EP0949315B1 - Process for the conversion of hydrocarbons by treatment in a distillation zone associated with a reaction zone and its application in the hydrogenation of benzene - Google Patents

Description

The invention relates to a process for the conversion of hydrocarbons. The process according to the invention associates a distillation zone with a conversion reaction zone hydrocarbon at least partly external to the distillation zone. So this process enables the selective conversion of hydrocarbons separated from hydrocarbon feed through the distillation zone.

More particularly, the process according to the invention is applicable to the reduction selective content of light unsaturated compounds (ie containing not more than six carbon atoms per molecule) containing possible olefins and benzene, of a hydrocarbon cut containing essentially at least 5 carbon atoms per molecule without significant loss of octane number.

Indeed, given the recognized harmfulness of benzene and olefins, unsaturated compounds, the general trend is to reduce the content of these constituents in the essences.

Benzene has carcinogenic properties and it is therefore necessary to limit at most any possibility of polluting the ambient air, in particular by excluding it virtually automotive fuels. In the United States the fuels reformulated must not contain more than 1% by volume of benzene; in Europe, it is recommended to gradually move towards this value.

Olefins have been recognized as being among the most reactants in the cycle of photochemical reactions with the oxides of nitrogen, which produced in the atmosphere and which leads to the formation of ozone. An elevation of the concentration of ozone in the air can be a source of respiratory problems. The decrease in the olefin content of the species, and more particularly the the lightest olefins that are most likely to volatilize fuel handling is therefore desirable.

The benzene content of a gasoline is very largely dependent on that of the Reform component of this essence. The reformate results from a treatment catalytic naphtha for producing aromatic hydrocarbons, consisting mainly of 6 to 9 carbon atoms in their molecule and whose very high octane number gives gasoline its anti-knock properties.

For the reasons of harm described above, it is therefore necessary to reduce at most the benzene content of the reformate.

The benzene of a reformate can be hydrogenated to cyclohexane. As he is it is impossible to selectively hydrogenate benzene from a hydrocarbon mixture also containing toluene and xylenes, it is therefore necessary to fractionate this mixture beforehand so as to isolate a cup containing no than benzene, which can then be hydrogenated.

Patent application WO 95/15934 describes a reactive distillation which is intended to selectively hydrogenate diolefins and C2-C5 acetylenic compounds. The distillate can be recovered separately from light ones. The catalytic zone hydrogenation is completely internal to the distillation column, which is not not allow a good dissolution of the hydrogen in the charge nor of power increase the pressure.

A process has been described in which the catalytic zone of hydrogenation of the benzene is internal to the distillation column that separates benzene from other Aromatic compounds (Benzene Reduction - Kerry Rock and Gary Gildert CDTECH - 1994 Conference on Clean Air Act Implementation and Reformulated Gasoline - Oct. 94), which allows a saving of equipment. It is appeared that the pressure drop across the catalyst bed (s) according to said process does not allow to obtain an intimate mixture between the liquid phase and the gas stream containing hydrogen. Indeed, according to this type of technology where the reaction and distillation proceed simultaneously in the same physical space, the liquid phase descends through any catalytic bed of the reaction zone into runoff streaming, so in nets of liquid. The gaseous fraction containing the vaporized charge fraction and the gaseous stream containing hydrogen rises to through said catalyst bed in gas columns. By this provision, the entropy of the system is strong and the pressure drop across the bed (s) cataiytic (s) is weak. As a result the way to operate according to this type of technology does not easily promote the dissolution of hydrogen in the liquid phase comprising the unsaturated compound (s).

The applicant's patent application EP 0 781 830 A1 describes a process of hydrogenation of benzene in which a distillation column is used associated with a reaction zone at least partly external. The effluent is recovered at the top of the column, then by a condenser, arrives in a balloon from which a new separation operation is necessary to recover the desired product. Indeed, the column head effluent comprises light gases such that excess hydrogen mixed with benzene-depleted reformate and the distillate liquid contains a lot of dissolved gas which may impose a step additional separation.

The process according to the present invention is an improvement of the demand for Patent EP 0 781 830 A1 of the applicant, all of whose characteristics are considered as included in this description.

The invention relates to a process for converting a hydrocarbon feedstock combining a distilling zone producing a vapor distillate and an effluent of bottom, and a reaction zone at least partly external to the distillation zone. At least one conversion reaction of at least a portion of at least one hydrocarbon takes place in a reaction zone comprising at least one bed catalytic converter, in the presence of a catalyst and a gas stream comprising hydrogen. The charge of the reaction zone is taken at the level of a sampling level and represents at least part of the liquid flowing in the distillation zone, and the effluent of the reaction zone is at least partly reintroduced into the distillation zone at the level of at least one level of reintroduction, so as to ensure the continuity of distillation. The invention is characterized in that a distillation distillate is withdrawn from the distillation zone. height of at least one level of withdrawal, said level being situated below the level of withdrawal of said steam distillate.

For the purposes of the present description, the term "liquid distillate" means a fraction liquid withdrawn from the distillation zone separate from the charge of the zone reaction.

The particular application of the process according to the invention to a process for the reduction of the bezene content of a hydrocarbon feed makes it possible to produce from a raw reformate, a reformate depleted in benzene or, if necessary, almost totally benzene and other unsaturated hydrocarbons containing not more than six carbon atoms per molecule such as light olefins, recovering directly stabilized liquid distillate, without significant loss of yield.

