Catalytic honeycombs for producing methane from CO2 and H2
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Tutor / director / evaluatorLlorca Piqué, Jordi
Document typeMaster thesis
Rights accessRestricted access - author's decision
In the experimental part of the work several catalysts are tested, in order to determine the best candidate among them to produce methane from the reaction between carbon dioxide and hydrogen. These catalysts are 10%Ni/Al2O3, (1%Ru-7%Mn-12%Cu)/Al2O3 and 10%Ni/CeO2. Alumina and ceria supports are prepared using different methods. Generally, CO2 conversion, CH4 selectivity and the yield have shown to be higher at higher temperature and pressure. Considering the supports, ceria has shown better results compared to alumina. Among the alumina supports, the one produced through direct calcination of Al(OH)3 presented better results. Regarding the catalytic properties of ceria supports they follow the trend: NICEO2-np > NICEO2-nr > NICEO2-nc ≈ NICEO2-H ≈ NICEO2-A, where the first 3 supports are prepared using an ultrasonic atomizer and a hydrothermal rector under conditions that give polycrystals, rods and cubes respectively. NICEO2-H and NICEO2-A are prepared by direct precipitation of Ce(NO3)3.6H2O with NaOH and ammonia solution, respectively. Polycrystalline ceria prepared using a hydrothermal reactor was found to be the best catalyst support among those tested, showing maximum methane production at 250°C under a pressure of 3 bar. In addition, ceria supported catalysts have demonstrated to be more selective to methane than alumina supported catalysts. Regarding the active metal, nickel offers better results. A monolithic honeycomb support is prepared by impregnating it with NICEO2-np catalyst and tested. The final yield is 73.4%, obtained using reactant flow rates of 25 mL/min of CO2 and 100 mL/min of H2 (GHSV = 1,500 h -1 ), at 350°C and under a pressure of 3 bar. After the catalytic tests, the catalysts are characterized using Scanning Electron Microscope and X-Ray Photoelectron Spectroscopy to verify composition, shape and particle size. There is evidence that the active metal impregnation didn’t influence the particles shape. The analysis of the used catalysts has demonstrated that the particles have suffered sintering effect and they are covered with carbon produced in the reaction. The results of XPS analysis show that if Ni/Ce ratio is high the methane production is lower. The second part of the work starts with the design of the ideal industrial system. After that it is scaled to two different applications of cement industry emissions, in Spain (Pamplona) and Germany (Mainz). A life cycle assessment through the SimaPro 8 software is performed. Three scenarios are compared: the system implemented in the Spanish and German factories and the natural gas extraction summed to CO2 emission impacts, which represent the non application of the system. The results show that to not apply the CO2 methanation system leads to a higher negative environmental impact with respect to its application. The methanation application phase which has the higher environmental impact is the construction phase of the wind energy plant. The manufacturing phase of the methanation system itself doesn’t cause high impacts. The Endpoint method indicates that the German system has a slightly higher environmental impact than the Spanish system. A sustainability analysis of the ideal industrial installation is carried out using MIVES software. The options are compared on economic, environmental and social plans. According to the assigned weight of the indicators, the application of a CO2 methanation system is a sustainable option. In particular, the German system application resulted in being the best option out of the three. In the chosen cement factory it can be an effective solution and the best compromise among the economic cost, the environmental benefit and the social effects.
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