Cumene Production

Robert J. SchmidtUOP LLC, Des Plaines, Illinois, U.S.A.

INTRODUCTION

The history of the cumene market has been examinedin great detail with much discussion regarding productusage, emerging markets, and process economics overthe past 10–20 yr.[1] With more than 90% of the world’sphenol production technology currently based on thecumene hydroperoxide route, it is the focus of thisentry to review the latest technology improvements incumene processing made over the past 10 yr. Currentstate-of-the-art processes for the production of cumeneas a feedstock for phenol involve zeolitic catalysttechnology offerings from UOP, Badger Licensing(formerly ExxonMobil and the Washington Group),and CDTech based on zeolitic catalysis. Much ofthe improvements in these technologies relate to yield,stability, and operating costs.

CUMENE PRODUCTION

Cumene is produced commercially through the alkyla-tion of benzene with propylene over an acid catalyst.Over the years, many different catalysts have been usedfor this alkylation reaction, including boron trifluoride,hydrogen fluoride, aluminum chloride, and phosphoricacid. Cumene processes were originally developedbetween 1939 and 1945 to meet the demand for high-octane aviation gasoline during World War II.[2,3] By1989, about 95% of cumene demand was used as anintermediate for the production of phenol and acetone.Today, nearly all cumene is used for production ofphenol and acetone with only a small percentage beingused for the production of a-methylstyrene. Thedemand for cumene has risen at an average rate of2–4% per year from 1970 to 2003.[4,5] This trend isexpected to continue through at least 2010.

Currently, over 80% of all cumene is produced byusing zeolite-based processes. Early processes usingzeolite-based catalyst systems were developed in thelate 1980s and included Unocal’s technology basedon a conventional fixed-bed system and CR&L’scatalytic distillation system based on an extensionof the CR&L MTBE technology.[6–9] At present, theQ-Max2 process offered by UOP and the BadgerCumene Technology developed by ExxonMobil andoffered by Badger Licensing represent the state-of-the-art zeolite-based catalyst technologies. A limited

number of cumene units remain using the fixed-bed,kieselguhr-supported solid phosphoric acid (SPA)catalyst process developed by UOP and the homoge-nous AlCl3 and hydrogen chloride catalyst systemdeveloped by Monsanto.

Solid Phosphoric Acid Catalyst

Although SPA remains a viable catalyst for cumenesynthesis, it has several important limitations: 1)cumene yield is limited to about 95% because of theoligomerization of propylene and the formation ofheavy alkylate by-products; 2) the process requires arelatively high benzene=propylene (B=P) molar feedratio on the order of 7=1 to maintain such a cumeneyield; and 3) the catalyst is not regenerable and mustbe disposed of at the end of each short catalyst cycle.Also, in recent years, producers have been givenincreasing incentives for better cumene product qualityto improve the quality of the phenol, acetone, andespecially a-methylstyrene (e.g., cumene requires a lowbutylbenzene content) produced from the downstreamphenol units.

For the UOP SPA catalyst process, propylene feed,fresh benzene feed, and recycle benzene are chargedupflow to a fixed-bed reactor, which operates at3�4MPa (400–600 psig) and at 200–260�C. The SPAcatalyst provides an essentially complete conversionof propylene on a one-pass basis. A typical reactoreffluent yield contains 94.8 wt% cumene and 3.1wt%diisopropylbenzene (DIPB). The remaining 2.1% isprimarily heavy aromatics. This high yield of cumeneis achieved without transalkylation of DIPB andis a key advantage to the SPA catalyst process. Thecumene product is 99.9 wt% pure. The heavy aro-matics, which have a research octane number (RON)of about 109, can be either used as high-octane gaso-line-blending components or combined with additionalbenzene and sent to a transalkylation section of theplant where DIPB is converted to cumene. The overallyield of cumene for this process based on benzeneand propylene is typically 97–98wt% if transalkylationis included or 94–96wt% without transalkylation.Generally, it has been difficult to justify the additionof a transalkylation section to the SPA process basedon the relatively low incremental yield improvementthat it provides.