The method according to the invention is characterized by the dissociation of the level of sampling of the liquid distillate from the sampling level of the gaseous distillate, the liquid distillate being taken at a level of recovery below the level recovery of the steam distillate. So the desired product is recovered as stabilized liquid distillate, that is to say rid of most of excess hydrogen and possibly light gases. Plus this recovery Distillate vapor distillate removes gaseous distillates from other gases that the hydrogen present in the gas flow mainly comprising the hydrogen introduced to carry out the conversion reaction.

Thus, for example, the method according to the invention, in its particular application, makes it possible to recover directly by withdrawing from the distillation zone a stabilized liquid distillate in which at least partially the selective hydrogenation of benzene and any compound has been carried out. unsaturated having not more than six carbon atoms per molecule and different from benzene, possibly present in the feed while limiting the hydrogenation of C ₇ + compounds (ie having at least seven carbon atoms per molecule)

The method according to the invention is for example a method of treating a charge, consisting mainly of hydrocarbons containing at least 5, preferably between 5 and 9 carbon atoms per molecule, and comprising at least less an unsaturated compound, including any olefins and benzene, such that said feedstock is treated in a distillation zone, associated with a zone hydrogenation reaction at least partially external, comprising at least a catalytic bed, in which the hydrogenation of at least a part is carried out unsaturated compounds having not more than six carbon atoms per molecule, that is to say comprising up to six (inclusive) carbon atoms per molecule, and contained in the feed, in the presence of a hydrogenation catalyst and a feedstock gaseous material, preferably for the most part hydrogen, the charge of the reaction zone being taken at the level of a sampling level and representing at least a portion, preferably most, of the liquid flowing in the distillation zone, the effluent of the reaction zone being at least in part, preferably for the most part, reintroduced into the distillation at the level of at least one level of reintroduction so as to to ensure the continuity of the distillation, and finally to leave a very distillate depleted in unsaturated compounds, said process being characterized in that distillate is withdrawn in liquid form and stabilized at at least one level of recovery that is below the level of recovery of the steam distillate containing hydrogen and light gases.

The recovered liquid distillate is stabilized. Indeed, the liquid distillate is withdrawn at a sampling level below the light gas recovery level containing excess hydrogen. The light gases pass in a condenser then in a reflux flask from which at least a portion of the liquid fraction is recycled in the distillation zone and at least part of the liquid fraction can possibly be recovered.

In the case of the hydrogenation of benzene, the stabilized liquid distillate contains essentially liquid compounds having at least 5 carbon atoms and used directly as fuels.

The level of reintroduction of the load converted at least partly in the area external reaction is usually located substantially below or substantially above or substantially at the same height of at least one level sampling, preferably from said level of taking the load of the distillation zone. Preferably, the level of reintroduction is located at above the sampling level.

The level of recovery of stabilized liquid distillate is generally located above or below or substantially at the same height of at least one level of reintroduction of the load converted at least partly in the area external reaction.

In a preferred shaping, the level of recovery of the liquid distillate stabilized is located above at least one level of the distillation zone.

The distillation zone generally comprises at least one column provided with minus one internal distillation chosen from the group formed by the trays, the bulk packings and structured packings, as is known to man of the trade, such that the total overall efficiency is at least five levels theoretical. In the cases known to those skilled in the art where the implementation of a column can cause problems, it is preferable to split the way to finally use at least two columns that, put end to end, realize said area.

The charge of the distillation zone is introduced at at least one level of introduction located below the level of withdrawal of the liquid towards the zone reactionary, usually at a level of 10 to 40 theoretical plateaus and preferably from 15 to 25 theoretical trays below the drawdown level of the liquid to said reaction zone, said level of withdrawal considered being the lower.

The reaction zone generally comprises at least one catalytic bed, preferably from 1 to 4 catalytic bed (s); in the case where at least two beds cataiytics are incorporated in the distillation zone, these two beds are optionally separated by at least one internal distillation.

In the particular application of the process according to the invention to selective reduction the content of light unsaturated compounds, including possible olefins and benzene from a hydrocarbon cut, the reaction zone is a zone hydrogenation. In this case, the reaction zone of hydrogenation less partially the hydrogenation of benzene present in the feed, in such a way that the benzene content of the stabilized liquid distillate at most equal to a certain content, and said reaction zone realizes at least in part, preferably for the most part, the hydrogenation of everything unsaturated compound containing not more than six carbon atoms per molecule and different from benzene, possibly present in the charge.

The reaction zone is at least partly external to the distillation zone. Generally, the process according to the invention comprises from 1 to 6, preferably from 1 to 4 sampling level (x) which feeds (s) the outer part of the area. A part of the outer part of the reaction zone which is fed by a level given sample, if the external part of the reaction zone comprises at least minus two levy levels, usually includes at least one reactor, preferably a single reactor.

The reactor being at least partly external, a flow rate of liquid equal to, greater than or less than the liquid traffic of the distillation zone below the level of withdrawal of the charge to be converted.

In the particular application of the conversion of charges to benzene content rather high, for example at a level greater than about 3% by volume, the liquid flow rate is preferably equal to or greater than the liquid traffic of the distillation zone below the level of withdrawal.

In the particular application of the conversion of charges to benzene content rather low for example at a content of less than about 3% by volume, the flow rate taken is preferably equal to or less than the liquid traffic of the zone of distillation below the level of withdrawal.

The method according to the invention makes it possible to convert a large part of the (or) compound (s) to be converted outside the distillation zone, possibly under conditions of pressure and / or temperature different from those used in the distillation zone.

