Patent Application
20200407649
This invention relates generally to a process for producing high octane gasoline and more particularly to processes which incorporate a dehydrogenation unit increase the octane value of a gasoline component by converting C7 saturated hydrocarbons to their corresponding olefins.
Gasoline specifications are becoming stricter and more difficult for refiners to meet. For hydrocracker-based refineries, which rely on the reforming and isomerization units to produce gasoline, it is difficult to meet the aromatics specifications in the Euro V gasoline standard while maximizing 95 RON (research octane number). Euro V standards limit gasoline to concentrations of no more than 35 lv % aromatics and no more than 1.0 lv % benzene with additional limitations on distillation and Reid vapor pressure (RVP). It is common that a refiner cannot process as much reformer feed due to the aromatics limitation thus resulting in the need to sell heavy naphtha that has lower value, thus reducing the refiner's profitability. A refiner can add oxygenates such as methyl tert-butyl ether (MTBE) or tertiary amyl methyl ether (TAME) to the gasolines to increase octane, but these can be expensive and there may be additional environmental regulations against these compounds. The Euro V specifications also limit the amount of olefins that can be added to the gasolines to 18 lv %. For hydrocracker-based, condensate-based or other refineries that do not add a significant amount of olefins to the gasolines, producing an olefin stream can be advantageous due to an increase in octane over paraffins. Since these refineries have low olefins in their gasolines, a significant amount of olefins can be blended into the gasolines up to the specification.
In a typical naphtha complex configuration, a naphtha splitter distillation column fractionates a hydrotreated full range naphtha stream into light naphtha and heavy naphtha. The light naphtha stream containing C5 and C6 species goes to the isomerization unit to make an isomerate and the heavy naphtha is processed in the reforming unit to make reformate. It would be desirable to increase the octane value of components from the heavy stream so that they can be used in the gasoline pool instead of as discussed above being sold as a lower value chemical or requiring additional components.
In the present invention, a C7 stream is fractionated from the naphtha splitter and further separated to produce at least one C7 stream rich in C7 iso-paraffins that is processed in a dehydrogenation zone and a second stream that is rich in n-heptane and methylcyclohexane that is processed in an isomerization zone. In the dehydrogenation zone, the stream rich in C7 isoparaffins is partially converted to higher octane C7 iso-olefins. In the isomerization zone, the stream rich in n-heptane and methylcyclohexane is partially converted to higher octane C7 isoparaffins and C7 cyclopentanes. It is desired in the present invention to control the separations to limit the amount of cyclohexane and methylcyclohexane in the feed to the dehydrogenation zone since these will dehydrogenate to benzene and toluene which are not desired due to the gasoline benzene and aromatic specifications. It is also desired to dehydrogenate a C7 stream rich in C7 isoparaffins since these components form higher octane mono-olefins as compared to a stream rich in n-heptane which will dehydrogenate to normal C7 mono-olefins with lower octanes.
There are several advantages for dehydrogenating the C7 compounds. First, the C7 compounds are not converted to aromatics in the reformer. Additionally, some of the C7 compounds are upgraded to higher octane via the production of high-octane C7 olefins and other C7 compounds are upgraded via from the production of higher octane C7 iso-paraffins and C7 cyclopentanes. These facilitate the production of a greater amount of gasoline that meets the Euro V specifications and reduce the amount of lower value heavy naphtha that needs to be sold. There is additional hydrogen generated by the dehydrogenation unit that can be recirculated to the reformer, isomerization unit or other process units.
The various processes described herein provide processes for efficiently and effectively processing feed streams that include appreciable amounts of MCH and minimize the conversion of MCH to toluene in the dehydrogenation reaction zone.
Therefore, the present invention may be broadly characterized, in at least one aspect, as providing a process for producing a gasoline blend by: separating a naphtha feed in a fractionation column into a stream comprising C6 and lighter boiling hydrocarbons, one or more C7 hydrocarbon streams comprising methylcyclohexane, iC7, and nC7, and a heavy stream comprising C8 hydrocarbons; isomerizing, in a C6 isomerization zone at isomerization conditions, at least a portion of the stream comprising C6 and lighter boiling hydrocarbons to form a C6 isomerization effluent; isomerizing, in a C7 isomerization zone at isomerization conditions, at least the nC7 from the one or more C7 hydrocarbon streams comprising methylcyclohexane, iC7, and nC7 to form a C7 isomerization effluent; dehydrogenating, in a C7 dehydrogenation zone at dehydrogenation conditions, the iC7 from the one or more C7 hydrocarbon streams comprising methylcyclohexane, iC7, and nC7 to form a C7 dehydrogenation effluent, wherein the methylcyclohexane of the one or more C7 hydrocarbon stream comprising methylcyclohexane, iC7, and nC7 bypasses the C7 dehydrogenation zone; reforming, in a reforming zone under reforming conditions, the heavy stream to form a reformate stream; and, blending the C6 isomerization effluent, the reformate stream, the C7 dehydrogenation effluent, and the C7 isomerization effluent to form the gasoline blend.
