|M.Sc Student||Kollmann Michael|
|Subject||Development of PES-made Hollow Fiber Catalytic Membrane|
Contactor for Nitrite Hydrogenation
of Animal Feeding Operations
|Department||Department of Civil and Environmental Engineering||Supervisor||Dr. Youri Gendel|
|Full Thesis text|
The quality of groundwater has been declining worldwide in recent decades, mostly due to nitrate and nitrite contamination, caused by an intense agricultural activity. Catalytic hydrogenation is the most promising technology for NO3- and NO2- reduction into the nitrogen gas. Nitrate/nitrite hydrogenation can be an efficient, robust and promising method, but its main drawbacks are ammonia production and mass transfer limitations. Ammonia production can be avoided by optimization of operational conditions, catalyst design and more. Mass transfer limitations can be minimized using advanced reactor configurations, such as catalytic membrane contactor (CMC). The CMC can also increase activity and selectivity of the process, reduce gas consumption (and H2-associated risks) and facilitate process control and make the scale-up simple. Hollow fiber (HF) membrane is a highly efficient geometry for membrane reactors, especially for CMCs. Polymeric HF are preferable because they are commercially available in many forms and with different properties, have a low cost and can be easily modified (e.g. loaded with catalysts or/and other active components).
In this study, polymeric microfiltration HF made of polypropylene (PP) and polyethersulfone (PES) were used to prepare a new CMC system for nitrate and nitrite hydrogenation processes. The PP hydrophobic HF’s were functionalized using chemical etching and/or plasma treatment techniques and loaded with a palladium-copper (Pd-Cu) catalyst. Unfortunately, very low hydrogenation rates were obtained for the PP-made CMCs. To improve their performance, the PP-HF were coated with a cross-linked polymeric skin with a dispersed nano-size Pd particles. Unfortunately, the hydrogenation results were still unsatisfactory. Lastly, Pd-Cu nanoparticles were made separately to be deposited on the PP HF’s wall, but the desired nano-size particles could not be obtained.
Thus, hydrophilic polyethersulfone (PES) HF were used instead of the PP-HF. The properties of pristine PES-HF’s were characterized using FTIR, NMR, SEM, streaming potential and other techniques. Two types of PES-made CMCs were prepared and tested: (i) CMCs made by direct coating of PES-made HFs with Pd catalysts, and (ii) CMCs loaded with polyelectrolytes (PE) bilayer prior to Pd catalyst application. The PE were loaded using an infiltration technique, followed by catalyst impregnation. Overall, four types of PES-made CMCs were formulated and tested for nitrite hydrogenation- with polyelectrolytes or without, impregnated by immersion or by infiltration techniques. The CMCs were characterized and tested for nitrite hydrogenation at various pressures of CO2:H2 mixture; H2 gas alone and at various pH values of nitrite solutions. The performance of novel CMCs was evaluated in terms of activity and N2 selectivity and compared with CMCs previously reported in scientific literature. The best performance was achieved in the system with polyelectrolytes with Pd impregnation applied via the infiltration technique. This CMCs showed the pseudo 1st order activity coefficient of 4.1 (1/g Pd, min) and 98% N2 selectivity in nitrite hydrogenation performed at CO2/H2 gauge pressure of 0.9 bar and pH 5-6. A simplistic evaluation of the CMC developed in this study shows that PES-made PE-loaded CMC outperforms the best NO2- hydrogenation polymeric HF contactors reported until the year 2020.