George Dowson

Fast and selective separation of carbon dioxide from dilute streams by pressure swing adsorption using solid ionic liquids

The need to create a new approach to carbon capture processes that are economically viable has led to the design and synthesis of sorbents that selectively capture carbon dioxide by physisorption. Solid Ionic Liquids (SoILs) were targeted because of their tunable properties and solid form under operational conditions. Molecular modelling was used to identify candidate SoILs and a number of materials based on the low cost, environmentally friendly acetate anion were selected. The materials showed excellent selectivity for carbon dioxide over nitrogen and oxygen and moderate sorption capacity. However, the rate of capture was extremely fast, in the order of a few seconds for a complete adsorb-desorb cycle, under pressure swing conditions from 1 to 10 bar. This showed the importance of rate of sorption cycling over capacity and demonstrates that smaller inventories of sorbents and smaller process equipment are required to capture low concentration CO2 streams. Concentrated CO2 was isolated by releasing the pressure back to atmospheric. The low volatility and thermal stability of SoILs mean that both plant costs and materials costs can be reduced and plant size considerably reduced.

Cellulose-Supported Ionic Liquids for Low-Cost Pressure Swing CO2 Capture

Reducing the cost of capturing CO2 from point source emitters is a major challenge facing Carbon Capture, Utilisation and Storage. While Solid Ionic Liquids (SoILs) have been shown to allow selective and rapid CO2 capture by pressure swing separation of flue gases, expectations of their high cost hinders their potential application. Cellulose is found to be a reliable, cheap and sustainable support for a range of SoILs, reducing the total sorbent cost by improving the efficiency of the ionic liquid through increased ionic surface area that results from coating. It was also found that cellulose support imparts surface characteristics, which increased total sorbent uptake. Combined, these effects allowed a 4 to 8-fold improvement in uptake per gram of ionic liquid for SoILs that have previously shown high uptake and a 9 to 39-fold improvement for those with previously poor uptake, offering the potential to drastically reduce the amount of ionic liquid required to separate a given gas volume. Furthermore, the fast kinetics are retained which means het rapid cycling can be achieved which results in high separation capacity relative to conventional temperature swing process. The projected reduction in plant size and operational costs represents a potentially ground-breaking step forward is carbon dioxide capture technologies.

Demonstration of CO2 Conversion to Synthetic Transport Fuel at Flue Gas Concentrations

A mixture of 1- and 2-butanol was produced using a stepwise synthesis starting with a methyl halide. The process included a carbon dioxide utilisation step to produce an acetate salt which was then converted to the butanol isomers by Claisen condensation of the esterified acetate followed by hydrogenation of the resulting ethyl acetoacetate. Importantly, the CO2 utilisation step uses dry, dilute carbon dioxide (12% CO2 in nitrogen) similar to those found in post-combustion flue gases. The work has shown a low reactivity of Grignard reagent has a slow rate of reaction in comparison to carbon dioxide, meaning that the costly purification step usually associated with carbon capture technologies can be omitted using this direct capture-conversion technique. Butanol isomers are useful as direct drop-in replacement fuels for gasoline due to their high octane number, higher energy density, hydrophobicity and low corrosivity in existing petrol engines. An energy analysis shows the process to be exothermic from methanol to butanol, however energy is required to regenerate the active magnesium metal from the halide by-product. The methodology is important as it allows electrical energy, which is difficult to store using batteries over long periods of time, to be stored as a liquid fuel that fits entirely with the current liquid fuels infrastructure. This means that renewable, weather-dependent energy can be stored across seasons, for example production in summer with consumption in winter. It also helps to avoid new fossil carbon entering the supply chain through the utilisation of carbon dioxide that would otherwise be emitted. As methanol has also been shown to be commercially produced from CO2, this adds to the prospect of the general decarbonisation of the transport fuels sector. Furthermore, as the conversion of CO2 to butanol requires significantly less hydrogen than CO2 to octanes, there is a potentially reduced burden on the so-called hydrogen economy.

Conversion of Carbon Dioxide to Oxygenated Organics

Abstract This chapter examines some of the possibilities and challenges of converting CO2 to oxygenated organic compounds, with a particular focus on methanol and dimethyl ether (DME). Several potential routes to their production, including both existing developed commercial pathways and recent discoveries, are shown with an emphasis on thermodynamic and hydrogen efficiency hurdles. The advantages of these products are demonstrated in their high energy density, synthetic flexibility, transportability and general stability as gateway products to fuels, plastics, fertilizers and medicines.