SANCHEZ LOPEZ ALEJANDRO

Synthesis and Analysis of ZSM-58 Zeolite Membrane Containing Silica and Aluminum

Himeno Shūji, Komatsu Toshiya

In this experiment two types of ZSM-58 zeolite membranes were synthesized: All-Silica Membrane which appellation is due to the only existence of Silica and Oxygen molecules in its composition, and Aluminum containing Membrane, which includes Silica, Oxygen and Aluminum molecules.  The recommended synthesis amount of both membrane types was of 60g/m2. 
21 All-Silica membrane samples were prepared, with a molar ratio of Si/Al:∞, H2O:52, MTI:0.1, NaOH:0.1, SiO2:1, and its synthesis was performed between 1~5 days, where it was found after 3 synthesis days the recommended synthesis amount could be reached. Also, the samples were detemplated employing only Ozonication due to a general low synthesis amount, making the zeolite layer support thin and not strong enough to endure RTP. DOH zeolite was formed in only one sample, with a high synthesis amount (146g/m2), affecting its permeance properties. The highest obtained permeance efficiency classified as α ratio was of 2.5, which is extremely low compared with the recommended α ratio of 100, so it was concluded that this type of silica is not good for gas separation use. 
Looking for an increasement of its effectiveness, Aluminum was added. 29 Aluminum-containing membrane samples were prepared, where its synthesis was performed with a molar ratio of Si/Al:70, H2O:52, MTI:0.05, NaAlO2:0.014, KOH:0.05, SiO2:1, between 4~5 days. Due to a high variation of the obtained synthesis amount, the most appropriated synthesis time to obtain the recommended synthesis amount could not be found. Additionally, DOH was formed in much more samples than All-Silica ones, even with a lower synthesis amount (44g/m2), showing how instable is and how easy DOH can be formed. Also, because the membrane gained high resistance for high temperatures and higher thickness by the addition of aluminum, RTP was much effective at detemplation than ozonication. The highest α ratio was of 25.7 (which was obtained by RTP and Ozonication), so it showed an increment of performance, however it is still low so more experimentation was needed.
In order to improve the zeolite membrane, the molar ratio of MTI was changed from 0.05 to 0.06, all the other molar ratios were kept the same. 10 samples were created, the synthesis time was configurated from 4.5 to 5 days. The synthesis amount stabilized after 4.75 days at a synthesis amount of 70g/m2, suggesting that amount should be the recommended one on this type of membrane. Once again RTP showed being the best detemplation method for this membrane, where also the α ratio of 87.5 could be obtained as well. Aluminum-containing ZSM-58 zeolite membrane with a MTI molar ratio of 0.06 showed to be the most effective membrane for separation of CH4/CO2 gas mixtures, overtaking the challenge by finding the best synthesis conditions to be able to create samples with constant properties, like finding the most optimal synthesis amount and high permeance effectiveness, so it can be said its improvement was successful, showing the potential this technology has for gas separation.