koksdeposition

Koksdeposition, or coke deposition, refers to the buildup of carbon-rich solid material on solid surfaces such as catalysts, reactor walls, and heat‑exchange surfaces during hydrocarbon processing. Coke deposits reduce the accessible active surface area, block pores, and impair heat transfer, leading to lower catalyst activity, altered selectivity, higher pressure drops, and potential equipment damage.

Coke forms when feed hydrocarbons crack, dehydrogenate, or polymerize at high temperatures, producing polycyclic aromatic compounds that condense into solid carbon. Coke can be partially gasified away by hydrogen, steam, or carbon dioxide, but when gasification does not keep pace with deposition, accumulations grow. Factors that promote coke formation include high process temperatures, feeds rich in heavy or polyaromatic components, low hydrogen partial pressure, and acidic catalyst surfaces. Diffusion limitations inside pores also favor surface condensation and solid carbon growth.

Different types of coke occur in various industrial contexts. Filamentous coke grows as carbon filaments on metal surfaces, notably on nickel-containing catalysts during steam reforming. Amorphous and graphitic coke form more continuous deposits on a range of catalysts and reactor internals, common in catalytic reforming, hydrocracking, and delayed cokers. In delayed cokers, heavy residues are processed to produce petroleum coke, which is later burned to recover heat. Coke on FCC, reforming, and hydrocracking catalysts typically contributes to activity loss, selectivity shifts, and heat-transfer inefficiencies.

Monitoring and mitigation approaches include process monitoring for signs of deactivation, and analytical methods such as thermogravimetric analysis and thermal oxidation to quantify coke content. Mitigation strategies involve catalyst design to reduce coke precursors, optimize temperature and feed composition, maintain adequate hydrogen partial pressure, and implement regeneration or decoking cycles to burn off deposited carbon and restore activity.