Encyclopedia of Chemical Processing DOI: 10.1081/E-ECHP-120026490Copyright # 2006 by Taylor & Francis. All rights reserved. 603

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ALCL3 AND HYDROGEN CHLORIDE CATALYST

Historically, AlCl3 processes have been used moreextensively for the production of ethylbenzene (EB)than for the production of cumene. In 1976, Monsantodeveloped an improved cumene process that uses anAlCl3 catalyst, and by the mid-1980s, the technologyhad been successfully commercialized. The overall yieldof cumene for this process can be as high as 99wt%based on benzene and 98wt% based on propylene.[10]

Detailed process flow information is widely publishedin the literature for this technology.[11] Dry benzene,both fresh and recycled, and propylene are mixed inan alkylation reaction zone with an AlCl3 and hydro-gen chloride catalyst at a temperature of less than135�C and a pressure of less than 0.4MPa (50 psig).[11]

The effluent from the alkylation zone is combined withrecycled polyisopropylbenzene and fed to a transalkyla-tion zone also using AlCl3 catalyst, where polyiso-propylbenzenes are transalkylated to cumene. Thestrongly acidic catalyst is separated from the organicphase by washing the reactor effluent with water andcaustic. The distillation section is designed to recovera high-purity cumene product. The unconverted ben-zene and polyisopropylbenzenes are separated andrecycled to the reaction system. Propane in the propy-lene feed is recovered as liquid petroleum gas (LPG).

ZEOLITE CATALYSTS

In the past decade, beta zeolite (given the universal BEA)has rapidly become the catalyst of choice for commercialproduction of EB and cumene. Mobil invented the basicbeta zeolite composition of matter in 1967.[12] Since thattime, catalysts utilizing beta have undergone a series ofevolutionary steps leading to the development of thestate-of-the-art catalysts such as QZ-20002 catalyst andQZ-20012 catalyst for cumene alkylation.

Much of the effort between 1967 and the early 1980sinvolved characterization of the perplexing structure ofbeta zeolite. It was quickly recognized that the BEAzeolite structure has a large-pore, three-dimensionalstructure, and a high acidity capable of catalyzingmany reactions. But it was not until early 1988 thatscientists at Exxon finally determined the chiral natureof the BEA structure, which is shown in Fig. 1.

While the structure of beta was being investigated,new uses for this zeolite were being discovered. Amajor breakthrough came in late 1988 when workersat Chevron invented a liquid phase alkylation processusing beta zeolite catalyst. Chevron patented theprocess in 1990.[13] While Chevron had significantcommercial experience with the use of Y (FAU) zeolitein liquid phase aromatic alkylation, Chevron quicklyrecognized the benefits of beta over Y as well and other

acidic zeolites used at that time, such as mordenite(MOR) or ZSM-5 (MFI).

Fig. 2 shows a comparison of the main channelsof these zeolites. Chevron discovered that the open12-membered ring structure characteristic of beta zeo-lite coupled with its high acidity made it an excellentcatalyst for aromatic alkylation. These properties werekey in the production of alkyl aromatics such as EBand cumene in extremely high yields and with productpurities approaching 100%. Moreover, Chevron dis-covered that the combination of high activity andporous structure imparted a high degree of toleranceto many typical feed contaminants.

From a technical perspective, the process developedby Chevron was a breakthrough technology in that thehigh cumene yields and purities were not attainable bythe other vapor phase or liquid phase processes of theday. Nevertheless, the manufacturing cost of betazeolite was still too high for catalyst producers to makea commercially viable catalyst. UOP, however,developed new manufacturing technology to make abeta zeolite based catalyst a commercial reality. In1991 a new cost-effective synthesis route was inventedby Cannan and Hinchey at UOP.[14] The new synthesisroute patented the substitution of diethanolamine, amuch less expensive templating agent, for a substantialfraction of tetraethylammonium hydroxide, which hadbeen used in the synthesis previously. Moreover, theroute further enables the use of tetraethylammoniumbromide (instead of the hydroxide) as an additionalcost saving approach. Finally, the new synthesis routeallows the practical synthesis of beta over a widerrange of silica to alumina ratios, a factor that has aprofound effect on the catalyst’s performance.

Subsequently, UOP sought to develop zeoliticcatalysts that would overcome the limitations of SPAincluding a catalyst that is regenerable, produces highercumene yield, and decreases the cumene cost ofproduction. More than 100 different catalyst materialswere screened, including mordenites, MFIs, Y-zeolites,

Fig. 1 Beta zeolite. (View this art in color at www.dekker.-com.)

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amorphous silica–aluminas, and beta zeolite. The mostpromising materials were modified to improve theirselectivity and then subjected to more rigorous testing.

On the process side, Unocal developed an earlyliquid phase fixed-bed reactor system based on aY-type zeolite catalyst in the 1980s.[15] The higheryields associated with the liquid phase based processwere quickly recognized and adapted by the industrywith the selectivity to cumene generally falling between70 and 90wt% based on converted benzene and propy-lene dependent on operating conditions. Major sideproducts in the process are primarily polyisopropyl-benzenes, which are transalkylated to cumene in aseparate reaction zone to give an overall yield ofcumene of about 99wt%. The distillation requirementsinvolve the separation of propane for LPG use, therecycle of excess benzene to the reaction zones, theseparation of polyisopropylbenzene for transalkylationto cumene, and the production of a purified cumeneproduct.

