MXPA99010590A - Benzene conversion in an improved gasoline upgrading process - Google Patents

Abstract

Low sulfur gasoline is produced from an olefinic, cracked, sulfur-containing naphtha by treatment over an acidic catalyst, preferably an intermediate pore size zeolite such as ZSM-5 to crack low octane paraffins and olefins under mild conditions with limited aromatization of olefins and naphthenes. A benzene-rich co-feed is co-processed with the naphtha to reduce the benzene levels in teh co-feed by alkylation. This initial processing step is followed by hydrodesulfurization over a hydrotreating catalyst such as CoMo on alumina. In addition to reducing benzene levels in the combined feeds, the initial treatment over the acidic catalyst removes the olefins which would otherwise be saturated in the hydrodesulfurization, consuming hydrogen and lowering product octane, and converts them to compounds which make a positive contribution to octave. Overall liquid yield is high, typically at least 90%or higher. Product aromatics are typically increased by no more than 25 wt.%relative to the combined feeds and may be lower than the feed.

Description

CONVERSION OF BENZENE IN AN IMPROVED PROCESS OF GASOLINE ENRICHMENT Field of the Invention This invention relates to a process for the enrichment of hydrocarbon streams. It relates more particularly to a process for * enriching petroleum fractions of the boiling range of gasoline containing substantial proportions of benzene and sulfur impurities while minimizing the loss of octane which occurs during removal. hydrogenating sulfur.

