FLOW CONTROL TO MEET E70 GASOLINE SPECIFICATIONS

Abstract

A process is presented for recovering the components for a gasoline blending pool to meet the E70 specifications. 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 having normal boiling points above 70 C., and to separate for adding to the feed to the reforming unit, hydrocarbons that have lower boiling points.

Claims

1. A process for improving stream cracker feed and processing gasoline blending components, comprising: passing a naphtha feedstream to a fractionation column to generate an overhead stream comprising hydrocarbons with normal boiling points below 90 C., and a bottoms stream comprising heavies; passing the overhead stream to a separation unit to generate an extract stream comprising normal hydrocarbons and a raffinate stream comprising non-normal hydrocarbons; passing the extract stream to a cracking unit; and passing the bottoms stream to a reforming unit.

2. The process of claim 1 wherein the fractionation column is operated to generate an overhead stream comprising hydrocarbons having normal boiling points below 72 C.

3. The process of claim 1 wherein the fractionation column is operated to generate an overhead stream comprising hydrocarbons having normal boiling points below 81 C.

4. The process of claim 1 wherein the fractionation column is operated to generate an overhead stream comprising hydrocarbons having normal boiling points below 98 C.

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

6. The process of claim 1 wherein the light desorbent is a normal paraffin with a boiling point lower than the lightest feed component, or higher than the boiling point of the heavies components.

7. The process of claim 1 further comprising passing the raffinate stream to the reforming unit.

8. The process of claim 1 further comprising passing the raffinate stream to a second fractionation column to generate a second overhead stream and a second bottoms stream.

9. The process of claim 8 wherein the overhead stream comprises isobutane and isopentane.

10. The process of claim 8 wherein the fractionation column has a side draw, and further comprising generating a side draw stream comprising high octane light naphtha product, wherein the high octane light naphtha product comprises isopentane, cyclopentane, methylcyclopentane and isohexane.

11. The process of claim 10 further comprising passing the high octane light naphtha product to a gasoline blending stock.

12. The process of claim 8 wherein the fractionation column has a side draw, and further comprising generating a side draw stream comprising high octane light naphtha product, wherein the high octane light naphtha product comprises isopentane, cyclopentane, methylcyclopentane, isohexanes, cyclohexane, benzene, and dimethylpentanes.

13. The process of claim 12 further comprising passing the high octane light naphtha product to a gasoline blending stock.

14. The process of claim 8 further comprising passing the second bottoms stream to the reforming unit.

15. The process of claim 8 further comprising passing the second overhead stream to the reforming unit.

16. The process of claim 1 wherein the reforming unit generates a reformate stream, and further comprising passing the reformate stream to an aromatics recovery unit to generate an aromatics stream and an aromatics raffinate stream comprising normal alkanes.

17. The process of claim 16 further comprising passing the aromatics raffinate stream to the cracking unit.

18. The process of claim 1 wherein the feed to the catalytic reforming unit has a feed that is depleted in normal hexane and rich in iso-hexane isomers such that the ratio of iso-hexanes to normal hexane is greater than 3.

19. The process of claim 1 wherein the feed to the catalytic reforming unit has a feed that is depleted in normal pentane and rich in iso-pentane such that the ratio of iso-pentane to normal pentane is greater than 3.

20. The process of claim 1 wherein the feed to the catalytic reforming unit has a feed that is depleted in normal butane and rich in iso-butane such that the ratio of iso-butane to normal butane is greater than 3.

21. A process for improving naphtha stream cracker feedstock and processing gasoline blending components, comprising: passing a naphtha feedstream to a fractionation column to generate an overhead stream comprising hydrocarbons with normal boiling points below 75 C., and a bottoms stream; passing the overhead stream to an adsorption separation unit to generate an extract stream comprising normal hydrocarbons and a raffinate stream comprising non-normal hydrocarbons; passing the raffinate stream to a second fractionation column to generate an overhead stream, a side stream and a second bottoms stream; passing the extract stream to a cracking unit; and passing the bottoms stream to a reforming unit to generate a reformate.

22. The process of claim 21 further comprising operating the second fractionation column with a second bottom product cut point of 70 C. (at atmospheric pressure) and sending the second bottoms product to the reforming unit.

23. The process of claim 21 further comprising operating the second fractionation column with a second top product cut point of about 30 C. (at atmospheric pressure) and sending the second overhead product to the reforming unit.

24. The process of claim 21 further comprising using the side product from the second fractionation column for gasoline blending.

25. The process of claim 21 wherein the adsorption separation column uses a light desorbent.

26. The process of claim 25 wherein the light desorbent is n-butane.

27. The process of claim 21 further comprising passing the reformate to an aromatics recovery unit to generate an aromatics stream, and an aromatics raffinate stream comprising non-aromatic compounds.

28. The process of claim 27 further comprising passing the aromatics raffinate stream to the adsorption separation unit.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0012] The FIGURE is a diagram of the process for removing normal paraffins from a light naphtha stream and to generate a more desirable gasoline blending mixture.