By 1992, UOP had selected the most promisingcatalyst, based on beta zeolite, for cumene productionand then began to optimize a liquid phase basedprocess design around this new catalyst. The result ofthis work led to the commercialization of the UOPQ-Max process and the QZ-2000 catalyst in 1996.More recently in 2001, UOP commercialized a newalkylation catalyst, QZ-2001, which offers improvedstability and operation as low as 2B=P molar feed

ratio. The low B=P feed ratio (2) represents the lowestin the industry and affords cumene producers theoption to expand capacity and=or revamp existingfractionation equipment with significant cost savings.

The Q-Max process flow scheme based on a liquidphase process is shown in Fig. 3. The alkylation reactoris divided into four catalyst beds contained in a singlereactor vessel. Fresh benzene feed is routed throughthe upper-mid section of the depropanizer column toremove excess water that may be present in the freshbenzene feed. Relatively dry benzene is withdrawnfrom the depropanizer for routing to the alkylationreactor. Recycle benzene to the alkylation and trans-alkylation reactors is recovered as a sidedraw fromthe benzene column. A mixture of fresh and recyclebenzene is charged downflow into the alkylationreactor. Propylene feed is divided into portions andinjected into the alkylation reactor between the catalystbeds and each portion is essentially completelyconsumed in each bed. An excess of benzene is usedin the alkylation reactor to avoid polyalkylation andto help minimize olefin oligomerization. The alkylationreaction is highly exothermic and the temperature risein the reactor is controlled by recycling a portion of thealkylation reactor effluent to the reactor inlet to act asa heat sink. In addition, the inlet temperature of eachdownstream bed is reduced to the same temperatureas the first bed inlet by injecting a portion of cooledreactor effluent between beds.

Fig. 2 Comparison of various zeo-lites. (View this art in color atwww.dekker.com.)

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Effluent from the alkylation reactor flows to thedepropanizer column, which removes any propane thatmay have entered with the propylene feed along withexcess water that may have entered with the freshbenzene feed. The bottom stream of the depropanizercolumn goes to the benzene column where excessbenzene is collected overhead and recycled. Any tracenonaromatics that may have been in the fresh benzenefeed can be purged from the benzene column to avoidan unacceptable accumulation of nonaromatic speciesin the benzene recycle stream. The benzene columnbottom stream goes to the cumene column where thecumene product is recovered overhead. The cumenecolumn bottoms stream, which contains predomi-nantly DIPB, goes to the DIPB column. If the propy-lene feed contains an excessive amount of butylenes,or if the benzene feed contains an excessive amountof toluene, higher levels of butylbenzenes and=orcymenes can be formed in the alkylation reactor. Thesecompounds are distilled out and purged from theoverhead section of the DIPB column. The DIPBstream leaves the DIPB column by a sidedraw and ispassed to the transalkylation reactor. The DIPBcolumn bottom stream consists of heavy aromaticby-products, which are normally blended into fueloil. Steam or hot oil typically provides the heat require-ments of the product fractionation section.

The sidedraw from the DIPB column containingmainly DIPB combines with a portion of the recyclebenzene and is charged downflow into the transalkyla-tion reactor. In the transalkylation reactor, DIPB andbenzene are converted to additional cumene. Theeffluent from the transalkylation reactor is then sentto the benzene column.

QZ-2000 or the newer QZ-2001 catalyst can be uti-lized in the alkylation reactor while QZ-2000 catalystremains the catalyst of choice for the transalkylation

reactor. The expected catalyst cycle length is 2–4yr,and the catalyst should not need replacement for at leastthree cycles with proper care. At the end of each cycle,the catalyst is typically regenerated ex situ via a simplecarbon burn by a certified regeneration contractor.However, the unit can also be designed for in situ regen-eration. Mild operating conditions and a corrosion-freeprocess environment permit the use of carbon–steelconstruction and conventional process equipment.

An alternative zeolite process was developed byCR&L and licensed by CDTech and is based on theconcept of catalytic distillation, which is a combinationof catalytic reaction and distillation in a single col-umn.[6–9] Catalytic distillation uses the heat of reactiondirectly to supply heat for distillation of the reactionmixture. This concept has been applied commerciallyfor producing not only cumene but also EB and methyltert-butyl ether (MTBE). The use of a single columnthat performs both the reaction and the distillationfunctions has the potential of realizing substantialsavings in capital cost by essentially eliminating theneed for a separate reactor section. Unfortunately,many available zeolite catalysts that are ordinarily veryeffective in promoting alkylation in a fixed-bedenvironment are much less effective when used in theenvironment of the catalytic distillation column. Also,a separate fixed-bed finishing reactor may be requiredto ensure that complete conversion (100%) of the olefinoccurs to avoid yield losses of propylene to the LPGproduct stream. As such, the amount of catalyst andphysical size of the distillation column may be substan-tially larger than the benzene column used in theconventional fixed-bed process. Thus, the savingsrealized by the elimination of the reactor section maybe more than offset by the increased catalyticdistillation column size, catalyst cost, and additionof a finishing reactor. Depending on the relative values

Fig. 3 Q-Max process. (View this art in color at www.dekker.com.)

