Applications of Y and ZSM-5 zeolites in VOCs adsorption
Date Issued
2015
Date
2015
Author(s)
Huang, Pin-Hao
Abstract
Volatile organic compounds (VOCs) are organic chemicals that have high vapor pressure at ambient temperature, and many of them are harmful to the environment and are toxic or even carcinogenic to the human being. Many technologies are available for VOCs control, such as adsorption, condensation, membrane separation, oxidation and biological treatment, among which adsorption is the most applicable technology because of the flexibility of the system, low energy, and inexpensive operation costs. Activated carbon has long been recognized as the most versatile adsorbent due to its low cost and excellent adsorption capacity. However, several drawbacks, such as hygroscopicity, pore clogging,and low thermal stability are associated with its use in adsorption processes. Hence, extensive efforts have been focused on finding alternative adsorbents. Zeolites are microporous molecular sieves with crystalline structures, high specific surfaces and thermal stabilities, have been proposed as potential adsorbents for VOCs adsorption/separation. In this study, zeolite Y and ZSM-5 were exchanged with different cations, including sodium, silver, copper and hydrogen or been treated with acid and base solution to create mesopores in zeolite structure. Futhermore, we synthesized zeolites with different amounts of Ti/Si ratio and used as the adsorbents of VOCs, including toluene, methylcyclopentane and crotonaldehyde. The materials were characterized by X-ray diffraction, nitrogen sorption, scanning electron microscope and elemental analysis. The uptakes of toluene, methylcyclopentane and steam over these zeolites were investigated by temperature programmed desorption. We found that under same experiment conditions, the amounts of cations was the key point to determine the amount of toluene adsorption; then was cation form; only when the adsorbent had similar cation amount and same cation form, the effect of specific surface area would show up. In the experiment of methylcyclopentane adsorption, we found that when the size of adsorbate molecules were similar to the pore size of adsorbent, adsorption capacity would increase and become hard to drsorb. In the experiment of crotonaldehyde adsorption, Y-type and ZSM-5 with silver, copper and hydrogen form would promote oxidation/cracking of crotonaldehyde, TS-1 only shows the adsorption/desorption peak without other reactions happened, the adsorption capacity was around 6 ~ 7 wt%. If we want to adsorption VOCs in dry condition, Na-Y3B is the best choice, because it has the largest adsorption for both toluene (21.0 wt%) and methylcyclopentane (13.8 wt%). H-Z120 is suitable for adsorption VOCs in normal condition, due to its hydrophobicity, has the highest toluene/steam selectivity (30.3) and methylcyclopentane/steam selectivity (44.8).
Subjects
Y-type zeolite
volatile organic compounds
toluene adsorption
Type
thesis