WO2014182294A1

WO2014182294A1 - Aromatics alkylation process

Info

Publication number: WO2014182294A1
Application number: PCT/US2013/040082
Authority: WO
Inventors: Shyh-Yuan H. Hwang; Dana E. Johnson
Original assignee: Badger Licensing Llc
Priority date: 2013-05-08
Filing date: 2013-05-08
Publication date: 2014-11-13
Also published as: RU2015148012A; TW201509877A; RU2017145651A; CN105339328B; RU2640595C2; RU2017145651A3; TWI654165B; CN105339328A; RU2756570C2

Abstract

In an aromatics alkylation process, an aromatic hydrocarbon feedstock comprising an alkylatable aromatic hydrocarbon, at least 150 ppm by weight water and at least one organic nitrogen impurity is supplied to a dehydration zone where water is removed from the aromatic hydrocarbon feedstock to provide a dehydrated aromatic feedstock having a water content of no more than 20 ppm by weight. The dehydrated aromatic feedstock is then contacted with a clay adsorbent under conditions including a temperature less than 130°C such that the adsorbent removes at least part of the organic nitrogen impurity contained in the feedstock and produces a treated aromatic feedstock. The treated aromatic feedstock is then supplied to an alkylation reaction zone and/or a transalkylation reaction zone.

Description

AROMATICS ALKYLATION PROCESS

FIELD

[0001] This invention relates to an aromatics alkylation process. BACKGROUND

[0002] Aromatics alkylation processes are of significant commercial importance, for example in the production of ethyl benzene and cumene. Such processes typically comprise a reaction section and a separation section. In the reaction section, an aromatic compound, such as benzene, is reacted with an alkylating agent, such as ethylene, propylene, butenes, methanol, ethanol, propanol, isopropanol or butanols, in the presence of an alkylation catalyst to produce an alkylated aromatic compound. The reaction section may also include provision for converting any polyalkylated species to additional monoalkylated product by reaction with additional aromatic compound in the presence of a transalkylation catalyst. The unconverted aromatic compound from the reaction section is then recovered in the separation section and is recycled back to the reaction section. Fresh aromatic compound can be fed either to the reaction section or to the separation section.

[0003] In most modern alkylation processes the acid catalyst used in the reaction section is a crystalline molecular sieve, such as MCM-22 or zeolite beta. The alkylation reaction can be conducted in vapor phase, liquid phase, or mixed phase. More recently, however, there has been interest in conducting the alkylation reaction in at least partial liquid phase, since this tends to reduce the production of unwanted by-products.

[0004] Water is often found in the aromatic feedstock to alkylation reactions, especially in the case of benzene feedstocks. Thus commercial benzene feeds are often water saturated, for example, when the feeds are recycled from a styrene monomer unit. However, the presence of high level of water may reduce the activity of molecular sieve alkylation catalysts. It is therefore normal to subject aromatic feedstocks to a drying step before they are employed in an alkylation process. For example, U.S. Patent No. 5,030,786 discloses the dehydration of the aromatic feedstock to a liquid phase aromatic conversion process to a water content of no more than 100 ppm, and preferably 50 ppm or less, by passage of the aromatic feedstock through a molecular sieve desiccant.

[0005] Other impurities present in the feedstocks to aromatic alkylation reactors include basic compounds, such as basic organic nitrogen compounds. These pose a particular problem since they can neutralize the active acid sites on the molecular sieve catalyst thereby adversely affecting both catalyst performance and catalyst life. Even very low nitrogen concentrations in the feed increase the frequency at which the catalyst must be regenerated to remove accumulated nitrogen compounds. As more active zeolite catalysts are employed in aromatic conversion reactions, the degradation of catalyst life by nitrogen impurities in the feedstock must be more carefully controlled. Most aromatic alkylation processes therefore provide for pretreatment of the aromatic feed to remove basic organic nitrogen compounds. For example, U.S. Patent No. 6,297,417 discloses an aromatics alkylation process which includes contacting a benzene feedstock with a solid acid, such as acidic clay or acidic zeolite, in a pretreatment zone at a temperature between about 130 °C and about 300 °C to remove impurities, such as organic nitrogen compounds, and thereby improve the lifetime of the alkylation catalyst.

[0006] U.S. Patent No. 8,013,199 discloses a process for the alkylation of an aromatic hydrocarbon stream having impurities in which a hydrocarbon feedstock is contacted with a first molecular sieve comprising Linde type X molecular sieve and having a Si/Al molar ratio of less than about 5 to remove at least a portion of said impurities and to produce a partially treated aromatic hydrocarbon stream; and then contacting said partially treated hydrocarbons stream with a second molecular sieve comprising a zeolite Y and having a Si/Al molar ratio of greater than about 5 to remove substantially all of the remaining portion of said impurities to produce a fully treated hydrocarbon feedstock having a reduced amount of impurities. The fully treated hydrocarbon feedstock is contacted with an alkylating agent in the presence of an alkylation catalyst under alkylation conditions to produce an alkylated aromatic hydrocarbon stream.

