Process for hydrogenation of a hydrocarbon feedstock comprising aromatic compounds

Abstract

Process for hydrogenation of aromatic compounds in a feedstock comprising hydrocarbons having at least five carbon atoms, comprising: a) contacting feedstock, a hydrogen gas, and a nickel or platinum hydrogenation catalyst at 100 to 400° C., 0.5 to 8 MPa, and a feedstock flow rate 0.5 to 5 h.sup.−1, as to produce a partially-hydrogenated hydrocarbon feedstock and gas; and b) contacting the partially-hydrogenated feedstock, and a nickel or platinum hydrogenation catalyst at 100 and 400° C., a pressure of between 0.5 and 8 MPa, with a flow rate of the partially-hydrogenated feedstock between 0.3 and 8 h.sup.−1, a ratio between the volume of hydrogen and the volume of the partially-hydrogenated feedstock between 0.3 and 3 Nm.sup.3/m.sup.3, and a ratio between the superficial mass flow rate of the partially-hydrogenated feedstock and the superficial mass flow rate of gas (Ul/Ug) at the inlet of the reactor between 50 and 500.

Claims

1. Process for hydrogenation of aromatic compounds contained in a feedstock comprising hydrocarbons having at least five carbon atoms, with the process comprising at least the following stages: a) bringing said feedstock, a gas stream comprising hydrogen, and a hydrogenation catalyst comprising nickel or platinum dispersed on a substrate into contact in a reactor, with the contact being made at a temperature of between 100 and 400° C., at a pressure of between 0.5 and 8 MPa, and with an hourly volumetric flow rate of the liquid feedstock at the inlet of the reactor of between 0.5 and 5 h.sup.−1, in such a way as to reduce the content of aromatic compounds by hydrogenation and produce an effluent comprising a partially-hydrogenated hydrocarbon feedstock having a content of aromatic compounds that is less than 1,000 ppm and a gas; and b) bringing the partially-hydrogenated feedstock that is obtained from stage a) in liquid form, a gas stream comprising hydrogen, and a hydrogenation catalyst comprising nickel or platinum dispersed on a substrate into contact in a reactor, with the contact being made at a temperature of between 100 and 400° C., at a pressure of between 0.5 and 8 MPa, with an hourly volumetric flow rate of the liquid partially-hydrogenated feedstock of between 0.3 and 8 h.sup.−1, with a ratio between the volume of hydrogen that is introduced and the volume of the partially-hydrogenated feedstock of between 0.3 and 3 Nm.sup.3/m.sup.3, and with a ratio between the superficial mass flow rate of the liquid partially-hydrogenated feedstock and the superficial mass flow rate of gas (Ul/Ug) at the inlet of the reactor of between 50 and 500.

2. Process according to claim 1, in which the ratio between the superficial mass flow rate of the liquid partially-hydrogenated feedstock and the superficial mass flow rate of gas (Ul/Ug) at the inlet of the reactor is between 60 and 450.

3. Process according to claim 1, in which in stage b), the superficial mass flow rate of gas comprising hydrogen is between 0.001 and 0.1 kg/(m.sup.2s).

4. Process according to claim 1, in which in stage a), the ratio between the superficial mass flow rate of the liquid feedstock that is to be treated and the superficial mass flow rate of gas (Ul/Ug) at the inlet of the reactor is higher than 500.

5. Process according to claim 1, in which the substrate of the catalysts of stages a) and b) is selected from among aluminas, silica, silica-aluminas, magnesia, titanium oxide, zirconia, zeolites, by themselves or in a mixture, and it has a specific surface area that is greater than 50 m.sup.2/g.

6. Process according to claim 1, in which when the catalyst of stage b) comprises nickel, said stage b) is carried out at a temperature of between 120 and 200° C.

7. Process according to claim 1, in which the catalyst of stage b) comprises nickel, and the mean diameter of the nickel particles measured by magnetic granulometry is between 20 angstroms and 80 angstroms.

8. Process according to claim 1, in which the catalyst of stage b) comprises platinum, and said stage b) is carried out at a temperature of between 200 and 350° C.