Background of the Invention Gasoline fractionated catalytically forms a major part of the combined or combined product of gasoline in the United States. When the feed for the fractionation contains sulfur, the products of the fractionation process usually contain sulfur impurities which normally require removal, usually by hydrotreating, to meet the relevant product specification. Ref.032064 These specifications are expected to become stricter in the future, possibly allowing no more than about 300 ppmw (parts per million by weight) of sulfur (even lower) in motor gasoline and other fuels. Although the sulfur produced can be reduced by the hydrodesulphurisation of fractionation feeds, this is expensive both in terms of capital for construction and in operating costs since large quantities of hydrogen are consumed. As an alternative to the desulfurization of the feed for fractionation, products that are required to meet low sulfur content specifications can be hydrotreated, usually using a catalyst comprising a Group VIII or a Group VI element, such as cobalt or molybdenum, either alone or in combination with each other, on a suitable substrate, such as alumina. In the hydrotreating process, the molecules containing the sulfur atoms are gently hydrofracted to convert the sulfur to an inorganic hydrogen sulfide, which can be removed from the liquid hydrocarbon product in a separator. Although this is an effective process that has been practiced in heavier gasoline and petroleum fractions for many years to produce satisfactory products, it has disadvantages. Fractionated naphtha, when it comes from the catalytic fractionator and without any of the additional treatments, such as purification operations, have a relatively high octane number as a result of the presence of olefinic components and as such, fractionated gasoline It is an excellent contributor to the gasoline octane group or combination. It contributes a large amount of the product in a high combination octane number. In some cases, this fraction can contribute as much as half of the gasoline in an industrial combined refinery. Other highly unsaturated fractions in the boiling range of gasoline, which are produced in some refineries or petrochemical plants, include gasoline obtained by pyrolysis, produced as a by-product in the fractionation of petroleum fractions to produce light olefins, mainly ethylene and propylene. Gasoline obtained by pyrolysis has a very high octane number but is very unstable in the absence of hydrotreatment because, in addition to the desirable olefins boiling in the boiling range of gasoline, they also contain a substantial proportion of gasoline. diolefins, which tend to form gums during storage or rest. The hydrotreating of these fractions of fractionated naphtha containing sulfur usually causes a reduction in the olefin content and consequently a reduction in the number of octanes; when the degree of desulfurization is increased, the octane number of the product of the boiling range of gasoline decreases. Some of the hydrogen can also cause some hydrofraction as well as saturation of the olefin, depending on the conditions of the hydrotreating operation. Several proposals have been made to remove the sulfur while retaining the olefins which make a positive contribution to the octane number. Such impurities tend to be concentrated in the heavy fraction of gasoline, as noted in U.S. Pat. No. 3,957,625 (Or in) which proposes a method to remove sulfur by hydrodesulfurization of the heavy fraction of catalytically fractionated gasoline to retain the contribution to octanes of olefins which are found mainly in the lighter fraction. In a conventional type of commercial operation, the fraction of heavy gasoline is treated in this way. As an alternative, the selectivity for hydrodesulfurization relative to olefin saturation can be displaced by a selection of the suitable catalyst, for example, by the use of a magnesium oxide support in place of the more conventional alumina. The U.S. Patent No. 4,049,542 (Gibson) discloses a process in which a copper catalyst is used to desulfurize a feed of olefinic hydrocarbons such as catalytically fractionated light naphtha. In any case, without taking into account the mechanism by which this happens, the reduction in the number of octanes that takes place as a consequence of the removal of sulfur by hydrotreatment, creates a tension between the need for growth to produce fuels of gasoline with a higher octane number and the need to produce fuels with low sulfur content, a cleaner burning, less polluting. This inherent tension is even more marked in the current supply situation of sweet crudes, of low cost. Other processes to treat catalytically fractionated gasolines have also been proposed in the past. For example, U.S. Pat. No. 3,759,821 (Brennan) describes a process for enriching catalytically fractionated gasoline by fractionating it into a lighter and heavier fraction and treating the heavier fraction over a ZSM-5 catalyst, after which the treated fraction is mixed again in the lightest fraction. Another process in which fractionated gasoline is separated or divided prior to treatment is described in U.S. Pat. No. 4,062,762 (Howard) which describes a process for desulfurizing naphtha by fractionation of naphtha into three fractions each of which is desulfurized by a different process, after which the fractions are recombined. The U.S. patents Nos. 5,143,596 (Maxwell) and EP 420 326 Bl describe processes for enriching the stocks of sulfur-containing raw materials in the gasoline range, reforming them with a sulfur-tolerant catalyst which is selective toward aromatization. Catalysts of this class include crystalline silicates containing a metal, including zeolites such as gallium-containing ZSM-5. The process described in U.S. Pat. No. 5,143,596 hydrotreates the aromatic effluent from the reforming step. The conversion of Naphthenes and olefins to the aromatic substances is at least 50% under the severe conditions used, typically at temperatures of at least 400 ° C (750 ° F) and usually higher, for example 500 ° C (930) ° F). Under similar conditions, conventional reformation is typically accompanied by significant and undesirable production losses, typically as large as 25%, and this is true of the processes described in these publications: C5 + yields in the range of 50 to 85% they are reported in EP 420 326. This process therefore suffers from the traditional disadvantage of reforming so that the problem of contemplating a process which is capable of reducing the sulfur level of fractionated naphthas while minimizing losses of production as well as the reduction of hydrogen consumption, it has subsisted. The U.S. patent No. 5,346,609 discloses a process for reducing the sulfur of the fractionated naphthas by first hydrotreating the naphtha to convert the sulfur to the inorganic form followed by the treatment on a catalyst such as the ZSM-5 to restore the octane loss during the hydrotreating step , mainly due to the selective fractioning in terms of the shape of the octane low level paraffins. This process, which has been commercially operated successfully, produces a low sulfur content naphtha product with a good performance, which can be incorporated directly into the industrial combination of gasoline. Another aspect of the recent regulation is the need to reduce levels of benzene, a suspected carcinogen, in motor gasolines. Benzene is found in many light refinery streams which are mixed in the refinery gasoline industrial mix, especially reforming which is desirable as a component of the industrial combination of gasoline because of its high octane number and low sulfur content. Its relatively high benzene content requires, however, that additional treatment be carried out to comply with future regulations. Various processes for reducing the benzene content of refinery streams have been proposed, for example, the fluid bed processes described in U.S. Pat. Nos. 4,827,069; 4,950,387 and 4,992,607 convert benzene to alkyl aromatic substances by alkylation with light olefins. Benzene can be derived from fractionated naphthas or benzene-rich streams such as reformates. Similar processes are described in which the removal of benzene is accompanied by reductions in sulfur in U.S. Requests. Nos. Of Series 08 / 286,894 (Mobil Case 6994FC) and 08 / 322,466 (Mobil Case No. 6951FC) and U.S. Pat. No. 5,391,288. A process for reducing the benzene content of light refinery streams such as reforming and light FCC gasoline by alkylation and transalkylation with heavy alkyl aromatic substances is disclosed in U.S. Pat. No. 5,347,061. A process for catalytically desulfurizing the separated or divided fractions in the boiling range of gasoline has now been contemplated, which makes it possible for the sulfur to be reduced to acceptable levels without substantially reducing the octane number. At the same time, the present process allows the levels of benzene in light refinery currents such as reforming to be reduced. The benefits of the present process include reduced hydrogen consumption and reduced mercaptan formation, compared to the process described in U.S. Pat. No. 5,346,609, as well as the concomitant capacity to reduce benzene levels in other streams. According to the present invention, the process for enriching fractionated naphthas comprises a first step of catalytic processing in which the fractionated naphtha feed is co-processed with a hydrocarbon stream containing benzene, light, to convert the benzene, the olefins and some paraffins in the combined feed on a zeolite or other acid catalyst. The reactions that are carried out are mainly the selective break in the form of the paraffins and olefins of low octane number and the alkylation reactions that convert the benzene to aromatic alkyl substances. Many of these increase the octane number of fractionated naphtha and greatly reduce their olefin content "which, in turn, reduces hydrogen consumption and octane loss during the subsequent hydrodesulfurization step. olefins and naphthenes are limited as a result of the mild conditions employed during the treatment on the acid catalyst, the aromatic content of the final hydrotreated product may in certain cases be lower than that of the combined feeds. normal practice, the process will involve connecting the feed (fraction fractionated sulfur-containing naphtha and a benzene-rich reforming coalition) in a first step with a medium pore size acid, solid, zeolite catalyst to a temperature from 177 to 427 ° C (350 to 800 ° F), a pressure of 2172 to 6998 kPa (300 to 1000 psig), a space velocity from 1 to 6 LHSV, and a ratio of hydrogen to hydrocarbons from 180 to 445 nlld1 (1000 to 2500 standard cubic feet of hydrogen per barrel of feed), to rent benzene in the feed combined with the olefins for forming aromatic alkyl substances and for fractionating olefins and low octane paraffins in the feed, with the conversion of the olefins and naphthenes to the aromatic substances which is maintained at levels less than 25% by weight and the conversion of benzene (to aromatic alkyl substances) from 10 to 60%. The intermediate product is then hydrodesulfurized in the presence of a hydrodesulfurization catalyst at a temperature of 260 ° to 427 ° C (500 to 800 ° F), a pressure of 2172 to 6998 kPa (300 to 1000 psig), a space velocity of 1 to 6 LHSV, and a ratio of hydrogen to hydrocarbons from 180 to 445 nlld1 (1000 to 2500 standard cubic feet of hydrogen per barrel of the feed), to convert the sulfur-containing compounds in the intermediate to sulfur inorganic and produce a desulfurized product with a total liquid yield of at least 90% by volume.