[0007] U.S. Patent No. 6,894,201 discloses a process and apparatus for removing nitrogen compounds from an alkylation substrate such as benzene. A conventional adsorbent bed, such as a clay or resin at ambient temperature to 38°C, can be used to adsorb basic organic nitrogen compounds and a hot adsorbent bed of acidic molecular sieve at or above 120°C can adsorb the weakly basic nitrogen compounds such as nitriles. Water is said to facilitate the adsorption of the weakly basic nitrogen compounds and so the water concentration to the hot adsorbent bed is generally adjusted to 20 to 500 ppmw by means of a fractionation column.

[0008] It will be understood from the foregoing that the purification of the aromatic hydrocarbon feedstock adds significant cost and complexity to aromatic alkylation processes. There is therefore a continuing interest in developing alternative purification schemes which simplify the overall alkylation process and or reduce or eliminate the need for expensive molecular sieve adsorbents without reducing catalyst performance. According to the present invention, it has now been found that, under certain conditions, clay treatment can be used to reduce or obviate the need for the more expensive molecular sieve adsorption to remove organic nitrogen compounds from aromatic hydrocarbon feedstocks. It has also been found that by treating the unconverted aromatic stream recycled from the separation section to the reaction section, it is possible to reduce or eliminate the need for treating fresh aromatic hydrocarbon feed. The recycle aromatic stream typically has a higher temperature and a lower moisture content than the fresh hydrocarbon feed. Both of these two differences improve the performance of certain adsorbents, particularly clays, making it advantageous to treat the recycle aromatic stream rather than the fresh hydrocarbon feed.

SUMMARY

[0009] In one aspect, the present invention resides in an aromatics alkylation process comprising:

(a) providing a aromatic hydrocarbon feedstock comprising an alkylatable aromatic hydrocarbon, at least 150 ppm by weight water and at least one organic nitrogen impurity;

(b) removing water from the aromatic hydrocarbon feedstock in a dehydration zone to provide a dehydrated aromatic feedstock having water content of no more than 20 ppm by weight;

(c) contacting the dehydrated aromatic feedstock with a clay adsorbent under conditions including a temperature less than 130°C such that the adsorbent removes at least part of the organic nitrogen impurity contained in the feedstock and produces a treated aromatic feedstock; and

(d) supplying the treated aromatic feedstock to an alkylation reaction zone and/or a transalkylation reaction zone.

[0010] In one embodiment, the dehydration zone comprises a distillation column.

[0011] Conveniently, the process also comprises:

(e) feeding an effluent from the alkylation reaction zone and/or the transalkylation reaction zone to the distillation column to remove unreacted aromatic hydrocarbon from said effluent; and (f) supplying the unreacted aromatic hydrocarbon together with the dehydrated feedstock to the treatment unit.

[0012] In a further aspect, the present invention resides in an aromatics alkylation process comprising:

(a) passing an aromatic hydrocarbon feed comprising a recycle aromatic hydrocarbon stream, and optionally fresh aromatic hydrocarbon, through a treatment unit containing a clay adsorbent under conditions such that the clay adsorbent removes at least part of the impurities contained in the aromatic hydrocarbon feed and produces a treated aromatic hydrocarbon stream;

(b) supplying at least part of said treated aromatic hydrocarbon stream to an alkylation zone;

(c) contacting said treated aromatic hydrocarbon stream in said alkylation zone with an alkylating agent in the presence of an acidic alkylation catalyst and under conditions such that at least part of the alkylating agent reacts with said treated aromatic hydrocarbon stream to produce an alkylation effluent containing an alkylated aromatic compound and unreacted aromatic hydrocarbon;

(d) supplying said alkylation effluent to a separation section to recover at least part of the unreacted aromatic hydrocarbon; and

(e) recycling at least part of said unreacted aromatic hydrocarbon recovered in (d) as said recycle aromatic hydrocarbon stream in (a).

[0013] In yet a further aspect, the present invention resides in an aromatics alkylation process comprising:

(b) supplying at least part of said treated aromatic hydrocarbon stream to a transalkylation zone;

(c) contacting said treated aromatic hydrocarbon stream in said transalkylation zone with a polyalkyl aromatic hydrocarbon stream in the presence of an acidic transalkylation catalyst and under conditions such that at least part of the polyalkyl aromatic hydrocarbon reacts with said treated aromatic hydrocarbon stream to produce a transalkylation effluent containing an alkylated aromatic compound, unreacted polyalkyl aromatic hydrocarbon, and unreacted aromatic hydrocarbon;

(d) supplying said transalkylation effluent to a separation section to recover at least part of the unreacted aromatic hydrocarbon; and

[0014] In still yet a further aspect, the present invention resides in an aromatics alkylation process comprising:

(a) providing a feedstock comprising an alkylatable aromatic hydrocarbon, up to 400 ppm by weight water, at least 0.01 wt of at least one alkylated aromatic hydrocarbon and at least one organic nitrogen impurity;

(b) passing at least part of the feedstock through a treatment unit containing a clay adsorbent under conditions including a temperature of 40°C to less than 130°C such that the adsorbent removes at least part of the organic nitrogen impurity contained in the feedstock and produces a treated feedstock; and

(c) supplying at least part of the alkylatable aromatic hydrocarbon from the treated feedstock to an alkylation reaction zone and/or a transalkylation reaction zone.

