TWO-STAGE HYDROCRACKING PROCESS FOR PRODUCING NAPHTHA, COMPRISING A HYDROGENATION STAGE IMPLEMENTED DOWNSTREAM OF THE SECOND HYDROCRACKING STAGE

Abstract

The present invention is based on the use of a two-step hydrocracking process for the production of naphtha, comprising a step of hydrogenation placed downstream of the second hydrocracking step, the hydrogenation step treating the effluent resulting from the second hydrocracking step in the presence of a specific hydrogenation catalyst. Furthermore, the hydrogenation step and the second hydrocracking step are performed under specific operating conditions and in particular under quite specific temperature conditions.

Claims

1. Process for producing naphtha from hydrocarbon feedstocks containing at least 20% by volume and preferably at least 80% by volume of compounds boiling above 340° C., said process comprising and preferably consisting of at least the following steps: a) a step of hydrotreating said feedstocks in the presence of hydrogen and at least one hydrotreating catalyst, at a temperature of between 200° C. and 450° C., under a pressure of between 2 and 25 MPa, at a space velocity of between 0.1 and 6 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is between 100 and 2000 NI/I, b) a step of hydrocracking at least one portion of the effluent resulting from step a), the hydrocracking step b) taking place, in the presence of hydrogen and at least one hydrocracking catalyst, at a temperature of between 250° C. and 480° C., under a pressure of between 2 and 25 MPa, at a space velocity of between 0.1 and 6 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is between 80 and 2000 NI/I, c) a step of high-pressure separation of the effluent resulting from the hydrocracking step b) to produce at least a gaseous effluent and a liquid hydrocarbon effluent, d) a step of distilling at least one portion of the liquid hydrocarbon effluent resulting from step c) performed in at least one distillation column, from which step the following are drawn off: a gaseous fraction, at least one fraction comprising the converted hydrocarbon products having at least 80% by volume of products boiling at a temperature below 250° C., preferably below 220° C., preferably below 190° C. and more preferably below 175° C., and an unconverted liquid fraction having at least 80% by volume of products having a boiling point above 175° C., preferably above 190° C., preferably above 220° C. and more preferably above 250° C., e) optionally a purging of at least one portion of said unconverted liquid fraction containing HPNAs, having at least 80% by volume of products having a boiling point above 175° C., before the introduction thereof into step f), f) a second step of hydrocracking at least one portion of the unconverted liquid fraction having at least 80% by volume of products with a boiling point above 175° C., resulting from step d) and optionally purged, said step f) being performed in the presence of hydrogen and of at least one second hydrocracking catalyst, at a temperature TR1 of between 250° C. and 480° C., under a pressure of between 2 and 25 MPa, at a space velocity of between 0.1 and 6 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is between 80 and 2000 NI/I, g) a step of hydrogenating at least one portion of the effluent resulting from step f) performed in the presence of hydrogen and of a hydrogenation catalyst, at a temperature TR2 between 150° C. and 470° C., under a pressure of between 2 and 25 MPa, at a space velocity of between 0.1 and 50 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is between 100 and 4000 NI/I, said hydrogenation catalyst comprising at least one metal from group VIII chosen from nickel, cobalt, iron, palladium, platinum, rhodium, ruthenium, osmium and iridium alone or as a mixture and not containing any metal from group VIB and a support chosen from refractory oxide supports, and in which the temperature TR2 is at least 10° C. below the temperature TR1, h) a step of high-pressure separation of the effluent resulting from the hydrogenation step g) to produce at least a gaseous effluent and a liquid hydrocarbon effluent, i) recycling, into said distillation step d), at least one portion of the liquid hydrocarbon effluent resulting from step h).

2. Process according to claim 1, in which said hydrocarbon feedstocks are chosen from VGOs or vacuum distillates VDs or gas oils, such as the gas oils resulting from the direct distillation of crude or from conversion units, such as FCC, coker or visbreaking units, and also feedstocks originating from units for the extraction of aromatics from lubricating oil bases or resulting from the solvent dewaxing of lubricating oil bases, or else distillates originating from the desulfurization or hydroconversion of ATRs (atmospheric residues) and/or VRs (vacuum residues), or else from deasphalted oils, or feedstocks resulting from biomass, or any mixture of the abovementioned feedstocks.

