Process for the production of olefins and of middle distillates from a hydrocarbon effluent resulting from the fischer-tropsch synthesis

Abstract

Process for the production of olefins and of middle distillates from a paraffinic feedstock, in which: a) a paraffinic feedstock resulting from a Fischer-Tropsch unit is recovered, the said feedstock containing a light fraction and a heavy fraction; b) the light fraction is sent to a catalytic cracking unit; c) the effluent resulting from the catalytic cracking unit is separated in a fractionation unit in order to obtain a fraction of light hydrocarbons, an olefinic fraction and a residual liquid fraction; d) the heavy fraction is sent to a hydrocracking/hydroisomerization unit; e) the effluent resulting from the hydrocracking/hydroisomerization unit is separated in a fractionation unit in order to obtain a middle distillates fraction, a naphtha cut having a maximum boiling point of less than 180 C. and an unconverted heavy fraction; f) a part of the naphtha cut resulting from the fractionation unit is sent to the catalytic cracking unit.

Claims

1. Process for the production of olefins and of middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis comprising at least the following stages: a) the said paraffinic feedstock resulting from a Fischer-Tropsch unit (A) is recovered, the said paraffinic feedstock comprising at least a light fraction, known as condensate, and a heavy fraction, known as waxes; b) at least a part of the said light fraction is sent to a catalytic cracking unit (C); c) the effluent resulting from the catalytic cracking unit is separated in a fractionation unit (D) in order to obtain at least a fraction comprising light hydrocarbons, at least an olefinic fraction and at least a residual liquid fraction; d) at least a part of the said heavy fraction is sent to a hydrocracking/hydroisomerization unit (F) in the presence of hydrogen and of a hydrocracking/hydroisomerization catalyst; e) the effluent resulting from the hydrocracking/hydroisomerization unit is separated in a fractionation unit (G) in order to obtain a middle distillates fraction, a naphtha cut having a maximum boiling point of less than 180 C. and an unconverted heavy fraction; f) at least a part of the said naphtha cut resulting from the fractionation unit is sent to the catalytic cracking unit.

2. Process according to claim 1, in which: an additional stage a) is carried out in which the said light fraction obtained in stage a) is fractionated in a fractionation unit (H) in order to obtain a light cut of the said light fraction, the final boiling point of which is less than 180 C., and a heavy cut of the said light fraction, the initial boiling point of which is greater than 120 C.; a stage b) is carried out in which the said light cut of the said light fraction resulting from stage a) is sent to the said catalytic cracking unit (C).

3. Process according to claim 2, in which an additional stage a) is carried out in which the said heavy cut of the said light fraction obtained on conclusion of stage a) is sent to the said hydrocracking/hydroisomerization unit (F), as a mixture with the said heavy fraction resulting from stage a).

4. Process according to claim 2, in which a stage g) is carried out in which the said heavy cut of the said light fraction obtained on conclusion of stage a) is sent to a hydrotreating unit (I) in order to obtain a hydrotreated heavy cut of the said light fraction.

5. Process according to claim 4, in which a stage h) is carried out in which the said hydrotreated heavy cut of the said light fraction obtained on conclusion of stage g) is sent to the isomerization unit (J).

6. Process according to claim 5, in which a stage i) is carried out in which the effluent resulting from the isomerization unit (J) of stage h) is sent to the fractionation unit (G), as a mixture with the effluent resulting from the hydrocracking/hydroisomerization unit (F).

7. Process according to claim 6, in which the catalyst of the isomerization unit (J) comprises at least one noble metal from Group VIII and a support comprising at least one IZM-2 zeolite and at least one binder.

8. Process according to claim 1, in which the said light fraction and/or the said heavy fraction obtained on conclusion of stage a) is/are sent, before stage b), to a hydrotreating unit.

9. Process according to claim 1, in which the said residual liquid fraction obtained on conclusion of stage c) is recycled, at least in part, in stage b).

10. Process according to claim 1, in which the said unconverted heavy fraction obtained on conclusion of stage e) is recycled, at least in part, in stage d).

11. Process according to claim 1, in which all of the said naphtha cut resulting from the fractionation unit is sent to the catalytic cracking unit.

12. Process according to claim 1, in which the catalytic cracking unit comprises a catalyst comprising a ZSM-5 zeolite.

13. Process according to claim 1, in which the catalyst of the hydrocracking/hydroisomerization unit (C) comprises at least one hydro/dehydrogenating metal chosen from the group formed by the metals of Group Vlb and of Group VIII and at least one Bronsted acid solid.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 illustrates an embodiment in which all of the light fraction of the condensate is sent to a naphtha catalytic cracking unit (C).