[0015] In one embodiment, at least part of the alkylated aromatic hydrocarbon is introduced into the feedstock in unreacted alkylatable aromatic hydrocarbon recycled from the alkylation reaction zone and/or the transalkylation reaction zone.

[0016] In another embodiment, at least part of the alkylated aromatic hydrocarbon is present in fresh alkylatable aromatic hydrocarbon supplied to the process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a flow diagram of an aromatic alkylation process according to a first embodiment of the invention.

[0018] Figure 2 is a flow diagram of an aromatic alkylation process according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The present invention provides an aromatics alkylation process in which an alkylatable atomatic compound, such as benzene, is reacted with an alkylating agent, such as ethylene or propylene, to produce an alkylated aromatic compound, such as ethylbenzene or cumene. In the present process, deleterious impurities, such as organic nitrogen-based compounds, present in the aromatic feed are adsorbed, using a clay adsorbent, from one or more aromatic process streams prior to alkylation and/or transalkylation. In some embodiments, rather than or in addition to treating the fresh aromatic hydrocarbon feed, impurity removal is effected on a recycle aromatic hydrocarbon stream, which typically has a higher temperature and a lower moisture content than the fresh aromatic hydrocarbon feed. In this way, the efficiency of the impurity removal process can be improved

Alkylatable Aromatic Hydrocarbons

[0020] The term "aromatic" in reference to the alkylatable compounds which are useful herein is to be understood in accordance with its art-recognized scope which includes alkyl substituted and unsubstituted mono- and polynuclear compounds. Compounds of an aromatic character which possess a heteroatom are also useful provided they do not act as catalyst poisons under the reaction conditions selected.

[0021] Substituted aromatic compounds which may be alkylated herein must possess at least one hydrogen atom directly bonded to the aromatic nucleus. The aromatic rings may be substituted with one or more alkyl, aryl, alkaryl, alkoxy, aryloxy, cycloalkyl, halide, and/or other groups which do not interfere with the alkylation reaction.

[0022] Suitable aromatic hydrocarbons include benzene, naphthalene, anthracene, naphthacene, perylene, coronene, and phenanthrene, with benzene being preferred.

[0023] Generally the alkyl groups which may be present as substituents on the aromatic compound contain from about 1 to 22 carbon atoms and usually from about 1 to 8 carbon atoms, and most usually from about 1 to 4 carbon atoms.

[0024] Suitable alkyl substituted aromatic compounds include toluene, xylenes, isopropylbenzene, normal propylbenzene, alpha-methylnaphthalene, ethylbenzene, mesitylene, durene, cymenes, butylbenzenes, pseudocumene, o-diethylbenzene, m- diethylbenzene, p-diethylbenzene, isoamylbenzene, isohexylbenzene, pentaethylbenzene, pentamethylbenzene; 1,2,3,4-tetraethylbenzene; 1,2,3,5-tetramethylbenzene; 1,2,4- triethylbenzene; 1,2,3-trimethylbenzene, m-butyltoluene; p-butyltoluene; 3, 5 -diethyl toluene; o-ethyltoluene; p-ethyltoluene; m-propyltoluene; 4-ethyl-m-xylene; dimethylnaphthalenes; ethylnaphthalene; 2,3-dimethylanthracene; 9-ethylanthracene; 2-methylanthracene; o- methylanthracene; 9,10-dimethylphenanthrene; and 3-methyl-phenanthrene. Higher molecular weight alkylaromatic hydrocarbons may also be used as starting materials and include aromatic hydrocarbons such as are produced by the alkylation of aromatic hydrocarbons with olefin oligomers. Such products are frequently referred to in the art as alkylate and include hexylbenzene, nonylbenzene, dodecylbenzene, pentadecylbenzene, hexyltoluene, nonyltoluene, dodecyltoluene, pentadecytoluene, etc. Very often alkylate is obtained as a high boiling fraction in which the alkyl group attached to the aromatic nucleus varies in size from about C₆ to about C₁₂.

[0025] Reformate or a cut thereof containing substantial quantities of benzene, toluene and/or xylenes constitutes a particularly useful aromatic feed for the alkylation process of this invention.

[0026] Another suitable aromatic feed for the present alkylation process is the benzene/toluene by-product stream generated in a styrene plant.

Alkylatin2 A2ent

[0027] The alkylating agent useful in the present process can be any aliphatic or aromatic organic compound having one or more available alkylating aliphatic groups capable of reaction with benzene. Examples of suitable alkylating agents include alkenes; such as ethylene and propylene; alcohols (inclusive of monoalcohols, dialcohols, trialcohols, etc.), such as methanol, ethanol, isopropanol and n-propanol; aldehydes, such as propionaldehyde; and halides, such as ethyl chloride and propyl chloride.

[0028] In one embodiment, the alkylating agent includes an alkene, which can be present as substantially pure alkene feed or as a dilute feed containing at least one alkane and typically at least one alkane having the same number of carbon atoms as the alkene. For example, where the alkene is ethylene, the alkane may be ethane. Typically, the dilute alkene feed comprises at least 10wt% of the alkene, such as from about 10 to about 80wt , for example from about 40 to about 80wt , of the alkene. One particularly useful feed is the dilute ethylene stream obtained as an off gas from the fluid catalytic cracking unit of a petroleum refinery.