The process according to the invention is such that the flow of the liquid to be converted is generally co-current with the flow of the gas stream comprising hydrogen, for any catalytic bed of the outer part of the reaction zone.

According to a preferred embodiment of the method according to the invention, the zone The reaction mixture is entirely external to the distillation zone. In case the outer part of the reaction zone comprises at least two catalytic beds, each catalytic bed is fed by a single level of sampling, preferably associated with a single level of reintroduction, the said level of sampling being distinct from the level of levy that feeds the other bed (s) catalyst (s).

According to a preferred embodiment of the method according to the invention, the charge to convert withdrawn from the distillation zone to the reaction zone is cooled before entering the reactor. Similarly, the converted load coming out of The reactor can be cooled before being reintroduced into the distillation zone. This cooling can create a circulating reflux. In fact, for the purposes of this the term "circulating reflux" designates a circulation of a liquid withdrawn from the distillation zone to a level and re-introduced at a level above at a temperature below the temperature of the liquid at the level of the withdrawal.

In the particular case of the process for reducing the benzene content of a hydrocarbon cutting, one of the preferred embodiments of the invention is such that that the level of reintroduction of the hydrogenated feed in the column is located above the level of taking the charge to be hydrogenated in an area where the benzene content is the lowest. Even more preferably the level of reintroduction is located at least 2 theoretical plateaus above the level of collection and, even more preferably, the level of reintroduction of the charge is located at least 4 theoretical plateaus above the level of withdrawal of said load.

The preferred implementation described above makes it possible to greatly reduce the amount of catalyst needed. Indeed, this implementation makes it possible to withdraw more liquid from the distillation zone in order to convert a larger amount of benzene into the reactor without disturbing the traffic of the column outside the zone where the profile is withdrawn and without disturbing the profile concentration of the column. Reintroduction to a level above therefore greatly reduces the amount of catalyst needed to get a quantity of benzene in the final effluent as low or weaker that in the methods according to the prior art.

In addition, this preferred embodiment of the invention generally makes it possible to to reduce the reboiling power necessary for the continuity of distillation.

For carrying out the hydrogenation according to a particular application of the process of the invention, the theoretical molar ratio of hydrogen necessary for the desired conversion of benzene is 3. The amount of hydrogen dispensed before or in the hydrogenation zone is possibly in excess with respect to this stoichiometry, and all the more so that one must hydrogenate, in addition to benzene present in the feed, at least partially any unsaturated compound comprising at most six carbon atoms per molecule and present in said charge.

In general, excess hydrogen, if it exists, can be advantageously recovered for example according to one of the techniques described below. According to a first technique, excess hydrogen leaving the zone reaction is recovered either directly at the level of the effluent at the outlet of the reaction zone, either in the gaseous distillate of the distillation zone, then compressed and reused in said reaction zone to create reflux. according to a second technique, the excess hydrogen leaving the reaction zone is recovered, then injected upstream of the compression steps associated with a unit catalytic reforming mixture with hydrogen from said unit, said unit operating preferably at low pressure, that is to say generally an absolute pressure of less than 0.8 MPa.

Hydrogen, included in the gas stream, used for example in the process of the invention for the hydrogenation of unsaturated compounds comprising not more than six carbon atoms per molecule may come from any source producing hydrogen at least 50% purity, preferably at least minus 80% purity volume and even more preferably at least 90% purity volume. For example, there can be mentioned hydrogen from processes catalytic reforming, methanation, P.S.A. (alternating adsorption of pressure), electrochemical generation or steam cracking.

One of the preferred embodiments of the method according to the invention, independent or previous embodiments, is such that the bottom effluent of the zone of distillation is mixed at least partly with the recovered stabilized liquid distillate at a recovery level below the recovery level of the steam distillate. In the particular case of the process for reducing the content of benzene, the mixture thus obtained may be used as fuel either directly, either by incorporation in the fuel fractions.

When the reaction zone is partly internal to the distillation zone, the operating conditions of the part of the reaction zone internal to the zone of distillation are related to the operating conditions of distillation. Distillation is carried out under an absolute pressure generally between 0.1 MPa and 2.5 MPa with a reflux ratio between 0.1 and 20. The temperature of the zone of distillation is between 10 and 300 ° C. In general, the liquid subjected to the conversion is mixed with a gas stream comprising hydrogen whose flow rate is at least equal to the stoichiometry of the conversion reactions performed and at most equal to the flow corresponding to 10 times the stoichiometry. In the outer portion of the reaction zone, the catalyst is disposed in any bed catalytic converter according to any technology known to those skilled in the art in operating conditions (temperature, pressure ...) independent or not, of preferably independent of the operating conditions of the distillation zone. In the part of the reaction zone external to the distillation zone, the Operating conditions are generally as follows. Absolute pressure required is generally between 0.1 and 6 MPa. Operating temperature is generally between 30 and 400 ° C. The space velocity within said reaction zone, calculated with respect to the catalyst, is generally included between 0.5 and 60 h-1. The flow of hydrogen corresponding to the stoichiometry of conversion reactions carried out is between 1 and 10 times said stoichiometry.