9. Process according to claim 1, in which the catalyst of stages a) and/or b) comprises nickel, and the nickel content is between 15 and 60% by weight of metal nickel relative to the total catalyst weight.

10. Process according to claim 1, in which the catalyst of stages a) and/or b) comprises platinum, and the platinum content is between 0.05 and 2% by weight of metal platinum relative to the total catalyst weight.

11. Process according to claim 1, in which the catalyst for hydrogenation of stages a) and b) comprises the same metal that is selected from among nickel and platinum, and the metal content of the catalyst of stage b) is less than that of the catalyst of stage a).

12. Process according to claim 1, in which the catalyst of stages a) and/or b) also comprises at least one metal that is selected from among palladium, iridium, molybdenum, and tungsten.

13. Process according to claim 12, in which the content of palladium or iridium, expressed in terms of metal palladium or metal iridium, is between 0.05 and 2% by weight relative to the total catalyst weight.

14. Process according to claim 12, in which the content of molybdenum or tungsten, expressed in terms of oxide, is between 0.5 and 10% by weight relative to the total catalyst weight.

15. Process according to claim 1, further comprising carrying out a stage for intermediate separation of the partially-hydrogenated hydrocarbon feedstock in liquid form and gas from the effluent that is obtained from stage a), and wherein the liquid fraction that is obtained from the intermediate separation is treated in stage b).

16. Process according to claim 1, further comprising carrying out a stage for intermediate distillation of the partially-hydrogenated feedstock that is obtained from stage a) which is carried out in such a way as to separate a first fraction that has a boiling point of between the boiling point of the hydrocarbons with five carbon atoms and T.sub.x° C., and a second fraction that has a boiling point that is higher than T.sub.x° C., with T.sub.x between 150 and 250° C., and the second fraction is treated in stage b).

17. Process according to claim 1, in which the feedstock comprising hydrocarbons having at least five carbon atoms is selected from among a light naphtha fraction, a heavy naphtha fraction, a desulfurized complete naphtha fraction, a raffinate from a unit for extraction of aromatic compounds, a raffinate from dewaxing units, a kerosene fraction, a desulfurized diesel fuel fraction, or a catalytic reforming gasoline.

18. Process according to claim 1, in which the ratio between the superficial mass flow rate of the liquid partially-hydrogenated feedstock and the superficial mass flow rate of gas (Ul/Ug) at the inlet of the reactor is between 70 and 300.

19. Process according to claim 1, in which the catalyst of stage b) comprises nickel, and the mean diameter of the nickel particles measured by magnetic granulometry is between 20 angstroms and 60 angstroms.

20. Process according to claim 1, further comprising: a stage for intermediate separation of the partially-hydrogenated hydrocarbon feedstock in liquid form and gas from the effluent that is obtained from stage a), and a stage for intermediate distillation of the partially-hydrogenated feedstock in liquid form that is obtained from the intermediate separation stage, which is carried out in such a way as to separate a first fraction that has a boiling point of between the boiling point of the hydrocarbons with five carbon atoms and T.sub.x° C., and a second fraction that has a boiling point that is higher than T.sub.x° C., with T.sub.x between 150 and 250° C., wherein the second fraction from the intermediate distillation is treated in stage b).

Description

BRIEF DESCRIPTION OF THE FIGURE

(1) The FIGURE below exhibits an advantageous embodiment of the process according to the invention.

(2) With reference to the FIGURE, the liquid hydrocarbon feedstock containing aromatic compounds is brought in via the pipes 1, 3 into a first hydrogenation reactor 5 so as to carry out stage a) of the process. The feedstock, before its introduction into the reactor 5, is mixed with a gas that comprises the hydrogen that is provided via the line 2.

(3) The mixture is then preheated by means of a heat exchanger 8, which is, for example, supplied by the hot effluent that is obtained from the first hydrogenation reactor 5. The preheated mixture is next heated, by means of a vapor exchanger 4, to the necessary temperature for carrying out hydrogenation.

(4) As indicated in the FIGURE, the liquid hydrocarbon feedstock comprising hydrogen and heated is sent into the reactor 5 according to an operating mode in downward flow (the feedstock being introduced at the top of the reactor). Within the framework of the invention, it is possible, however, to use an operating mode in upward flow for the liquid hydrocarbon feedstock in a mixture with hydrogen.

