RU2066339C1 - Method for continuous hydrodesulfurization - Google Patents

Abstract

FIELD: petroleum chemistry. SUBSTANCE: liquid sulfur-containing hydrocarbon raw material is subjected to hydrodesulfurization in the zone including column reactor with trays installed one above another. Each tray corresponds to reaction stage capable of retaining the preset volume of fluid and catalyst load and has means for discharge of fluid connected with each reaction tray and designed to ensure passage of fluid downward with solid- phase catalyst held on trays, device for ascending motion of gas connected with each reaction tray and designed for gas supply to under the tray. Initial raw material is supplied to the upper tray and hydrogen- containing gas, to under the lower tray. Withdrawn from the upper tray is hydrogen sulfide. Mixing of fluid mixture and catalyst is effected on each reaction tray due to supply from below to tray of ascending flow of gas. Liquid hydrocarbon product with low content of sulfur is discharged from the lower tray. Method is carried out at pressure of 2.0-15.0 MPa and temperature of 240-400 C. Preferably, use is made of trays of definite design. EFFECT: higher efficiency. 7 cl, 6 dwg

Description

 The invention relates to a method for hydrodesulfurization of hydrocarbons.

Crude oils, fractions of their direct distillation and decomposition and other petroleum products contain sulfur in various quantities, depending on the origin of the crude oil and any subsequent processing to which they may be subjected. In addition to elemental sulfur, numerous sulfur compounds have been identified in crude oil, including hydrogen sulfide (H ₂ S), C ₁ -C ₅ primary alkyl mercaptans, C ₃ -C ₈ secondary alkyl mercaptans, C ₄ -C ₆ tertiary alkyl mercaptans, cyclic mercaptans (such as cyclopentanol , cyclohexanethiol or cis-2-methylcyclopentantiol), open-chain sulfides with the general formula RS-R ', where the radicals R and R' are C ₁ -C ₄ alkyl groups, mono-, bi- and tricyclic sulfides thiophene, alkyl substituted thiophenes condensed thiophenes (such as benzo (b) thiophene, and otionaften, dibenzothiophene, and benzo (b) naphtho (2,1-d) thiophene), thienothiophenes, alkiltsikloalkilsulfidy, alkyl aryl, 1-tiaindany, aromatic thiols (such as thiophenol), and cyclic thiols such as cyclohexane.

Generally speaking, crude oils with a low density, expressed in degrees from the American Petroleum Institute, contain more sulfur than crude oils with a high density expressed in degrees, although there are some exceptions. Moreover, the nature of the distribution of sulfur compounds in various oil fractions varies significantly depending on the range of variation of the boiling points of such fractions. So lighter fractions, such as naphtha, contain less sulfur compounds, while the content of sulfur compounds also increases with increasing boiling point, or density, expressed in degrees from the American Petroleum Institute, or the molecular weight of the fraction. Most of the sulfur compounds that are definitely identified as components of crude oil are in the temperature range below about 200 ^° C. Many other sulfur compounds with a high molecular weight and high boiling point remain unidentified in the crude oil.

 For a number of reasons, it is necessary to treat the crude oil and oil fractions obtained from it in order to remove the sulfur compounds present in them. Otherwise, subsequent processing may be difficult, for example, because sulfur compounds will undesirably affect the performance of the catalyst. If the hydrocarbon fraction is supposed to be used as fuel, then during the combustion of the fuel all kinds of sulfur components present in it will form, turning into sulfur oxides, which have a destructive effect on the environment.

 For these reasons, it is necessary to remove sulfur as much as possible from hydrocarbon fractions obtained from crude oil, such as gasoline fractions, diesel fuel, gas oils and the like. Typically, such sulfur removal is carried out by carrying out a process generally known as hydrodesulfurization. In such a process, the hydrocarbon fraction is mixed with hydrogen and passed over the catalyst at the appropriate temperature and pressure. In carrying out such a process, the goal is to break the bonds between carbon and sulfur in the substances in the raw material and saturate them with hydrogen to obtain free valencies or olefinic double bonds at this stage of cleavage. In carrying out this process, the goal is to turn the maximum possible portion of the organic sulfur content into hydrocarbons and hydrogen sulfide. Typical equations for the main types of sulfur compounds subjected to hydrodesulfurization are given below.

c) бициклические

4. Тиофены:

5. Бензотиофены:

6. Дибензотифоены:

В общем случае циклические серусодержащие соединения гидрогенизировать труднее чем соединения с открытой цепью, и в пределах данного класса циклических серусодержащих соединений чем больше оказывается число колец, тем труднее становится разрывать связи между углеродом и серой.1. Thiols:
RSH + H ₂ _ → RH + H ₂ S
2. Diosulfides:
RSSR ′ + 3H ₂ _ → RH + R′H + 2H ₂ S
3. Sulfides:
a) open circuit
RSR ′ + 2H ₂ _ → RH + R′H + H ₂ S
b) cyclic

c) bicyclic

4. Thiophenes:

5. Benzothiophenes:

6. Dibenzotifoenes:

In the general case, cyclic sulfur-containing compounds are more difficult to hydrogenate than open-chain compounds, and within this class of cyclic sulfur-containing compounds, the larger the number of rings, the more difficult it becomes to break the bonds between carbon and sulfur.

 In addition to the presence of sulfur oxides in the gaseous products of combustion of hydrocarbon fuels, other environmentally undesirable components of such gaseous products of combustion typically include aromatic hydrocarbons that may appear due to incomplete combustion, and carbon particles, often containing polycyclic aromatic hydrocarbons, metal compounds, oxidized organic substances and other potentially toxic substances.

 Owing to the existing views on pollution by various national laws of the world, increasingly stringent limits are imposed on the levels of permissible content of impurities in hydrocarbon fuels, such as diesel fuel. In particular, the US Environmental Protection Agency recently proposed rules by which the limit on the weight content of sulfur should be no more than 0.05% and the volumetric content of aromatic substances no more than 20% if we talk about highway diesel fuels (see, for example, the article "Higher Diecel Quality Would Constict Retining" by George H. Unzelman, and Gas Journal, June 19, 1987, pages 55 to 59). Such rules put cleaning specialists in the need to satisfy additional requirements for the processing of diesel fuel and the need for increased investment and operating costs. It is not possible in the near future to predict additional restrictions on permissible levels of sulfur and aromatic substances.

 When treating a hydrocarbon feed with hydrogen in the presence of an appropriate catalyst, other reactions can also occur in order to carry out hydrodesulfurization. In view of the foregoing, the hydrogen treatment method is often used as a more general method of carrying out not only hydrodesulfurization reactions, but also other reactions that can occur, including hydrocracking, hydrogenation, and other hydrogenolysis reactions. The term "hydrotreating" is extensively explained in the article "Here is anomenclature-system proposed for hydroprocessing", The Oil and Journal, October 7, 1968, pages 174 to 175.

There are four main hydrogenolysis reactions, of which hydrodesulfurization is probably the most significant, then hydrodenitrogenation proceeds, then hydrodeoxygenation and hydrodemetallization proceed. Among the catalysts that have been proposed for such hydrotreating reactions are molybdenum disulfide, tungsten sulfide, sulfidated nickel-molybdate catalysts (NiMoS _x ) and cobalt-molybdenum sulfide alumina (Co-Mo / alumina).

