Catalyst Characterization - From Fresh to Spent
Characterization of catalysts, both prior to reaction and in their spent form, can provide valuable information about the efficiency of the catalytic process and guide future design of new catalysts. Through determination of the pore size, pore volume, active surface area, particle size, surface acidity, fluidization behavior, cohesion strength and elutriation rate with Anton Paar instruments, insights can be derived that contribute to catalyst development and quality control.
Catalysts, particularly heterogeneous catalysts, are used in many different industries to enhance efficiency and quality in material production. Structural, particle, and powder flow information of both fresh and spent catalysts can aid researchers and manufacturers in optimizing catalyst design for the desired application. While this report uses examples of catalysts from the oil and gas industry, specifically Fluidized Catalytic Cracking (FCC) zeolites, the techniques outlined here are of benefit to all catalyst researchers.
FCC is an important part of the world’s energy production and responsible for half of gas and kerosene output. Developed to rapidly scale up fuel production in the beginning of World War II, to this day it remains one of the most intensively used chemical engineering processes in the world. FCC is a fluidized bed process which uses hot, gaseous heavy fractions left over after initial distillation in a fuel refinery and breaks them down further into useful portions for subsequent distillation steps.
Characterization plays a crucial role in the development process of all new catalysts and is of great importance for FCC catalysts in the oil and gas industry. Pore size and connectivity within FCC zeolite catalysts can affect the transport of molecules to the catalytic sites. Gas sorption (physisorption) is used to determine the micro- and mesoporous structure of the pores within the zeolite. Advanced techniques such as interpretation of the hysteresis loop and hysteresis scanning can also be used to determine pore connectivity, which drives transport and diffusion to the active catalytic sites. Flow chemisorption experiments such as ammonia temperature programmed desorption (TPD) are used to determine the acid site quantity and strength within the zeolite and to differentiate between Lewis and Brønsted acid sites.
In addition to the characterization of fresh catalysts, the continuous running of an FCC reactor is a challenging environment for the catalysts themselves and characterization of spent catalysts is equally important. High temperature, oxidative reaction of fuel leads to coking in seconds, which makes a regeneration step necessary. Coking effects on catalysts are studied via surface area and pore size changes in the material. Furthermore, high shear rates and many collisions (due to the fluidized bed) provide an environment where physical degradation of the zeolite catalysts becomes an issue.
A large part of degradation of catalysts in an FCC process is due to attrition. Attrition is one of the two mechanisms by which a granular medium in a fluidized bed process is broken apart. In contrast to breakage, in an attritive process, the bulk solid is not broken into parts that are of roughly the same dimension, but rather pieces are shorn off, which results in a fine fraction one or multiple orders of magnitude smaller than the original particle. Because these new fractions are all but invisible to most traditional methods such as sieving or visual inspection, it is challenging to quantify the amount of lost material. An insight into these processes becomes possible with the broad portfolio of Anton Paar instruments.
1. Y-C. Ray, T-S. Jiang, C.Y. Wen. Powder Technology, 1987, 49.3, 193-206.
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