Thread Content
I. Basic principles of pre-hydrogenation: 1. Purpose: The purpose of pre-hydrogenation is to remove impurities from the feedstock in order to protect the reforming catalyst. 2. Main chemical reactions: Pretreatment hydrogenation involves the catalytic and hydrogen-pressure-assisted decomposition of sulfur-containing, nitrogen-containing, and oxygen-containing compounds in the feed oil to produce H2S, NH3, and water, which are then separated and removed. Olefins are formed in the raw materials along with hydrocarbons. Metal compounds such as arsenic, lead, and copper contained in the raw material are hydrogenated to decompose the metals, which are then adsorbed on the hydrogenation catalyst. (1) Hydrogenation for desulfurization: Under pre-hydrogenation conditions (catalyst, hydrogen pressure, temperature), the sulfur-containing compounds in the feedstock undergo hydrogenolysis to be converted into corresponding hydrocarbons and hydrogen sulfide, thereby removing sulfur. Thiol RSH + H2 → RH + H2S (2) Hydrodenitration reaction: During hydrogenation, nitrides react with hydrogen to produce NH3 and hydrocarbons. R-NH2 + H2 → R-H + NH3 (3) Hydrodeoxidation reaction: Petroleum fractions contain little amount of oxygen-containing compounds; they are mainly naphthenes, and these oxygen-containing compounds are converted into hydrocarbons and water during hydrogenation. 2RCOOH + H2 → 2RCH3 + 2H2O (4) Hydrogenation of olefins: In crude oil fractions, the content of unsaturated olefins is low, but fractions of refined oils contain large amounts of such olefins, which can be easily hydrogenated. RCH = H2 + H2 → RCH3 + CH3; alkenes tend to undergo condensation and polymerization reactions at high temperatures, thereby depositing on the surface of the catalyst and affecting its activity. The hydrogenation saturation of olefins is an exothermic reaction; when hydrogenating oils with a high content of unsaturated hydrocarbons, it is necessary to pay attention to temperature control. (5) Hydrodesulfurization reaction: Petroleum fractions contain small amounts of metal-organic compounds such as arsenic, lead, and copper. Under hydrogenation conditions, these metal compounds undergo hydrolysis, resulting in the formation of free metals that deposit on the surface of the catalyst, thereby removing the metals from the oil. (6) Hydrodehalogenation reaction: RCL + H2 → RH + HCl