DETAILED DESCRIPTION OF THE INVENTION

[0013] 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 and cyclohexane, and naphthenes. It is also advantageous to remove normal C5 and C6 hydrocarbons from the feed to the reforming unit.

[0014] The present invention allows for increasing the normal hydrocarbon content to be passed to a cracking unit, while separating desirable aromatic to be passed to a reforming unit, and separating out desirable components from a naphtha feedstream for the use in meeting gasoline blending conditions that satisfy E70 gasoline specifications.

[0015] By removing n-hexane, one increases the amount of components that have a higher boiling point and help customers meet the E70 specification. n-hexane has a low octane and is not desirable in gasoline. It also has a normal boiling point of 69 C. which is close to other light naphtha components such as methylcyclopentane (72 C.) that do have high octane and are desirable for gasoline blending. By separating the n-hexane using LD MaxEne or another separation technology, more methylcyclopentane can be blended into gasoline to help refiners meet the E70 specification.

[0016] The present invention includes the processing of a naphtha feedstream to improve the feed to a steam cracker, 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, and boiling points are normal boiling points. 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, and can determine the temperature shift from the Clausius-Clapeyron equation. 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.

[0017] The process, as shown in the FIGURE, includes passing a naphtha feedstream 8 to a first fractionation column 10, wherein the fractionation column 10 is operated to generate an overhead stream 12 comprising hydrocarbons with normal boiling points below 90 C., and a bottoms stream 14 comprising heavies. The overhead stream 12 is passed to a separation unit 20 to generate an extract stream 22 having normal hydrocarbons and a raffinate stream 24 having non-normal hydrocarbons. The extract stream 22 is passed to a cracking unit 30 and the bottoms stream 14 is passed to a reforming unit 40. By sending components with normal boiling points below 90 C, such as dimethylpentanes, these components can be further separated from the normal paraffins in the overhead stream 12, and recovered in the raffinate stream 24 for collection into a gasoline blending pool. In a preferred embodiment, the separation unit 20 is an adsorption separation unit, and is operated with a light desorbent. The light desorbent is a normal paraffin with a boiling point lower than the lightest feed component, or higher than the boiling point of the heavies components. The choice of desorbent can be determined for optimum separation and recovery of the desorbent. One such desorbent is n-butane.

[0018] An alternate process is to operate the fractionation column 10 to generate an overhead stream 12 comprising hydrocarbons with normal boiling points below 98 C. By operating at a higher temperature, the overhead stream 12 will include heavier paraffins, such as n-heptane. The overhead stream 12 is then separated to recover the n-heptane and other normal paraffins, and the normal paraffins are then passed to the cracking unit 30, to generate a cracking process stream 32 comprising light olefins. The removal of n-heptane reduces the heat requirements and improves the efficiency of the reformer.

[0019] By operating the fractionation column 10 at higher temperatures, the feed 14 to a reforming unit 40 will have an improved quality, and reduce the energy load in converting the heavier hydrocarbons C8+ to aromatics. In addition, the overhead stream 12 after passing through the separation unit 20 will have a raffinate 24 lower in normal hydrocarbons and higher in iso-paraffins and other non-normal compounds, such as cyclohexane. The compounds in the raffinate stream 24 will be of higher quality for passing to the reforming unit 40 and operation of the reforming unit 40 can be at less severe conditions, or lower temperatures.

[0020] A further alternate process is to operate the fractionation column 10 to generate an overhead stream 12 comprising hydrocarbons with normal boiling points below 81 C. By operating at a lower temperature, the overhead stream 12 will include hydrocarbon components such as benzene and cyclohexane. The overhead stream 12 is then separated to recover the benzene and cyclohexane components into the raffinate stream 24, and then to pass the raffinate stream 24 to the reformer 40, wherein the cyclohexane is converted to benzene. The benzene will pass through the reformer 40 without reacting.

[0021] A further alternate process is to operate the fractionation column 10 to generate an overhead stream 12 comprising hydrocarbons having normal boiling points below 72 C. By operating at a still lower temperature, the overhead stream 12 will include hydrocarbon components such as methylcyclopentane. The overhead stream 12 is then separated to recover methylcyclopentane into the raffinate stream 24, and then to pass the raffinate stream 24, or a portion thereof, to a gasoline blending pool.

[0022] In one embodiment, the process includes passing the raffinate stream 24 to the reforming unit 40 to generate a reformate stream 42 comprising aromatics. In an alternate embodiment, the raffinate stream 24 is passed to a second fractionation column 50. The second column 50 generates a second overhead stream 52 and a second bottoms stream 54. In one embodiment, the second fractionation column 50 is operated to generate the overhead stream 52 containing isobutane and isopentane that is sent to the reforming unit 40. The second bottoms stream 54 can be passed to the reforming unit 40.