In the particular case of the hydrogenation of benzene and other unsaturated compounds, the operating conditions are as follows. When the hydrogenation zone is partly internal to the distillation zone, the operating conditions of the portion of the hydrogenation zone internal to the distillation zone are related to the operating conditions of the distillation. The distillation is carried out under an absolute pressure generally of between 0.2 and 2 MPa, preferably between 0.4 and 1 MPa, with a reflux ratio of between 0.1 and 10, and preferably between 0.2 and 1. The zone head temperature is generally between 30 and 180 ° C and the zone background temperature is generally between 120 and 280 ° C. The hydrogenation reaction is carried out under conditions which are most generally intermediate between those established at the top and at the bottom of the distillation zone, at a temperature of between 100 and 200 ° C., and preferably between 120 and 180 ° C. , and at an absolute pressure of between 0.2 and 3 MPa, preferably between 0.4 and 2 MPa. The liquid subjected to the hydrogenation is mixed with a gaseous flow comprising hydrogen whose flow rate depends on the concentration of benzene in said liquid and, more generally, unsaturated compounds containing at most six carbon atoms per molecule of the charge. of the distillation zone. The flow rate of hydrogen is generally at least equal to the flow rate corresponding to the stoichiometry of the hydrogenation reactions carried out (hydrogenation of benzene and the other unsaturated compounds containing at most six carbon atoms per molecule, included in the hydrogenation charge) and at most equal to the flow rate corresponding to 10 times the stoichiometry, preferably between 1 and 6 times the stoichiometry, even more preferably between 1 and 3 times the stoichiometry. In the part of the hydrogenation zone external to the distillation zone, the operating conditions are generally as follows. The absolute pressure required for this hydrogenation step is generally between 0.1 and 6 MPa absolute, preferably between 0.2 and 5 MPa and even more preferably between 0.5 and 3.5 MPa. The operating temperature of the hydrogenation zone is generally between 100 and 400 ° C, preferably between 120 and 350 ° C and preferably between 140 and 320 ° C. The space velocity within said hydrogenation zone, calculated relative to the catalyst, is generally between 1 and 60 and more particularly between 1 and 40 h ^-1 (volume flow rate of charge per volume of catalyst). The hydrogen flow rate corresponding to the stoichiometry of the hydrogenation reactions carried out is between 1 and 10 times said stoichiometry, preferably between 1 and 6 times said stoichiometry and even more preferably between 1 and 3 times said stoichiometry. But the conditions of temperature and pressure can also, in the context of the process of the present invention, be between those which are established at the top and at the bottom of the distillation zone.

For the purposes of this description, reflux ratio is the ratio of mass flow rate of reflux on the feed mass flow rate of the column.

In the particular case where the reaction zone is a hydrogenation zone of the benzene and possibly olefins, the catalyst used in the zone of hydrogenation generally comprises at least one metal selected from the group VIII, preferably selected from the group consisting of nickel and platinum, used as which or preferably deposited on a support. The metal usually has to find in reduced form at least 50% by weight of its totality. But all Another hydrogenation catalyst known to those skilled in the art can also be selected.

In the case of the use of nickel, the proportion of nickel relative to the total weight of catalyst is between 5 and 70%, more particularly between 10 and 70% and preferably between 15 and 65%. In addition, generally using a catalyst such that the average size of the nickel crystallites is less than 100.10 ^-10 m, preferably less than 80.10 ^-10 m, even more preferably less than 60.10 ^-10 m.

The support is generally chosen from the group formed by alumina, silica-aluminas, silica, zeolites, activated carbon, clays, aluminous cements, rare earth oxides and alkaline earth oxides, alone or in mixture. A carrier based on alumina or silica, with a specific surface area of between 30 and 300 m ² / g, preferably between 90 and 260 m ² / g, is preferably used.

Figures 1 and 2 are each an illustration of a possibility of performing the method according to the invention. Similar devices are shown by the same numbers in all figures.

A first embodiment of the process is shown in FIG. of hydrocarbons is sent in column 2 by line 1. Said column contains distillation internals, which are for example in the case shown in Figure 1 trays or lining, represented in part by lines dotted on said figure.

At the bottom of the column, the least volatile fraction of the reformate is recovered by the line 5, a part is reboiled in the exchanger 6 and a part is evacuated by line 7. The reboiling vapor is reintroduced into the column via line 8. The stabilized liquid distillate is extracted via line 18, hydrogen and light hydrocarbons are sent through line 9 in a condenser 10 and then in a balloon 11 from which they are extracted by line 14 in the form of a purge steam. The liquid phase of the balloon 11 is partially returned by the line 12, in column head to ensure reflux, and another part of the liquid phase can be retrieved by line 13.

By means of a draw-off plate placed in the distillation zone, by the line 15 a liquid that is sent to the top of a reactor 3, after addition of hydrogen through line 4. The reactor effluent is cooled in the exchanger 16 then recycled to the column by line 17.

According to a second embodiment of the method, represented in FIG. The process is the same as that described in Figure 1 except that one extract the liquid distillate through line 18 at a column level below the level of reintroduction of the hydrocarbon feedstock in the column by the line 17.

EXAMPLES

The examples which follow illustrate a particular application of the invention, that is to say the selective reduction in unsaturated compounds and benzene of a cut hydrocarbons. They are realized by numerical simulation using the software PRO / II® from Simulation Sciences Incorporated.

Example 1 : (comparative)

This example implements the process as described in the patent application of Applicant EP 0.781.830 A1, and refers to FIG. patent application to which a third reactor 3c is added.

A metal distillation column with a diameter of 2.90 m is used, the column has from head to foot 45 theoretical trays that are numbered from up and down (including condenser and reboiler). The power of reboiling is then 8900 kw.

Three hydrogenation reactors located outside the distillation column are used which together contain 37.4 m ³ of catalyst.