3. Process according to claim 1, in which the hydrotreating step a) is performed at a temperature of between 300° C. and 430° C., under a pressure of between 5 and 20 MPa, at a space velocity of between 0.2 and 5 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is between 300 and 1500 NI/I.

4. Process according to claim 1, in which the hydrocracking step b) is performed at a temperature of between 330° C. and 435° C., under a pressure of between 3 and 20 MPa, at a space velocity of between 0.2 and 4 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is between 200 and 2000 NI/I.

5. Process according to claim 1, in which the following are drawn off from the distillation step d): at least one fraction comprising the converted hydrocarbon products having at least 80% by volume of products boiling at a temperature below 190° C., and an unconverted liquid fraction having at least 80% by volume of products having a boiling point above 190° C.

6. Process according to claim 1, in which the following are drawn off from the distillation step d): at least one fraction comprising the converted hydrocarbon products having at least 80% by volume of products boiling at a temperature below 175° C., and an unconverted liquid fraction having at least 80% by volume of products having a boiling point above 175° C.,

7. Process according to claim 1, in which the hydrocracking step f) is performed at a temperature TR1 of between 320° C. and 450° C., very preferably between 330° C. and 435° C., under a pressure of between 9 and 20 MPa, at a space velocity of between 0.2 and 3 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is between 200 and 2000 NI/I.

8. Process according to claim 1, in which said hydrogenation step g) is performed at a temperature TR2 of between 180° C. and 320° C., under a pressure of between 9 and 20 MPa, at a space velocity of between 0.2 and 10 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is between 200 and 3000 NI/I.

9. Process according to claim 1, in which step g) is performed at a temperature TR2 at least 20° C. lower than the temperature TR1.

10. Process according to claim 9, in which step g) is performed at a temperature TR2 at least 50° C. lower than the temperature TR1.

11. Process according to claim 10, in which step g) is performed at a temperature TR2 at least 70° C. lower than the temperature TR1.

12. Process according to claim 1, in which the hydrogenation step g) is performed in the presence of a catalyst comprising, and preferably consisting of, nickel and alumina.

13. Process according to claim 1, in which the hydrogenation step g) is performed in the presence of a catalyst comprising, and preferably consisting of, platinum and alumina.

Description

LIST OF FIGURES

[0124] FIG. 1 illustrates one embodiment of the invention.

[0125] The VGO-type feedstock is sent a via pipe (1) to a hydrotreating step a). The effluent resulting from step a) is sent a via pipe (2) into a first hydrocracking step b). The effluent resulting from step b) is sent a via pipe (3) into a high-pressure separation step c) to produce at least a gaseous effluent (not shown in the figure) and a liquid hydrocarbon effluent which is sent a via pipe (4) into the distillation step d). The following are are drawn off in the distillation step d): [0126] a gaseous fraction (5), [0127] optionally a light petroleum fraction (6) having at least 80% by volume of products having a boiling point between 20° C. and 80° C., [0128] a fraction comprising the converted hydrocarbon products having at least 80% by volume of products boiling at a temperature below 250° C., (7) and [0129] an unconverted liquid fraction having at least 80% by volume of products having a boiling point above 175° C. (8).

[0130] At least one portion of the unconverted liquid fraction containing HPNAs is purged in a step e) via pipe (9).

[0131] The purged unconverted liquid fraction is sent via pipe (10) into the second hydrocracking step f). The effluent resulting from step f) is sent a via pipe (11) into a hydrogenation step g). The hydrogenated effluent resulting from step g) is sent a via pipe (12) into a high-pressure separation step h) to produce at least a gaseous effluent (not shown in the figure) and a liquid hydrocarbon effluent which is recycled via pipe (13) into the distillation step d).

EXAMPLES

[0132] The examples that follow illustrate the invention without limiting the scope thereof.

