Acid stability evaluation of CHA-type zeolites synthesized by interzeolite conversion of FAU-type zeolite and their membrane application for dehydration of acetic acid aqueous solution

摘要

High-silica CHA-type zeolites with various Si/Al ratios were prepared by interzeolite conversion of FAU-type zeolite using the benzyltrimethylammonium (BTMA~+) cation as a structure-directing agent (SDA), and the acid-resistance (structure stability and composition stability) of these materials was compared with SSZ-13 zeolite synthesized using the rV,N,N-trimethyl-1-adamantammonium (TMAda~+) cation as a conventional SDA. Si/Al ratios of zeolite ranging from 5 to 10 produced no difference in the 90 vol% acetic acid stability between the high-silica CHA synthesized with BTMA~+ and the SSZ-13 synthesized with TMAda~+. In the case of Si/Al ratio >10, considerable differences were observed in the composition stability. To elaborate, an increase in the Si/Al ratio was observed for the SSZ-13 after acetic acid treatment, whereas no differences in the Si/Al ratios prior and subsequent to the treatment were observed for the CHA synthesized with BTMA~+. These findings strongly indicate a high acetic acid stability of the CHA-type zeolite synthesized by the interzeolite conversion method. Their high acid stability towards several common mineral acids, such as HC1, H2SO4, and HNO3, was also confirmed. The CHA-type zeolite membrane was fabricated on a porous α-alumina tube, and the membrane performance was measured in a feed mixture of water/ acetic acid (50/50 wt%) at 75 °C The membrane demonstrated a high separation factor, α(H2O/CH3COOH), of ca. 2500 with a permeate flux of ca. 8 kg m~2 h~(-1).