WO2014109766A1

WO2014109766A1 - Process for balancing gasoline and distillate production in a refinery

Info

Publication number: WO2014109766A1
Application number: PCT/US2013/021389
Authority: WO
Inventors: Ronald Birkhoff; Erik MOY
Original assignee: Badger Licensing Llc
Priority date: 2013-01-14
Filing date: 2013-01-14
Publication date: 2014-07-17

Abstract

In a process for balancing gasoline and distillate production in a refinery, benzene in a refinery gasoline stream is contacted with a C₂ to C₅ alkylating agent under alkylation conditions in an alkylation zone to produce an alkylation effluent comprising one or more monoalkylbenzenes and one or more polyalkylbenzenes. At least part of said alkylation effluent can then be supplied to gasoline production whereas, depending on refinery needs, a varying amount of the one or more polyalkylbenzenes in the alkylation effluent is supplied to distillate production.

Description

PROCESS FOR BALANCING GASOLINE AND DISTILLATE PRODUCTION IN A

REFINERY

FIELD

[0001] The present application relates to a process for balancing gasoline and distillate production in a refinery.

BACKGROUND

[0002] The production of gasoline and distillates (including kerosene and diesel fuels) in a refinery needs to be balanced with market demand and with seasonal variations. Flexibility to balance the production of distillate and gasoline fuels is of great value to refining economics. In this respect, the term "gasoline" is used herein to mean a hydrocarbon fraction having a boiling range of about 40°C to about 210 °C, whereas the term "distillate" is used herein to mean a hydrocarbon fraction having a boiling range of about 175 °C to about 350 °C.

[0003] In a typical fuels refinery, the reformate stream is used entirely to produce gasoline, as the reformate stream contains a high concentration of aromatics with very good octane blending properties, which offsets lower grade blendstock in the refinery to optimize the blend economics. However, the reformate stream is also normally the predominant source of benzene in the refinery, whereas benzene is considered to be environmentally hazardous. As a result, the State of California and the United States Environmental Protection Agency have instituted regulations to limit the amount of benzene which may be present in gasoline. As of January 2011, the US MSAT-2 (Mobile Source Air Toxics) regulation has required reduction of this annual average benzene content in gasoline to no greater than 0.62 volume %.

[0004] Alkylation of benzene with light olefins (e.g. , ethylene, propylene, butenes or pentenes) is commercially practiced in refineries to reduce the content of benzene in reformate and other gasoline streams. In the process, the benzene is converted to alkylaromatic compounds with the light olefin. As a result, the molecular weight is increased and with it, the boiling point and flowrate of reformate. Mono-, di-, and tri-alkyl benzenes are the majority of the products produced. Initially formed is monoalkylbenzene, which can react with additional light olefin in a series reaction to form dialkylbenzene, and so on. Specifically, when propylene is the light olefin, isopropylbenzene (cumene), diisopropylbenzene (DIPB) and triisopropylbenzene (TIPB) are produced. Since the benzene alkylation process increases the octane value, and the quantity of reformate, more gasoline product is able to be produced from both the increased reformate flow and from the indirect benefit of upgrading the lower grade components in the pool.

[0005] It has now been found that polyalkylaromatic compounds produced in the benzene alkylation process (e.g. , DIPB and TIPB) are acceptable blend components in the distillate pool. Separation of polyalkylaromatic compounds, for example, by conventional distillation techniques, from the alkylated reformate stream allows for diversion of at least a portion of the reformate product to distillate production when market conditions are favorable. On the other hand, when market conditions dictate (e.g. , demand for gasoline is higher), the entire reformate stream can be diverted to the gasoline pool. In addition, in the alkylation process, the amount of polyalkylaromatic compounds produced can be adjusted to further enhance the degree of flexibility, which can be achieved by increasing the amount of light olefin reacted with the benzene and/or recycling reaction product to enhance the conversion of monoalkylaromatic compound(s) (e.g. , cumene) to polyalkylaromatic compound(s) (e.g. , DIPB), if necessary.

