Explanation Of Various Physical Properties Of Catalysts

physical property
The physical properties represent the appearance, structure, density, particle size, and other properties of the catalyst. It usually includes five main items: specific surface area, pore volume, apparent bulk density, wear index, and sieve composition. Below are brief descriptions:
1. Specific surface area
The specific surface area of a catalyst is the sum of the internal surface area and the external surface area. The internal surface area refers to the surface area inside the catalyst micropores, while the external surface area refers to the surface area outside the catalyst micropores. Typically, the internal surface area is much larger than the external surface area. The surface area of a catalyst per unit weight is called the specific surface area.
Specific surface area is an important indicator for measuring the performance of catalysts. Different products have no direct correlation between specific surface area and activity due to different carriers and preparation processes.
The method used to determine the specific surface area is the nitrogen adsorption capacity method.
2. Pore volume
Pore volume is a physical quantity that describes the pore structure of a catalyst. The pore structure not only affects the activity and selectivity of the catalyst, but also affects its mechanical strength, lifespan, and heat resistance.
Pore volume is the total volume of micropores within porous catalyst particles, expressed in milliliters per gram. The size of pore volume is mainly closely related to the support in the catalyst. For the same type of catalyst, the pore volume will decrease and the pore diameter will increase during use.
The method used for measuring pore volume is the water droplet method.
3. Wear index
An excellent catalytic cracking catalyst should not only have high activity and good selectivity, but also have a certain degree of wear resistance and mechanical strength. Catalysts with poor mechanical strength not only suffer from excessive loss during operation, increase catalyst usage, and pollute the environment, but in severe cases, they can disrupt the reasonable distribution of catalysts in the dilute and dense phases, and even make production units unable to operate.
The strength of catalyst wear resistance is determined by the type of binder used during the preparation process. Generally, the catalyst with aluminum sol as the binder has the best strength and the lowest wear index; The catalyst with fully synthesized silica aluminum sol as the binder has the worst strength and higher wear index.
Currently, the "wear index" is used to evaluate the wear resistance of microsphere catalysts. The measurement method is to put a certain amount of catalyst into the wear index measurement device, blow and grind at a constant gas speed for 5 hours, and the first hour blow out is<15 μ Discard the samples and calculate the average percentage of wear per hour for the samples blown out after 4 hours of collection (<15% blown out per hour) μ The proportion of samples in the original sample is>15 μ The weight percentage of the part), which is the wear index of the catalyst, expressed in% h-1.
The current analysis method for catalyst wear index is the straight tube method.
4. Particle size distribution (sieving)
The catalytic cracking catalyst should have a good particle distribution to ensure a good fluidized state. General requirement for catalyst particles<40 μ M is not greater than 25%, 40 μ M~80 μ M not less than 50%,>80 μ M is not greater than 30%.
Under fluidized state, the catalyst undergoes wear and impact, resulting in<20 μ The fine powder of m can easily escape from the cyclone separator.