Adsorption Nitrogen, Water vapor

Other papers in this series dealt with silicates which, unfortunately, were not chemically uniform. The mineral tobermorite (Ca3Si207, 2 H20) was made from Ca2Si04 under various experimental conditions180). Strangely, the yalues of nAp derived from the adsorption of nitrogen were in some instances only one-third or one-quarter those calculated from the adsorption of water vapor. When only the latter data were counted, then Qp appeared to be a roughly linear function of nAp, and Us was 388 + 30 erg/cm2. The Us for the trihydrate Ca3Si207, 3 H20 was said to be 320 70 erg/cm2. 

An atom or molecule that approaches the surface of a solid always experiences a net attractive potential ). As a result there is a finite probability that it is trapped on the surface and the phenomenon that we call adsorption occurs. Under the usual environmental conditions (about one atmosphere and 300 K and in the presence of oxygen, nitrogen, water vapor and assorted hydrocarbons) all solid surfaces are covered with a monolayer of adsorbate and the build-up of multiple adsorbate layers is often detectable. The constant presence of the adsorbate layer influences all the chemical, mechanical and electronic surface properties. Adhesion, lubrication, the onset of chemical corrosion or photoconductivity are just a few of the many macroscopic surface processes that are controlled by the various properties of a monolayer of adsorbates. 

Table 1.7. Specific surface areas of phyllosilicates determined by nitrogen, water vapor, or iV-cetyl pyridinium bromide adsorption...

The water vapor [23] and nitrogen gas [24] adsorption isotherms determined by using automatic adsorption apparatus have been reported. On the other hand, the manual adsorption method for the adsorption of water vapor and nitrogen gas is discussed in Refs. 25 and 4, respectively. The amount adsorbed is determined by using a Shibata moisture and surface area apparatus. Model P-850 [Shibata Scientific Technology, Ltd., Tokyo, Japan) [25]. The amounts of water vapor and nitrogen gas adsorbed are determined by the gravimetric method [25] and volumetric method [4], respectively. 

Postcombustion processes are designed to capture NO, after it has been produced. In a selective catalytic reduction (SCR) system, ammonia is mixed with flue gas in the presence of a catalyst to transform the NO, into molecular nitrogen and water. In a selective noncatalytic reduction (SNCR) system, a reducing agent, such as ammonia or urea, is injected into the furnace above the combustion zone where it reacts with the NO, to form nitrogen gas and water vapor. Existing postcombustion processes are costly and each has drawbacks. SCR relies on expensive catalysts and experiences problems with ammonia adsorption on the fly ash. SNCR systems have not been proven for boilers larger than 300 MW. 

Effect of heating on microcrystalline synthetic goethite. Clays Clay Min. 34 17-24 Koch, F. Cohen, J.B. (1969) The defect structure of Fei.xO. Acta Cryst. B 25 275-287 Koch, G. Mailer, P.J. (1987) Adsorption of nitrogen and water vapor onto goethite surfaces. Thermochim. Acta 114 139-144... 

Naono, H. Sonoda, J. Oka, K. Hakuman, M. (1993) Evaluation of microporous texture of undecomposed and decomposed p-FeOOH fine particles by means of adsorption isotherms of nitrogen gas and water vapor. Proc. IVth Int. Conf on Fundamentals of Adsorption, Kyoto 1992, 467-474 Naumann, F. (1855) Elemente der Mineralogie. 4. Auflage, Leipzig... 

When water vapor adsorbs only on a portion of a surface, the degree of surface hydrophilicity of a solid can be rated from the ratio of the effective water area to the nitrogen area or by immersional heat values in water. Adsorption measurements were used by Young to follow the conversion of... 

At the beginning of the hydration of calcined H-SAPO-34 (i.e., after the start of the injection of nitrogen loaded with water vapor into the spinning MAS NMR rotor), only a change in the H MAS NMR spectra was observed (Figs 23b and c, left). After a water adsorption of 0.8 mmol/g, a significant decrease of the signal of... 

