Materiais zeolíticos de estrutura MWW: síntese e caracterização

Abstract

In this paper a synthesis parameters study was conducted in order to optimize the obteinment of MCM-22 (MWW structure) and increase its accessibility, getting higher external surface and generating mesopores. Syntheses with Si / Al = 15 and Si / Al = 50 ratios were performed under static conditions at different temperatures and with seeds induction, which resulted in MCM-22 pure and crystalline (Si / Al ratio = 15) after 3 days and Si / Al = 50 after 11 days. The reduction of hexamethyleneimine content (HMI) was studied in the stirring synthesis and a HMI reduction of 47% was possible through the mother liquor reuse, in addition, a specific area of 481 m² / g has been obtained in the fourth synthesis day. Regarding the increase of accessibility of the MCM-22 zeolite skeins of MCM-22 plates with about 2 μm were obtained, through the use of dissolved silica, addition of seeds, increased temperature and synthesis time of 2 days. A significant value of specific area was found for this material, around 500 m² / g. Also with respect to the increase of MCM-22 accessibility, treatment with oxalic acid concentration of 0.5 mol / L and silanization of proto-zeolitic units resulted in the mesopores formation . Furthermore, silanization still favored reduction of 70 % in crystal size and a specific area of 566 m² / g.