In a second aspect, the present invention may be generally characterized, in at least one aspect, as providing a process for producing a gasoline blend, the process comprising separating a naphtha feed into a stream comprising C6 and lighter boiling hydrocarbons, a C7 hydrocarbon stream comprising methylcyclohexane, iC7, and nC7, and a heavy stream comprising C8 hydrocarbons; isomerizing, in a C6 isomerization zone at isomerization conditions, at least a portion of the stream comprising C6 and lighter boiling hydrocarbons to form a C6 isomerization effluent; separating the C7 hydrocarbon stream in a C7 separation zone into an iC7 stream and an nC7 and methylcyclohexane stream; isomerizing, in a C7 isomerization zone at isomerization conditions, the nC7 and methylcyclohexane stream from the C7 separation zone to form a C7 isomerization effluent; dehydrogenating, in a C7 dehydrogenation zone at dehydrogenation conditions, the iC7 from the C7 separation zone to form a C7 dehydrogenation effluent; reforming, in a reforming zone under reforming conditions, the heavy stream to form a reformate stream; and, blending the C6 isomerization effluent, the reformate stream, the C7 dehydrogenation effluent, and the C7 isomerization effluent to form the gasoline blend.
According to a third aspect, the present invention may be broadly characterized as providing a process for producing a gasoline blend by: separating a naphtha feed into a stream comprising C6 and lighter boiling hydrocarbons, a C7 hydrocarbon stream comprising methylcyclohexane, iC7, and nC7, and a heavy stream comprising C8 hydrocarbons; isomerizing, in a C6 isomerization zone at isomerization conditions, at least a portion of the stream comprising C6 and lighter boiling hydrocarbons to form a C6 isomerization effluent; isomerizing, in a C7 isomerization zone at isomerization conditions, the C7 hydrocarbon stream comprising methylcyclohexane, iC7, and nC7 to form a C7 isomerization effluent; separating the C7 isomerization effluent in a C7 separation zone into an iC7 stream and an MCH rich stream; dehydrogenating, in a C7 dehydrogenation zone at dehydrogenation conditions, the iC7 stream; reforming, in a reforming zone under reforming conditions, the heavy stream to form a reformate stream; and, blending the C6 isomerization effluent, the reformate stream, the C7 dehydrogenation effluent, and the C7 isomerization effluent to form the gasoline blend.
Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.
In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.
Additional aspects, embodiments, and details of the invention, all of which may be combinable in any manner, are set forth in the following detailed description of the invention.
One or more exemplary embodiments of the present invention will be described below in conjunction with the following drawing figures, in which:
As mentioned above, various processes have been invented which minimize the dehydrogenation of MCH to toluene and promotes C7 paraffin and C7 cyclo-paraffin dehydrogenation to form C7 olefins and cyclo-olefins to improve the octane value of the C7 spilt from a naphtha feed stream. This invention allows achieving the octane pool requirements, aromatic requirements, processing of heavy naphtha, and does not require addition of MTBE. These processes provide for lower costs, both initial and operating, compared to processes which include C7 isomerization that contain large deisoheptanizer column recycle streams. Specifically, this invention utilizes new configurations of C7 isomerization, fractionation and C7 dehydrogenation specifically to produce olefin-containing streams for addition to the gasoline pool that meet the aromatic spec limit of Euro V gasoline.
A key aspect of these configurations is that the C7 compounds that would form aromatics in the reformer are routed away from the reformer. Cyclohexane and MCH are also routed away from the dehydrogenation reactor so as to minimize the formation of aromatics and prevent quenching of C7 paraffin dehydrogenation reactions to olefins.
To provide lower cost, the C7 isomerization zone can consist of a single reactor operating as hydrocarbon once-through and hydrogen once-through. The isomerization catalyst contains a group VIII element, preferably Pt, on a catalyst support such as chlorided alumina, sulfated-zirconia or zeolitic-containing base. In some embodiments, two or more C7 isomerization reactors in series can be utilized in the isomerization zone.
The dehydrogenation unit has a single reactor. The selective dehydrogenation catalyst contains a group VIII component, a promoter such as Sn, and an alkali and/or alkaline earth component.
