Alkylation of Aromatics With Ethylene and Propylene Recent Developments in Commercial Processes

Applied Catalysis A: General 221 (2001) 283–294

Alkylation of aromatics with ethylene and propylene: recentdevelopments in commercial processes

Thomas F. Degnan Jr.∗, C. Morris Smith, Chaya R. VenkatExxonMobil Research and Engineering Company, Annandale, NJ 08801, USA

Abstract

This paper provides an overview of current industrial alkylation processes for the production of ethylbenzene and cumene.In recent years, zeolite catalysts have begun to displace the conventional aluminum chloride and solid phosphoric acid (SPA)Friedel–Crafts catalysts used in both ethylbenzene and cumene processes. This transformation has been particularly rapid inthe case of cumene technology, where more than 50% of the worldwide cumene capacity has converted to zeolite catalysts inthe last 5 years. © 2001 Elsevier Science B.V. All rights reserved.

Keywords: Industrial processes; Cumene; Ethylbenzene; Aromatics alkylation; Zeolites

1. Introduction

Ethylbenzene and cumene are commercially thetwo largest volume derivatives of benzene. Combined,these two chemicals account for nearly 75% of theworld’s consumption of petrochemical grade benzene.The markets and the applications for both chemicalsare fairly well established. The worldwide capacity forethylbenzene is currently estimated to be 23 millionmetric tons per year (1 metric ton= 1000 kg) with anannual growth rate projected to be approximately 4%.Over 90% of the world’s production of ethylbenzeneis used in the manufacture of styrene. Other applica-tions include paint solvents and pharmaceuticals.

Cumene capacity topped 9.5 million metric tons in1998 and is projected to reach 10.4 million metric tonsby the end of 2003 [1]. Like ethylbenzene, cumene isused almost exclusively as a chemical intermediate.Its primary use is in the co-production of phenol and

∗ Corresponding author. Tel.:+1-609-224-2875.E-mail address: [email protected] (T.F. Degnan Jr.).

acetone through cumene peroxidation. Phenolic resinsand bisphenol A are the main end uses for phenol.Bisphenol A, which is produced from phenol and ace-tone, has been the main driving force behind increasedphenol demand. Its end use applications are in polycar-bonate and epoxy resins. The growth rate of cumeneis closely related to that of phenol and is expected tobe approximately 5.1% per year worldwide over thenext 5 years. Process technologies for both chemicalshave been moving away from conventional aluminumchloride and phosphoric acid catalyzed Friedel–Craftsalkylation of benzene, toward zeolite-based processes.

1.1. Ethylbenzene processes

Nearly 40% of the world’s ethylbenzene capacitystill utilizes the AlCl3-based Friedel–Crafts alkylationprocess first introduced in the 1950s. This processoperates at low benzene:ethylene (B:E) ratio (2:3.5)and reasonable temperatures (250◦C). However, overthe past 20 years, the operating costs associatedwith the corrosivity of AlCl3, and other problems

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284 T.F. Degnan Jr. et al. / Applied Catalysis A: General 221 (2001) 283–294

Table 1Commercial zeolite-based ethylbenzene processes

Process Year firstannounced

Licensed capacity(million metricton per year)

Mobil–Badger ethylbenzene 1976 8350Mobil–Badger dilute ethylene 1987 820Mobil–Badger EBMax 1995 5000Lummus–UOP 1989 3650SINOPEC 1993 30CDTech 1995 880Dow Chemical

dilute ethylene1998 Unknown

Albene 1992 Unknown

associated with its safe handling and disposal haveinduced most manufacturers to move toward zeolitecatalyzed processes. Zeolite catalyzed processes arelicensed by Mobil–Badger, Lummus–UOP, CDTech,and Dow Chemical. Table 1 summarizes the manufac-turing volume share of each of the licensed processtechnologies for ethylbenzene manufacture. Over thelast several years, the industry has moved to moreselective ethylbenzene dehydrogenation catalysts,making the purity of ethylbenzene of even greater im-portance. Fig. 1 shows the major reactions associated

Fig. 1. Primary alkylation and transalkylation chemistry for ethylbenzene production.

with ethylbenzene synthesis. Fig. 2 shows the majorside reactions. The selectivity to the monoethylatedproduct is very important in ethylbenzene synthe-sis, whereas ethylene oligomerization is normally asecondary consideration.

