Reverse engineering and synthesis of self-assembling photo-responsive surfactants for CO2 solubilization

A new way to control properties of liquid CO2 will be found. This will allow the liquid properties of CO2 to be remote-controlled, using light as a switch. Today, reduction in atmospheric CO2 levels is the greatest challenge facing scientists, engineers, politicians and economists.1 Of all the solutions proposed CO2 capture, sequestration and storage is recognized as a viable approach to control CO2 levels. However, CO2 entrapment and storage technologies will require efficient and effective command over the fluid properties of CO2; obviously, vast volumes of liquid CO2 will need to be handled and processed. For example, CO2 sequestration in sandstone or limestone reservoirs that occurs during CO2 enhanced oil recovery (EOR) would be more economically viable and technically efficient if viscous fingering could be suppressed by thickening the CO2. Although on paper the concept appears to be straightforward, that is find scCO2-compatible additives, as is commonly done for water (soaps and detergents, synthetic and bio-polymers, salts and co-solvents), in practice there are significant physico-chemical barriers to overcome. What it all comes down to is the inescapable fact that feeble intermolecular interactions make CO2 a very weak solvent, being essentially in a class of its own when compared to water and any other polar or apolar organic solvents. The upshot is that most commercially available solutes are incompatible with scCO2, and so the scope for solvent modification using readily available additives is at best extremely limited. Simply put, CO2 is one of the most stubborn of all chemical beasts, and taming it presents a great chemical engineering challenge. This project will design and generate new additives (surfactants) which and be using external light: this will allow us to control the CO2 fluid properties at the flick of a switch , as this cannot be done using any of the currently available chemicals. . This would open the doors to optimization of CO2 for industrial chemistry processes, as an environmentally friendly solvent, and also for processing and handling fluid CO2 in carbon capture technologies, for effective subterranean storage.

Impact on society The research aims to provide potential alternatives to the portfolio of processes for CO2 capture and resource recovery technologies. Addressed here is sequestration of anthropogenic CO2, since these are high volume applications. Potentially the planet could benefit from reduced CO2 emissions that will be possible through these technologies. To remove CO2 from the atmosphere and lock it away underground (for what ever purpose) will require modifications of the natural fluid properties of CO2. The additives produced in this program will optimize the surface tension, wettability and viscosity of CO2 to facilitate these developments. Without the ability to tailor CO2 properties certain promising engineering and processing approaches to reducing global warming may not be possible. Impact on peers - communication and engagement This proposal is unique as it bridges between two well-established groups with complementary expertise. The Imperial College group has extensive experience in the molecular modelling of self-assembling fluids and pioneers the development of bridges between molecular-level information (coarse grained intermolecular potentials) and engineering-level macroscopic group contribution methods. On the other hand, the Bristol group is on the forefront of the chemical synthesis of self-assembling surfactants and has an comprehensive experience in characterizing self-assembled structures. There is a very fundamental paradigm to be established whereby in silico design of molecules can drive and be closely linked with traditional chemical synthesis. The conceptual idea is taken into practice on a very topical application, as we focus on optimizing surfactants for the solution CO2 in water. The immediate results may be taken forward as engineering solutions for CO2 capture and storage. Exploitation The research is still in a blue-skies stage. However, the program seeks to provide a viable means for enhancing surfactant and water solubilities in CO2, and triggering stability/instability transitions by light. The systems to be developed will extend the scope of CO2 as a green alternative, which may impinge on a number of other emerging technologies (e.g. design of CO2-soluble ligands for homogeneous catalysis and nanoparticles for impregnation of medical devices, CFC-free dry-cleaning). As a supercritical fluid, CO2 has advantages over traditional solvents: it is readily available from renewable resources, recyclable and biocompatible. It is also unique as a solvent (apart from water) in that it is 100% bio-recyclable, through photosynthetic pathways. CO2 dry cleaning has been successfully commercialized: ICI and Linde have a joint venture { A. Tullo, ICI enters CO2 dry cleaning . Chem. Eng. News., 80 (35), 12 (2002)}. Interestingly, CO2 has also been touted as a cleaning solution for space missions and moon colonization {http://www.asi.org/adb/04/03/05/co2-dry-cleaning.html}. Hence, by providing CO2 soluble surfactants the research also has potential to contribute towards improved cleaning efficiencies in this area.