BRPI0405793B1 - process for treating a naphtha stream - Google Patents

Abstract

PROCESS FOR THE TREATMENT OF A NAFTA CHAIN ". A process is presented for the desulfurization of a naphtha current with full boiling range, in which a naphtha with full boiling range is simultaneously divided into a column reactor of catalytic distillation, in a light naphtha and a heavy naphtha, and the light naphtha is thioeterified, only the heavy naphtha is treated to remove poisons from the organic nitrogen compounds of the catalyst and then it is hydrodesulfurized. subjected to a final hydrodesulfurization in the polishing reactor.

Description

BACKGROUND OF THE INVENTION Field of invention

[0001] This order claims priority for the previous American provisional order, serial number 60 / 454,259, filed on 3/13/2003.

[0002] The current invention relates to the hydrodesulfurization of a total boiling point naphtha, which contains organic and nitrogen compounds. More particularly, the invention relates to an improvement in the process for treating cracked fluid naphtha, to remove organic sulfur compounds, through hydrodesulfurization. More particularly, the invention relates to catalytic distillation column reactions and the restriction of organic nitrogen compounds from contact with the hydrotreating catalyst.

Related information

[0003] Petroleum distillate streams contain a variety of organic chemical components. Currents are generally defined by their boiling point ranges, which determine their compositions. The processing of the currents also affects the composition. For example, products from catalytic cracking or thermal cracking processes contain high concentrations of olefinic materials, as well as saturated materials (alkanes) and polyunsaturated materials (diolefins). In addition, these components may be any of the various isomers of the compounds.

[0004] The composition of untreated naphtha, as it originates from the raw distiller, or the direct distillation naphtha, is mainly influenced by the raw source. Naphtha from paraffinic crude sources has more saturated straight-chain or cyclic compounds. As a general rule, most "sweet" crude and naphtha (low sulfur) are paraffinic. Naphthenic crudes contain more unsaturated and cyclic and polycyclic compounds. High-sulfur raw products tend to be naphthenic. The treatment of the different naphthas of direct distillation may be slightly different, depending on their compositions, due to the source of crude.

[0005] Reformed or reformed naphtha generally does not require additional treatment, except perhaps distillation or solvent extraction, to remove valuable aromatic products. Reformed naphthas essentially contain no sulfur contaminants, due to the severity of their pretreatment for the process and the process itself.

[0006] Cracked naphtha, as it leaves the catalytic cracker, has a relatively high octane number, as a result of the olefinic and aromatic compounds contained therein. In some cases, this fraction may contribute as much as half of the gasoline in the mixture made at the refinery, along with a significant portion of octanes.

[0007] A boiling point material from catalytically cracked naphtha gasoline currently forms a significant part (= 1/3) of the gasoline product mixture in the USA, and it provides the largest portion of sulfur. Sulfur impurities may require removal, usually through hydrotreating, to meet product specifications or to ensure compliance with environmental regulations.

[0008] The most common method of removing sulfur compounds is through hydrodesulfurization (HDS), in which the petroleum distillate is passed over a solid particle catalyst, comprising a hydrogenation metal supported on an alumina base. In addition, large amounts of hydrogen are included in the diet. The following equations illustrate the reactions in a typical HDS unit: (1) RSH + H2 ^ RH + H2S (2) RCl + H2 ^ RH + HCl (3) 2RN + 4H2 ^ 2RH + 2NH3 (4) ROOH + 2H2 ^ RH + 2H2O

[0009] Typical operating conditions for HDS reactions are: Temperature, 600 - 780 ° F (316 - 416 ° C) Pressure, 600 - 3000 psig (4.14 - 20.7 MPa) H2 recycle flow, SCF / bbl 1500-3000 (42.5-84.9 Nm3 / bbl) Additional H2 replacement, SCF / bbl 700 - 1000 (19.8 - 28.3 Nm3 / bbl)

[00010] The reaction of organic sulfur compounds with hydrogen in a refinery stream, over a catalyst, to form H2S, is typically called hydrodesulfurization. Hydrotreatment is a broad term that includes the saturation of olefins and aromatics and the reaction of organic nitrogen compounds to form ammonia. However, hydrodesulfurization is included and is sometimes simply referred to as hydrotreatment. After the hydrotreatment is finished, the product can be fractionated or simply expanded to release the hydrogen sulfide and collect the naphtha, now desulfurized.

