RU2241021C2 - Process of hydrodeculfurization of oil feedstock and process of hydrodesulfurization of cracked naphtha (options) - Google Patents

Abstract

FIELD: petroleum processing and petrochemistry.

SUBSTANCE: oil feedstock stream is subjected to hydrodesulfurization wherein only insignificant amount of olefins become saturated. Process is accomplished in two stages involving interstage removal of hydrogen sulfide over pipelines to prevent formation of recombinant mercaptans. Optionally, cracked naphtha can be subjected to the same hydrodesulfurization process.

EFFECT: increased degree of desulfurization with reduced loss in olefin content.

9 cl, 2 dwg, 3 ex

Description

The present invention relates to a method for desulfurization of catalytically cracked naphtha with a full boiling range by reaction of hydrogen with organic sulfur compounds present in the feed in the presence of hydrodesulfurization catalysts. In particular, the present invention can use catalytic distillation steps that reduce sulfur to very low levels, make hydrogen use more efficient, and cause less olefin hydrogenation in the case of a full boiling range naphtha stream.

Oil distillate streams contain a variety of organic chemical components. Typically, streams characterize them with boiling ranges that determine the composition. Stream processing also affects composition. For example, the products of either catalytic cracking or thermal cracking processes contain high concentrations of olefin substances, as well as saturated substances (alkanes) and polyunsaturated substances (diolefins). In addition, these components may be any of a variety of isomers of these compounds.

The composition of the crude naphtha obtained from the oil cube, or the fraction of the direct race naphtha, is primarily affected by the source of crude oil. Naphtha from sources of paraffin oil feed contains more saturated linear or cyclic compounds. The general rule is that most of the low-sulfur (low-sulfur) crude oil and naphtha is paraffinic. Naphthenic crude oil contains more unsaturated, cyclic and polycyclic compounds. Higher sulfur crude oils tend to be naphthenic. The processing of various fractions of direct race naphtha may vary slightly depending on their composition due to the source of raw materials.

The reformed naphtha or reformate product typically does not require any further processing, except possibly distillation or solvent extraction to remove the valuable aromatic product. Reformed naphtha essentially has no sulfur impurities due to the rigidity of its pretreatment for the process and the process itself.

The cracked naphtha obtained in the catalytic cracking unit has a relatively high octane number due to the olefinic and aromatic compounds contained therein. In some cases, this fraction can make such a large contribution that it makes up half the gasoline in the processed pool together with a significant part of the octane.

The catalytically cracked naphtha material of the gas boiling range currently forms a significant part (~ 1/3) of the gasoline product pool in the USA and it gives the largest share of sulfur. Sulfur impurities may require removal by hydrotreating, in order to meet product specifications or to comply with environmental regulations. Some consumers want the sulfur content in the final product to be below 50 parts by weight per million.

The most common method for removing sulfur compounds is hydrodesulfurization (HDS), when the petroleum distillate is passed over a particulate solid catalyst comprising a hydrogenation metal supported on an alumina support. The feed contains additional significant amounts of hydrogen.

The following equations illustrate the reactions in a typical HDS setup:

(1) RSH + H ₂ → RH + H ₂ S

(2) RCl + H ₂ → RH + HCl

(3) 2RN + 4H ₂ → RH + NH,

(4) ROOH + 2H ₂ → RH + H ₂ 0

Typical operating conditions for HDS reactions are:

Temperature ° F 600-780

Pressure, psi inch hut 600-3000

The recirculation rate of H ₂ std. ft / barrel 1500-3000

Replenishment of fresh H ₂ , stand. cubic foot / barrel 700-1000

After hydrotreating is complete, the product can be fractionated or simply distilled to isolate hydrogen sulfide and collect desulfurized naphtha. Loss of olefins during accidental hydrogenation is detrimental due to a decrease in the octane number of naphtha and a decrease in the olefin pool for other applications.

In addition to supplying high octane mixed components, cracked naphtha is often used as a source of olefins in other processes, such as esterification. Hydrotreating conditions of the naphtha fraction to remove sulfur will also saturate a certain amount of olefinic compounds in the fraction, lowering the octane number and causing a loss of the source of olefins.

