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Reactive distillation
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  International Journal of ChemTech ResearchCODEN( USA): IJCRGG ISSN : 0974-4290Vol.5, No.2, pp1024-1029, April-June2013 ICGSEE-2013[14 th  – 16 th  March 2013]International Conference on Global Scenario in Environment and Energy Simulation Of Reactive Distillation Column PriyankaGautam 1 ,Piyush Pratap Singh 1 , Animesh Mishra 1 ,AbhishekSingh 2 ,Shakti Nath Das 1 *, S.Suresh 1 * 1 Department of Chemical Engineering, Maulana Azad National Institute of Technology,Bhopal-462 051,India. 2 Department of Chemical Engineering,J.M.I.T,Radaur,India. * Corres., Abstract: Reactive distillation processes couple chemical reactions and physical separations into a single unitoperation. The ethyl acetate production by esterification reaction is equilibrium limited and is suitable to becarried out in a distillation column. In the present work, a reactive distillation column for the production of ethylacetate is simulated using Aspen Plus.The component compositions and temperature at each stage of thecolumn are predicted. The effect of feed stream(s) arrangement on the simulation results is presented. Keywords: Reactive distillation; ethyl acetate; Aspen Plus; compositions; simulation. Introduction Distillation is one of the most important separation processes in chemical industry. All around the globe, inalmost all the chemical industries a significant fraction of capital investment and operating cost involvesdistillation. As a result any kind of improvement of distillation operation can be very beneficial economically.Reactive distillation (RD) is one major step in the history of distillation in achieving these goals. Reactivedistillation processes couple chemical reactions and physical separations into a single unit operation. Theseprocesses as a whole are not a new concept as the first patent dates back to the 1920s. While the concept existedmuch earlier, the first real-world implementation of reactive distillation took place in 1980s. The relatively largeamount of new interest in reactive distillation is due to the numerous advantages it has over ordinary distillation.A distillation column can be used advantageously as a reactor for systems in which chemical reactions occur attemperatures and pressures suitable to the distillation of components.Several organic reactions are carried out ina liquid phaseusing a homogeneous catalyst. These reactionscan be easily carried out in a boiling phase usinganappropriate distillation column. Inequilibrium limited reaction the continual removal of products from thereaction mixture via distillationfavorably alters theequilibrium and minimizes undesirable chain and sidereactions. Conversely, difficult phase separations ofclosely boiling mixtures or azeotropes become feasibleif one of the components can be transformed viaa chemical reaction.  Shakti Nath Das  et al   /Int.J.ChemTech Res.2013,5(2)  1025 The Computational methods used for reactive distillation are extensions to the algorithms developed for thesolution of the equations for conventional distillation. The first attempts to model reactive distillation were byusing the simplified plate-to-plate calculations. Rigorous mathematical models for Computer simulation was notdeveloped until the 1970's. Since that time, various techniques have been developed that allow the rigoroussolution of the equations. These techniques include equation partitioning methods, and Newton-Raphson basedmethods. A brief description of computer based tray-to-tray calculations for the RD of ethylene oxide and waterwas givenin 1 . Tray-to-tray calculations and parametric studies for the simulation andoptimization of an RDcolumn for trioxane synthesis are describedin 2 . The bubble-point method 3  was extendedin 4  to be able to dealwith chemical react ions. The θ method developed for conventional distillation columns by Holland and h ismany collaborators 5  was extended to RD operations and named the multi- θ - η method 6 .More recent papers inthis field 7,8  use the simultaneous solution of all the independent equations using Newton's method or a variant of this method. Reactive distillation column for the production of ethyl acetate usingsimultaneous solution afterlinearization and inside-outside method, a tearing algorithm is compared in 9 using a 13 tray ethyl acetateproducing column. The convergence is shown to be faster with inside-outside algorithm.The inside-out algorithmis described in 10 known as RADFRAC that is part of the commercial program AspenPlus. Inside-out methods involve the introductionof new parameters into the model equations to be used asprimary iteration variables.In thisworkethyl acetate production through reactive distillation is simulated usingAspenPlus. MODEL Description In this paper, an equilibrium model isused for the simulation of reactive distillation of ethyl acetate production(C 2 H 5 COOCH 3 ),using acetic acid (CH 3 COOH) and ethanol (C 2 H 5 OH),ina plate column.The reaction iscarried out using a homogeneous catalyst.The reaction kinetics data is taken from 9 . A thirteen stage column example is taken from C.D. Holland’s book  5 .A constant-pressure adiabatic column, a total condenser, and apartial reboiler are assumed. The liquid feed enters the column on stage 6.Stages are numbered from topcondenser being stage 1 and reboiler stage 13. RADFRAC representation of the column is shown in Fig. 1. Figure 1. Radfracrepresentation of RD column The specifications of the RD columnand the other parametersused for simulation study are given in Table 1.  Shakti Nath Das  et al   /Int.J.ChemTech Res.2013,5(2)  1026 Table 1.Columnspecificationsand other parameters used for simulations Feed Temperature340 KPressure1 atmTotal Stages13(including Reboiler & condenser)Feed Stage6Distillate Rate0. 208mol/sHoldup1 l for reboiler, 0.3 l for each stagesAcetic Acid0.4962Ethanol0.4808Water0.023Component molfractionsEthyl acetate0.0Property methodUNIFAC-HOCReactionCH 3 COOH+C 2 H 5 OH  C 2 H 5 COOCH 3 +H 2 O Results And Discussion The simulations are carried out using Aspen Plus.Reflux ratioof 10 was selected as optimum as beyond thisvalue the increased reflux had little effect on ethyl acetate purity in the distillate.All further simulations weredone using a reflux ratio equal to10.Figs. 3, 4, and 5show the results ofcomponent concentration profiles,temperatureand ethyl acetate generation rateat each stage. The resultscompare well with the results reportedin 1 .    S   t  a  g  e  n  u  m   b  e  r Component mole fraction    1 .   0   6 .   0   1   1 .   0 Acetic acidEthyl acetateEthanolWater  Figure 3. Predicted componentcompositionprofiles Block RADFRAC: Temperature Profile    S   t  a  g  e  n  u  m   b  e  r Temperature (deg C)    1 .   0   6 .   0   1   1 .   0 C Figure 4.PredictedTemperature Profile  Shakti Nath Das  et al   /Int.J.ChemTech Res.2013,5(2)  1027 Stage number     E   t   h  y   l  a  c  e   t  a   t  e  m  o   l  e  -   f   l  o  w    0 .   0   2 .  e  -   0   0   4   4 .  e  -   0   0   4 Component generation ethyl acetate Figure 5. Ethyl acetate generation rateT-xy variation:
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