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and trade-off of these considerations including utilityvalues, catalytic distillation may still be an appro-priate option for producers in certain circumstances,although market interest in this process option forcumene production has been low in recent years.

Zeolitic Alkylation Chemistry

The production of cumene proceeds by a modifiedFriedel–Crafts alkylation of benzene with propylene.This reaction can be promoted with varying degreesof effectiveness using many different acid catalysts.The basic alkylation chemistry and reaction mechanismare shown in Fig. 4. The olefin forms a carbonium ionintermediate, which attacks the benzene ring in an elec-trophilic substitution. The addition of propylene to thebenzene ring is at the middle carbon of C3 olefin doublebond, in accordance with Markovnikov’s rule. Thepresence of the isopropyl group on the benzene ringweakly activates the ring toward further alkylation,producing DIPB and heavier polyalkylate by-products.

Because new high-activity beta zeolite catalysts suchas QZ-2000 catalyst are such strong acids, they can beused at lower reaction temperatures than SPA catalystor other relatively lower-activity zeolites such asMCM-22 catalyst.[16,17] The lower reaction tempera-ture in turn reduces the olefin oligomerization reactionrate, which is relatively high for SPA catalyst. Theresult is that beta zeolite catalysts tend to have higherselectivity to cumene and lower selectivity to bothnonaromatics that distill with cumene (such as olefins,which are analyzed as Bromine Index, and saturates)and heavy by-products. For example, although butyl-benzene is typically produced from traces of butylene

in the propylene feed, there is always the potential alsofor butylbenzene to form through the oligomerizationof propylene to nonene, followed by cracking andalkylation to produce butylbenzenes and amylbenzenes.As a result of having relatively high activity and oper-ating at relatively low temperature, beta zeolite catalystsystems tend to eliminate oligomerization. This resultsin essentially no butylbenzene formation other thanthat formed from the butylenes in the propylene feed.The cumene product from a beta zeolite based processsuch as the Q-Max process unit fed with a butylene-freepropylene feedstock typically contains less than15wt ppm butylbenzenes.

The Q-Max process typically produces near-equilibrium levels of cumene (between 85 and 95mol%)and DIPB (between 5 and 15mol%). The DIPB isfractionated from the cumene and reacted with recyclebenzene at transalkylation conditions to produce addi-tional cumene. The transalkylation reaction is believedto occur by the acid catalyzed transfer of one isopropylgroup from DIPB to a benzene molecule to form twomolecules of cumene, as shown in Fig. 5

Beta zeolite catalyst is also an extremely effectivecatalyst for the transalkylation of DIPB to producecumene. Because of the high activity of beta zeolite,transalkylation promoted by beta zeolite can takeplace at very low temperature to achieve high conver-sion and minimum side products such as heavy aro-matics and additional n-propylbenzene as highlightedin Fig. 6. Virtually no tri-isopropyl benzene is pro-duced in the beta system owing to the shape selectivityof the three-dimensional beta zeolite structure, whichinhibits compounds heavier than DIPB from forming.

As a result of the high activity and selectivityproperties of beta zeolite, a beta zeolite based catalyst

Fig. 4 Alkylation chemistry. (View this art in color at www.dekker.com.)

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(e.g., QZ-2001 catalyst or QZ-2000 catalyst) is specifiedfor both the alkylation and the transalkylation sectionsof the Q-Max process.

With both alkylation and transalkylation reactorsworking together to take full advantage of theQZ-2001=QZ-2000 catalyst system, the overall yieldof cumene based on benzene and propylene feed in

the Q-Max process can be at least 99.7wt% or higher.Because the Q-Max process uses small, fixed-bed reac-tors and carbon–steel construction, the erected cost isrelatively low. Also, because the QZ-2001=QZ-2000catalyst system is more tolerant of feedstock impurities(such as water, p-dioxane, sulfur, etc.) compared toother catalysts available, the Q-Max process requires

Fig. 5 Transalkylation chemistry. (View this art in color at www.dekker.com.)

Fig. 6 Possible alkylation side reactions. (View this art in color at www.dekker.com.)

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minimal pretreatment of the feeds, which furtherminimizes the capital costs.

This is in distinct contrast to other technologiesbased on zeolites other than beta where extensive feedcontaminant guard beds are required to protect thecatalyst from rapid and precipitous deactivation andloss of conversion when exposed to trace amounts ofsulfur, water, oxygenates, and nitrogen.