Various suggestions have been made to remove sulfur, while at the same time retaining the more essential olefins. Since the olefins in cracked naphtha are mainly contained in the low boiling fraction of this naphtha, and sulfur-containing impurities tend to concentrate in the high boiling fraction, the most common solution was pre-fractionation before hydrotreating. Pre-fractionation gives the naphtha of the boiling range of light naphtha, which boils in the range of C ₅ to about 250 ° F, and the naphtha of the boiling range of light naphtha, which boils in the range of about 250-475 ° F.

The predominant light or low boiling sulfur compounds are mercaptans, while thiophenes and other heterocyclic compounds are heavier or high boiling compounds. Separation by fractionation alone will not remove mercaptans. However, in the past, mercaptans were removed by oxidative methods, including alkaline washing. The combination of oxidative removal of mercaptans, followed by fractionation and hydrotreating of heavier fractions, is described in US Pat. No. 5,320,742. In the oxidative removal of mercaptans, mercaptans are converted to the corresponding disulfides.

U.S. Pat. with diolefins with the formation of sulfides, which are removed in excesses together with higher boiling sulfur compounds. The undercuts are hydrodesulfurized in a second distillation column reactor, where the sulfur compounds are converted to H ₂ S and removed.

The use of two or more sequential treatments with catalytic hydrodesulfurization was carried out in practice for the processing of petroleum feeds to remove organic sulfur compounds, however, in these previous processes, the product contains a significant amount of “recombinant sulfur”. By recombinant sulfur is meant new organic sulfur compounds, mainly mercaptans, which are formed in the reverse reaction of H ₂ S from previous hydrodesulfurization or hydrodesulfurization in subsequent hydrodesulfurization processes with olefins contained in the feed. H ₂ S can recombine to form mercaptans, thus increasing the amount of sulfur in the product. In addition, the presence of H ₂ S can cause greater saturation of olefins, leading to loss of octane number and consumption of hydrogen.

The product of successive multilayer desulfurization processes, of course, has a lower sulfur content than the raw materials that underwent less processing, but each subsequent processing had less efficiency than expected due to the sulfur obtained by recombination.

In the present method, the efficiency of the subsequent processing was increased by separating H ₂ S from the processed raw materials before the raw materials arrived for subsequent hydrodesulfurization.

An advantage of the present invention is that the full boiling range naphtha stream is hydrodesulphurised, while the olefin content is high relative to the content in the feed by sequential hydrodesulphurisation with the removal of H ₂ S after each hydrodesulphurisation step. It is believed that H ₂ S was not removed between the hydrodesulfurization treatments in successive hydrodesulfurization steps in the prior art, but rather the previous practice was the removal of H ₂ S after the final hydrodesulfurization.

SUMMARY OF THE INVENTION

In a broad context, the present invention relates to a method for hydrodesulfurization of petroleum feedstocks containing organic sulfur compounds and preferably olefins by at least two sequential treatments of the feedstock with hydrogen in the presence of a hydrodesulfurization catalyst to convert part of the organic sulfur compounds to H ₂ S, where the improvement is removal of H ₂ S from the feed after each treatment indicated.

In one embodiment, in practice of the present invention, a full boiling range naphtha is subjected to a two-step process to remove organic sulfur compounds by hydrodesulfurization. In the first stage the full boiling range naphtha is subjected to desulfurization in a distillation column reactor which acts as a stripper bleed overheads hydrodesulfurized light naphtha formed in the reactor with H ₂ S. A significant proportion of H ₂ S is removed from the overhead receiver / separator. The heavier fraction is subjected to hydrodesulfurization and removed as undercuts. The undercuts and overheads are then fed to the H ₂ S desorption column, where the remaining H ₂ S is separated from the desulfurized naphtha. The bottoms from the H ₂ S separation column are then fed to a second reactor (either a standard single-pass reactor or a second distillation column reactor). Removal of H ₂ S serves two purposes. It prevents the formation of recombinant organic sulfur compounds and allows the use of less stringent conditions for the same sulfur removal, while at the same time preventing the hydrogenation of olefins.

