Naphtha hydroprocessing

A combination of column adsorption chromatography on basic alumina and GC of the eluate served for characterization of the trace fraction of nitrogen-containing compounds in hydroprocessed naphtha. These were subdivided into groups of four types, namely pyridines, pyrroles (the most abundant), anilines and indoles125. 

Also known as mercaptans, thiols possess very unpleasant odors and are most commonly found in the naphtha fraction. These low-boiling compounds typically contain from one to eight carbon atoms and can be linear, branched, or cyclic. Most thiols are removed from crude oil and petroleum products through hydroprocessing or sweetening. 

Severe hydroprocessing to remove sulfur from naphtha and distillate fractions produces hydrogen sulfide. Although most hydrogen sulfide is removed as off-gas or stripped from fuel streams, the possibility exists for low levels of hydrogen sulfide to remain in fuel fractions. 

Liquid products contain sulfur and nitrogen and must be hydroprocessed to improve quality. Separate hydroprocessing units for upgrading the naphtha, kerosene, and gas oil fractions can be used to optimize the overall process. Refined gas oil or diesel fuel is aromatic in character and contains more cycloparaffins than conventional crude oil. The resulting fuel is low in cetane number, high in density, and typically has very good low-temperature handling properties. 

Vacuum gasoil and heavier fractions have to be hydroprocessed to remove contaminants such as sulfru, nitrogen and metals. They can also be hydrocracked to obtain light and heavy naphtha, jet fuel (kerosene) and desel. Even if the heavy fractions are to be hydrocracked they have always to be treated to eliminate S and N by a hydrodesulfuration (HDS) and hydrodenitrification (HDN) process. 

The appropriate selection of hydroprocessing catalysts depends on a careful inspection of the chemical properties of the feedstock and the expected products. For conventional distillate HDT (naphtha, kerosene, and gas oil), the specific surface area and the composition of the active phase are the most relevant features. CoMo-based catalysts are the traditional HDS catalysts used in the industry. NiMo catalysts are better for saturation reactions and HDN due to their higher hydrogenation power. Therefore, Ni-promoted catalysts are preferred over CoMo catalysts when the chemistry of the process proceeds through the hydrogenation route (i.e., gas oil feeds containing aromatic S- and N-compounds). NiW catalysts exhibit remarkable hydrogenation properties, but they are rarely used in... 

For hydroprocessing units, product specifications are set to meet plantwide objectives. For example, the naphtha that goes to catalytic reforming and isomerization units must be (essentially) sulfur free. Before it can be sold as... 

Reactors, Catalyst Beds and Quench Zones. As shown in Table 4, most hydroprocessing reactions are exothermic. The heat released in naphtha and kerosene hydrotreaters is relatively low, so units designed for these feeds may use just one reactor that contains a single catalyst bed. However, for heavier feeds and/or feeds that contain large amounts of sulfur, aromatics or... 

I 6 Predictive Modeling of the Hydroprocessing Units Light Naphtha (ASTM D86)... 

Hydroprocessing reactors generally are three-phase (gas-liquid-solid) reaction systems. The gas phase is composed majorly of hydrogen, gaseous reaction products, and partially vaporized hydrocarbons the hydrocarbon feed is the liquid phase, whereas the catalyst bed is the solid phase. The only exception is naphtha HDT, which exhibits just two phases (gas-solid) as a result of the complete vaporization of the hydrocarbon. The coexistence of these three phases puts hydroprocessing FBRs... 

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