Design of Cumene Producing Plant

Contents ABSTRACT.............................................................................................................................vii WORK PLAN............................................................................................................................ix 1.INTRODUCTION.................................................................................................................10 2.MARKET ANALYSIS...........................................................................................................11 3.PROCESSES DESCRIPTIONS............................................................................................13 3.1. 3-DDM (3-Dimensional dealuminated mordenite) Process..........................................13 3.1.1. 3-DDM Block diagram...............................................................................................14 3.1.2.Overall Material Balance.............................................................................................15 3.1.3. 3-DDM DOW PROCESS EQUIPMENT SUMMARY TABLE................................17 3.2.Mobil Badger Process.....................................................................................................18 3.2.1.Block diagram..............................................................................................................20 3.2.2. Overall Material Balance............................................................................................21 3.2.3.MOBIL BADGER PROCESS EQUIPMENT SUMMARY TABLE..........................22 3.3.Enichem Process.............................................................................................................23 3.3.1.Block Diagram.............................................................................................................25 3.3.2.Overall Material Balance.............................................................................................26 3.4.CD Tech’s Cumene Process............................................................................................26 3.4.1.Block diagram..............................................................................................................28 3.4.2.Overall Material Balance.............................................................................................32 3.4.3.Catalytıc Distillation....................................................................................................40 3.4.4.Vacuum Distillation.....................................................................................................42 3.4.3.CD TECH PROCESS EQUIPMENT SUMMARY TABLE.......................................44 3.4.5.Process Flow Sheet......................................................................................................45 4.RESULT AND DISCUSSION...............................................................................................47

4.1.Comparison of Catalysts.................................................................................................48 4.2.Reactor Type Effects of Cumene Production..................................................................49 5.CONCLUSION......................................................................................................................51 6.REFERENCES......................................................................................................................53 7.APPENDIX............................................................................................................................55 Thermal Effects At Distillation Column...............................................................................55 Chemical Equilibrium At Distillation Column.....................................................................56

FIGURE LIST Figure 1. World Consumption of Cumene...........................................................................................12 Figure 2. DOW-Chemical process a de-aluminated mordenite............................................................13 Figure 3. 3DDM (3-Dimensional dealuminated mordenite) Process Block Diagram..........................14 Figure 4. Mobil Badger Process Block Diagram.................................................................................20 Figure 5. Enichem Process of Block Diagram.....................................................................................25 Figure 6. CDTech Process of Block Diagram.................................................................................... ..28 Figure 7. Catalytic Distillation Reactor...............................................................................................40 Figure 8. CDTech Process Flow Sheet................................................................................................45

Figure 9. Molar ratio benzene/propene – adiabatic rise……………………………………...55 Figure 10. Molar ratio benzene/propene – selectivity IPB..............………………………....56 TABLE LİST Table 1. Capacity for cumene processes..............................................................................................12 Table.2. Overall process material balance after Dow - Kellog technology ........................................15 Table 3. DDM Dow Process Equipment Summary Table....................................................................17 Table 4. Comparison of MCM-22 and zeolite beta catalysts for cumene synthesis..............................19 Table 5. Overall process material balance after Mobile-Badger..........................................................21 Table 6. Mobil Badger Process Equipment Summary Table................................................................22 Table 7. Enichem process Features and Benefits………………………………………………….24 Table 8. Enichem process of overall material balance..........................................................................26 Table 9. Selectivity obtained with different zeolite catalysts in cumene synthesis...............................29 Table10. Selectivity and DIPB distribution at different temperature and propylene conversions.........29 Table 11. Overall Material Balance..................................................................................................... 39 Table 12. Cumene Product Quality......................................................................................................40 Table 13. CDTech Process Equipment Summary Table.......................................................................44 Table 14. Cdtech Process Stream Summary Table In The Product Purification...................................46 Table 15. Cumene Processes Comparison Table..................................................................................47 Table 16. Manufacturing Costs............................................................................................................52

MEMORANDUM TO

: Che 452-2012-13/Senior Design Engineers

SUBJECT :Preliminary Design of Cumene Producing Plant Remember the interoffice letter on the request of cumene production search .Cumene is the common name for isopropylbenzene (IPB), is an aromatic hydrocarbon. It is an important chemical in the present industrial world and its uses are steadily increasing. It is an intermediate for the production of of phenol and its co-product acetone and there is a demand for the cumene with a purity of 98.5%. Commercial production of cumene is by friedel crafts alkylation of benzene with propylene with the following reactions; C3H6 + C6H6 C3H6 + C6H5-C3H7

C6H5-C3H7 (C9H12,cumene,IPB) C3H7-C6H4-C3H7 (C12H18, diisopropylbenzene; DIPB)

The possibly formed triisopropylbenzene(TIPB) also react with benzene yielding cumene and DIPB. C3H6 + (C3H7)3-C6H3

C6H5-C3H7 + C3H7-C6H4-C3H7

There is also the prospect for increased demand for some of the cuemene by-products such as DIPB. The production of diphenols from DIPB is important for synthesis of resorcinol (from m-DIPB) and hydroquinone(from DIPB). Well the cumeen formation reaction can be occured in liquid and gas phases, but high conversion values are obtained at gas phase reactions using catalyst. Early years virtually all cumene was produced using either solid phosphoric acid(SPA). The SPA catalyst consist of a complex mixture of orthosiliconphosphate, pyrosiliconphospate, and polyphosphoric acid supported on kieselguhr. SPA process conditions include pressures that range from 3.0 to 4.1 Mpa, (29-40 bar) temparetures that range from 1800C to 2300C, benzene to propylene ratio from 5 to 7, and weight hourly space velocities(WHSVs) between 1 and 2. To maintain the desired level of activity, small amounts of water continuously fed inti the reactor. The water continually liberates H3PO4 causing some downstream corrosion. Approximately 4-5 wt.% of the product consist of di- and tri- isopropylbenzenes.