[0029] It is to be appreciated that the alkylating agent feed sources may also undergo purification prior to being fed to the present process. Such purification techniques are well known to those of ordinary skill in the art.

[0030] In one embodiment, the fresh aromatic hydrocarbon feedstock comprises benzene, the alkylating agent comprises propylene and/or isopropanol, and the alkylated aromatic compound comprises cumene. In another embodiment, the fresh aromatic hydrocarbon feedstock comprises benzene, the alkylating agent comprises ethylene and/or ethanol, and the alkylated aromatic compound comprises ethylbenzene.

[0031] In one embodiment, comprising transalkylation, the fresh aromatic hydrocarbon feedstock comprises benzene, the polyalkyl aromatic hydrocarbon stream comprises diisopropylbenzenes, and the alkylated aromatic compound comprises cumene. In another embodiment, the fresh aromatic hydrocarbon feedstock comprises benzene, the polyalkyl aromatic hydrocarbon stream comprises diethylbenzenes, and the alkylated aromatic compound comprises ethylbenzene.

Aromatic Alkylation Process

[0032] In the present process, an alkylatable aromatic compound is reacted with alkylating agent (e.g., alkene feedstock) in an alkylation reaction system. The reaction system comprises one or a plurality of series-connected alkylation reaction zones, each containing an alkylation catalyst and each typically located in a single reaction vessel. The or each alkylation reaction zone in the alkylation reaction system is preferably operated under conditions effective to cause alkylation of the alkylatable aromatic compound by the alkylating agent, while ensuring that the alkylatable aromatic compound is at least partially or predominantly in the liquid phase. In one embodiment, where the alkylatable aromatic compound includes benzene, the alkene includes ethylene and the alkylaromatic compound includes ethylbenzene, the conditions in the or each alkylation reaction zone include a temperature of about 120°C to about 270°C and a pressure of about 500 kPa to about 8,300 kPa. In another embodiment, where the alkylatable aromatic compound includes benzene, the alkylating agent includes propylene and/or isopropanol and the alkylaromatic compound includes cumene, the conditions in the or each alkylation reaction zone include a temperature of about 40°C to about 300°C and a pressure of about 500 kPa to about 8,300 kPa. Typically, the molar ratio of alkylatable aromatic compound to alkylating agent in each alkylation reaction zone is in the range of 100:1 to 0.3:1.

[0033] In one embodiment, the alkylation catalyst employed in the or each alkylation reaction zone of the alkylation reaction system comprises at least one medium pore molecular sieve having a Constraint Index of 2-12 (as defined in U.S. Patent No. 4,016,218). Suitable 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.

[0034] In another embodiment, the alkylation catalyst employed in the or each alkylation reaction zone of the alkylation reaction system comprises at least one molecular sieve of the MCM-22 family. As used herein, the term "molecular sieve of the MCM-22 family" (or "material of the MCM-22 family" or "MCM-22 family material" or "MCM-22 family zeolite") 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.

[0035] 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.

[0036] 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), and mixtures thereof. Related zeolite UZM-8 is also suitable for use as the present alkylation catalyst.

[0037] In a further embodiment, the alkylation catalyst employed in the or each alkylation reaction zone of the alkylation reaction system comprises 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-14 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.

[0038] Preferred molecular sieves for the alkylation reaction comprise zeolite beta, molecular sieves having a Constraint Index of 2-12, especially ZSM-5, and molecular sieves of the MCM-22 family.

[0039] 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.

Alkylation Effluent Separation

[0040] In addition to the desired alkylaromatic product, the effluent from the alkylation reaction tends to contain significant quantities of unreacted alkylatable aromatic compound (e.g., benzene) and, in some cases, may also contain polyalkylated aromatic compounds (e.g., di- and tri- isopropylbenzenes). Thus, the effluent is passed to a product separation system, such as a distillation train, that not only serves to recover unreacted aromatic compound and desired monoalkylated product, but also separates the polyalkylated species. The unreacted aromatic compound is recycled to the alkylation section and/or the transalkylation section after treatment to remove deleterious impurities, such as nitrogen-based compounds, as described below. In one embodiment, the recycle aromatic hydrocarbon stream contains 0.01 to less than 15wt , for example 0.1 to 10 wt , of the alkylated aromatic compound.

[0041] Fresh aromatic hydrocarbon feedstock (e.g., benzene) can be fed either to the alkylation section, the transalkylation section or to the separation section. In some embodiments, the fresh aromatic feedstock is supplied to the product separation system to reduce the water content of the feedstock to less than 20 ppm by weight, such as less than 10 ppm by weight. Thus, the aromatic hydrocarbon stream passed through the treatment unit may contain fresh as well as recycled aromatic hydrocarbon feedstock.

