PTQ Q2 2026 Issue

Clean-up of fixed-bed reactor naphtha feed streams: Part 2

Commercial applications for cleaning feed stream corrosion precursors to a hydrodesulphurisation reactor or hydrocracker

Chi-Yao Chen, Mark Zih-Yao Shen, Tzong-Bin Lin, Fu-Ming Lee, Maw-Tien Lee, Yin-Hsien Chen, Kao-Chih Ricky Hsu, Fang-Pin Chen Shin Chuang Technology Co. Ltd Kevin Gagen Unicat Catalyst Technologies, LLC

A one-inch-diameter test unit of the MagAFS filter was installed and operated commercially to clean up the naphtha feed stream to the hydrodesulphurisation ( HDS) reactor at Aroma No.2 plant of the Formosa Plastics Group. The filter has operated smoothly from 04/12/2024 to 02/01/2025 without any incidents of pressure fluctu - ation or increased pressure drop due to plugging. During the test period, the conventional cartridge filter had to shut down three times for cleaning and cartridge replacement. The iron sulphide (FeS) particles are the root cause of hydrocracker pressure drop problems. The fresh feed and the recycle oil (RO) streams to the hydrocracker contain a significant amount of FeS. Cleaning up these streams should be the ideal application for the filter discussed in Part 1 (published in PTQ Catalysis 2026 ) and further explored in Part 2, solving the major pressure drop (or plugging) prob - lems in the hydrocracker with minimal investment and low operational costs, maximising throughput. Reactor filtration Process streams in refinery and petrochemical plants generally contain solid particles of FeS, iron oxides (FeO/ Fe₂O₃), other metal oxides, silica, and carbonaceous mate - rials. These particles are generated from the corrosion of the carbon steel plant equipment with hydrogen sulphide (H₂S), organic sulphur compounds, and other acidic com - pounds in crude oil, in addition to in-plant petroleum or petrochemical streams. Problems are compounded by the processing of cheaper, high-acid and high-sulphur oppor - tunity crude oils. Consequently, severe plugging problems occur in reactors, such as the HDS reactor, hydrocracker, or other fixed-bed reactors, and rely mainly on filtration or other means to minimise the problems. In addition to plugging problems, solid particles in the feed stream to the HDS reactor or hydrocracker normally contain substantial amounts of iron (Fe) compounds, which can serve as catalysts for polymerising dienes and olefins in the feed stream at elevated temperature and pressure within the reac - tor. In the HDS reactor, iron compounds may also promote dehydrogenation reactions, producing activated unsaturated species that can generate additional polymers and sludge, accelerating pressure drop and plugging problems.

Conventional filter cartridges and/or filtering screens are normally used to remove solid particles from process streams. As previously mentioned in Part 1 , they can only remove large solid particles (larger than 25-50 µm) from the process streams and are easily plugged by the solid parti - cles, requiring frequent cleaning or costly cartridge replace - ments. Frequent cleaning and replacing filter cartridges not only disrupts the process operating cycle but also increases the chance of a reactor air leak, promoting the polymeri - sation of dienes and olefins in the reactor, which results in even more severe pressure drop and plugging problems. Conventional filter cartridges and/or filtering screens can only remove large solid particles (larger than 25-50 µm) from the process streams and are easily plugged by the solid particles, requiring frequent cleaning or costly cartridge replacements Reticulated top-bed trap material (RTM) is often used in the reactor to trap additional particles, with sizes ranging from 1 to 1,500 µm, to minimise pressure drop and improve flow distribution. However, it requires the process to shut down to replace and dispose of spent RTM packings and HDS catalyst. The costs of reactor shutdown and restart, as well as material expenses for RTM packings and HDS cata - lyst, are high. Smaller particles (<1 µm) passing through the RTM packings will certainly shorten catalyst life. The filter technology discussed in Parts 1 and 2 can pre - vent particles larger than 0.4 µm from entering the HDS reactor, hydrocracker, and other fixed-bed reactors. Cleaning up naphtha feed stream The HDS unit at Aroma No. 2 Plant of the Formosa Plastics Group treats the naphtha feed stream for a CCR unit for producing the BTX aromatics. The feed stream to the HDS

PTQ Q2 2026