 Although in existing methods the simultaneous occurrence of certain hydrogenation reactions, such as hydrogenation of olefins and aromatic hydrocarbons, is considered as not of interest to the hydrodesulfurization process, since the aromatic content of the product was within the established requirements and since the consumption of valuable hydrogen for carrying out unnecessary hydrogenation reactions was considered undesirable, there is a growing decline in the availability of light crude oil. Thus, current and future trends in the use of medium shoulder straps and heavier oil fractions mean that the hydrogenation of aromatic substances will become an increasingly necessary component of oil refining operations. Therefore, taking into account existing conditions and increasing requirements in the future, it is undesirable to combine hydrodesulfurization with hydrogenation of aromatic substances.

 In contrast to the foregoing, except for the treatment of high molecular weight residues, in the case of most oil refining operations with hydrotreating, hydrocracking reactions should be avoided as much as possible, since they are highly exothermic and may be accompanied by thermal destruction of the catalysts and reaction vessels, and also lead to the deposition of carbonaceous substances leading to in loss of activity of the catalyst. For example, one of the operators of a hydrodesulfurization plant reports in his article (Refiners seek improved hybrogen production, Oil and Gas Journal, July 20, 1987, pages 48 and 49) that operating reactors undergo severe overheating, even before destruction, due to undesired hydrocracking reactions.

 The danger of such hydrocracking reactions can be minimized if the catalyst remains adequately sulphided.

 A number of articles related to hydrodesulfurization technology have appeared in the literature; These include the following articles.

(a) "Kinetics of Thiophene Hydrogenolysis on a Cobalt Molybdate Catalyst", by Charles N. Satterfield et al, AIChE Journal, Vol.14, No.1 (January 1968), pages 159 to 164;
(b) "Hydrogenation of Aromatic Hydrocarbons Catalysed by Sulfided CoO-MoO ₃ / gamma Al ₂ O _3. Reactivities and Reaction Networks" Ajit V. Sapre et al, Ind. Eng. Chem. Process Des. Dev, Vol. 20, No.1, 1981, pages 68 to 73;
(c) "Hydeogenation of Biphenyl Catalyzed by Sulfided CoO-MoO ₃ / gamma Al ₂ O _3. The Reaction Kinetics", by Ajit V. Sapre et al, Ind. Eng. Chem. Process Des. Dev, Vol. 21, No.1, 1982, pages 86 to 94;
(d) "Hydrogenolysis and Hydrogenation of Dibenzothiophene Catatysed by Sulfided CoO-MoO ₃ / gamma Al ₂ O ₃ : The Reaction Kinetics" by DHBroderick et al, AIChE Journal, Vol.27, No.4, July 1981, pages 663 to 672 ; and
(e) "Hydrogenation of Aromatic Compounds Catalysed by Sulfided CoO-MoO ₃ / gamma Al ₂ O ₃ " by DHBroderick et al, Journal of Catalysis, Vol.73, 1982, pages 45 to 49.

 A review of hydrogen reactivity data on sulfide catalysts, such as those used as hydrotreating catalysts, is available on pages 584 to 607 of Moyes’s book (Hydrogen Effects of Catalysis by Richand B. Moyes, publiched by Marcel Deccek, Inc. (1988) )

A review of industrial use of hydrotreating processes is published annually in the journal Hydrocarbon
Processing ", usually in the September issue. For example, you can refer to the journal" Hydrocarbon Processing ", September 1984, 20 and later to the journal" Hydrocarbon Processing ", September 1988, pp. 61-91.

 Three well-known hydrotreating methods are described in the Handbook (Hydrocarbon Procedding 1988 Refining Handbook on pages 78 and 79 of Hidrocarbon Processing, September 1988). In the case of one of the methods ("Chevron RDS / VRDS Hydrotreating Process"), a mixture consisting of fresh liquid hydrocarbon feeds that have undergone hydrogen preparation and recycle hydrogen is fed to a "single" reactor. As illustrated, the reactor contains three layers, and interlayer cooling is carried out by injecting additional amounts of recycle hydrogen. Recycled hydrogen is passed through a hydrogen sulfide scrubber. In the case of another method ("HYVAHL Process"), the liquid feed is also exposed once. Here, again, in order to remove hydrogen sulfide from recycle hydrogen, an amine flush is used. In the case of another method ("Unionfining Process"), the liquid feed is also exposed once. Liquid and hydrogen move in a direct flow. Unreacted hydrogen is recycled.

 In the case of all three methods, recycle gas is used to cool the catalyst bed, and thereby minimizes the risk of thermal degradation resulting from the release of significant amounts of heat during hydrotreatment. The fact that gas recycle is used means that inert gases tend to accumulate in the recycle gas, which, in turn, implies that in order to maintain the required partial pressure of hydrogen, the total working pressure must increase in accordance with the increase in pressure of the recirculating inert gases, which should be increased size and cost of the gas recycle compressor and that will have to put up with increased operating costs.

 A method of using inkjet technology is described in (New Shell Hydrodesulfurization Process Shows These Features, Petroleum Refiner, Vol. 32, No. 5 (May 1953), page 137 etseg.). In fig. 1 of this article illustrates a reactor with four catalyst beds with the introduction of a mixture of hot gas and gas oil at the inlet end of the first layer and with the supply of cold portions of gas oil between subsequent layers.

 In the case of these hydrodesulfurization methods, the conditions existing at the inlet end of the catalyst layer are critical, since it is here that the risk of hydrocracking is most pronounced, especially if the level of catalyst sulfurization decreases. This can, for example, occur when a low-sulfur feed begins to flow into the plant, or when a feed is used, in which the sulfur-containing impurities are mainly polycyclic compounds.

 A method of hydrotreating a feedstock, which is naphtha, is described in U.S. Pat. No. 4,243,519. It, apparently, is mainly based on conducting a completely vapor-phase process.

 A multistage method of hydrodesulfurization of an oil residue with the movement of the catalyst between the steps in the opposite direction with respect to the movement of gas and liquid is described in US patent A-3809644.

 U.S. Pat. No. 3,847,799 describes a process for converting dark petroleum oil to low sulfur liquid fuels in two reactors. The prepared hydrogen is fed into the second reactor, but it is fed in a mixture with hydrogen leaving the first reactor, which has been purified to remove hydrogen sulfide from it. Therefore, hydrogen is removed from the first reactor and recycled to the second reactor in a mixture with inert gases, which, accordingly, tend to accumulate in the gas recycle loop. Any condensate from the first reactor is mixed with the product leaving the second reactor.

 In a gas recycle hydrodesulfurization unit, some of the generated hydrogen sulfide, usually a small part of it, will remain in the liquid phase after separation of the product, while the rest of the hydrogen sulfide, usually the main part of it, will remain in the gas phase. Even in plants where interlayer cooling is practiced by introducing “cold portions” of recycle gas, the released hydrogen sulfide remains in the gas-liquid mixture as these phases pass through the catalyst bed. Therefore, the partial pressure of hydrogen sulfide is usually greatest at the output end of the catalyst layer or the final layer if more than one layer is used. Since the catalytic activity against hydrodesulfurization decreases with increasing partial pressure of hydrogen sulfide, the catalytic activity is the lowest at the output end of the layer, i.e. exactly where the highest catalytic activity is actually required, if less pliable polycyclic organic sulfur compounds are subjected to hydrodesulfurization.