[00011] The predominant light sulfur or lower boiling compounds are mercaptans, while the heavier or higher boiling compounds are thiophenes and other heterocyclic compounds. Separation through fractionation alone will not remove mercaptans. However, in the past mercaptans were often removed by oxidative processes involving washing with caustics. A combined oxidative removal of mercaptans, followed by fractionation and hydrotreating of the heavier fraction, is disclosed in U.S. patent 5,320,742. In the oxidative removal of mercaptans, mercaptans are converted to the corresponding disulfides.

[00012] In addition to treating the lighter portion of naphtha to remove mercaptans, the lighter fraction has traditionally been used as feed for a catalytic reform unit, to increase the number of octanes, if necessary. The lighter fraction can also be subjected to additional separation to remove the valuable C5 olefins (amylenes), which are useful in the preparation of ethers.

[00013] More recently, a new technology has been released for the treatment and simultaneous fractionation of petroleum products, including naphtha, especially catalytic cracked fluid naphtha (FCC naphtha). See, for example, U.S. patents 5,510,568; 5,597,476; 5,779,883; 5,807,477 and 6,083,378.

[00014] Organic nitrogen compounds have long been known to inhibit the hydrodesulfurization reaction and to a certain extent, the hydrogenation reaction. See, for example, "Poisoning of Thiophene Hydrodessulfurization by Nitrogen Compounds", by Vito LaVopa and Charles N. Satterfield, published in the "Journal of Catalysis", volume 110 (1988), on pages 375 - 387. In addition, it has been studied the effect of water and ammonia on hydrotreating catalysts. See "Influence of Water and Ammonia on Hydrotreating Catalysts and Activity for Tetralin Hydrogenation", published in "Catalysis Today", vol. 29 (1996), on pages 229 - 233.

[00015] An advantage of the current invention is that the contact of the organic nitrogen compounds of the total naphtha feed does not make contact with the catalysts used in the hydrotreatment. A special advantage is that the catalytic distillation reaction allows the separation of the feed, in a lighter portion for hydrotreating and the concentration of organic nitrogen compounds in a heavier portion of the feed, thus comprising less than the entire feed, thus allowing a smaller volume of the food, which constitutes the gasoline product, to have to contact the adsorbent of the organic nitrogen compound. A feature of the current invention is that both the hydrodesulfurization catalyst and the thioeterification catalyst are protected from contact with organic nitrogen compounds. These and other advantages and features will be obvious, based on the descriptions that follow.

SUMMARY OF THE INVENTION

[00016] Briefly, the invention comprises the treatment of a total boiling point naphtha (boiling point in the range of C5 to about 420 ° F (215 ° C)) under catalytic distillation conditions, to remove the compounds organic sulfur in which mercaptans are removed through thioeterification, while naphtha is simultaneously divided into a light fraction with a boiling point in the range of C5 to 160 ° F (71 ° C), which is removed as a top product , and a heavy fraction, with a boiling point in the range of 160 - 420 ° F (71 - 215 ° C), which is removed as a bottom product. The thioeterification catalyst is located in the upper portion of the column where the light naphtha fraction migrates and where mercaptans and olefins, preferably diolefins, are reacted to form heavier sulfide products, which fall into the bottom product, compound of the heavy naphtha fraction. The bottom products are treated to remove organic nitrogen compounds, preferably by passing them through an adsorber unit, where most of the organic nitrogen compounds are adsorbed from the stream. The effluent from the organic nitrogen removal unit is then fed together with hydrogen to a second distillation column reactor containing a hydrodesulfurization catalyst, where most of the organic sulfur compounds are converted to hydrogen sulfide. If desired, the effluent from the bottom product of the second distillation column reactor and / or the side naphtha extraction product in the middle temperature range of the first distillation column reactor, after removal of hydrogen sulfide, can be fed to a polishing reactor, to obtain the desired level of desulfurization.

