Choosing a Molecular Sieve:
1. The preferential adsorption of one molecule over another depends upon pore diameter and mesh size.
2. The dynamic capacity of the silica gel for adsorbing a particular compound is governed by the internal surface area; the greater the surface area, the greater the dynamic capacity.
3. Rate of adsorption and sharpness of resolution are dependent chiefly on particle size and column packing; a fine particle size gives optimum sharpness of resolution.
4. Liquids are most readily adsorbed from solvents in which they are least soluble; a good solvent makes a good desorbing agent.
5. Highly polar liquids are readily adsorbed. Compounds having hydroxyl groups, or containing oxygen are strongly adsorbed.
6. For similar compounds, the higher the molecular weight the higher the selectivity.
7. For hydrocarbons of similar molecular weight, adsorptivity increases with the number of double bonds.
Molecular sieves are crystalline metal aluminosilicates having a three-dimensional interconnecting network of silica and alumina tetrahedra. Natural water of hydration is removed from this network by heating to produce uniform cavities which selectively adsorb molecules of a specific size. The 3A form is made by substituting potassium cations for the inherent sodium ions of the 4A structure, reducing the effective pore size to ~3Å, excluding molecules of diameter >3Å (for example: ethane). The 8 to 12-mesh type is common in liquid-phase applications. Molecular sieves are considered a universal drying agent in polar and nonpolar media.
Molecular sieves, 3Å is a UOP-type zeolite 3Å.It is widely employed as a sorbent.
Regeneration or Activation:
A saturated molecular sieve can be restored to its original capacity by regeneration, the principle of which involves changing the conditions surrounding the adsorbent to correspond to a very low equilibrium capacity. In general, the greater the difference between the equilibrium capacities of adsorption and regeneration, the more rapid and complete the regeneration.
The sieve may be regenerated in one of four ways:
1. Thermal reactivation –The maximum regeneration temperature for Silica is 300°C.
2. Pressure reactivation
3. Passing an appropriate fluid through the gel bed at normal temperature and pressure.
4. Displacement of adsorbates by passing a high concentration of molecules in a fluid through the bed.
The kinetics of the adsorption of water-vapor by employing molecular sieve 3Å has been studied in various temperature ranges (25-80°C and water dew points from -69 to 17°C).
3.Jie Guan, Leilei Luo, Ruijing Su, Yaoguang Guo, Chenglong Zhang, Ruixue Wang, Xiaolong Song, Xuning Zhuang, Xihua Zhang, Xiaojiao Zhang, Hongcheng Wu, Weixing Gu. (2022) Microwave-assisted chlorination extraction of valuable metals from spent power ternary lithium-ion batteries. INTERNATIONAL JOURNAL OF ENVIRONMENTAL ANALYTICAL CHEMISTRY, [PMID:]
4.Xiaowei Xu, Xinyue Hao, Jing Hu, Weisheng Gao, Nanying Ning, Bing Yu, Liqun Zhang, Ming Tian. (2022) Recyclable silicone elastic light-triggered actuator with a reconfigurable Janus structure and self-healable performance. Polymer Chemistry, 13 (6):(829-837). [PMID:]
5.Yue Teng, Guangqing Song, Rong Chen, Xiao Zhang, Yongjun Sun, Haixia Wu, Biming Liu, Yanhua Xu. (2022) Carboxymethyl β-cyclodextrin immobilized on hydrated lanthanum oxide for simultaneous adsorption of nitrate and phosphate. Journal of the Taiwan Institute of Chemical Engineers, 132 (104153). [PMID:]
6.Jing Bai, Canwei Cheng, Yong Liu, Chenguang Wang, Yuhe Liao, Lungang Chen, Longlong Ma. (2021) Selective hydrogenation of levulinic acid to γ-valerolactone on Ni-based catalysts. Molecular Catalysis, 516 (112000). [PMID:]
7.Bencang Cui,Jing Li,Huining Wang,Yuanhua Lin,Yang Shen,Ming Li,Xuliang Deng,Cewen Nan. (2017-05-21) Mechanical properties of polymer-infiltrated-ceramic (sodium aluminum silicate) composites for dental restoration.. Journal of dentistry, 62 (91-97). [PMID:28526443]
References
1.Zhengxiang Zhou, Gebin Shen, Xinrong Huang, Chuanhui Yang, Yingfeng Yu. (2023) Preparation and Properties of Low Internal Stress Polyimide-b-Polysiloxane with a Hyperbranched Structure. ACS Applied Polymer Materials, 5 (11):(9337–9345). [PMID:19383767]
3.Jie Guan, Leilei Luo, Ruijing Su, Yaoguang Guo, Chenglong Zhang, Ruixue Wang, Xiaolong Song, Xuning Zhuang, Xihua Zhang, Xiaojiao Zhang, Hongcheng Wu, Weixing Gu. (2022) Microwave-assisted chlorination extraction of valuable metals from spent power ternary lithium-ion batteries. INTERNATIONAL JOURNAL OF ENVIRONMENTAL ANALYTICAL CHEMISTRY, [PMID:]
4.Xiaowei Xu, Xinyue Hao, Jing Hu, Weisheng Gao, Nanying Ning, Bing Yu, Liqun Zhang, Ming Tian. (2022) Recyclable silicone elastic light-triggered actuator with a reconfigurable Janus structure and self-healable performance. Polymer Chemistry, 13 (6):(829-837). [PMID:]
5.Yue Teng, Guangqing Song, Rong Chen, Xiao Zhang, Yongjun Sun, Haixia Wu, Biming Liu, Yanhua Xu. (2022) Carboxymethyl β-cyclodextrin immobilized on hydrated lanthanum oxide for simultaneous adsorption of nitrate and phosphate. Journal of the Taiwan Institute of Chemical Engineers, 132 (104153). [PMID:]
6.Jing Bai, Canwei Cheng, Yong Liu, Chenguang Wang, Yuhe Liao, Lungang Chen, Longlong Ma. (2021) Selective hydrogenation of levulinic acid to γ-valerolactone on Ni-based catalysts. Molecular Catalysis, 516 (112000). [PMID:]
7.Bencang Cui,Jing Li,Huining Wang,Yuanhua Lin,Yang Shen,Ming Li,Xuliang Deng,Cewen Nan. (2017-05-21) Mechanical properties of polymer-infiltrated-ceramic (sodium aluminum silicate) composites for dental restoration.. Journal of dentistry, 62 (91-97). [PMID:28526443]
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