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Cleavage Reactor Section

Cleavage Reactor SectionMohamed Ali Rauff (A0069475N)

IntroductionDetails of design of cleavage unit of Phenol and Acetone producing plantCleavage reaction: Breakdown of cumene hydroperoxide (CHP) into phenol and acetoneHighly exothermic hence most challenging and vital part of entire plant Proposed design: 1 CSTR: 78.5 m3 at 60oC at 1 atm1 PFR: 4.98 m3 at 120oC at 6 bar of pressureIntroductionKinetics from Chen et al and V. Zakoshansky Input contents contained 80wt% CHP Effluent stream from PFR would have Phenol: Acetone: Cumene ratio of 1.62:1:0.2 (mass)All CHP reacted before sent for purificationAcid concentration at 0.1wt% of CSTR input streamCosting calculations based on 3rd edition of Product and Process Design Principles by Seider W.D., J.D. Seader and D.R. LewinBare module cost estimated as S$ 2,746,100.00 and purchase cost as S$ 1,572,000.00General Design SettingsConversion of 60% of CHP fixed in CSTR for good control of heat released, PFR to decompose remain CHPPFR Reactions: All CSTR reactions with decomposition of DCPReactions assumed to take place simultaneously and in reactor only Differences in SimulationAbsence of kinetic data of formation and decomposition of dicumyl peroxide (DCP)Complex kinetics of DCP breakdown was simplified 40% of DMPC from cumene oxidation converted to DCP prior input to cleavage reactor CSTRHypothetical component: Sodium Phenate (NaPh) for neutralisation of H2SO4 Simulated neutraliser gave endothermic value but should be exothermicSimulation with Sodium Hydroxide (NaOH) for realisable energy producedOptions Available3 CSTRs and 1 PFR in seriesCSTRs: 50oC at 1 atmospheric pressure and PFR: 110oC at 5 barAcid concentration as 150ppm, similar to ILLA operating conditionsVolumes of CSTR: 650, 1100 and 1450 m3 and PFR: 312 m3Too large hence high cost and maintenanceAgitation in large CSTR would be high safety concernOptions Available (Recommended)1 CSTR at 60oC ,pressure of 1 atm and 1 PFR at 120oC of 6 bar in series0.1wt% of acid catalyst for safetyConfiguration proposed by Sifniades et al. (US Patent 4,358,618)Isothermal gives high conversion per unit energy suppliedSimpler to operate isothermal than adiabatic reactorAMS dimers and cumylphenol generated reduced by 2 stage reactionCSTR at 78.5 m3 and PFR at 4.98 m3 More economicalRecommended ProcessCSTR (1st Stage)Isothermal since adiabatic produces outlet temperature of b.p. higher than of acetonePFR could not be used as size would be too large for heat controlling PFR (2nd Stage)120oC and pressurised to 6 bar Heated to maximise dehydration of DMPC to AMS High pressure to ensure acetone does not evaporateRecommended Process - PFD

Meets The RequirementsComplete decomposition of CHPMaximized production of AMSUtilizes NaPh produced in downstream for neutralization to produce more phenolEnd Yield: 582 kmol/h of cumene to 472 kmol/h of phenol and 474 kmol/h of acetoneRequired: 350,000 tonnes of phenol/ year at product purity of 99.2% Produced: 355 512 tonnes/yrCSTR Features

CSTR Features1 Pitched blade impeller with 6 BladesFlat blades set at 45 angles, for simultaneous axial and radial flow Height above floor = 1.23 mLength of Blade = 0.31 mWidth of Blade = 0.25 mImpeller Speed = 77.6 rpmAssuming 85 % efficiency, Actual Power = 17.9 hp

Mechanical Design of PFRTotal Volume as 4.98m3 at 6.6 barLength of 8.00 m and diameter of 0.89 mIdeal PFR has turbulent flow for mixing in radial direction and reduce axial mixingRe = 105516, flow is turbulent hence baffles not requiredMaterial of construction: SS 316 since contents are same as CSTRThickness of PFR with corrosion allowance is 3.61 mmOptimisation of CSTRAcid content of 0.1wt% gives lowest volumeCurves approach plateau after 60% of CHP generallyBigger size gives slight increase in conversionMost economical size of 78.5m3Optimisation of CSTRLowest temperature profile requires volume higher than 200m3 for 60% CHP conversion Highest temperature gives least reactor volume but unsuitable as acetone vapour formsMost suitable is 60oC Optimisation of PFRMain reactions: Decomposition of CHP and DCPSized according to length by Adjust moduleAll peroxides exhaust at 8mIterations gave PFR volume of 4.98m3

Conversion Ratio OptimisationPercentage of CHP conversion was varied for CSTR and PFRCHP conversion has to take place mostly at CSTRDespite decrease in PFR size, increase in CSTR volume is drasticMore capital invested in CSTR volume increase than savings from PFR volume decreaseCHP conversion for CSTR was fixed as 60%CSTR Conversion (%)CSTR VolumePFRConversion (%)PFR Volume0 to 6077.4960 to 1004.970 to 6599.3935 to 1004.430 to 70131.230 to 1003.67Double Pipe Heat ExchangerMost economical choice, simple to operate and maintainUo as 750 Wm-2K-1 (Richard Coulson)Cooling water in @ 25C and out @40CAssuming a bend of 12ftConclusion1 CSTR of size 78.5 m3 at 60oC at 1 atm Bare Module: SGD 527 000.00Purchase: SGD 186 000.001 PFR of size 4.98 m3 at 120oC at 6 bar Bare Module: SGD 182 000.08Purchase: SGD 88 000.00Upon optimisation, total bare module cost was SGD 2,746,000.00.