SUMMARY

[0006] Accordingly, the invention resides in one aspect in a process for balancing gasoline and distillate production in a refinery, the process comprising:

(a) contacting benzene in a refinery gasoline stream with a C₂ to C₅ alkylating agent under alkylation conditions in an alkylation zone to produce an alkylation effluent comprising one or more monoalkylbenzenes and one or more polyalkylbenzenes;

(b) supplying at least part of said alkylation effluent to gasoline production; and

(c) according to one or more defined parameters, supplying a varying amount of said one or more polyalkylbenzenes in said alkylation effluent to distillate production.

[0007] In a further aspect, the invention resides in one aspect in a process for balancing gasoline and distillate production in a refinery, the process comprising:

(a) contacting benzene in a refinery gasoline stream with a C₂ to C₅ alkylating agent under alkylation conditions in an alkylation zone to produce an alkylation effluent comprising one or more monoalkylbenzenes and one or more polyalkylbenzenes; (b) separating said alkylation effluent into a light fraction comprising at least part of said one or more monoalkylbenzenes and a heavier fraction comprising at least part of said one or more polyalkylbenzenes; and

(c) according to one or more defined parameters, adjusting the amount of said light fraction supplied to gasoline production and the amount of said heavier fraction supplied to distillate production.

[0008] Generally, the separating (b) comprises distillation in one or more distillation columns.

[0009] In one embodiment, the process further comprises controlling the contacting (a) according to said one of more defined parameters to vary the amount of polyalkylbenzenes produced. Conveniently, controlling the contacting (a) comprises varying the molar ratio of C₂ to C₅ alkylating agent to benzene fed to the alkylation zone and/or recycling a varying amount of the alkylation effluent to the alkylation zone.

[0010] Typically, said one or more defined parameters include market demand and seasonal conditions.

DETAILED DESCRIPTION

[0011] The benzene content of refinery gasoline streams is reduced by alkylating the benzene with a C₂ to C₅ alkylating agent. The process produces not only monoalkylbenzenes, which are suitable as gasoline blending components, but also produces polyalkylbenzenes, which have now been found to be suitable blending components for both the refinery gasoline pool and the refinery distillate pool. By varying amount of polyalkylbenzenes that are routed to the distillate pool, rather than the gasoline pool, a simple process is provided for balancing gasoline and distillate production according to one or more defined parameters, such as market demand and/or seasonal conditions.

Refinery Gasoline Streams

[0012] Refinery streams which may be alkylated by the present process to decrease their benzene content include streams comprising benzene and alkylbenzenes. Examples of such streams include reformates and naphtha streams, especially light naphtha streams (typically boiling in the range from about 40 °C to about 150 °C at atmospheric pressure). Blends of refinery streams may also be alkylated. The refinery streams employed in the present process typically comprise at least 2 volume % benzene, such as from 4 volume % to 40 volume % benzene.

Alkylation Process

[0013] The present alkylation process comprises contacting the refinery gasoline stream with a C₂ to C₅ alkylating agent under conditions such that at least part of the benzene in the stream is alkylated to produce an alkylation effluent comprising one or more monoalkylbenzenes and one or more polyalkylbenzenes.

[0014] Examples of suitable C₂ to C₅ alkylating agents for use in the present process include ethylene, propylene, butenes, and pentenes. Mixtures of light olefins are especially useful as alkylating agents in the alkylation process of this invention. Accordingly, mixtures of ethylene, propylene, butenes, and/or pentenes which are major constituents of a variety of refinery streams, e.g., fuel gas, gas plant off-gas containing ethylene, propylene, etc., naphtha cracker off-gas containing light olefins, refinery FCC propane/propylene streams, and FCC off-gas, etc., are useful alkylating agents herein. Compositions of examples of olefin containing streams suitable for use as alkylating agents are described, for example, in U.S. Patent No. 7,476,774.

[0015] The alkylation process is desirably conducted in the presence of a suitable catalyst, particularly a catalyst containing an acidic molecular sieve. Suitable catalysts comprise at least one medium pore molecular sieve having a Constraint Index of 2-12 (as defined in U.S. Patent No. 4,016,218). Typical medium pore molecular sieves include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, and ZSM-48. ZSM-5 is described in detail in U.S. Patent Nos. 3,702,886 and Re. 29,948. ZSM-11 is described in detail in U.S. Patent No. 3,709,979. ZSM-12 is described in U.S. Patent No. 3,832,449. ZSM-22 is described in U.S. Patent No. 4,556,477. ZSM-23 is described in U.S. Patent No. 4,076,842. ZSM-35 is described in U.S. Patent No. 4,016,245. ZSM-48 is more particularly described in U.S. Patent No. 4,234,231.