 The catalysts used for hydrodesulfurization also typically have the ability to effectively affect the hydrogenation of aromatic compounds, provided that the sulfur content is low. The conditions necessary for hydrogenation of aromatic compounds are usually similar to the conditions necessary for hydrodesulfurization. But since the use of high temperatures is not conducive to achieving equilibrium in the reaction, the conditions necessary for hydrodesulfurization of cyclic and polycyclic organic sulfur compounds in a conventional plant do not contribute to the hydrogenation of aromatic compounds. In addition, since the design of conventional hydrodesulfurization plants is such that the partial pressure of hydrogen sulfide is high at the outlet end of the plant, the catalytic activity is accordingly reduced, and these conditions do not lead to a significant decrease in the content of aromatic substances in the raw materials being processed. As stated in an article entitled “Panel gives hydrotreating guides,” Hydrocarbon Processing, March 1989, pages 113 to 116, p.114 states the following.

The fundamental kinetic fact is that at pressures existing in conventional desulphurization apparatus of medium shoulder straps (at excess pressures from 500 to 800 psi (from 35.2 to 56.2 kg / cm ² >, it is difficult to achieve noticeable saturation Thus, if the level of aromatic substances in the raw material significantly exceeds a value of 20%, little can be done using typical desulfurization plants, using any catalysts we know to significantly reduce the aromatic content .

 Then there remain only unattractive alternatives in the form of using plants with high pressure, in the form of extraction of aromatic substances and all other "alternatives".

 The removal of hydrogen sulfide from a hydrodesulfurization unit with a gas recirculation system is usually facilitated by washing the recycle gas with an amine. Since the washing section must be large enough to remove sulfur contaminants at the highest levels possibly present in the raw materials to be cleaned, the washing equipment must be designed with the proper capacity, even if the installation will often run on raw materials with low sulfur content. The capital costs of creating such flushing equipment are significant.

It would be desirable to develop a more effective method for carrying out hydrodesulfurization of liquid hydrocarbon feedstocks, in particular a method where the risk of hydrocracking reactions is substantially eliminated. It would be further desirable to develop a hydrodesulfurization process in which the activity of the catalyst is controlled by the reactor such that at a given operating pressure, higher levels of hydrodesulfurization are achieved compared to those that can be achieved using the conventional method. It would also be desirable to develop a hydrodesulfurization process that would achieve a simultaneous significant reduction in the content of aromatic substances in the processed raw materials, especially in those types of raw materials where the aromatic content exceeds about 20%
The present invention accordingly makes an attempt to propose a method in which hydrodesulfurization can be carried out more efficiently in comparison with the conventional hydrodesulfurization method. An attempt is also being made to propose a hydrodesulfurization method in which the activity of the catalyst is controlled appropriately by the reactor, ensuring the achievement of elevated levels of hydrodesulfurization of the feed. Further, an attempt is made to propose a method of hydrodesulfurization, which also provides a significant reduction in the content of aromatic substances in the feedstock, which is achieved simultaneously with hydrodesulfurization.

According to the present invention, there is provided a hydrodesulfurization process for continuously conducting hydrodesulfurization of a liquid sulfur-containing hydrocarbon feed, which includes:
a) the formation of a hydrodesulfurization zone maintained under hydrodesulfurization conditions and including a column reactor with a plurality of reaction plates mounted on top of each other, where each plate corresponds to a corresponding reaction stage capable of holding a given volume of liquid and loading a sulfidized solid-phase hydrodesulfurization catalyst, liquid draining means associated with each reaction plate and designed to ensure the passage of liquid down the column p actor with such plates while holding thereon loading solid catalyst and the ascending gas movement means associated with each reaction tray adapted to feed gas to such a plate from under it and the mixture of liquid and catalyst on that tray;
b) supplying liquid sulfur-containing hydrocarbon feed to the uppermost plate of said set of reaction plates;
b) the supply of hydrogen-containing gas under the lowest plate of the said set of reaction plates;
d) allowing liquid to pass down the column reactor from plate to plate;
d) allowing hydrogen-containing gas to pass up the column reactor from plate to plate;
e) extracting from the uppermost plate of said set of reaction plates an exhaust gas containing hydrogen sulfide formed during hydrodesulfurization; and
g) extraction from the lowest plate of the said set of reaction plates of a liquid hydrocarbon product with a low sulfur content.

 Typically, the gas entering the uppermost plate contains a sufficient amount of hydrogen sulfide, and (simultaneously or separately) the liquid feed contains a sufficient amount of sulfur-containing material selected from hydrogen sulfide and active sulfur-containing materials, which is necessary to maintain the catalyst charge therein in sulfated form.

Active sulfur-containing substances are understood to mean substances that very quickly form hydrogen sulfide under conditions of hydrodesulfurization in the presence of a hydrodesulfurization catalyst. Examples of such substances are, for example, CS ₂ , COS, alkyl mercaptans, dialkyl sulfides and dialkyl disulfides.

The solid sulfidized catalyst used in the implementation of the method of the present invention is preferably selected from the group consisting of molybdenum disulfide, tungsten sulfide, cobalt sulfide, mixed tungsten nickel sulfide, mixed cobalt and tungsten sulfide, sulfated nickel-molybdate catalysts (NiMoS _x ) , sulfidized catalyst composition CoO-MoO ₃ / gamma-Al ₂ O ₃ and mixtures thereof.

Typical hydrodesulfurization conditions are conditions using pressures in the range of about 20 bar (2 • 10 ⁶ Pa) and up to about 150 bar (1.5 • 10 ⁷ Pa) and temperatures in the range of about 240 ^o C and about 400 ^o C Preferred conditions include conditions using a pressure in the region of from about 25 bar (0.5 • 10 ⁶ Pa) to about 100 bar (1 • 10 ⁷ Pa) and a temperature in the region of from about 250 ° C to about 370 • C.

 The liquid sulfur-containing hydrocarbon feed may be a mixture of saturated hydrocarbons, such as n-paraffins, isoparaffins and naphthenes, in different ratios. It may further comprise one or more aromatic hydrocarbons present in bulk amounts from about 1% and up to about 30% or more. If the feed is low in aromatic hydrocarbons, then hydrodesulfurization will be the dominant reaction. However, if the feedstock has a significant content of aromatic hydrocarbons, then, along with hydrodesulfurization, hydrogenation of these partially or fully saturated hydrocarbons can also occur to some extent. In this case, the hydrogen consumption will be correspondingly increased. The degree of occurrence of such hydrogenation of aromatic hydrocarbons will depend on the selected reaction conditions, and therefore, the degree of dearomatization of the feed that can be achieved will be affected by the selected reaction conditions.