Transalkylation

[0042] The polyalkylated species recovered from the alkylation effluent may be fed to a transalkylation reactor, which is normally separate from the alkylation reactor. In the transalkylation reactor, additional monoalkylated product is produced by reacting the polyalkylated species with additional aromatic compound in the presence of a transalkylation catalyst. Typically, the transalkylation reactor is operated under conditions such that the polyalkylated aromatic compounds and the alkylatable aromatic compound are at least partially or predominantly in the liquid phase.

[0043] Suitable conditions for carrying out the transalkylation of benzene with polyethylbenzenes may include a temperature of from about 100°C to about 300°C, a pressure of 8,000 kPa or less, a WHSV based on the weight of the total liquid feed to the reaction zone of from about 0.5 to about 100 hr^"1 and a mole ratio of benzene to polyethylbenzene of from about 1:1 to about 30:1. Particular conditions for carrying out the transalkylation of benzene with polyisopropylbenzenes may include a temperature of from about 100°C to about 300°C, a pressure of 8,000 kPa or less, a WHSV based on the weight of the total liquid feed to the reaction zone of from about 0.1 to about 50 hr^"1 and a mole ratio of benzene to polypropylbenzene of from about 1:1 to about 20:1. Particular conditions for carrying out the transalkylation of benzene with polybutylbenzenes may include a temperature of 100 to 300°C, a pressure of 500 to 8,000 kPa, a weight hourly space velocity of 0.1 to 50 hr^"1 on total feed, and a benzene to polybutylbenzene molar ratio of 1 : 1 to 20: 1.

[0044] The transalkylation catalyst can comprise one or more of any of the molecular sieves discussed above in relation to the alkylation system and can be used with or without a binder or matrix. Generally, however, the transalkylation catalyst is selected from zeolite beta, zeolite Y, Ultrastable Y (USY), Dealuminized Y (Deal Y), mordenite, ZSM-3, ZSM-4, ZSM-5, ZSM-11, ZSM-18, ZSM-20, MCM-22, PSH-3, SSZ-25, ERB-1, ITQ-1, ITQ-2, MCM-36, MCM-49, MCM-56, UZM-8, and mixtures thereof.

Transalkylation Effluent Separation

[0045] The effluent from the transalkylation system will tend to contain monoalkylated aromatic compound, unreacted polyalkyl aromatic hydrocarbon, and unreacted aromatic hydrocarbon. Thus, the effluent is passed to a product separation system that not only serves to recover unreacted aromatic compound and desired alkylated aromatic compound, but also separates the unreacted polyalkyl aromatic hydrocarbon. Typically, the same product separation system is used to separate the alkylation effluent and the transalkylation effluent. The unreacted aromatic compound may be recycled for treatment to remove deleterious impurities, such as nitrogen-based compounds, as described below. In one embodiment, unreacted aromatic compound separated from the transalkylation effluent is combined with unreacted aromatic compound separated from the alkylation effluent and recycled for treatment to remove deleterious impurities, such as nitrogen-based compounds, as described below.

Aromatic Hydrocarbon Treatment

[0046] As noted above, most commercially available aromatic hydrocarbon feedstocks contain significant quantities, up to 10 ppm as nitrogen by weight, of organic nitrogen impurities, such as N-methylpyrrolidone (NMP), N-formylmorpholine (NFM), pyridine and dimethylformamide (DMF). For example, alkylation grade benzene normally contains up to 20 ppm by weight, such as 0.05 to 2 ppm by weight, as nitrogen, of organic nitrogen impurities. In addition, aromatic hydrocarbon feedstocks are also often saturated with water, meaning they may contain from 500 to 1000 ppm by weight of water. For example, the benzene/toluene by-product stream from a styrene plant typically contains about 70% toluene, 25% benzene, up to 5% of ethylbenzene, about 300 ppm water, and a high level (typically from 0.5 to 10 ppmw as nitrogen) of nitrogen compounds.

[0047] Since these impurities, and especially the organic nitrogen compounds, can have a deleterious effect on the alkylation catalyst and, where present, the transalkylation catalyst, their level must be reduced in the total reaction mixture contacting the catalyst(s). In the present process, at least part of the required reduction in the level of these impurities is achieved by passing the fresh aromatic feedstock, optionally after drying and optionally in combination with an aromatic recycle stream, through a clay treatment unit containing one or more clay adsorbents before the feedstock is supplied to the alkylation reaction zone and/or the transalkylation reaction zone. The clay treatment is generally conducted at a temperature less than less than 130°C, such as from 40°C to less than 130°C, for example from 50°C to 125°C. Under these conditions, clay treatment is effective to remove most of the deleterious nitrogen impurities, without promoting unwanted side-reactions. For example, in a cumene plant, residual cumene in the benzene stream passed through the clay treater can be isomerized to n-propylbenzene, which is difficult to separate from the cumene product. As shown in the subsequent Examples, the present clay treatment process is found to minimize the isomerization of cumene to n-propylbenzene.

[0048] The clay treatment unit may comprise any conventional reactor design, including continuous and intermittent flow, batch and fixed-bed reactors. The treatment unit may be constructed as a separate reactor which is connected in series to an alkylation/transalkylation reactor. Alternatively, the treatment unit may comprise only one section of a reactor containing both treatment and alkylation or transalkylation zones. Alternatively, a multi-bed reactor may be used wherein the first bed comprises the treatment unit, wherein the alkylating/trans alkylating agent is introduced at the second bed and further beds along a multi-bed chain, and wherein further along the chain a transalkylation reactor may be placed.