2

In the early 1980s, a process catalyzed by AlCl3 based on the same chemistry used in the ethyl benzene process was introduced. This process can be at lower benzene to propylene ratio than the SPA process because AlCl3 can transalkylate the polyalkylated benzenes back to cumene. The process also operates at temperatures lower than the SPA process because the more highly acidic anhydrous AlCl3 tends to produce significantly more undesired npropylbenzene at equivalent temperatures. Since the mid-1990s cumene producers have begun to convert to the more environmentally friendly and more efficent zeolite-based processes operating around 25 atm pressure. In addition to the reduced maintanence cost, success most of the di- ısoprophylbenzene(DIPB) by-product is converted to cumene in seperate transalkylation processes, this process produces higher cumene yields than the previous conventional processes. The recycle DIPB combines with a portion of the recycle benzene and is also chard downflow through the transalkylation reactor and DIPB and unreacted benzene are converted to more cumene with the following reaction; C3H7-C6H4-C3H7 + C6H6

2C6H5-C3H7 (cumene, IPB)

The catalytic exothermic alylation reaction is held in either shell and tube reactors or packed fixed bed reactors under temperature control. The propylene feed may either be pure or contain a substantial amount of propane, which can come from a refinery fluid catalytic cracking operation. however, the feed must be essentially free of ethylene and buthylenes to avoid contamination of the product wwith ethyl and buthyl benzenes. Current zeolite catalyst already operate at process temperatures that require minimal external heat addition. heat integration and heat management will be of increasing concern at the lower benzene - to propylene ratios because the cumene synthesis reaction is so highly exothermic. Recycle particularly in the alkylation reactor is likely to become increasingly important as a heat management strategy. Since manufacturers prefer cheaper and consequently lower quality feed stocks, how to limit build-up of by-products and feed impurities in these recycle loops is important parameter.

3

The current zeolite-based processes allow for significant debottlenecking of SPA plants with little additional capital. Although the zeolite processes have been able to produce cumene with purities that cannot be approached by either the SPA or the AlCl3 process additional researches have undoubtly been directed towards identifiying improved alkylation and transalkylation catalysts. Alkylation catalysts that operate at benzene-to-propylene ratios of 3 or possibly even lower are desirable because they greatly reduce the need for costly seperation capacity. Transalkylation and alkylation catalyst that produce even lower by-product concentration at low benzene to propylene levels are likely to be preferable. The Mobil-Badger cumene process commercialized in 1994, consist of a fixed bed alkylator, a fixed bed transalkylator and the separation section. The high cumene purity around 99.97wt.% at 99.7wt% yield is primarily attributable to the high monoalkylation selectiviy of the mcm-22 catalyst with low benzene- to - propylene ratios in the range of 2-4M. Ethyl benzene , prophyl benzene and buthylbenzene levels are an order of magnitude lower than those obtained with the SPA catalyst process. commercially the catalys has demonstrated cycle lengths in excess of 2 years with an ultimate catalyst life in excess of 5 years. The EniChem cumene process commercialized in 1996 operates at a benzene to propylene ratio of 4:1 with cumene yields and selectivities both greater than 99% using a modified beta catalyst. The flow scheme of UOP's Q-Max process commercialized in 1996 is uses MgAPSO-31 catalyst that is very active and selective for cumene reportedly eliminated the formation of npropylbenzene. Dow's 3-DDm cumene process uses a highly deluminated mordenite catalyst in a two stage fixed bed alkylation and transalkylation process operating with a lower benzene-to-propylene ratios than the conventional SPA process. The mordenite-based transalkylation stage of this process has operated commercially since 1992. Dow's mordenite compenent corresponding to a zeolite with a low acid side density which reduces the rates of hydrogen transfer and propylene oligomerization, but high acid side strength which allows the reaction to be run at lower temperatures (below 1700C). In transalkylation p-IPB are transalkylated with benzene at a reactor temperature of approximately 1500 C. DIPB conversions of up to 65% with greater than 90% selectivity toward cumene have been reported.

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CDTech's CD cumene process has the effect of rising the benzene-to-propylene ratio in the bulk phase surrounding the catalyst. Cumene yields in excess of 99% are claimed for this dual operations alkylation is carried out isothermally at relativelly low temperatures and pressures of approximately 5 bar in the overhead. The mild reaction conditions are reported to produce cumene of very high purity with the maine impurities as ethylbenzene(220ppm) and npropylbenzene(350ppm). Cd Tech's patents refer to zeolites Y, omega and beta. Current zeolite catalysts already operate at process temperatures that require minimal external heat addition. Heat integration and heat management will be of increasing concern at the lower benzene-to-propylene raitos because the cumene synthesis reaction is so highly exothermic(∆Hf= -98 kj/mol). Recycle, particularly in the alkylation reactor is likely to become increasingly important as management strategy. The key will be how to limit the build-up of by-products and feed impurities in these recycle loops, particularly as manufacturers seek cheaper and consequently lower quality feedstocks. The last semester you carried out preliminary study to gain rough estimate on the suitability of construction of cumene cumene producing plant in Turkey and decision on the capacity. You mainly focused on the process with the fixed bed alkylation reactor using the zeolite-based catalyst for the cumene production and carried out the design of some equipments for this process. Now you are rudely say something about economical suitability of construction of the plant. However, due to lack of time you skipped the "process analysis", "market analysis" anad "detailed feasibilty search" for the selecting most suitable pathway. Your job in this semester is the complete design of a cumene plant. You are responsible for selecting the production route in addition to capacity selection and plant location. In the deciding all, you must also concentrated on the product, raw materials and by-product specifications. In your design stıdy you must consider (i) environmental problems, waste disposal and suggested precuations, (ii) safety and health concerns and (iii) process controllability and flexibility (iv) energy recovery and preserving the sources. The main objective of your study is to carry out complete economical analysis(manufacturing cost and profitability analysis).

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For the final decision of the company about the construction, the report will be posted at the end of the january, so please report me no later than 4 january, 2013. The success of a design study needs good timing. In the time period allocated to cumene plant design you are expected to subdevidethe work to several phases. You will be requesteed to submit writeen reports on the production pathway selection. We will have a discussiion meeting on october 19, 2012 to decide on the process flow sheeting. You will submit an informal report summarizing the result of production path way selection. In your report, you should give the process description and the detailed flow sheet with the necessary summary tables. now you are requested planning the work packages to complete this particular project till september, 28, 2012. please be ready for the discussion of time-table (both for the first report and the whole design study) on next lecture and also prepare the design basis.

