Two-stage hydrocracking process comprising a hydrogenation stage upstream of the second hydrocracking stage, for the production of middle distillates

Abstract

The present invention is based on the use of a two-step hydrocracking process comprising a step of hydrogenation placed upstream of the second hydrocracking step, the hydrogenation step treating the unconverted liquid fraction separated in the distillation step in the presence of a specific hydrogenation catalyst. Furthermore, the hydrogenation step and second hydrocracking step are carried out under specific operating conditions and in particular under very specific temperature conditions.

Claims

1. A process producing middle distillates from hydrocarbon feedstocks containing at least 20% by volume of compounds boiling above 340° C., said process comprising at least the following: a) hydrotreating said feedstocks in the presence of hydrogen and at least one hydrotreating catalyst, at a temperature of 200° C. to 450° C., under a pressure of 2 to 25 MPa, at a space velocity of 0.1 to 6 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 100 to 2000 Nl/l, b) hydrocracking at least one portion of the effluent resulting from a), hydrocracking b) taking place, in the presence of hydrogen and at least one hydrocracking catalyst, at a temperature of 250° C. to 480° C., under a pressure of 2 to 25 MPa, at a space velocity of 0.1 to 6 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 80 to 2000 Nl/l, c) high-pressure separation of effluent resulting from hydrocracking b) to produce at least a gaseous effluent and a liquid hydrocarbon effluent, d) distilling at least one portion of the liquid hydrocarbon effluent resulting from c) carried out in at least one distillation column, from which the following are drawn off: a gaseous fraction, at least one petroleum fraction having at least 80% by volume of products boiling at a temperature below 150° C., at least one middle distillates fraction having at least 80% by volume of products having a boiling point 150° C. to 380° C., an unconverted heavy liquid fraction having at least 80% by volume of products having a boiling point above 350° C., e) optionally purging of at least one portion of said unconverted heavy liquid fraction containing HPNAs, having at least 80% by volume of products having a boiling point above 350° C., before the introduction thereof into f), f) hydrogenating at least one portion of the unconverted heavy liquid fraction having at least 80% by volume of products having a boiling point above 350° C. resulting from d) and optionally purged, f) taking place, in the presence of hydrogen and a hydrogenation catalyst, at a temperature TR1 of 150° C. to 470° C., under a pressure of 2 to 25 MPa, at a space velocity of 0.1 to 50 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 100 to 4000 Nl/l, said hydrogenation catalyst comprising at least one non-noble metal from group VIII of the Periodic Table that is nickel, cobalt, iron, or a mixture thereof, and not comprising any noble metal from group VIII or metal from group VIB, and a refractory oxide support, g) a second hydrocracking at least one portion of effluent resulting from f), g) taking place, in the presence of hydrogen and at least one second hydrocracking catalyst, at a temperature TR2 of 250° C. to 480° C., under a pressure of 2 to 25 MPa, at a space velocity of 0.1 to 6 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 80 to 2000 Nl/l, and in which the temperature TR2 is at least 10° C. higher than the temperature TR1, h) high-pressure separation of effluent resulting from the hydrocracking g) to produce at least a gaseous effluent and a liquid hydrocarbon effluent, i) recycling, to distillation d), at least one portion of the liquid hydrocarbon effluent resulting from h).

2. The process according to claim 1, in which said hydrocarbon feedstocks are VGOs, vacuum distillates (VDs), gas oils, feedstocks originating from units for the extraction of aromatics from lubricating oil bases or resulting from the solvent dewaxing of lubricating oil bases, distillates originating from the desulfurization or hydroconversion of ATRs (atmospheric residues) and/or VRs (vacuum residues), or from deasphalted oils, feedstocks resulting from biomass or any mixture of the abovementioned feedstocks.

3. The process according to claim 1, in which hydrotreating a) takes place at a temperature of 300° C. to 430° C., under a pressure of 5 to 20 MPa, at a space velocity of 0.2 to 5 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 300 to 1500 Nl/l.

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

5. Process according to claim 1, in which hydrogenation f) takes place at a temperature TR1 of 180° C. to 320° C., under a pressure of 9 to 20 MPa, at a space velocity of 0.2 to 10 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 200 to 3000 Nl/l.