In comparison with the treatment sequence described in U.S. Pat. No. 5,346,069, wherein the fractionated naphtha is first subjected to hydrodesulfurization followed by treatment on an acid catalyst such as ZSM-5, the present process operates with a reduced hydrogen consumption as a result of the initial removal of the olefins. Also, by placing the hydrodesulfurization after the initial treatment, the formation of mercaptans by the combination of H2S-olefin on the zeolite catalyst is eliminated, potentially leading to a higher desulfurization or mitigating the need to treat the product additionally, for example, as is described in the US Application Serial No. 08 / 001,681. The process can be used to desulfurize fractions of light naphtha and full range while maintaining the octane number to avoid the need to reform such fractions, or at least, without the need to reform such fractions to the extent previously considered necessary. In practice it may be desirable to hydrotreate the fractionated naphtha before contacting it with the catalyst in the first aromatization / fractionation step to reduce the content of dienes in the naphtha and thus extend the length of the catalyst cycle. Only a very limited degree of olefin saturation occurs in the pre-processor and only a minor amount of desulfurization is carried out at this time.

Detailed description Feeding One of the feeds to the process comprises a fraction of oil containing sulfur, which boils in the boiling range of gasoline. * Feeds of this type typically include light naphthas that typically have a boiling range of C6 at 166 ° C (330 ° F), full range naphtha typically having a boiling range of C5 at 216 ° C (420 ° C) F), the heavier naphtha fractions boiling in the range of 127 to 211 ° C (260 to 412 ° F), or the heavy gasoline fractions that boil at, or at least within, the range of 166 to 260 ° C (330 to 500 ° F), preferably 166 to 211 ° C (330 to 412 ° F). In many cases, food will have a point of 95 percent (determined in accordance with ASTM D 86) of at least 163 ° C (325 ° F) and preferably at least 177 ° C (350 ° F), for example, 95 percent points of at least 193 ° C (380 ° F) and at least 220 ° C (400 ° F). The catalytic fractionation is an adequate source of fractionated naphtha, usually the catalytic fractionation of the fluid (FCC) but thermal fractionation processes such as coking can also be used to produce usable feeds such as coker's naphtha, gasoline obtained by pyrolysis and other thermally fractionated naphtha. The process can be operated with the complete gas fraction obtained from a catalytic or thermal fractionation step or, alternatively, with part of it. Because the sulfur tends to be concentrated in the higher boiling fractions, it is preferable, particularly when the unit capacity is limited, to separate the higher boiling fractions and process them through the steps of the present unprocessed process the lower boiling cut. The cut-off point between treated and untreated fractions may vary according to - with the sulfur compounds present but usually, a cut-off point in the range from 38 ° C (100 ° F) to 150 ° C (300 ° F), more usually in the range of 93 ° C (200 ° F) ) up to 150 ° C (300 ° F) will be adequate. The exact cutoff point selected will depend on the sulfur specification for the gasoline product as well as the type of sulfur compounds present: the lower cutoff points will typically be necessary for the sulfur specifications of the product. The sulfur which is present in the components that boil below 65 ° C (150 ° F) is mainly in the form of mercaptans which can be removed by extractive type processes such as Merox but the hydrotreatment is appropriate for the removal of the thiophene and other cyclic sulfur compounds present in the components of higher boiling point, for example, fractions of components boiling above 82 ° C (180 ° F). The treatment of the lower boiling fraction in a process of the extractive type coupled or linked with the hydrotreatment of the higher boiling component, may therefore represent a preferred economic process option. Higher cutting points will be preferred to minimize the amount of feed that is passed to the hydrotreater and the final selection of the cut point along with other process options such as extractive type desulfurization will therefore be made in accordance with Product specifications, food restrictions and other factors. The sulfur content of the separated or divided fraction will depend on the sulfur content of the feed to the fractionator as well as the boiling range of the selected fraction used as the feed in the process. The lighter fractions, for example, will tend to have lower sulfur contents than the higher boiling fractions. As a practical matter, the sulfur content will exceed 50 ppmw and will usually be in excess of 100 ppmw and in most cases in excess of 500 ppmw. For fractions that have 95 percent points above 193 ° C (380 ° F), the sulfur content can exceed 1000 ppmw and can be as high as 4000 or 5000 ppmw and even higher, as shown below. The nitrogen content is not as characteristic of the feed as the sulfur content and is preferably not higher than 20 ppmw although higher nitrogen levels typically of up to 50 ppmw can be found in certain higher boiling point feeds 95 percent in excess of 193 ° C (380 ° F). The level of nitrogen, however, will usually not be greater than 250 or 300 ppmw. As a result of the fractionation that has preceded the steps of the present process, the feed to the hydrodesulfurization step will be olefinic, with an olefin content of at least 5% and more typically in the range of 10 to 20%, for example, 15 to 20 % in weigh; preferably, the feed has an olefin content of 10 to 20% by weight, a sulfur content of 100 to 5000 ppmw, a nitrogen content of 5 to 250 ppmw and a benzene content of at least 5% by volume. The dienes are frequently present in the thermally fractionated naphthas but, as described below, they are preferably removed in a hydrogenating manner as a pretreatment step. Coalimentation to the process comprises a light fraction, which boils within the boiling range of gasoline, which has a relatively high amount of aromatic substances, especially benzene. This benzene-rich feed typically will contain at least 5% by volume of benzene, more specifically 20% by volume, up to 60% by volume of benzene. A specific refinery source for the fraction is a fraction of the reformed. The fraction contains smaller amounts of lighter hydrocarbons, typically less than 10% C5 and lower hydrocarbons and small amounts of heavier hydrocarbons, typically less than 15% hydrocarbons with C7 +. These reformed co-feeds usually contain very low amounts of sulfur because they have usually been subjected to desulfurization prior to reformation. Examples include reforming from a fixed-bed, wobble-bed or bed-bed reformer. The most useful fraction of the reformed is a reformed of central cut, that is to say a reformed one with the lightest and heaviest portions removed by distillation. This is preferably the reformed having a narrow boiling range, ie, a fraction with Ce or Cß / C? . This fraction can be obtained as a complex mixture of hydrocarbons recovered as the part that exits above a dehexanizer column downstream of a depentanizing column. The composition will vary over a wide range or range, depending on a number of factors including the severity of the operation in the reformer and the reformer feed. These currents will usually have the hydrocarbons of C5, C4 and lower, removed in the depentanizer and debutanizer. Therefore, usually, the reforming of the central cut will contain at least 70% by weight of hydrocarbons with Ce, and preferably at least 90% by weight of hydrocarbons with Ce. Other sources of a benzene-rich feed include a light naphtha, a petrol coker or gasoline obtained by pyrolysis. By boiling range, these benzene-rich fractions can be defined by a final boiling point of 121 ° C (250 ° F), and preferably not higher than 110 ° C (230 ° F). Preferably, the boiling range falls between 38 ° C (100 ° F) and 180 ° C (212 ° F), and more preferably between the range of 66 ° C (150 ° C) to 93 ° C (200 ° F) and even more preferably within the range of 71 ° to 93 ° C (160 ° F to 200 ° F). The following Table 1 describes the properties of a C6-C7 central cut reforming of 121 ° C (250 ° F) useful.

