In this paper, three of the leading options for large scale CO 2 capture are reviewed from a technical perspective. We consider solvent-based chemisorption techniques, carbonate looping technology and the so-called oxy-fuel process. For each technology option, we give an overview of the technology, listing advantages and disadvantages. Subsequently, a discussion of the level of technological maturity is presented, and we conclude by identifying current gaps in knowledge and suggest areas with significant scope for future work. We then investigate the suitability of using ionic liquids as novel, environmentally benign solvents with which to capture CO 2 . In addition, we consider alternatives to simply sequestering CO 2 -we present a discussion on the possibility of recycling captured CO 2 and exploiting it as a C 1 building block for the sustainable manufacture of polymers, fine chemicals and liquid fuels. Finally, we present a discussion of relevant systems engineering methodologies in carbon capture system design.

The article reviews recent developments (mostly since 2004 until June 2010) in catalysts for CO(2)/epoxide copolymerisation and in the properties of the polycarbonates.

A novel di-iron(III) catalyst for the copolymerisation of cyclohexene oxide and CO 2 to yield poly(cyclohexene)carbonate, under mild conditions, is reported. The catalyst selectivity was completely changed on addition of an ammonium co-catalyst to yield only the cis-isomer of the cyclic carbonate, also under mild 10

The reaction kinetics of the copolymerization of carbon dioxide and cyclohexene oxide to produce poly(cyclohexene carbonate), catalyzed by a dizinc acetate complex, is studied by in situ attenuated total reflectance infrared (ATR-IR) and proton nuclear magnetic resonance ((1)H NMR) spectroscopy. A parameter study, including reactant and catalyst concentration and carbon dioxide pressure, reveals zero reaction order in carbon dioxide concentration, for pressures between 1 and 40 bar and temperatures up to 80 °C, and a first-order dependence on catalyst concentration and concentration of cyclohexene oxide. The activation energies for the formation of poly(cyclohexene carbonate) and the cyclic side product cyclohexene carbonate are calculated, by determining the rate coefficients over a temperature range between 65 and 90 °C and using Arrhenius plots, to be 96.8 ± 1.6 kJ mol(-1) (23.1 kcal mol(-1)) and 137.5 ± 6.4 kJ mol(-1) (32.9 kcal mol(-1)), respectively. Gel permeation chromatography (GPC), (1)H NMR spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry are employed to study the poly(cyclohexene carbonate) produced, and reveal bimodal molecular weight distributions, with narrow polydispersity indices (≤1.2). In all cases, two molecular weight distributions are observed, the higher value being approximately double the molecular weight of the lower value; this finding is seemingly independent of copolymerization conversion or reaction parameters. The copolymer characterization data and additional experiments in which chain transfer agents are added to copolymerization experiments indicate that rapid chain transfer reactions occur and allow an explanation for the observed bimodal molecular weight distributions. The spectroscopic and kinetic analyses enable a mechanism to be proposed for both the copolymerization reaction and possible side reactions; a dinuclear copolymerization active site is implicated.

Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymerization (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides, and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers-ε-caprolactone, cyclohexene oxide, phthalic anhydride, and carbon dioxide-are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity, resulting in block sequence control and predictable compositions (esters and carbonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically controlled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.

A detailed study of the mechanism by which a dizinc catalyst copolymerizes cyclohexene oxide and carbon dioxide is presented. The catalyst, previously published by Williams et al. (Angew. Chem. Int. Ed200948931), shows high activity under just 1 bar pressure of CO2. This work applies in situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) to study changes to the catalyst structure on reaction with cyclohexene oxide and, subsequently, with carbon dioxide. A computational investigation, using DFT with solvation corrections, is used to calculate the relative free energies for various transition states and intermediates in the cycle for alternating copolymerization catalyzed by this dinuclear complex. Two potentially competing side reactions, sequential epoxide enchainment and sequential carbon dioxide enchainment are also investigated. The two side-reactions are shown to be thermodynamically disfavored, rationalizing the high selectivity exhibited in experimental studies using 1. Furthermore, the DFT calculations show that the rate-determining step is the nucleophilic attack of the coordinated epoxide molecule by the zinc-bound carbonate group in line with previous experimental findings (ΔΔG 353 = 23.5 kcal/mol; ΔG ‡ 353 = 25.7 kcal/mol). Both in situ spectroscopy and DFT calculations indicate that just one polymer chain is initiated per dizinc catalyst molecule. The catalyst adopts a “bowl” shape conformation, whereby the acetate group coordinated on the concave face is a spectator ligand while that coordinated on the convex face is the initiating group. The spectator carboxylate group plays an important role in the catalytic cycle, counter-balancing chain growth on the opposite face. The DFT was used to predict the activities of two new catalysts, good agreement between experimental turn-over-numbers and DFT predictions were observed.

The preparation of a,u-hydroxy-telechelic poly(cyclohexene carbonate) from a dizinc catalyst is reported. The telechelic polymer, with an yttrium initiator, can be used to polymerize lactide, yielding new triblock copolymers, substantially derived from renewable resources.

A six-membered cyclic carbonate derived from natural sugar ᴅ-mannose was prepared using CO 2 as a C1 building block at room temperature and atmospheric pressure. The monomer was synthesized in two steps from a commercially available mannopyranose derivative. Polycarbonates were rapidly prepared at ambient temperature by controlled ringopening polymerization (ROP) of the monomer, initiated by 4-methylbenzyl alcohol in the presence of 1,5,7-triazabicyclo[5.4.0]dec-5-ene (TBD) as the organocatalyst. Head-to-tail regiochemistry was indicated by NMR spectroscopy and is supported by DFT calculations. These aliphatic polycarbonates exhibit high-temperature resistance and demonstrate potential for post-polymerization functionalization, suggesting future application as high-performance commodity and biomedical materials.