Cumene Product Impurities

Beta zeolite catalyst can be optimized to nearly elimi-nate all undesirable side reactions in the productionof cumene. The improvement in beta zeolite catalystquality has occurred to the point that any significantimpurities in the cumene product are governed largelyby trace impurities in the feeds. The selectivity of thecatalyst typically reduces by-products to a level result-ing in production of ultrahigh cumene product puritiesup to 99.97wt%. At this level, the only significant by-product is n-propylbenzene with the catalyst producingessentially no EB, butylbenzene, or cymene beyondprecursors in the feed. Fig. 7 shows the reactions ofsome common feedstock impurities that produce thesecumene impurities.

Beta Catalyst Resistance toFeed Contaminants

Beta zeolite is a large pore zeolite with optimized acidsite densities that exhibits:

� Good mass transfer properties.

� Significant reduction in undesirable polymerizationand by-product side reactions.

� High tolerance to feedstock impurities and poisons.

The resistance of new zeolitic catalysts to temporaryand permanent catalyst poisons is essential to the eco-nomic and commercial success of a zeolitic basedcumene process. The following commercial dataobtained using beta zeolite as a catalyst illustrates theoutstanding ability of beta zeolite to cope with a widerange of feedstock contaminants:

Cyclopropane

n-Propylbenzene (nPB) is formed by alkylation ofbenzene with cyclopropane or n-propanol, and byanti-Markovnikov alkylation of benzene with propy-lene. Cyclopropane is a common impurity in propylenefeed and approximately half of this species is convertedto nPB in the alkylation reactor. Essentially, all alkyla-tion catalysts produce some nPB by anti-Markovnikovalkylation of propylene. The tendency to form nPBrather than cumene decreases as the reaction tempera-ture is lowered, making it possible to compensate forcyclopropane in the feed to some extent. As the operat-ing temperature of zeolitic alkylation catalyst isdecreased, the deactivation rate increases. However,because of the exceptional stability of the beta zeolitecatalyst system, a unit operating with beta zeolitecatalyst can be operated for extended cycle lengthsand still maintain an acceptable level of nPB in thecumene product. For example, with FCC-grade propy-lene feed containing typical amounts of cyclopropane,

Fig. 7 Reactions of feed impurities. (Viewthis art in color at www.dekker.com.)

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a beta zeolite based process can produce an overallcumene product containing 250–300wt ppm nPB whileachieving an acceptable catalyst cycle length.

Water

Water can act in this environment as a Bronsted baseto neutralize some of the weaker zeolite acid sites. Thiseffect is not harmful to any appreciable extent to thebeta zeolite catalyst at typical feed stock moisturelevels and under normal alkylation and transalkylationconditions. This includes processing of feedstocks upto the normal water saturation condition (typically500–1000 ppm) resulting in 10–150 ppm water in thefeed to the alkylation reactor dependent on feedand=or recycle stream fractionation efficiency.

Oxygenates

Small quantities of methanol and ethanol are some-times added to the C3s in pipelines to protect againstfreezing because of hydrate formation. Although thebeta zeolite catalyst is tolerant of these alcohols,removing them from the feed by a water wash may stillbe desirable to achieve the lowest possible levels of EBor cymene in the cumene product. Cymene is formedby the alkylation of toluene with propylene. Thetoluene may already be present as an impurity in thebenzene feed, or it may be formed in the alkylationreactor from methanol and benzene. Ethylbenzene isprimarily formed from ethylene impurities in thepropylene feed. However, similar to cymene, EB canalso be formed from ethanol.

p-Dioxane is sometimes present in benzene fromextraction units that use ethylene glycol based solvents.It is reported to cause deactivation in some zeolitic alky-lation catalysts even at very low ppm levels. However,beta zeolite catalyst appears to be tolerant to p-dioxaneat levels typically found in benzene extraction processesand does not require costly removal of this impurity.

Sulfur

Sulfur has no significant effect on beta zeolite catalystat the levels normally present in olefin and benzenefeeds considered for cumene production. However,even though the beta zeolite catalyst is sulfur tolerant,trace sulfur that makes its way into the finishedcumene unit product may be a feed quality concernfor downstream phenol processors where the typicalsulfur specification is <1 ppm. The majority of sulfurcompounds associated with propylene (mercaptans)and those associated with benzene (thiophenes) areconverted to by-products outside the boiling rangeof cumene. Because some sulfur compounds form

by-products that boil within the boiling range of cumene,the sulfur content of the cumene product depends on thesulfur content of the propylene and especially benzenefeeds to a certain extent. Sulfur at the levels usuallypresent in propylene and benzene feeds considered forcumene production will normally result in cumeneproduct sulfur content that is within specifications.