6. The process according to claim 1, in which said hydrocracking g) takes place at a temperature TR2 of 320° C. to 450° C., under a pressure of 9 to 20 MPa, at a space velocity of 0.2 to 3 h.sup.−1 and with an amount of hydrogen introduced such that the litre of hydrogen/litre of hydrocarbon volume ratio is 200 to 2000 Nl/l.

7. The process according to claim 1, in which g) is carried out at a temperature TR2 at least 20° C. higher than the temperature TR1.

8. The process according to claim 7, in which g) is carried out at a temperature TR2 at least 50° C. higher than the temperature TR1.

9. The process according to claim 8, in which g) is carried out at a temperature TR2 at least 70° C. higher than the temperature TR1.

10. The process according to claim 1, in which hydrogenation f) is carried out in the presence of a catalyst comprising nickel and alumina.

11. The process according to claim 2, wherein the feedstock is gas oils resulting from the direct distillation of crude or from conversion units.

12. The process according to claim 11, wherein the conversion units are FCC, coker or visbreaking units.

13. The process according to claim 10, in which the catalyst consists of nickel and alumina.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an embodiment of the invention.

(2) The VGO-type feedstock is sent via the pipe (1) to a hydrotreating step a). The effluent resulting from step a) is sent via the pipe (2) to a first hydrocracking step b). The effluent resulting from step b) is sent via the pipe (3) to a high-pressure separation step c) to produce at least a gaseous effluent (not represented in the FIGURE) and a liquid hydrocarbon effluent which is sent via the pipe (4) to the distillation step d). The following are drawn off from the distillation step d): a gaseous fraction (5), at least one petroleum fraction having at least 80% by volume of products boiling at a temperature below 150° C. (6), at least one middle distillates fraction having at least 80% by volume of products having a boiling point between 150° C. and 380° C. (7), and an unconverted heavy liquid fraction having at least 80% by volume of products having a boiling point above 350° C. (8).

(3) Optionally, a portion of the unconverted heavy liquid fraction containing HPNAs is purged in a step e) via the pipe (9).

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

EXAMPLES

(5) The following examples illustrate the invention without limiting the scope thereof.

Example No. 1 not in Accordance with the Invention: Basic Case of a Two-Step Hydrocracking Process Comprising No Hydrogenation Step

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

(7) TABLE-US-00001 TABLE 1 Type VGO Flow rate t/h 37 Density — 0.93 Initial boiling point (IBP) ° C. 320 Final boiling point (FBP) ° C. 579 S content wt % 2.71 N content ppm by 1510 weight

(8) The VGO feedstock is injected into a preheating stage and then into a hydrotreating reactor under the following conditions set out in Table 2:

(9) TABLE-US-00002 TABLE 2 Reactor R1 Temperature ° C. 375 Total pressure MPa 14 Catalyst — NiMo on alumina HSV h.sup.−1 1.67

(10) The effluent from this reactor is subsequently injected into a second “hydrocracking” reactor R2 operating under the conditions of Table 3:

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

(12) R1 and R2 constitute the first hydrocracking step, the effluent from R2 is then sent to a separation step composed of a train 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 H.sub.2S, a petroleum cut, a middle distillates (kerosene and gas oil) cut, and an unconverted heavy liquid fraction (UCO). A purge corresponding to 2% by weight of the flow rate of the VGO feedstock is taken as distillation bottoms from said unconverted heavy liquid fraction.

(13) Said unconverted heavy 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:

(14) TABLE-US-00004 TABLE 4 Reactor R3 Temperature (TR2) ° C. 340 Total pressure MPa 14 Catalyst — Metal/zeolite HSV h.sup.−1 2

(15) This second hydrocracking step is carried out in the presence of 200 ppm of equivalent sulfur and 10 ppm of equivalent nitrogen, which originate from the H.sub.2S and NH.sub.3 present in the hydrogen and from the sulfur- and nitrogen-containing compounds still present in said unconverted heavy liquid fraction.

(16) 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 then into the distillation step.

Example No. 2 in Accordance with the Invention

(17) Example 2 is in accordance with the invention in so far as it is a two-step hydrocracking process (according to Example 1) in which a step of hydrogenation in the presence of a hydrogenation catalyst consisting of Ni and of an alumina support is carried out upstream of the second hydrocracking step in a hydrogenation reactor RH and in which the temperature TR1 in the hydrogenation step is at least 10° C. below the temperature TR2 of the second hydrocracking step.