Generally, the processes of the present invention fall into two different categories: one C7 stream is provided by the naphtha splitter, or two C7 streams are provided by the naphtha splitter.
In cases falling into the two C7 streams withdrawn from the naphtha splitter, one stream is iC7 rich and the other stream is nC7+MCH rich. The iC7 rich stream is fractionated such as to minimize cyclohexane and benzene. The nC7+MCH rich stream cut is sent to isomerization to form higher octane iC7 isomers and C7 cyclopentanes and then separated to make an iC7 rich stream and MCH-rich stream. The iC7 rich stream can be combined with the iC7 stream from the naphtha splitter and sent to C7 dehydrogenation for octane upgrading. The MCH-rich stream is sent to the gasoline pool but it can be partially recycled to isomerize remaining low octane C7 paraffins.
In cases in which a single C7 stream is withdrawn from the naphtha splitter, the C7 stream from the naphtha splitter can be further split to give an iC7 overhead stream and nC7+MCH rich streams. The nC7+MCH rich stream goes to the isomerization reactor to form higher octane iC7 isomers and C7 cyclopentanes. The isomerization exit stream can again be split making iC7 and MCH-rich streams. The MCH-rich stream is sent to the gasoline pool but it can be partially recycled to isomerize remaining low octane C7 paraffins. This minimizes the aromatization of MCH to toluene in the dehydrogenation zone. The iC7 can join the iC7 overhead stream and go directly to the C7 dehydrogenation unit, giving the highest single pass conversion opportunity and highest octane yield.
With these general principles in mind, one or more embodiments of the present invention will be described with the understanding that the following description is not intended to be limiting. Additionally, in the various FIGS., identical elements in the various embodiments have identical reference numbers.
As shown in
Hydrotreating is a process in which hydrogen gas is contacted with a hydrocarbon stream in the presence of suitable catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen, and metals from the hydrocarbon feedstock. In hydrotreating, hydrocarbons with double and triple bonds may be saturated. Aromatics may also be saturated. Typical hydrotreating reaction conditions include a temperature of about 290° C. (550° F.) to about 455° C. (850° F.), a pressure of about 3.4 MPa (500 psig) to about 6.2 MPa (900 psig), a liquid hourly space velocity of about 0.5 h−1 to about 4 h−1, and a hydrogen rate of about 168 to about 1,011 Nm3/m3 oil (1,000-6,000 scf/bbl). Typical hydrotreating catalysts include at least one Group VIII metal, preferably iron, cobalt and nickel, and at least one Group VI metal, preferably molybdenum and tungsten, on a high surface area support material, preferably alumina. Other typical hydrotreating catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from palladium and platinum.
A hydrotreated effluent 16 is passed to the fractionation zone 14 which comprises at least one fractionation column 18, which may be a naphtha splitter. In the fractionation column 18, according to the embodiments of the present invention shown in
To accommodate the MCH and avoid conversion of the MCH to toluene (and the quenching of the dehydrogenation of the other C7 hydrocarbons), the present invention provides various processes. For example, as shown in
In another embodiment (not shown), separation zone 28 can contain a three-cut fractionation column that provides an overhead stream that contains multi-branched iC7s, cyclohexane and benzene, a side draw stream that contains single-branched iC7s, and a bottoms stream that contains nC7 and MCH. The overhead stream can be sent to gasoline blending or to a benzene saturation unit and then to gasoline blending. The sidedraw stream is passed to the dehydrogenation zone. The bottoms stream is passed to the C7 isomerization zone.
As mentioned above, iC7 stream 32 is combined with a hydrogen stream (not shown), heated and passed to the C7 dehydrogenation zone 36. The C7 dehydrogenation zone 36 comprises a reactor 38 which contains a catalyst to convert a portion of the saturated hydrocarbons in the iC7 stream 32 to olefins in the presence of hydrogen over a selective platinum dehydrogenation catalyst. Specifically, C7 iso-paraffins are dehydrogenated to the corresponding iso-C7 mono-olefins. For example, a multibranched iC7, 2,4-dimethylpentane is dehydrogenated to 2,4-dimethyl-1-pentene and 2,4-dimethyl-2-pentene. A single-branched iC7, 2-methylhexane is dehydrogenated to 2-methyl-1-hexene, 2-methyl-2-hexene, cis-2-methyl-3-hexene, trans-2-methyl-3-hexene, 5-methyl-1-hexene, cis-5-methyl-2-hexene and trans-5-methyl-2-hexene. Cyclopentane compounds are dehydrogenated to cyclopentene compounds.