[0023] In another embodiment, the second fractionation column 50 can include a side draw stream 56. The side draw stream 56 comprises high octane light naphtha product wherein the high octane light naphtha product includes isopentane, cyclopentane, methylcyclopentane and isohexane. This high octane light naphtha product can be passed to a gasoline blending stock, wherein the high octane light naphtha product provides a mixture of hydrocarbons that will help meet the E70 specifications for gasoline. The second fractionation column 50 can be a divided wall column, or other set up for providing separation of the raffinate stream 24 into three process streams. This is also intended to include the possibility of using two separate fractionation columns for the second fractionation column 50.

[0024] In one embodiment, the second overhead stream 52 is passed to the reforming unit 40. The second overhead stream 52 will generally isomerize to a mixture of normal and isoC4 and C5 paraffins. The reforming catalyst will isomerize a portion of the lower molecular weight hydrocarbons as they will not aromatize. The reforming unit 40 generates a reformate stream 42, which is passed to an aromatics recovery unit 60. The aromatics recovery unit 60 will generate an aromatics stream 62 and an aromatics raffinate stream 64. The aromatics raffinate stream 64 comprises normal paraffins and some isoparaffins.

[0025] The aromatics raffinate stream 64 can be passed to the cracking unit 30, or can be passed to the adsorption separation unit 20. When the raffinate stream 64 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 60.

[0026] In one embodiment, the feed to the catalytic reforming unit 40 includes the bottoms stream 14, and a portion of, or all of the raffinate stream 24. The feed to the catalytic reforming unit is depleted in normal paraffins in the C4 to C6 range. The feed is rich in iso-paraffins in the C4 to C6 range. In one embodiment, the ratio of iso-paraffins to normal paraffins for each of butanes, pentanes, or hexanes, will be greater than 3. The catalyst in the reforming unit 40 also will isomerize the iso-paraffins to normal paraffins in the C4 to C6 range. The normal paraffins will be passed out in the reformate stream 42, and will be separated in the aromatics recovery unit 60. The normal paraffins will be passed out in the aromatics raffinate stream 64. The aromatics raffinate stream 64 can be passed to the cracking unit 30. In an alternative, the aromatics raffinate stream 64 can be passed to the adsorption separation unit 30 to separate iso-paraffins in the C4 to C6 range and recycle them to the reforming unit 40 for further isomerization.

[0027] In one embodiment, the process is for generating gasoline blending components. The process includes passing a naphtha feedstream 8 to a first fractionation column 10 to generate an overhead stream 12 comprising hydrocarbons with normal boiling points below 75 C., and a bottoms stream 14. The overhead stream 12 is passed to an adsorption separation unit 20 to generate an extract stream 22 comprising normal hydrocarbons and a raffinate stream 24 comprising non-normal hydrocarbons. The raffinate stream 24 is passed to a second fractionation column 50 to generate an overhead stream 52, a side stream 56 and a second bottoms stream 54. The bottoms stream 14 is passed to the reforming unit 40 to generate a reformate 42.

[0028] The raffinate stream 24 comprises hydrocarbons that are useful for a gasoline blending pool. The second fractionation column 50 is operated to generate the second bottoms product with a cut point of 70 C. (at atmospheric pressure), and sending the second bottoms stream 54 to the reforming unit 40. The second fractionation column 50 is operated to generate the second top product cut point of 30 C. (at atmospheric pressure), and sending the second overhead stream 52 to the reforming unit 40 to isomerize the isoparaffins. The side stream 56 from the second fractionation column 50 is passed to a gasoline blending pool.

[0029] While to present invention is aimed at optimizing the yields of the two process units, a cracking unit and a catalytic reforming unit, the process can also be used to improve the yields of each individual unit. Hydrocarbon streams comprise a complex mixture. The first separation process is typically around boiling points, where cuts are made on boiling point ranges. Other means of separation are also employed downstream to pull out specific classes of hydrocarbons.

[0030] It has been found that more intricate separations of the hydrocarbon streams can increase yields for downstream process units, while maintaining substantially constant flow rates to the downstream processing units. A typical feedstream to a cracking unit, and a reforming unit is a straight run naphtha feedstream. But it is intended that other feedstreams can be used for this process, and as used hereinafter, the term naphtha feedstream is meant to encompass other potential hydrocarbon feedstreams that can be used in cracking and reforming.

[0031] The second separation unit 20 is preferably an adsorption-separation unit, and the separation is controlled by the choice of adsorbent and desorbent. For the present process, the separation unit 20 is designed for separating normal hydrocarbons in the light naphtha stream 12. The normal hydrocarbons are separated and sent out in the extract stream 22, with a raffinate stream 24 comprising non-normal hydrocarbons.

[0032] The raffinate stream 24 can be passed to a reforming unit 40 to generate a process stream 42 comprising aromatics. The process stream 42 can be passed to an aromatics complex for conversion to higher value products.

[0033] 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.