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ABSTRACT This study focus on deciding the suitable production pathway and deciding the flowsheet of the choosen Cumene production process. Today, the cumene is used almost exclusively for manufacturing phenol and acetone. The global demand for phenol has been steadily increasing over the last 10 years. In 2000, global phenol demand stood at 6,000,000 tons, before increasing to 8,000,000 tons in 2010. Those phenol production companies want the purity of cumene at least %99,5. All cumene production processes checked for this market analysis which helped to decide capacity and purity. The most using processes are MobileBadger cumene process, Enichem cumene process, 3-DDM cumene process and CDCumene process. In this case all investigations were searched for those four processes. The Mobil Badger Process; high cumene purity is primarily attributable to the high monoalkylation selectivity of the MCM-22 catalyst. But MCM-22 is the most expensive one comparing to Other types of catalysts (Beta Zeolite, Zeolite Y, etc). MCM-22 ensures high selectivity of cumene/DIPB however Additonally operational conditions includes high pressures and temperatures and it causes extra risks. The Enichem Process operates at a benzene to propylene ratio of 4:1. Cumene yields and selectivities are both greater than 99%. This benzene to propylene ratio brings extra raw material and extra utilities with those benefits. Enichem’s process uses a modified beta catalyst. Beta catalyst is not much expensive but it causes more side reactions (oligomerization, nPB like TIPB...). Besides propylene conversion is lower with beta catalyst. Dow’s 3-DDM cumene process uses a highly dealuminated mordenite catalyst in a two-stage fixed-bed alkylation and transalkylation process. Disadvantages of being nonregenerable and of posing catalyst disposal problems. It also points out that because of the lower benzene: propylene ratio 'it may be possible to achieve additional capacity at a relatively inexpensive cost. Dow’s 3-DDM Cumene Process operates at a benzene to propylene ratio more than 5:1. It causes extra raw material that extra cost. CDCumene Process is using catalytic distilaltion reactor for alkylation reaction. Simple adiabatic reactor technology is appropriate, but the operating pressure should be sufficiently high to ensure only liquid - phase reaction. To limit the formation of by products by consecutive polyalkylation a large ratio benzene/propylene is used, which in turn implies large benzene recycle and considerable energy consumption.

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The energy spent for benzene recycling can be reduced considerably by heat integration, namely by double - effect distillation. In addition, the heat developed by reaction can be advantageously recovered as medium - pressure steam. Profitability guess of CD-Tech Cumene Process is done with using raw materials’ cost as outcomes and product price as incomes. Profitability is 36 % of Cumene sales. As a conclusion studies shows that CD Tech Cumene Process is the most suitable process.

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FINAL REPORT

SECOND REPORT FIRST REPORT (19.10.2012)

WORK PLAN WORK PACKAGE Market Analysis

WORK TO BE DONE Manufacturing cost and capital cost calculation

OUTPUT Capacity selection

TIME 04.10.2012

Choosing the true production pathway

Process selection

Process name

11.10.2012

Design Basis

Process Flow Diagram

Process Flow Sheeting

Operational conditions

Material and energy balance calculation Product, raw materials and by-product

Utility Equipment size and operational safety risks Determined phase and compositions Preparing of specification sheet according to ending

specifications Plant Layout

calculation data Equipment distances were determined

Detailed Equipment design

Survey of the Plant Layout Standards

Estimation of; Manufacturing Cost Capital Investment of Given Capacities Profitability Cost Analysis

Analysis Checking the Profitability Environmental Safety

Final Assesment

Conditions

9

16.10.2012 Equipment summary table Stream summary table Raw material versus product cost Utility Cost

18.10.2012

Land Requirement Specification Sheets of

08.11.2012

equipments

26.11.2012

Economically Profitable Process Price of the product

18.12.2012

Optimum Process

02.01.2013

1.INTRODUCTION Cumene process is an industrial process for developing phenol and acetone which are important for the chemical industry from benzene and propylene. In this report, it has been done process analysis, market analysis and detailed feasibility report for cumene process. There are different processes about production of cumene like Mobil-Badger, 3-DDM Dow, EniChem, CD-Tech. All of them these process have the same reactions which are reacts in alkylation reactor and transalkylation reactor. However operating conditions and flow diagrams are different. This report including comparison of these processes about capacities, product purities, operational conditions, as a result of material balance mass flow rate of raw materials, energy recovery, total annulized cost, risk factors and also catalyst. The alkylation of benzene with propylene to produce cumene, a starting material for the production of acetone and phenol ,is very important in hydrocarbon processes. Traditionally, some mineral acids including AlCl3 and others are employed, which present good catalytic performance , while raising serious environmental problems such as corrosion and waste disposal. In order to overcome some drawbacks of the traditional mineral acid catalysts, technologies such as the Mobil-Badger process using MCM-22,the CD-Tech and EniChem process using Y and Beta zeolites and the 3-DDM Dow process using Mordenite have made great progress in recent years. This report presents as a result of comparison these four processes cause of highest Energy recovery, ultra high purity cumene using a proprietary zeolite catalyst that is noncorrosive and environmentally, and also Alkylation reactor has operational benefit like catalytic distillation reactor that involves a combination of catalysis and distillation in a single column decided to produce cumene with CD-Tech Cumene process. CD-Tech Cumene process is seen as most economical processes for producing cumene, but there are some limitations for using CD-Tech Cumene Process. Catalyst price, catalyst life and process control of Alkylation reactor is most important factor in catalytic distillation reactor. Because deactivation of catalyst is higher in CDCumene, there are two works which are distillation and reaction and it effects to heat of reaction.

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2.MARKET ANALYSIS

Worldwide cumene market analyzed to learn customers of cumene and decide capacity and product properties. In market cumene is used with at least purity %99: 1. As feed back for the production of Phenol and its co-product acetone 2. The cumene oxidation process for phenol synthesis has been growing in popularity since the 1960’s and is prominent today. The first step of this process is the formation of cumene hydroperoxide. The hydroperoxide is then selectively cleaved to Phenol and acetone. 3. Phenol in its various formaldehyde resins to bond construction materials like plywood and composition board (40% of the phenol produced) for the bisphenol A employed in making epoxy resins and polycarbonate (30%) and for caprolactum, the starting material for nylon-6 (20%). Minor amounts are used for alkylphenols and pharmacuticals. 4. The largest use for acetone is in solvents although increasing amounts are used to make bisphenol A and methylacrylate. 5.

∝- Methylstyrene is produced in controlled quantities from the cleavage of cumene

hydroperoxide, or it can be made directly by the dehydrogenation of cumene. 6. Cumene in minor amounts is used as a thinner for paints, enamels and lacquers and to produce acetophenone, the chemical intermediate dicumylperoxide and diiso propyl benzene. 7. Cumene is also used as a solvent for fats and raisins. [4] Essentially, all world cumene is consumed for the production of phenol and acetone. As a result, demand for cumene is strongly tied to the phenol market. Trade in cumene accounts for only 4% of world production. The largest exporters of cumene are the United States (to Germany) and Japan (to the Republic of Korea). Taiwan also imports large volumes of cumene for phenol production. As of early 2011, the U.S. cumene market was tight—primarily as a result of a shortage of feedstock propylene. Scheduled plant maintenance by several large cumene manufacturers was also planned for early to mid-2011. Because of the cumene shortages, phenol and acetone plant operating rates have been reduced significantly, which in turn has

11

restricted phenol exports to Europe and higher-demand regions such as Asia and South America.