The dehydrogenation process may utilize any suitable selective dehydrogenation catalyst. Generally, one preferred suitable catalyst comprises a Group VIII noble metal component (e.g., platinum, iridium, rhodium, and palladium), an alkali metal component, and a porous inorganic carrier material. The catalyst may also contain promoter metals which advantageously improve the performance of the catalyst. The porous carrier material should be relatively refractory to the conditions utilized in the reaction zone and may be chosen from those carrier materials which have traditionally been utilized in dual function hydrocarbon conversion catalysts. A preferred porous carrier material is a refractory inorganic oxide, with the most preferred an alumina carrier material. The particles are usually spheroidal and have a diameter of from about 1.6 to about 3.2 mm (about 1/16 to about ⅛ inch) about 1.6 to about 3.2 mm, although they may be as large as about 6.4 mm (about ¼ inch). Newer dehydrogenation catalysts can also be used in this process.
For example, one such catalyst comprises a layered catalyst composition comprising an inner core, and outer layer bonded to the inner core so that the attrition loss is less than 10 wt % based on the weight of the outer layer. The outer layer is a refractory inorganic oxide. Uniformly dispersed on the outer layer is at least one platinum group metal, and a promoter metal. The inner core and the outer layer are made of different materials. A modifier metal is also dispersed on the outer layer. The inner core is made from alpha alumina, theta alumina, silicon carbide, metals, cordierite, zirconia, titania, and mixtures thereof. The outer refractory inorganic oxide is made from gamma alumina, delta alumina, eta alumina, theta alumina, silica/alumina, zeolites, non-zeolitic molecular sieves, titania, zirconia, and mixtures thereof. The platinum group metals include platinum, palladium, rhodium, iridium, ruthenium, osmium, and mixtures thereof. The platinum group metal is present in an amount from about 0.01 to about 5 wt % of the catalyst composition. The promoter metal includes tin, germanium, rhenium, gallium, bismuth, lead, indium, cerium, zinc, and mixtures thereof. The modifier metal includes alkali metals, such as potassium and lithium, alkaline earth metals, and mixtures thereof. Further discussion of two layered dehydrogenation catalysts can be found in U.S. Pat. No. 6,617,381, which is incorporated herein by reference, for example.
The process conditions utilized for dehydrogenation are usually 0 to 345 kPa (0 to 50 psig), 0.5 to 6 hydrogen/hydrocarbon mole ratio, inlet reactor temperatures of 450 to 600° C. (845 to 1112° F.), and 1 to 30 h−1 LHSV. Conditions preferred for C7 hydrocarbon feed stocks are 138 to 276 kPa (20 to 40 psig), about 3 to 5 hydrogen/hydrocarbon mole ratio, inlet reactor temperatures of about 520 to 560° C. (968 to 1040° F.), and about 5 to 10 h−1 LHSV. Adiabatic radial-flow reactors are used to minimize pressure drop within an efficient reactor volume. Hydrogen and some by-product light ends are typically separated (not shown) from the C7 dehydrogenation effluent 40, and a part of this hydrogen gas may be recycled back to the dehydrogenation reactor 38 to minimize coking and enhance catalyst stability.
The C7 dehydrogenation effluent 40 comprising an increased olefins content compared to an olefins content of the C7 stream 24 may be added to a gasoline pool to bolster octane value of the gasoline blend. Although not depicted as such, the C7 stream 24 may first be passed to a selective hydrogenation zone (not shown in the FIGS.) for the selective conversion of diolefins to mono-olefins. In such a process, a hydrogen stream is also charged to the selective hydrogenation reactor. Typical selective hydrogenation conditions utilized are 25 to 350° C. (77 to 662° F.), 276 kPa to 5.5 MPa) (40 to 800 psig), 5-35 h−1 LHSV and a hydrogen to diolefin mole ratio of between about 1.4 to 2.0. The selective hydrogenation reactor effluent passes to a stripper (not shown) where dissolved light hydrocarbons are removed and the stripper bottoms, a mixture of mono-olefin hydrocarbons and unconverted saturated hydrocarbons stream are sent for blending in gasoline pool. Other streams from the process are also blended to form the gasoline.
The C7 isomerization zone 42 comprises at least one reactor 44 as well as feed-effluent heat exchangers, inter-reactor heat exchangers, driers, sulfur guards, separator, stabilizer, compressors, deisopentanizer column, recycle streams and other equipment as known in the art (not shown). The reactor 44 of the C7 isomerization zone 42 includes an isomerization catalyst and is operated under conditions for converting normal and single branched paraffins in the nC7 and MCH stream 34 into multi-branched paraffins. Additionally, within the C7 isomerization zone 42 some C7 cyclopentanes and MCH are also isomerized.