1.2. Mobil–Badger ethylbenzene process

First introduced in 1980, the Mobil–Badger vaporphase process is still the most widely used zeolitecatalyzed ethylbenzene manufacturing process. Sinceits initial commercial application in 1981, over 35units have been licensed with a total annual capacityof nearly 8 million metric tons. In the Mobil–Badgerprocess, benzene is alkylated in a fixed-bed reac-tor with ethylene in the gas phase using a ZSM-5based catalyst [2,3]. Fig. 3 is a simplified processflow diagram of the first generation Mobil–Badgerprocess. Fresh and recycled benzene is combinedwith a diethylbenzene-rich recycle stream and fed,together with fresh ethylene, to an alkylation reactor.The process operates with a B:E ratio of 5:20 (M) attemperatures ranging from 370 to 420◦C and pres-sures ranging from 0.69 to 2.76 MPa (6.8–27.2 bar).Weight hourly space velocities (WHSVs), based on

T.F. Degnan Jr. et al. / Applied Catalysis A: General 221 (2001) 283–294 285

Fig. 2. Side reactions typical for the acid catalyzed reaction of benzene with ethylene.

Fig. 3. The Mobil–Badger vapor-phase ethylbenzene process.


fresh feed, range from 300 to 400 hr−1. The processhas an overall ethylbenzene yield of at least 99.0%.

Together with the Badger Technology Center ofRaytheon Engineers & Constructors, Mobil intro-duced second and third generation processes in 1986and 1991. These next generation processes providedimproved cycle lengths and higher yields [4]. Cyclelengths improved from 60 days to more than 1 year,and yields improved to greater than 99.5%. Selec-tivity losses to both heavy aromatics and xylenesdropped by more than 50%. The energy efficiencyof the Mobil–Badger process is reported to be high.Essentially, all of the exothermic heat of reaction isrecovered.

The Mobil–Badger process has also been modifiedto use dilute ethylene from FCC off-gas streams as afeedstock. The dilute ethylene process was first com-mercialized at Shell’s Stanlow UK refinery in 1991and has been in continuous use ever since.

1.3. Mobil–Badger EBMax process

EBMax is a liquid phase ethylbenzene process thatuses Mobil’s proprietary MCM-22 zeolite as the cat-alyst. This process was first commercialized at theChiba Styrene Monomer Co., Chiba, Japan in 1995[5–7]. The MCM-22-based catalyst is very stable.Cycle lengths in excess of 3 years have been achievedcommercially. The MCM-22 zeolite catalyst is moremonoalkylate selective than large pore zeolites in-cluding zeolites beta and Y. This allows the processto use low feed ratios of benzene to ethylene. Typicalbenzene to ethylene ratios are in the range of 3 to5. The lower benzene to ethylene ratios reduces thebenzene circulation rate which, in turn, improves theefficiency and reduces the throughput of the benzenerecovery column. Because the process operates witha reduced benzene circulation rate, plant capacitycan be improved without adding distillation capacity.This is an important consideration, since distillationcolumn capacity is a bottleneck in most ethylbenzeneprocess units. The EBMax process operates at lowtemperatures, and therefore the level of xylenes in theethylbenzene product is very low, typically less than10 ppm.

In the EBMax process, benzene is fed to the bot-tom of the liquid-filled multi-bed reactor. Ethylene isco-fed with the benzene and also between the catalyst

beds. Polyethylbenzenes (PEB), which are almostexclusively diethylbenzenes, undergo transalkylationwith benzene in a second reactor. Mobil–Badgeroffers both liquid phase and vapor phase transalky-lation processes. The vapor phase process removesbenzene feed co-boilers such as cyclohexane andmethylcyclopentane as well as propyl and butylben-zenes. Because the EBMax process produces verylow levels of propyl and butylbenzenes, for mostapplications, the more energy efficient liquid phaseprocess is preferred. Worldwide, there are currently10 licensed EBMax units with a cumulative ethyl-benzene production capacity of 5 million metric tonsper year.

