What is the purpose of sulfurizing hydrogenation catalysts?

In new catalysts or catalysts that have not been used yet, the active elements such as tungsten, molybdenum, and nickel are in an oxidized state. The active components of hydrogenation catalysts, on the other hand, exhibit higher activity only when they are in a sulfided state; their hydrogenation activity and thermal stability must both be improved in order to meet the requirements of hydrogenation reactions. Therefore, it is necessary to pre-sulfidize the catalyst before it comes into contact with oil, so that it can react with sulfides and switch to a sulfided state, thereby restoring the catalyst’s activity. The sulfidation reactions are usually as follows: 3NiO+H2+2H2S→Ni3S2+3H2O; MoO3+H2+2H2S→MoS2+3H2O; 9CoO+8H2S+H2→Co9S8+9H2O; CS2+4H2→2H2S+CH4

The sulfidation of hydrogenation catalysts is one of the key technologies for improving catalyst activity, optimizing the operation of the reactor, extending its service life, and enhancing economic efficiency. Hydrogenation catalysts mainly consist of a metal component and a support. The metal components are supported on a porous carrier in their oxidized state, facilitating reactions such as hydrodeamination, hydrodesulfurization, hydrodearomatization, hydrodemetallization, and hydrodeoxygenation. Only by subjecting the catalyst to a sulfidation pretreatment, thereby converting the metal components from their oxidized state to their sulfided state, can the catalyst exhibit high activity, stability, and selectivity, as well as strong resistance to poisoning and a long service life, thus enabling it to fulfill its functions as a hydrogenation catalyst to the fullest extent. Sulfidation of metal oxides is an exothermic reaction. The ideal sulfidation reactions are as follows: MoO3 + 2H2S + H2 = MoS2 + 3H2O – 163.3 kJ/mol; 9CoO + 8H2S + H2 = Co9O8 + 9H2O; 3NiO + 2H2S + H2 = Ni3S2 + 3H2O – 129.8 kJ/mol; WO3 + 2H2S + H2 = WS2 + 3H2O. Classification methods for sulfidation techniques: Depending on the location where the sulfidation reaction takes place, hydrogenation catalyst sulfidation can be divided into in-reactor sulfidation and out-of-reactor sulfidation. In-vessel sulfiding refers to the sulfiding process that takes place after the catalyst is loaded into the hydrogenation reactor. Extrareactor vulcanization refers to the process of combining the hydrogenation catalyst with a vulcanizing agent before placing it into the reactor; once inside the reactor, only hydrogen and oil need to be fed in, after which the temperature is raised to carry out vulcanization. Vulcanization methods: Catalyst vulcanization is generally divided into wet vulcanization and dry vulcanization. Wet sulfidation is the process of sulfiding hydrocarbons or distillate oils containing sulfides in a liquid or semi-liquid state in the presence of hydrogen ； Dry sulfidation is a process in which sulfidation is carried out directly in the presence of hydrogen, either by using hydrogen sulfide at a certain concentration or by injecting organic sulfides into the circulating hydrogen. Wet sulfiding is further divided into two types: in one type, the sulfur required for the catalytic sulfiding process is supplied from external sulfides (such as dimethyldisulfide, CS3, etc.) ； Another method relies on the sulfur present in the sulfurized oil itself for vulcanization. It is now recommended to use off-reactor pre-sulfiding catalysts. After being placed in the reactor, such catalysts are purged with nitrogen to ensure airtightness; without the need for heating and drying, they can be directly subjected to hydrogen purging and heating to start operation. The startup process is simple and fast, reducing the time required for startup significantly. The safe sulfiding of the catalysts as well as the shortened startup time of the plant lead to a notable improvement in the economic efficiency of the enterprise.

What was said upstairs about the purposes and functions of sulfidation is absolutely correct. But as far as I know, most manufacturers currently use external sulfidation for catalyst sulfidation, employing CS2 as the sulfiding agent instead of H2S.

May I ask: when sulfiding a hydrogenation catalyst, should the main reactor be sulfided first or the pre-reactor?

In simple terms, passivation reduces catalyst activity

To improve catalyst activity, the active components of hydrogenation catalysts exhibit higher activity only in their sulfided state.

The active components of newly manufactured or regenerated catalysts are mostly oxides of tungsten, molybdenum, nickel, and cobalt, whereas the active components of hydrogenation catalysts exhibit higher activity only in their sulfided state. After sulfidation, the hydrogenation activity and thermal stability of the catalyst are **improved**, which is necessary to meet the requirements of hydrogenation reactions. Therefore, the catalyst must be pre-sulfidized before being exposed to oil, so that it can react with sulfides and be converted into a sulfided state, thereby enabling its high hydrogenation activity.

There are many methods for enhancing the activity of catalysts, as well as numerous sulfiding agents

Sulfidation is generally carried out using CS2 in order to put the catalyst in a sulfided state, so that the catalyst can exhibit higher activity. This post was last edited by grjq on 2009-1-7 19:17]

Today, dimethyldisulfide (DMDS), CH3－S-S-CH3, is generally used for presulfurization due to its lower toxicity. CS2 is highly irritating to the skin and has relatively high toxicity; it is now hardly used at all.

Sulfurize the main reaction first, then the pre-reaction! ! ! !

Not long ago, coke oven gas containing hydrogen sulfide was used as a sulfiding agent

Hydrogenation catalysts are inactive in their oxidized state; only in their sulfided state do they possess hydrogenation activity, as well as stability and selectivity. Therefore, to convert the oxidized forms of the active elements such as tungsten, molybdenum, nickel, and cobalt in the catalysts into their sulfided forms, two methods are used: dry method and wet method

The hydrogenation catalysts initially loaded into the reactor exist in an oxidized state and are not reactive; they only exhibit hydrogenation activity, as well as stability and selectivity, when in a sulfide state. Therefore, fresh or regenerated hydrogenation catalysts should be sulfided before use. The starting temperature for wet vulcanization is usually controlled at 150–160℃ ； Generally, domestic plants determine the starting temperature for dry vulcanization based on the vulcanizing agent: the sulfur injection temperature for carbon disulfide is 150°C, while it is 175°C for DMDS.

Hydrorefining catalysts come in oxidized and presulfided forms; they can be sulfurized either inside or outside the reactor, and through wet or dry sulfiding methods