[0049] By passage of the unreacted alkylatable aromatic compound through the treatment unit, the level of organic nitrogenous impurities in the aromatic feed to the alkylation reactor and/or the transalkylation reactor can be reduced to less than 0.03 ppm by weight, and preferably to below measurable levels.

[0050] As will be illustrated in the embodiments shown in the accompanying drawings, the clay treatment process of the present invention can be employed in a variety of configurations to lower the level of nitrogenous impurities in aromatic alkylation feedstocks. For example, where the aromatic feed is the benzene/toluene by-product stream generated in a styrene plant, this stream can be either (a) clay treated to remove nitrogen compounds and then distilled to recover benzene before sending the benzene stream to an ethylbenzene plant as part of the fresh benzene feed, (b) distilled and dried to recover dried benzene which is then clay treated to remove nitrogen compounds before it is sent to an ethylbenzene plant, or (c) distilled to recover benzene which is then sent to an ethylbenzene plant and clay treated as a part of the fresh benzene feed to remove nitrogen compounds..

[0051] Referring to Figure 1, in an aromatic alkylation process of a first embodiment of the invention, an alkylation section 11 receives a clay-treated aromatic hydrocarbon stream via line 12 and an alkylating agent stream via line 13. The alkylation section 11 comprises one or more reaction zones, where the clay-treated aromatic hydrocarbon stream and the alkylating agent are contacted with an acidic alkylation catalyst under conditions such that at least part of the alkylating agent reacts with the aromatic hydrocarbon to produce an alkylation effluent comprising the desired alkylated aromatic compound, unreacted aromatic hydrocarbon and generally some polyalkyl aromatic compounds. Generally, the conditions in the alkylation section 11 are such that the aromatic hydrocarbon is at least partially in the liquid phase.

[0052] The effluent from the alkylation section 11 is fed by line 14 to a separation section 15, which also receives, via line 16, fresh aromatic hydrocarbon feedstock containing organic nitrogen impurities and at least 150 ppm by weight, typically up to 400 ppm by weight, water. The separation section 15 typically comprises a distillation chain comprising a first distillation tower for separating fresh and unreacted aromatic hydrocarbon in line 17, a second distillation tower for recovering the desired alkylated aromatic compound in line 18 and a third distillation tower for separating polyalkyl aromatic compounds in line 19. Generally, the first distillation tower is operated to remove water impurities introduced in the fresh aromatic hydrocarbon feedstock so that the aromatic hydrocarbon stream exiting the separation section 15 in line 16 contains less than 20 ppm by weight, such as less than 10 pppm by weight of water. In an alternative embodiment (not shown), the fresh aromatic hydrocarbon feedstock is passed through a separate drying section before being supplied to the separation section 15.

[0053] The aromatic stream in line 17 contains organic nitrogen impurities introduced with the fresh aromatic hydrocarbon feedstock and is passed through a clay treatment unit 21 which is operated at a temperature of 50°C to 125°C. The clay treatment unit reduces the level of organic nitrogenous impurities in the aromatic stream to less than 0.03 ppm by weight so that the treated aromatic stream exiting the clay treatment unit 21 via line 22 can be fed directly to the alkylation section 11 via line 12.

[0054] In the embodiment shown, part of the treated aromatic stream exiting the clay treatment unit 21 via line 22 is also supplied to a transalkylation section 23 together with the polyalkyl aromatic compounds in line 19. The transalkylation section 23 comprises one or more reaction zones, where the treated aromatic hydrocarbon and the polyalkyl aromatic hydrocarbon are contacted with an acidic transalkylation catalyst under conditions such that at least part of polyalkyl aromatic hydrocarbon reacts with the treated aromatic hydrocarbon stream to produce a transalkylation effluent containing the desired alkylated aromatic compound, unreacted polyalkyl aromatic hydrocarbon, and unreacted aromatic hydrocarbon. Generally, the conditions in the transalkylation section 23 are such that the aromatic hydrocarbon is at least partially in the liquid phase. The transalkylation effluent is fed by line 24 to the separation section 15 for recovery of the desired alkylated aromatic compound in line 18 and separation of the unreacted aromatic hydrocarbon and unreacted polyalkyl aromatic hydrocarbon in lines 17 and 19 respectively

[0055] A second embodiment of the invention is shown in Figure 2, in which a fresh aromatic hydrocarbon feedstock containing water and organic nitrogen impurities is fed by line 31 through an optional drying section 32 to a clay treatment unit 33. The clay treatment unit 33 is operated at a temperature of 50°C to 125°C and reduces the level of organic nitrogen impurities in the aromatic feedstock so that the treated aromatic stream exiting the clay treatment unit 33 via line 34 contains less than 0.03 ppm by weight of such impurities. The treated aromatic stream is fed by line 34 to an alkylation section 35, which also receives an alkylating agent in line 36, and a transalkylation section 37, which also receives polyalkyl aromatic hydrocarbon via line 38. The alkylation and transalkylation sections 35, 37 operate as described with reference to Figure 1 to produce the desired alkylated aromatic compound. The effluents from the alkylation and transalkylation sections 35, 37 are supplied by lines 39, 41 to a separation section 42, where the desired alkylated aromatic compound is recovered via line 43 and unreacted polyalkyl aromatic hydrocarbons are removed in line 38. Unreacted aromatic hydrocarbon is also separated in separation section 42 and can be recycled via line 44 through the clay treatment unit 33 or via line 45 to the alkylation and transalkylation sections 35, 37.