Figure 1. World Consumption of Cumene Increased demand for bisphenol A and phenolic resins will result in strong demand for phenol, particularly in Asia (excluding Japan). As a result, consumption of cumene for phenol is forecast to grow at approximately 8% per year in the region. China alone is expected to add over a million metric tons of cumene capacity during 2011–2015 (with most capacity coming onstream in 2013) to supply its phenol/acetone plants that are slated to come onstream during that period. Overall, worldwide cumene consumption for the production of phenol/acetone is forecast to grow at an average annual rate of about 4.5% during 2010–2015. That growing effected to capacity selection. Table 1. Capacity for cumene processes

CAPACITY(ton/year)

COMPANY

CDTech Process [2]

270,000

Formosa Chemicals and Fibre Corporation Taiwan

Dow Process [1]

144,000

USA Noveon

Mobil Badger Process [3]

200,000

LG Chemical LTD

Enichem Process[7]

130,000

Polimeri Europa

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3.PROCESSES DESCRIPTIONS 3.1. 3-DDM (3-Dimensional dealuminated mordenite) Process

Dow’s 3-DDM cumene process uses a highly dealuminate dmordenite catalyst in a two-stage fixed-bed alkylation and transalkylation process to produce Cumene with 144000 Ton/year capacity. Alkylation is carried out in a multi-bed fixed-bed reactor. Heat from the reaction is recovered through feed-effluent heat exchangers. Dow has been able to circumvent the coking problems typically associated with mordenite through its proprietary dealumination process [8]. (At DOW-Chemical process a de-aluminated mordenite has been developed by calcining H-mordenite and treating the zeolit with mineral acids that are code 3DDM (3-Dimensional dealuminated mordenite) .

Figure 2. DOW-Chemical process a de-aluminated mordenite [9] At this Process; benzene and propylene are reacted in the alkylation reactor in a large excess of benzene (more than 5:1 molar ratio) at sufficiently high pressure that ensures only one liquid phase at the reaction temperature, usually between 160 and 240 °C in the presence of (3DDM) zeolite catalyst to produce cumene. Some DIPB are also formed; very little triisopropylbenzes and by-products are formed due to the shape- selectivity of the catalyst. The DIPB's are recovered in the distillation section and recycled to the reaction section for transalkylation with benzene to form additional cumene. The reactor section effluent, consisting of unreacted benzene, cumene, and DIPB's is fractionated in four distillation columns operating in series. Light components, present in the propylene feed, are removed; unreacted benzene is recovered and recycled; pure cumene is separated as a product, and finally the DIPB's are recovered and recycled to the transalkylator. A small heavies purge is taken to fuel. [10] 13

3.1.1. 3-DDM Block diagram

Figure 3. 3DDM (3-Dimensional dealuminated mordenite) Process Block Diagram R – 1: alkykation, R – 2: transalkylation, C – 1: propane column, C – 2: benzene recycle column, C – 3: cumene column, C – 4: polyispropylbenzenes column. The following reactor performance in recycle is the aim: over 99.9% per/pass propylene conversion over 88% cumene selectivity, adiabatic temperature rise below 70 ° C, but a maximum catalyst temperature of 250 °C. The inlet pressure should be sufficiently high to ensure only one liquid phase. Thermodynamic calculations at 35 bar indicate bubble temperatures of 198 and 213 ° C for propylene/ benzene ratios of 1/4 and 1/7, respectively. At the reactor outlet the reaction mixture has a temperature of 230 ° C and a pressure of 34 bar, the molar composition being 86.6% benzene, 12.6% cumene and 0.8% DIPB. Other components are lights, in this case the propane entered with the feed, and heavies, lumped as tri-propylbenzene. 14

The first separation (C-1) is the depropanizer column. A pressure of 12 bar is convenient for (C-1) because it gives a bottoms temperature below 200 ° C and a condenser temperature of 34°C. The pressure is selected so as to ensure the condensation of the top product by air cooling. The following configuration ensures a high recovery of propane with less than 100 ppm benzene: 16 theoretical stages with feed on 5 and a temperature of 150 ° C, and a reflux of 4300 kg/h. Next, follows the separation of the ternary mixture benzene/IPB/DIPB. The recovery of benzene takes place in the column (C-2). The recycle column(C-2) has high recovery of benzene in top is desirable (over 99.9%) but small amounts of cumene are tolerated. If follows the separation cumene/DIPB in the column (C-3), this time operated under vacuum and constrained by the reboiler temperature. The column (C-3) for cumene distillation operates under vacuum to avoid an excessive bottom temperature. A number of 30 stages and a reflux ratio of 1.2 are sufficient to ensure good - purity cumene with less than 100 ppm benzene. DIPB recovered from heavies in the vacuum distillation column (C-4) is sent to the transalkylation, together with an appropriate amount of recycled benzene.

3.1.2.Overall Material Balance Table.2. Overall process material balance after Dow - Kellog technology [11] Material

MT/MT cumene

Benzene (100 %)

0.653

Propylene (100%)

0.352

Cumene (Product)

1.000

Cumene heavies

0.006

LPG

Variable

Disadvantages of being non-regenerable and of posing catalyst disposal problems for solid zeolit cataliyst like SPA or AlCl3/HCl. The potential for use of zeolite catalysts has been 15

known for some time but not commercialised because of two disadvantages that the mordenite zeolite overcomes: the tendency to form hard-to-remove impurities such as ethylbenzene and butylbenzene via disproportionation reactions, and the tendency of the catalyst to deactivate rapidly. A further advantage of the zeolite system over the acid catalysts is the ability to transalkylate the byproduct diisopropylbenzene (DIPB) back into cumene more easily. The optimization variable is the flow rate of the recycled benzene. As a constraint, the outlet reactor temperature is limited at 250°C. The alkylation reactions are exothermic so temperature have to control above 250 °C continuosly, it occurs extra cost. [11]

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3.1.3. 3-DDM DOW PROCESS EQUIPMENT SUMMARY TABLE Table 3. DDM Dow Process Equipment Summary Table

Name

Code

Function

Operational

Operation

temperature

al pressure

(0C)

(atm)

Type

Risk

Precaution *Choosing true zeolit cataliyst

Alkylation reactor

To produce cumene R-1

160-250

25-35

(mordanite) instead of solid

reactor

*hard-to-remove impurities

cataliyst to large excess of benzene

R-2

from DIPB and

(more than 5 : 1 molar ratio) 150

15

Fixed bed

benzene To seperate propan Depropanizer

*nonregenerable and of posing catalyst

benzene To produce cumene

Transalkylation reactor

from propylene and

Fixed bed

C-1

from the feed

-

-

reactor Distillation T:200

12

column

-

-

1,2

Distillation

Higher load to reboiler or condenser

Charge drum is placed after the

B: 34 To seperate benzene from Benzene column

C-2

-

cumene and

column

catalytic reactor and condenser

DIPBTo purificate freshbenzene feed To seperate cumene

Cumene column C-3

from DIPB

Distillation -

1,2

column

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*excessive bottom temperature.