Table 1 Reformed Central Court of C6-C7 RON 82.6 MON 77.3 Composition,% by weight I-C5 0.9 n-C5 1.3 Naf. With C5 1.5 I-C6 22.6 n-C6 11.2 Naft. With C6 1.1 Benzene 32.0 I-C7 8.4 n-C7 2.1 Naft. With C7 0.4 Toluene 17.7? -c8 0.4 n-C8 0.0 Arom. With C8 0.4 Table 2 describes the properties of a more preferred benzene-rich, central fraction, which is more paraffinic.

Table 2 Refozrmado of the Central Cut Rich in Benzene RON 78.5 MON 74.0 Composition,% by weight I-C5 1.0 n-C5 1.6 Naft. With C5 1.8 I-C6 28.6 n-C6 14.4 Naft. With C6 1.4 Benzene 39.3 I-C-, 8.5 n-C7 0.9 Naft. With C-7 0.3 Toluene 2.3 Process Configuration The boiling range feed of the selected sulfur-containing gasoline, together with the benzene-rich coalition, is treated in two steps by first passing the naphtha plus the co-feed on an acid catalyst, selective in shape. In this step, the olefins in the fractionated naphtha alkylate the benzene and other aromatic substances to form alkyl aromatic substances while, at the same time, the increasing olefins are produced by the selective fractionation in the form of the paraffins with low levels of octanes and the olefins of one or both of the components of the food. Olefins and naphthenes can undergo conversion to aromatic substances but the degree of aromatization is limited as a result of the relatively mild conditions, especially temperature, used in this step of the process. The effluent from this step is then passed to a hydrotreating step in which the sulfur compounds present in the naphtha feed, which are mostly unconverted in the first step, are converted to the inorganic form (H2S ), allowing removal in a separator after hydrodesulfurization. Because the first treatment step on the acid catalyst does not produce any of the products that interfere with the operation of the second step, the effluent from the first stage can be cascaded directly to the second stage without the need for separation interetapas.

The particle size and the nature of the catalysts used in both stages will usually be determined by the type of process used, such as: a fixed-bed, liquid-phase, down-flow process; a process of distillation or drip phase, fixed bed, upward flow; a boiling, fluidized bed process; or a fluidized bed process, transport. All of these different process schemes are well known, although the fixed-bed downflow arrangement is preferred for simplicity of operation.