[0056] The invention will now be more particularly described with reference to the following Examples.

EXAMPLE 1

[0057] A test was carried out in a fixed bed treatment unit, made from a ½ inch (1.3 cm) diameter Schedule 40 Stainless Steel 316 pipe with a total length of 24 inches (61 cm). The treatment unit was housed in a hot oil jacket to preheat the feed to the desired inlet temperature and to maintain the treatment unit temperature. A storage tank was used for aromatic feed and a positive displacement pump was used for feeding the aromatic feed into the treatment unit. The flow rate of the aromatic feed was set by pump setting and monitored by an electronic weight scale. The treatment unit operating conditions were controlled and monitored by an automatic control system. The feedstock and treatment unit effluent were analyzed by a Hewlett Packard 5890 Series II Gas Chromatograph equipped with a Flame Ionization Detector (FID) and a Chrompack CP- Wax 52CB column having an inside diameter of 0.25 mm, film thickness of 0.5 μιη, and length of 60 meters.

[0058] Twenty grams of fresh BASF F-24 Clay was loaded into the treatment unit. The treatment unit was heated up in pure benzene and the clay dried out at 125°C for four days. An aromatic feed containing 95.5wt benzene, 4.5wt cumene, 25 parts per million by weight (wtppm) water and 10 parts per million by weight (wtppm) n-propylbenzene (NPB) was then introduced. The composition of this aromatic feed is similar to that of a recycle benzene stream in a cumene plant, which typically contains some alkylaromatics in addition to the impurities that were in the fresh benzene (e.g., the recycle benzene in a cumene plant typically contains about 0.1 to about 10 wt cumene). The feed weight hourly space velocity (WHSV) was 5 hr ¹, the treatment unit temperature was varied between 95 and 183°C, and the treatment unit outlet pressure was maintained between 420 and 450 PSIG. The treatment unit effluent was collected and analyzed periodically. The concentrations of NPB in the treatment unit effluent are listed in Table 1 below.

Table 1

[0059] It is noted that the amount of NPB made in the treatment unit increased rapidly with increasing treatment unit temperature. As NPB boils very close to cumene, it cannot be economically separated from cumene once it is formed. Any NPB made in the treatment unit will therefore contaminate the cumene product and reduce the purity of the cumene product. Depending on the design and operation of the cumene plant, each 1 wtppm of NPB made in the treatment unit can increase the NPB concentration in the cumene product by 2 to 4 wtppm and reduce the cumene product purity by the same amount. The estimated increase of NPB content in cumene product for each treatment unit temperature is also listed in Table 1 above.

[0060] Thus, it is advantageous to operate the treatment unit at low temperatures, preferably at 125°C or below, to avoid excessive production of NPB in the treatment unit and significant negative impact on cumene product purity.

EXAMPLE 2

[0061] The same experimental apparatus and control system described in EXAMPLE 1 were also used in this example. In addition, the feedstock and treatment unit effluent were also analyzed for nitrogen.

[0062] Twenty grams of fresh BASF F-24 Clay was loaded into the treatment unit. The treatment unit was heated up in pure benzene and the clay dried out at 125°C for four days. An aromatic feed containing 98wt benzene, 2wt cumene, 6 wtppm NPB, 25 wtppm water, 5.8 wtppm pyridine, 3.8 wtppm N-methylpyrrolidone (NMP), and 4.4 wtppm N- formylmorpholine (NFM) was then introduced. The feed weight WHSV was 5 hr^"1, the treatment unit temperature was maintained between 123 and 125°C, and the treatment unit outlet pressure was maintained between 420 and 450 PSIG. The treatment unit effluent was collected and analyzed periodically for NPB and nitrogen species. The concentrations of NPB and the nitrogen species detected in the treatment unit effluent are listed in Table 2 below.

Table 2

[0063] As demonstrated by the data above, the present invention was able to remove the nitrogen-containing poisons in the aromatic feedstock effectively for an extended period of time. The example also demonstrated that no detectable level of NPB was made from cumene in the feed.

[0064] While the present invention has been described and illustrated by reference to particular embodiments, those of ordinary skill in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.