 In the method of the present invention, stoichiometric amounts of the required hydrogen can, therefore, depend not only on the sulfur content of the feed, but they will also depend on the aromatic content. Actual hydrogen consumption will depend on the severity of the selected reaction conditions, i.e. accepted values of temperature and pressure. So, for example, under conditions of high stringency are understood the conditions under which a high working pressure, a high working temperature, or a combination thereof are applied. Generally speaking, the higher the temperature to which the hydrocarbon feed is heated under conditions of hydrodesulfurization at a given partial pressure of hydrogen, the closer the degree of hydrogenation of aromatic substances (or the degree of dearomatization) to that value that corresponds to the theoretical value of the achievable concentration. Thus, the amount of hydrogen consumed in the implementation of the method corresponding to the present invention depends not only on the nature of the feed, but it also depends on the severity of the conditions used.

If the feed is, for example, crude diesel fuel, then typically the reaction conditions in the method of the present invention are selected such that the weight residual sulfur content is reduced to about 0.5% or less, for example, to about 0 , 3% or less, and even to about 0.05% or less, and the volume content of aromatic substances decreased to about 27% or less, for example, to about 29% or less. If the required product is a light oil of "technical purity", then the process conditions are chosen with the expectation of lowering the sulfur content to very low levels and to the utmost reduction of the content of aromatic substances. Typically, the aim is to lower the aromatic content to a level that is sufficient to produce a light oil that is colorless, substantially non-aromatic, and is a mixture of paraffin and naphthenic oils that meet the following specifications:
Saybolt color + 20
Ultraviolet Absorbance Limits
Maximum spectral absorption per centimeter
280-289 μm 4.0
290-299 μm 3.3
300-329 μm 2.3
330-350 μm 0.8
If the desired end product is a light medical grade oil that meets the existing requirements of the U.S. Department of Food and Drug Administration, then the goal is to obtain a product with a maximum ultraviolet absorption capacity per centimeter at 260-350 nm of 0, 1, which is measured on dimethyl sulfoxide extract using the method described in the US Pharmacopoeia. According to other specifications, the sample should give a limit to weak staining in the test with hot acid when using sulfuric acid and not interact in the test with sodium plumbite. To meet these stringent requirements, it is necessary that all aromatic hydrocarbons present in the feedstock undergo hydrogenation effectively.

 In the method of the present invention, an amount of hydrogen should be used that is equivalent to at least the stoichiometric amount of hydrogen required to desulfurize the feed and achieve the desired degree of dearomatization. It is usually desirable to use an amount of hydrogen that is at least about 1.05 times the stoichiometric amount of hydrogen. In addition, consideration should be given to compensating for hydrogen dissolved in the recovered processed feed.

 In the method of the present invention, the feed rate of the hydrogen-containing gas should typically correspond to a molar ratio of incoming hydrogen to incoming raw materials, ranging from about 2: 1 to about 20: 1; it is desirable that this ratio be in the range of from about 3: 1 to about 7: 1.

Hydrogen-containing gas can be obtained in a known manner, for example, by vapor-phase reforming or partial oxidation of a hydrocarbon feed such as natural gas, followed by conventional steps, such as a water-gas shift reaction, CO ₂ recovery and pressure adsorption.

 On various reaction plates, different hydrodesulfurization conditions can be created. So, for example, the temperature on the uppermost reaction plate, which forms the first hydrodesulfurization zone, may be lower than on the next lower plate, where, in turn, it may be lower than on the next lower plate, etc.

 It is also conceivable that the temperature may rise from plate to plate in the direction from the topmost plate to the intermediate lower plate, but then the temperature drops from plate to plate on subsequent lower plates. Thus, the method can be implemented under conditions where the temperature rises from plate to plate, starting from the uppermost plate and moving to the intermediate plate, and then it decreases from plate to plate as the liquid phases move down the column reactor. In this mode of operation, the feed will be progressively exposed to hotter conditions at a substantially constant pressure and at progressively lowering partial pressures of hydrogen sulfide with the successive movement of the feed down the reaction plates. Since the partial pressure of hydrogen sulfide is lower on the second plate and on the subsequent plates in comparison with the top plate, the catalyst is effectively less sulfidized and, therefore, more active on the lower plates in comparison with the top plate. In this case, the efficiency of hydrodesulfurization is increased, since the conditions existing on the lower plates are more favorable for the interaction of the remaining sulfur-containing compounds, which tend to be the least reactive compounds, such as polycyclic sulfur-containing compounds. In addition, with a decrease in temperature on the lower plates and also an increase in catalytic activity on these plates due to a decrease in the partial pressure of hydrogen sulfide on these plates, the conditions turn out to be more favorable for the hydrogenation of aromatic compounds of raw materials, the equilibrium interaction of which, although it increases the partial pressure of hydrogen, appears to be limited at elevated temperatures.

 Since the hydrogen-containing gas flowing to the uppermost plate comes from the next lower plate, it usually contains some hydrogen sulfide. Since fresh gas mixed with recycle gas is fed under the lowest plate, the concentration of hydrogen sulfide in the gas is the highest in the gas entering the highest plate. The level of organic sulfur-containing compounds is the lowest in the liquid stream entering the lowest plate, but such compounds are the least reactive. Taking into account that sufficient partial pressure of hydrogen sulfide must be maintained on the lowest plate so that the catalyst present on this plate is in sufficiently sulfidized form, which eliminates the risk of hydrocracking on such a plate, the activity of the catalyst will tend to become highest on this plate, as a result where the conditions existing on this plate turn out to be favorable not only for hydrodesulfurization, but they also turn out to be favorable To effecting hydrogenation of aromatic compounds. Therefore, under appropriate operating conditions, a significant reduction in the content of aromatic hydrocarbons in the feed can be achieved while effectively removing more difficult to remove sulfur-containing substances, such as cyclic and polycyclic organic sulfur compounds.

 In the method of the present invention, it is also possible to use different catalysts on different plates. In this case, a catalyst that promotes hydrodesulfurization rather than hydrogenation of aromatic compounds can be used on the uppermost plate or on the uppermost several plates, while a catalyst having increased activity for hydrogenation of aromatic compounds is used on the lower plates.

 Means may be provided to allow the mixture of catalyst and liquid phase to be removed from one or more plates. Using appropriate valves and pumps, the same removal tools can also be used to charge fresh catalyst onto each plate, which is done either to change the amount of catalyst in response to a change in feed or feed conditions, or to replace the catalyst charge.

It is advisable to control the sulfur content in the gas and in the liquid feed on the very top plate so that it is certain that the amount of hydrogen sulfide there is sufficient to maintain the catalyst in sulfated form. It often turns out that the feed contains a sufficient amount of active sulfur-containing substance or the hydrogen-containing gas that enters there contains a sufficient amount of hydrogen sulfide, or both, which makes it possible to maintain the catalyst in a sufficiently sulfidized form. If for any reason a dangerously low level of hydrogen sulfide or active sulfur-containing substance can occur on the top plate, then a sufficient amount of hydrogen sulfide or an active sulfur compound such as CS ₂ should be added to the feed to the top plate. , COS, alkyl mercaptan, dialkyl sulfide or dialkyl disulfide, thereby ensuring the restoration of a safe level of sulfur on such a plate.

It is usually sufficient to create a sulfur concentration on the top plate in the form of hydrogen sulfide or active sulfur substance in the range of about 1 part per million parts (1 • 10 ^-4 ), and preferably at least about 5 parts per million (5 • 10 ^-4 %), and up to about 1000 parts per million (1 • 10 ^-1 %). Typically, the sulfur concentration may vary with an upward increase from about 10 parts per million (1 • 10 ^-3 %), for example, from about 40 parts per million (4 • 10 ^-3 %) and up to about 100 parts per million (0.01%).