(2) FIG. 2 illustrates an embodiment in which the light fraction of the condensate is fractionated in order to obtain a light cut of the said light fraction, the final boiling point of which is less than 180 C., and a heavy cut of the said light fraction, the initial boiling point of which is greater than 120 C. In this embodiment, the light cut of the light fraction is sent to a catalytic cracking unit (C) and the heavy cut of the light fraction is sent to a hydrocracking/hydroisomerization unit (F), as a mixture with the heavy fraction of waxes.

(3) FIG. 3 illustrates an embodiment in which the light fraction of the condensate is fractionated in order to obtain a light cut of the said light fraction, the final boiling point of which is less than 180 C., and a heavy cut of the said light fraction, the initial boiling point of which is greater than 120 C. In this embodiment, the light cut of the light fraction is sent to a catalytic cracking unit (C) and the heavy cut of the light fraction is sent to a hydrotreating unit (I) and then to a hydroisomerization unit (J).

(4) FIG. 4 is a diagrammatic representation of a process according to the prior art in which the light fraction resulting from the Fischer-Tropsch synthesis is sent to a steam cracking unit.

(5) In FIGS. 1, 2, 3 and 4, the same references denote identical or analogous elements.

(6) In FIG. 1, the synthesis gas 1, a gas composed predominantly of carbon monoxide and of hydrogen, is directed to a Fischer-Tropsch synthesis unit (A). The gas fraction under the operating conditions of the Fischer-Tropsch synthesis is composed of the unconverted gas fraction, of the light hydrocarbons part and of the water formed by the Fischer-Tropsch synthesis. These three phases are separated by cooling and then flash distillation. The gas fraction is preferably recycled with the synthesis gas 1 so as to increase the total conversion and the material yield. The aqueous fraction is treated before being returned to the process or to the outside. For its part, the light fraction 2, or condensate, is sent to a hydrotreating unit (B). This hydrotreating stage is optional. The effluent 3 resulting from the hydrotreating stage no longer contains olefinic compounds and oxygen-comprising compounds. The effluent 3 resulting from the hydrotreating stage is sent to a unit for the catalytic cracking of naphtha (C), after removal of the water and of the gas fraction containing hydrogen, carbon monoxide and carbon dioxide. The effluent 4 produced by the sequence of the stage of hydrotreating and of catalytic cracking of naphtha predominantly contains compounds which are gaseous under standard conditions, i.e. at a temperature of 20 C. and at atmospheric pressure (1013.25 hPa). The effluent 4 is sent to a separation unit (D) in order to recover at least a light hydrocarbons fraction 5, at least an olefinic fraction 6 and at least a residual liquid fraction 7. The separation is carried out by any process known to a person skilled in the art but more particularly by a succession of distillations. A part of the liquid fraction 7 can be recycled to the unit for the catalytic cracking of naphtha (C) via the line 8.

(7) The heavy fraction 9 resulting from the Fischer-Tropsch synthesis corresponds to the liquid fraction under the operating conditions of the reaction section. The heavy cut 9 can be directed to a hydrotreating unit (E). This hydrotreating stage is optional as this part of the effluent contains little in the way of olefins and little in the way of oxygen-comprising compounds, which compounds are mainly present in the light fraction 2 produced by the Fischer-Tropsch synthesis. The effluent 10 is sent, after removal of the water, to a hydrocracking/hydroisomerization unit (F). The effluent 11 resulting from the sequence of the hydrotreating and hydrocracking/hydroisomerization stages is sent to a separation unit (G). The separation is carried out by any process known to a person skilled in the art but more particularly by distillation. On conclusion of this separation stage, four main streams are produced: a light cut 12 similar to a naphtha, the maximum boiling point of which is less than 180 C., an intermediate cut 13 equivalent to a kerosene with an initial boiling point of greater than 120 C. and a final boiling point of less than 250 C., a heavy cut 14, equivalent of a gas oil composed of product with boiling points of between 120 C. and 370 C., and a very heavy cut 15 corresponding to the fraction not converted in the hydrocracking/hydroisomerization stage. This effluent 15 can be recycled to the hydrocracking/hydroisomerization unit (F). The cut 12 can be sent, completely or partially, to the catalytic cracking unit (C), via the line 16, in order to maximize the yield of light olefins resulting from the process for the catalytic cracking of naphtha.