[00017] The removal of organic nitrogen compounds from the feed to the hydrodesulfurization reactor benefits the process in three ways: 1. A catalytic activity of the order of 20 - 50% greater is possible; 2. The selectivity of the system will be improved, allowing a conversion of smaller olefins to any given level of desulfurization; and 3. The life of the catalyst will be improved.

[00018] As used herein, the term "distillation column reactor" means a distillation column that also contains catalyst, such that the reaction and distillation take place simultaneously in the column. In a preferred embodiment, the catalyst is prepared as a distillation structure, and serves as both a catalyst and a distillation structure. The term "reactive distillation" is used to describe the reaction and simultaneous fractionation in a column. For purposes of the present invention, the term "catalytic distillation" includes reactive distillation and any other simultaneous reaction process of fractional distillation in a column, regardless of the nomenclature applied to it.

BRIEF DESCRIPTION OF THE DRAWING

[00019] The FIGURE is a flowchart in schematic form of the preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED ACHIEVEMENT

[00020] The benefit of using a catalytic distillation mode in conjunction with nitrogen adsorption, is that the stream is separated and the organic nitrogen compounds that are characteristic of naphtha tend to fall well within the boiling point range of heavy naphtha. The light fraction of naphtha, which is substantially free of organic nitrogen compounds, is not sent through adsorption, thereby reducing the load on the adsorption plant, which reduces the cost of installation and operation. The nitrogen-containing compounds found in cracked naphthas of full boiling range, may include nitriles, carbazoles, benzocarbazoles, indoles, pyridines, quinolines, acridines and tetrahydroquinolines and are characterized as naturally occurring polar compounds.

[00021] Cracked naphtha is the preferred food for the process of the current invention, because it has the desired light olefins and undesirable nitrogen and sulfur compounds. A typical cracked, fluid naphtha has a boiling point in the C5 range at about 420 ° F (215 ° C) and typically contains mercaptans and the lightest thiophenic compounds. The lower boiling point portion (C5 to about 160 ° F (71 ° C)) of naphtha, which contains most of the valuable olefins, is therefore not subjected to the hydrodesulfurization catalyst, but to a less severe treatment, where the mercaptans contained therein are reacted with the diolefins contained therein to form sulfides (thioeterification), which have a higher boiling point and can be removed with heavier naphtha. Typically, the reaction is performed on a nickel or palladium catalyst, in the presence of hydrogen, in a naphtha separator, where a light fraction is removed at the top and a heavy fraction is removed at the bottom. Advantageously, the sulfides are removed with the bottom products and are eventually subjected to hydrodesulfurization.

THIOETERIFICATION

[00022] A suitable catalyst for the reaction of diolefins with mercaptans is 0.4% by weight of Pd in Al2O3 (alumina) spheres of mesh 7 to 14, supplied by Sud-Chemie, called G-68C. Typical physical and chemical properties of the catalyst, as supplied by the manufacturer, are as follows: Table 1

[00023] Another useful catalyst for the reaction between mercaptans-diolefins is that with 58% by weight of Ni in alumina spheres of mesh 8 to 14, supplied by Calcicat, called E-475-SR.

[00024] The typical physical and chemical properties of the catalyst, as supplied by the manufacturer, are as follows: TABLE II

[00025] The flow of hydrogen to the reactor must be sufficient to maintain the reaction, but be kept below that which would cause the flooding of the column, which is understood to be "the effective amount of hydrogen", as that term is used here . The molar ratio of hydrogen to diolefins and acetylenes in the feed is at least 1.0 to 1.0 and is preferably 2.0 to 1.0.

HYDRODESULFURIZATION

[00026] The reaction of organic sulfur compounds with hydrogen in a refinery stream, over a catalyst, to form H2S, is typically called hydrodesulfurization. Hydrotreatment is a broad term, which includes the saturation of olefins and aromatics and the reaction of organic nitrogen compounds to form ammonia. However, hydrodesulfurization is included and is sometimes simply referred to as hydrotreatment.

