Patent Application
20150045597
The present invention relates to a process and system for the production of aromatics from a heavier hydrocarbon stream. In particular, this process provides for increasing yields and flexibility of the production of aromatics and light olefins from hydrocarbon feedstock.
The reforming of petroleum raw materials is an important process for producing useful products. One important process is the separation and upgrading of hydrocarbons for a motor fuel, such as producing a naphtha feedstream and upgrading the octane value of the naphtha in the production of gasoline. However, hydrocarbon feedstreams from a raw petroleum source include the production of useful chemical precursors for use in the production of plastics, detergents and other products.
The upgrading of gasoline is an important process, and improvements for the conversion of naphtha feedstreams to increase the octane number have been presented in U.S. Pat. Nos. 3,729,409; 3,753,891; 3,767,568; 4,839,024; 4,882,040; and 5,242,576. These processes involve a variety of means to enhance octane number, and particularly for enhancing the aromatic content of gasoline.
Processes include splitting feeds and operating several reformers using different catalysts, such as a monometallic catalyst or a non-acidic catalyst for lower boiling point hydrocarbons and bi-metallic catalysts for higher boiling point hydrocarbons. Other improvements include new catalysts, as presented in U.S. Pat. Nos. 4,677,094; 6,809,061; and 7,799,729. However, there are limits to the methods and catalysts presented in these patents, and which can entail significant increases in cost.
Light olefins have traditionally been produced through the process of steam or catalytic cracking, and comprise ethylene and propylene. Light olefins are also derived from the same feedstocks as gasoline. Because of the limited availability and high cost of petroleum sources, the cost of producing light olefins from such petroleum sources has been steadily increasing. The ability to shift components in the feedstock for light olefins and gasoline pools enables producers to economically choose the most important product line and to shift some of the hydrocarbon components in an efficient manner.
A process for improving gasoline yields is presented. A first embodiment of the invention is a process for converting a treated hydrocarbon feedstream, comprising passing the treated hydrocarbon feedstream to a separation unit to generate an extract stream enriched in normal paraffins, and a raffinate stream having a reduced normal hydrocarbon content; passing the extract stream to an extract separation system to generate an extract overhead stream comprising nC5 and nC6 compounds, an extract intermediate stream comprising nC7 to nC11 compounds, and an extract bottoms stream comprising desorbent; passing the raffinate stream to a raffinate separation system to generate a raffinate overhead stream comprising iC5 and iC6 compounds, an intermediate raffinate stream comprising aromatics and non-normal hydrocarbons in the C6 to C11 carbon range, and a raffinate bottoms stream comprising desorbent; and passing the intermediate raffinate stream to a reforming unit to generate an aromatics stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising passing a hydrocarbon feedstream to a fractionation unit to generate an overhead stream comprising C4 and lighter hydrocarbons, and a bottoms stream comprising C5+ hydrocarbons; hydrotreating the bottoms stream to generate the treated hydrogenated stream; passing the treated hydrogenated stream to the separation unit. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising passing a portion of the extract overhead stream to an isomerization unit to generate an isomerized stream comprising C5 and C6 compounds. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising passing the isomerized stream to the separation unit.
A second embodiment of the invention is a process for converting a naphtha feedstream, comprising fractionating the naphtha feedstream to generate a naphtha overhead stream comprising C4 and lighter hydrocarbons, and a naphtha bottoms stream comprising C5+ hydrocarbons; hydrotreating the naphtha bottoms stream to generate a hydrogenated stream having a reduced acetylene, diolefins, sulfur and nitrogen content; passing the hydrogenated stream to a separation unit to generate an extract stream enriched in normal hydrocarbons and a raffinate stream; passing the extract stream to a extraction separation system to generate an extract overhead stream comprising nC5 and nC6 compounds, an extract intermediate stream comprising nC7 to nC11 compounds, and an extract bottoms stream comprising desorbent; passing the raffinate stream to a raffinate separation system to generate a raffinate overhead comprising iC5 and iC6 compounds, an intermediate raffinate stream comprising C6 to C11 aromatics and non-normal hydrocarbons, and a raffinate stream comprising desorbent; passing the intermediate extract stream and the naphtha overhead stream to a naphtha cracking unit to generate light olefins; and passing the intermediate raffinate stream to a reforming unit to generate an aromatics stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising passing a portion of the extract overhead stream to an isomerization unit to generate an isomerized stream comprising C5 and C6 compounds. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising passing the isomerized stream to the separation unit.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art from the following detailed description and drawings.
The present embodiment provides an efficient use of hydrocarbon feedstocks. The production of useful higher value products from lower value hydrocarbon feedstocks is important for the economics of a petroleum processing plant. Flexibility in the production of higher-value products is desirable for responding to shifting demands in different product lines.
The present embodiment provides flexibility in the processing of a hydrocarbon feedstream for the production of light olefins and/or aromatics. The process, as shown in
Normal components in the hydrocarbon stream are more readily cracked to form light olefins than non-normal components. The normal components are also more difficult to reform to aromatics than non-normal components. The separation of normal and non-normal components, combined with passing the different stream to appropriate downstream processing units improves flexibility and the economics of cracking and reforming naphtha. The ability to convert normal components to non-normal components allows the shifting of hydrocarbon components from the stream fed to a cracking unit to a stream for generating gasoline components.