*vacuum distillation column

3.2.Mobil Badger Process

The Mobil–Badger Cumene process consists of a fixed-bed alkylator, a fixed-bed transalkylator and a separation section and Figure 4 is a schematic description of the process with 200,000 Ton /per year Cumene capacity. Fresh

and

the alkylation reactor

recycled

benzene

where

are

the propylene is

combined

with

completely

liquid propylene in reacted.

Recycled

polyisopropylbenzenes (PIPB) are mixed with benzene and sent to the transalkylation unit to produce additional cumene. Trace impurities are removed in the depropanizer column. Byproduct streams consist of LPG (mainly propane contained in the propylene feedstock) and a small residue stream, which can be used as fuel oil. The production of cumene by alkylation of benzene with propylene has, in the past, been carried out commercially over two catalyst systems: solid phosphoric acid (SPA) or aluminum chloride (AlCl3). Both SPA and AlCl3 present severe environmental problems; SPA catalyst is wet, corrosive, and might contain hydrocarbons, while waste AlCl 3 is a corrosive liquor that also might contain hydrocarbons. Both are classified as hazardous wastes. The Mobil/Badger Cumene process uses a new zeolite catalyst developed by Mobil (MCM-22), tested by Badger, and first commercialized in 1996. The Mobil–Badger process produces very pure cumene, 99.97 wt.% at 99.7 wt.% yield. The high cumene purity is primarily attributable to the high monoalkylation selectivity of

the

MCM-22

catalyst.

minimize propyleneoligomerization

This while

catalyst still

is

unique

exhibiting

very

in

its

ability

to

high

activity

for

benzene alkylation. Commercially, the catalyst has demonstrated cycle lengths in excess of 2 years. Ultimate catalyst life is in excess of 5 years.

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The selectivity of the MCM-22 catalyst reduces the size requirements for the fractionation section, and also reduces the coke forming reactions, which tend to shorten the cycle length. A key result of the catalyst’s low oligomerization selectivity is the ability to design for low benzene-to-propylene ratios in the range of 2–4M.Table 4 compares the selectivities and activities of MCM-22 and zeolite beta zeolites in single pass alkylation of benzene with propylene. The zeolite beta catalyst produces significantly more propylene oligomer, but has a slightly lower selectivity for PIPB. Table 4. Comparison of MCM-22 and zeolite beta catalysts for cumene synthesis

Propylene conversiona Benzene:propylene (mole ratio)

MCM-22

Zeolite beta

98.0 3

94.4 3

1.7 84.9 13.4 11.3

9.2 79.1 11.7 10.8

4.7 95.3

21.4 78.6

Total product selectivity (wt%) Propylene oligomers, Cumene PIPB PIPB/cumene (M, %)

Propylene balance, liquid product (wt.%) Propylene oligomers Alkylated aromatic products

Although the conventional catalysts are effective for alkylation, they suffer some important disadvantages. Firstly, they are corrosive which implies that the reactor section of the process must be constructed of special materials. Secondly the use of such catalyst results in wate disposal problems. Although the Mobil-Badger process has the advantages mentioned above, it has suffered the disadvantage of rather rapid catalyst deactivation(weeks) due to coke deposition. This problem has been overcome in later version of the process.Recently a new liquid phase alkylation process based on a very selective zeolit called MCM-22 was developed .The catalyst is reported to be highly active for alkylation but inactive for oligomerization, permitting operation at low benzene:propyene ratios, while achieving the highest yield and product purity. However experience with this process is limited and information rather scarce. [12]

19

3.2.1.Block diagram

Figure 4. Mobil Badger Process Block Diagram R – 1: alkykation, R – 2: transalkylation, C – 1: propane column, C – 2: benzene recycle column, C – 3: cumene column, C – 4: polyispropylbenzenes column. The process is based on ExxonMobil’s proprietary MCM22 catalyst and was jointly de veloped by the ExxonMobil and the Washington Group. The process includes a fixed bed alkylation reactor, a fixed bed transalkylation reactor, anda distillation section. Propylene and benzene are premixed and fed to the alkyla-tion reactor where propylene is completely reacted in the liquid phase. The alkylator effluent flows to the depropanizer where nonreactive propane is recoveredas LPG. The depropanizer bottoms flows to the recycle column where excess benzene is recovered and recycled to the reactors. The crude cumene from the benzene column bottoms flows to the cumene column where high purity cumene product is recovered overhead. The cumene column bottoms is sent to the PIPB column where PIPB is recovered and sent to the transalkylator. In the transalkylator PIPB reacts with benzene to form additional cumene. The transalkylation effulent joins the depropanizer bottoms and flows to the recycle colum.

20

The plant consists of a fixed bed alkylation reactor, fixed bed transalkylation reactor and a distillation section. Liquid propylene and fresh and recycle benzene are premixed before being fed to the alkylation reactor where the propylene is completely reacted. Separately, recycled poly-isopropyl-benzene (PIPB) is pre-mixed with benzene and fed to the transalkylation reactor where the PIPB reacts with the benzene to form additional cumene. [13]

3.2.2. Overall Material Balance Table 5. Overall process material balance after Mobile-Badger [11] Material

MT/MT cumene

Benzene (100 %)

0.653

Propylene (100%)

0.352

Cumene (Product)

1.000

Cumene heavies

0.006

LPG

Variable

.

21

3.2.3.MOBIL BADGER PROCESS EQUIPMENT SUMMARY TABLE Table 6. Mobil Badger Process Equipment Summary Table Operational Name

Code

0

Function

temperature( C)

Operational pressure (atm)

Risk

Precaution

*Low B/P ratio in reactor

*Increase recycle Benzene flow

Fixed bed

feed

to reactor

reactor

*catalyst deactivation isn’t

*choosing very selective and

well so coke deposition *side product is produced

active cataliyst

Fixed bed

in Transalkylator because

*Reduce temp in

benzene

reactor

of high temperature

Transalkylator.