It is further desirable to control the sulfur concentration at least on one of the lower plates, for example, on the lowest plate and, possibly, on each lower plate located under the highest plate, and introduce it into the stream entering such a plate, if any necessary, sufficient active sulfur-containing material, such as CS _2, COS, or an alkyl mercaptan, dialkyl sulfide or dialkyl disulfide, than it is possible to maintain the sulfur concentration in the range of about from 1 part per million (1 • 10 ^-4%) and example to about 1,000 ppm (0.1%), e.g., in the range from about 5 parts per million (5 • 10 ^-4%) to about 100 ppm (0.01%).

 Liquid hydrocarbon feedstocks can, for example, be selected from the group consisting of naphtha, kerosene, medium oil epaulettes (lighting kerosene), vacuum gas oils, lubricating bright stocks, diesel fuels, gas oils produced at atmospheric pressure, light recycle gas oils, light distillate fuels and similar materials.

 In a preferred method, the reaction plates have a pad that is inclined at an angle equal to or greater than the angle of repose of the catalyst particles in the liquid. So, each of the reaction plates may have a platform in the form of a truncated cone with a slope equal to or greater than the angle of repose of the catalyst particles in the liquid on the plate. Or each of the reaction plates may have a pad and a wall, where the pad consists of an inner part that is tilted down and inward from the central part, and an outer part that is tilted down and inward from the wall, and the tilt of each of the inner and outer parts equal to or greater than the angle of repose of the catalyst particles in the liquid on the plate.

 The gas supply means associated with each reaction plate may include one or more caps of a conventional design. In particular, the preferred design of each such cap may be a relatively high protruding tube, the height of which is sufficient to prevent drainage of liquid from the plate in case of temporary disruption of the upward movement of gas for any reason. This relatively high protruding tube is covered with a corresponding inverted relatively high cap. Such a protruding tube may also be provided with a check valve.

 If the required degree of desulfurization or dearomatization is not achieved in one pass through the column reactor, then the material to be processed can be subjected to a new treatment in a subsequent column reactor or in a different type of hydrodesulfurization reactor under more severe conditions.

 For a clearer understanding of the essence of the invention and for easier implementation, a preferred method corresponding to the present invention will now be described, which is done solely by way of example with reference to the attached schematic drawings, which have the following meaning.

 FIG. 1 is a flow diagram of a hydrodesulfurization unit for use in implementing the method of the present invention.

 FIG. 2 is a cross-sectional view of a plate of a column reactor of a hydrodesulfurization plant shown in FIG.

 FIG. 3 is the same cross section of a plate of a modified column reactor design.

 FIG. 4 is a flow chart of an experimental device.

 Figure 5 is a diagram of the reaction plate of the device shown in Fig. 4.

 FIG. 6 is a graph showing the relationship between the aromatic content of a product and the operating temperature.

 Specialists working in this field understand that, since FIG. 1 is a schematic, the industrial installation will also have other structural elements, such as heaters, coolers, temperature sensors, temperature controllers, pressure sensors, pressure relief valves, control valves, level controls and the like. The need to use such auxiliary structural elements is not associated with the present invention and follows from normal chemical engineering practice.

 According to FIG. 1, a hydrodesulfurization unit comprises a column reaction vessel 1 provided with a plurality of reaction plates 2, each of which holds the charge of the sulfidized hydrodesulfurization catalyst in the form of particles and a predetermined volume of liquid. Hydrogen-containing gas enters the reaction vessel 1 through line 3. The bubblers 4 installed on each plate 2 provide an upward movement of gas through the liquid on each plate 2. The sulfur-containing hydrocarbon feed to be processed is fed to the installation through line 5 and mixed with the recirculating liquid in line 6, forming a mixed defect in line 7, which enters the uppermost plate 2 of the reaction vessel 1. Discharges 8 provide the movement of liquid down the column reaction vessel 1 from the plate 2 to the next location laid below the plate and, finally, in the collection of 9 column reactor. Additional structural elements of one of the plates 2 with two different devices bubbler 4 and drain 8 are given below in connection with the description of figure 2 and 3.

 It can be seen from the foregoing that in the columned reaction vessel, gas and liquid move in countercurrent.

 Each plate 2 is equipped with a corresponding heat exchanger 10. Each plate 2 is equipped with a temperature controller II, and it controls the operation of the corresponding control valve 12, which controls the flow entering the corresponding heat exchanger 10, of the heat exchange medium entering the wiring 14 from line 13. For reasons of simplicity, figure 1 shows only one temperature controller II for the uppermost plate 2; in fact, each other plate 2 has its own corresponding temperature controller 11). Position 15 shows the layout of the return flow, and position 16 shows the reverse flow line of the heat transfer medium. In this way, it is possible to individually control the temperature on each plate 2.

 Exhaust gas is discharged from the upper part of the column reaction vessel 1 along line 17. It consists of vapors of liquid feed, gaseous products generated during the hydrodesulfurization reaction, including hydrogen sulfide, and inert gases contained in the incoming gas supplied to line 3. Vapor substances condense when passing through the condenser 19, and a two-phase mixture of gas and condensate enters through line 19 to the gas separator 20, equipped with a droplet stopper 21.

 The condensate is discharged from the separator 20 through lines 22 and 23 through the pump 24, and it is recycled to the separator 20 through lines 25 and 26 through a flow restrictor 27, which thereby creates a pressure in lines 25 and 26, which exceeds the pressure in the separator 20. Part of the fluid flowing through line 25 is returned to the column reactor 1 along lines 28, 29 and 6, which is controlled by a valve 30, which, in turn, is controlled by a level regulator 31 connected to the separator 20. The selected fluid stream flows through the line 28 through line 32 and through valve 33 and d tchik stream 34 to a selected lower tray 2; 1, a bottom plate 2 is selected in which line 32 is suitable, however a plate 2 located above the bottom plate can be taken. The flow passing through the valve 33 is controlled by a flow regulator 35, which is connected to the flow sensor 34. This feed liquid, flowing through line 32 to the lower part of the column reactor 1, characterizes the way in which reactive sulfur compounds can flow to the lower plates 2, what provides the ability to control the activity of the catalyst located on the lower plate 2, as will be discussed below.

 Gas from the separator 20 is discharged from the installation via line 36 and passes through a pressure relief valve 37 in lines 38 and 39, through which gas is discharged from the installation. This exhaust gas contains hydrogen sulfide obtained by hydrodesulfurization purification and can be further processed (for example, hydrogen sulfide can be removed and subjected to subsequent conversion to elemental sulfur by partial oxidation).

 The fluid accumulating in collector 9 enters line 40 and passes through flow control valve 41 to refrigerator 42. Flow regulator 43 controls valve 41. Chilled fluid with desorbed hydrogen (which is less soluble in cold liquid hydrocarbons compared to hot liquid hydrocarbons ) passes through line 44 to the separator 45, where the gas is separated from the liquid. It is equipped with a droplet chipper 46 and a gas return line 47, through which gas is returned to the bottom of the column reactor 1. The liquid collected in the separator 45 passes to line 48 through a valve 49, which is controlled by a level 50, to the separator 51, where the separation takes place gas from the liquid. This separator is equipped with a droplet stopper 52 and a gas exhaust line 53, as well as a product recovery line 54.