(18) The hydrotreating step in R1, first hydrocracking step in R2 and second hydrocracking step in R3 are carried out on the same feedstock and under the same conditions as in Example 1. A purge corresponding to 2% by weight of the flow rate of the VGO feedstock is also taken as distillation bottoms from the unconverted heavy liquid fraction.

(19) The unconverted heavy liquid fraction resulting from the distillation is sent to a hydrogenation step carried out in a reactor RH placed upstream of a hydrocracking reactor R3 in which the second hydrocracking step is carried out. In this case, the temperature TR1 in the hydrogenation step is 60° C. below the temperature TR2 of the second hydrocracking step.

(20) The operating conditions of the hydrogenation step in the hydrogenation reactor RH used upstream of the hydrocracking reactor R3 are set out in Table 5.

(21) TABLE-US-00005 TABLE 5 Reactor RH Temperature (TR1) ° C. 280 Total pressure MPa 14 Catalyst — Ni/Alumina HSV h.sup.−1 2

(22) The catalyst used in the reactor RH has the following composition: 28 wt % Ni on gamma alumina.

(23) The hydrogenated effluent resulting from RH is then sent to the second hydrocracking step carried out in the reactor R3 before being sent to the high-pressure separation then being recycled to the distillation step.

Example No. 3 not in Accordance with the Invention

(24) Example 3 is not in accordance with the invention in so far as it is a two-step hydrocracking process (according to Example 1) in which a step of hydrogenation in the presence of a hydrogenation catalyst comprising Pt and an alumina support is carried out upstream of the second hydrocracking step in a hydrogenation reactor RH and in which the temperature TR1 in the hydrogenation step is equal to the temperature TR2 of the second hydrocracking step.

(25) The hydrotreating step in R1, first hydrocracking step in R2 and second hydrocracking step in R3 are carried out on the same feedstock and under the same conditions as in Example 1. A purge corresponding to 2% by weight of the flow rate of the VGO feedstock is also taken as distillation bottoms from the unconverted heavy liquid fraction.

(26) The unconverted heavy liquid fraction resulting from the distillation is sent to a hydrogenation step carried out in a reactor RH placed upstream of a hydrocracking reactor R3 in which the second hydrocracking step is carried out. In this case, the temperature TR1 in the hydrogenation step is equal to the temperature TR2 of the second hydrocracking step and is 340° C.

(27) The operating conditions of the hydrogenation step in the hydrogenation reactor RH used upstream of the hydrocracking reactor R3 are set out in Table 6.

(28) TABLE-US-00006 TABLE 6 Reactor RH Temperature (TR1) ° C. 340 Total pressure MPa 14 Catalyst — Pt/Alumina HSV h.sup.−1 2

(29) The catalyst used in the reactor RH has the following composition: 0.3 wt % Pt on gamma alumina.

(30) The hydrogenated effluent resulting from RH is then sent to the second hydrocracking step carried out in the reactor R3 before being sent to the high-pressure separation then being recycled to the distillation step.

Example No. 4 not in Accordance with the Invention

(31) Example 4 is not in accordance with the invention in so far as it is a two-step hydrocracking process (according to Example 1) in which a step of hydrogenation in the presence of a hydrogenation catalyst comprising Pt and an alumina support is carried out upstream of the second hydrocracking step in a hydrogenation reactor RH and in which the temperature TR1 in the hydrogenation step is at least 10° C. below the temperature TR2 of the second hydrocracking step.

(32) The hydrotreating step in R1, first hydrocracking step in R2 and second hydrocracking step in R3 are carried out on the same feedstock and under the same conditions as in Example 1. A purge corresponding to 2% by weight of the flow rate of the VGO feedstock is also taken as distillation bottoms from the unconverted heavy liquid fraction.

(33) The unconverted heavy liquid fraction resulting from the distillation is sent to a hydrogenation step carried out in a reactor RH placed upstream of a hydrocracking reactor R3 in which the second hydrocracking step is carried out. In this case, the temperature TR1 in the hydrogenation step is 60° C. below the temperature TR2 of the second hydrocracking step.

(34) The operating conditions of the hydrogenation step in the hydrogenation reactor RH used upstream of the hydrocracking reactor R3 are set out in Table 7.