1.4. Lummus–UOP process

In 1989, Unocal–ABB Lummus Crest introduceda liquid-phase process based on a modified zeoliteY catalyst. The process design is very similar to theMobil–Badger EBMax process, and uses two reac-tors, one for benzene alkylation and the other fordiethylbenzene transalkylation. The reactors operateat close to the critical temperatures of the reactionmixtures in order to maximize the yield. Reactiontemperatures are typically less than 270◦C. Oper-ating pressure is approximately 3.8 MPa (37 bar).UOP acquired the right to the Unocal patents inthis area when it purchased the technology rights in1997. ABB Lummus Global and UOP now licensethe process. This liquid phase process has severallicensed units with a total ethylbenzene capacity of2.8 million metric tons per year. It is believed thatthe Lummus–UOP liquid phase ethylbenzene tech-nology has recently shifted to the use of catalystsbased on zeolite beta. In 1994, Lummus also acquiredworldwide licensing rights to a dilute ethylene-basedprocess developed in China by SINOPEC and theDalian Institute of Chemical Physics. The process,which is based on a ZSM-5 “type” zeolite, is cur-rently operating in a 30,000 metric ton per year unit inChina [8].

1.5. CDTech process

The CDTech process uses the company’s pro-prietary catalytic distillation (CD) technology [9].CDTech is a partnership between ABB Lummus


Global and Chemical Research & Licensing. CatalystRecovery Inc. (CRI), an affiliate of Shell, acquiredthe right to CDTech’s technology when it purchasedthe company in 1997. CDTech’s CD column consistsof two sections. The upper section is packed with therequired catalysts and the lower section is equippedwith distillation trays. Ethylene is fed into the CDcolumn at the bottom of the catalyst bed and benzeneis introduced to the top of the column via the refluxdrum. The counter-current flow reduces coke forma-tion and limits the production of unwanted byprod-ucts. The catalyst is packed in specially designedbales of steel mesh and fiberglass fabric. These balesare placed in a column similar to structured packings.The CDTech process uses zeolite Y as a catalyst [10].Fig. 4 is a schematic description of the reactive dis-tillation unit. Operating temperatures are reportedlylower than the Lummus–UOP process. The productremoved from the bottom of the column is a mixtureof ethylbenzene and PEB. Ethylbenzene is removedin a separate column and the PEB is sent to a separatetransalkylation reactor. The principal attributes of theCDTech process reportedly are its long catalyst lifeand high product selectivity. There are two commer-cial units in operation with a total capacity of morethan 850,000 metric tons per year.

Fig. 4. Schematic representation of the reactor/distillation columnused in the CDTech ethylbenzene process (Chen [9]).

1.6. Albene process

In 1992, the Indian Petrochemicals Corporation(IPCL) introduced a process that uses dilute ethanolrather than ethylene as the alkylating agent. Ethanolhas no distinct advantage over ethylene except that itcan be derived from waste streams or from biomass.The process reportedly uses [Fe]ZSM-5 as the cata-lyst. There are no reported commercial units that usethis process.

1.7. Dow Chemical’s dilute ethylene process

Dow Chemical has recently introduced a dualstage ethane dehydrogenation to benzene alkylationethylbenzene process [11]. This process mimics thedilute ethylene process referred to earlier. Ethane isdehydrogenated over a mordenite catalyst that con-tains zinc or gallium or one of the platinum groupmetals. In one Dow Chemical patent example [12],gallium-exchanged mordenite produced 86% ethy-lene selectivity at 50% conversion per pass. The samepatent cites a number of zeolites as possible alkyla-tion catalysts including beta, Y and ZSM-5. The DowChemical process allows for the use of low cost diluteethylene without the need to be directly tied to anFCC unit. Compared to the conventional FCC deriveddilute ethylene processes, this process eliminates con-cerns about dienes and acetylene, which are knownalkylation catalyst poisons. Because pretreatment pro-visions are reduced or eliminated, this process can bemore cost effective. There are no published reports ofcommercial application of this process.

1.8. Other processes

In 1996, DSM introduced a process for convertingbutadiene into ethylbenzene. Chiyoda acquired rightsto the process for license to third parties [13]. Thetwo-step process converts butadiene into vinylcyclo-hexene and then into ethylbenzene. No details regard-ing the catalyst have been made public. It is not knownwhether the process is practiced commercially.

1.9. Cumene processes

The primary alkylation and transalkylation reac-tions in the synthesis of cumene are shown in Fig. 5.


Fig. 5. Primary alkylation and transalkylation chemistry for cumene production.