An industrial reformate charge is used. The simulation of the operation of process is carried out for a flow rate of 305.9 kmol / h of reformate having the composition shown in Table 1.

The charge for the column is injected via line 1 to the plate 33. The charges for the three reactors 3a, 3b and 3c are withdrawn from the trays 6, 8 and 10 respectively via the lines 15a, 15b and 15c. Hydrogen is introduced through lines 4a, 4b and 4c before entering the reactors operating in downflow and 1.5 MPa absolute pressure. The reactors are loaded respectively with 4.4, 13.4 and 16.6 m ³ of nickel catalyst sold by PROCATALYSE under the reference LD746. The reactor positioned in the bottom of the column contains the least catalyst. The hydrogen / benzene molar ratio is 3.1. The effluents from the reactors 3a, 3b and 3c are re-injected respectively into the column via the lines 16a, 16b and 16c to the plates 5, 7 and 9. The effluent depleted of unsaturated compounds is withdrawn at the top of the column.

The absolute pressure of the reflux flask is 0.5 MPa, the reflux temperature is 50 ° C. The temperature of the liquid before mixing with hydrogen is between 120 and 150 ° C and that of hydrogen is 25 ° C. The ratio by weight reflux / load is 1.72.

Simulated compositions of light reformate fractions (13), purge vapor (14) and heavy reformate (7) are shown in Table 1.

Example 2 (according to the invention)

The unit of Example 2 is shown in Figure 2 appended to the text of the this request.

A distillation column having a diameter of 1.83 m is used.

The same catalyst is used, the same charge as in Example 1, but here it operates with a single hydrogenation reactor located outside the distillation column. The charge for the column is injected via line 1 to plate 33. The charge for reactor 3 is withdrawn from plate 12 via line 15. Hydrogen is introduced via line 4 before entering the reactor operating in flow. down and under 1.5 MPa. The reactor is charged with 8 m ³ of LD746 catalyst. The hydrogen / benzene molar ratio is 3.1. The effluent from reactor 3 is cooled and then re-injected into the column via line 17 to plate 8. The liquid distillate (18) is extracted from plate number 5, hydrogen and light hydrocarbons are extracted from the reflux flask. the column (11) in the form of a steam distillate (14). The absolute pressure at the reflux flask is 0.5 MPa. The simulated compositions of the light reformate (18), purge vapor (14) and heavy reformate (7) fractions are shown in Table 2.

Example 3: Process Performance

Table 3 summarizes the values of the RVP vapor pressure, the amount of benzene present in the final effluent consisting of stabilized liquid distillate and the column bottom effluent, the reboil power, the total volume of catalyst used and the diameter of the column in the process according to Example 1 and in the process according to Example 2.

Traffic at the top of the column results in a light reformate at a RVP (Reid Vapor Pressure) vapor pressure of less than 0.1 MPa. The reboiling power is 2.7 times lower in the process according to the present invention compared with the method according to the prior art as described in Example 1. In addition, the reflux ratio is in the process according to the present invention of 0.6, whereas it is 1.7 in Example 1. Another advantage of the process according to the present invention is that for higher performance, only 8 m ³ of catalyst is used compared with 37.4 m ³ Example 1. Finally, the process according to the present invention makes it possible to reduce the diameter of the column.

Examples 4, 5 and 6 describe a method with a column charge different from the charge used in Examples 1 and 2, the charge containing three times more heavy reformat.

Example 4 : (comparative)

This example describes a process without distillate stabilization with a single reactor hydrogenation located outside the distillation column and with reintroduction of the hydrogenated feed 4 trays above the level of racking.

The simulation of the operation of the process is carried out for a flow rate of 1318.64 kmol / h of reformate with a composition as defined in the table 4.

The column includes 45 theoretical plates (including condenser and reboiler) and at a diameter of 3.50 m.

The desired olefin depleted effluent is withdrawn at the top of the column with the light gases. The reintroduction level in the column is 4 trays higher at the sampling level. The unit is similar to that of FIG. 1 appended to the text of the present application but without withdrawal at 18. The charge for the column is injected via line 1 to plate 33. The charge for reactor 3 is withdrawn from plate 12 via line 15. The hydrogen is introduced via line 4 before entering the reactor operating in downflow and 1.5 MPa absolute pressure. The reactor is charged with 12 m ³ of LD746 catalyst. The hydrogen / benzene molar ratio is 2.8. The effluent from reactor 3 is cooled by an exchanger and then re-injected into the column via line 17 to plate 8. The absolute pressure at the reflux flask is 0.5 MPa. The simulated compositions of the light reformate (13), purge vapor (14) and heavy reformate (7) fractions are shown in Table 4. The performances are shown in Table 7.

The reflux ratio is 0.40. The reboiling power is 15.660 kw.

Example 5 (according to the invention)

The process has a configuration according to the invention with withdrawal of a stabilized liquid distillate below the distillation of a vapor distillate and with a level of reintroduction of the hydrogenated feed 4 trays over the racking tray. The unit is shown in FIG.

The column includes 45 theoretical plates (including condenser and reboiler) and has a diameter of 3.20 m.

The reflux ratio with respect to the diet is 0.51. The power of reboiling is 13,370 kw.

The process is carried out with an external hydrogenation reactor containing 12 m ³ of catalyst and operating at an absolute pressure of 1.5 MPa.