Unsaturates

Use of beta zeolite catalyst does not require thebenzene feed to be clay treated prior to use in alkyla-tion service. Some of the unsaturated material in thebenzene can lead to the formation in the alkylationreactors of polycyclic-aromatic material which willget preferentially trapped in some zeolites having rela-tively small-sized pores. This can lead to increaseddeactivation rates in such small-pore zeolites. Betazeolite’s large pore structure makes it possible to moreeasily handle this polycyclic-aromatic material and as aresult does not require further treatment of the benzenefeed to remove unsaturated material. In addition,alpha-methylstyrene (AMS) is produced by alkylationof benzene with methylacetylene or propadiene. Someof the AMS alkylates with benzene, forming diphenyl-propane, a heavy aromatic that leaves the unit with theDIPB column bottoms.

Nitrogen, Metal Cations, and Arsine

The presence of trace amounts of organic nitrogencompounds and metal cations in the benzene feed orarsine in the olefin feed has been known to neutralizethe acid sites of any zeolite catalyst. Good feedstocktreating practice or proven guard-bed technologyeasily handles these potential poisons. For example,basic nitrogen, which can sometimes be present in thebenzene fresh feed, is easily removed using very low-cost UOP guard-bed technology. To facilitate monitor-ing of feeds for potential nitrogen based contaminants,UOP has developed improved analytical techniques tohelp in the evaluation. These methods include UOP971 (‘‘Trace Nitrogen in Light Aromatic Hydrocar-bons’’ by Chemiluminescence) used to detect totalnitrogen down to 30 ppb and UOP 974 (‘‘NitrogenCompounds in Light Aromatic Hydrocarbons’’ byGC) used to detect individual nitrogen species downto about 100 ppb.

CURRENT STATE-OF-THE-ARTCUMENE TECHNOLOGY

Currently, the major processes for cumene productionare liquid phase technologies offered by UOP and

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Badger Licensing (ExxonMobil technology) based onbeta zeolite (such as QZ-2001 and QZ-2000 catalysts)and MCM-22 catalyst, respectively. Over the pastdecade, great progress has been made in improvingand optimizing catalyst formulations for use in applica-tions to produce cumene from benzene alkylation. Forexample, the ability to synthesize beta zeolite in a widerange of Si=Al2 ratios has given catalyst designers theability to tailor the zeolite into a form that optimizesactivity and selectivity. A parametric study on theeffects of Si=Al2 ratio on activity and selectivity waspublished by Bellusi.[18] In this work, it was found thatas the silica to alumina ratio was increased from 28 to70, there was a decrease in both activity and selectivitytoward isopropylbenzene-type compounds. Addition-ally, the less active catalysts had a greater tendency

toward oligomerization and were more prone towardcoking.

This study parallels work performed at UOP, where,through the use of nonconventional synthesis techni-ques, samples have also been prepared with Si=Al2ratios as low as 10. Through this work it has beenfound that with a Si=Al2 ratio of 25, the catalystmaintains sufficient activity to achieve polyalkylateequilibrium (e.g., DIPB equilibrium) and, at the sametime, minimizes the formation of heavier diphenyl com-pounds (and hence maximizes yield) in cumene service.

Perhaps the most critical understanding was devel-oped with regard to the need to minimize the Lewisacidity of the catalyst and at the same time maintainhigh Brønsted acidity. Studies at UOP demonstratedthat olefin oligomerization was directly related to the

Fig. 8 Effect of framework Al on betacatalyst stability. (View this art in colorat www.dekker.com.)

Fig. 9 Stability of QZ-2001 catalyst vs. QZ-2000catalyst. (View this art in color at www.dekker.-com.)

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Lewis acid function of the catalyst. Olefin oligomeriza-tion reactions can lead to the formation of heavy com-pounds (coke type precursors), which have a negativeeffect on catalyst stability. Thus, minimization of theLewis character of the beta leads to a catalyst with highstability. Generally, Lewis acidity in beta zeolite hasbeen attributed to the existence of nonframework alu-minum atoms. The most common mechanism for theformation of nonframework alumina is through steamdealumination during the catalyst calcination step ofthe manufacturing process. By careful control of thetemperature, time, and steam levels during the manu-facturing process, it is possible to produce a catalystthat is extremely stable at typical alkylation conditions.

From a commercial standpoint this knowledge hashad the additional benefit of developing a regenerationprotocol that is extremely robust. It has been demon-strated in commercial in situ and ex situ procedures thatthe beta zeolite catalyst can be regenerated with excellentresults providing complete restoration of fresh catalystperformance. The feature of complete regenerability isanother attribute that distinguishes beta zeolite catalysts

from other commercially available zeolite catalysts suchas MCM-22 catalyst, where significant activity and selec-tivity can be lost upon regeneration.[19] The ability toregenerate catalyst is essential in a commercial environ-ment to provide additional flexibility to cope with a widerange of feedstock sources, feedstock contaminants, andpotential operational upsets.