Fig. 6 shows the principal side reactions. While themechanisms are quite similar to ethylbenzene syn-thesis, oligomerization is much more important incumene synthesis since propylene reacts 2 to 3 ordersof magnitude faster than ethylene over Bronsted acidcatalysts.

Fig. 6. Side reactions typical of the acid catalyzed reaction of benzene with propylene.

Prior to 1992, virtually all cumene was producedby propylene alkylation of benzene using either solidphosphoric acid (SPA) or aluminum chloride as cat-alysts. The SPA process, currently licensed by UOP,was developed in the 1940’s primarily to producecumene for aviation fuels [14,15]. More than 40 SPA


Fig. 7. Flow schematic representation of the SPA process.

plants have been licensed worldwide. The SPA cat-alyst consists of a complex mixture of orthosilicon-phosphate, pyrosiliconphosphate, and polyphosphoricacid supported on kieselguhr. To maintain the desiredlevel of activity, small amounts of water are continu-ously fed into the reactor. The water continually liber-ates H3PO4 causing some downstream corrosion. SPAprocess conditions include pressures that range from3.0 to 4.1 MPa, (29–40 bar), temperatures that rangefrom 180 to 230◦C, benzene:propylene ratio from 5to 7, and WHSVs that are between 1 and 2. Approx-imately 4–5 wt.% of the product consists of di- andtri-isopropylbenzenes. A schematic description of theSPA process is shown in Fig. 7.

In the early 1980s, Monsanto introduced an AlCl3process based on the same chemistry used in theethylbenzene process. This process can be operated atlower benzene:propylene ratio than the SPA processbecause AlCl3 can transalkylate the polyalkylatedbenzenes back to cumene. The process also operatesat temperatures lower than the SPA process becausethe more highly acidic anhydrous AlCl3 tends to pro-duce significantly more undesiredn-propylbenzene atequivalent temperatures. This technology is currentlyused in five plants.

Over the last 7 years, cumene producers have be-gun to convert to the more environmentally friendlyand more efficient zeolite-based processes. Principalamong these are processes licensed by Dow, CDTech,Mobil–Badger, Enichem and UOP. The zeolite-basedprocesses produce higher cumene yields than the con-ventional SPA process because most of the diisopropy-lbenzene (DIPB) byproduct is converted to cumenein separate transalkylation processes. Operating andmaintenance costs are reduced because there is nocorrosion associated with the zeolite catalysts. Finally,environmental concerns associated with the disposalof substantial amounts of phosphoric acid laden kiesel-guhr or AlCl3 are eliminated by the use of zeolites be-cause they are regenerable and can be safely disposedof through digestion or landfilling. Table 2 summa-rizes the manufacturing volume of each of the licensedzeolite process technologies for cumene manufacture.

1.10. Mobil–Badger cumene process

First commercialized at Georgia Gulf, Pasadena, TXplant in 1994, the Mobil–Badger Cumene process con-sists of a fixed-bed alkylator, a fixed-bed transalkylatorand a separation section [16,17]. Fig. 8 is a schematic


Table 2Commercial zeolite-based cumene units

Process Year first announced No. of commercial units Licensed capacity (mil-lion metric ton per year)

Mobil–Badger 1993 7 3125UOP Q-Max 1995 4 625CDTech CDCumene 1995 2 440Enichem 1995 1 265Dow Chemical 3-DDM 1992 1a 410

a Zeolite catalyst is used in the transalkylation unit only.

description of the process. Fresh and recycled benzeneare combined with liquid propylene in the alkylationreactor where the propylene is completely reacted. Re-cycled polyisopropylbenzenes (PIPB) are mixed withbenzene and sent to the transalkylation unit to produceadditional cumene. Trace impurities are removed inthe depropanizer column. Byproduct streams consistof LPG (mainly propane contained in the propylenefeedstock) and a small residue stream, which can beused as fuel oil.

Fig. 8. The Mobil–Badger liquid phase cumene process flow schematic.

