What is the purpose of the first reactor for the hydrogenation of C9 produced by ethylene cracking?

The primary purpose of the first reactor in the hydrogenation of C9 hydrocarbons derived from ethylene cracking is usually to selectively hydrogenate the unsaturated hydrocarbons present in the feedstock (such as dienes and olefins), thereby reducing the levels of gums and diene content, while also protecting subsequent catalysts from coking or poisoning. This step is crucial for improving the stability of the C9 feedstock and reducing carbon deposition in subsequent reactors. After the reaction is complete, the key parameters for evaluation usually include: diene value (or bromine value), sulfur content, gum content, as well as the temperature at the reactor outlet or the degree of temperature rise. When evaluating the completion degree of the reaction, the rate of change in the diene values of the feed and product can be compared to determine whether the designed conversion rate has been achieved; meanwhile, the reactor pressure difference and temperature rise can be used to assess whether the catalyst activity is normal. However, differences can occur under different process conditions (such as catalyst type, space velocity, hydrogen-to-oil ratio). It is recommended that you determine this based on your facility’s specific process documentation or operation manual, or it is safer to consult the on-site process engineer.

The primary purpose of the first reactor in the hydrogenation of carbon nine derived from ethylene cracking is to selectively saturate highly reactive dienes and alkenyl aromatics (such as dicyclopentadiene and styrene), converting them into monoolefins or alkyl aromatics. This helps to prevent polymerization and coking, as well as to stabilize the material, thereby preparing it for further deep hydrogenation or separation. The main purpose of the first reactor is to eliminate the risk of polymerization: it hydrogenates highly self-polymerizable diolefins (such as DCPD and cyclopentadiene) and alkenyl aromatics (such as styrene) into more stable monoolefins or saturated hydrocarbons, thereby preventing blockages in subsequent equipment and rapid deactivation of catalysts. Control of reaction temperature rise: By utilizing the exothermic nature of selective hydrogenation, operations are carried out under mild conditions (usually in the liquid phase or at low temperatures in the gas phase), thereby preventing excessive temperature rises in the catalyst bed that could lead to aromatic ring saturation or cracking side reactions. Protection of the second-stage catalyst: Removes highly active components that are toxic to or prone to causing coking on the second-stage hydrogenation catalyst, thereby extending the overall lifespan of the catalyst. The main indicator after the reaction is complete is the Bromine Number: it is the most crucial parameter, reflecting the remaining degree of unsaturation (primarily the content of monoolefins). After a certain period of time, this value should usually be reduced to a specific range (such as 12–16 gBr₂/100g, depending on the process design); there is no need to achieve extremely low values. Diene value: It directly indicates the residual amount of dienes; after one stage of processing, it should approach 0 or remain at a very low level (e.g

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