55 indicates the line by which a controlled amount of hydrogen sulfide or an active sulfur-containing substance such as CS ₂ , COS, alkyl mercaptan with the formula RSH. an alkyl sulfide with the formula RSR or a dialkyl disulfide with the formula RS-SR where R is an alkyl group, such as n-butyl, which can usually be supplied as a solution in a hydrocarbon solvent, as is necessary for the operation of the hydrodesulfurization unit, as will be described below.

Under the operation of the installation shown in Fig. 1, the liquid feed to line 5 passes through the reactor 1 and ultimately leaves the installation through line 43. When passing through the reactor 1, organic sulfur compounds are mainly converted to hydrogen sulfide, some of which is in the installation in line 53, being in the liquid product in a dissolved state. The separation of hydrogen sulfide from the liquid product can be carried out in a known manner, for example, by desorption in an installation located in the processing line below (not shown). Although the fresh hydrogen-containing gas mixed with recycle located in line 3 is substantially free of sulfur, the liquid entering the bottom plate 2 of reactor 1 usually contains a sufficient amount of hydrogen sulfide, which makes it possible to find the hydrodesulfurization catalyst on it in an adequately sulfided state and, therefore, , minimizes any risk of hydrocracking reactions occurring on the bottom plate 2 of reactor 1. On the overlying plates 2, the gas stream comes from the lower container Christmas tree 2, and, thus, it will contain hydrogen sulfide, which appears due to contact with the liquid phase located on such a plate. Therefore, on each plate 2 of reactor 1, the partial pressure of hydrogen sulfide will be sufficient to find the catalyst charge in an adequately sulfidized state. If for some reason the partial pressure of hydrogen sulfide on some plate 2 of reactor 1 should fall below a safe level, then an appropriate amount of a sulfur-containing substance, preferably H ₂ S, CS ₂ , COS or an active organic sulfur-containing substance, such as alkyl mercaptan (for example, n-butyl mercaptan), dialkyl sulfide (such as di-n-butyl sulfide) or dialkyl disulfide (e.g. di-n-butyl disulfide), is fed (usually as a solution in a hydrocarbon solvent) to line 54, which increases the sulfur content in the stream, post falling onto the appropriate plate 2. Since CS ₂ , COS, alkyl mercaptans, dialkyl sulfides and dialkyl disulfides are easily and quickly converted to hydrogen sulfide, you can be sure that the catalyst load on each plate 2 of reactor 1 will be in an adequately sulfided state, which excludes any risk of significant hydrocracking in reactor 1.

 Figure 2 illustrates the design of the plate 2, suitable for use in a relatively small reactor 1. In this case, the truncated-conical part or diaphragm 70 reaches the wall 71 of the reactor 1 and completely covers the cross-section of the reactor 1, excluding those places where the drain 72 for liquid and gas inlet 73. The slope of the truncated-conical diaphragm 72 is equal to or greater than the angle of repose of the solid powder hydrodesulfurization catalyst when it is on a plate 2 under a layer of liquid.

 The gas inlet 73 consists of an axial tube 74, which is open at its upper end and which is covered by a cap 75. The annular element of the mesh type 76 prevents the catalyst particles from becoming sucked under the cap 75.

 The cylindrical baffle 77 symmetrically surrounds the cap 75, and it is located so that it is below the liquid level 78, located on the plate 2, and the height of the liquid level is determined by the height of the upper end of the drain 72. The top of the drain 72 is equipped with a grid 79, which returns the catalyst particles back to plate 2. Position 80 shows the drain coming from the next plate 2 above (which is not shown in the figure).

 The baffle 77 facilitates mixing of the suspension from the liquid and the catalyst with the incoming gas. The vertical extent of the septum 77 is not critical, but in general it should be 1/3 to 3/4 of the vertical height, counting from the surface of the diaphragm 70 to the surface of the liquid 78. It is desirable that the vertical position of the septum 77 be symmetrical or almost symmetrical . In the zone located inside the partition 77, the fluid flow is usually directed upward, while behind the partition 77 the fluid movement usually occurs downward. It is desirable that the area of the zone located inside the partition 77 is approximately equal to the total area behind the partition 77.

 The gas inlet 73 is provided with a valve 81 preventing back suction.

 The temperature of the liquid and catalyst located on the plate 2 can be controlled by means of a heat exchanger 82.

 Under operating conditions, the ascending gas is bubbled through the liquid located on the plate 2, and the mixture of the liquid and the catalyst is mixed, which ensures that the catalyst particles stay in the form of a suspension. The baffle 77 promotes good circulation in the liquid on the tray 2. At the proper gas supply rate, gas bubbles, generally shown at 83, keep most of the catalyst particles (shown at 84) in a suspended state. (It should be noted that, in order not to complicate the drawing, the figures show only a few gas bubbles 83 and a few catalyst particles 84).

 In FIG. 3 shows another possible design of the plate 2 of the reactor 1 of the installation shown in figure 1. The horizontal diaphragm, or baffle 100 extends to the wall 101 and completely covers the cross-section of the reactor 1, excluding those places where there is a drain 102 for liquid and gas inlet 103. The baffle 100 has an axial truncated-conical part 104 surrounding the gas inlet 103, and an annular the inclined portion 105 adjacent to the wall 101. The plate 2 can thereby hold a volume of liquid whose surface is indicated by 106 and the volume of which is determined by the height of the overflow level at the drain 102, counting from the partition 100. Each plate 2 is Also, there is some loading of a solid sulfidized hydrodesulfurization catalyst, the particles of which are shown schematically at 107. Such particles 107 are in suspension in a liquid on a plate 2 under the influence of stirring with rising gas, as will be described below. To prevent the entrainment of particles 107 with the flowing liquid through the drain 102, the top of the drain 102 is provided with a mesh 108. The inclination of the truncated-conical part 104 and the inclination of the part 105 are equal to or greater than the angle of repose of the solid catalyst particles when they are in the liquid on the plate 2.

 The gas inlet 103 delivers upward gas to the annular bubbler 109, which surrounds the truncated-conical part 104, which is carried out through the spider from the pipes 110. The back suction of liquid into the inlet 103 is prevented by the presence of an anti-air valve III.

 The annular traction screens or baffles 112 and 113 are located in the mass of liquid on the plate 2, one of the baffles being inside and the other outside the annular bubbler 109, which ensures mixing of the suspension from the liquid and the catalyst with ascending gas. The vertical extent of the screens 112 and 113 is not critical, but in the general case it should be from 1/3 to 3/4 of the vertical height, counting from the diaphragm 100 to the surface of the liquid 106. It is desirable that the screens 112 and 113 are located symmetrically in the vertical direction or almost symmetrically. In the annular zone located between the screens 112 and 113, the liquid usually moves upward, while inside the screen 112 and outside of the screen 113 the liquid usually moves downward. It is desirable that the area of the annular zone located between the screens 112 and 113 be approximately equal to the sum of the areas inside of the screen 112 and outside of the screen 113.