As used herein, the term “distillation column reactor” means a distillation column that also contains a catalyst, such that reaction and distillation simultaneously occur in the column. In a preferred embodiment, the catalyst is prepared in the form of a structure for distillation and it serves as a catalyst and as a structure for distillation.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a simplified process diagram using two straight-through hydrodesulfurization reactors, which are arranged one after the other, and where H ₂ S is removed between the two reactors.

Figure 2 is a simplified process diagram using two hydrodesulfurization reactors that are arranged one after the other, the first being a catalytic distillation reactor having two hydrodesulfurization zones, one for a lighter fraction and one for a higher boiling point, which are separately processed are then combined in a stripping column to remove H ₂ S before being fed to the hydrodesulfurization unit with a direct passage.

DETAILED DESCRIPTION

Process feeds include a sulfur-containing oil fraction, in particular a fraction from a catalytic fluidized bed cracking unit (FCCU), which boils in the gas boiling range (C ₅ to 420 ° F). Typically, the method is useful for naphtha boiling range material from products of a catalytic cracking unit since they contain desirable olefins and undesired sulfur compounds. The straight race naphtha contains very little olefin material, and if the source of the crude oil is not “sulphurous”, very little sulfur.

The sulfur content in the fractions subjected to catalytic cracking will depend on the sulfur content in the raw materials for the cracking unit, as well as on the boiling range of the selected fraction used as raw material for the process. Lighter fractions will have a lower sulfur content than higher boiling fractions. The head fraction of naphtha contains most of the high octane olefins, but a relatively small amount of sulfur. The sulfur compounds in the head fraction are mainly mercaptans and typical compounds are methyl mercaptan (T _boil. 43 ° F), ethyl mercaptan (T _boil. 99 ° F), n-propyl mercaptan (T _boil. 154 ° F), isopropyl mercaptan ( _bp. 135-140 ° F), izobutilmerkaptan _(bp. 190 ° F), tert-butyl mercaptan _(bp. 147 ° F), n-butyl mercaptan _(bp. 208 ° F), sec-butyl mercaptan _{(bp .} 203 ° F), izoamilmerkaptan _(bp. 250 ° F), n-amilmerkaptan (bp. 259 ° F), α -metilbutilmerkaptan _(bp. 234 ° F), α -etilpropilmerkaptan _(bp. 293 ° F) , n-hexyl mercaptan (T _bp. 304 ° F), 2-mercaptohexane (T _bp. 284 ° F) and 3-mercaptohexane (T _boiling. 135 ° F). Typical sulfur compounds found in the higher boiling fraction include heavier mercaptans, thiophenes, sulfides and disulfides.

The reaction of organic sulfur compounds in a process stream with hydrogen over a catalyst to form H ₂ S is usually called hydrodesulfurization. Hydrotreating is a broader term that includes the saturation of olefins and aromatics and the reaction of organic nitrogen compounds to form ammonium. However, hydrodesulfurization is included in it and sometimes it is simply called hydrotreatment.

Catalysts that are useful for the hydrodesulfurization reaction include Group VIII metals, such as cobalt, nickel, palladium, individually or in combination with other metals, such as molybdenum or tungsten, on a suitable support, which may be alumina, silica - alumina, titanium dioxide - zirconia or the like. Usually, metals are present in the form of metal oxides supported on extrudates or spheres, and as such they are generally not useful as a structure for distillation.

Additionally, the catalysts may contain components from metals of groups V and VIB of the Periodic Table or mixtures thereof. Group VIII metals give increased overall average activity. Catalysts containing Group VIB metals such as molybdenum and Group VIII metals such as cobalt or nickel are preferred. Catalysts suitable for the hydrodesulfurization reaction include cobalt-molybdenum, nickel-molybdenum and nickel-tungsten. Typically, metals are present in the form of metal oxides supported on a neutral substrate, such as alumina, silica-alumina or the like. Metals are reduced to sulfide either during use or prior to use by exposure to streams containing a sulfur compound.

