FLOW CONFIGURATIONS USING A NORMAL PARAFFIN SEPARATION UNIT WITH ISOMERIZATION IN THE REFORMING UNIT

Abstract

A process is presented for recovering the hydrocarbon components from a naphtha feed to pass to a gasoline blending pool or to change the operations to increase the production of light olefins. The process includes the separation of the naphtha feedstock into a light naphtha stream and a heavy naphtha stream. The process further includes separating the light naphtha stream to recovery high quality non-normal hydrocarbons, and to separate normal hydrocarbons to the feed to the cracking unit.

Claims

1. A process for increasing light olefin yields from naphtha, comprising: passing a naphtha feedstream to a naphtha splitter to generate a light naphtha stream and a heavy naphtha stream, wherein the naphtha splitter is operated to split the naphtha stream around the normal boiling point of methylcyclopentane; passing the heavy naphtha stream to a reforming unit to generate a reformer effluent comprising aromatics; passing the light naphtha stream to a separation unit to generate an extract stream comprising normal hydrocarbons and a raffinate stream comprising non-normal hydrocarbons; and passing the extract stream to a cracking unit.

2. The process of claim 1 wherein the naphtha splitter is operated increasing the temperature to split the naphtha stream around the normal boiling point of cyclohexane.

3. The process of claim 1 wherein the naphtha splitter is operated increasing the temperature to split the naphtha stream around the normal boiling point of dimethylpentane.

4. The process of claim 1 further comprising: passing the reformer effluent to an aromatics recovery unit to generate an aromatics stream and a recovery unit aromatics raffinate stream.

5. The process of claim 4 further comprising passing the recovery unit raffinate stream to the separation unit.

6. The process of claim 1 wherein the separation unit is an adsorption separation unit.

7. The process of claim 6 wherein the adsorption separation unit uses a light desorbent.

8. The process of claim 7 wherein the light desorbent is n-butane or n-pentane.

9. The process of claim 1 further comprising passing the raffinate stream to a gasoline blending pool.

10. The process of claim 4 further comprising passing the aromatics raffinate stream to the cracking unit.

11. The process of claim 4 further comprising passing the aromatics raffinate stream to the separation unit.

12. The process of claim 4 further comprising passing the aromatics stream to an aromatics complex.

13. A process for increasing gasoline blending stock from naphtha, comprising: passing a naphtha feedstream to a naphtha splitter to generate a light naphtha stream and a heavy naphtha stream, wherein the naphtha splitter is operated to split the naphtha stream around the normal boiling point of methylcyclopentane; passing the heavy naphtha stream to a reforming unit to generate a reformer effluent comprising aromatics; passing the light naphtha stream to a separation unit to generate an extract stream comprising normal hydrocarbons and a raffinate stream comprising non-normal hydrocarbons; passing the raffinate to a raffinate splitter to generate a raffinate splitter bottoms stream and a raffinate splitter overhead stream; and passing the extract stream to a cracking unit.

14. The process of claim 13 wherein the raffinate splitter includes a side draw stream.

15. The process of claim 13 wherein the raffinate splitter is operated to send iC5 and iC4 into the overhead stream, further comprising passing the raffinate splitter overhead stream to the reformer to isomerize the iC5 and iC4 components to nC5 and nC4.

16. The process of claim 15 further comprising passing the reformer effluent stream to an aromatics recovery unit to generate an aromatics stream and an aromatics raffinate stream.

17. The process of claim 16 further comprising passing the aromatics raffinate stream to the separation unit to recover normal paraffins.

18. The process of claim 13 wherein the adsorption separation unit uses a light desorbent.

19. The process of claim 14 wherein the raffinate splitter is operated to send iC5, cyclopentane, iC6 and methylcyclopentane into the side draw stream.

20. The process of claim 14 further comprising passing the side draw stream to a gasoline blending stock.

21. The process of claim 14 further comprising passing the raffinate splitter bottom stream to the reforming unit to convert methylcyclopentane and heavier components to aromatics.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0016] FIG. 1 is a flow diagram for increasing the steam cracker feed and to increase the yields of light olefins; and

[0017] FIG. 2 is a flow diagram for increasing the production of gasoline blending components.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention is a process that improves flexibility in the operation of a refinery, and enables the refiner to readily shift product with minimal additional equipment. The operation of the new and existing equipment allows for shifting of production to increase higher value products as the market shifts. Market shifts include the price of raw materials, or oil, and the demand for different products such as precursor materials to plastics, such as light olefins or aromatics, or increased production of gasoline blending streams. Traditional processing of a naphtha feedstream is to only use the naphtha splitter, which segregates according to boiling point ranges. However, there are significant overlaps of boiling points of different hydrocarbons, wherein the operation of a cracking unit works most efficiently with normal hydrocarbons, and the reforming unit performs more efficiently on heavier hydrocarbons and aromatic precursors such as methylcyclohexane, cyclohexane and higher naphthenes. It is also advantageous to remove normal C5 and C6 hydrocarbons from the feed to the reforming unit.

[0019] It is desirable to have a naphtha complex that is flexible to maximize light olefin yields, or to have flexible production of high octane light naphtha to meet changing market demands, or to have a flexible aromatics production to control the generation of benzene and xylenes.