As Table 3 shows, the Mobil–Badger process pro-duces very pure cumene, 99.97 wt.% at 99.7 wt.%yield. Ethylbenzene, propylbenzene, and butylben-zene levels are an order of magnitude lower thanthose obtained with the SPA catalyzed process. Thehigh cumene purity is primarily attributable to thehigh monoalkylation selectivity of the MCM-22 cata-lyst. This catalyst is unique in its ability to minimizepropylene oligomerization while still exhibiting veryhigh activity for benzene alkylation. Commercially,


Table 3Product properties from Mobil–Raytheon cumene process [17,18]

Other zeolites MCM-22

Cumene (wt%) 99.90 99.95–99.97Ethylbenzene (ppm) 200 25n-Propylbenzene (ppm) 300 200Butylbenzene (ppm) 20 15Bromine index (ppm) 50 <5

the catalyst has demonstrated cycle lengths in excessof 2 years. Ultimate catalyst life is in excess of 5 years.The Mobil–Badger process is used in seven commer-cial units worldwide. The seven plants have a com-bined cumene capacity of 3.1 million metric tons peryear, or approximately 50% of the worldwide cumenecapacity. An additional three plants are scheduled tostart up with this process by 2001. This will increasethe total licensed capacity to 4.1 million metric tons.

The selectivity of the MCM-22 catalyst reduces thesize requirements for the fractionation section, andalso reduces the coke forming reactions, which tend toshorten the cycle length. A key result of the catalyst’slow oligomerization selectivity is the ability to designfor low benzene-to-propylene ratios—in the range of2–4M. Table 4 compares the selectivities and activ-ities of MCM-22 and zeolite beta zeolites in singlepass alkylation of benzene with propylene. The zeolitebeta catalyst produces significantly more propyleneoligomer, but has a slightly lower selectivity for PIPB.

Table 4Comparison of MCM-22 and zeolite beta catalysts for cumenesynthesis

MCM-22 Zeolite beta

Propylene conversiona 98.0 94.4Benzene:propylene (mole ratio) 3 3

Total product selectivity (wt%)Propylene oligomers, 1.7 9.2Cumene 84.9 79.1PIPB 13.4 11.7

PIPB/cumene (M, %) 11.3 10.8

Propylene balance, liquid product (wt.%)Propylene oligomers 4.7 21.4

Alkylated aromatic products 95.3 78.6

a Propylene conversion is not complete since this is a once-thrutest at high liquid hourly space velocity (LHSV).

1.11. Enichem process

The Enichem cumene process was announced in1995 and then commercialized at Enichem’s PortoTorres, Sardinia plant in March 1996 [19]. The pro-cess operates at a benzene to propylene ratio of 4:1.Cumene yields and selectivities are both greater than99%. Enichem’s process uses a modified beta cat-alyst [10,20]. The process is reported to be readilyretrofit into existing cumene units. Few additional de-tails about this process have been released.

1.12. UOP Q-Max process

UOP’s Q-Max process was first commercialized atBTL Specialty Resin, Blue Island, IL plant in 1996[21]. The process has also been licensed to Chevronwhere it has been in use at Chevron, Port Arthur, TXplant since 1997 [22,23]. The flow scheme is virtu-ally identical to the Mobil–Raytheon process designshown in Fig. 8. UOP has not revealed the compositionof the catalyst used in its process. In fact, very littleadditional information is available about this process.UOP is reportedly working on a MgAPSO-31 cata-lyst that is very active and selective for cumene [10].By adjusting the level of Mg in the framework, UOPhas been able to optimize the acidity and reportedlyeliminate the formation ofn-propylbenzene.

1.13. Dow chemical 3-DDM process

Dow’s 3-DDM cumene process uses a highly dea-luminated mordenite catalyst in a two-stage fixed-bedalkylation and transalkylation process [24–26]. Themordenite-based transalkylation stage of this pro-cess has operated commercially since 1992 at Dow’sTerneuzen, The Netherlands plant [27]. Alkylationis carried out in a multi-bed fixed-bed reactor. Heatfrom the reaction is recovered through feed-effluentheat exchangers.

Dow has been able to circumvent the coking prob-lems typically associated with mordenite through itsproprietary dealumination process. Dealuminationproduces a system of mesopores that change the ef-fective unidimensional pore system of mordenite intoa pseudo-three-dimensional system. The generationof other means to access the 12-membered ring poresretards the ability of coke to block access to the active


sites. Dow’s mordenite component reportedly has asilicon-to-aluminum ratio of 70 corresponding to azeolite with a low acid site density, but high acid sitestrength [10]. The low acid site density reduces therates of hydrogen transfer and propylene oligomeriza-tion, both of which typically accelerate coke forma-tion. The high acid site strength allows the reaction tobe run at temperatures below whichn-propylbenzeneformation becomes significant. The first stage, whichproduces cumene and significant levels of DIBP, op-erates at temperatures below 170◦C. Because of theshape selectivity of the first stage mordenite catalyst,p-DIPB is the principal C12 isomer in the product.Triisopropylbenzene makes are very low.