(5) The first reactor 5 comprises a hydrogenation catalyst bed based on nickel or platinum dispersed on a substrate. The catalyst, in the presence of hydrogen, makes possible the at least partial conversion of the aromatic compounds into their saturated equivalent compounds. For example, the benzene is converted into cyclohexane.

(6) In the case where the hydrocarbon feedstock comprises monosaturated compounds (e.g., olefins), or polyunsaturated compounds (e.g., dioefins), the latter are also hydrogenated in their corresponding alkanes.

(7) The hydrogenation reaction consists of bringing reagents into contact with the hydrogenation catalyst. Thus, in this first hydrogenation stage, the hydrocarbon feedstock inside the reactor can be either in the liquid phase or in the vapor phase. Preferably, the temperature and pressure conditions are regulated in such a way that the hydrocarbon feedstock is in liquid form.

(8) As shown in the FIGURE, the effluent comprising the partially-hydrogenated hydrocarbon feedstock, i.e., whose aromatic compound content has been reduced, in a mixture with hydrogen that has not reacted, is drawn off from the reactor 5 via the line 7. Preferably, the first hydrogenation stage makes it possible to provide a hydrogenated feedstock that has an aromatic compound content of less than 1,000 ppm by weight, preferably less than 150 ppm by weight.

(9) The effluent is cooled by means of the heat exchanger 8 in which the heat is exchanged with the hydrocarbon feedstock that is to be treated, before being sent via the line 9 into a liquid/gas separation device 10, such as, for example, a flash drum. This device makes it possible to separate a gaseous fraction that contains hydrogen that has not reacted in the first stage and a liquid fraction comprising the partially-hydrogenated hydrocarbon feedstock.

(10) Alternatively, the liquid/gas separation device can be replaced by a distillation column (not shown) that is designed so as to carry out a fractionation of the effluent into two light and heavy fractions as described above. According to this alternative and to the extent that the light fraction corresponds to specifications of aromatic compounds, only the heavy fraction is next treated by itself in the second hydrogenation stage of stage b).

(11) With reference to the FIGURE, the gaseous fraction containing hydrogen is drawn off from the liquid/gas separation device 10 via the line 11 and is optionally recycled in the hydrogenation reactor 5 via the line 12.

(12) The liquid fraction comprising the hydrocarbon feedstock that is partially-hydrogenated and low in hydrogen is drawn off via the line 13. All or a portion of the liquid fraction is sent, after heating by means of the heat exchanger 14, via the line 15 into the hydrogenation reactor 16 of the second stage b). The hydrogenation reactor 16 comprises a catalyst bed 17 based on nickel or platinum dispersed on a substrate as described above. An addition of hydrogen is also provided via the line 22 so as to carry out the second hydrogenation stage.

(13) According to the invention, this second hydrogenation stage consists in bringing the liquid feedstock or a fraction (or hydrocarbon fraction) constituting the feedstock that is obtained from stage a) of the hydrogen into contact with a hydrogenation catalyst.

(14) This second stage also complies with the following hydrodynamic conditions: the ratio of the superficial mass flow rates of liquid and gas, Ul/Ug is between 50 and 500, preferably between 60 and 450, and in a more preferred manner between 70 and 300, with the superficial mass flow rates Ug or Ul of the gas or liquid that are calculated by the following formula Ux (kg/(m.sup.2.Math.s))=flow rate of the fluid (in kg/s)/cross-section of the reactor (m.sup.2).

(15) Preferably, the superficial mass flow rate of the gas (Ug) is preferably between 0.001 and 0.1 kg/(m.sup.2.Math.s), in a more preferred manner between 0.001 and 0.08 kg/(m.sup.2.Math.s), and in a very preferred manner between 0.005 and 0.07 kg/(m.sup.2.Math.s).

(16) As indicated in the FIGURE, the hydrocarbon feedstock that is hydrogenated and that has an aromatic compound content that is less than 30 ppm by weight, preferably less than 20 ppm by weight, and in a more preferred manner less than 10 ppm by weight is drawn off via the line 18.