The properties of a typical hydrodesulfurization catalyst are shown in the table below.

Typically, the catalyst is in the form of extrudates having a diameter of 1/8, 1/16 or 1/32 inch and L / D from 1.5 to 10.

The catalyst may also be in the form of spheres having the same diameter. In the case of the correct form, they form too compact a mass, and preferably they are obtained in the form of structures for catalytic distillation. The catalytic distillation structure must be able to function as a catalyst and as a mass transfer medium. Catalytic distillation structures useful for this purpose are described in US Pat. Nos. 4,731,229, 5,073,236, 5,431,890 and 5,266,546, which are incorporated herein by reference.

The use of a reactive distillation (catalytic distillation) system reduces deactivation and gives longer cycles than a fixed bed hydrogenation unit and is preferred for the first reactor. The distillation column reactor is advantageously used to react with heavier or higher boiling sulfur compounds. Overhead pressure is maintained at about 0 to 250 psi. inch hut with an appropriate temperature in the reaction distillation zone of between 400 and 700 ° F. A partial hydrogen pressure of 0.1 to 70 psi can be used. inch abs. In one preferred embodiment, a partial pressure of hydrogen of 0/1 to 10 psi is used. inch abs. As a rule, the partial pressure of hydrogen in the range from 0.5 to 50 psi gives optimal results. inch abs.

The second reactor may be a single phase downward flow reactor, since most of the sulfur compounds have been removed. Since H ₂ S and more difficult sulfur compounds have already been removed, the reactor can operate under milder conditions, for example at a pressure of about 200 psi. inch barg, reactor temperature 500 ° F and hourly space velocity of liquid equal to 3.

If a second distillation column is used, hydrodesulfurization requires a lower total pressure in the range of 25 to less than 300 psi. inch hut and a partial pressure of hydrogen of less than 150 psi. inch, preferably up to 0.1 psi can be used. inch, preferably about 15 to 50 psi. inch. The temperature in the reaction distillation zone is in the range of 400 to 750 ° F. Hydrogen for the second distillation column reactor is supplied in the range of one to ten standard cubic feet (SCF) per pound of feed. The nominal hourly average liquid feed rates (liquid volume of feed per unit volume of catalyst) in the second column are in the range of 2-5.

Typical conditions in the reaction distillation zone (second and next column) of a distillation column reactor for the hydrodesulfurization of naphtha are:

Temperature 450-700 ° F

Total pressure 75-300 psi inch hut

The partial pressure of N ₂ 6-75 psi. inch abs.

Naphtha average hourly space velocity Approximately 1-5

Speed H ₂ 10-1000 std. cubic foot / barrel

The operation of a distillation column reactor leads to the formation of both a liquid and a vapor phase in the reaction distillation zone. A significant part of the vapor is hydrogen, while part is a vaporous hydrocarbon from the oil fraction. Actual separation can only be achieved with further consideration.

Without limiting the scope of the invention, it is contemplated that a mechanism that provides hydrogenation efficiency in a distillation column reactor is the condensation of a portion of the vapors in the reaction system that absorb sufficient hydrogen in the condensed liquid to obtain the necessary close contact between hydrogen and sulfur compounds in the presence of a catalyst leading to their hydrogenation. In particular, sulfur compounds are concentrated in a liquid, while olefins and H ₂ S are concentrated in the vapor phase, giving a high conversion of sulfur compounds with a low conversion of olefin compounds.

The result of the method in the distillation column reactor is the possibility of using lower partial hydrogen pressures (and thus lower total pressures). As in many cases of distillation, a temperature gradient exists within the distillation column reactor. The lower part of the column contains a higher boiling material and, thus, is at a higher temperature than the upper part of the column. The fraction boiling at a lower temperature, which contains more easily removable sulfur compounds, is subjected to lower temperatures in the upper part of the column, which gives higher selectivity, i.e. less hydrocracking or saturation of the necessary olefin compounds. The higher boiling portion is exposed to higher temperatures in the lower portion of the distillation column reactor to reveal sulfur-containing cyclic compounds and to hydrogenate sulfur.

