Water vapor adsorption generation

Phe adsorption experiments were carried out using the laboratory scale rig shown in Figure 1, where a Phe vapor stream with pure Helium as carrier at different steam percentages (0%, 5%, 10% and 20%) and CO2 percentages (0%, 10%, 20% and 30%) was generated. In this system, which was described in detail elsewhere [9], a water vapor generator was added to generate a gas stream with a constant moisture concentration and another mass flow controller was included to ensure a constant CO2 flow. The CA-3... 

Various organic wastes were carbonized with super-heated water vapor using a rotary drum super-heated water vapor generator (SJH-IOM, Johnson Boiler, Japan) and a rotary kiln (JBT-1OM, Johnson Boiler, Japan). The organic wastes were processed at 623 K for 30 - 90 min. Process data and properties of various carbonized materials are summarized in Table 1. An activated carbon (Granular Shirasagi GS3 x 4/6, Takeda Chemical Industries Ltd., Japan) and an activated carbon prepared for alkaline gas adsorption (GAH 4-8, Cataler Corp., Japan) were used as controls. 

Appreciable interest has been generated in the use of activated carbons for flue gas cleanup, especially for the removal of SOx and NO the adsorption of mercury from flue gases was discussed earlier. From the environmental point of view, emissions from the combustion of fossil fuels in power plants and similar industrial processes are major contributors to a lowering of air quality. The flue ga.ses carry traces of SOi and NO, which can be oxidized and converted to their acid forms in the presence of atmospheric water vapor, and they may also combine with other volatile organics to form ozone and smog. Similarly, low level SOj and NOx emissions from automobiles, while insignificant for individual vehicles, become a large source of pollution when multiplied by the millions of vehicles that are on the roads. 

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.

A solvent dissolution, a vapor adsorption, any kind of surface-active substance exchange between the surface and the adjacent subphase, or heating makes the surface tension locally vary, thus generating Marangoni stresses and convection. Then, gravitocapillary waves (wavelength X and amplitude q) excited and sustained by the Marangoni effect in the shallow water waves approximation can be described by the equation ... 

In the case of zero gas generators, the above-named contaminants are usually removed by adsorption because this separation process is the easiest to handle (for instance in comparison to washing processes). Gas is sucked in through a dust niter and is compressed to between 7 and 8 bar. If possible each adsorption step should be settled in this region, because the grades of separation rise in conjunction with the partial pressure. Water vapor is removed from the air initially, because water vapor is the most prevalent accompanying component (yH20 approximately 3<7o absolute). 

The results of a very recent study by Attia [3], summarized in Fig. 1, are a good illustration. Carbons of varying surface area were produced by carbonization and activation of date pits in steam, air, or carbon dioxide (at different temperatures and to different extents of burnoff). The correlations of water vapor and pyridine uptakes with the total surface area are seen to be very poor. The author concludes that water vapour adsorption is related to the chemistry of the surface rather than to the extent of the surface area but does not identify, let alone quantify, this chemistry. Regarding pyridine adsorption, the author notes that activation of carbons at low temperatures created acidic sites while treatment at high temperatures led to the generation of basic sites on the surface, but she does not identify these sites. 

The reason for the lowered cracking onset temperature at higher humidity is not known. However, there are some possibilities. One is the post-hydrolysis at the gel fihn surface by water vapor, which could induce polycondensation reaction at the surface, leading to stress gradient across the thickness. Second, adsorption of water on the fihn surface could increase the capillary pressure, resulting in an increase in tensile stress. Further study on the effect of humidity on stress generation should be made by means of in situ measurement of stress in films under controlled humidity. 

Englezos et al. (1987a,b) generated a kinetic model for methane, ethane, and their mixtures to match hydrate growth data at times less than 200 min in a high pressure stirred reactor. Englezos assumed that hydrate formation is composed of three steps (1) transport of gas from the vapor phase to the liquid bulk, (2) diffusion of gas from the liquid bulk through the boundary layer (laminar diffusion layer) around hydrate particles, and (3) an adsorption reaction whereby gas molecules are incorporated into the structured water framework at the hydrate interface. 

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