First Stage of Processing The combined feeds are first treated by contact with an acid catalyst under conditions which lead to the alkylation of the benzene by the olefins to form alkyl aromatics. The volume of the benzene comes from the coalification, for example the reformate, although some isomerization of the olefins which are present in the naphtha feed can take place to form an additional benzene. The mild conditions, especially the temperature, used in this step, usually avoid a very large degree of isomerization of olefins and naphthenes. Normally, the conversion of olefins and naphthenes to new aromatic substances is not greater than 25% by weight and is usually lower, typically not more than 20% by weight. Under the milder conditions in the first stage, the total aromatic content of the final hydrotreated product may actually be lower than that of the combined feeds as a result of some aromatic hydrogenation occurring during the second stage of the reaction. Selective fractionation of the form of low octane paraffins, mainly the n-paraffins, and the olefins, takes place to increase the octanes of the product with the production of increasing olefins which can also lead to the alkylation of the aromatic substances, especially of the benzene. These reactions take place under relatively mild conditions and the yield losses are kept at a low level. On both steps of the process, the total liquid yields are typically at least 90% by volume and can be higher, for example, 95% by volume. In some cases, the performance of the liquid may be up to 100% by volume as a result of volume expansion since the reactions are taking place. Compositionally, the first stage of the processing is marked by a selective fractionation of the shape of the octane low number components in the feed, related or linked with the alkylation of the alkylation of the aromatic substances. The olefins are derived from the feed as well as an increasing amount of the fractionation of the combined paraffins and olefins of the feed. Some isomerization of the n-paraffins to the branched chain paraffins of higher octane numbers can be carried out, making an additional contribution to the octane number of the final product. Benzene levels are reduced when the degree of alkylation is increased at higher first stage temperatures, with the conversion of benzene typically in the range of 10 to 60%, more usually from 20 to 50%. The conditions used in this step of the process are those favorable for these reactions. Typically, the temperature of the first step will be from 150 ° to 455 ° C (300 ° to 850 ° F), preferably 177 ° to 425 ° C (350 ° to 800 ° F). The pressure in this zone of the reaction is not critical since the hydrogenation is not being carried out although a lower pressure in this stage will tend to favor the production of olefin by the fractionation of the low octane components of the feeding. The pressure, therefore, will mostly depend on the convenience of operation, will typically be 445 to 10445 kPa (50 to 1500 psig), preferably 2170 to 7000 kPa (300 to 1000 psig) with space velocities typically from 0.5 to 10 LHSV (h_), normally 1 to 6 LHSV (h -i, Hydrogen to hydrocarbon ratios typically from 0 to 890 nll 1 (0 to 5000 SCF / Bbl), preferably 18 to 445 nlld1 (100 to 2500 SCF) / Bbl), will be selected to minimize the aging of the catalyst A change in the volume of the boiling range material of gasoline is typically carried out in the first step.Any reduction in the liquid volume of the product occurs as a result of conversion to lower boiling products (C5-) but conversion to C5- products is typically not greater than 10% by volume and will usually be below 5% by volume.A further reduction in volume is normally carried Abo as a consequence of the conversion of the olefins to the aromatic compounds or their incorporation into the aromatic substances but with limited aromatization, this normally is not significant. If the feed includes significant amounts of the higher boiling components, the amount of C5- products may be relatively lower and for this reason, the use of higher boiling point naphthas is favored, especially. fractions with 95 percent points above 177 ° C (350 ° F) and even more preferably above 193 ° C (380 ° F) or higher, for example, above 205 ° C (400 ° F). Normally, however, the 95 percent point will not exceed 270 ° C (520 ° F) and will usually not be greater than 260 ° C (500 ° F). The catalyst used in the first step of the process has sufficient acid functionality to cause fractionation reactions, aromatization and alkylation desired. For this purpose, it will have a significant degree of acid activity, and for this purpose the most preferred materials are the solids of crystalline molecular sieve catalytic materials, solids, which have an intermediate pore size and the topology of a behavioral material. zeolitic, which, in the form of the aluminosilicate, has a restriction or shrinkage index of 2 to 12. The catalysts preferred for this purpose are the catalytic materials of intermediate pore size zeolitic behavior, exemplified by the acid-acting materials that they have the topology of the intermediate pore size aluminosilicate zeolites. These zeolitic catalytic materials are exemplified by those which, in their aluminosilicate form, have a Restriction or Shrinkage index of between 2 and 12. U.S. Pat. No. 4,784,745 for a definition of the Restriction or Shrinkage index and a description of how this value is measured as well as the details of a number of catalytic materials that have the appropriate topology and structure of the pore system that will be useful in this service. Preferred intermediate pore size aluminosilicate zeolites are those having the topology of ZSM-5, ZSM-11, ZSM-12, ZSM-21, ZSM-22, ZSM-23, ZSM-35, ZSM-48. , ZSM-50 or MCM-22, MCVM-36, MCM-49 and MCM-56, preferably in the form of aluminosilicate.

(The most recent catalytic materials identified by the MCM numbers are described in the following patents: MCM-22 zeolite is described in US Patent No. 4,954,325, MCM-36 in US Patent Nos. 5,250,277 and 5,292,698; MCM -49 in US Patent No. 5,236,575, and MCM-56 in US Patent No. 5,362,697). However, other catalytic materials having the appropriate acid functionality can be used.

A particular class of catalytic materials that can be used are, for example, the zeolite materials of large pore sizes which have a Restriction or Shrinkage index of up to 2 (in the form of the aluminosilicate). Zeolites of this type include mordenite, beta zeolite, faujasites such as zeolite Y and ZSM-4. Other solid refractory materials which have the desired acid activity, pore structure and topology can also be used. The catalyst must have sufficient acid activity to convert the appropriate components of the feed naphtha as described above. A measurement of the acid activity of a catalyst is its alpha number. The alpha test is described in U.S. Pat. No. 3,354,078 and J. Catalysis, 4, 527 (1965); 6, 278 (1966); and 61, 395 (1980). The experimental conditions of the test used to determine the alpha values referred to in this specification include a constant temperature of 538 ° C and a variable flow rate as described in detail, in J. Catalysis, 61, 395 (1980). The catalyst used in this process step suitably has an alpha activity of at least 20, usually in the range of 20 to 800 and preferably at least 50 to 200. It is inappropriate for this catalyst to have too high an acid activity because of it is only desirable to break and rearrange as much of the feed gasoline as is necessary to maintain the octane number without severely reducing the product volume of the boiling range of gasoline. The active component of the catalyst, for example, the zeolite, will usually be used in combination with a binder or substrate because the particle sizes of the pure zeolitic materials are too small and lead to an excessive pressure drop in a catalyst bed. This binder or substrate, which is preferably used in this service, is suitably any refractory binder material. Examples of these materials are well known and typically include silica, silica-alumina, silica-zirconia, silica-titania, alumina. The catalyst used in this process step can be free of any metallic hydrogenation component or it can contain a metal hydrogenation function. If it is found to be desirable under the current conditions used with particular feeds, metals such as Group VIII base metals, especially molybdenum, or combinations, will normally be found suitable. Noble metals such as platinum or palladium normally offer no advantage over nickel or other base metals.