Between the two reactors is a H ₂ S separation column, which effectively removes the entire H ₂ S product from the first column. This prevents the contact of H ₂ S and olefins with the catalyst and the formation of recombinant organic sulfur compounds, and makes it possible to use less stringent conditions in the second reactor with the same sulfur removal, while at the same time preventing the hydrogenation of olefins.

Figure 1 shows a simplified process diagram of one embodiment of the practice of the invention. Naphtha is fed to the first reactor with a fixed bed and a single passage 10 through line 1, and hydrogen is supplied to the reactor 10 through line 2. The reactor 10 contains a layer 11 of the corresponding hydrodesulfurization catalyst. In the first reactor 10, part of the organic sulfur compounds reacts with hydrogen to form H ₂ S. The conditions in the first reactor are mild according to hydrodesulfurization standards. For example, temperatures range from 550 to 600 ° F, and pressures range from 50 to 150 psi. inch hut and the hourly average fluid rate (LHSV) is in the range of 5 to 10 volumes of naphtha per volume of catalyst. The degree of desulfurization is thus somewhat less than normal, approximately 95%.

The effluent from the first reactor 10 is fed to the first stripping column 20, where H ₂ S and excess hydrogen are separated in the overheads via line 4. Condensable materials in the overheads are condensed in the condenser 21 and separated from H ₂ S and hydrogen in the separator 22. Excess hydrogen and H ₂ S are removed through line 12. The condensed material is returned to the stripping column in the form of reflux through line 13.

Nedogon from the stripping column 20 is fed into the second reactor with a fixed bed and a single passage 20 through the pipe 5 with replenishment of hydrogen supplied to the reactor 20 through the pipe 2. The reactor 20 contains a second layer 21 of the corresponding hydrodesulfurization catalyst. The conditions in the second reactor are adjusted to provide the desired degree of desulfurization. The effluent from the second reactor 20 is fed to a second stripping column 40, where the excess hydrogen and H ₂ S formed in the second reactor 20 are separated together with the overheads via line 8. Again, the condensed materials in the overheads are condensed in the condenser 41 and separated from hydrogen and H ₂ S in the separator 42 and return to the second stripping column through the pipe 14 in the form of reflux. Excess hydrogen and H ₂ S are removed via line 14. The final product is removed as overtaking via line 9. Since H ₂ S is removed between the reactors, milder conditions can be used in the second reactor, and thus olefins are not exposed to hydrogenation conditions.

Consider now figure 2. It shows a second embodiment of the invention, where the first reactor is a distillation column reactor 10 containing two layers 11a and 11b of a hydrodesulfurization catalyst in the form of structures for catalytic distillation. Naphtha is fed between the layers through line 1, and hydrogen flows below the layers through line 2. Since the catalytic distillation column can operate at lower pressures, less olefins will be saturated. In addition, the catalytic distillation column is more effective in the hydrogenation of heavy sulfur compounds such as thiophenes and benzothiophenes. Light naphtha is selected in the form of overheads by means of pipeline 4 together with an excess of hydrogen and most of the H ₂ S formed in the layers. The condensable material is condensed in a condenser 50 and collected in a separator 60, where the vapors, including H ₂ S and excess hydrogen, are removed via line 12. A portion of the condensed liquids is returned to the distillation column reactor 10 in the form of a reflux by line 13. The remaining portion of the liquid overhead served in the upper part of the stripping column 20. Undertaking from the distillation column of the reactor 10 is also served in the stripping column 20, but to the lower part, through the pipe 3.

The stripping column separates the H ₂ S in the overheads through the pipe 15. The condensed materials in the overheads are condensed in the condenser 21 and collected in the separator 22, where they are separated from the excess hydrogen and H ₂ S. The excess hydrogen and H ₂ S are removed from the separator through the pipeline 16, while the liquid is returned to the stripping column in the form of reflux through the pipe 23. The final product is removed in the form of nedogonov through the pipe 9.

