CHEE 2404: Industrial Chemistry
Hydrotreating
Group 8
Nguyễn Khoa Nghị
Nguyễn Ngọc Sơn
Nguyễn Quốc Khánh
Hoàng Thu Thảo
Nguyễn Văn Chí
Phan Công Thắng
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Hydrotreating
I> Objective
Catalytic hydrotreating is one of the hydrogenation process used to remove about 90% of contaminants such as nitrogen, sulfur, oxygen, and metals from liquid petroleum fractions.
If these contaminants are not removed from the petroleum fractions they can have detrimental effects on equipment, catalysts, and the quality of the finished product.
The lighter materials such as naphtha are generally treated for subsequent processing in catalyst reforming units
the heavier distillates, ranging from jet fuel to heavy vacuum gas oils, are treated to meet strict product quality specifications or for use as feedstocks elsewhere in the refinery
Typically, hydrotreating is done prior to processes such as catalytic reforming so that the catalyst is not contaminated by untreated feedstock. Hydrotreating is also used prior to catalytic cracking to reduce sulfur and improve product yields, and to upgrade middle-distillate petroleum fractions into finished kerosene, diesel fuel, and heating fuel oils.
In addition, hydrotreating converts olefins and aromatics to saturated compounds.

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II> Catalytic Process
The hydrotreating reactions proceed in the following descending order of ease: (organometallic) metals removal, olefin saturation, sulfur removal, nitrogen removal, oxygen removal, and halide removal.

In general, the ‘main messages’ concerning hydrotreating reaction rates, heats of reaction and hydrogen consumption are:
Desulfurization and olefin saturation are the most rapid reactions
Olefin saturation liberates the most heat per unit of hydrogen consumed
Denitrogenation and aromatic saturation are the most difficult reaction
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1. Hydrotreating for sulfur removal is called hydrodesulfurization.
In a typical catalytic hydrodesulfurization unit, the feedstock is deaerated and mixed with hydrogen, preheated in a fired heater (315°-425° C) and then charged under pressure (up to 70 bar) through a trickle-bed catalytic reactor.
In the reactor, the sulfur and nitrogen compounds in the feedstock are converted into H2S and NH3
The reaction products leave the reactor and after cooling to a low temperature enter a liquid/gas separator. The hydrogen-rich gas from the high-pressure separation is recycled to combine with the feedstock, and the low-pressure gas stream rich in H2S is sent to a gas treating unit where H2S is removed.
The clean gas is then suitable as fuel for the refinery furnaces. The liquid stream is the product from hydrotreating and is normally sent to a stripping column for removal of H2S and other undesirable components.
In cases where steam is used for stripping, the product is sent to a vacuum drier for removal of water.
Hydrodesulfurized products are blended or used as catalytic reforming feedstock.
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Sulfur removal occurs via the conversion to H2S of the organic sulfur compounds present in the feedstock.
Most of the reactions are straightforward with the exception of the desulfurization of aromatic sulfur species. This reaction is more complex because it must start with ring opening and sulfur removal followed by saturation of the resulting olefin
Desulfurization mechanism:

2. Nitrogen Removal:
Nitrogen is mostly found in the heaviest end of petroleum fractions in five- and sixmembered aromatic ring structures. Both the molecular complexity and quantity of nitrogen containing molecules increases with increasing boiling range, making them more difficult to remove. The denitrogenation reaction proceeds through a different path from that of desulfurization. While in desulfurization the sulfur is removed first and the olefin created as an intermediate is saturated, in denitrogenation, the aromatic is saturated first and then the nitrogen is removed.
Ditrogenation mechanism:
Nitrogen is more difficult to remove and consumes more hydrogen than sulfur removal because the reaction mechanism involves aromatic ring saturation prior to nitrogen removal. In desulfurization, the sulfur is less often associated with aromatic rings and when it is, the sulfur can be removed without ring saturation
3. Oxygen Removal:
Most petroleum crudes contain low levels of oxygen. The oxygen-containing compounds are converted, by hydrogenation, to the corresponding hydrocarbon and water.The lower molecular weight compounds are easily hydrogenated.
4. Olefin Saturation
Olefins are not found in petroleum, but are formed when processed in thermal or catalytic units. In general, fractions containing olefins are unstable and thus must be protected from contact with oxygen prior to hydrotreating to prevent the formation of polymer gums.
Olefin saturation reactions are very rapid and highly exothermic. While the denitrogenationreaction shows a heat of reaction of 1 Btu/lb of feed for each 100 ft3 of H2 consumed, and the desulfurization reaction generates 1 Btu/lb of feed for each 10 ft3 H2 consumed, the olefin saturation generates 1 Btu/lb of feed for each 2 ft3 of H2 consumed. If proper care is not exercised during operations, it can result in mechanical problems such as excessive coking that can lead to pressure drop build up and/or poor liquid flow distribution through the catalyst bed(s).
Aromatic Saturation
Saturation of aromatics is desirable for improvement of the properties of petroleum products. E.g: smoke point, diesel index, etc. The aromatics found in the naphtha to gas oil boiling range are present as one, two and three ring aromatics- often referred to as mono, di, and tri aromatics. Typical reactions are shown below:
III> Deep HDS combined with octane recovery processing
ExxonMobil’ OCTGain process of selective naphta HDS
Heater
hydrogen
Desulfurization to H2S
Recover octane
Liquid
Gas
Stripper
stripper
IV> Hydrotreating Catalyst
Hydrotreating catalysts are high surface area materials consisting of an active component and a promoter, which are uniformly dispersed on a support.The catalyst support is normally gamma alumina (γ-Al2O3), sometimes with small amounts of silica or phosphorous added, which is prepared in such a way so as to give a high surface area and an appropriate pore structure.
Cobalt–Molybdenum Catalysts:
CoMo catalysts have been designed primarily for desulfurization, but some denitrogenation and demetallation is also achieved.
CoMo catalysts exhibit the highest sulfur removal per unit of hydrogen consumed, therefor they are best suited for desulfurization
Nickel–Molybdenum Catalysts:
NiMo catalysts have been designed for desulfurization, but particularly for hydrogenation and denitrogenation. Metal removal can also be achieved.
Other catalysts
Other catalysts used in hydrotreating are NiW and NiCoMo. NiW catalysts have applications in treating feeds where higher hydrogenation activity is required than is available from either NiMo or CoMo.
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Group 8
Nguyễn Khoa Nghị
Nguyễn Ngọc Sơn
Phan Công Thắng
Hoàng Thu Thảo
Nguyễn Văn Chí
Nguyễn Quốc Khánh