To seperate propan

Distillation

Sudden pressure rising

Pressure relief valve

To produce cumene Alkylation reactor

R-1

from propylene and

200

35

Type

benzene To produce cumene Transalkylation

R-2

from DIPB and

reactor

Depropanizer

Benzene column

C-1

Tin=150

34

column

from

Tin=90

12

Distillation

cumene

and

C-2

DIPBTopurificate

C-3

freshbenzene feed To seperate cumene To

C-4

-

from the feed To seperate benzene

Cumene column DIPB column

-

from DIPB seperate DIPB

from heavy ends

column Distillation Tin=160

1,3

column Distillation

Tin=160

0,4

column

22

3.3.Enichem Process

The Enichem cumene process was announced in 1995 and then commercialized at Enichem’s Porto Torres, Sardinia plant in March 1996. First industrial application dates back to March 1996 when, at Porto Torres site (Sardinia, Italy), a first industrial test-run based on an initial cumene capacity of 70 kt/y was done. In 1997 the new zeolite based technology was extended to 130 kt/y cumene capacity. In 2000, following four years of continuous troublefree test-run operation, the fully proven technology was applied to the revamp of the existing cumene plant for a total of 400 kt/y cumene capacity at Syndial (a subsidiary of Eni SpA) Porto Torres site. Polimeri Europa, a wholly owned subsidiary of the Italian oil company Eni, operates in the business of olefins and aromatics, basic intermediate products, chlorine derivatives, polyethylene, polystyrene and elastomers.[14] Polimeri Europa and Lummus Technology, a CB&I company, offer the Polimeri/Lummus technology

for the production of high purity cumene. The

Polimeri/Lummus cumene process uses Polimeri’s proprietary zeolite catalyst PBE-1, which has been used in commercial operation since the mid 1990s. PBE-1 has a higher selectivity to cumene than other common zeolite catalysts, and is equally effective for alkylation of benzene as well as the transalkylation of polyisopropylbenzenes to cumene. It is noncorrosive, regenerable and environmentally.[15]

23

Table 7. Enichem process Features and Benefits [15] Process Features

Process Benefits  Product yield of 99.7 wt%  High

activity

minimal  Proprietary, non-corrosive PBE-1 zeolite

and

formation

selectivity of

with

by-product

impurities

catalyst

 Typical cumene purity is 99.95% or higher • Extremely tolerant to poisons  Proven run-lengths of up to five years  Low catalyst cost

 Low pressure and low temperature

 All carbon steel construction

operation

 Low investment and plant maintenance costs  Low energy costs  Low operating cost

 No chemicals required  No acidic waste streams and minimal fugitive emissions  Can be designed to process chemical and

 Low environmental impact

refinery grade propylene feedstocks in

 Improves plant economics

addition to polymer grade propylene

3.3.1.Block Diagram

24

Figure 5. Enichem Process of Block Diagram Cumene is made by the alkylation of benzene with propylene, which yields a mixture of alkylated and polyalkylated benzenes. Excess benzene is used so propylene reacts completely. Propylene is injected before each catalyst bed to improve catalyst selectivity and enhance its activity and stability. The mixture of alkylated and polyalkylated benzenes is sent to a distillation train that consists of a benzene column, cumene column and polyisopropylbenzene (PIPB) column. The polyalkylated benzenes recovered in the PIPB column are transalkylated with benzene to produce additional cumene for maximum cumene yield. The alkylation and transalkylation effluents are fed to the benzene column, where the excess benzene is taken as the overhead product for recycle to the reactors. The benzene column bottoms goes to the cumene column, where product cumene (isopropylbenzene) is taken as the overhead product. The cumene column bottoms is sent to the PIPB column, where overhead PIPB is recycled back to the transalkylation reactor. The bottoms of the PIPB column is composed of a small amount of high boilers that can be used as fuel. Propane and other non-condensables contained in the propylene feed pass through the process unreacted and are recovered as propane product or as fuel. The cumene unit has considerable flexibility to meet a variety of local site conditions (i.e., utilities) in an efficient manner.

25

The process operates at a benzene to propylene ratio of 1:1. Cumene yields and selectivities are both greater than 99%. Cumene purity was founded 99.95 wt.%. Enichem’s process uses a modified beta catalyst(PBE-1 zeolite catalyst) and The process is reported to be readily retrofit into existing cumene units. Few additional details about this process have been released.

3.3.2.Overall Material Balance Table 8. Enichem process of overall material balance Material

MT/MT cumene

Benzene (100 %)

0.653

Propylene (100%)

0.352

Cumene (Product)

1.000

Cumene heavies

0.006

LPG

Variable

3.4.CD Tech’s Cumene Process

The CD Tech’s Cumene process 270,000 Ton /per year Cumene capacity. The CD Cumene process, marketed by ABB, produces ultra high purity cumene using a proprietary zeolite Y catalyst that is non-corrosive and environmentally. The CDCumene technology is one of a family of process technologies developed and commercialized by Catalytic Distillation Technologies. An efficient process can be designed for the manufacturing of cumene by the alkylation of benzene by making use of zeolite catalysts available today. Simple adiabatic reactor technology is appropriate, but the operating pressure should be sufficiently high to ensure only liquid - phase reaction. To limit the formation of by products by consecutive polyalkylation a large ratio benzene/propylene is used, which in turn implies large benzene recycle and considerable energy consumption. The energy spent for benzene recycling can be reduced considerably by heat integration, namely by double - effect distillation. In addition, the heat developed by reaction can be advantageously recovered as medium - pressure steam. 26

The performance indices of the conceptual design based on literature data are in agreement with the best technologies. Reactive Distillation (RD) is a combination of reaction and distillation in a single vessel owing to which it enjoys a number of specific advantages over conventional sequential approach of reaction followed by distillation or other separation techniques. Improved selectivity, increased conversion, better heat control, effective utilization of reaction heat, scope for difficult separations and the avoidance of azeotropes are a few of the advantages that reactive distillation offers. The unique catalytic distillation column combines reaction and fractionation in a single unit operation. The alkylation reaction takes place isothermally and at low temperature. Reaction products are continuously removed from the reaction zones by distillation. These factors limit the formation of by-product impurities, enhance product purity and yields, and result in expected reactor run lengts in excess of two years. Low operating temperatures result in lower equipment design and operating pressures, which help to decrease capital investment, improve safety of operations, and minimize fugitive emissions. All waste heat, including the heat of reaction, is recovered for improved energy efficiency. The alkylation reaction is promoted by acid - type catalysts. The synthesis can be performed in gas or liquid phase. Before 1990 gas – phase alkylation processes dominated, but today liquid - phase processes with zeolite catalysts prevail. Recent developments make use of reactive distillation. Propylene is dissolved in a large excess of benzene (more than 5:1 molar ratio) at suffi ciently high pressure that ensures only one liquid phase at the reaction temperature, usually between 160 and 240 ° C.

