Sorption properties of high silica zeolites: ZSM-35 and ZSM-5

Tütüncü, Göknur
The use of high silica zeolites is widespread for numerous important processes throughout the chemical and petroleum industries. To use these zeolites in an efficient way, sorption behaviour should be understood. This study investigated how the capacities and rates of sorption on a high silica zeolite ZSM-35 changed with sorbate properties and sorbent properties at different temperatures by gravimetric method using an electrobalance. In this study also another high silica zeolite ZSM-5 was synthesized with a small amine template, n-propyl amine and characterized by XRD, TGA methods and sorption capacities for n-hexane and methanol at 23 °C. The results of this experimental study indicated that limiting sorption capacities decreased as temperature increased for NaZSM-35 and HZSM-35 both for methanol and ethanol with an exceptional case at 0°C for ethanol sorption. From fractional uptake curves, it was seen that ethanol had slower sorption rate than methanol in spite of having nearly the same kinetic size. It can be attributed to configuration of the adsorbate since ethanol has a longer chain. However, equilibrium adsorption capacities of ethanol were greater than that of methanol probably due to more efficient packing effect. At 0°C in addition to having the slower sorption rate, ethanol had the least limiting sorption capacities for Na and H forms of ZSM-35 which were 0.070 and 0.0686 cm3/g, respectively compared to the other temperatures. Ethanol sorption rates were found much more dependent to temperature than methanol, especially at 0°C, 23 °C and 40°C. Moreover, it was confirmed that the ion-exchange influenced the sorption capacity and since having stronger sorbate- sorbent interaction, NaZSM-35 had greater limiting sorption capacity than HZSM-35 at all temperatures used in this study. Additionally, the highest methanol sorption capacity was found as 0.1312 cm3/g at 0°C and from ethanol the highest sorption capacity was found as 0.1356 cm3/g at 23°C. These values were greater than the volume of the channel with 10-membered pore opening, 0. 1 cm3/g and then it can be concluded that both methanol and ethanol molecules could diffuse into 8-membered ring channels at least partially. Synthesis of ZSM-5 with n-propyl amine templated studies showed that the ZSM-5 synthesis at 170°C, 71 hours was possible but with an amorphous structure. The template and water molecules constituted nearly 7.8% by weight and the sample necessitated for calcination at about 600°C. n-hexane limiting sorption capacity was 0. 1 1 1 cm3/g and methanol capacity was found as 0.094 cm3/g with a sigmoid uptake curve.


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Citation Formats
G. Tütüncü, “Sorption properties of high silica zeolites: ZSM-35 and ZSM-5,” M.S. - Master of Science, Middle East Technical University, 2003.