Photo-catalytic Microbubble reactor for conversion of CO2 to Fuels

Many research studies have clearly established correlation between carbon dioxide concentration in earth's atmosphere and global warming. To mitigate the effect of large concentration of atmospheric carbon dioxide, UK government has committed the 80% reduction in greenhouse gas emission by 2050. According to Energy Statistics by the Department of Energy and Climate Change (DECC) report, the contribution of renewable to gross UK consumption has increased from 6.6 to 7.4 per cent in 2010. However, in order to reach the target of the 15% reduction by 2020, massive increase in speed of investment and planning permission approval process will be required. According to report, planning permission and investment are the main hurdles in achieving the renewable energy targets. In such scenario, the transient solution of capturing and converting carbon dioxide would provide alternative route to carbon free future. In low carbon vision 2050 report, it is envisaged that the power plant with carbon capture and storage would be a major technology in clean power segment by 2020.

The simultaneous reduction of carbon dioxide with water splitting in presence of sun light and semiconductor catalyst is considered to be attractive strategy in securing low carbon energy in short term. However, this conversion process suffers from the low yield and high processing cost. One way to improve the efficiency is to use novel or modified catalyst. The membrane, nano-TiO2 tubes, and fluidised bed based solutions for CO2 conversion have recently been proposed by the researcher. However, these methods require efficient dispersion of carbon dioxide and mechanism to prevent clogging of porous catalyst nano-particles or nano-tubes. In alternative method, CO2 dissolved in liquid phase is employed to overcome the problem of clogging. But, this method suffers from the low CO2 dissolution in water. Hence, key consideration for this work is to address three problems viz. (i) low dissolution of CO2 in water, (ii) low photoacitivity of TiO2 and (iii) inefficient transfer of electron at interface.

This project will employ our novel microbubbling device to prepare the carbon dioxide core microbubbles foam in TiO2 aqueous suspension. The diameter of bubble in few tens of micrometer range promotes the dissolution of CO2. Subsequently foam will be injected into the continuous flow microfluidics photo-reactor where sun light beam will be focused orthogonally to the direction of foam flow. Main advantage of the device is that it can generate the surface plasmon at the interface of two consecutive bubbles. The interface thickness in range of few hundreds nanometre acts as a waveguide and generates the surface plasmon which will be absorbed by the TiO2 particle adsorbed at the bubble interface. Surface plasmon increases the photoactivity of the TiO2 particle and thus, enhances its ability to increase the product yield of the reaction. It is first time foam will be used to generate the surface plasmon. This will allow avoiding costly catalyst surface modification steps.

The microfluidics/optofluidics mediated catalysis enhancement project led by Dr. Ketan Pancholi at The Robert Gordon University is designing reactor based on microfluidics that can generate the surface plasmon at the liquid-catalyst nano-particle interface to increase the photocatalytic activity of catalyst. This is a novel approach of employing foam (gas-liquid phase reaction such as CO2 and water) or emulsion (liquid-liquid phase reaction in organic synthesis) as template to generate surface plasmon capable of increasing yield of photocatalytic reaction. The project impact includes:

(i) Sunlight mediated conversion of CO2 to fuel at high yield is key for commercialisation of clean energy technologies. Many methods demonstrating increase in efficiency using nano-tube membrane, catalyst suspension are proposed. However, they suffer from problem such as low yield, clogging and low dissolution of CO2 in water. The proposed method will attempt to solve these problems by increasing the dissolution via microbubbling and the photoactivity of the catalyst using sunlight induced surface plasmon. Method does not involve expensive modification of catalyst nano-particles or use of nano-tubes. Additionally, it uses environmental friendly sunlight as a natural light source. Hence, it will be cheaper route to increase CO2 to fuel conversion rate.

(ii) Using foam as a wave-guide to generate surface plasmon effect can have scientific impact in context of understanding the role of bubbles or foam in generating such effect. The fundamental understanding on interaction of wave with heterogeneous fluid media can be understood precisely. This can lead to cheaper production of the photonics structure using fluid jetting technique.

(iii) Similar reactor design can help improving the efficiency of the synthesis of organic compound (Pharmaceutics) and waste reduction process. Hence, it can increase the competitiveness of UK pharmaceutical and environmental industries by keeping cost of manufacturing down.

(iv) Outcome will benefit research across the disciplines health care (new material for photodynamic therapy), energy (novel reactor for efficient hydrogen production). This research can also be applied to bacteria encapsulation for bio-fuel generation. These areas form a part of BBSRC and MRC priority e.g. (i) green fuel (ii) health and well being.

(v) Development of clean energy tech and efficient drug reaction (cheaper drugs) can be result of this project. This improves the quality of life of general public.

(vi) Project contributes to training of high skilled personnel for growing catalysis research area. A person working on this project will be confident user of the many scientific instruments for characterising materials. Additionally, an experience in the experiment planning, awareness of current literature, operating laboratory equipment, and catalysis process can be gained by the research assistant on this project. These skills are required in various industries such Glaxo-Smithkline Ltd. for organic synthesis, Johnson Matthey and SRG for consultancy and reactor design. The skills imparted via working on this project are essential for scientist working on catalysis related industries.