The same catalyst, the same charge as those described in Example 4, is used, but the procedure according to the present invention is followed, that is to say that the stabilized liquid distillate (light reformate) is recovered from the plate 5. and the steam distillate at the top of the column. The charge for the column is injected via line 1 to plate 33. The charge for reactor 3 is withdrawn from plate 12 via line 15. Hydrogen is introduced via line 4 before entering the reactor operating in flow. downward and under 1.5 MPa absolute pressure. The reactor is charged with 12 m ³ of LD746 catalyst. The hydrogen / benzene molar ratio is 3.0. The effluent from reactor 3 is cooled and then re-injected into the column via line 17 to plate 8. The absolute pressure at the reflux flask is 0.5 MPa.

Simulated compositions of stabilized liquid distillate fractions (light reformate) (18), purge steam (14) and heavy reformate (7) are shown in Table 5. The performances are shown in Table 7.

It is found that the process according to the present invention, where there is a single reactor of hydrogenation of benzene and olefinic compounds of the charge located at outside the distillation zone, an exchanger for cooling the effluent, a return to a higher level in the column (+ 4 trays in this example), a withdrawal of the liquid distillate from the plate 5 makes it possible to obtain a liquid distillate "Stabilized" with a lower reboil power than that of Example 4, and with a better conversion of benzene.

The addition of the pasteurization zone in relation to the operating mode described in Example 4 improves the quality of reformat but also the performance in terms of benzene removal and reboil power.

This configuration makes it possible to obtain a "stabilized" distillate, ie a R.V.P. less than a required value, in this example we obtain a PVR of 0.08 MPa much more efficient than the RVP of Example 4 (0.41 MPa).

In addition, it achieves higher conversion performance than those described in Example 4, here 0.46% volume of benzene is obtained in the product formed by the mixture of light reformate and heavy reformate instead of 0.59% vol. in example 4 while in example 4 we increased the order 20% of the reboiling power compared to that used in the present example.

Example 6 (according to the invention)

The unit is represented by FIG.

The same scheme is used, the same hydrogenation reactor located outside of the column, the same catalyst, the same charge as in Example 5 but the re-injection position of the reactor effluent is 7 trays above the take-off tray and liquid distillate withdrawal takes place at tray 6. The Reflux (reflux / feeding) is 0.23. This reboiling is 12,350 kw.

In this example, additional cooling is carried out on the effluent of the reactor.

The column includes 45 theoretical plates (including condenser and reboiler) and has a diameter of 3.05 m.

The charge for the column is injected via line 1 to plate 33. The charge for reactor 3 is withdrawn from plate 12 via line 15. Hydrogen is introduced via line 4 before entering the reactor operating in downward flow. and under 1.5 MPa absolute pressure. The reactor is charged with 20.4 m ³ of LD746 catalyst. The hydrogen / benzene molar ratio is 2.9. The effluent from reactor 3 is cooled and then re-injected into the column via line 17 to plate 5. The liquid distillate (18) is withdrawn from plate 6 under the return of line 17. The absolute pressure at the reflux flask is 0.5 MPa. The simulated compositions of the light reformate (13), purge vapor (14) and heavy reformate (column bottom effluent) fractions (7) are shown in Table 6. The performances are shown in Table 7.

The method according to this implementation makes it possible to work with a weak reboiling power for conversion to benzene as good as known methods.

Example 7 : Process Performance

Table 7 summarizes the values of the RVP vapor pressure, the amount of benzene present in the final effluent consisting of stabilized liquid distillate and column bottom effluent, reboil power and total volume of catalyst used.

In the method according to the present invention, ie as described for example in Examples 5 and 6, a liquid distillate with a vapor pressure is obtained significantly lower than the vapor pressure of the overhead effluent of Example 4, which shows that the liquid distillate according to Example 5 and according to Example 2 contains essentially liquid compounds having at least 5 carbon atoms and cleared of light gaseous components.

In addition, the method according to the invention makes it possible to operate with a device of distillation of lower circumference.

