Ethylene removal by Ag-based ZSM-5 adsorbents for the preservation of climacteric fruits

Ferreira, R.; Lopes, H.; Lourenço, J. P.; Silva, J. M.; João, I. M.; Ribeiro, M. F.; Fernandes, A.

http://hdl.handle.net/10400.1/20468

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Ethylene removal is crucial for fruits and vegetables preservation because even a very low concentration (<0.1ppm) can induce ripening during storage and transportation. Ag+ exchanged ZSM-5 zeolites were investigated as adsorbents for the efficient removal of ethylene. Two ZSM-5 materials (Si/Al ratios of 15 and 40), with different amounts of Ag (up to 6 % by weight) and two compensating cations, Na+ and H+, were used for this purpose. The adsorbents were characterized by X-ray Diffraction, diffuse reflectance spectroscopy and H2- TPR experiments. Their performance in ethylene adsorption was determined by the means of breakthrough curves experiments, mimicking the atmospheric conditions of industrial fruits cold storage chambers, particularly the high relative humidity levels. Results show that adsorbents are highly efficient in removing ethylene (max. 500 µmol.g-1 in the absence of water). Monovalent Ag+ species have been identified as the main contributors to the excellent performance of the different adsorbents, as they can easily interact with ethylene through strong π interaction. Moreover, statistical analysis (ANOVA) results confirmed that, in the presence of water, Ag-based ZSM-5 materials with a higher Si/Al ratio and Na+ as the charge balancing cation, i.e., those with a higher hydrophobic character, are the best adsorbents for ethylene removal.