Example 1

Not in Accordance with the Invention: Basic Case of a Two-Step Hydrocracking Process not Comprising a Hydrogenation Step

[0133] A hydrocracking unit treats a vacuum gas oil (VGO) feedstock described in Table 1:

TABLE-US-00001 TABLE 1 Type VGO Flow rate t/h 37 Density — 0.92 Initial boiling point (IBP) ° C. 304 Final boiling point (FBP) ° C. 554 S content wt % 2.58 N content ppm by 1461 weight

[0134] The VGO feedstock is injected into a preheating step and then into a hydrotreating reactor under the following conditions set out in Table 2:

TABLE-US-00002 TABLE 2 Reactor R1 Temperature ° C. 385 Total pressure MPa 14 Catalyst — NiMo on alumina HSV h.sup.−1 1.67

[0135] The effluent from this reactor is subsequently injected into a second “hydrocracking” reactor R2 operating under the conditions of Table 3:

TABLE-US-00003 TABLE 3 Reactor R2 Temperature ° C. 390 Total pressure MPa  14 Catalyst — Metal/zeolite HSV h.sup.−1  3

[0136] R1 and R2 constitute the first hydrocracking step, the effluent from R2 is then sent into a separation step composed of a chain for recovery of heat and then for high-pressure separation including a recycle compressor and making it possible to separate, on the one hand, hydrogen, hydrogen sulfide and ammonia and, on the other hand, the liquid hydrocarbon effluent feeding a stripper and then an atmospheric distillation column in order to separate streams concentrated in H2S, a “Light Naphtha” light petroleum cut (of which 97% by volume of the compounds have a boiling point of between 27° C. and 80° C.), a “Heavy Naphtha” heavy petroleum cut (of which 96% by volume of the compounds have a boiling point of between 80° C. and 175° C.) and an unconverted liquid fraction (UCO) (of which 97% by volume of the compounds have a boiling point above 175° C.). A purge corresponding to 2% by mass of the flow rate of the VGO feedstock is taken as distillation bottoms from said unconverted liquid fraction.

[0137] Said unconverted liquid fraction is injected into a hydrocracking reactor R3 constituting the second hydrocracking step. This reactor R3 is used under the following conditions set out in Table 4:

TABLE-US-00004 TABLE 4 Reactor R3 Temperature (TR1) ° C. 330 Total pressure MPa  14 Catalyst — Metal/zeolite HSV h.sup.−1  2

[0138] This second hydrocracking step is performed in the presence of 80 ppm of equivalent sulfur and 4 ppm of equivalent nitrogen, which originate from the H25 and NH.sub.3 present in the hydrogen and from the sulfur and nitrogen compounds still present in said unconverted liquid fraction.

[0139] The effluent from R3 resulting from the second hydrocracking step is subsequently injected into the high-pressure separation step downstream of the first hydrocracking step and then into the distillation step.

Example 2

In Accordance with the Invention

[0140] Example 2 is in accordance with the invention insofar as it is a two-step hydrocracking process maximizing the production of the “heavy naphtha” fraction in which the effluent resulting from the second hydrocracking step is sent into a hydrogenation step in the presence of a hydrogenation catalyst comprising Ni and an alumina support and in which the temperature TR2 in the hydrogenation step is at least 10° C. below the temperature TR1 in the second hydrocracking step.

[0141] The hydrotreating step in R1, first hydrocracking step in R2 and second hydrocracking step in

[0142] R3 are performed on the same feedstock and under the same conditions as in Example 1. A purge corresponding to 2% by mass of the flow rate of the VGO feedstock is also taken as distillation bottoms from the unconverted liquid fraction.

[0143] A step of hydrogenation of the effluent resulting from R3 is performed in a reactor R4 10 downstream of R3. The operating conditions for R4 are given in Table 5. In this case, TR2 is 60° C. below TR1.

TABLE-US-00005 TABLE 5 Reactor R4 Temperature (TR2) ° C. 270 Total pressure MPa  14 Catalyst — Ni/Alumina HSV h.sup.−1  2

[0144] The catalyst used in the reactor R4 has the following composition: 28 wt % Ni on gamma alumina.

[0145] The hydrogenated effluent resulting from R4 is then sent into a high-pressure separation step before being recycled into the distillation step.