The historical development of beta zeolite showedthat early versions of beta catalyst demonstrated lessthan optimum performance when compared to today’sstate-of-the-art formulation. Fig. 8 is a plot of the rela-tive stability of beta zeolite as a function of the Si=Al2ratio of the beta zeolite structure in which the dominat-ing influence of this parameter is evident. Uop haslearned to stabilize the zeolite structure through carefulprocess and chemical means. This has resulted ina catalyst system that is extremely robust, highlyregenerable, and tolerant of most common feedstockimpurities.

Additional studies of beta zeolite have come to similarconclusions. For example, Enichem has found that betazeolite is the most effective catalyst for cumene alkylation

Fig. 10 JLM commercial data

on catalyst stability. (View thisart in color at www.dekker.com.)

Fig. 11 JLM commercial data on sulfur in propylenefeed. (View this art in color at www.dekker.com.)

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among other zeolites tested including Y, mordenite, andan isostructural synthesis of MCM-22 catalyst.[20]

The principles described above also led to thedevelopment of the new-generation QZ-2001 alkylationcatalyst.[21] In Fig. 9, results from accelerated stabilitytesting of QZ-2000 and QZ-2001 catalysts demonstratethe superior stability of the latest catalyst system. QZ-2001 catalyst exhibits as much as twice the stability whencompared to QZ-2000 catalyst. The benefit afforded byQZ-2001 catalyst can be utilized by cumene producersin several ways. It can be taken directly through reduc-tion of the catalyst loading for a specific run length,or alternatively as a convenient way to increase runlength, or to increase throughput through the cumeneunit, by allowing operation at a lower B=P feed ratio.

Long-Term Stability of Beta Zeolite Catalyst

Commercial operation with a wide variety of olefinfeedstocks from different sources has demonstratedthe flexibility of beta zeolite in the Q-Max process.

Refinery grade, chemical grade, or polymer grade pro-pylene feedstocks have been successfully used to makehigh-quality cumene product in the Q-Max process.

A good example of the ruggedness of the betazeolite catalyst can be found in the case of JLM’s BlueIsland (Illinois) Q-Max operation. The operationstarted in August 1996 as the first Q-Max processoperation with UOP beta zeolite catalyst. Initial oper-ating results were reported in 1997.[22] The unit hascontinued to operate with stable performance for morethan 7 yr without catalyst regeneration in spite of thepresence of significant levels of feed contaminants.

Excellent monoalkylation selectivity has also beenobserved over many years of service in the JLM opera-tion as shown in Fig. 10. Under the normal operatingconditions of the unit, an equilibrium cumene selectivityof about 91mol% is predicted. Thus, results clearly showthat the beta zeolite catalyst is active enough to achievenear-equilibrium selectivity. This is an important featureof the catalyst as the amount of dialkylate that must beprocessed in the transalkylator and the subsequent costof processing this material are minimized.

Fig. 12 JLM commercial data on alkylation reactormoisture content. (View this art in color at www.dekker.com.)

Fig. 13 JLM commercial data on benzene feedp-dioxane content. (View this art in color at www.dekker.com.)

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Feed contaminants such as sulfur, water, andp-dioxane were monitored very closely during the first2 yr onstream as shown in Figs. 11–13.

The impact of these impurities on cumene productquality was negligible during this period. The customerwas able to maintain extremely high-quality cumenethroughout the life of the beta catalyst, as shown inFig. 14.

Another important observation is that sulfur levelsfrom 3 to 7 ppm, moisture levels of 30–70 ppm, andeven p-dioxane excursions up to 70 ppm had virtually

no impact on catalyst stability or performance, as seenin Figs. 10 and 15. Note that the alkylation catalystselectivity and catalyst bed inlet temperature andweight average bed temperature remain virtuallyunchanged after years of operation.

Beta Zeolite Catalyst Regeneration

As a result of beta’s high activity and robustness,catalyst requirements are minimized. At the end of

Fig. 14 JLM commercial data on cumene product purity. (View this art in color at www.dekker.com.)

Fig. 15 JLM commercial data. (View this art in color at www.dekker.com.)

614 Cumene Production

each cycle, the catalyst can be regenerated ex situ by acertified regeneration contractor. The regenerability ofbeta zeolite catalyst provides an ultimate life of threecycles or more if appropriate processing and regenera-tion guidelines are followed. If desired, the Q-Max

process unit can be designed to accommodate in situcatalyst regeneration. Both options have been success-fully demonstrated in commercial operation.

