Structure of cracking catalysts

Chemical Characteristics and Structure of Cracking Catalysts A. G. Oblad, T. H. Milliken, Jr., and G. A. Mills... 

Since nitrogen adsorption-desorption isotherms provide considerable information on the physical structure of cracking catalysts, the methods used in interpreting isotherm data will be briefly considered. In this connection it will be convenient to refer to the isotherms of some representative cracking catalysts and certain related materials presented in Fig. 2. More detailed plots of the isotherms may be found in subsequent sections. In all cases of hysteresis presented in Fig. 2 the upper portion of the hysteresis loop represents desorption and the lower curve represents adsorption. Catalyst characteristics of principal significance obtained from these plots are listed in Table I. As pointed out above the adsorption-desorption isotherms yield at once surface area, pore volume, and pore radius information. 

Stereochemistry, of unsaturated hydrocarbon hydrogenation, 16, 123 Structure, of cracking catalysts, 4, 87 Surface area measurements, for studying contact catalysts, 1, 66 Surface barrier effects, in adsorption, 7, 269... 

Structure and Sintering Properties of Cracking Catalysts and Related Materials... 

Obviously the contribution of the pore walls—according to the current density distribution—to cathodic hydrogen evolution becomes negligible beyond 10 fim pore depth so that for a perfect, undivided Raney-nickel coating of 100 fim thickness, only 7 to 8% utilization is anticipated. This is the reason why the fissures and cracks, the so-called tertiary structure of the catalyst, formed in Raney-nickel coatings by the leaching process are so important for improving its utilization. 

The activity decay of cracking catalysts chemical and structural deactivation by coke... 

The high surface area and porosity of catalysts play an important role in forming of the structure of cracked hydrocarbons. There are several properties of catalysts that are important to cracking (acidic sites of macropores, microporesX The catalyst selectivity is affected by the crystalline structure of zeolites and their characteristics. 

Micro activity test (MAT). This test was developed and standardized by ASTM (ASTM-D-3907). In the MAT test, a sample of cracking catalyst is contacted with gas oil in a fixed-bed reactor. Gas chromatographic analysis on gas and liquid products is used to determine the yield structure. Recently, the MAT conditions have been adapted to simulate commercial units more accurately in terms of contact times. A higher catalyst activity results in improved conversion and higher regenerator temperature. 

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