[0016] Alternatively, the alkylation catalyst may comprise one or more large pore molecular sieves having a Constraint Index less than 2. Suitable large pore molecular sieves include zeolite beta, zeolite Y, Ultrastable Y (USY), Dealuminized Y (Deal Y), mordenite, ZSM-3, ZSM-4, ZSM-18, and ZSM-20. Zeolite ZSM-4 is described in U.S. Patent No. 3,923,636. Zeolite ZSM-20 is described in U.S. Patent No. 3,972,983. Zeolite Beta is described in U.S. Patent Nos. 3,308,069, and Re. No. 28,341. Low sodium Ultrastable Y molecular sieve (USY) is described in U.S. Patent Nos. 3,293,192 and 3,449,070. Dealuminized Y zeolite (Deal Y) may be prepared by the method found in U.S. Patent No. 3,442,795. Zeolite UHP-Y is described in U.S. Patent No. 4,401,556. Mordenite is a naturally occurring material but is also available in synthetic forms, such as TEA-mordenite (i.e., synthetic mordenite prepared from a reaction mixture comprising a tetraethylammonium directing agent). TEA-mordenite is disclosed in U.S. Patent Nos. 3,766,093 and 3,894,104.

[0017] Desirably, the alkylation catalyst comprises a molecular sieve of the MCM-22 family. The term "MCM-22 family material" (or "material of the MCM-22 family" or "molecular sieve of the MCM-22 family"), as used herein, includes one or more of:

• molecular sieves made from a common first degree crystalline building block unit cell, which unit cell has the MWW framework topology. (A unit cell is a spatial arrangement of atoms which if tiled in three-dimensional space describes the crystal structure. Such crystal structures are discussed in the "Atlas of Zeolite Framework Types", Fifth edition, 2001, the entire content of which is incorporated as reference);

• molecular sieves made from a common second degree building block, being a 2- dimensional tiling of such MWW framework topology unit cells, forming a monolayer of one unit cell thickness, preferably one c-unit cell thickness;

• molecular sieves made from common second degree building blocks, being layers of one or more than one unit cell thickness, wherein the layer of more than one unit cell thickness is made from stacking, packing, or binding at least two monolayers of one unit cell thickness. The stacking of such second degree building blocks can be in a regular fashion, an irregular fashion, a random fashion, or any combination thereof; and

• molecular sieves made by any regular or random 2-dimensional or 3-dimensional combination of unit cells having the MWW framework topology.

[0018] Molecular sieves of the MCM-22 family include those molecular sieves having an X- ray diffraction pattern including d-spacing maxima at 12.4+0.25, 6.9+0.15, 3.57+0.07 and 3.42+0.07 Angstrom. The X-ray diffraction data used to characterize the material are obtained by standard techniques using the K-alpha doublet of copper as incident radiation and a diffractometer equipped with a scintillation counter and associated computer as the collection system. [0019] Materials of the MCM-22 family include MCM-22 (described in U.S. Patent No. 4,954,325), PSH-3 (described in U.S. Patent No. 4,439,409), SSZ-25 (described in U.S. Patent No. 4,826,667), ERB-1 (described in European Patent No. 0293032), ITQ-1 (described in U.S. Patent No 6,077,498), ITQ-2 (described in International Patent Publication No. WO97/17290), MCM-36 (described in U.S. Patent No. 5,250,277), MCM-49 (described in U.S. Patent No. 5,236,575), MCM-56 (described in U.S. Patent No. 5,362,697), UZM-8 (described in U.S. Patent No. 6,756,030), and mixtures thereof.