This paper presents isotherms for the adsorption of methane, nitrogen, carbon dioxide, and water vapor on a Pocahontas No. 3 (lvb) and a Pittsburgh (hvab) coal. Rate data for the adsorption of methane on these coals will be described in a subsequent paper. 

The character of the chemisorption of nitrogen can be also judged from the results of studies of ammonia synthesis kinetics at the reversible poisoning of the catalyst with water vapor (102,103). If a gas mixture contains water vapor, an adsorption-chemical equilibrium of adsorbed oxygen, hydrogen gas, and water vapor sets in on the iron catalyst. 

I believe that this is a fine confirmation of the correctness of the Vm values obtained by water vapor adsorption. On the other hand, nitrogen adsorption gave surface areas that ranged from 20 to 100% of the surface areas obtained by water vapor adsorption. I said that nitrogen did not measure the total surface, and I give one evidence for it now and one later. Dr. Copeland determined the specific surface of a hydrated portland cement by small-angle x-ray scattering. The value he obtained checked the water adsorption value within 2 or 3%. On the other... 

Because of the importance of the surface chemistry of bone mineral in physiological systems, we have undertaken a series of gas adsorption studies on hydroxyapatite in the form of anorganic bone. In a recent publication from this laboratory (4) results of calorimetric studies of the adsorption of water and methanol vapors on bone mineral and on synthetic hydroxyapatite were reported. The adsorption potential for nitrogen on dehydrated hydroxyapatite, whether from bone or from synthetic sources, was rather profoundly altered by the addition to the surface of chemisorbed methanol or water prior to the adsorption of nitrogen at —195° C. This effect was reflected in the specific surface areas, in the BET C values, and in the resultant values of Ex — EL (net heats of adsorption) as shown in Table I of the above paper. 

The addition of nitrogen or water vapor changes the pattern of monomer adsorption, release of sorbed monomer, and the rate of monomer vapor consumption by polymerization considerably, as seen in the similar plots shown in Figures 34.10-34.12. With the addition of water vapor, the hydrophilicity of the porous substrate plays an important role that can be seen in the difference of pressure change observed when reversing the order of exposure to monomer and to water vapor. Namely, the amount of water vapor sorbed by hydrophilic Millipore filter is greater when water vapor is introduced first, whereas hydrophobic polysulfone sorbs more water when relatively more hydrophilic (than polysulfone) 4-vinylpyridine monomer is introduced first. Results shown in Figures 34.11 and 34.12 indicate that excessive water vapor prevents vapor phase polymerization... 

Mesoporous melamine-formaldehyde and phenolic-formaldehyde resins were synthesized in the process of polymerization in the presence of fumed silica as an inorganic template. The surface and structural characteristics of the obtained sorbents were investigated using XPS technique and sorption from gas phase. The parameters characterizing porous structure of the synthesized resins in a dry state were determined from nitrogen adsorption/desorption isotherms. The sorption processes of benzene and water vapor accompanied by simultaneous swelling of both polymers were also studied. 

Figure 3. Comparison of nitrogen, benzene and water vapor adsorption isotherms on PHD and MEA resins.

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. 

Naono, H., Hakuman, M., Tanaka, T., Tamura, N., and Nakai, K. 2000. Porous texture and surface character of dehydroxylated and rehydroxylated MCM-41 mesoporous sihcas— Analysis of adsorption isotherms of nitrogen gas and water vapor. Journal of Colloid and Interface Science 225, 411 25. 

Figure 5 The six types of International Union for Physical and Applied Chemistry isotherms. The type I isotherm is typical of microporous solids and chemisorption isotherms. Type II is shown by finely divided nonporous solids. Types III and V are typical of vapor adsorption (i.e., water vapor on hydrophobic materials). Types V and VI feature a hysteresis loop generated by the capillary condensation of the adsorbate in the mesopores of the solid. The rare type VI, the step-like isotherm, is shown by nitrogen adsorbed on special carbon.

Figure 5. Part a Nitrogen (77 K) (O and ), argon (77 K) (U) and water vapor (298 K) (A and A) isotherms for Silicalite I. Part b detailed low relative pressure data. Clear symbols denote adsorption dark symbols denote desorption.

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