Claims

1. An aromatics alkylation process comprising:

(a) providing an aromatic hydrocarbon feedstock comprising an alkylatable aromatic hydrocarbon, at least 150 ppm by weight water and at least one organic nitrogen impurity;

2. The process of claim 1, wherein the conditions in the contacting (a) include a temperature from 50 °C to 125 °C.

3. The process of claim 1 or claim 2, wherein the dehydration zone comprises a distillation column.

4. The process of claim 3, wherein the treated aromatic feedstock is supplied to an alkylation reaction zone and the process further comprises:

(e) contacting said treated aromatic feedstock in said alkylation zone with an alkylating agent in the presence of an acidic alkylation catalyst and under conditions such that at least part of the alkylating agent reacts with the alkylatable aromatic hydrocarbon stream to produce an alkylation effluent containing an alkylated aromatic compound and unreacted aromatic hydrocarbon;

(f) supplying said alkylation effluent to said distillation column to recover at least part of the unreacted aromatic hydrocarbon; and

(g) contacting the unreacted aromatic hydrocarbon recovered in (f) together with the dehydrated aromatic feedstock with the clay adsorbent in (c).

5. The process of claim 3, wherein the treated aromatic feedstock is supplied to a transalkylation reaction zone and the process further comprises:

(h) contacting said treated aromatic feedstock in said transalkylation zone with a polyalkyl aromatic compound in the presence of an acidic transalkylation catalyst and under conditions such that at least part of the polyalkyl aromatic compound reacts with the alkylatable aromatic hydrocarbon stream to produce an transalkylation effluent containing an alkylated aromatic compound and unreacted aromatic hydrocarbon;

(i) supplying said transalkylation effluent to said distillation column to recover at least part of the unreacted aromatic hydrocarbon; and

j) contacting the unreacted aromatic hydrocarbon recovered in (i) together with the dehydrated aromatic feedstock with the clay adsorbent in (c).

6. The process of any preceding claim wherein the aromatic hydrocarbon feedstock is supplied to said dehydration zone without prior treatment to remove organic nitrogen impurities.

7. An aromatics alkylation process comprising:

(a) passing an aromatic hydrocarbon feed comprising a recycle aromatic hydrocarbon stream, and optionally fresh aromatic hydrocarbon, through a treatment unit containing a clay adsorbent under conditions such that the clay adsorbent removes impurities contained in the aromatic hydrocarbon feed and produces a treated aromatic hydrocarbon stream;

(d) supplying said alkylation effluent to a separation section to recover at least part of the unreacted aromatic hydrocarbon; and (e) recycling at least part of said unreacted aromatic hydrocarbon recovered in (d) as said recycle aromatic hydrocarbon stream in (a).

8. The process of claim 7, wherein said aromatic hydrocarbon feed comprises fresh aromatic hydrocarbon which has been dried to a water level of no more than 20 pppm by weight.

9. The process of claim 7 or claim 8, wherein the conditions in (a) include a temperature from 50 °C to 125 °C.

10. The process of any one of claims 7 to 9, wherein a polyalkyl aromatic hydrocarbon stream is recovered from the separation section of step (d), the process further comprising:

(f) supplying at least part of said treated aromatic hydrocarbon stream to a transalkylation zone;

(g) contacting said treated aromatic hydrocarbon stream in said transalkylation zone with the polyalkyl aromatic hydrocarbon stream recovered from the separation section of step (d) in the presence of an acidic transalkylation catalyst and under conditions such that at least part of polyalkyl aromatic hydrocarbon reacts with said treated aromatic hydrocarbon stream to produce a transalkylation effluent containing an alkylated aromatic compound, unreacted polyalkyl aromatic hydrocarbon, and unreacted aromatic hydrocarbon;

(h) supplying said transalkylation effluent to a separation section to recover at least part of the unreacted aromatic hydrocarbon from the transalkylation effluent; and

(i) recycling at least part of said unreacted aromatic hydrocarbon recovered in (h) as said recycle aromatic hydrocarbon stream in (a).

11. An aromatics alkylation process comprising:

(b) supplying at least part of said treated aromatic hydrocarbon stream to a transalkylation zone; (c) contacting said treated aromatic hydrocarbon stream in said transalkylation zone with a polyalkyl aromatic hydrocarbon stream in the presence of an acidic transalkylation catalyst and under conditions such that at least part of the polyalkyl aromatic hydrocarbon reacts with said treated aromatic hydrocarbon stream to produce a transalkylation effluent containing an alkylated aromatic compound, unreacted polyalkyl aromatic hydrocarbon, and unreacted aromatic hydrocarbon;

12. The process of claim 11, wherein said aromatic hydrocarbon feed comprises fresh aromatic hydrocarbon which has been dried to a water level of no more than 20 pppm by weight.

13. The process of claim 11 or claim 12, wherein the conditions in (a) include a temperature from 50 °C to 125 °C.

14. An aromatics alkylation process comprising:

15. The process of claim 14 and further comprising:

(d) removing water from the feedstock in a dehydration zone so that the remainder of the feedstock supplied to the treatment unit in (b) contains no more than 20 ppm by weight of water.

16. The process of claim 14 or claim 15, wherein at least part of the alkylated aromatic hydrocarbon is introduced into the feedstock in unreacted alkylatable aromatic hydrocarbon recycled from the alkylation reaction zone and/or the transalkylation reaction zone.

17. The process of any one of claims 14 to 16, wherein at least part of the alkylated aromatic hydrocarbon is present in fresh alkylatable aromatic hydrocarbon supplied to the process.

18. The process of any preceding claim, wherein the alkylatable aromatic hydrocarbon comprises benzene