In the second stage, PIPB are transalkylated withbenzene at a reactor temperature of approximately150◦C. DIPB conversions of up to 65% with greaterthan 90% selectivity toward cumene have been re-ported. The process operates at lower benzene-to-pro-pylene ratios than the conventional SPA process.

1.14. CDTech CDCumene process

CDTech’s CDCumene process involves the appli-cation of CD in a process that uses virtually the samedesign as the aforementioned CDTech ethylbenzeneprocess [9,28,29]. CD has the effect of raising thebenzene-to-propylene ratio in the bulk phase sur-rounding the catalyst. Cumene yields in excess of99% are claimed for this dual stage process. Catalystlifetimes are projected to be greater than 2 years incommercial operations based on pilot plant tests thathave lasted over 6000 h on a single catalyst charge.Alkylation is carried out isothermally at relativelylow temperatures and pressures of approximately5 bar in the overhead. The mild reaction conditionsare reported to produce cumene of very high pu-rity. The main impurities are reportedly ethylbenzene(220 ppm) andn-propylbenzene (350 ppm). As inMobil’s and Dow’s processes, DIPB produced in thealkylation stage are converted to cumene in a secondstage transalkylation reactor.

The nature of CDTech’s alklyation and transalky-lation catalysts has not been disclosed, althoughCDTech patents refer to zeolites Y, omega and beta.Till date, there is one operating unit which is licensedto GP–Orgetelko-Dzeryinsk, in Nizhny Novgrod,Russia [9]. The unit has a total cumene capacity

of 170 million metric tons per year. Another unit inTaiwan with a capacity of 240 million metric tons, isslated to be commissioned in 2000.

A related technology, CDTech’s Catstill process,combines CDTech’s cumene and ethylbenzene pro-cesses with the objective of removing benzene fromreformate by alkylation with FCC off-gas.

1.15. Other processes

Lummus–Unocal reportedly have been developinga cumene process that is similar to their commercialethylbenzene process. The process, which has been runon a pilot-plant scale, uses a modified trilobe Y zeolitecatalyst that produces improved product selectivities[10].

In other laboratory scale cumene process stud-ies, Du Pont’s nafion–silica composites have shownvery good activity for liquid phase alkylation un-der very mild conditions. The catalyst consists ofnanometer-sized nafion particles dispersed in a highlyporous silica matrix [30].

1.16. Future developments—ethylbenzene

The approximately 40% of the world’s ethylben-zene capacity that still uses AlCl3 is testimony to theefficiency and economy of this process. To capture thissegment of the industry, zeolite catalysts will have tobe developed that operate at close to the same verylow benzene-to-ethylene ratios that make the AlCl3process economically attractive. Heat management infixed-bed reactors becomes a design concern at the lowbenzene-to-ethylene ratios that characterize the AlCl3process. Hence, process and catalyst innovations willhave to evolve concurrently to achieve the goal of lowbenzene-to-ethylene ratios.

Another opportunity for advancement in ethylben-zene synthesis is in the development of liquid phaseprocesses that can handle low cost feedstocks includ-ing dilute ethylene such as ethane–ethylene mixtures.The use of dilute ethylene has become increasinglyattractive since it has the potential to debottleneckethylene crackers. Currently, higher temperature, va-por phase technologies can tolerate contaminants thatenter with the dilute ethylene feed from FCC units.However, these same contaminants can acceleratecatalyst aging in lower temperature, liquid phase


operations because they are more strongly adsorbedat the lower temperatures. Acid catalysts that toler-ate elevated levels of contaminants would facilitatethe development of dilute ethylene-based processes.These same catalysts could be useful in applicationswhere lower cost or lower quality benzene feeds areall that are available.

Future ethylbenzene alkylation catalyst develop-ment efforts will also undoubtedly focus on systemsthat convert less conventional feedstocks includingethane and ethanol. The two-step Dow ethane-basedprocess for ethylbenzene production is believed to beuneconomical because of its high capital investmentrequirement [31]. However, it is a very attractive con-cept, and could be implemented if more efficient cata-lysts or improved process designs could be developed.

