What are the reasons for the increase in nitrogen content in the crude benzene hydrogenation unit?
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In the 10-ton/year crude benzene hydrogenation unit, after the catalyst replacement at the end of 2025, the nitrogen content in the reaction gas stream increased from 1.05% to 3.56%, while the initial purity of hydrogen decreased from 91% to 88%. What is the reason for this increase in the nitrogen content in the system?
Changes in the hydrogen content in the hydrogen production system output； Check for nitrogen leakage ； Changes or decomposition of nitrogen-containing compounds in benzene
An increase in nitrogen content in the crude benzene hydrogenation unit may stem from raw materials, process conditions, equipment, and operational factors. The reasons are analyzed from various aspects below. Raw material-related factors: A high initial nitrogen content in the crude benzene feedstock directly increases the nitrogen load in the product ； If the raw materials contain high-nitrogen secondary processing components such as catalytically cracked naphtha, or if nitrogen-containing additives such as corrosion inhibitors and coating amines are used, it may lead to nitrogen contamination ； Furthermore, when the dry point of the raw material is too high, the content of nitrogen-containing heterocyclic compounds that are difficult to hydrogenate increases, making denitration more challenging. Process conditions and operating parameters: Too low a reaction temperature will reduce the rate of denitrification (as denitrification is an endothermic reaction), while too high a temperature may accelerate catalyst deactivation ； Insufficient hydrogen partial pressure (due to low pressure or low purity of the recycled hydrogen) reduces the hydrogen supply, thereby inhibiting the hydrogenation saturation and denitration reactions ； Excess air velocity (high feed rate) results in insufficient residence time of the reactants, leading to inadequate nitrogen removal ； A decrease in catalyst activity (due to metal impurities or carbon deposition, for example) reduces the conversion efficiency of organic nitrides. Equipment and system issues: An insufficient design pressure for the pre-hydrogenation unit may result in a hydrogen partial pressure that does not meet the denitration requirements ； System leaks or poor sealing may introduce external nitrogen ； In a pressure swing adsorption hydrogen production unit, if the adsorbent fails or the operation is not proper, it may affect the purity of hydrogen, indirectly leading to an increase in nitrogen content.
The friend upstairs explained it in great detail. The hydrogenation process operates at high temperatures and pressures, so the possibility of contamination or leakage from external gas sources is virtually non-existent. It is necessary to check whether there are any potential leakage points at the connections for high-pressure nitrogen, such as that used for emergency purging ； Secondly, nitrogen leakage may occur during the hydrogen supply process and the pressure increase process ； For the possible reasons in the final reaction process, you can refer to the judgment of the friend above