Second Hydrotreatment Step The hydrotreating of the effluent from the first stage can be effected by the contact of the feed with a hydrotreating catalyst. Under the hydrotreating conditions, at least some of the sulfur present in the naphtha which passes unchanged through the fractionation / aromatization step, is converted to hydrogen sulfide which is removed when the hydrodesulfurized effluent is passed to the separator. continuation of the hydrotreator. The hydrodesulfurized product boils in substantially the same boiling range as the feed (boiling range of gasoline), but which has a lower sulfur content than the feed. The sulfur levels of the product are typically below 300 ppmw and in most cases below 50 ppmw. Nitrogen is also reduced to levels typically below 50 ppmw, usually below 10 ppmw, by the conversion to ammonia which is also removed in the separation step. If a pretreatment step is used before the catalytic processing of the first stage, the same type of hydrotreating catalyst can be used as in the second step of the process but conditions can be smoother to minimize olefin saturation and consumption. of hydrogen. Since the saturation of the first double bond of the dienes is kinetically / thermodynamically favored over the saturation of the second double bond, this objective is capable of being achieved by the appropriate choice of conditions. Suitable combinations of processing parameters such as temperature, hydrogen pressure and especially space velocity can be found by empirical means. The pre-treater effluent can be cascaded directly to the first stage of processing, with any slight exotherms resulting from the hydrogenation reactions, which provide a sudden increase in temperature useful for initiating the mainly endothermic reactions of the first stage of processing. Consistent with the goal of maintaining octanes and product volume, conversion to products boiling below the boiling range of gasoline (C5-) during the secondary hydrodesulfurization step is kept to a minimum. The temperature of this step is suitably from 220 to 454 ° C (400 to 850 ° F), preferably 260 to 400 ° C (500 to 750 ° F) with the exact selection dependent on the desulfurization required for a given feed with the chosen catalyst . There is a rise in temperature under the conditions of the exothermic reaction, with values of 11 to 55 ° C (20 to 100 ° F) that are typical under most conditions and with reactor inlet temperatures in the range from 260 to 400 ° C (500 to 750 ° F) preferred. Since the desulfurization of the fractionated naphthas is normally carried out easily, low to moderate pressures may be used, typically from 445 to 10443 kPa (50 to 1500 psig), preferably 2170 to 7,000 kPa (300 to 1000 psig). The pressures are the pressure of the total system, at the entrance of the reactor. The pressure will normally be chosen to maintain the desired aging rate for the catalyst in use. The space velocity (hydrodesulfurization step) is typically from 0.5 to 10 LHSV (h "1), preferably 1 to 6 LHSV (h_1) The ratio of hydrogen to hydrocarbons in the feed is typically 90 to 900 n.1.1" 1 (500 to 5000 SCF / Bbl), usually 180 to 445 n.1.1"1 (1000 to 2500 SCF / B) The degree of desulfurization will depend on the sulfur content of the feed and, of course, the sulfur specification of the product with the selected reaction parameters according to With this, the process will normally be operated under a combination of conditions such that the desulfurization must be at least 50%, preferably at least 75%, when compared to the sulfur content of the feed. at very low levels of nitrogen but low levels of nitrogen can improve the activity of the catalyst in the second step of the process Normally, the denitrogenation which accompanies the desulphurisation will lead to an acceptable organic nitrogen content in the feed to the second step of the process. The catalyst used in the hydrodesulfurization step is suitably a conventional desulfurization catalyst composed of a Group VI and / or Group VIII metal on a suitable substrate. Group VI metal is usually molybdenum or tungsten and Group VIII metal usually nickel or cobalt. Combinations such as Ni-Mo or Co-Mo are typical. Other metals which possess the functionality of hydrogenation are also useful in this service. The support for the catalyst is conventionally a porous solid, usually alumina, or silica-alumina, but other porous solids such as magnesia, titania or silica, either alone or mixed with alumina or silica-alumina can also be used, when it is convenient. The size of the particle and the nature of the catalyst will usually be determined by the type of the conversion process which is being carried out, such as: a fixed-bed, liquid-phase, down-flow process, a liquid-phase process , of fixed bed, of upward flow; a liquid or gaseous phase process, with a fixed fluidized bed, with distillation or runoff; or a fluidized bed process, of transport, in liquid or gaseous phase, as indicated above, with the type of fixed bed, downflow, preferred operation.

Examples Three parts by volume of a fraction of 99 ° C + (210 ° F) of an FCC naphtha were combined with a part of a central-cut reformed to produce a feed combined with the composition and properties given in Table 3. The combined feed was co-incinerated with the hydrogen co-feed to a fixed bed reactor containing a ZSM-5 catalyst having the properties described in Table 4.

