Chemical vapor adsorption method

Yamakita S, Katada N, Niwa M (2005) Shape-selective adsorption of substituted benzalde-hyde isomers by a molecular sieving silica overlayer prepared by the chemical vapor deposition method using organic template on tin oxide. Bull Chem Soc Jpn 78 1425... 

Kyotani and coworkers [81] systematically demonstrated the preparation of micro-porous carbons using zeolite templates, whereas early studies [82-84] described the pyrolysis of carbon precursors to make carbon materials in the presence of zeolites. Subsequently, Mallouk and coworkers [85] employed zeolites Y, L, and P as templates to prepare microporous carbons with a specific surface area as high as 1580 m /g. It was reported that the zeolite template has a direct relationship with the structural and topological properties of the resultant carbon. Rodri-guez-Mirasol et al. [71] described the preparation of microporous carbons with a wide distribution of pore sizes, well-developed mesoporosity, and high adsorption capacity. Zeolite Y was used as template, and a chemical vapor infiltration method was employed to deposit carbon in the template pores. It was found that the apparent surface area of the resultant carbons increased with increasing deposition temperatures. Meyers et al. [72] synthesized porous carbon materials with a surface area of about 1000 m /g using zeolites Y, p, and ZSM-5 as templates and acrylonitrile, FA, pyrene, and vinyl acetate as carbon precursors. The template-encapsulated carbon precursors were pyrolyzed at 600 C, and the resultant materials were observed to be composed of disordered carbon arrays. 

Recently, an anisotropic surface has been fabricated by micropatterned organic monolayers, which were prepared by the chemical vapor adsorption (CVA) method [17]. The CVA is one of the excellent and suitable processes for microfabrication based on photolithography of nanofihns because it produces a remarkably uniform surface without defects or aggregates [18,19]. We reported previously that the line-patterned fluoroalkylsilane monolayers with l-20- jm width showed an anisotropic wetting by a macroscopic water droplet with a 0.5-5-mm diameter [20]. Using this method, an anisotropic friction surface without microtrough or step structure can be... 

The special case involving the removal of a low (2—3 mol %) mole fraction impurity at high (>99 mol%) recovery is called purification separation. Purification separation typically results in one product of very high purity. It may or may not be desirable to recover the impurity in the other product. The separation methods appHcable to purification separation include equiUbrium adsorption, molecular sieve adsorption, chemical absorption, and catalytic conversion. Physical absorption is not included in this Hst as this method typically caimot achieve extremely high purities. Table 8 presents a Hst of the gas—vapor separation methods with their corresponding characteristic properties. The considerations for gas—vapor methods are as follows (26—44). 

Multiwall carbon nanotubes (MWCNTs) have been synthesized by catalytic chemical vapor deposition (CCVD) of ethylene on several mesoporous aluminosilicates impregnated with iron. The aluminosilicates were synthesized by sol-gel method optimizing the Si/Al ratios from 6 to 80. The catalysts are characterized by nitrogen adsorption, X-ray diffraction, 27A1 NMR, thermogravimetric analysis (TGA) and infrared. The MWCNTs are characterized by TGA and transmission and scanning electron microscope. 

Even though most chemical purification methods are not carried out at low temperatures, they are useful in several cryogenic gas separation systems. Ordinarily water vapor is removed by refrigeration and adsorption methods. However, for small-scale purification, the gas can be passed over a desiccant, which removes the water vapor as water of crystallization. In the krypton-xenon purification system, carbon dioxide is removed by passage of the gas through a caustic, such as sodium hydroxide, to form sodium carbonate. 

The surface chemical properties of the carbon materials were characterized as follows measurement of pH of carbon slurries (in 0.1 M NaCl solution) [89] neutralization with bases of different strength and dilute HCl according to Boehm s method [63,66] determination of total oxygen/nitrogen content by elemental analysis (with an accuracy of 0.2%) [170] mass loss of carbon samples after heat treatment in a vacuum. Additionally, the number of primary adsorption centers (a,)) was determined from water vapor adsorption isotherms according to the Dubinin-Serpinsky method [171], as was the heat of immersion in water for selected samples [111,172]. The results of these operations are pre.sented in Table 3. For all samples transmission Fourier Transform Infrared (FTIR) spectra and X-ray photoelectron spectra (XPS) were recorded. 

VOCs can also be removed by adsorption processes (vapor recovery). In this case, ACCs are used in preference over GAC because they are more easily contained, have faster adsorption kinetics and higher adsorption capacities, and can be regenerated, in situ, by electro-thermal methods (resistive heating). ACCs have been chemically modified by treatment with ammonia (to introduce basic nitrogen complexes), chlorine (to introduce polar —Cl groups) and nitric acid (to introduce acidic oxygen complexes). In this way, the water vapor adsorption capacity can be tailored to obtain ACCs with enhanced adsorption of individual VOCs in the presence of humidity. 

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