(8) In FIG. 2, the synthesis gas 1 is directed to a Fischer-Tropsch synthesis unit (A). The light fraction 2, or condensate, is sent to a separation unit (H). The separation is carried out by any process known to a person skilled in the art but more particularly by distillation. The separation is carried out so as to obtain a light cut 17, the final boiling point of which is less than 180 C., and a heavy cut 18, the initial boiling point of which is greater than 120 C. The light cut 17 is sent to the hydrotreating unit (B). This hydrotreating stage is optional. The effluent 3 resulting from the hydrotreating stage no longer contains olefinic compounds and oxygen-comprising compounds. The effluent 3 resulting from the hydrotreating stage is sent to a unit for the catalytic cracking of naphtha (C), after removal of the water and of the gas fraction containing hydrogen, carbon monoxide and carbon dioxide. The effluent 4 produced by the sequence of the stage of hydrotreating and of catalytic cracking of naphtha predominantly contains compounds which are gaseous under standard conditions, i.e. at a temperature of 20 C. and at atmospheric pressure (1013.25 hPa). The effluent 4 is sent to a separation unit (D) in order to recover a light hydrocarbons fraction 5, an olefinic fraction 6 and a residual liquid fraction 7. All or a part of the liquid fraction 7 can be recycled to the unit for the catalytic cracking of naphtha (C) via the line 8.

(9) The heavy fraction 9 resulting from the Fischer-Tropsch synthesis corresponds to the liquid fraction under the operating conditions of the reaction section. This fraction is mixed with the cut 18 resulting from the separation unit (H) in order to form the stream 19. The stream 19 can be directed to a hydrotreating unit (E). This hydrotreating stage is optional as this part of the effluent contains little in the way of olefins and little in the way of oxygen-comprising compounds, which compounds are mainly present in the light fraction 2 produced by the Fischer-Tropsch synthesis. The effluent 10 is sent, after removal of the water, to a hydrocracking/hydroisomerization unit (F). The effluent 11 resulting from the sequence of the hydrotreating and hydrocracking/hydroisomerization stages is sent to a separation unit (G). The separation is carried out by any process known to a person skilled in the art but more particularly by distillation. On conclusion of this separation stage, four main streams are produced: a light cut 12 similar to a naphtha, the maximum boiling point of which is less than 180 C., an intermediate cut 13, equivalent to a kerosene with an initial boiling point of greater than 120 C. and a final boiling point of less than 250 C., a heavy cut 14, equivalent of a gas oil composed of product with boiling point of between 120 C. and 370 C., and a very heavy cut 15 corresponding to the fraction not converted in the hydrocracking/hydroisomerization stage. This effluent 15 can be recycled to the hydrocracking/hydroisomerization unit (F). The cut 12 can be sent, completely or partially, to the catalytic cracking unit (C), via the line 16, in order to maximize the yield of light olefins resulting from the process for the catalytic cracking of naphtha.

(10) In FIG. 3, the synthesis gas 1 is directed to a Fischer-Tropsch synthesis unit (A). The light fraction 2, or condensate, is sent to a separation stage (H). The separation is carried out by any process known to a person skilled in the art but more particularly by distillation. The separation is carried out so as to obtain a light cut 17, the final boiling point of which is less than 180 C., and a heavy cut 18, the initial boiling point of which is greater than 120 C. The light cut 17 is sent to the hydrotreating unit (B). This hydrotreating stage is optional. The effluent 3 resulting from the hydrotreating stage no longer contains olefinic compounds and oxygen-comprising compounds. The effluent 3 resulting from the hydrotreating stage is sent to a unit for the catalytic cracking of naphtha (C), after removal of the water and of the gas fraction containing hydrogen, carbon monoxide and carbon dioxide. The effluent 4 produced by the sequence of the stage of hydrotreating and of catalytic cracking of naphtha predominantly contains compounds which are gaseous under standard conditions, i.e. at a temperature of 20 C. and at atmospheric pressure (1013.25 hPa). The effluent 4 is sent to a separation unit (D) in order to recover a light hydrocarbons fraction 5, an olefinic fraction 6 and a residual liquid fraction 7. All or a part of the liquid fraction 7 can be recycled to the unit for the catalytic cracking of naphtha (C) via the line 8.

(11) The heavy cut 18 resulting from the separation stage is sent to a hydrotreating unit (I). The effluent 20 resulting from the hydrotreating stage no longer contains olefinic compounds and oxygen-comprising compounds. The effluent 20 resulting from the hydrotreating stage is sent to a hydroisomerization unit (J).