[0020] The present invention, as shown in FIG. 1, is a process for increasing light olefin yields from a naphtha feedstream. The naphtha feedstream 8 is passed to a naphtha splitter 10 to generate a light naphtha stream 12 and a heavy naphtha stream 14. The naphtha splitter 10 is operated to split the naphtha stream around the normal boiling point of methylcyclopentane, or around 72 C. The heavy naphtha stream 14 is passed to a reforming unit 40 to generate a reformer effluent stream 42 comprising aromatics. The light naphtha stream 12 is passed to a separation unit 20 to generate an extract stream 22 comprising normal hydrocarbons and a raffinate stream 24 comprising non-normal hydrocarbons. The extract stream 22 is passed to a cracking unit 30 to generate a cracking process stream 32 comprising light olefins. The raffinate stream 24 is passed to the reforming unit 40.

[0021] In one embodiment, the separation unit 20 is an adsorption separation unit, and uses a light desorbent to displace the adsorbed normal paraffins. The light desorbent is selected from hydrocarbons that have a boiling point lower than the components in the light naphtha stream 12. The light desorbent can comprise a light normal paraffin, such as n-butane, or n-pentane.

[0022] The process further includes passing the reformer effluent stream 42 to an aromatics recovery unit 50 to generate an aromatics stream 52 and an aromatics recovery unit raffinate stream 54. The aromatics stream 52 is passed to an aromatics complex 60. The recovery unit raffinate stream 54 comprises iso and normal hydrocarbons, and in one embodiment, is passed to the cracking unit 30. In an alternate embodiment, the recovery unit raffinate stream 54 is passed to the separation unit 20. When the raffinate stream 54 is passed to the separation unit 20, it may be first hydrotreated, or passed to a hydrotreatment unit 80, before being passed to the separation unit 20. The hydrotreatment unit 80 can be used to hydrogenate olefins, or facilitate the removal of any sulfur that is obtained from the aromatics recovery unit 50. The separation unit 20 separates the normal paraffins for passage to the cracking unit, and the non-normal hydrocarbons, and in particular the isobutane, isopentanes and isohexanes, are passed to the reforming unit 40. The reforming catalyst will isomerize the iso-paraffins, and will increase the amount of normal paraffins that can be sent to the cracking unit 20.

[0023] In one embodiment, the invention is a process for increasing the content for a gasoline blending pool from the naphtha feedstream. In one embodiment, the naphtha splitter 10 is operated to increase the temperature to split the naphtha stream around the normal boiling point of cyclohexane, or around 81 C. The naphtha splitter 10 can also be operated at conditions to have the split around the normal boiling point of dimethylpentanes, or a temperature greater than 80 C., or in the range of 80 C. to 90 C.

[0024] The present invention includes the processing of a naphtha feedstream to improve the feed to a steam cracker, or to improve the feed to a reforming unit, and to improve the composition of a gasoline blending stock. The present invention is presented in the form wherein the temperatures are temperatures for a fractionation process operated at, or near, atmospheric pressures. The invention is intended to include appropriate shifts in temperatures for changes in operating pressures. One of ordinary skill in the art working with hydrocarbons would readily understand and know the temperature shifts for fractionation at either higher or lower pressures. For example, the boiling points are expected to rise for operations with increased pressures, and to drop for operations with decreased pressures, relative to atmospheric pressure.

[0025] The raffinate stream 24 from the separation unit 20 is passed to a second fractionation column 70 to generate a second fractionation overhead stream 72, and a second fractionation bottoms stream 76. In one embodiment, the second fractionation column 70 can have a side draw stream 74. The second fractionation column 70 can be a divided wall column, or is intended to include a two column system for producing the three streams.

[0026] In one embodiment, the raffinate stream 24 can be passed to the gasoline blending pool. In another embodiment, either the second overhead stream 72 or the side draw stream 74 comprise gasoline components for passing to the gasoline pool. The second bottoms stream 76 is passed to the reformer 40, to aromatize cyclohexane, and to isomerize iso-paraffins.

[0027] In another embodiment, the process, as shown in FIG. 2, is directed to increasing the selection of hydrocarbons for passing to a gasoline blending pool. The process includes passing a naphtha feed stream 8 to a naphtha splitter 10 to generate a light naphtha stream 12 and a heavy naphtha stream 14. The heavy naphtha stream 14 is passed to a reforming unit 40 to generate a reformer effluent 42. The light naphtha stream 12 is passed to a separation unit 20 to generate an extract stream 22 and a raffinate stream 24. The extract stream 22 comprising normal hydrocarbons, and the raffinate stream 24 comprising non-normal hydrocarbons. The extract stream 22 is passed to a cracking unit 30. The raffinate stream 24 includes iso-paraffins, and naphthenes that are removed from the light naphtha stream 12. The raffinate stream 24 can also include some benzene. The amount of benzene will be subject to the operating conditions of the naphtha splitter 10.

[0028] The reformer effluent stream 42 is passed to an aromatics recovery unit 50 to generate an aromatics stream 52 and a recovery unit raffinate stream 54. The aromatics stream 52 is passed to an aromatics complex 60. The recovery raffinate stream 54 is passed to the separation unit 20. The reformer 40 isomerizes a portion of the reformer feed 14 that is not aromatized. The separation unit 20 further separates the aromatics raffinate stream 54 to direct normal hydrocarbons to the extract stream 22 and non-normal hydrocarbons to the raffinate stream 24. The recovered non-normal hydrocarbons are directed to a gasoline blending pool.

[0029] While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.