Economical and environmental aspects are the main motivation for research on energy efficient processes and the search for environment friendly materials for CO2 capture. Currently, CO2 capture is dominated by amine-based (e.g., monoethanolamine) technologies, which are very energy intensive and less attractive from an environmental point of view due to emissions of the used volatile solvent components. Ionic liquids have been proposed as a promising alternative to the conventional volatile solvents, because of their low volatility and other interesting properties. This remarkable interest has led to a rapid growth of literature on this specific subject. The aim of the present review paper is to provide a detailed overview of the achievements and difficulties that has been encountered in finding a suitable ionic liquid for CO2 capture from flue-gas streams. A major part of this review includes an overview of the experimental data of CO2 solubility, selectivity, and diffusivity in different ionic liquids. The effect of anions, cations, and functional groups on the CO2 solubility, biodegradability, and toxicity of the ionic liquids are highlighted. Recent developments on task-specific ionic liquids and supported ionic liquid membranes are also discussed. Scarcely available results of molecular simulations, which is a valuable tool in designing and evaluating ionic liquids, are also reviewed. The trends highlighted here can be used by solvent designers to navigate through the massive amount of theoretically possible ILs.

A high pressure semicontinuous batch electrolyzer is used to convert CO2 to formic acid/formate on a tin-based cathode using bipolar membranes (BPMs) and cation exchange membranes (CEMs). The effects of CO2 pressure up to 50 bar, electrolyte concentration, flow rate, cell potential, and the two types of membranes on the current density (CD) and Faraday efficiency (FE) for formic acid/formate are investigated. Increasing the CO2 pressure yields a high FE up to 90% at a cell potential of 3.5 V and a CD of ∼30 mA/cm2. The FE decreases significantly at higher cell potentials and current densities, and lower pressures. Up to 2 wt % formate was produced at a cell potential of 4 V, a CD of ∼100 mA/cm2, and a FE of 65%. The advantages and disadvantages of using BPMs and CEMs in electrochemical cells for CO2 conversion to formic acid/formate are discussed.

A new formulation of the Reaction Ensemble Monte Carlo technique (RxMC) combined with the Continuous Fractional Component Monte Carlo method is presented. This method is denoted by serial Rx/CFC. The key ingredient is that fractional molecules of either reactants or reaction products are present and that chemical reactions always involve fractional molecules. Serial Rx/CFC has the following advantages compared to other approaches: (1) One directly obtains chemical potentials of all reactants and reaction products. Obtained chemical potentials can be used directly as an independent check to ensure that chemical equilibrium is achieved. (2) Independent biasing is applied to the fractional molecules of reactants and reaction products. Therefore, the efficiency of the algorithm is significantly increased, compared to the other approaches. (3) Changes in the maximum scaling parameter of intermolecular interactions can be chosen differently for reactants and reaction products. (4) The number of fractional molecules is reduced. As a proof of principle, our method is tested for Lennard-Jones systems at various pressures and for various chemical reactions. Excellent agreement was found both for average densities and equilibrium mixture compositions computed using serial Rx/CFC, RxMC/CFCMC previously introduced by Rosch and Maginn (Journal of Chemical Theory and Computation, 2011, 7, 269–279), and the conventional RxMC approach. The serial Rx/CFC approach is also tested for the reaction of ammonia synthesis at various temperatures and pressures. Excellent agreement was found between results obtained from serial Rx/CFC, experimental results from literature, and thermodynamic modeling using the Peng–Robinson equation of state. The efficiency of reaction trial moves is improved by a factor of 2 to 3 (depending on the system) compared to the RxMC/CFCMC formulation by Rosch and Maginn.

We present a new molecular simulation code, Brick-CFCMC, for performing Monte Carlo simulations using state-ofthe-art simulation techniques. The Continuous Fractional Component (CFC) method is implemented for simulations in the NVT/ NPT ensembles, the Gibbs Ensemble, the Grand-Canonical Ensemble, and the Reaction Ensemble. Molecule transfers are facilitated by the use of fractional molecules which significantly improve the efficiency of the simulations. With the CFC method, one can obtain phase equilibria and properties such as chemical potentials and partial molar enthalpies/volumes directly from a single simulation. It is possible to combine trial moves from different ensembles. This enables simulations of phase equilibria in a system where also a chemical reaction takes place. We demonstrate the applicability of our software by investigating the esterification of methanol with acetic acid in a two-phase system.

We use a high-pressure semicontinuous batch electrochemical reactor with a tin-based cathode to demonstrate that it is possible to efficiently convert CO 2 to formic acid (FA) in low-pH (i.e., pH < pK a ) electrolyte solutions. The effects of CO 2 pressure (up to 50 bar), bipolar membranes, and electrolyte (K 2 SO 4 ) concentration on the current density (CD) and the Faraday efficiency (FE) of formic acid were investigated. The highest FE (∼80%) of FA was achieved at a pressure of around 50 bar at a cell potential of 3.5 V and a CD of ∼30 mA/cm 2 . To suppress the hydrogen evolution reaction (HER), the electrochemical reduction of CO 2 in aqueous media is typically performed at alkaline conditions. The consequence of this is that products like formic acid, which has a pK a of 3.75, will almost completely dissociate into the formate form. The pH of the electrolyte solution has a strong influence not only on the electrochemical reduction process of CO 2 but also on the downstream separation of (dilute) acid products like formic acid. The selection of separation processes depends on the dissociation state of the acids. A review of separation technologies for formic acid/formate removal from aqueous dilute streams is provided. By applying common separation heuristics, we have selected liquid−liquid extraction and electrodialysis for formic acid and formate separation, respectively. An economic evaluation of both separation processes shows that the formic acid route is more attractive than the formate one. These results urge for a better design of (1) CO 2 electrocatalysts that can operate at low pH without affecting the selectivity of the desired products and (2) technologies for efficient separation of dilute products from (photo)electrochemical reactors.