3.4.1.Block diagram

27

Figure 6. CDTech Process of Block Diagram

Catalysts for the Alkylation of Aromatics Types of zeolites are the most applied like; beta, Y, MCM - 22 and mordenite. These catalysts are characterized by large pore opening necessary for achieving high selectivity. Since industrial catalysts are employed as pellets, the mass - and heat – transfer effects can play an important role. The internal diffusion is often the critical step controlling the overall process rate. Table 8 presents some global yield data, including transalkylation. Zeolite – beta is often mentioned among the best suited for fixed - bed operation, with selectivity in cumene around 90%.

Table 9. Selectivity obtained with different zeolite catalysts in cumene synthesis [8]

Overall selectivity on propylene (%)

Zeolite-beta 99.87

28

Modenite 98.61

MCM-22 98.74

Zeolite-Y 98.30

Other studies prefer MCM - 22 because of better stability against deactivation. As Table 8 shows, the selectivities of zeolite - beta and MCM - 22 are similar in the range of temperature of 180–220° C and benzene/propylene ratios of 3.5 – 7.2. Modified Y - type zeolites were found capable of selectivity over 97% at lower temperature, and are therefore recommended for catalytic distillation. Recent patents show that the new superactive zeolite catalysts are suitable for both alkylation and transalkylation reactions.[8] Table 10. Selectivity and DIPB distribution at different temperature and propylene conversions [8] Catalyst MCM-22

Beta

T(ᵒC)

Xpropylenea

Selectivityb

Iso /n

DIPBs distribution (%)

(%) 76.05

Cumene DIPB Oligo 92.12 7.34 0.32

ratio 1650

Ortho meta

para

180

10

30

60

97.97

90.56

9.03

0.27

830

8

32

60

91.70

90.78

8.84

0.18

790

7

33

60

220

96.28

89.54

9.60

0.11

460

5

38

57

180

76.25

92.16

6.96

0.41

920

6

42

52

220

97.34 89.90

90.76 89.34

8.33 10.07

0.25 0.21

900 720

5 5

44 46

51 49

98.34

88.67

10.58

0.15

460

3

51

46

Process Features 1. Catalytic distillation structures provide efficient vapor liquid contacting, and combine 2. 3. 4. 5. 6.

reaction and fractionation in a single unit operation Proprietary zeolite catalyst Controlled low and constant alkylation temperature. Simple, low pressure operation Improved heat integration and heat recovery Adaptable to processing chemical and refinery grade propylene feed-stocks [16]

Advantages 1.    

High selectivity and lowered by-product formation ; high product purity without drag benzene high product quality (ultra low bromine index) without clay treatment high product yield reduced plot area

29

2. Meets evolving environmental requirements; 

continuous operation



transalkylation capability maximizes yield



Eliminates corrosive acidic effluents and associated disposal problems



lower maintenance costs 3. Extends reactor run lengths (over one year without regeneration) ;



sustains high conversion and selectivity 4. Decreases capital investment sustains high conversion and selectivity;  Improves safety and operability  applicable to conversion of existing cumene plants 5. Reduces utilities and operating costs;  recovers all waste heat and heat of reaction 6. Improves economics;  plants can be custom  designed to process specific feedstocks, including the less expensive feedstocks [16]

DESIGN BASIS Capacity, (kmol/h), 110 Alkylation reactor type catalytic distillation reactor Catalyst, Zeolite-Y Catalyst regeneration frequency, years 2 Catalyst life, years 6 Temperature, °C (top-bottom) 198-249 30

Pressure, bar 14 B/P feed ratio, mole/mole 1.64 Conversion, % : Propylene %100 Benzene % 55 Transalkylation reactor type: Single catalyst bed Catalyst Zeolite-Y Catalyst life, years 6 Temperature, °C 140-150 Benzene/DIPB feed ratio, mole/mole 5.2 Conversion of DIPB, %50 Overall yields, mol% Seperations Units: 

Benzene column: Type

: Distillation column

Purity of Top Product

: %100 Benzene

Purity of Bottom Product : %78.5 Cumene Operational Conditions

: Tin: 1030C

Tbottom :124 0C

Operational pressure: 0.3 bar    Cumene column: Type Purity of Top Product Purity of Bottom Product

: Distillation column : %100 Cumene : %100 DIPB , 31

Ttop :45

: Tin : 124 0C Tbottom: 172 0C

Operational Conditions Operational pressure

Ttop: 1100C

: 0.3 bar

3.4.2.Overall Material Balance Reaction’s in the Alkylation Reactor : C3H6+C6H6

C6H5 - C3H7 (Cumene,IPB)

C3H6 + C6H5 - C3H7

C3H7 – C6H4 - C3H7 (diisopropylbenzene;DIPB; C6H4[CH(CH3)2])

Reaction’s in the Trans-Alkylation Reactor : C3H7 – C6H4 - C3H7+C6H6

2(C6H5 - C3H7 )

Conversion of Propylene in Alkylation reactor Reactor Conversion for Transalkylation reactor Capacity: 13234 ton/year product

SYSTEM = OVERALL SYSTEM

Figure : Overall System Boundary 32

: %100 : %50

Basis: 110 kmole/ h Cumene is producing in Alkylation and Transalkylation reactors. Degrees of Freedom +3 unknowns (m1, m2, m3) -1 Equations (m1+m2=m3) -1 Basis (110 kmol/h Cumene produced) Degrees of Freedom = +1 so problem is not soluble. Calculations are made for alkylation and transalkylation reactors with Cumene production rate basis. SYSTEM=ALKYLATION REACTOR

In alkylation reactor there are two reactions. One is main reaction and other is side reaction. C3H6+C6H6

C6H5 - C3H7 (Cumene,IPB)

C3H6 + C6H5 - C3H7

C3H7 – C6H4 - C3H7 (diisopropylbenzene;DIPB; C6H4[CH(CH3)2])

We know that selectivity of cumene per DIPB 8:1. So when x mole DIPB produced, 8*x cumene produced in main reaction.