(35) TABLE-US-00007 TABLE 7 Reactor RH Temperature (TR1) ° C. 280 Total pressure MPa 14 Catalyst — Pt/Alumina HSV h.sup.−1 2

(36) The catalyst used in the reactor RH has the following composition: 0.3 wt % Pt on gamma alumina.

(37) The hydrogenated effluent resulting from RH is then sent to the second hydrocracking step carried out in the reactor R3 before being sent to the high-pressure separation then being recycled to the distillation step.

Example No. 5 in Accordance with the Invention

(38) Example 5 is in accordance with the invention in so far as it is a two-step hydrocracking process (according to Example 1) in which a step of hydrogenation in the presence of a hydrogenation catalyst consisting of Ni and of an alumina support is carried out upstream of the second hydrocracking step in a hydrogenation reactor RH and in which the temperature TR1 in the hydrogenation step is at least 10° C. below the temperature TR2 of the second hydrocracking step.

(39) The hydrotreating step in R1, first hydrocracking step in R2 and second hydrocracking step in R3 are carried out on the same feedstock and under the same conditions as in Example 1. This time, a purge corresponding to 1% by weight of the flow rate of the VGO feedstock is taken as distillation bottoms from the unconverted heavy liquid fraction.

(40) The unconverted heavy liquid fraction resulting from the distillation is sent to a hydrogenation step carried out in a reactor RH placed upstream of a hydrocracking reactor R3 in which the second hydrocracking step is carried out. In this case, the temperature TR1 in the hydrogenation step is 60° C. below the temperature TR2 of the second hydrocracking step.

(41) The operating conditions of the hydrogenation step in the hydrogenation reactor RH used upstream of the hydrocracking reactor R3 are set out in Table 8.

(42) TABLE-US-00008 TABLE 8 Reactor RH Temperature (TR1) ° C. 280 Total pressure MPa 14 Catalyst — Ni/Alumina HSV h.sup.−1 2

(43) The catalyst used in the reactor RH has the following composition: 28 wt % Ni on gamma alumina.

(44) The hydrogenated effluent resulting from RH is then sent to the second hydrocracking step carried out in the reactor R3 before being sent to the high-pressure separation then being recycled to the distillation step.

Example 6—Process Performance

(45) Table 9 summarizes the performance of the processes described in Examples 1 to 5 in terms of yield of middle distillates, cycle time of the process and overall conversion of the process. The conversion of coronene (HPNA with 7 aromatic rings) carried out in the hydrogenation step is also reported.

(46) TABLE-US-00009 TABLE 9 1 (not in 2 (in 3 (not in 4 (not in 5 (in accordance accordance accordance accordance accordance with the with the with the with the with the Examples invention) invention) invention) invention) invention) Catalyst in — 28% Ni/ 0.3% Pt/ 0.3% Pt/ 28% Ni/ RH alumina alumina alumina alumina Purge (%) 2  2  2  2  1 TR1 (° C.) — 280 340 280 280 TR2 (° C.) 340  340 340 340 340 Coronene 0  81  4  60  81 conversion (%)(1) Yield of Base Base Base Base Base + 1 middle point distillates Cycle time Base Base + 6 Base + 1 Base + 3 Base + 4 months month months months Overall 98   98  98  98  99 conversion (%)

(47) 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 a maximum absorption.

(48) 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, yield of middle distillates or overall conversion of the process.

(49) Thus, with the process of Example 2 in accordance with the invention using a hydrogenation reactor upstream of the second hydrocracking step, the cycle time is lengthened by 6 months relative to a process without a hydrogenation reactor (illustrated by Example 1). Specifically, at 280° C., the Ni/alumina hydrogenation catalyst makes it possible to greatly convert the HPNAs. The deactivation of the catalyst of the second hydrocracking step is therefore slowed down, which allows a longer cycle. Furthermore, the cycle time is longer than that obtained with a hydrogenation catalyst based on Pt (Examples 3 and 4 not in accordance with the invention), owing to the lower hydrogenation temperature and the better resistance of the Ni to the sulfur-containing compounds still present in the unconverted heavy fraction. Example 5 in accordance with the invention illustrates that the process according to the invention also makes it possible to reduce the degree of purge, since the HPNAs are hydrogenated in the hydrogenation reactor, which leads to an increase in the overall conversion and in the yield of middle distillates, while retaining a lengthened cycle time.