[00027] Catalysts that are useful for the hydrodesulfurization reaction include metals of group VIII, such as cobalt, nickel, palladium, alone or in combination with other metals, such as molybdenum or tungsten, on a suitable support, which may be alumina , silica-alumina, titania-zirconia, or the like. Metals are normally supplied as oxides of metals supported on extrudates or spheres, and as such are not generally useful as distillation structures.

[00028] The catalysts contain components of the metals of the group V, VIB, VIII of the Periodic Table or mixtures thereof. The use of the distillation system reduces deactivation and enables longer runs than the fixed bed hydrogenation units of the prior art. Group VIII metals produce an increased overall average activity. Catalysts containing a metal of the VIB group, such as molybdenum and one of the group VIII, such as cobalt or nickel, are preferred. Suitable catalysts for the hydrodesulfurization reaction include cobalt-molybdenum, nickel-molybdenum and nickel-tungsten. Metals are usually present as oxides supported on a neutral base, such as alumina, silica-alumina or the like. Metals are reduced to sulfide during use or before use, through exposure to currents containing sulfur compounds. The catalyst may also catalyze the hydrogenation of the olefins and polyolefins contained within the light cracked naphtha and, to a lesser extent, the isomerization of some of the monoolefins. Hydrogenation, especially of monoolefins, in the lightest fraction, may not be desirable.

[00029] The properties of a typical hydrodesulfurization catalyst are shown in the table below. Table 111

[00030] Catalysts are typically in the form of extrudates, having a diameter of 1/8 inch (3.175 mm), 1/16 inch (1.563 mm) or 1/32 inch (0.781 mm) and an L / D of 1, 5 to 10. The catalyst may also be in the form of spheres having the same diameters. They can be loaded directly into standard, single-pass, fixed-bed reactors, which include supports and reagent distribution structures. However, in their regular form, they form a very compact mass and therefore must be prepared in the form of a catalytic distillation structure. The catalytic distillation structure must be able to function as a catalyst and as a mass transfer medium. The catalyst must be adequately supported and spaced within the column, to act as a catalytic distillation structure. In a preferred embodiment, the catalyst is within a woven wire mesh structure, as disclosed in U.S. Patent 5,266,546, which is incorporated herein by reference. Most preferably, the catalyst is contained in a large number of wire mesh tubes, closed at either end, and placed along a sheet of woven wire mesh, like a mist-removing wire. The plate and tubes are then wrapped in a bale to be placed inside the distillation column reactor. This realization is described in U.S. patent 5,431,890, which is incorporated herein by reference. Other catalytic distillation structures useful for this purpose are disclosed in U.S. Patents 4,731,229, 5,073,236, 5,431,890 and 5,730,843, which are also incorporated herein by reference.

[00031] The suitable conditions for the desulfurization of naphtha in a distillation column reactor are very different from those of a standard drip bed reactor, especially with regard to the total pressure and the partial pressure of hydrogen. Typical conditions in a distillation and reaction zone for a naphtha distillation and hydrodesulfurization reactor are: Temperature 450 - 700 ° F (232 - 371 ° C) Total pressure 75 - 300 psig (0.52 - 2.1 MPa ) Partial pressure of H2 6 - 75 psia (0.42 - 5.25 bars) LHSV or naphtha around 1 - 5 Flow of H2 10 - 1000 SCFB (0.29 - 283 Nm3 / bbl)

[00032] The operation of the distillation column reactor results in a liquid phase and a vapor phase, within the reaction and distillation zone. A considerable portion of the vapor is hydrogen, while a portion of the oil fraction is composed of hydrocarbons in the vapor phase. Actual separation may only be a secondary consideration.

[00033] Without limiting the scope of the invention, it is proposed that the mechanism that produces the effectiveness of the current process is the condensation of a portion of the vapors in the reaction system, which retains enough hydrogen in the condensed liquid to obtain the required intimate contact between the hydrogen and sulfur compounds in the presence of the catalyst, resulting in their hydrogenation. Especially, sulfur species are concentrated in the liquid, while olefins and H2S are concentrated in steam, allowing a greater conversion of sulfur compounds, with a low conversion of olefin species.

[00034] The result of operating the process in the distillation column reactor is that lower partial pressures of hydrogen (and therefore lower total pressures) can be used.

