Estudo da ReaÃÃo de Desidro-aromatizaÃÃo nÃo oxidativa do Metano em Reator de Leito Fixo Diferencial com catalisador Ru- Mo/HZSM-5

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Chemical routes suitable for the activation of methane to produce valuable products are limited and its achievement consists in a challenge to the chemistry of the natural gas conversion. Although remarkable progresses have been achieved on the methane dehydroaromatization (MDA) reaction, low conversion caused by severe thermodynamic limitations, coke formation and catalysis deactivation remain the main drawbacks to this reational process implementation. Molybdenum catalysts supported in the HZSM-5 zeolite rank among the most promising catalysts and the addition of a second metal promoter was demonstrated to enhance catalysis activity and selectivity to benzene. In the present work, 0,5%Ru-3,0%Mo/HZSM-5 catalyst were synthesized by the method of co-impregnation with excess of solvent and characterisized using several techniques such as X-ray Diffraction (XRD), Scanning Electronic Microscopy â Energy Dispersive X-ray (SEM-EDS), Infrared Spectroscopy with Fourier Transformed (FTIR), Thermogravimetric Analysis (TGA) and Surface Area and Porosity Analysis (BET). Catalytic tests were performed at 973K, 1atm and at contact times between 2639 and 5624 g.h/m3 (STP) which corresponds to a space velocity between 178 and 379 mL(STP)/g.h. A 50:50 v/v% methane-argon mixture was fed after catalysis pretreatment with hydrogen for 2 hours. The characterization methods showed that, in spite of being submitted to several treatments used during catalysts synthesis, support maintains its crystalline framework even after 45 hours of reaction. No additional peaks were detected in the DRX and FT-IR spectras after Ru/Mo impregnation probably due to completely dispersion of the metals over the surface of the HZSM-5 or metals migration into the zeolite channels. The synthesized catalyst achieved conversion and selectivity to benzene as high as 10 and 70%, respectively, although this performance was influenced by contact time and methane inlet molar fraction. The evaluation of the hidrogen/benzene molar ratio showed that it is contact time dependent achieving different values form that one previewed form reaction estequiometry. Carbon deposited onto catalytic surface was analyzed in order to determinate carbon and hydrogen content which was revealed to be contact-time dependent. A model based on Langmuir- Hinshelwood mechanisms using the approach suggested by Hougen and Watson was validated using adsorption constants values from literature. The kinetic constant calculated from experimental data was 3.8Â0.9 x 10-3 mol/g.h.atm

ASSUNTO(S)

engenharia quimica methane dehydro-aromatization cinÃtica catalysis desidro-aromatizaÃÃo do metano kinetics differential reactor ru-mo/hzsm-5 reator diferencial ru-mo/hzsm-5 catÃlise

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