[0020] The above molecular sieves may be used as the alkylation catalyst without any binder or matrix, i.e., in so-called self -bound form. Alternatively, the molecular sieve may be composited with another material which is resistant to the temperatures and other conditions employed in the alkylation reaction. Such materials include active and inactive materials and synthetic or naturally occurring zeolites as well as inorganic materials such as clays and/or oxides such as alumina, silica, silica-alumina, zirconia, titania, magnesia or mixtures of these and other oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica and metal oxides. Clays may also be included with the oxide type binders to modify the mechanical properties of the catalyst or to assist in its manufacture. Use of a material in conjunction with the molecular sieve, i.e., combined therewith or present during its synthesis, which itself is catalytically active may change the conversion and/or selectivity of the catalyst. Inactive materials suitably serve as diluents to control the amount of conversion so that products may be obtained economically and orderly without employing other means for controlling the rate of reaction. These materials may be incorporated into naturally occurring clays, e.g., bentonite and kaolin, to improve the crush strength of the catalyst under commercial operating conditions and function as binders or matrices for the catalyst. The relative proportions of molecular sieve and inorganic oxide matrix vary widely, with the sieve content ranging from about 1 to about 90 percent by weight and more usually, particularly, when the composite is prepared in the form of beads, in the range of about 2 to about 80 weight percent of the composite.

[0021] The alkylation process may be conducted such that the organic reactants, i.e., the refinery gasoline stream and the alkylating agent, are brought into contact with a catalyst composition in a suitable alkylation reaction zone, such as, for example, in a flow reactor containing a fixed bed of the catalyst composition, under alkylation conditions effective to produce an alkylated effluent which has reduced benzene content as compared with said refinery gasoline stream.

[0022] Suitable alkylation conditions include a temperature from about 0 °C to about 500 °C, for example, from about 50 °C to about 300 °C, and a pressure from about 0.2 to about 250 atmospheres, for example, from about 1 to about 50 atmospheres. The feed weight hourly space velocity (WHSV) will generally be from 0.1 hr ¹ to 500 hr^-1, for example, from 0.5 hr ¹ to 100 hr ¹. The latter WHSV is based upon the total weight of active catalyst (and binder if present). Generally, the molar ratio of C₂ to C₅ alkylating agent to benzene in the refinery gasoline stream in the feed to the alkylation reaction zone is from about 1.0: 1 to about 2.5: 1. By adjusting this molar ratio, it is possible to vary the relative amounts of monoalkylbenzenes and polyalkylbenzenes in the alkylated effluent and hence the relative amount of each component available for gasoline or distillate production. For example, to increase the amount of monoalkylbenzenes in the alkylated effluent, the molar ratio of C₂ to C₅ alkylating agent to benzene in the alkylation feed may be set at the lower end of the above range, for example, from about 1.0: 1 to about 1.5: 1. Alternatively, to increase the amount of polyalkylbenzenes in the alkylated effluent, the molar ratio of C₂ to C₅ alkylating agent to benzene in the alkylation feed may be set at the upper end of the above range, for example, from about 1.5: 1 to about 2.5: 1.

[0023] The reactants may be in the vapor phase or the liquid phase or in a mixture of liquid and vapor phases during the alkylation reaction. The reactants may be neat, i.e., free from intentional admixture or dilution with other material, or they can be brought into contact with the alkylation catalyst with the aid of carrier gases or diluents such as, for example, hydrogen or nitrogen.

[0024] The alkylation reaction may be conducted in one or more than one alkylation reaction zones connected in series or in parallel. When more than one alkylation zone is used, fresh refinery gasoline feed or fresh alkylating agent feed may, optionally, be introduced between one or more zones. In one embodiment, the reaction zone is in a single stage, fixed bed reactor, and all of the alkylating agent, all of the fresh refinery gasoline stream and all of the recycled effluent are introduced into the inlet of the reactor. Processing of Alkylation Effluent

[0025] The alkylation effluent has a higher concentration of monoalkylbenzenes and polyalkylbenzenes than the refinery gasoline feed stream and typically contains at least 50 % less, such as at least 75 % less, benzene as compared with the refinery gasoline stream. Desirably, the alkylation effluent is essentially free (that is contains less than 0.1 wt%) of the alkylating agent.

[0026] All of the alkylation effluent may be removed from the alkylation zone and sent to the gasoline pool or to one or more distillation units for recovery of the monoalkylbenzenes and polyalkylbenzenes. In certain embodiments, however, an aliquot part of the alkylation effluent is recycled to the alkylation zone before the remainder of the alkylation effluent is sent to the distillation units(s). By varying the amount of the alkylation effluent that is recycled to the alkylation zone, it is possible to vary the concentration of polyalkylbenzenes in the effluent fraction sent to distillation.

