Cracking catalysts specificity

This review will endeavor to outline some of the advantages of Raman Spectroscopy and so stimulate interest among workers in the field of surface chemistry to utilize Raman Spectroscopy in the study of surface phenomena. Up to the present time, most of the work has been directed to adsorption on oxide surfaces such as silicas and aluminas. An examination of the spectrum of a molecule adsorbed on such a surface may reveal information as to whether the molecule is physically or chemically adsorbed and whether the adsorption site is a Lewis acid site (an electron deficient site which can accept electrons from the adsorbate molecule) or a Bronsted acid site (a site which can donate a proton to an adsorbate molecule). A specific example of a surface having both Lewis and Bronsted acid sites is provided by silica-aluminas which are used as cracking catalysts. 

The catalyst chosen for this study was a low metal, equilibrium, commercial zeolite-containing cracking catalyst obtained from Phillips Petroleum Company. No specific characterization of the catalyst is available. 

Wheeler [16] proposed that the mean radius, r, and length, L, of pores in a catalyst pellet (of, for that matter, a porous solid reactant) are determined in such a way that the sum of the surface areas of all the pores constituting the honeycomb of pores is equal to the BET (Brunauer, Emmett and Teller [17]) surface area and that the sum of the pore volume is equed to the experimental pore volume. If represents the external surface area of the porous particle (e.g. as determined for cracking catalysts be sedimentation [18]) and there are n pores per unit external area, the pore volume contained by nSx cylindrically shaped pores is nSx nr L. The total extent of the experimentally measured pore volume will be equal to the product of the pellet volume, Vp, the pellet density, Pp, and the specific pore volume, v. Equating the experimental pore volume to the pore volume of the model... 

Despite much recent progress, the energetic relationships and specific mechanistic steps involved in these reactions require more detailed experimental examination to provide explanation of all the observed facts and to enable more reliable prediction of new reactions. Likewise, the specific interaction between cracking catalyst and hydrocarbon, which also has been the subject of recent work (8, 9), is a promising field for mechanistic studies. 

The Society s Committee D-32 on Catalysts [8c] has developed specifications for a number of analytical methods pertinent to catalysts, and has issued a recommended procedure for testing fluidized cracking catalysts. It is believed that a number of reference materials, particularly those acting as analytical standards, may be available, but their use is not widely described in the scientific literature. 

Comparing the results obtained in Table II and in Table III, it can be observed that the adsorption coefficients for cracking catalyst decrease moderately with temperature, are significantly affected by the specific lump considered (K,g is about three times smaller than Kg ) and are relatively insensitive to the C/O ratio. 

More specifically, over microporous catalysts such as zeolites, cracking catalysts and clays, the lower the catalyst acidity ... 

The acid cracking catalysts produce carbonium ions by the addition of protons to polyolefin chains or by abstraction of hydride ions from hydrocarbon molecules. This is followed by chain scission, which yields C30-C50 oligomeric hydrocarbons. Secondary cracking by P-scission of the C30-C50 hydrocarbons yields liquid (C10-C25) hydrocarbon fuel. Specific advantages of the Polymer-Engineering Process include ... 

Cracking catalysts are highly porous materials with large internal surface areas. Thus, for example, a fresh synthetic silica-alumina catalyst typically has a pore volume of about 0.5 cc./g. and a specific surface of the order of 500 m.Vg., equivalent to about 56 acres (almost 0.1 square mile) per pound. Compared with the internal pore surface, the external surface of the discrete particles of catalyst used in commercial plants is insignificant. This is illustrated by the following tabulation, which shows the external surface areas of spherical particles of the diameters employed commercially. A particle density of 1.0 g./cc. was assumed, about equal to the observed particle density for fresh synthetic silica-alumina. 

One of the most important characteristics of a catalyst is its porous texture (specific surface area, pore volume, pore size and size distribution) which must allow good reactant and product circulations in the catalyst bulk. According to its use, it is necessary to give to a catalyst a tailor-made texture. As they present many advantages, silica-aluminas are widely used as matrices (for cracking catalysts) or supports (supported metals) of catalytic phases. 

FCC. (1) Abbreviation for Food Chemicals Codex, a publication giving specifications and test methods for chemicals used in foods. (2) Abbreviation for fluid-cracking catalyst as used in the petroleum refining industry. Examples are powdered silica alumina, in which alumina is impregnated with dry synthetic silica gel, and various natural clays impregnated with alumina. 

In contrast to the results described previously, the high specificity of the surface of the silica-alumina cracking catalyst compared to that of the silica gel has been amply demonstrated by the adsorption spectra of triphenylmethane and arylethylene vapors, using the high vacuum technique (S6-89). 

Cracking Catalyst from Hydrocarbons Properties SiO2,24% AEO, 20% water, BET specific surface area 268 m7g [2279]. 

Surface area is important in all applications where the process is surface-dependent like in mass and heat transfer, flow through packed beds or fluidization. Activity of drugs, setting time of cement and effectiveness of cracking catalysts are just three examples of direct dependence on specific surface. Some such materials, like fillers or catalysts, are often specified in units of specific surface rather than in particle size and its distribution. Specific surface also offers some practical advantages, in favourable cases, in the ease and speed of measurement and also in that it gives a... 

The pillaring of clays has become an established technique of preparing a new class of porous materials. While their promise as cracking catalysts has not been fulfilled, never-the-less they exhibit interesting catalytic behavior. We have extended the technique to the pillaring of many other types of non-clay layered compoimds which include phosphates, oxides and layered double hydroxides. This extension broadens the field to the point where one can choose the degree of acidity or basicity and framework metals required for specific catalytic processes. 

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