Problems with catalytic cracking and thermal cracking

1. Catalytic cracking is not merely catalysis. . . 2. Catalytic cracking relies primarily on the catalytic action of catalysts. . . 3. Catalytic cracking still contains a large proportion of exothermic reactions. . . 4. The role of a catalyst is to provide and increase the contact area, as well as to reduce the reaction activation energy, thereby lowering the threshold for the thermal cracking reaction of the catalytic feedstock. . . 5. The combination of exothermic reactions that can break chains on their own when the temperature reaches a certain level, without the need for a catalyst, to achieve the desired product specifications, and catalytic reactions that require a catalyst to facilitate chain breaking, constitutes the current conditions for catalytic cracking processes. . . 6. The presence of a catalyst can effectively reduce the rate at which gum and asphaltenes rapidly polymerize to form coke, and accelerate the decomposition and chain scission of beneficial components. . . 7. Your facility adopts a high reaction temperature in order to accommodate the production technology options for gasoline or gas 2 selected under the current economic market conditions. . . Gasoline is selling a bit better at the moment. . . Diesel, especially catalytic diesel, has seen poor sales since 2008 and remains sluggish. . . :lol

Catalytic cracking is a hydrogen transfer reaction, while thermal cracking is a dehydrogenation reaction; in the catalytic cracking process, thermal cracking occurs simultaneously as an inevitable consequence. The degree of thermal cracking reaction cannot be determined based on a single piece of data; a comprehensive consideration is required. Factors such as catalyst activity, reaction time, amount of terminator added, and the hydrogen-to-methane ratio in the dry gas play a role; whether thermal cracking is excessive depends on the requirements for the target product and whether the final yield is maximized. The goal is to maximize economic benefits.

The actual reaction temperature for catalytic cracking is 500–700°C, while thermal cracking can generally proceed at temperatures above 390°C. The higher the temperature, the more intense the reaction; therefore, thermal cracking reactions inevitably occur simultaneously during the catalytic cracking process.

It’s really rare to see you being so diligent when you’ve just started learning about *catalytic reactions*. Thermal cracking of hydrocarbon molecules can occur at temperatures of 425–650°C in the absence of a catalyst. Therefore, thermal cracking reactions generally occur during the reaction in our catalytic cracking units. A value of C4/(C3+C4) between 0.65 and 0.7 indicates a predominance of catalytic cracking; values below 0.5 imply intense thermal cracking reactions, although this is also merely empirical data. It is also possible to use (C1+C2)/i-C4 for judgment: a value less than 0.6 indicates primarily catalytic cracking, while a value greater than 1.2 indicates intense thermal cracking reactions. When thermal cracking is too intense, gas and coke yields increase, liquid yield decreases, and the stability of gasoline and diesel deteriorates. The thermal cracking reaction is directly related to the reaction properties of the catalyst and the contact condition between the catalyst and the oil. Although reducing the reaction temperature can suppress the thermal cracking reaction, the effect is not significant below 540°C. The selection of the reaction temperature also depends on factors such as the properties of the raw materials, the production plan, and the yield of the product, with the goal of achieving the best overall economic efficiency.

Does C4/(C3+C4) refer to a mass ratio or a molar ratio, and does (C1+C2)/i-C4 refer to a mass ratio?

Thermal cracking follows a free radical reaction mechanism, whereas catalytic cracking operates via a carbocation reaction mechanism; the former produces more ethylene in the case of lower carbon compounds, while the latter yields more propylene – this is a key distinction to keep in mind

There is a brief mention in the catalytic cracking operation guidelines that C4/(C3+C4) should not exceed 0.65, but in practice, it is generally not used as a criterion for judgment.