge to applications

Ionic liquids (ILs) are organic salts with melting points near room temperature (or by convention below 100 degrees C). Recently, their unique materials and solvent properties and the growing interest in a sustainable, "green" chemistry has led to an amazing increase in interest in such salts. A huge number of potential cation and anion families and their many substitution patterns allows the desired properties for specific applications to be selected. Because it is impossible to experimentally investigate even a small fraction of the potential cation-anion combinations, a molecular-based understanding of their properties is crucial. However, the unusual complexity of their intermolecular interactions renders molecular-based interpretations difficult, and gives rise to many controversies, speculations, and even myths about the properties that ILs allegedly possess. Herein the current knowledge about the molecular foundations of IL behavior is discussed.

Understanding Ionic Liquids at the Molecular Level: Facts, Problems, and Controversies

Experimental and molecular modeling studies are conducted to investigate the underlying mechanisms for the high solubility of CO2 in imidazolium-based ionic liquids. CO2 absorption isotherms at 10, 25, and 50 °C are reported for six different ionic liquids formed by pairing three different anions with two cations that differ only in the nature of the “acidic” site at the 2-position on the imidazolium ring. Molecular dynamics simulations of these two cations paired with hexafluorophosphate in the pure state and mixed with CO2 are also described. Both the experimental and the simulation results indicate that the anion has the greatest impact on the solubility of CO2. Experimentally, it is found that the bis(trifluoromethylsulfonyl)imide anion has the greatest affinity for CO2, while there is little difference in CO2 solubility between ionic liquids having the tetrafluoroborate or hexafluorophosphate anion. The simulations show strong organization of CO2 about hexafluorophosphate anions, but only small diffe...

Why Is CO2 so soluble in imidazolium-based ionic liquids?

A combined experimental and molecular dynamics study has been performed on the following pyridinium-based ionic liquids:  1-n-hexyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide ([hmpy][Tf2N]), 1-n-octyl-3-methylpyridinium bis(trifluoromethanesulfonyl)imide ([ompy][Tf2N]), and 1-n-hexyl-3,5-dimethylpyridinium bis(trifluoromethanesulfonyl)imide ([hdmpy][Tf2N]). Pulsed field gradient nuclear magnetic resonance spectroscopy was used to determine the self-diffusivities of the individual cations and anions as a function of temperature. Experimental self-diffusivities range from 10-11 to 10-10 m2/s. Activation energies for diffusion are 44−49 kJ/mol. A classical force field was developed for these compounds, and molecular dynamics simulations were performed to compute dynamic as well as thermodynamic properties. Evidence of glassy dynamics was found, preventing accurate determination of self-diffusivities over molecular dynamics time scales. Volumetric properties such as density, isothermal compressibil...

Molecular modeling and experimental studies of the thermodynamic and transport properties of pyridinium-based ionic liquids.

Results of a molecular dynamics study of several triazolium-based ionic liquids are reported. Triazolium cations include 1,2,4-triazolium, 1,2,3-triazolium, 4-amino-1,2,4-triazolium, and 1-methyl-4-amino-1,2,4-triazolium. Each cation was paired with a nitrate or perchlorate anion. These materials are part of a class of ionic compounds that have been synthesized recently but for which little physical property data are available. Properties of the more common ionic liquid, 1-n-butyl-3-methylimidazolium nitrate, are also computed and compared with the properties of the triazolium-based compounds. A molecular mechanics force field was developed for these materials using a mix of ab initio calculations and parameter fitting using the molecular compound 1H-1,2,4-triazole as a basis for the triazolium cations. Liquid-phase properties that were computed include heat capacities, cohesive energy densities, gravimetric densities/molar volumes as a function of temperature and pressure, self-diffusivities, rotational time constants, and various pair correlation functions. In the solid phase, heat capacities and lattice parameters were computed. Of all of these properties, only lattice parameters have been measured experimentally (and only for four of the triazolium compounds). The agreement with the experimental crystal structures was good. When compared with that of the imidazolium-based ionic liquid, the triazolium-based materials have much smaller molar volumes, higher cohesive energy densities, and larger specific heat capacities. They also tend to be less compressible, have a higher gravimetric density, and have faster rotational dynamics but similar translational dynamics.

Molecular Simulation Study of Some Thermophysical and Transport Properties of Triazolium-Based Ionic Liquids

This work is encouraged by the growing interest and recent success of quantum mechanics-based methods in modeling of thermodynamic properties in the field of chemical engineering and life sciences. Among those, the COSMO-RS model has become one of the most popular methods to predict phase equilibria in complex bio-related systems. Recently, we have shown that the quality of predictions of n-octanol/water and micelle/water partition coefficients is improved when the weighted mixtures of conformers are used to represent molecules, thereby demanding that the conformation analysis is performed for each component of the system. In this paper, different methods for performing the conformational search are evaluated. Micelle/water partition coefficients of solutes from different homologous series in aqueous solutions of Triton X100 as well as the n-octanol/ water partitioning of three common drugs (aminopinicillanic acid, ampicillin, and penicillin G) are calculated and compared with experimental data. Conformational analysis is made by the HyperChem program for the molecules placed in vacuum as well as by using the molecular dynamics simulation in a solvent medium (n-octanol and water). It is demonstrated that molecular dynamics simulation is a promising tool to conduct conformational analysis. Along with the possibility of providing the conformers for large surfactant and pharmaceutical molecules, the method accounts for the solvent in a realistic manner. The results for micelle/water partition coefficients illustrate that n-octanol is a reasonable approximation for the "micelle-like" medium in molecular dynamics (MD) simulations. Predicted n-octanol/water partition coefficients of three penicillins are in a good agreement with literature data and values calculated by a common quantitative structure-activity relationship (QSAR).

Cesar Cadena

Papers

Why Is CO2 so soluble in imidazolium-based ionic liquids?

Molecular modeling and experimental studies of the thermodynamic and transport properties of pyridinium-based ionic liquids.

Molecular Simulation Study of Some Thermophysical and Transport Properties of Triazolium-Based Ionic Liquids

COSMO‐RS Calculations of Partition Coefficients: Different Tools for Conformation Search