TABLE 3 Properties of Naphtha / Reformed FCC Composition,% by weight N-pentane 0.4 Iso-pentane 0.3 Cyclopentane 0.5 n-Paraffins with Ce-Cio 5.0 Isoparaffins with C6-C? 0 16.3 Olefins and cycloolefins with C6-C? 0 11.4 Naphthenes with Cß-Cio 5.8 Benzene 9.2 Aromatics with C7-C? Or 34.2 CU + - 17.0 Total Sulfur,% by weight 0.14 Nitrogen, ppmw 71 Table 3 (Cont.) Octane of Research Claro 90.9 Octanes of the engine 80.6 Number of Bromine 36.3 Density, 60 ° C, g.cc "" 1 0.7977 TABLE 4 Properties of ZSM-5 Catalyst Zeolite ZSM-5 Alumina binder Zeolite load,% by weight 65 Binder,% by weight 35 Alpha catalyst 110 Surface area, m2g-1 315 Vol. Of Poro, cc.g. 1 0.65 Density, real, g.cc. "1 2.51 Density, particle, g.ccd1 0.954 The total effluents from the first reactor are cascaded to a second fixed-bed reactor containing a commercial CoMo / Al203 catalyst (Akzo K742-3Q). The feed rate was constant in such a way that the hourly space velocity of the liquid on the ZSM-5 catalyst was 1.0 h_1 and 2.0 h "1 on the hydrotreating catalyst.The total reactor pressure was maintained at 4171 kPa ( 590 psig) and hydrogen co-generation was constant at 356 n.1.1"1 (200 SCF / Bbl) of the naphtha feed. The temperature of the ZSM-5 reactor was varied from 205 to 427 ° C (400 to 800 ° F) while the temperature of the HDT reactor was 260 to 370 ° C (500 to 700 ° F). The results are shown in Table 5.

Table 5 Results of Naphtha Enrichment / Combined Reforming Temperature ZSM-5, ° C / ° F 204/400 388/750 427/800 427/800 Temperature HDT, ° C / ° F 371/700 371/700 371/700 260/500 Conversion of Benzene, 13 39 41 38 percent Consumption of H2, scbf 360 250 260 30 Yield C5 +,% in vol. 101.7 95.6 92.1 90.8 of the feed Aromatization of the (22) (2) 20 olefins / naphthenes with Cß-Cio Yield,% by weight of HC C feed - C2 0.1 0.3 0.6 0.5 Propane 0.0 1.3 2.7 2.5 N-butane 0.0 1.5 2.3 2.3 Isobutane 0.0 1.6 2.2 2.1 N-pentane 0.5 1.2 1.4 1.4 Isopentane 0.2 2.5 2.3 2.1 Pentene 0.0 0.0 0.0 0.2 C6 + Totals 99.7 91.8 88.7 88.8 N-paraffins with C6-C? 0 8.0 4.7 3.8 3.8 Isoparaffins with C6-C? 0 23.2 17.0 15.6 15.3 Olefins with C6-C? 0 0.0 0.0 0.0 0.6 Benzene 7.9 5.6 5.4 5.6 Naphthenes with C6-C? 0 13.6 12.3 11.1 7.8 Aromatics with C7-C10 31.7 37.5 38.9 41.2 Cu + 15.2 15.4 14.2 14.0 Total Sulfur, ppmw 75 32 20 31 Nitrogen, ppmw 2 3 3 56 Table 5 (Cont.) Octanos de investiga- 77.4 88.2 ¡9.5 91.8 C5 + Octans of the Engine of 72.9 81.2 ¡83.3.3 Cs + Note: The values shown in () represent negative values (reductions) and reflect less aromatic substances in the product than in the food.

As shown in Table 5, the increase in the temperature of the ZSM-5 at a constant HDT severity leads to increasing octane yields and reduced C5 + yields. Significant benzene conversions of about 40% were also observed at ZSM-5 temperatures of 399 ° to 427 ° C (750 ° to 800 ° F) compared to 13% due to saturation on the HDT catalyst. Desulfurization levels above 98 percent can be achieved. The consumption of hydrogen is reduced with increasing ZSM-5 temperature due to the increased conversion of the fractionated naphtha olefins on the acid catalyst in place of the hydrogen-consuming reactions on the HDT catalyst; the hydrogen consumption can be further reduced by lowering the temperature of HDT to 260 ° C (500 ° F) with a small effect during hydrodesulfurization. This lower HDT temperature also leads to an octane number of the product increased when the aromatic saturation is reduced. The aromatization of the olefins and the naphthenes of feeding is maintained at a low level and on both steps of the process, the level of the aromatic substances can still be reduced with respect to the food. The liquid yields are high in all cases, with the highest yields that are obtained at low temperatures of the first step when increments in product volume can be achieved.