[00035] As with any distillation, there is a temperature gradient inside the distillation column reactor. The temperature at the bottom end of the column contains higher boiling point material and therefore is at a higher temperature than the top end of the column. The lower boiling point fraction, which contains the most easily removable sulfur compounds, is subjected to lower temperatures at the top of the column, because it provides greater selectivity, that is, less hydrocracking or saturation of the desirable olefinic compounds. The larger boiling point portion is subjected to higher temperatures at the lower end of the distillation column reactor, to crack the sulfur-containing ring compounds and to hydrogenate the sulfur.

[00036] It is believed that the current reaction of the distillation column is beneficial, primarily because the reaction is occurring simultaneously with the distillation, the products of the initial reaction and other components of the stream are removed from the reaction zone as quickly as possible, reducing the possibility of side reactions. Second, as all components have boiling points at the reaction temperature, which is controlled by the boiling point of the mixture at the system pressure. The heat of the reaction simply creates more boiling, but no increase in temperature at a given pressure. As a result, a large amount of control over the reaction speed and the distribution of products can be acquired by controlling the system pressure. Another benefit that this reaction can obtain from the reactions of the distillation column is the washing effect, which the internal reflux provides to the catalyst, thus reducing the generation and coking of the polymers. Finally, the hydrogen that drains upwards acts as a gutting agent to help remove the H2S that is produced in the reaction and distillation zone.

[00037] The adsorption unit may have two fixed beds with one bed adsorbing, while the other is desorbing. The adsorption unit may also have a fluidized bed, with continuous removal and regeneration of the adsorbent. Adsorbents are characterized as solid particulate materials capable of selectively adsorbing organic nitrogen compounds. Examples of available adsorbents include activated alumina, white acid clay, Füller earth, active carbon, zeolite, hydrated alumina, silica gel and ion exchange resins. The adsorbent can be regenerated with a heated gas, such as hydrogen or nitrogen.

[00038] Referring now to the FIGURE, a schematic flowchart of an embodiment of the invention is shown. Naphtha is fed through the flow line 101 to the first distillation column reactor 10, containing two beds 12 and 14 of the thioeterification catalyst at the upper end or grinding section below the beds. The hydrogen is fed through the 101A flow line, which is necessary to keep the catalyst in the hydride state. Mercaptans and diolefins in naphtha react in the catalyst beds to form disulfides. At the same time, naphtha is divided into a smaller boiling point fraction that boils in the C5 range up to about 160 ° F (71 ° C), which is removed as a top product through the flow line 103 The top products, having removed most of the mercaptans, have a reduced sulfur content. A portion of the top product is condensed and returned to the distillation column reactor as a reflux (not shown). A cut in the middle boiling range containing predominantly thiophene as the sulfur constituent is removed between beds 12 and 14, through flow line 104.

[00039] The lighter components are gutted from naphtha in the gutting section of the distillation column reactor 10 which contains the standard distillation structure 16, such as molecular trays and sieves, bubble covers or structured filling. The lighter components thus gutted are removed with the top product. The bottom stream, containing organic nitrogen compounds, higher boiling sulfides and thiophene compounds, are removed via flow line 102 and fed to an adsorption unit 20, where organic nitrogen compounds are removed . The effluent from the adsorption unit 20 in the flow line 105 is fed to a second distillation column reactor 30 containing the beds 32 and 34 of the hydrodesulfurization catalyst. Hydrogen is fed below the beds through the 105A flow line. The organic sulfur compounds in the effluent are reacted with hydrogen to produce hydrogen sulfide. At the same time, the effluent is divided into a fraction with a lower boiling point, with a boiling point in the range of about 160 - 350 ° F (71 - 177 ° C), which includes gaseous hydrogen sulfide and any other hydrocarbon. light that results from the light hydrocracking of the feed by the catalyst. The minor boiling point fraction is removed as a top product, via flow line 106, and the bottom product is removed via flow line 107. A portion of the top product is condensed and returned to the column reactor distillation as reflux, as needed (not shown). The bottom product and the top product are combined in the flow line 108 and are passed to the separation vessel 40, as in a standard distillation column, where the hydrogen sulfide is removed through the flow line 109. The liquid formed in the separation vessel 40 it is removed through flow line 110 and is combined with a cut in the range of medium boiling point in flow line 104 and is fed to the polishing reactor 50, which contains a hydrodesulfurization catalyst bed 52 , where the sulfur content is reduced to the desired level, for example, <50 wppm. Hydrogen is fed to the polishing reactor, as required, through flow line 111A. Finally, the effluent from the polishing reactor 50 is removed through the flow line 112 to a second separation vessel, where the hydrogen sulfide produced in the polishing reactor is removed through the flow line 113 and the desulfurized naphtha is removed through the flow line 114 and combined with the top product in flow line 103 of the thioeterification reactor 10 in flow line 115.

