Abstract:
A process for increasing the yields of hydrocarbon components to gasoline blending pools from a hydrocarbon feedstock is presented. The process includes separating a naphtha feedstock to components to a first stream that are more readily processed in a cracking unit and to components in a second stream that are more readily processed in a reforming unit. 
     The process includes the ability to convert components from the cracking stream to the reforming stream.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/863,025 filed on Aug. 7, 2013. 
     
    
     FIELD OF THE INVENTION 
       [0002]    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. 
       BACKGROUND 
       [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
       SUMMARY 
       [0007]    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. 
         [0008]    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. 
         [0009]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]      FIG. 1  is a flow schematic of the process; and 
           [0011]      FIG. 2  is a specific embodiment of the present process. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    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. 
         [0013]    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  FIG. 1 , includes passing a treated hydrocarbon stream  8  to a separation unit  10 . The separation unit  10  generates an extract stream  12  enriched in normal hydrocarbons, and a raffinate stream  14  having a reduced normal hydrocarbon content. The extract stream  12  is passed to an extract separation system  20  to generate an extract overhead stream  22 . The extract separation system  20  can also generate an extract intermediate stream  24 , and an extract bottoms stream  26 . 
         [0014]    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. 
         [0015]    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. 
         [0016]    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. 
         [0017]    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 . 
         [0018]    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. 
         [0019]    In a specific embodiment, the process, as shown in  FIG. 2 , processes a naphtha feedstream. A naphtha feedstream comprises many hydrocarbon components, and is often passed to a cracking unit for the production of light olefins. However, the composition of a naphtha stream includes components that do not crack well to light olefins and this leads to further processing. A naphtha feedstream also include useful hydrocarbons for converting to aromatics. The present embodiment seeks to separate a naphtha feedstream to increase the yields and efficiencies of naphtha cracking units and reforming units. A naphtha feedstream  76  is passed to a fractionation unit  70  to generate an overhead stream  72  comprising C4 and lighter hydrocarbons, and a bottoms stream  74  comprising C5 and higher hydrocarbons. The overhead stream  72  is passed to a cracking unit  40  to generate a light olefins product stream  42 . 
         [0020]    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. 
         [0021]    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. 
         [0022]    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. 
         [0023]    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 . 
         [0024]    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. 
         [0025]    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. 
         [0026]    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. 
         [0027]    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.