Silica poisoning, effect

These tests show that composition of the additive has little effect on controlling deactivation from silica poisoning. On an equal initial activity basis, four of the five additives tested showed very similar deactivation. Alumina, however, had a much higher susceptibility. 

Fig. 10. Poisoning effect of amines on cumene cracking over silica-alumina catalyst 1, quinoline 2, quinaldine 3, pyrrole 4, piperidine 5, decylamine 6, aniline (32). (Reprinted with permission of the American Chemical Society.)...

A second important poison is AS2O3 but its poisoning effect is much less than that of sulphur [17], The mechanism of AS2O3-poisoning is based on the formation of an alloy with nickel. The arsenic typically originates from the solutions used in carbon dioxide wash of the catalyst or is present as an impurity in some zinc oxide sulphur removal beds. Also silica is mentioned as a pore mouth poison by physically blocking the entrance to the pore system by which the catalyst activity is decreased [18],... 

Hall and co-workers have reported on the poisoning effect of ammonia on neopentane cracking over high-silica zeolites, i.e. H-ZSM-5,... 

Siloxanes also have a poisoning effect on SOFCs performances. Segregated silica can deposit in porous cermet anodes [7, 38, 39], also on steam reforming catalysts and FC anodes, causing their silication and consequent deactivation. [17]. Moreover it also affects many other components of the fuel cell system, such as heat exchangers, catalysts, and sensors [3,40]. 

We have shown a new concept for selective chemical sensing based on composite core/shell polymer/silica colloidal crystal films. The vapor response selectivity is provided via the multivariate spectral analysis of the fundamental diffraction peak from the colloidal crystal film. Of course, as with any other analytical device, care should be taken not to irreversibly poison this sensor. For example, a prolonged exposure to high concentrations of nonpolar vapors will likely to irreversibly destroy the composite colloidal crystal film. Nevertheless, sensor materials based on the colloidal crystal films promise to have an improved long-term stability over the sensor materials based on organic colorimetric reagents incorporated into polymer films due to the elimination of photobleaching effects. In the experiments... 

This paper identifies alumina, rare earths, platinum, and magnesia as important SOx capture materials. Alumina is either incorporated directly into the matrix of a cracking catalyst or added as a separate particle. Cerium is shown to promote the capture of SO2 on high alumina cracking catalyst, alumina, and magnesia. Other rare earths are ranked by their effectiveness. The promotional effect of platinum is shown between 1200 and 1400 F for SO2 capture on alumina. Silica, from free silica or silica-alumina in the matrix of cracking catalyst, acts as a poison by migrating to the additive. 

SOx emissions from FCCU s can be reduced by the use of SOx catalysts, especially SOx additives which can be added to the FCCU independently of the cracking catalyst. The effectiveness of these catalysts is favored by lower regenerator temperatures, the presence of combustion promoter, and higher oxygen concentrations. Deactivation of these catalysts occurs by loss of surface area and poisoning by silica. We believe that SOx additives will eventually be used by most refiners to control SOx emissions from FCCU s, either on a spot or continuous basis. 

Tomida et al. (73) investigated the temperature-programmed desorption of n-butylamine from silica-alumina and alumina. The desorbed amine products were different in the two cases. n-Butylamine and n-butene were obtained from silica-alumina dibutylamine and n-butene were obtained from alumina. In a subsequent paper by Takahashi et al. (73a), the authors conclude that two types of adsorption sites on silica-alumina account for the desorption behavior of n-butylamine. One type chemisorbs the amine and the other catalyzes the decomposition of the amine to lower olefins at temperatures above 300°C. On the other hand, amine decomposition was not observed when pyridine was desorbed from silica-alumina. The effects of sodium poisoning on desorption behavior of n-butylamine and pyridine were also examined. 

As expected for silica-alumina as a mixed oxide (see also Section IV.B.5), the PyH+ and PyL species are observed simultaneously (160, 205,206,221-223). Two distinct types of Lewis acid sites could be detected (19b mode at 1456 and 1462 cm-1, respectively) on a specially prepared aluminum-on-silica catalyst (160). On water addition, the Lewis sites can be converted into Br nsted sites (160, 205, 221), The effect of Na+ ions on the acidity of silica-aluminas has been studied by Parry (205) and by Bourne et al. (160). It can be concluded from Parry s results that Na+ ions affect both types of acid sites, so that alkali poisoning does not seem to eliminate the Br nsted sites selectively. For quantitative determination of the surface density of Lewis and Br nsted acid sites by pyridine chemisorption, one requires the knowledge of at least the ratio of the extinction coefficients for characteristic infrared absorption bands of the PyH+ and PyL species. Attempts have been made to evaluate this ratio for the 19b mode, which occurs near 1450 cm-1 for the PyL species and near 1545 cm-1 for the PyH+ species (160,198,206,221,224,225). The most reliable value as calculated from the data given by Hughes and White (198) seems to be... 

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