Citas bibligráficas
Zavala, C., (2016). Síntesis y aplicación de catalizadores basados en óxidos de Mn, Cu, Pr, Ce para la eliminación de N-Hexano [Tesis, Universidad Nacional de Ingeniería]. http://hdl.handle.net/20.500.14076/3935
Zavala, C., Síntesis y aplicación de catalizadores basados en óxidos de Mn, Cu, Pr, Ce para la eliminación de N-Hexano [Tesis]. : Universidad Nacional de Ingeniería; 2016. http://hdl.handle.net/20.500.14076/3935
@mastersthesis{renati/706884,
title = "Síntesis y aplicación de catalizadores basados en óxidos de Mn, Cu, Pr, Ce para la eliminación de N-Hexano",
author = "Zavala Inga, César Humberto",
publisher = "Universidad Nacional de Ingeniería",
year = "2016"
}
The total removal of highly toxic volatile organic compounds (VOC’s) without secondary pollutants requires the most promising technology in particular when their elimination has to be ensured at moderate temperatures and consequently, saving in energy costs. The catalytic combustion is a more efficient technology than thermal incineration due to application of lower temperatures usually bellows 400 ºC, avoiding the formation of NOx. This research is concerned with the development of efficient catalytic systems with thermal stability, selective to CO2 and of low cost for total combustion of n-hexane, in concentrations usually found in the gas emissions from industrial processes (initial concentration of 2000 ppm). The n-hexane has been selected as a model molecule due to its extensive use as high-diffusion solvent in the industry of paints, lacquers and petrochemical. In order to meet the final purpose requirements, some bulk catalysts have been prepared based on Ce-Mn, Cu-Mn and Ce-Pr to be used for combustion of n-hexane to study preliminary experimental conditions of active phase formation ensuring a high surface area, thermal stability and presence of selective sites for total combustion products. Once the synthesis conditions were defined, the catalysts based on Ce-Mn were prepared by co-precipitation, which consists in the dropwise addition of precipitating agent (sodium carbonate, 0.250 M) to the working mixed system, previously prepared from an equal volume of metal nitrate solutions in defined concentrations until a pH corresponding to complete precipitation. After complete precipitation, the solids were aged for different times: 4, 18 and 24 h, under an inert atmosphere of nitrogen at room temperature and pH corresponding to complete precipitation, then were filtered, washed several times with deionized water until stabilization of pH and dried at 120 ◦C for 24 h. Finally, the precipitate was calcined in 2 stages: first at 250 ºC for 2 h, and then at 500 ºC for 3 h, with a heating rate of 2 ºC per minute in all cases. Catalysts based on Cu-Mn mixed oxides (with molar ratio Cu/Mn in the range of 0,33 to 3) have been prepared by the self- combustion, using citric acid and ethylenglycol as combustion agents; in each case an organic complex is formed and the metal oxides are obtained after calcination treatments. Catalysts based on Ce-Pr mixed oxides were prepared by co-precipitation (Ce/Pr ranged from 0,1 to 0,9) using ammonium as precipitating agent. Additionally, in all cases, simple oxides have been synthesized using the same procedure of their mixed counterparts for comparison reasons. Catalysts were characterized by sorption of N2, X-ray diffraction (XRD), thermogravimetric analysis (TGA), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The analysis of adsorption isotherms of catalysts showed profiles of type IV, with the prevalence of mesoporosity. In the case of Ce-Mn, the specific surfaces were higher with the aging times. The X-ray diffractogram patterns for pure and mixed oxide catalysts show the majority presence of stable fluorite phase with the exception of Cu-Mn which showed diffraction lines attributed to spinnel hopcalite phase and Mn simple oxide which matched diffraction peaks corresponding to Mn2O3, Mn3O4 and MnO2. The catalysts activity was measured by plotting of ignition curves for the combustion of n- hexane. The catalytic tests were carried out in a fixed bed reactor with a starting concentration of alkane of 2000 ppm and weight hourly space velocity (WHSV) of 80 h-1. Ce-Mn samples exhibited higher activities than the corresponding simple oxides regardless of the aging time. The sample Ce0.67Mn0.33O2 with 24h of aging time showed the highest performance probably due to the presence of major defective sites promoted by the incorporation of MnOx species into CeO2 structure, its highest surface area and best reducibility. Ce-Mn samples are also showed thermal stability in contrast with Mn oxide in which a depletion of surface area was observed. The Cu-Mn samples activities were measured according to their specific rate (moles converted n-hexano per hour for a specific surface SBET m2 per gram of catalyst), showed that mixed oxides with more Mn content were the best; additionally, the sample prepared Cu1-Mn3, using citric acid as combustor agent was more active than the corresponding values to simple oxides, probably due to the better specific surface and the better spinel-hopcalite structure obtained. Similarly to Ce-Mn samples, Ce0.9Pr0.1O2 oxide with the highest specific rate is obtained with a value 32.2mmol.m2 / g, compared to the corresponding to that of the other mixed oxides and simple oxides pure as a result of increased surface area. Finally, in the case of Ce-Mn samples, the catalytic reaction followed kinetics of a pseudo-1st-order reaction and the kinetic model of Langmuir-Hinshelwood fitted quite well the experimental data according to model selection criterion (MSC) proposed by Akaike and whose final expression the disappearance rate of the n-hexano calculated to temperature of 170 ° C according to this model is 1.3x10-8 xCn-hexano/(1+12.5xCn-hexano)2.
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