[0027] Distillation of the alkylation effluent is arranged to produce at least one light fraction comprising the monoalkylbenzenes and generally some of the polyalkylbenzenes in the effluent and at least one heavy fraction comprising the remainder of the polyalkylbenzenes in the effluent. Typically, the light fraction boils below 210 °C, such as from 25 °C to less than 210 °C, whereas the heavy fraction boils at or above 210 °C, such as from 210 °C to 340 °C. The light fraction can then be blended in the refinery gasoline pool, while the heavy fraction is combined with the distillate pool. In most cases, the light fraction contains less than 2 volume , typically less than 0.62 volume , benzene. In certain embodiments, depending on the requirements of the refinery, all of the alkylation effluent may be directed to the gasoline pool without fractionation to separate the mono- and polyalkylated components.

[0028] The invention will now be more particularly described with reference to the following non-limiting Example.

Example

[0029] In one application it was desired to blend a portion of the effluent from a process for alkylating refinery gasoline with propylene into the distillate pool, and to vary the amount of the blend depending on market conditions. A product splitter was placed in the design, with the overhead typically 94% of the alkylation effluent being sent to motor gasoline blending. The balance of the alkylation effluent was sent to distillate blending.

[0030] In addition, blend testing of the alkylation effluent in the distillate pool determined that up to 17% of said effluent could be sent to the distillate pool. Therefore, when more distillate is desired, the overhead product of the splitter sends only 83% of the alkylation effluent to motor gasoline blending. The remainder (splitter bottoms) flows to distillate blending.

Claims

1. A process for balancing gasoline and distillate production in a refinery, the process comprising:

2. The process of claim 1 and further comprising controlling the contacting (a) according to said one of more defined parameters to vary the amount of polyalkylbenzenes produced.

3. The process of claim 2, wherein controlling the contacting (a) comprises varying the molar ratio of C₂ to C₅ alkylating agent to benzene fed to the alkylation zone.

4. The process of claim 2 or claim 3, wherein controlling the contacting (a) comprises recycling a varying amount of the alkylation effluent to the alkylation zone.

5. The process of any preceding claim, wherein said one or more defined parameters include market demand and seasonal conditions.

6. A process for balancing gasoline and distillate production in a refinery, the process comprising:

(b) separating said alkylation effluent into a light fraction comprising at least part of said one or more monoalkylbenzenes and a heavier fraction comprising at least part of said one or more polyalkylbenzenes; and (c) according to one or more defined parameters, adjusting the amount of said light fraction supplied to gasoline production and the amount of said heavier fraction supplied to distillate production.

7. The process of claim 6 and further comprising controlling the contacting (a) according to said one of more defined parameters to vary the amount of polyalkylbenzenes produced.

8. The process of claim 7, wherein controlling the contacting (a) comprises varying the molar ratio of C₂ to C₅ alkylating agent to benzene fed to the alkylation zone.

9. The process of claim 7 or claim 8, wherein controlling the contacting (a) comprises recycling a varying amount of the alkylation effluent to the alkylation zone.

10. The process of any one of claims 1 to 9, wherein the separating (b) comprises distillation in one or more distillation columns.

11. The process of any preceding claim, wherein the alkylating agent comprises an olefin.

12. The process of any preceding claim, wherein the contacting is conducted in the presence of a catalyst.

13. The process of claim 12, wherein said catalyst comprises at least one zeolite catalyst selected from the group consisting of ZSM-3, ZSM-4, ZSM-5, ZSM-11, ZSM-12, ZSM-14, ZSM-18, ZSM-20, ZSM-22, ZSM-23, ZSM-35, ZSM-48, zeolite beta, zeolite Y, Ultrastable Y (USY), Dealuminized Y (Deal Y), mordenite, MCM-22, PSH-3, SSZ-25, ERB-1, ITQ-1, ITQ-2, MCM-36, MCM-49, MCM-56, and UZM-8.

14. The process of claim 12, wherein said catalyst comprises a molecular sieve of the MCM- 22 family.