Question
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What is the purpose of Multi-catalyst Bed philosphy in hydrotreating of Diesel and Vaccum gas oil cuts?
Besides this, for Multi - Catalyst bed configuration, some x or y % of HDS / HDN / HDA happens in each bed, before getting admitted into next catalyst bed. How and who (factors) controls that x or y%?
Dec-2022
Answers
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Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br
The main purpose of the multi-catalyst bed in hydrotreating units is to ensure a volume swell in the reactor leading to the optimization of the processing unit.
Normally, the grading of hydrotreating catalysts involves the use of guard beds in the top of the reactor aiming to control the contaminants concentration through the use of macro porous catalysts which have the function to retain fouling agents like corrosion products, metals, organo-metallic compounds, and diolefins which tends to raise the pressure drop in the reactors and reduce de operational lifecycle of the hydrotreating unit. The following regions of the hydrotreating reactor is filled aiming to maximize the hydrogen uptake, the major part of the HDS and polyaromatic hydrogenation reactions are carried out in the region immediately bellow of the guard bed.
The following zone is normally dedicated to promoted the HDN and monoaromatic saturation reactions, and the following catalyst region is dedicated to promote hydrogenation reactions once the limitation by nitrogen content tends to be minimized in this section. The percentages of HDS/HDN/HDA in each region relies on the characteristics of the processing unit like the total and partial hydrogen pressure, temperature, quench strategy, the characteristics of the employed catalysts, and from the characteristics of the feedstock.
Dec-2022
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