 Reference numeral 114 shows a drain from the next tray located above the tray shown in FIG. 3. The liquid level in the drain 114 is shown at 115, and the height H of this liquid level above the liquid level 116 located on the plate 2 is determined by the sum of the liquid level on the plate that feeds the drain 114 (i.e., on the plate located above the illustrated plate 2) and pressure drop arising due to the existence of resistance to flow.

 The temperature at the plate 2, shown in figure 3, can be controlled by means of a heat exchanger 117.

 In yet another possible device (not shown), a heat exchanger 117 is absent, but an external heat exchanger is connected to the column reactor through which liquid taken from the plate 2 can be pumped to regulate the temperature.

 The invention is further illustrated by the following example.

 Example.

 The process of hydrodesulfurization of a synthetic mixture of an organosulfur compound (dibenzothiophene) dissolved in a saturated hydrocarbon solvent (n-hexadecane) was studied in the apparatus shown in FIG. 4.

The liquid feed consists of a solution of dibenzothiophene in normal hexadecane (114 g of dibenzothiophene per 1 liter of solution), and it is contained in the feed tank 201. The feed tank 201 is loaded with pre-prepared solution through line 202 and then purged with dry nitrogen through lines 202 and 203. The tank supply 201, a distribution line 204, a metering pump 205 and a supply line 206 are placed in a chamber (not shown) in which hot air circulates and which is thermostated at 50 ± 5 ^o С, which completely eliminates the possibility of formation of a solid substance ( since the melting point of n-hexadecane is approximately 20 ^o C). The liquid flow into the column reactor 207 is supplied by a metering pump 205, and it is checked from time to time by a burette located in a chamber with hot air (also not shown). An electric resistance heater 208 is wound around the feed line 206, as a result of which the feed liquid can be preheated before being fed to the top of the column reactor 207. The column reactor consists of a vertical metal cylinder 2.0 m high and an inner diameter of 7.5 cm, containing eight reaction tray sections from 209 to 216. (The design of one of the plates from 209 to 216 is shown in more detail in figure 5 and is explained in detail below). Hydrogen is supplied to a line 212 connected to the lower part of the reactor 207 (above the liquid level in its collector 218), and the required hydrogen flow is established by means of the mass flow controller 219.

 The entire reactor 207 is enclosed in a casing with electric heating and forced circulation of heated air (casing not shown).

The liquid moves downward from the uppermost reaction tray 209 to the lowest reaction tray 216, sequentially flowing from one tray to the next tray below; and while the hydrogen-containing gas passes up through the plates from 216 to 209, bubbling through the liquid located on each plate. The fluid is collected in a collector 218, located at the base of the reactor 207, discharged from the system via line 220 and cooled by a 45 ^° C refrigerator, which is controlled by a valve 222 operating from a level regulator 223. Samples of liquid are taken for analysis from line 224.

The gas phase leaves the reactor 207 via line 225 and is cooled by a condenser 226, which receives water at a temperature of 40 ^o C; and the cooled gas and condensate passes through line 227 and enters the drum 228. The gas phase then passes through line 229 and a pressure control valve in flow 230, which sets the total operating pressure in the system. The gas passes to an analytical flow measuring device and to a combustion device (they are not shown). The fluid collected in the drum 228 can be returned to the plate 209 via line 231, which is controlled by a valve 232 that operates from a level sensor 233 mounted on the drum 228, or the sample can be removed via line 234 through a manual control valve 235.

 An example of the design of one of the reaction plates from 209 to 216 is shown in FIG. The vertical walls of the column reactor are shown at 240. The plate is also provided with a loading and unloading tube 241, which is equipped with a blocking valve 242 used to load or unload the catalyst slurry from the corresponding reaction plate.

The horizontal cross section of the column reactor 207 is covered by a truncated-conical diaphragm shown in the vertical cross section at 243 and 244. The inclined portion of the diaphragm 243 forms an angle of 30 ^° with the horizontal line. The horizontal part of the diaphragm 244 is 4 cm in diameter, and vertical tubes with an inner diameter of 4 mm pass through it in two places.

 The tube 245 passes through the diaphragm along the vertical axis of the reactor and extends upward under the cap 246 to a distance of 22 cm. The part of the tube 243 protruding below the lower surface of the horizontal part 244 is small and can be considered equal to zero. The outer diameter of cap 246 is 20 mm; a 2 mm gap between the lower edge of the cap 246 and the upper surface of the horizontal portion 244 is covered by a screen 247, which is a fine stainless steel mesh that prevents particles of catalyst from entering the inner region of the cap 246.

 The tube 248 protrudes 9 cm above the horizontal part 244 and passes downward, ending in the space under part 244. It is covered by a grid 249, which eliminates the possibility of ingress of catalyst particles. The height of the top of the tube 248 determines the height of the liquid 250 on the plate. The lower end of the tube 248 is below the liquid level present on the underlying plate (or in the case of the plate 216, the lower end of the tube 248 is below the surface of the liquid present in the collector 218 of the reactor 207).

 Under operating conditions, the plate (i.e., one of the plates from 209 to 216) receives liquid from the overlying plate through the tube 248, as described above (or in the case of the plate 209, the liquid comes from line 206); the liquid flows through the catalyst holding device 249 and flows to the next underlying tray. The gas passes through the tube 245, the inner region of the cap 246, the screen 247 and bubbled through the liquid on the plate; due to the mixing initiated by the bubbles, the catalyst particles 252 are in a state of turbulent suspension. The gas phase leaving the surface of the liquid 250 passes through the axial tube of the overlying tray (or, in the case of the tray 209, it passes through line 225). In this way, the liquid phase passes down from the plate 209 to the plate 210, etc. to plate 216 and collector 218; and the liquid phase, thereby, is in countercurrent contact with the gas phase passing through the plate 216 up to the plate 215, etc. higher on plate 209 and in line 225.

 After purging the installation with nitrogen and loading the power tank 201 with the feed solution, the discharge line 229 is opened into the atmosphere, for which a bypass line is opened around the valve 230 (not shown).

With valve 242 open, line 241 is loaded onto each of the plates 209 to 216 with catalyst slurry. In this way, 35 cm ^{3 of} catalyst in the form of particles ranging in size from 0.1 to 0.5 mm, located in 290 cm ^{3 of} n-hexadecane, are loaded onto each of the plates 209 to 216. The catalyst is CoO-MoO ₃ / gamma-alumina (sulfidized form), which has previously been reduced in hydrogen, cooled and immersed in n-hexadecane. To remove the catalyst from line 241 per plate, the line is washed with 45 cm ^{3 of} n-hexadecane. Then, valve 242 is closed. A nitrogen stream is supplied through line 217, and it passes through column 207 and is discharged into the atmosphere through line 229. The nitrogen stream is replaced by a hydrogen stream, and the pressure in the installation is slowly brought to 35 bar (3.5 • 10 ⁶ Pa ) (in absolute value), and, using a column heater, in 4 hours the temperature is increased from 30 ^o C to 325 ^o C.