The side stream is taken from the stripping column 20 using a pipeline 5 and fed to a single-pass reactor 30 with a fixed bed containing a layer 31 of a suitable hydrodesulfurization catalyst, where lighter organic sulfur compounds react with hydrogen, which is fed through a pipe 6. The effluent from the reactor 20 fed through line 32 to the evaporation drum 40, where hydrogen and H ₂ S are distilled off from the effluent and fed to the top of the stripping column 20 via line 42. The liquid from the evaporation drum is fed to the middle the second section of the stripping column 20 through line 41, where the remaining amount of H ₂ S is separated from the product.

EXAMPLE 1

Full boiled cracked naphtha having the following characteristics is first processed in a catalytic distillation column containing 11032 g of a commercial cobalt / molybdenum catalyst Criterion DC-130, placed in the form of a catalytic structure, as described in US patent 5730843 located with a nominal diameter of 3 "in two sections of a 50-foot column with 15.1 feet of catalyst below the feed point and 18.7 feet of catalyst above the feed point. Hydrocarbon feed is taken between two catalyst beds.

Description of raw materials

Total sulfur 2086 mg / l

Total nitrogen 64 mg / L

Bromine number 52

Density 0.8005 g / cm ³ @ 15.66 ° C

ASTM D-2887 Distillation

5% 160 ° F

10% 174

20% 205

30% 231

40% 258

50% 283

60% 320

70% 338

80% 382

90% 419

95% 442

The catalytic distillation column operates at an overhead pressure of 230 psi. in. h., giving the temperature of the catalyst layer 570 ° F. A catalytic distillation column reactor operating alone produces a sulfur removal of 96.7% with a loss of bromine number (loss of olefins) of 46.47%. Data from a commercial one-stage fixed bed hydrotreatment apparatus show that approximately 85% olefin loss (bromine number) would occur at the same level of sulfur removal.

Only the overheads are separated from H ₂ S and excess hydrogen, and then they are processed in a conventional post-treatment reactor with a fixed bed and a single pass of the second stage containing the same catalyst under the following conditions:

The average hourly feed rate of oil 8

The hydrogen rate is 113.4 std. cube ft / gallon

Average Temperature 470 ° F

Pressure 200 psi inch hut

The total degree of desulfurization equal to 97.2% is obtained with a loss of olefins equal to only 43.4%. Perhaps in very mild conditions. This clearly shows the selectivity of the two-step process of the present invention compared to the one-step process.

EXAMPLE 2

The raw materials, as described in example 1, are processed in a distillation column reactor of example 1. Only the overheads are separated from H ₂ S and excess hydrogen and processed under the following conditions in a post-treatment reactor to achieve naphtha containing 27 parts per million:

Hourly average feed rate 8

Hydrogen feed rate 104 std. cube ft / barrel

Average Temperature 510 ° F

Pressure 275 psi inch hut

The total saturation of olefins 51.5%

The total conversion of S is 98.96%. Saturation of olefins is 51.5%.

Data from a commercial one-stage fixed bed setup show that approximately 92% of olefins should be expected to lose at the same level of desulfurization.

EXAMPLE 3

Cracked naphtha having the following characteristics is processed in the catalytic distillation column of Example 1 containing a commercial Criterion DC-130 cobalt / molybdenum catalyst as described.

Description of raw materials

Total sulfur 1554 mg / l

Total nitrogen 132 mg / L

Bromine number 30.5

Density 0.8288 g / cm ³ @ 15.66 ° С

ASTM D-2887 Distillation

5% 195 ° F

10% 229

20% 265

30% 288

40% 322

50% 336

60% 362

70% 384

80% 399

90% 412

95% 428

The catalytic distillation column reactor operates at an overhead pressure of 195 psi. in. h., giving the temperature of the catalyst layer 590 ° F. A catalytic distillation column reactor operating alone produces a sulfur removal of 98.98% with a loss of olefins of 66.15%. However, the total sulfur content is 24 wt.h / million

The combined overhead and bottoms are separated from H ₂ S and excess hydrogen and processed under the following conditions in a post-treatment reactor to achieve naphtha containing only 7 ppmw:

The average hourly feed rate of 12

Hydrogen Speed 88 std. cube ft / gallon

Medium Temperature 510 ° F

Pressure 230 psi inch hut

The cumulative saturation of olefins 67.4% at a sulfur conversion of 99.7%

Data from a fixed-bed commercial single-stage hydrotreatment apparatus show that olefins would lose about 95% at the same level of sulfur removal.

