An in-situ ATR-FTIR Study of the Adsorption Properties of MFI Type Zeolites for Upgrading of Biofuels

Sammanfattning: With the depleting reservoirs of fossil fuels, increasing environmental concerns for flue-gas emissions from fossil-fuel combustion and growing world population, the need for the development of new sustainable fuels is higher than ever. However, to be able to compete with today’s mature technologies for production of fuels from fossil sources, new efficient processing alternatives for upgrading of biofuels must be developed. Bio-fuels produced by e.g. fermentative processes are promising alternatives to traditional chemicals and fuels produced from fossil sources. Recovery of biofuels by selective membranes and adsorbents has been identified as promising energy efficient recovery routes. In this work, the adsorption of water and butanol vapor in silicalite-1 and ternary adsorption of methane, water and carbon dioxide in zeolite Na-ZSM-5 were studied using in-situ ATR-FTIR spectroscopy in order to understand the adsorption properties of these zeolites. Single component adsorption isotherms of butanol and water vapor were determined at different temperatures using ATR-FTIR spectroscopy. The Langmuir model was successfully fitted to experimental data, and the fitted parameters obtained in this work were in very good agreement with values reported in the literature. The butanol/water adsorption selectivity determined was as high as 107 for a model ABE vapor mixture which shows that the adsorption of butanol silicalite-1 was very favorable compared to that of water. Biogas (methane) is another promising biofuel that is commonly produced by anaerobic degradation of biomass. However, before it may be used, contaminants have to be removed from the gas; two of the most abundant contaminants in biogas are carbon dioxide and water vapor. Adsorption of a ternary mixture of methane, carbon dioxide and water vapor in zeolite Na-ZSM-5 has been studied at various compositions and temperatures using ATR–FTIR spectroscopy. The amount adsorbed determined from experimental data were compared to predictions by the Ideal Adsorbed Solution Theory (IAST). For a model biogas mixture with the composition of 66, 0.4 and 33.6 mol % of CH4, H2O and CO2, respectively, the H2O/CH4, H2O/CO2 and CO2/CH4 selectivities were determined to be 2600, 130 and 20 respectively, showing that the zeolite showed the highest affinity for water followed by carbon dioxide. This result confirms that Na-ZSM-5 could be a promising membrane material for upgrading of biogas.

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