Carbon deposition problem in reforming units

Fewer aromatics and cycloalkanes mean that more straight-chain alkane isomerization reactions and alkane dehydrogenation-cyclization reactions are required. What does this have to do with carbon deposition? I don’t understand it

The measures to reduce carbon deposits mainly fall into two categories: optimizing reaction conditions and selecting appropriate catalysts. Firstly, optimizing reaction conditions by adjusting parameters such as temperature, pressure, and catalyst dosage can reduce the formation of carbon deposits. This can improve reactivity and selectivity, reduce the formation of by-products, and thus lower the rate of carbon deposit formation. Secondly, selecting an appropriate catalyst is also an important measure to reduce carbon buildup. The activity and stability of the catalyst have a significant impact on the formation of carbon deposits. On the one hand, an appropriate catalyst can enhance the adsorption and dissociation capabilities of the reactants, thereby facilitating the reaction and reducing the formation of carbon deposits. On the other hand, a stable catalyst can resist the accumulation of carbon deposits, extending its service life and reducing time and cost expenses. As for why it is not possible to choose feedstocks with a low aromatic potential content in order to reduce the problem of carbon deposition, there are mainly two reasons: First, feedstocks with a low aromatic potential content usually contain a higher proportion of saturated hydrocarbons. Saturated hydrocarbons tend to form carbon deposits more easily in pyrolytic short-chaining reactions because they possess higher stability during these reactions. Therefore, feed with a low potential aromatic content may lead to more carbon deposition. Secondly, feedstocks with low aromatic potential content usually contain higher levels of impurities and contaminants. These impurities and contaminants can easily cause adverse reactions such as catalyst poisoning during the reaction, thereby leading to the formation of carbon deposits. Therefore, choosing a feed with a low aromatic potential content may increase the difficulty of carbon deposition issues. Regarding what reactions occur in the reactor with low-quality feed, reactions such as cracking, recombination, and reduction generally take place. Cleavage refers to the breakdown of long-chain hydrocarbon molecules into shorter-chain hydrocarbon molecules with lower carbon numbers under high temperature and the action of a catalyst ； Recombination refers to the process by which short-chain hydrocarbon molecules are rearranged and combined on the surface of a catalyst through adsorption and dissociation processes to form hydrocarbon molecules with longer carbon chains ； Reduction refers to the dehydrogenation of saturated hydrocarbons in hydrocarbon molecules, with hydrogen being replaced by a reducing agent. During these reaction processes, the issue of carbon deposition arises due to the presence of the catalyst. Carbon deposits are usually formed by the aggregation of reactants and residues from the catalyst. The formation of carbon deposits reduces the catalyst’s activity and selectivity, leading to a decrease in reaction efficiency and potentially causing the catalyst to become ineffective. Therefore, reducing carbon deposition is one of the important measures to improve reaction efficiency and catalyst lifespan. .

If you choose feed with a low aromatic potential, then why go through reforming?