It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims (10)

1. A hydrodesulfurization process of a combined hydrocarbon feed comprising the fractions containing sulfur, olefins and benzene and to reduce the benzene content of the feed, the process is characterized in that it comprises: (a) contacting a combined feed comprising (i) a feed fraction of fractionated sulfur-containing naphtha, boiling in the boiling range of gasoline, including paraffins containing n-paraffins, olefins and low octane aromatics, and (ii) a fraction boiling in the boiling range of gasoline, containing benzene, in a first step under mild fractionation conditions comprising a temperature of between 204 ° C to 427 ° C with a solid acid catalyst consisting essentially of a zeolite of ZSM-5 intermediate pore size having an acidic activity, comprising an alpha value between 20 and 200 for alkylate the benzene with olefins to form alkyl aromatics and to fractionate the paraffins and the defines in the feed and to form an intermediate product of reduced benzene content relative to the combined feeds, and (b) in a second step to put in contact the intermediate product with a hydrodesulfurization catalyst under a combination of elevated temperature, high pressure and an atmosphere comprising hydrogen, to convert the sulfur-containing compounds in the intermediate product to inorganic sulfur and produce a desulfurized product comprising a normally liquid fraction in the boiling range of gasoline.

2. The process according to claim 1, characterized in that the fractional naphtha feedstock comprises a light naphtha fraction having a boiling range within the range of C6 at 166 ° C.

3. The process according to claim 1, characterized in that the fraction of the naphtha feed comprises a naphtha fraction of the entire range having a boiling range within the range of C5 at 216 ° C.

4. The process according to claim 1, characterized in that the fractional naphtha feedstock comprises a heavy naphtha fraction having a boiling range in the range of 166 ° to 260 ° C.

5. The process according to claim 1, characterized in that the fractionated naphtha feed is a fraction of catalytically fractionated olefinic naphtha.

6. The process according to claim 1, characterized in that the fraction containing benzene is a fraction of the reformed.

7. The process according to claim 1, characterized in that the hydrodesulfurization catalyst comprises a Group VIII and Group VI metal.

8. The process according to claim 1, characterized in that the first stage is carried out at a pressure of 379 to 10446 kPa, a space velocity of 0.5 to 10 LHSV, and a ratio of hydrogen to hydrocarbons from 0 to 890 nlld1 of hydrogen per barrel of the feed.

9. The process according to claim 1, characterized in that the hydrodesulfurization is carried out at a temperature of 204 ° to 427 ° C, a pressure of 379 to 10446 kPa, a space velocity of 0.5 to 10 LHSV, and a ratio of hydrogen to hydrocarbons from 89 to 890 n.l.ld1 of hydrogen per barrel of the feed.

10. An enrichment process of a sulfur containing feed fraction, boiling in the boiling range of gasoline containing mononuclear aromatics including benzene, olefins and paraffins, and reducing the benzene content of the fraction, such a process is * characterized in that it comprises: contacting a fraction of the boiling feed in the boiling range of gasoline, which contains mononuclear aromatic substances including benzene, olefins and paraffins of low octane levels, and which comprises a fraction fractionated naphtha containing sulfur and a benzene-rich reforming coalition, in a first step under fractionation conditions which comprise a temperature between 204 ° and 427 ° C with a solid, acid intermediate pore size catalyst, consisting essentially of zeolite ZSM-5 having an acid activity comprising an alpha value between 20 and 200 at a pressure from 2172 to 6998 kPa, a space velocity of 1 to 6 LHSV, a ratio of hydrogen to hydrocarbons from 17.8 to 445 nlld1 of hydrogen per barrel of the feed, to rent the benzene with the olefins to form aromatic substances of alkyl and to fractionate olefins and paraffins low octane number in the feed, the conversion of olefins and naphthenes to subs aromatic substances which are less than 25% by weight, with the conversion of benzene from 10 to 60%, to form an intermediate product of reduced benzene content in relation to the feed, hydrodesulfurize the intermediate product in the presence of a hydrodesulphurisation catalyst at a temperature of 260 ° to 427 ° C, a pressure of 2171 to 6998 kPa, a space velocity of 1 to 6 LHSV and a ratio of hydrogen to hydrocarbons from 178 to 445 nlld1 of hydrogen per barrel of the feed , to convert the sulfur-containing compounds in the intermediate product to the inorganic sulfur and produce a desulphurized product with a total liquid yield of at least 90% by volume; and of the naphthenes with respect to the aromatic substances which is less than 25% by weight, with the conversion of benzene from 10 to 60%, to form an intermediate product of reduced benzene content in relation to the feed, hydrodesulfurize the product intermediate in the presence of a hydrodesulfurization catalyst at a temperature of 260 ° to 427 ° C, a pressure of 2172 to 6998 kPa, a space velocity of 1 to 6 LHSV, and a ratio of hydrogen to hydrocarbons of 178 to 445 nlld1 of hydrogen per barrel of feed, to convert the sulfur-containing compounds in the intermediate product to inorganic sulfur compounds and produce a desulfurized product with a total liquid yield of at least 90% by volume. SUMMARY OF THE INVENTION The present invention relates to a gasoline of low sulfur content which is produced from a naphtha containing sulfur, fractionated, olefinic, by treatment on an acid catalyst, preferably a zeolite of intermediate pore size such as ZSM-5. to fractionate low octane number paraffins and olefins under mild conditions with limited aromatization of olefins and naphthenes. A coalition rich in benzene is coprocessed with naphtha to reduce benzene levels in the alkylation coalition. This initial processing step is followed by hydrodesulfurization over a hydrotreating catalyst such as CoMo on alumina. In addition to reducing the levels of benzene in the combined feeds, the initial treatment on the acid catalyst removes the olefins which could otherwise be saturated in the hydrodesulfurization, consuming the hydrogen and lowering the octane number of the product, and converting them into compounds which make a positive contribution to octane. The total liquid yield is large, typically at least 90% or greater. The aromatic substances of the product are typically increased by no more than 25% by weight relative to the combined feeds and may be of a lower value than in the feed.