Any suitable isomerization catalyst may be used in the C7 isomerization zone 42. Suitable isomerization catalysts include acidic catalysts using chloride for maintaining the sought acidity and sulfated catalysts. The isomerization catalyst may be amorphous, e.g., based upon amorphous alumina, or zeolitic. A zeolitic catalyst would still normally contain an amorphous binder. The catalyst may include a sulfated zirconia and platinum as described in U.S. Pat. No. 5,036,035 and European application 0 666 109 or a platinum group metal on chlorided alumina as described in U.S. Pat. Nos. 5,705,730 and 6,214,764. Another suitable catalyst is described in U.S. Pat. No. 5,922,639. U.S. Pat. No. 6,818,589 discloses a catalyst including a tungstated support of an oxide or hydroxide of a Group IVB (TUPAC 4) metal, for example zirconium oxide or hydroxide, at least a first component which is a lanthanide element and/or yttrium component, and at least a second component being a platinum-group metal component.
Contacting within the reactor 44 of the C7 isomerization zone 42 may be effected using the catalyst in a fixed-bed system, a moving-bed system, a fluidized-bed system, or in a batch-type operation. A fixed-bed system may be employed in an exemplary embodiment. The reactants may be contacted with the bed of catalyst particles in upward, downward, or radial-flow fashion. The reactants may be in the liquid phase, a mixed liquid-vapor phase, or a vapor phase when contacted with the catalyst particles.
Isomerization conditions in the within the reactor 44 of the C7 isomerization zone 42 may include reactor temperatures that may be from 40 to 250° C. Lower reaction temperatures (within the stated range) may be employed in order to favor multi-branched iC7 component equilibrium mixtures having the highest concentration of high-octane highly branched isoalkanes and to minimize cracking of the feed to lighter hydrocarbons. Temperatures from 100 to 200° C. (212 to 392° F.) may be employed in some embodiments. Reactor operating pressures may be from 100 kPa to 10 MPa absolute (14.5 to 1,450 psi), for example from 0.5 MPa to 4 MPa absolute (72.5 to 580 psi). Liquid hourly space velocities may be from 0.2 to 25 volumes of isomerizable hydrocarbon feed per hour per volume of catalyst, for example from 0.5 to 15 hr−1.
A C7 isomerization effluent 46 may be blended with the C7 dehydrogenation effluent 40 in the gasoline pool. Additionally, a portion 46a of the C7 isomerization effluent 46 may be recycled to the fractionation column in the C7 separation zone 28 so that iC7 in the C7 isomerization effluent 46 can be converted in the C7 dehydrogenation zone 36.
Turning to
Returning to the fractionation zone 14 in
Similarly, as shown in
The second C6 stream 66, which will also include, for example, nC5 hydrocarbons, is passed to an C6 isomerization zone 68 where the C5 and C6 hydrocarbons will be isomerized. The C6 isomerization zone 68 can be any type of isomerization zone that takes a stream of C5 and C6 straight-chain hydrocarbons or a mixture of straight-chain, branched-chain, cyclic hydrocarbons, and benzene and converts straight-chain hydrocarbons in the feed mixture to branched-chain hydrocarbons and branched hydrocarbons to more highly branched hydrocarbons, thereby producing an effluent having branched-chain and straight-chain hydrocarbons. The cycloparaffins can isomerize between cyclopentanes and cyclohexane compounds. Benzene can be saturated to form cyclohexane.
In some embodiments, the C6 isomerization zone 68 can include one or more isomerization reactors 70, as well as feed-effluent heat exchangers, inter-reactor heat exchangers, driers, sulfur guards, separator, stabilizer, compressors, pumps, hydrogen recycle stream and other equipment as known in the art (not shown). A hydrogen-rich gas stream (not shown) is typically mixed with the second C6 stream 66 and heated to reaction temperatures. The hydrogen-rich gas stream, for example, comprises about 50-100 mol % hydrogen. The hydrogen can be separated from the reactor effluent, compressed and recycled back to mix with the light stream. The second C6 stream 66 and hydrogen are contacted in the C6 isomerization zone 68 with an isomerization catalyst forming a C6 isomerization effluent 72.