(17) According to an alternative embodiment that is also shown in the FIGURE, the hydrogenated hydrocarbon feedstock that is obtained from stage b) is sent into a separation unit, for example a distillation column 19 or splitter (according to English terminology) that is designed and operated in such a way as to extract: At the top of the column 19, via the line 20, a hydrocarbon fraction that has, for example, a boiling point of between the boiling point of the hydrocarbons with five carbon atoms and T.sub.x° C., and; At the bottom of the column 19, via the line 21, a hydrocarbon fraction that has a boiling point of higher than T.sub.x° C.,
with T.sub.x generally between 150 and 250° C.

(18) The two fractions that are thus extracted from the distillation column 19 can be used as a base for the production of solvents corresponding to the specifications of aromatic compounds.

EXAMPLES

(19) In the following examples, a process is carried out with two stages for hydrogenation on catalysts based on nickel supported on alumina.

(20) These catalysts have been prepared by means of two successive dry impregnations. The impregnation method consists in using the ammoniacal method described in the U.S. Pat. No. 4,490,480.

(21) For each of the impregnation stages, an aqueous solution that contains nickel bicarbonate and ammonia, with a pH of 10.5 and heated to 50° C., is prepared so as to form the complex Ni(NH.sub.3).sub.6CO.sub.3 in solution. This solution is impregnated on the extruded alumina substrate, and then the temperature of the batch is brought within 2 hours to 90° C. and maintained for 3 hours at this temperature, which brings about the gradual decomposition of the complex and the precipitation of a nickel compound in the pores of the alumina.

(22) The impregnated precursor that is obtained is dried at 100° C. for 5 hours, and then calcined at 400° C. for 1 hour after each of the two impregnation stages.

(23) The catalyst that is used in the first hydrogenation stage a) comprises 35% by weight of nickel deposited on the cubic gamma-alumina in the form of extrudates whose surface is 185 m.sup.2/g before deposition of the nickel.

(24) The catalyst of the second hydrogenation stage b) comprises 27% by weight of nickel deposited on the same cubic gamma-alumina. The nickel particles have a mean diameter determined by magnetism of 52 angstroms.

(25) The hydrocarbon feedstock that is used has the composition described in Table 1. This feedstock was hydrotreated in advance to remove the nitrogen-containing, chlorinated and sulfur-containing compounds; it contains less than 1 ppm by weight of sulfur, less than 1 ppm by weight of nitrogen, and less than 0.1 ppm by weight of chlorine.

(26) The feedstock that is to be treated is sent into the first hydrogenation stage a) under the following operating conditions: The reactor operates in a downward flow mode (downflow); Average temperature of the bed (WABT): 160° C.; Pressure: 1.8 MPa; L.H.S.V.: 1 h.sup.−1; A gas containing 95% by volume of hydrogen is introduced into the reactor with an H.sub.2/feedstock ratio by volume of 500 Nm.sup.3/m.sup.3; Ul/Ug ratio=800; The exotherm of the reactor is controlled by means of a recycling of the cooled liquid effluent.

(27) The operating conditions used in the second hydrogenation stage b) are as follows: The reactor is operated in the upward flow mode (upflow); Average temperature of the bed (WABT): 160° C.; Pressure: 1.8 MPa; L.H.S.V.: 1 h.sup.−1

(28) A separation of the liquid and gas is carried out by cooling on the effluent that is obtained from the first hydrogenation stage a), and the thus separated liquid is sent into the second hydrogenation stage b). The separation column that is used comprises between 30 plates and is operated with a pressure of 0.7 MPa at the top of the column and with a bottom temperature of 320° C.

Example 1 (According to the Invention)

(29) The second hydrogenation stage is operated under the following hydrodynamic conditions at the inlet of the reactor: Ug=0.02 kg/(m.sup.2s) and Ul/Ug=150.

(30) A gas that contains 99.9 mol % of hydrogen is introduced into the reactor with an H.sub.2/feedstock ratio in a volume of 1 Nm.sup.3/m.sup.3.

(31) Table 1 below summarizes the composition of the hydrocarbon feedstock that has an initial boiling point of 220° C. and a final point of 350° C. and the composition of the effluents that are obtained.