Finally, one of the implementations of the process according to the present invention in which the reactor is totally external makes it possible to have a lower reboiling power, that is to say that there is energy saving spent in the reactor. exchanger 6 for vaporizing a portion of the least volatile fraction of the reformate recovered at the bottom of the column and reintroduced into the column. Composition and flow rate of the feedstock and effluents for Example 1 Body / kmoles / h Charge H2 Steam purge Light Reform Heavy Reformat H2 0.00 60.05 5.13 0.39 0.00 methane 0.00 2.30 1.74 0.57 0.00 ethane 0.00 1.84 0.83 1.01 0.00 propane 0.00 1.05 0.18 0.87 0.00 butanes 17,20 0.53 1.34 16.39 0.00 iso pentanes 15.14 0.54 14.60 0.00 normal pentanes 24.61 0.70 23.91 0.00 dimethylbutane 24.24 0.38 23.86 0.00 hexanes 16,15 0.14 16,21 0.02 C7 paraffins 21, 39 0.00 0.00 21,39 C8 paraffins 1.37 0.00 0.00 1.37 methylcyclopentane 26.24 0.23 25.69 0.31 cyclohexane 0.00 0.02 4.04 14,03 methylcyclohexane 0.00 0.00 0.00 0.00 hexenes 0.22 0.00 0.00 0.00 Benzene 19.42 0.00 0.11 1.21 Toluene 40.72 0.00 0.00 40.72 C8 aromatics 40,20 0.00 0.00 40,20 Aromatic C9 24.98 0.00 0.00 24.98 aromatic C10 34,02 0.00 0.00 34,02 305.90 65.77 11.23 127.66 178.26 Composition and flow rate of the feedstock and effluents for Example 2 Body / kmoles / h Charge H2 Steam purge Light Reform Heavy Reformat H2 0.00 59.80 5.20 0.02 0.00 methane 0.00 2.29 2.26 0.03 0.00 ethane 0.00 1.83 1.79 0.04 0.00 propane 0.00 1.05 0.97 0.07 0.00 butanes 17,20 0.52 11.87 5.85 0.00 iso pentanes 15.14 0.93 14,21 0.00 normal pentanes 24.61 0.88 23,74 0.00 dimethylbutane 24.24 0.04 24,20 0.00 hexanes 16,15 0.00 16.35 0.02 C7 paraffins 21,39 0.00 0.01 21.38 C8 paraffins 1.37 0.00 0.00 1.37 methylcyclopentane 26.24 0.00 26.06 0.18 cyclohexane 0.00 0.00 17.97 0.15 methylcyclohexane 0.00 0.00 0.00 0.00 hexenes 0.22 0.00 0.00 0.00 Benzene 19.42 0.00 0.17 1.13 Toluene 40.72 0.00 0.00 40.72 C8 aromatics 40,20 0.00 0.00 40,20 Aromatic C9 24.98 0.00 0.00 24.98 aromatic C10 34,02 0.00 0.00 34,02 305.90 65.49 23.95 128.71 164.15 example 1 2 RVP MPa 0.41 0.09 Benzene% vol. 0.31 0.31 Q rewarming 1.E6 kcal / h 8,900 3.340 total catalyst volume m ³ 37.4 8 Column diameter m 2.90 1.83 Composition and flow rate of the feedstock and effluents for Example 4 Body / kmoles / h Charge H2 Steam purge Light Reform Heavy Reformat H2 0.00 218.24 10.41 1.02 0.00 methane 0.00 8.37 5.71 2.66 0.00 ethane 0.00 6.69 2.38 4.31 0.00 propane 0.00 3.82 0.51 3.32 0.00 butanes 18,00 1.91 1.00 18.91 0.00 iso pentanes 63.54 1.63 61.91 0.00 normal pentanes 46.43 0.97 46.32 0.00 dimethylbutane 18.50 0.21 18.29 0.00 other paraffins C6 109.27 0.90 111.17 0.02 C7 paraffins 60.75 0.11 34.24 26,80 C8 paraffins 7.46 0.00 0.00 7.46 paraffins C9 + 3.47 0.00 0.00 3.47 cyclopentane 2.99 0.04 2.95 0.00 methylcyclopentane 5.00 0.03 4.95 0.03 cyclohexane 0.83 0.31 66.42 0.19 methylcyclohexane 4.50 0.00 0.06 5.93 C8 naphthenes 0.62 0.00 0.00 0.62 pentenes 2.37 0.04 1.46 0.00 hexenes 3.32 0.00 0.49 0.00 heptenes 1.60 0.00 0.00 1.17 Benzene 76.77 0.05 7.15 3.5 Toluene 331.01 0.00 0.00 329.52 C8 aromatics 371.99 0.00 0.00 371.99 Aromatic C9 165.74 0.00 0.00 165.74 Aromatic C10 24.49 0.00 0.00 24.49 TOTAL 1318.64 239.04 24.32 385.62 940.93 Composition and flow rate of the feedstock and effluents for Example 5 Body / kmoles / h Charge H2 Steam purge Light Reform Heavy Reformat H2 0.00 230.20 14.23 0.04 0.00 methane 0.00 8.82 8.74 0.09 0.00 ethane 0.00 7.06 6.94 0.12 0.00 propane 0.00 4.03 3.84 0.20 0.00 butanes 18,00 2.02 14,90 5.12 0.00 iso pentanes 63.54 6.69 56.85 0.00 normal pentanes 46.43 2.30 45.24 0.00 dimethylbutane 18.50 0.06 18.43 0.00 other paraffins C6 109.27 0.09 112.24 0.01 C7 paraffins 60.75 0.00 44.27 17.26 C8 paraffins 7.46 0.00 0.00 7.46 paraffins C9 + 3.47 0.00 0.00 3.47 cyclopentane 2.99 0.02 2.97 0.00 methylcyclopentane 5.00 0.00 4.98 0.02 cyclohexane 0.83 0.00 69.35 0.07 methylcyclohexane 4.50 0.00 0.36 5.87 C8 naphthenes 0.62 0.00 0.00 0.62 pentenes 2.37 0.15 1.11 0.00 hexenes 3.32 0.00 0.24 0.00 heptenes 1.60 0.00 0.01 0.80 Benzene 76.77 0.00 4.20 4.00 Toluene 331.01 0.00 0.00 329.27 C8 aromatics 371.99 0.00 0.00 371, 99 Aromatic C9 165.74 0.00 0.00 165.74 Aromatic C10 24.49 0.00 0.00 24.49 TOTAL 1318.64 252.14 57.96 365.82 931.07 Composition and flow rate of the feedstock and effluents for Example 6 Body / kmoles / h Charge H2 Steam purge Light Reform Heavy Reformat H2 0.00 223.67 9.94 0.00 0.00 methane 0.00 8.57 8.56 0.01 0.00 ethane 0.00 6.86 6.83 0.03 0.00 propane 0.00 3.92 3.80 0.12 0.00 butanes 18,00 1.96 14.04 5.92 0.00 iso pentanes 63.54 5.71 57.83 0.00 normal pentanes 46.43 1.94 46.35 0.00 dimethylbutane 18.50 0.05 18,45 0.00 other paraffins C6 109.27 0.08 112.46 0.03 C7 paraffins 60.75 0.00 41.93 19.36 C8 paraffins 7.46 0.00 0.00 7.46 paraffins C9 + 3.47 0.00 0.00 3.47 cyclopentane 2.99 0.02 2.97 0.00 methylcyclopentane 5.00 0.00 4.96 0.04 cyclohexane 0.83 0.00 69.27 0.12 methylcyclohexane 4.50 0.00 0.44 4.84 C8 naphthenes 0.62 0.00 0.00 0.62 pentenes 2.37 0.04 0.46 0.00 hexenes 3.32 0.00 0.01 0.00 heptenes 1.60 0.00 0.01 1.05 Benzene 76.77 0.00 1.13 7.09 Toluene 331.01 0.00 0.01 330.22 C8 aromatics 371.99 0.00 0.00 371.99 Aromatic C9 165.74 0.00 0.00 165.74 Aromatic C10 24.49 0.00 0.00 24.49 TOTAL 1318.64 244.99 51,01 362.35 936.53 example 4 5 6 RVP MPa 0.41 0.08 0.06 Benzene% vol. 0.56 0.46 0.46 Q rewarming 1.E6 kcal / h 15,660 13,370 12,350 total catalyst volume m ³ 12 12 20.4 Column diameter m 0.50 3.20 3,050