The catalyst composites that can be used in the C6 isomerization zone 68 include traditional isomerization catalysts including chlorided platinum alumina, crystalline aluminosilicates or zeolites, and other solid strong acid catalysts such as sulfated zirconia and modified sulfated zirconia. Suitable catalyst compositions of this type will exhibit selective and substantial isomerization activity under the operating conditions of the process. Operating conditions within the C6 isomerization zone 68 are selected to maximize the production of isoalkane product from the feed components. Temperatures within the isomerization zone will usually range from about 40 to about 235° C. (100 to 455° F.). Lower reaction temperatures usually favor equilibrium mixtures of isoalkanes versus normal alkanes. Lower temperatures are particularly useful in processing feeds composed of C5 and C6 alkanes where the lower temperatures favor equilibrium mixtures having the highest concentration of the most branched isoalkanes. When the feed mixture is primarily C5 and C6 alkanes, temperatures in the range of from about 60 to about 160° C. (140 to 320° F.) are suitable. The C6 isomerization zone 68 may be maintained over a wide range of pressures. Pressure conditions in the isomerization of C4 to C6 paraffins range from about 700 kPa(a) to about 7,000 kPa(a) (102 to 1,015 psi). In other embodiments, pressures for this process are in the range of from about 2,000 kPa(g) to 5,000 kPa(g) (290 to 725 psi). The feed rate to the reaction zone can also vary over a wide range. These conditions include liquid hourly space velocities ranging from about 0.5 to about 12 h−1 however, with some embodiments having space velocities between about 1 and about 6 h−1.
The C6 isomerization effluent 72 is passed to a fractionation zone 74 comprising, for example, a deisohexanizer column 76 to separate the components of the C6 isomerization effluent 72 into a plurality of streams, including, an overhead stream 78 comprising iC5 and nC5, and an iC6 stream 80, a recycle stream 82 comprising nC6 hydrocarbons, and a bottoms stream 84 comprising C7 and heavier hydrocarbons. The bottoms stream 84 and the iC6 stream 80 streams may be blended to form one stream for gasoline pool blending. The overhead stream 78 may be recycled to the fractionation column 62, while the recycle stream 82 is combined with the C6 isomerization feed stream 66.
Turning to
Turning to
In
Another embodiment is shown in
Turning to
In the embodiment of
In the embodiment of
In the embodiments shown in
Finally, in the embodiments of
When nC7 is dehydrogenated to the corresponding normal C7 mono-olefins, the octane numbers range between 54.5 to 90.2 RON with an average of 77.0 RON as listed in Table 1, below. When a single-branched iC7 paraffin such as 3-methylhexane for example is dehydrogenated to the corresponding iC7 mono-olefins, the octane numbers range between 82.2 to 98.6 RON with an average of 92.5 RON. When multi-branched iC7 paraffins such as 2,2-dimethylpentane, 2,4-deimethylpentane and 3,3-deimethylpentane for example are dehydrogenated to the corresponding multi-branched iC7 mono-olefins, the octane numbers range from 99.2 to 105.3 RON with averages of 100.2-103.1 RON as shown in Table 1. Therefore, in terms of octane increase, it is more advantageous to dehydrogenate single-branched iC7 paraffins as compared to nC7 and it is most advantageous to dehydrogenate multi-branched iC7 paraffins which have the highest mono-olefin octanes.
Table 2, below, shows that it is important to fractionate as much of the cyclohexane and benzene from the front end of the iC7 stream that is sent the dehydrogenation zone to prevent cyclohexane from dehydrogenating to form benzene. It is evident that some multi-branched iC7 paraffins co-boil with cyclohexane and will be excluded. The iC7 stream will contain some multi-branched iC7 paraffins but will be rich in single-branched iC7 paraffins. Table 2 also shows that nC7 and MCH have relatively close boiling points and above the iC7 paraffins, therefore a nC7+MCH stream can be fractionated. To obtain the desired cuts, it is envisioned that additional trays can be added to the fractionation columns, or a divided wall can be utilized inside the columns or other known techniques to improve the fractionation between the C7 species can be utilized.
From pilot plant data, a dehydrogenation model was formulated and placed into a process simulator to estimate the temperature drop over a single dehydrogenation reactor and the products formed. The process conditions of the dehydrogenation reactor (layered catalyst with the outer layer comprising gamma alumina with dispersed metals Pt, Sn, and Li) were set to 565° C. (1049° F.) inlet temperature, 137.9 kPa (20 psig), 10 h−1 LHSV, and hydrogen/hydrocarbon mole ratio of three. A dehydrogenation feed that was MCH-free was selected to demonstrate the effect of allowing MCH into the dehydrogenation reactor. The MCH-free feed consisted of 11.7 wt % n-heptane, 21.3 wt % 2-methylhexane, 19.9 wt % 3-methylhexane, 1.6 wt % 3-ethylpentane, 34.3 wt % multi-branched C7 isoparaffins, and 11.2 wt % C7 cyclopentanes.
