Catalytic cracking - Session

In a broad sense, it generally refers to a cracking reaction using a catalyst, but in a narrow sense, it refers to the reaction and operation of cracking heavy petroleum fractions using solid acid catalysts such as zeolite to produce high-octane gasoline. While normal thermal cracking is a radical reaction, catalytic cracking is a carbenium ion reaction, and the products are rich in branched alkanes and branched alkenes, and also contain relatively large amounts of aromatic hydrocarbons. As a result, the octane number of the gasoline produced is much higher than that of thermal cracking, and the octane number of catalytic cracking gasoline is generally 90 or higher. In industrial operations, it is carried out in the gas phase at normal pressure at around 500 °C, and there are two types: a fluidized bed type using a powdered fluidized catalyst and a moving bed type using a granular catalyst. The fluidized bed type is the mainstream, and various fluidized bed methods are used in Japan. Traditionally, silica-alumina catalysts were the main catalyst, but nowadays zeolite catalysts are used, and the latter has a higher gasoline yield and less gasification loss.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

広義には，一般に触媒を用いる分解反応をいうが，狭義には，石油の重質留分をゼオライトなどの固体酸触媒を用いてクラッキングし，高オクタン価ガソリンを製造する反応および操作をいう．通常の熱分解はラジカル反応であるのに対し，接触分解はカルベニウムイオン反応で，生成物は分枝アルカン，分枝アルケンに富み，また芳香族炭化水素も比較的多い．このため，熱分解法に比べてはるかに生成ガソリンのオクタン価が高く，一般に接触分解ガソリンのオクタン価は90以上である．工業的操作としては，常圧気相で約500 ℃ 前後で行われ，粉末状の流動触媒を用いる流動層式と，粒状触媒を用いる移動層式とがある．流動層式が主力で，わが国では各種の流動層方式が採用されている．触媒としては，従来，シリカ-アルミナ触媒が主体であったが，現在ではゼオライト触媒が用いられ，後者のほうがガソリン収率が高く，ガス化損失が少ない．

出典　森北出版「化学辞典（第2版）」化学辞典 第2版について　情報