Catalysis 2026 Issue

Clean-up of fixed-bed reactor naphtha feed streams: Part 1

Commercial demonstration of cleaning feed streams like coal tar naphtha feed to a hydrodesulphurisation reactor using an unconventional filter

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

F ilter technology developed by Shin Chuang Technology Co., Ltd. (SCTC) and Unicat Technology, LLC (UNICAT) has been implemented commercially to clean up the most difficult feed stream (coal tar naphtha) to the hydrodesulphurisation (HDS) reactor at a China Steel Chemical Corporation (CSCC) plant. It has replaced both the front-end basket filter and cartridge filter, and eliminated the need for reticulated trapping material (RTM) in the HDS reactor, allowing more room for an expanded catalyst bed. Pressure drops in both the front-end heat exchanger and the HDS reactor are essentially unchanged, and the reac- tor temperature increases only 1ºC (essentially no change) during five years of smooth operations. The proprietary MagAFS filter is capable of removing most of the larger particles in the feed stream, allowing only a small quan- tity of tiny particles with sizes ranging from 6.6 to 22.5 nm (mostly around 13 nm [0.013 µm]) and from 260 to 1,000 nm (mostly around 400 nm [0.4 µm]) into the HDS reactor. The quantity is so small that it did not cause much pressure drop or catalyst deactivation problems in the reactor during the five years of operations. Coal tar naphtha from steel mills contains significant amounts of solid particles of iron sulphide (FeS), iron oxides (FeO/Fe2O₃), other metal oxides, silica, and carbonaceous materials from coal fines. These particles are generated by the corrosion of carbon-steel plant equipment with hydro- gen sulphide (H₂S), organic sulphur compounds, and other acidic compounds in coal tar liquid. In general, it has lower quality than the petroleum-based naphtha in terms of solid particle contamination. Consequently, severe plugging problems occur in the HDS reactor, and it relies mainly on filtration or other means to minimise them. Figure 1 shows the conventional filter cartridge and/or filtering screens normally used to remove solid particles from process streams. However, they can only remove large solid particles (larger than 25-50 µm) from process streams. Furthermore, they are easily plugged by solid particles and require frequent cleaning or costly cartridge replacements, disrupting the process operating cycle at high costs. Frequent cleaning and replacing filter cartridges also increases the chance of air (oxygen) getting into the filter and reactor, promoting polymerisation of dienes and olefins in the HDS reactor, resulting in an even more severe

Reticulated top bed material for

ltration and distribution

Basket lter (20/80 mesh)

Furnace or heater

Catalyst bed

Cartridge lter

Fixed-bed (HDS) reactor

(lter supplied by Catalyst Company for removing larger than 50/25 micron particles)

pressure drop and plugging problems in the reactor, caus- ing the plant to shut down. Presently, many refineries and petrochemical plants use reticulated top-bed trap material (RTM) packed in the HDS reactors above the catalyst bed for removing 1 to 1,500 µm particles, thereby minimising pressure drop and improving flow distribution. More realistically, it removes particles between 25 and 50 µm up to 1,500 µm. Two significant drawbacks of this type of technology are:  It requires a process shutdown to open the reactor, as well as replace and dispose of the spent RTM packings and HDS catalyst. The costs of reactor shutdown and restart, as well as the material expenses of RTM packings and HDS catalyst, are significant. v Current RTM packings can only remove solid particles much larger than 1 µm (1,000 nm). The ‘non-removed’ smaller particles (<1 µm) remaining in the feed stream will certainly shorten the life of catalyst and RTM packings, requiring more frequent shutdowns for materials replace- ment and disposal. RTM is even less effective at treating lower-quality coal tar naphtha in the HDS reactor. Therefore, industries need long-lasting, safer, and lower-cost filtration methods capa - ble of removing particles smaller than 1 µm, as well as larger particles, from naphtha streams, preventing them Figure 1 Conventional filtration for feed stream to a fixed- bed (HDS) reactor

Catalysis 2026