Table 3, below, shows the results of the process simulations for the MCH-free feed and the feeds that contained increasing amounts of MCH. For the MCH-free feed, the highest C7 conversion to olefins and the highest product octane was realized. The small amount of toluene formed was due to C7 paraffin reaction to aromatics via a sequential dehydrogenation pathway that is thought to occur on the metal sites at high temperatures. As the MCH increased in the dehydrogenation feed, the outlet temperature was lower (quench), the conversion of C7 paraffins to olefins decreased, the octane decreased, and the toluene produced increased substantially. Therefore, to achieve appreciable conversions to olefins and to minimize the production of toluene, it is important to route MCH away from the dehydrogenation reactor.
Any of the above lines, conduits, units, devices, vessels, surrounding environments, zones or similar may be equipped with one or more monitoring components including sensors, measurement devices, data capture devices or data transmission devices. Signals, process or status measurements, and data from monitoring components may be used to monitor conditions in, around, and on process equipment. Signals, measurements, and/or data generated or recorded by monitoring components may be collected, processed, and/or transmitted through one or more networks or connections that may be private or public, general or specific, direct or indirect, wired or wireless, encrypted or not encrypted, and/or combination(s) thereof; the specification is not intended to be limiting in this respect.
Signals, measurements, and/or data generated or recorded by monitoring components may be transmitted to one or more computing devices or systems. Computing devices or systems may include at least one processor and memory storing computer-readable instructions that, when executed by the at least one processor, cause the one or more computing devices to perform a process that may include one or more steps. For example, the one or more computing devices may be configured to receive, from one or more monitoring component, data related to at least one piece of equipment associated with the process. The one or more computing devices or systems may be configured to analyze the data. Based on analyzing the data, the one or more computing devices or systems may be configured to determine one or more recommended adjustments to one or more parameters of one or more processes described herein. The one or more computing devices or systems may be configured to transmit encrypted or unencrypted data that includes the one or more recommended adjustments to the one or more parameters of the one or more processes described herein.
It should be appreciated and understood by those of ordinary skill in the art that various other components such as valves, pumps, filters, coolers, etc. were not shown in the drawings as it is believed that the specifics of same are well within the knowledge of those of ordinary skill in the art and a description of same is not necessary for practicing or understanding the embodiments of the present invention.
While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.
A first embodiment of the invention is a process for producing a gasoline blend, the process comprising separating a naphtha feed in a fractionation column into a stream comprising C6 and lighter boiling hydrocarbons, one or more C7 hydrocarbon streams comprising methylcyclohexane, iC7, and nC7, and a heavy stream comprising C8 hydrocarbons; isomerizing, in a C6 isomerization zone at isomerization conditions, at least a portion of the stream comprising C6 and lighter boiling hydrocarbons to form a C6 isomerization effluent; isomerizing, in a C7 isomerization zone at isomerization conditions, at least the nC7 from the one or more C7 hydrocarbon streams comprising methylcyclohexane, iC7, and nC7 to form a C7 isomerization effluent; dehydrogenating, in a C7 dehydrogenation zone at dehydrogenation conditions, the iC7 from the one or more C7 hydrocarbon streams comprising methylcyclohexane, iC7, and nC7 to form a C7 dehydrogenation effluent, wherein the methylcyclohexane of the one or more C7 hydrocarbon stream comprising methylcyclohexane, iC7, and nC7 bypasses the C7 dehydrogenation zone; reforming, in a reforming zone under reforming conditions, the heavy stream to form a reformate stream; and, blending the C6 isomerization effluent, the reformate stream, the C7 dehydrogenation effluent, and the C7 isomerization effluent to form the gasoline blend. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the fractionation column provides a hydrocarbon stream comprising methylcyclohexane, iC7, and nC7 as the one or more C7 hydrocarbon streams comprising methylcyclohexane, iC7, and nC7. 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 separating, in a C7 separation zone, the hydrocarbon stream comprising methylcyclohexane, iC7, and nC7 into an iC7 stream and an nC7 and MCH 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 the iC7 stream from the C7 separation zone to the C7 dehydrogenation zone; and, passing the nC7 and MCH stream from the C7 separation zone to the C7 isomerization zone. 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 recycling a portion of the C7 isomerization effluent to the C7 separation zone. 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 separating, in a second C7 separation zone, the C7 isomerization effluent into a second iC7 stream and an MCH rich 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 the second iC7 stream from the second C7 separation zone to the C7 dehydrogenation zone. 