Claims (9)

1. The method of hydrodesulfurization of petroleum feedstocks containing organic sulfur compounds by at least two successive treatments of the feedstock by contact with added fresh hydrogen in each of these successive treatments in the presence of a hydrodesulfurization catalyst to convert part of the organic sulfur compounds to H ₂ S, where H ₂ S removed from the raw material after each specified treatment. 2. The method according to claim 1, where the two treatments are sequential. 3. A method for hydrodesulfurization of a cracked naphtha stream, comprising the steps of a) supplying hydrogen and a naphtha stream containing organic sulfur and olefins to a first reaction zone containing a suitable hydrodesulfurization catalyst under conditions suitable for reacting a portion of the organic sulfur compounds with hydrogen to form H ₂ s; b) supplying an effluent from said first reaction zone to a stripping zone, where a portion of said H ₂ S is removed to produce a first stream with a reduced H ₂ S content; c) supplying said first stream with a reduced content of H ₂ S and fresh hydrogen to a second reaction zone containing a suitable hydrodesulfurization catalyst, under conditions suitable for reacting a portion of the remaining organic sulfur compounds with hydrogen to form H ₂ S; and d) supplying an effluent from said second reaction zone to a stripping zone of step b), where a portion of said H ₂ S is removed to produce a second stream with a reduced H ₂ S content having a further reduced content of organic sulfur compounds, compared to said naphtha stream and the specified first stream with a low content of H ₂ S. 4. The method according to claim 3, where the specified first reaction zone includes a hydrodesulfurization catalyst in such a form as to ensure simultaneous reaction and distillation of the reaction mixture of the specified stream of naphtha and hydrodesulfurization products. 5. The method according to p. 4, comprising supplying a stream from said second reaction zone to a stripping zone of step b), where part of said H ₂ S is removed to form a second stream with a reduced content of H ₂ S having a further reduced content of organic sulfur compounds, compared with the specified stream of naphtha and the specified first stream with a low content of H ₂ S. 6. The method according to claim 3, where the conditions are such as not to contribute to the saturation of olefins contained in the specified naphtha. 7. The method according to claim 3, where the content of organic sulfur compounds from the second stream with a low content of H ₂ S is less than 50 wt. ppm 8. A method for hydrodesulfurization of a cracked naphtha stream, comprising the steps of a) supplying hydrogen and a naphtha stream containing organic sulfur and olefins to a distillation reactor column containing a desulfurization catalyst; b) simultaneously in said distillation reactor column, (1) contacting said cracked naphtha and said hydrogen with said hydrodesulfurization catalyst under hydrodesulfurization conditions, whereby a portion of said organic sulfur compounds reacts with said hydrogen to form H ₂ S, said conditions being as follows that said olefins remain unsaturated; and (2) separating said naphtha as a light fraction boiling below about 250 ° F and a heavy fraction boiling above about 250 ° F; (c) removing said light fraction in the form of overheads from said distillation column reactor together with H ₂ S and unreacted hydrogen; (d) removing said heavy fraction as bottoms from said distillation column reactor; (e) combining said heavy fraction and said light fraction to obtain a first combined fraction and removing H ₂ S from it; (f) feeding a portion of the first pooled fraction after removal of H ₂ S into a fixed bed and a single pass reaction zone containing a hydrodesulfurization catalyst, where a portion of the remaining organic sulfur compounds reacts with hydrogen to form H ₂ S, and to obtain a second pooled fraction; (g) removing H ₂ S from said second pooled fraction from step (f); and (h) obtaining a product stream containing significantly less organic sulfur compounds than said cracked naphtha stream. 9. The method of claim 8, wherein the second combined fraction from step (g) is combined with the first combined fraction and H ₂ S is removed.

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