Adsorber-reactor specifications

The description in the literature of early gas desulphurization processes that utilize zeolites does not mention duly the formation of COS during the removal of H2S, if CO2 is present in the feed gas, except in a few cases, e.g., ref. [20,28,65]. Since modern desulphurization plants work in accordance with the same principles and utilize identical zeolite types, the COS formation reaction may have strong implications for the currently employed processes for desulphurization of gases by means of those sorbents. Therefore, it is necessary to investigate (i) the COS formation as dependence on the zeolite type, the type and content of cations in the sorbent, the concentration and contact time of reactants with the sorbent, the temperature and the conditions of co-adsorption (ii) the mechanism of that reaction on the sorbent with specific emphasis on its sorption and catalytic properties and (iii) to develop a mathematical model to simulate dynamic processes that proceed in adsorbers/reactors of technical dimension. This investigation should lead to novel formulations of modified zeolite sorbents and to alternatives with regard to operating conditions of sorption plants with the purpose of either minimization or maximization of the formation of COS. 

We have also tried the trapping reactor system, in which ammonia is trapped on the catalyst/adsorbent and microwave is irradiated intermittently. However, due to the small specific surface area and the small ammonia adsorption capacity on the employed CuO, the trapping system was not effective compared to the continuous irradiation. Further study should be made to develop a material having high ammonia adsorption capacity and high efficiency for microwave absorption. Supported CuO on high surface area material or preparation of high surface area CuO can be effective. 

Notably, these reactions are catalysed by the Ba component or involve a specific reactivity of adsorbed NO since no reaction was observed between N02 and H2 in an empty reactor up to 500°C. 

Gas-Solid Heterogeneous Reaction Mixtures. Gas-solid heterogeneous reaction mixtures may be advantageously irradiated in annular (immersion-type) photochemical reactors. Again, the content of solid particles is limiting the size and the productivity of the reactor system. This is of particular importance when the solid support is used to specifically adsorb substrates or products of the photochemical reaction the first to enhance specificity of radical substitution reactions [20], the latter to reach better photostability and to ensure optimal purity. 

The third means of radionuclide production involves target irradiation by ions accelerated in a cyclotron. One example of this approach is provided by the production of Ge, which decays with a 280 day half-life to the positron emitter Ga. Proton irradiation of Ga produces Ge in a (p,2n) reaction. After dissolution of the target material a solution of the Ge product in concentrated HCl is prepared and adsorbed on an alumina column which has been pre-equilibrated with 0.005 M EDTA (ethylenediaminetetraacetate) solution. The Ga daughter may then be eluted using an EDTA solution in a system which provides the basis of a Ga generator. Cyclotron production of radionuclides is expensive compared with reactor irradiations, but higher specific activities are possible than with the neutron capture process. Also, radionuclides with particularly useful properties, and which cannot be obtained from a reactor, may be prepared by cyclotron irradiation. In one example, cyclotron produced Fe, a positron emitter, may be used for bone marrow imaging while reactor produced Fe, a /3-emitter, is unsuitable. " ... 

Equilibrium constants for empirical models are determined from measurements of the activity of a solute in water and the equilibrium adsorbed concentration. Experiments usually consist of a series of batch reactors where a solid phase is suspended in solutions that have a range of known solute concentrations. Equilibrium constants are then derived from various types of plots of the adsorbed and aqueous concentrations. These equilibrium constants are highly dependent on solution and solid composition. Eor example, values of Kl and Kp for As adsorption have been shown to be a function of pH, the concentration of competing ions, and the mineralogy of the adsorbent (Darland and Inskeep, 1997a Ghosh and Yuan, 1987 Kingston et al., 1971 Hsia et al., 1992 Pierce and Moore, 1982 Sakata, 1987). Therefore, empirical models are limited to the specific experimental conditions used to determine the Log K s. 

An adsorption isotherm is useful for scaling up small-scale batch processes usually carried out in a laboratory. Once the laboratory data are fitted to an isotherm, one can predict the amount of adsorbent required to reach a specific effluent solute concentration (in terms of a batch reactor) or the breakthrough time (for a plug-flow column). 

At present there are no totally satisfactory methods of commercially removing limonoid bitterness. Several new approaches are being developed which may lead to a more complete solution to the problem. These include specific adsorbents of limonoids, a biological reactor that uses immobilized bacterial cells, and the preharvest approaches which are presented in the text. 

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