SYSTEM=TRANSALKYLATION REACTOR

33

In transalkylation reactor, cumene produce with DIPB which is coming from alkylation reactor. C3H7 – C6H4 - C3H7+C6H6

2(C6H5 - C3H7 )

For x mole DIBP coming from alkylation reactor, x mole Cumene will be produced. Cumene Balance For Overall System  Selectivity is 8:1 of cumene to DIPB.  Conversion of propylene is 100 % in alkylation reactor.  For x kmole / h DIPB formed in Alkylation reactor, formed cumene will be 8*x. Some Cumene is producing in transalkylation reactor with 3rd reaction and the conversion of DIPB is %50 and also molar ratio of benzene to DIPB 5:1 in transalkylation reactor. Total Producing Cumene = 110 kmol / h= Producing In Alkylation Reactor + Producing In Transalkylation Reactor 110 kmol/h = 8*x + 2*x x=11 kmole / h DIPB 2x DIPB is going to Transalkylation reactor: 2x= 22,22 kmol/h  Produced Cumene In Transalkylation Reactor =2*22,2*0,5 = 22,2 kmole /h Cumene  Produced Cumene In Alkylation Reactor= 8*x = 8*11= 88 kmole/h Cumene

Reactants’ Balances For Alkylation Reactor

34

      

Propylene required for Cumene is 9*x. Propylene required for DIPB is x. Conversion of Propylene is %100 in Alkylation Reactor. Total propylene required= 10*x=10*11=110 kmol/h Benzene required for Cumene is equal to produced Cumene in main reaction. Required Benzene = 110 kmol/h %60 excess benzene so total benzene: 110/0,6 = 180 kmol/h

Inlets of Alkylation Reactor:  Propylene : 110 kmole/h  Benzene : 180 kmole/h

Outlets of Alkylation Reactor:  Benzene  DIPB  Cumene

:180 – [9*11] = 81 kmole/h :11 kmole / h :8*11 = 88 kmole / h

These outlets are sending to Benzene Column.

SYSTEM=BENZENE COLUMN

Inlets of Benzene Column: From Outlet of Alkylation Reactor: 35

 Benzene  Cumene  DIPB

:81,37 kmole / h :88 kmole / h :11 kmole / h

From Outlet of Transalklyation Reactor:  Benzene  Cumene  DIPB

: 104,86 kmole/h : 22,11 kmole/h : 11,23 kmole/h

Outlets Of Benzene Column: Top:  Benzene : = 186 kmol / h Bottom:  Cumene : 110 kmole/h  DIPB : 22,22 kmole/h The bottom stream of benzene column is going to cumene column. SYSTEM=CUMENE COLUMN

Inlet of the Cumene Column:  Cumene : 110,11 kmole/h  DIPB : 22,22 kmole/h

36

Outlet of the Cumene Column: Top:  Cumene: 110,11 kmole/h Bottom:  DIPB

: 22,22 kmole /h

The bottom stream of the cumene column which includes DIPB, is going to Transalkylation reactor. Transalkylation Reactor Inlets of Transalkylation Reactor: Outlet of the Cumene column is going to Transalkylation Reactor. Molar ratio of Benzene to DIPB to send Transalkylation Reactor is about 5,2. Outlet of the Benzene column’s top feed merge with fresh benzene then split for going to Alkylation reactor and Transalkylation reactor. DIPB: 22,22 kmole/h Benzene: 22,22*5,2= 115,86 kmole/h Dividing Ratio Alkylation Reactor To Transalkylation Reactor:

æ ö Benzen to Transalkylation Reactor 115,86 ÷ =ç *100 = %0,39 ÷ ç RecoveredBenzene+FreshBenzene ç è296, 23 ÷ ø

37

Divider sending %39 of recyled benzene to transalkylation reactor which is 115,86 kmole/h Benzene. So the other part of recyled benzene, %61 is being sended to alkylation reactor. 296*0,61=180,4 kmole / h

Overall System With Calculated Values

Inputs: Propylene (Pure)

n1 = 110 kmole/h,

m1=4628,8 kg/h

Benzene (Pure)

n2 = 110,2 kmole/h,

m2=8605 kg/h

Outputs: Cumene (%99,9 Purity)

n4 = 110,1 kmol/h

38

m4=13234 kg/h

Table 11. Overall Material Balance MT/MT Cumene Product Feeds Propylene (100% basis)

0.352

Benzene (100% basis)

0.652

Products Cumene

1.00

Heavy residue

0.004

Propane

*

*Varies with purity of propylene feed

Table 12. Cumene Product Quality Purity

99.97 wt %

Specific gravity 20º / 20º C

0.864

Distillation range Including 152.5 º C Bromine index

< 1º C 700° F

Flammable limits in Air, % by volume

Hazard Class

Lower: 1.55

Upper: 9.60

ID No. UN 1075

Extinguishing Media:

Dry chemical, Foam or Carbon dioxide

2.1 Flammable Gas

Thermal Effects At Distillation Column A critical issue in reactor design is exploiting at best the high exothermicity of the alkylation reaction. Note that the thermal effect corresponds roughly to the evaporation of 3.67 moles benzene. A measure of exothermicity is the adiabatic temperature rise illustrated in Figure 8 as a function of the molar ratio benzene/propylene with the inlet temperature as a parameter.

Figure 9. Molar ratio benzene/propene – adiabatic rise Higher dilution with benzene can make it fall signifi cantly, from 120 ° C to less than 60 ° C; the inlet temperature plays a minor role. On the other hand, higher benzene/propylene ratio gives better selectivity, but increases the cost of separations. As a result, the ratio 54

benzene/propylene is a key optimization variable. Other measures for better temperature control could be employed, such as a series of reactors with intermediate cooling, or injection of a cold inert. The simulation shows that these methods have no signifi cant effects on the overall yields, although they may offer a better protection of the catalyst in long – time operation.

Chemical Equilibrium At Distillation Column

Figure 10. Molar ratio benzene/propene – selectivity IPB Chemical equilibrium indicates that more than 99% conversion of propylene may be achieved for benzene/propylene ratios larger than three. However, the selectivity remains a problem. Figure shows the variation of selectivity defined as cumene formed per mole of propylene, when only di - isopropylbenzene is the by product. Increasing the ratio from 3 to 9 moles gives a significant selectivity improvement from 82% to over 92%. From this point of view the performance of beta - zeolites reported in Table 6.6 seems to achieve its thermodynamic limit. Higher temperature is benefi cial for getting higher yield, but the effect is limited.

55