Claims (14)

1. A process for converting a hydrocarbon feed in which said feed is treated in a distillation zone producing an overhead vapour distillate and a bottom effluent, associated with an at least partially external reaction zone and comprising at least one catalytic bed, in which at least one reaction for converting at least a portion of at least one hydrocarbon is carried out in the presence of a catalyst and a gas stream comprising hydrogen, the feed for the reaction zone being drawn of at the height of at least one draw-off level and representing at least a portion of the liquid flowing in the distillation zone, at least part of the effluent from the reaction zone being re-introduced into the distillation zone at the height of at least one reintroduction level, so as to ensure continuity of distillation, said process being characterized in that a stabilised liquid distillate is withdrawn from the distillation zone at the height of at least one withdrawal level, said level being located below the vapour distillate withdrawal level and which is free of the major portion of excess hydrogen and possibly light gases.
2. A process according to claim 1, comprising a single level for drawing off the feed for the reaction zone.
3. A process according to claim 1 or claim 2, in which the level for withdrawing the liquid distillate is located above the level for drawing off the feed for the reaction zone.
4. A process according to any one of claims 1 to 3, in which the level for re-introducing effluent from the reaction zone is located above the level for drawing off feed for the reaction zone.
5. A process according to claim 4, in which the level for re-introducing effluent from the reaction zone is at at least the second theoretical plate above the level for drawing off feed for the reaction zone.
6. A process according to any one of claims 1 to 5, in which the reaction zone is completely external to the distillation zone.
7. A process according to any one of claims 1 to 6, in which distillation is carried out at an absolute pressure in the range 0.1 to 2.5 MPa with a reflux ratio in the range 0.1 to 20 and at a temperature in the range 10°C to 300°C.
8. A process according to any one of claims 1 to 7, in which for the portion of the conversion reaction external to the distillation zone, the absolute pressure required for this conversion step is in the range 0.1 to 6 MPa, the temperature is in the range 30°C to 400°C, the space velocity in the conversion zone, calculated with respect to the catalyst, is generally in the range 0.5 to 60 h^-1 (volume of feed per volume of catalyst per hour) and the hydrogen flow rate is in the range one to ten times the flow rate corresponding to the stoichiometry of the conversion reactions carried out.
9. A process according to any one of claims 1 to 8, in which a feed the major portion of which is constituted by hydrocarbons comprising at least 5 carbon atoms per molecule and comprising at least one unsaturated compound, comprising benzene and possibly at least one olefin, is treated.
10. A process according to claim 9, in which the reaction zone is a hydrogenation zone, in which at least a portion of the unsaturated compounds containing at most six carbon atoms per molecule and contained in the feed is hydrogenated in the presence of a hydrogenation catalyst.
11. A process according to claim 9 or claim 10, in which distillation is carried out at an absolute pressure in the range 0.2 to 2 MPa, with a reflux ratio in the range 0.1 to 10, the temperature at the head of the distillation zone being in the range 30°C to 180°C and the temperature at the bottom of the distillation zone being in the range 120°C to 280°C.
12. A process according to any one of claims 9 to 11 in which, for the portion of the hydrogenation reaction external to the distillation zone, the absolute pressure required for the hydrogenation step is in the range 0.1 to 6 MPa, the temperature is in the range 100°C to 400°C, the space velocity in the hydrogenation zone, calculated with respect to the catalyst, is generally in the range 1 to 60 h^-1 (volume of feed per volume of catalyst per hour), and the hydrogen flow rate is in the range one to ten times the flow rate corresponding to the stoichiometry of the hydrogenation reactions carried out.
13. A process according to any one of claims 9 to 12 in which, for the portion of the hydrogenation reaction internal to the distillation zone, the hydrogenation step is carried out at a temperature of 100°C to 200°C, at an absolute pressure in the range 0.2 to 3 MPa, and the hydrogen flow rate supplying the hydrogenation zone is in the range one to ten times the flow rate corresponding to the stoichiometry of the hydrogenation reactions carried out.
14. A process according to any one of claims 9 to 13, in which the catalyst used in the hydrogenation reaction zone comprises at least one metal selected from the group formed by nickel and platinum.

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