Example 3

In Accordance with the Invention

[0146] Example 3 is in accordance with the invention insofar as it is a Two-Step Hydrocracking Process maximizing the production of the “heavy naphtha” fraction in which the effluent resulting from the second hydrocracking step is sent into a hydrogenation step in the presence of a hydrogenation catalyst comprising Pt and an alumina support and in which the temperature TR2 in the hydrogenation step is at least 10° C. below the temperature TR1 in the second hydrocracking step.

[0147] The hydrotreating step in R1, first hydrocracking step in R2 and second hydrocracking step in R3 are performed on the same feedstock and under the same conditions as in Example 1. A purge corresponding to 2% by mass of the flow rate of the VGO feedstock is also taken as distillation bottoms from the unconverted liquid fraction.

[0148] A step of hydrogenation of the effluent resulting from R3 is performed in a reactor R4 downstream of R3. The operating conditions for R4 are given in Table 6. In this case, TR2 is 55° C. below TR1.

TABLE-US-00006 TABLE 6 Reactor R4 Temperature (TR2) ° C. 275 Total pressure MPa  14 Catalyst — Pt/Alumina HSV h.sup.−1  2

[0149] The catalyst used in the reactor R4 has the following composition: 0.3 wt % Pt on gamma alumina.

[0150] The hydrogenated effluent resulting from R4 is then sent into a high-pressure separation step before being recycled into the distillation step.

Example 4

In Accordance with the Invention

[0151] Example 4 is in accordance with the invention insofar as it is a two-step hydrocracking process maximizing the production of the “heavy naphtha” fraction in which the effluent resulting from the second hydrocracking step is sent into a hydrogenation step in the presence of a hydrogenation catalyst comprising Ni and an alumina support and in which the temperature TR2 in the hydrogenation step is at least 10° C. below the temperature TR1 in the second hydrocracking step.

[0152] The hydrotreating step in R1, first hydrocracking step in R2 and second hydrocracking step in R3 are performed on the same feedstock and under the same conditions as in Example 1. This time, a purge corresponding to 1% by mass of the flow rate of the VGO feedstock is taken as distillation bottoms from the unconverted liquid fraction.

[0153] A step of hydrogenation of the effluent resulting from R3 is performed in a reactor R4 downstream of R3. The operating conditions for R4 are given in Table 7. In this case, TR2 is 60° C. below TR1.

TABLE-US-00007 TABLE 7 Reactor R4 Temperature (TR2) ° C. 270 Total pressure MPa  14 Catalyst — Ni/Alumina HSV h.sup.−1  2

[0154] The catalyst used in the reactor R4 has the following composition: 28 wt % Ni on gamma alumina.

[0155] The hydrogenated effluent resulting from R4 is then sent into a high-pressure separation step before being recycled into the distillation step.

Example 5: Process Performance

[0156] Table 8 summarizes the performance of the processes described in Examples 1 to 4 in terms of “Heavy Naphtha” yield, process cycle time and overall conversion of the process. The conversion of coronene (HPNA containing 7 aromatic rings) performed in the hydrogenation step is also reported.

TABLE-US-00008 TABLE 8 1 (not in 2 (in 3 (in 4 (in accordance accordance accordance accordance with the with the with the with the Examples invention) invention) invention) invention) Scheme R3 alone R3 + R4 R3 + R4 R3 + R4 Catalyst in R3 — 28% Ni/ 0.3% Pt/ 28% Ni/ alumina alumina alumina Purge (%)  2  2  2  1 TR1 (° C.) 330 330 330 330 TR2 (° C.) — 270 275 270 Coronene  0  95  82  95 conversion (%) (1) “Heavy Naphtha” Base Base Base Base + 1 yield point Cycle time Base Base + 7 Base + 4 Base + 5 months months months Overall  98  98  98  99 conversion (%)

[0157] The coronene conversion is calculated by dividing the difference in the amounts of coronene measured upstream and downstream of the hydrogenation reactor by the amount of coronene measured upstream of this same reactor. The amount of coronene is measured by high-pressure liquid chromatography coupled to a UV detector (HPLC-UV), at a wavelength of 302 nm for which coronene has maximum absorption.

[0158] These examples illustrate the advantage of the process according to the invention which makes it possible to obtain improved performance in terms of cycle time, “Heavy Naphtha” yield or overall conversion of the process.