Claims (6)

1. Process for the treatment of a naphtha stream, comprising the steps of: (a) feeding hydrogen (101A) and a naphtha stream (101) containing olefins, diolefins, mercaptans, thiophene, thiophene compounds and organic nitrogen compounds , for a first distillation column reactor (10); (b) simultaneously in the first distillation column reactor (10): (i) reacting the diolefins with the mercaptans in the presence of a thioeterification catalyst (12, 14), in a zone of the distillation reactor, to produce sulfides, and (ii) separating naphtha into at least two fractions, comprising a first lower boiling fraction having a reduced sulfur content and a first higher boiling fraction containing the sulfides, thiophene, thiophene compounds, and organic compounds of nitrogen, (c) removing the first minor boiling point fraction from the first distillation column reactor (10), as a top product (103); characterized by the fact that it comprises the steps of: (d) removing the first major boiling point fraction from the first distillation column reactor (10), as a bottom product (102); (e) treating the first bottom product (102) to remove organic nitrogen compounds and to produce an effluent (105) having a reduced content of nitrogen compounds; and, (f) feeding hydrogen (105A) and the effluent (105) to a hydrodesulfurization reactor containing a hydrodesulfurization catalyst (32, 34), where a portion of sulfides, thiophene and thiophene compounds is reacted with hydrogen to form hydrogen sulfide. 2. Process according to claim 1, characterized by the fact that the treatment of step (e) consists of feeding the first bottom product (102) to a nitrogen adsorption unit (20). 3. Process according to claim 1, characterized by the fact that the hydrodesulfurization reactor is composed of a second distillation column reactor (30) and the effluent is simultaneously separated into a second minor boiling point fraction, containing the hydrogen sulfide, and a second major boiling point fraction, and further comprising the steps of: (g) removing the second minor boiling point fraction from the second distillation column reactor (30), as a second top product (106); (h) removing the second major boiling point fraction from the second distillation column reactor (30) as a second bottom product (107); and, (i) combining and feeding the second top product (106) and the second bottom product (107) to a hydrogen sulfide separation vessel (40), where the hydrogen sulfide is separated as a gas (109 ) from a liquid effluent (110); (j) feeding hydrogen (111A) and liquid effluent (110) from the hydrogen sulfide separation vessel (40), to a polishing reactor (50) containing a hydrodesulfurization catalyst, where additional sulfides, thiophene and thiophene compounds they are reacted with hydrogen, to form hydrogen sulfide and an effluent with a reduced sulfur content (112); and, (k) separating the hydrogen sulfide from the effluent with reduced sulfur content (112). 4. Process according to claim 3, characterized by the fact that the first distillation column reactor (10) contains two thioeterification catalyst beds (12, 14) in the distillation reaction zone, and a fraction of boiling in the middle range (104) containing thiophene is removed between the beds and is combined with the liquid effluent (110) from the hydrogen sulfide separation vessel (40) and is fed into the polishing reactor (50). 5. Process according to claim 2, characterized by the fact that the adsorption unit (20) is composed of solid particulate materials capable of selectively adsorbing organic nitrogen compounds. 6. Process according to claim 5, characterized by the fact that solid particulate materials capable of selectively adsorbing organic nitrogen compounds comprise alumina, white acid clay, Füller earth, active carbon, zeolites, hydrated alumina, silica gel, ion exchange resins, and mixtures thereof.

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