When the working pressure is reached, which occurs after about 45 minutes, the hydrogen flow rate is increased to 465 l / h (under normal conditions of temperature and pressure). At this moment, a solution of carbon disulfide СS ₂ in n-hexadecane with a concentration of 10 g / l is completed on a plate 216 through line 241 at a speed of 500 cm ³ / h, which ensures that the catalyst is in a sulfated state. After three hours, the supply of carbon disulfide solution to the plate 216 is stopped, a feed liquid is started to be supplied to the plate 209, and its feed rate is set to 587 cm ³ / h. Over time, the liquid level in the collector 12 rises, and then the liquid begins to leave the installation, which occurs under the control of the level sensor 223 and control valve 222.

 From time to time, a liquid product is taken from line 224, and analyzed for dibenzothiophene by gas-liquid chromatography. After 12 hours of stationary operation, the analysis results began to indicate that dibenzothiophene turned 99.1% into sulfur-free products and chromatographic recordings showed quantitatively unidentifiable traces of tetrahydro- and hexahydro derivatives of dibenzothiophene. Over the next three days of operation, the degree of conversion of dibenzothiophene progressively increased to a value of 99.5% and it stabilized at this level.

Comparative example
In a comparative example, 280 cm ^{3 of} the same catalyst in the form of tablets with a diameter of 1 mm and a length of 1-3 mm were loaded into a reactor with an inner diameter of 25 mm, resulting in a catalyst layer 57 cm high. When this conventional reactor is operated under direct gas conditions and liquid down, using a feed solution of the same composition and at the same temperature, pressure and gas and liquid flow rates as those in the example above, we obtained the degree of dibenzothiophene conversion of only 96.4%, which means flax worst characteristics in comparison with the countercurrent column (the amount of unreacted DBT is more than seven times higher).

 The hydrogenation of aromatic compounds in the presence of a hydrodesulfurization catalyst depends on a number of factors, including thermodynamic and kinetic factors, as well as catalytic activity and its effectiveness.

 From the point of view of thermodynamics, the hydrogenation of an aromatic compound, for example, an aromatic hydrocarbon, is an exothermic process. In addition, the depth of the reaction under certain conditions is limited by considerations such as equilibrium under these conditions. In general, equilibrium is less favorable at high temperatures. Therefore, it is advantageous to conduct the process at reduced interaction temperatures, if this is possible.

 The kinetics of hydrogenation of aromatics hydrogenation reactions are favored by high temperatures. Thus, the rate of hydrogenation of aromatic compounds increases significantly with increasing temperature at a given fixed value of the partial pressure of hydrogen, which is true if the concentration of aromatic substances in the reaction mixture exceeds the equilibrium value at the temperature considered.

 The ability of a given catalyst mass with a specified range of particle size to catalyze the hydrogenation reaction of aromatic compounds is a function of the washing intensity of the catalyst particles, the degree of sulfidation of the catalyst, and the mass transfer rates of hydrogen and hydrogen sulfide to and from the catalyst surface. Generally speaking, the highest catalytic activity in relation to the hydrogenation of aromatic substances is manifested by a catalyst with a low degree of sulfidation, which is affected by a turbulent biphasic (gas-liquid) mixed stream.

 Fig. 6 is a graph schematically illustrating the effect of these various factors on the hydrogenation reaction of aromatic compounds. Figure 6 shows the percentage of aromatic compounds in the product depending on the temperature at a given partial pressure of hydrogen. Line AA 'shown in FIG. 6, characterizes the change with temperature (at a fixed partial pressure of hydrogen) of the kinetically limited content of aromatic compounds in a product obtained from this raw material with a certain aromatic content on a fixed amount of catalyst. Line B-B 'characterizes the content of aromatic compounds in the product obtained in the same reaction system, limited by equilibrium, depending on temperature. At this temperature, the line XV (or X'Y ') characterizes the excess content of aromatic compounds in the product and, therefore, is a measure of the driving force developed by the catalyst. Point O characterizes the lowest content of aromatic compounds achievable on this system, and it is achievable only with the proper combination of the most favorable kinetic conditions and less favorable equilibrium conditions, the favorableness of which decreases with increasing temperature.

 If the activity of the catalyst can be somehow increased, for example, by a controlled change in the degree of sulfidation of it, then a new curve can be obtained, such as curve C-C ', on which a new lower level of optimal content of aromatic compounds appears (point O' )

 In practice, the crude oil feed contains many different aromatic compounds and sulfur compounds, each of which is characterized by its own kinetics of hydrogenation and hydrodesulfurization. Preliminary removal of less heat-resistant substances and removal of bound hydrogen sulfide from sulfur compounds, i.e. a possible way of implementing the present invention makes it possible to obtain significant advantages when using the method corresponding to the present invention, in comparison with the usual practice of the hydrodesulfurization process.

Claims (7)

 1. A method of continuous hydrodesulfurization of liquid sulfur-containing hydrocarbon feedstocks by forming a hydrodesulfurization zone maintained under hydrodesulfurization conditions and including a column reactor with a plurality of reaction plates mounted one above the other, where each plate corresponds to a corresponding reaction stage capable of holding a predetermined volume of liquid and loading of sulfidized solid phase hydrodesulfurization catalyst having liquid draining means associated with each rea plate and designed to ensure the passage of liquid down the column reactor from the plate while holding on the last load of solid-phase catalyst, means for the upward movement of gas associated with each reaction plate and designed to supply gas under the plate, feed the feed to the upper reaction plate, feed hydrogen-containing gas under the lower plate, ensuring the passage of liquid from top to bottom through the column reactor from the plate to the plate, ensuring the passage of hydrogen-containing gas from the bottom up the knee reactor from plate to plate, draining from the upper plate gas containing hydrogen sulfide formed during hydrodesulfurization, draining from the lower plate a liquid hydrocarbon product with a low sulfur content, characterized in that the mixture of liquid is mixed on each reaction plate and the catalyst due to the supply of bottom up plate gas flow. 2. The method according to claim 1, characterized in that they use a solid sulfidized catalyst selected from the group consisting of molybdenum disulfide, tungsten sulfide, cobalt sulfide, sulfated nickel-molybdate catalysts (NiMoS _x ), sulfated catalyst CoO MoO ₃ / gamma-Al ₂ O ₃ and mixtures thereof. 3. The method according to PP.1 and 2, characterized in that they maintain the pressure of hydrodesulfurization 2 15 MPa and a temperature of 240 400 ^o C. 4. The method according to claim 1, characterized in that they maintain the pressure of hydrodesulfurization 2.5 to 10.0 MPa and a temperature of 250 370 ^o C.  5. The method according to claims 1 to 3, characterized in that the reaction plates are used, each of which has a bottom inclined at an angle equal to or greater than the angle of repose of the catalyst particles in the liquid.  6. The method according to claims 1 to 4, characterized in that the reaction plates are used, each of which has a truncated-conical bottom with a slope equal to or greater than the angle of repose of the catalyst particles in the liquid on the plate.  7. The method according to PP.1 to 5, characterized in that the use of reaction plates, each of which has a bottom and a surrounding wall, and the bottom consists of a Central bottom part, which is tilted down from the center of the bottom to the periphery, and a peripheral bottom part, which is tilted down from the surrounding wall to the center, and the angle of inclination of the central and peripheral bottom is equal to or greater than the angle of repose of the catalyst particles in the liquid present on the plate.

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