The extract overhead stream 22 can comprise normal C5 and C6 compounds, the extract intermediate stream 24 can comprise normal C7 and heavier compounds, and the extract bottoms stream 26 can comprise a recycle stream passed back to the separation unit 10. The extract intermediate stream 24 is passed to a cracking unit 40 to generate light olefins. In one embodiment, the cracking unit 40 is a naphtha steam cracking unit.
In one embodiment, the separation unit 10 is an adsorption separation unit, and the recycle stream 26 is the desorbent recycle from the extract separation system 20 to the separation unit 10. The extract separation system 20 can comprise one or more fractionation columns for separating the extract stream from the desorbent. The extract separation system 20 can also separate the extract stream 12 into multiple streams. Options in the separation process include a divided wall column, or other means for separating hydrocarbon streams.
The raffinate stream 14 is passed to a raffinate separation system 30 to generate a raffinate overhead stream 32, an intermediate raffinate stream 34 and a raffinate bottoms stream 36. The raffinate overhead stream 32 will comprises isopentanes and isohexanes, the intermediate raffinate stream 34 comprises aromatics, naphthenes, and non-normal hydrocarbons in the C6 to C11 range, and the raffinate bottoms stream 36 comprises a recycle stream that is returned to the separation unit 10.
With an adsorption separation system 10, the raffinate recycle is the desorbent used in the adsorption separation process. The intermediate raffinate stream 34 is passed to a reforming unit 50 to generate a reformate stream 52, comprising aromatics.
In a specific embodiment, the process, as shown in
A naphtha feedstream will typically comprise hydrocarbons in the C4 to C11 range. The adsorption separation unit 10 will therefore utilize an appropriate desorbent, which is normally outside this range. One desorbent that works for a light naphtha having components in the C4 to C11 range is n-C12.
The naphtha bottoms stream 74 is passed to a hydrotreating unit 80 to generate a treated hydrocarbon stream 8. The hydrotreating of the naphtha bottoms stream 74 removes sulfur impurities and nitrogen impurities. The hydrotreating can also perform some hydrogenation of reactive components, such as acetylenes and diolefins. The hydrotreated, or hydrogenated, stream 8 is passed to an adsorption separation unit 10 to generate an extract stream 12 and a raffinate stream 14. The adsorbent in the adsorption separation unit 10 is selected for separating normal hydrocarbons, and in particular normal paraffins, from non-normal hydrocarbons. The extract stream 12 comprises normal hydrocarbons and the raffinate stream 14 comprises non-normal and aromatic hydrocarbons.
The raffinate stream 14 is passed to a raffinate separation system 30. The raffinate separation system 30 generates a raffinate overhead stream 32, an intermediate raffinate stream 34 and a raffinate bottoms stream 36. The raffinate separation system 30 can comprise two fractionation columns, a divided wall column, or other means for separating a mixture into two or three streams. Fractionation is preferred, as the components in the raffinate stream are readily separated by their boiling point differences. The adsorption separation system 10 uses a desorbent, and the raffinate bottoms stream 36 comprises desorbent that is recycled to the adsorption separation system 10. The raffinate overhead stream comprises iC5 and iC6 compounds, and can be used for downstream processing, including adding to a gasoline blending pool. The intermediate raffinate stream 34, comprising aromatics and non-normal hydrocarbons that have higher boiling points than iC5 or iC6 compounds, is passed to a reforming unit 50 to generate a reformate 52 having an increased aromatics content.
The extract stream 12 is passed to an extraction separation system 20 to generate an extract overhead stream 22, an extract intermediate stream 24, and an extract bottoms stream 26. The extract separation system 20 can comprise multiple fractionation columns, with a preferred system using a divided wall column. The extract bottoms stream 26 includes desorbent that is recycled to the separation unit 10. The extract intermediate stream 24 is passed to a cracking unit 40 to convert the normal paraffins to light olefins 42. A typical cracking unit is a naphtha steam cracking unit, but can also comprise a catalytic cracking unit. The extract overhead stream 22 can also be passed to the cracking unit 40, but in an alternative, the extract overhead stream can be passed to an isomerization unit 60.
The isomerization unit 60 converts the overhead stream 22 having normal C5 and C6 paraffins to a isomerized stream 62 having a mixture of normal and iso-C5 and C6 paraffins. The isomerized stream 62 is passed to the separation unit 10, where the non-normal components of the isomerized stream 62 are then removed in the raffinate stream 14. This provides for more hydrocarbons passed to either the reforming unit 50 to increase reformate 52, or to the raffinate overhead stream 32 for downstream processing, including passing to the reforming unit 50 as an option.
A preferred embodiment is for the integration of a separation system, an isomerization system, and a catalytic reforming process into an integrated refinery-petroleum operation. The process provides for shifting hydrocarbons between a cracking process to generate light olefins, and a reforming process for generating aromatics. Thus providing flexibility for a plant to generate a desired product stream.
In a preferred embodiment, the extract separation system, or the raffinate separation system will utilize a divided wall column to produce three separate streams. This will save on capital and operating costs. This process will allow flexibility in the area of gasoline production, through shifting of hydrocarbon components, and in particular C5 and C6 components in a naphtha feedstream, from a cracking stream to a reforming stream, or for directing to a gasoline blending pool.
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.
This application claims the benefit of U.S. Provisional Application No. 61/863,025 filed on Aug. 7, 2013.
| Number | Date | Country | |
|---|---|---|---|
| 61863025 | Aug 2013 | US |