(32) TABLE-US-00001 TABLE 1 Liquid Phase Effluent After the 1.sup.st Obtained from Gaseous Phase Hydrogenation the 2.sup.nd After the 1st Stage and Hydrogenation Content Hydrogenation Separation (% Stage (% (% by Stage (% by or ppm by or ppm by Compounds Weight) Volume) Weight) Weight) Paraffins 53 3 54 54 Olefins <1 — 0 0 Naphthenes 16 — 46 46 Aromatic 30 — 300 ppm 8 ppm Compounds Total 100 100 100 100

(33) Thus, the process according to the invention makes it possible to produce an effluent that is obtained from the second hydrogenation stage that has a content of aromatic compounds that is less than 10 ppm by weight, thus corresponding to the requirement of hydrocarbons with a low content of aromatic compounds, in particular in applications such as solvents.

Example 2 (Comparative)

(34) The second hydrogenation stage b) is performed under the following hydrodynamic conditions: At the inlet of the reactor: Ug=0.003 kg/(m.sup.2s) and Ul/Ug=700 (outside of the invention). The hydrogen is introduced into the reactor with an H.sub.2/feedstock ratio by volume of 0.5 Nm.sup.3/m.sup.3.

(35) Table 2 below summarizes the results that are obtained:

(36) TABLE-US-00002 TABLE 2 Liquid Phase After the 1.sup.st Effluent Obtained Hydrogenation from the 2.sup.nd Stage and Separation Hydrogenation Stage Compounds (% or ppm by Weight) (% or ppm by Weight) Paraffins 54 54 Olefins 0 0 Naphthenes 46 46 Aromatic 300 ppm 260 ppm Compounds Total 100 100

(37) It is noted that when the Ul/Ug ratio of stage b) is equal to 700, beyond the range 50-500, the effluent that is obtained after this second hydrogenation stage has a content of aromatic compounds that is considerably higher than the targeted value of 10 ppm by weight.

Example 3 (Comparative)

(38) The process of Example 1 is carried out under the conditions described above with the exception that the second hydrogenation stage b) is performed under the following hydrodynamic conditions: At the inlet of the reactor: Ug=0.07 kg/m.sup.2s and Ul/Ug=30 (outside of the invention). Hydrogen is introduced into the reactor with an H2/feedstock ratio by volume of 6 Nm.sup.3/m.sup.3.

(39) Table 3 below summarizes the results that are obtained.

(40) TABLE-US-00003 TABLE 3 Liquid Phase After the 1.sup.st Effluent Obtained Hydrogenation from the 2.sup.nd Stage and Separation Hydrogenation Stage Compounds (% or ppm by Weight) (% or ppm by Weight) Paraffins 54 54 Olefins 0 0 Naphthenes 46 46 Aromatic 300 ppm 79 ppm Compounds Total 100 100

(41) It is noted that when the Ul/Ug ratio of stage b) is equal to 30, beyond the range 50-500, the effluent that is obtained after this second hydrogenation stage has a content of aromatic compounds that is considerably higher than the targeted value of 10 ppm by weight.

Example 4 (Comparative)

(42) The second hydrogenation stage b) is performed under the following hydrodynamic conditions: At the inlet of the reactor: Ug=0.3 kg/m.sup.2s and Ul/Ug=10 (outside of the invention). Hydrogen is introduced into the reactor with an H2/feedstock ratio in a volume of 12 Nm.sup.3/m.sup.3.

(43) Table 4 below summarizes the results that are obtained.

(44) TABLE-US-00004 TABLE 4 Liquid Phase After the 1.sup.st Effluent Obtained Hydrogenation from the 2.sup.nd Stage and Separation Hydrogenation Stage Compounds (% or ppm by Weight) (% or ppm by Weight) Paraffins 54 54 Olefins 0 0 Naphthenes 46 46 Aromatic 300 ppm 79 ppm Compounds Total 100 100

(45) Again, it is observed that when the Ul/Ug ratio of stage b) is equal to 10, beyond the range 50-500, the effluent that is obtained after this second hydrogenation stage has a content of aromatic compounds that is greater than the specification of 10 ppm by weight.