There are similar opportunities for improvedtransalkylation catalysts and processes. Heavies madewith the current zeolite-based transalkylation cata-lysts are already very low, however, improved cata-lysts could lead to even lower byproduct makes andyield losses due to residue formation. The majority ofthe reaction by-products in the zeolite-catalyzed pro-cesses are produced in the transalkylator. There areopportunities to develop more active transalkylationcatalysts that allow operation at lower temperatureswhere by-product formation can be minimized.

Process development efforts will likely focus on in-creased integration of the alkylation and transalkyla-tion stages. The two processes frequently operate atdifferent temperatures. The challenge here is to matchactivities and aging rates. Other efforts will likely fo-cus on improved process heat integration.

1.17. Future developments—cumene

It is virtually inevitable that zeolite catalyzed, liquidphase production of cumene will eventually displacethe SPA and AlCl3 based processes. The situation isnot analogous to ethylbenzene, since the predominantcompeting technology that zeolite processes face is thefar less efficient and environmentally undesirable thanSPA process. The current zeolite-based processes al-low for significant debottlenecking of SPA plants withlittle additional capital. More importantly, the zeoliteprocesses have been able to produce cumene with pu-rities that cannot be approached by either the SPAor the AlCl3 process. Tighter product specifications,

brought about by the more selective zeolite processeswill drive all manufacturers to select one of the afore-mentioned zeolite technologies, possibly in the verynear term.

Additional research will undoubtedly be directed to-wards identifying improved alkylation and transalky-lation catalysts. Alkylation catalysts that operate atbenzene-to-propylene ratios of 3 or possibly evenlower are desirable because they greatly reduce theneed for costly separation capacity and because theycan debottleneck existing units. Transalkylation andalkylation catalysts that produce even lower byproductconcentrations at low benzene to propylene levels arelikely to be the focus of future research and develop-ment efforts. The challenge of combining both lowerby-product make and lower benzene-to-propylenefeed ratios involves overcoming higher aging ratesimplicit in using higher propylene feed concentra-tions and identifying more monoalkylation selectivecatalysts with activity similar to today’s zeolite cata-lysts. Materials that surpass even MCM-22’s superiorability to operate at high propylene concentrationswithout catalyzing excessive oligomerization couldlead to important advances in cumene synthesis.

Current zeolite catalysts already operate at processtemperatures that require minimal external heat addi-tion. Heat integration and heat management will be ofincreasing concern at the lower benzene-to-propyleneratios because the cumene synthesis reaction is sohighly exothermic (�H f = −98 kJ mol−1). Recycle,particularly in the alkylation reactor is likely to be-come increasingly important as a heat managementstrategy. The key will be how to limit the build-upof by-products and feed impurities in these recycleloops, particularly as manufacturers seek cheaper andconsequently lower quality feedstocks. As in the caseof ethylbenzene, process and catalyst innovations willhave to develop concurrently.

Recently, there have been several process devel-opments that allow for the production of phenolwithout co-production of acetone. These would tendto compete directly with the need to produce cumene.Developments include the AlphOx process, a jointdevelopment of Solutia and the Boreskov Institute ofCatalysis [32–35] which allows for the direct oxida-tion of benzene to produce phenol. Economic analyseshave shown that these are attractive only in specific in-stances where, e.g. a cheap source of N2O is available.


Nevertheless, these developments have shown thatdirect oxidation is possible and further innovations inthis area should probably be expected. The demandsfor acetone and phenol have generally trended to fol-low each other. However, as bisphenol A becomes aneven more important end use for phenol and acetone,there will be a need for a separate source of phenol.The synthesis of bisphenol A requires 2 mol of phenolfor every 1 mol of acetone, while the peroxidation ofcumene produces 1 mol of each. Still, processes suchas the direct oxidation of benzene are unlikely to havea major impact on cumene demand in the short termsince there are competing processes such as Mitsui’sfor converting acetone back to propylene.

There is also the prospect for increased demandfor some of the cumene by-products such as DIPB.The production of diphenols from DIPB is importantfor synthesis of resorcinol (fromm-DIPB) and hydro-quinone (fromp-DIPB). It is likely that the market maysoon see the introduction of cumene-based processesthat specifically produce these isomers with high de-grees of selectivity.

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Alkylation of Aromatics With Ethylene and Propylene Recent Developments in Commercial Processes

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