Prospecção de adsorventes para captura de vapores de metais alcalinos

• Ano de defesa: 2017
• Autor(a) principal: Moreno, Jimmy Degaule Lima
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Engenharia química; Adsorção; Minerais; Metais alcalinos; Vapores alcalinos
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/27263

Among other processes, biomass gasification is an attractive alternative to generate energy. Syngas (CO+H2) produced from the gasification of biomass can be used in the chemical and petrochemical industry to produce liquids hydrocarbons, including fuels, by the Fischer-Tropsch synthesis. Energy generation by direct use of such gas in turbines is another application. Nevertheless, when biomass is gasified, gas thus produced is loaded with alkali metal vapors in considerable amounts. The concentration of alkali (especially sodium and potassium) ordinarily reaches more than 10 ppm during the gasification process, leading to several problems, such as: decreased catalytic activity, corrosion of turbines blades and undesirable deposition on downstream equipment. Adsorption on aluminosilicates is thought to be an appropriate option to reduce the concentration of these alkalis ions in syngas, because theuy may potentially adsorb these metals at the high temperature range of biomass gasifiers outlet streams. Hence, this study has focused on screening and characterizing low cost mineral sorbents. Six samples excelled in preliminary tests when were exposed to sodium vapors at high temperature and under moist conditions. Then, various analytical techniques (textural analysis, TGA, XRD and XRF) were applied before and after the exposure to humid alkali vapors, in order to shed some light on the govening retention mechanisms. In the most of cases, chemisorption is primary binding mechanism, whose reactions form silicates and aluminosilicate salts. Sorbents with higher Al content showed potential for application of capturing alkali metal vapors at high temperature fixing sodium as nepheline. Sorbents with higher silica content showed irreversible fixation of Na, which could not be recovered even upon acid leaching. Likewise, a method for adsorption isotherm measurements was developed using a thermogravimetric analyser coupled to a mass spectrometer. Isotherm parameters of isotherms could be estimated for 775 degrees Celsius and 1 bar allowing for the implementation of simulation models of column operation.