(12) The heavy fraction 9 resulting from the Fischer-Tropsch synthesis corresponds to the liquid fraction under the operating conditions of the reaction section. The heavy fraction 9 can be directed to a hydrotreating unit (E). This hydrotreating stage is optional as this part of the effluent contains little in the way of olefins and little in the way of oxygen-comprising compounds, which compounds are mainly present in the light cut produced by the Fischer-Tropsch synthesis. The effluent 10 is sent, after removal of the water, to a hydrocracking/hydroisomerization unit (F). The effluent 11 resulting from the sequence of the hydrotreating and hydrocracking/hydroisomerization stages is mixed with the effluent 21 resulting from the hydroisomerization unit (J). The mixture 22 is sent to a separation unit (G). The separation is carried out by any process known to a person skilled in the art but more particularly by distillation. On conclusion of this separation stage, four main streams are produced: a light cut 12 similar to a naphtha, the maximum boiling point of which is less than 180 C., an intermediate cut 13, equivalent to a kerosene with an initial boiling point of greater than 120 C. and a final boiling point of less than 250 C., a heavy cut 14, equivalent of a gas oil composed of product with boiling points of between 120 C. and 370 C., and a very heavy cut 15 corresponding to the fraction not converted in the hydrocracking/hydroisomerization stage. This effluent 15 can be recycled to the hydrocracking/hydroisomerization unit (F). The cut 12 can be sent, completely or partially, to the catalytic cracking unit (C), via the line 16, in order to maximize the yield of light olefins resulting from the process for the catalytic cracking of naphtha.

(13) Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

(14) In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

(15) The entire disclosures of all applications, patents and publications, cited herein and of corresponding application No. FR 1856667, filed Jul. 18, 2018 are incorporated by reference herein.

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

EXAMPLES

Example 1 (in Accordance with the Invention)

(17) Example 1 illustrates the embodiment according to FIG. 1.

(18) The effluent resulting from the Fischer-Tropsch synthesis unit comprises two fractions: a light fraction, known as condensate, and a heavy fraction, known as waxes. The characteristics of the light fraction resulting from the Fischer-Tropsch synthesis are given in Table 1 below.

(19) TABLE-US-00002 TABLE 1 Composition of the light fraction Unit Content Paraffins [wt %] 73 Olefins [wt %] 20 Oxygen-comprising compounds [wt %] 7

(20) The light fraction and heavy fraction are respectively sent to a stage of hydrotreating in the presence of a hydrotreating catalyst comprising 11.4 wt % of NiO and 8% by weight of MoO.sub.3 on an alumina support and which operates at a temperature of 330 C., at a pressure of 0.65 MPa, at a hydrogen flow rate adjusted in order to obtain a ratio of 600 standard litres per litre, and at an hourly space velocity of 2 h.sup.1.

(21) The hydrotreated light fraction, the final boiling point of which is less than 370 C., is sent to the catalytic cracking stage b). This stage is carried out at high severity (T=650 C., C/O=15) in the presence of a catalyst 100% composed of ZSM-5.

(22) The hydrotreated heavy fraction is sent to a stage d) of hydrocracking and of hydroisomerization in the presence of a hydrocracking and hydroisomerization catalyst comprising 0.3% by weight of Pt on a SiAl support and which operates at a temperature of 360 C., at a pressure of 0.65 MPa, at an hourly space velocity of 2 h.sup.1, and at a hydrogen flow rate adjusted in order to obtain a ratio of 600 standard litres of hydrogen per litre of feedstock.

(23) The effluent resulting from the hydrocracking and hydroisomerization stage d) is subsequently sent to the fractionation stage e) in order to separate a petrol fraction, a middle distillates fraction (kerosene and gas oil), an unconverted fraction and a naphtha cut which is sent to the catalytic cracking stage b).

(24) The effluent resulting from the catalytic cracking unit is subsequently sent to stage c) in order to obtain at least a fraction comprising light hydrocarbons, at least an olefinic fraction and at least a residual liquid fraction.

(25) The material balance according to the scheme is given in Table 2 below. As the hydrogen consumption is very low, it is disregarded in this example.

(26) TABLE-US-00003 TABLE 2 Material balance according to the scheme, with reference to the stream of FIG. 1 Residual Light liquid Description Condensate Olefins hydrocarbons fraction (Stream) [] (2) (6) (5) (7) Flow rate [t/h] 55 34 8 13 The flow rate of olefins is increased by 17 wt % with respect to Example 2 illustrating a scheme not in accordance with the invention.

Example 2 (not in Accordance with the Invention)

(27) Example 2 is not in accordance with the invention in that the light fraction resulting from the Fischer-Tropsch synthesis is sent to a steam cracking unit (temperature: 850 C.; pressure: 0.25 MPa; steam content: 0.25% by weight) according to a scheme represented in FIG. 4. Furthermore, the cut similar to the naphtha cut resulting from the unit for fractionation (G) of the hydrocracking/hydroisomerization effluent is not sent to the steam cracking unit.

(28) The operating conditions and the catalysts used in Example 2 are identical to those used in Example 1 according to the invention in the hydrocracking and hydroisomerization stages. The material balance according to the scheme is given in Table 3.

(29) TABLE-US-00004 TABLE 3 Material balance according to the scheme of the prior art with reference to the streams of FIG. 4 Residual Light liquid Condensate Olefins hydrocarbons fraction Description [] (2) (6) (5) (7) Flow rate [t/h] 55 29 13 13

(30) The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

(31) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.