As a result of high rates of nitrogen fertilization, the concentration of nitrate in water supplies in many agricultural areas of the EU exceeds the maximum admissible level for many industrial or human uses. This proposal concerns the fundamental study of a new
technological solution to this problem, which could impact
significantly on :
the food processing and beverage industry and
civil communities located in areas contaminated by agricultural production. Current technologies are inadequate to address this problem, particularly with respect to flexible and easily manageable small to medium size plants.
Water treatment technologies using a solid catalyst and a gas phase reagent have been proven to offer several advantages in terms of rate of reaction, operating conditions and process economics over conventional techniques of waste or polluted groundwater treatment. In this project, it is proposed the study of permselective catalytic diffusers for the selective hydrogenation of nitrate to nitrogen. This is a completely new and original catalyst design that needs to be studied thoroughly from a fundamental point of view. Areas covered will be 1.2.2.L and 2.1.3.L.
Catalytic diffusers are based on membrane technology and will be made from a macroporous ceramic, coated externally with a thin film of oxide with controlled porosity and thickness employed as catalyst support. A noble metal active phase, will be deposited on the membrane like support. The diffusers will be put into the water solution containing nitrate. In this way, hydrogen will be physically separated from water and will diffuse on the surface of the catalyst where it will be immediately used for nitrate hydrogenation. Hydrogen throughput through the membrane will be controlled by the pressure differential allowing a tuning of the reaction rate. This catalyst design allows extensive innovation, namely: it improves the three phase contact (hydrogen/nitrate in water/solid catalyst) avoiding mass transport limitations, it avoids the possible formation of suspended particles in water, it allows a fine tuning of the reaction rate to suit variable situations (different nitrate conc., rate of water flow, etc.) and it can be easily scaled up. It also limits greatly safety problems by having separate hydrogen and water flow.
The development of this catalyst design towards a potential
practical application will require extensive study with respect to: all the synthesis parameters of the membrane like diffusors (content of metal and dopants, porosity and thickness of the support, mechanical resistance, etc.);
a detailed characterization of the samples before and after the catalytic tests using a combination of physico chemical techniques to determine the textural, morphological and structural properties of supports and active phases, the surface reactivity, the dispersion of components, the particle size and concentration profiles of the supported metals;
a screening of the reactivity of the catalysts in the hydrogenation reaction analyzing the effects of the metal loading, the porosity and thickness of the primary support, the pressure differential through the membrane, etc. on both the reaction rate of nitrate reduction and the selectivity to nitrogen formation;
all the engineering aspects including the intrinsic reaction kinetics, the interaction of the reaction and the hydrogen mass transfer through the diffuser, a detailed mathematical modelling of all relevant transport and reaction steps to identify the crucial parameters which might limit the observable activity and selectivity of the catalytic membrane, the selection of the most suitable catalyst/membrane design to be tested in a small bench scale plant. In the final stage of the project, the optimum catalyst/membrane configuration selected, will be tested in a bench scale plant using real water feeds to collect relevant experimental data on the performance of the new technology under real world operating conditions. In addition, a comparative technical economical
feasibility study of the technology under development with respect to alternative commercial processes for water denitrification will be carried out, including an evaluation of their environmental impact and operational safety.
If successful, the project will provide the basis for the
subsequent development of an economically viable, effective, reliable, and easily scaleable new technology for nitrate removal from ground or surface water by selective catalytic hydrogenation. Moreover, the application of the new technology is not restricted to the specific case under study. It may be applied to other water treatment processes (like catalytic ozonization) as well, which may also benefit from the separation of the gas phase from the liquid phase and from the easy scale up.
Funding SchemeCSC - Cost-sharing contracts