Figs. 16 and 17 show an example of the perfor-mance of QZ-2000 catalyst after multiple in situ

Fig. 16 Commercial Q-Max process data. Effect of in situ QZ-2000 catalyst regeneration on cumene selectivity. (View this art incolor at www.dekker.com.)

Fig. 17 Commercial Q-Max

process data. Effect of in situQZ-2000 catalyst regenerationon cumene purity. (View thisart in color at www.dekker.com.)

Cumene Production 615

C

regenerations in a commercial cumene unit. Thecumene unit experienced premature deactivationbecause of excessive basic nitrogen levels in the feedas well as unsatisfactory plant operation.

Taking advantage of the in situ regenerationcapability, the customer opted to regenerate the cata-lyst three times during this period. The results showthe remarkable resilience of the beta zeolite catalystto the stresses of regeneration with virtually no lossin monoalkylate selectivity or cumene product qualityas a result of repeated regenerations.

CONCLUSIONS

Fixed-bed zeolitic cumene technology is the process ofchoice for the cumene=phenol industry. Most of thepreviously installed cumene capacity based on olderAlCl3 and SPA technologies has now been replacedwith the newer zeolitic technology over the past 10 yr.The result is greatly improved yields and reduced oper-ating and capital costs. UOP’s Q-Max process based onbeta zeolite has emerged as the leader for cumenetechnology. This is primarily due to the high activity,robustness, and lower operating costs associated withoperating a beta zeolite based catalyst system.

REFERENCES

1. Bentham, M., et al. Process improvements for achanging phenol market. In DeWitt Petro-chemical Review Conference, Houston, TX, Mar19–21, 1991.

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3. Keim, W.; Roper, M. In Ullmann’s Encyclopediaof Industrial Chemistry; Gerhartz, W., Ed.; VCHVerlagsgesellschaft: Weinheim, 1985; Vol. A1, 185.

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8. Stadig, W.P. Cumene. Chem. Process. 1987, 50 (2),27.

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10. Canfield, R.C.; Unruh, T.L. Improving cumeneyields via selective catalysis. Chem. Eng. 1983,90 (6), 32.

11. Canfield, R.C.; Cox, R.C.; McCarthy, D.M.Monsanto=Lummus crest process produces low-est cost cumene. In AICHE 1988 Spring Meeting,New Orleans, LA, Apr 6–10, 1986.

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13. Innes, R.A.; Zones, S.I.; Nacamuli, G.J. LiquidPhase Alkylation or Transalkylation ProcessUsing Zeolite Beta. U.S. Patent 4,891,458, Jan 2,1990. Chevron Research and TechnologyCompany: San Francisco, CA.

14. Cannan, T.R.; Hinchey, R.J. Synthesis of ZeoliteBeta. U.S. Patent 5,139,759, Aug 18, 1992. UOP:Des Plaines, IL.

15. Inwood, T.V.; Wight, C.G.; Ward, J.W. Liquid-phase Alkylation and Transalkylation Process.U.S. Patent 4,459,426, Jul 10, 1984, Union Oil.

16. Cheng, J.C., et al. A comparison of zeolitesMCM-22, beta, and USY for liquid phase alkyla-tion of benzene with ethylene. Sci. Technol. Catal.1998, 6, 52–60.

17. Cheng, J.C., Smith, C.M.; Venkat, C.R.; Walsh,D.E. Continuous Process for Preparing Ethylben-zene Using Liquid Phase Alkylation and VaporPhase Transalkylation. U.S. Patent 5,600,048,Feb 4, 1997, Mobil Oil Corporation,

18. Bellussi, G., et al. Liquid phase alkylation ofbenzene with light olefins catalyzed by betazeolites. J. Catal. 1995, 157, 227–234.

19. Dandekar, A.B., et al. Regeneration of AromaticAlkylation Catalysts Using Hydrocarbon Strip-ping. WO 01=83408, Nov 2001. Mobil Oil Corp,Baytown, TX.

20. Perego, C., et al. Experimental and computationalstudy of beta, ZSM-12, Y, modernite and ERB-1in cumene synthesis. Microporous Mater 1996, 6,395–404.

21. Schmidt, R.; Zarchy, A.; Petersen, G. Newdevelopments in cumene and ethylbenzene alkyla-tion—Paper 124b. In 1st Annual AromaticProducers Conference—AIChE Spring Meeting,New Orleans, LA, Mar 10–14, 2002.

22. Jeanneret, J.; Greer, D.; Ho, P.; McGehee, J.;Shakir, H. The UOP Q-Max process: setting thepace for cumene production, Presented at the22nd Annual De Witt Petrochemical Review,Houston, TX, Mar 18–20, 1997.

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