Water carbon dioxide adsorption effects

Sensors based on adsorption of species onto or into lattice structures have been reported for molecules besides water. For example, devices based on the detection of carbon dioxide adsorption onto semiconductor materials have been developed [10]. In other cases, dielectric materials that have some degree of chemical specificity have been used for making chemically-sensitive layers. One such application is the use of the highly porous zeolite lattice to detect adsorbed hydrocarbons [11]. The specific dimensions and shape of the zeolite pores allows for size and chemical selectivity in the lattice. As in the case of the humidity devices, the adsorbed molecules dipoles cause a local change in the electric fields that can be detected through a capacitive effect. 

There may be problems from other adsorbing species in the house. Carbon-dioxide and water vapor have been found to have an adverse effect on the adsorption coefficient (Strong and Levins, 1978 Siegwarth et al., 1972). The likeliest place for indoor radon to accumulate in houses is in the basement or crawl space where a large surface area is in direct contact with the soil, and thus the most likely place to put an adsorption system is in these locations. However, these areas are also commonly used to store various household chemicals such as painting supplies, etc. These household items stored in basements can release contaminants that may be classified into 4 broad categories aromatics, paraffins,... 

The kinetics and mechanism of methane combustion have been the subject of many investigations, e.g.. Refs. 43-47, because of the importance of natural gas as a potential fuel for catalytic combustors. Under conditions expected in catalytic combustors, i.e., excess oxygen, a first order in methane is generally observed [48], whercas a variety of orders has been observed for other hydrocarbons [13]. The actual mechanism appears to be quite complex and depends on the fuel used. For instance, inhibiting effects are observed for the products carbon dioxide and water in methane combustion over supported palladium catalysts [49,50]. The inhibition of methane adsorption and the formation of a surface palladium hydroxide were proposed to explain the observation. 

Normally adsorption is conducted at or as near ambient temperature as possible and regeneration is at 350-500°F. A process developed by Union Carbide Corp, the AHR process (adsorption heat recovery), allows the temperature to rise to 200 00°F as a result of the heat of adsorption and effects the desorption at comparable temperatures with a stream of inert gas such as nitrogen or carbon dioxide which is recycled after the water is condensed out. The process is applied to removal of as much as 20% of water from ethanol with cycle times of the order of 1 hr, instead of the common 24 hr, even for much smaller contents of water (Anon, April 15, 1985). 

The adsorption of hydrogen is often of a more specific character. At low temperatures it is preferentially adsorbed on n-type or stoichiometric oxides. The adsorption of hydrogen on zinc oxide is of considerable interest. At room temperature and below, there is very little adsorption unless the oxide has been heated in vacuum at about 400°, in which process water or carbon dioxide is lost. Treatment with hydrogen at 300° followed by evacuation is also effective. In these processes the oxide is reduced. There are probably two steps in the process of reduction, in the first of which oxygen is lost from the surface, giving F centers, and in the second the F centers give rise to interstitial zinc atoms, e.g.,... 

Ferreira D, MagaUraes R, Taveira P, Mendes A (2011) Effective adsorption eqrriUbrirrm isotherms and breakthroughs of water vapor and carbon dioxide on different adsorbents. Ind Eng Chemist Res 50 10201-10210... 

The porosity can be widened by gasification with water vapor, oxygen or carbon dioxide (hydrogen is also a gasifying agent for production of methane - effects on porosity appear not to have been examined). The parent materials may also be impregnated with zinc chloride, potassium hydroxide or phosphoric acid, these treatments improving adsorption characteristics, a process known as activation. 

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