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 combining the C7 stream comprising C7 hydrocarbons with the C6 isomerization effluent and passing the combined stream to the C7 isomerization zone. 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 separating, in a second C7 separation zone, a portion of the combined C6 and C7 isomerization effluent into a second iC7 stream and an MCH rich 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 the second iC7 stream from the second C7 separation zone to the C7 dehydrogenation zone. 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 hydrocarbon stream comprising methylcyclohexane, iC7, and nC7 to the C7 isomerization zone. 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 separating, in a C7 separation zone, a portion of the C7 isomerization effluent into an iC7 stream and an MCH rich stream; and, passing the iC7 stream to the C7 dehydrogenation zone. 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 recycling a portion of the MCH rich stream to the C7 isomerization zone. 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 combining the C7 stream comprising C7 hydrocarbons with the C6 isomerization effluent and passing the combined stream to the C7 isomerization zone. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the fractionation column provides, as the one or more C7 hydrocarbon streams comprising methylcyclohexane, iC7, and nC7, a first C7 hydrocarbon stream comprising iC7 and a second C7 hydrocarbon stream comprising methylcyclohexane and nC7. 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 first C7 hydrocarbon stream to the C7 dehydrogenation zone; and, passing at least a portion of the second C7 hydrocarbon stream to the C7 isomerization zone. 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 separating, in a C7 separation zone, the second C7 hydrocarbon stream into an MCH rich stream and an nC7 rich stream; passing the nC7 rich stream to the C7 isomerization zone; and, passing the C7 isomerization effluent to the C7 dehydrogenation zone. 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 separating, in a C7 separation zone, the C7 isomerization effluent into an iC7 rich stream and an MCH rich stream; and, passing the iC7 rich stream to the C7 dehydrogenation zone. 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 recycling a portion of the MCH rich stream to the C7 isomerization zone. 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 separating, in a second C7 separation zone, a stream of nC7 from the isomerization effluent, wherein the stream of nC7 comprises the portion of the MCH rich stream recycled to the C7 isomerization zone. 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 combining the C7 stream comprising C7 hydrocarbons with the C6 isomerization effluent and passing the combined stream to the C7 isomerization zone. 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 separating, in a second C7 separation zone, a portion of the combined C6 and C7 isomerization effluent into a second iC7 stream and a methylcyclohexane rich stream. 23 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 second iC7 stream from the second C7 separation zone to the C7 dehydrogenation zone.
A second embodiment of the invention is a process for producing a gasoline blend, the process comprising separating a naphtha feed into a stream comprising C6 and lighter boiling hydrocarbons, a C7 hydrocarbon stream comprising methylcyclohexane, iC7, and nC7, and a heavy stream comprising C8 hydrocarbons; isomerizing, in a C6 isomerization zone at isomerization conditions, at least a portion of the stream comprising C6 and lighter boiling hydrocarbons to form a C6 isomerization effluent; separating the C7 hydrocarbon stream in a C7 separation zone into an iC7 stream and an nC7 and methylcyclohexane stream; isomerizing, in a C7 isomerization zone at isomerization conditions, the nC7 and methylcyclohexane stream from the C7 separation zone to form a C7 isomerization effluent; dehydrogenating, in a C7 dehydrogenation zone at dehydrogenation conditions, the iC7 from the C7 separation zone to form a C7 dehydrogenation effluent; reforming, in a reforming zone under reforming conditions, the heavy stream to form a reformate stream; and, blending the C6 isomerization effluent, the reformate stream, the C7 dehydrogenation effluent, and the C7 isomerization effluent to form the gasoline blend.
A third embodiment of the invention is a process for producing a gasoline blend, the process comprising separating a naphtha feed into a stream comprising C6 and lighter boiling hydrocarbons, a C7 hydrocarbon stream comprising methylcyclohexane, iC7, and nC7, and a heavy stream comprising C8 hydrocarbons; isomerizing, in a C6 isomerization zone at isomerization conditions, at least a portion of the stream comprising C6 and lighter boiling hydrocarbons to form a C6 isomerization effluent; isomerizing, in a C7 isomerization zone at isomerization conditions, the C7 hydrocarbon stream comprising methylcyclohexane, iC7, and nC7 to form a C7 isomerization effluent; separating the C7 isomerization effluent in a C7 separation zone into an iC7 stream and an MCH rich stream; dehydrogenating, in a C7 dehydrogenation zone at dehydrogenation conditions, the iC7 stream; reforming, in a reforming zone under reforming conditions, the heavy stream to form a reformate stream; and, blending the C6 isomerization effluent, the reformate stream, the C7 dehydrogenation effluent, and the C7 isomerization effluent to form the gasoline blend.
Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.
In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.
