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SupercriticalFluidScienceandTechnology SeriesEditor– ErdoganKiran Vol.1 SupercriticalFluidsandOrganometallicCompounds:FromRecovery ofTraceMetalstoSynthesisofNanostructuredMaterials. ByCanErkey Vol.2 High-PressureFluidPhaseEquilibria:PhenomenologyandComputation. ByUlrichK.DeitersandThomasKraska Elsevier Radarweg29,POBox211,1000AEAmsterdam,TheNetherlands TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UK Copyright©2013ElsevierB.V.Allrightsreserved Nopartofthispublicationmaybereproduced,storedinaretrievalsystem ortransmittedinanyformorbyanymeanselectronic,mechanical,photocopying, recordingorotherwisewithoutthepriorwrittenpermissionofthepublisher PermissionsmaybesoughtdirectlyfromElsevier’sScience&TechnologyRights DepartmentinOxford,UK:phone(+44)(0)1865843830;fax(+44)(0)1865853333; email:permissions@elsevier.com.Alternativelyyoucansubmityourrequestonlineby visitingtheElsevierwebsiteathttp://elsevier.com/locate/permissions,andselecting ObtainingpermissiontouseElseviermaterial Notice Noresponsibilityisassumedbythepublisherforanyinjuryand/ordamagetopersons orpropertyasamatterofproductsliability,negligenceorotherwise,orfromanyuse oroperationofanymethods,products,instructionsorideascontainedinthematerial herein.Becauseofrapidadvancesinthemedicalsciences,inparticular,independent verificationofdiagnosesanddrugdosagesshouldbemade BritishLibraryCataloguing-in-PublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary LibraryofCongressCataloging-in-PublicationData AcatalogrecordforthisbookisavailablefromtheLibraryofCongress ISBN:978-0-444-56364-4 ISSN:2212-0505 ForinformationonallElsevierpublications visitourwebsiteatwww.store.elsevier.com PrintedandboundinGreatBritain 13 14 15 16 17 10 9 8 7 6 5 4 3 2 1 Foreword It is with pleasure that I introduce the third volume in the Elsevier Book Series on Supercritical Fluid Science and Technology, Phase Equilibrium Engineering, which has been authored by Drs. Esteban Brignole and Selva Pereda from Universidad National del Sur, Argentina, with one chapter also contributed by Drs. Martin Cismondi and Marcelo S. Zabaloy from Universi- dad National de Co´rdoba and Universidad National del Sur, Argentina, respectively. They are all well-recognized names in the supercritical fluids and phase equilibria community. The book reflects and benefits from their many years of accumulated knowledge and practical expertise. Phaseequilibriumisattheheartofchemicalprocesses,andphaseequilib- rium at high pressures is a central theme in any application involving super- critical fluids. The topic becomes even more relevant when systems under consideration involve chemical transformations along a reaction coordinate whichcontinuallyalterthecompositionalmakeupandtherebyalterthephase equilibrium conditions. This book starts out with a clear statement of the significance of phase equilibrium in process development where there is a critical need to fill the gap between reaction and separation stages by designing and controlling thephaseconditionsthatareessentialforthesuccessoftheprocess.Thebook emphasizes the importance and the need for effective information flow along thepathwaysconnectingthechemicalplantorprocesstothelaboratory,tothe thermodynamics and phase equilibria, and to modeling and simulations. This four-node grid and their interplay form the essence of Phase Equilibrium Engineering. Toprovideapedagogicaldevelopmentoftherelevantengineeringconcepts, theauthorsstartinChapter2withabriefreviewofintermolecularforces(attrac- tiveandrepulsive)andmolecularinteractions(dispersive,polar,electrostatic, induceddipole)thatareimportantinphaseequilibriaandseparationprocesses. Chapter 3 provides the background on thermodynamics of phase equilibrium andreviewsthephasediagramsforpuresubstancesandbinaryfluidmixtures within the framework of the van Konynenburg and Scott classification of the differenttypesofphasebehavior.Theauthorsprovideaclearandelegantgraph- ical description of the changes in the binary mixture phase diagrams and the behaviorofthecriticallines fromTypeItoTypeVIwith changesinthesize of the molecules and the nature of the molecular interactions and the energy asymmetriesencountered.Thischapterfurtherprovidesaclassificationforter- narymixturephasediagramsthatarebasedonthepartialmiscibilityinone,two, xi xii Foreword orthreeofthebinarypairs,whicharegraphicallydescribedinGibb’striangles. Multicomponentsystemsarealsodiscussedintermsofpseudocomponentsthat areusedtorepresentsimilarmolecules. Chapter 4 is devoted to thermodynamic models and provides guidelines for selecting the appropriate model from among the various options, ranging from cubic equations of state to SAFT (Statistical Associating Fluid Theory) for different scenarios which are accomplished by using real case studies for separations of different levels of complexity. A comprehensive treatment of a methodology for general phase equilibrium calculations and generation of phase diagrams is provided in Chapter 5. Chapter6shiftsthefocustoengineeringandprovidesapracticalperspective on how the fundamental thermodynamics and phase equilibrium calculations andpredictionsareusedinaddressingcomplexseparationprocessesusingsev- eral case studies such as the supercritical biodiesel production process. These arecontinuedinChapter7bydemonstratinghowphaseequilibriumengineering comesintoplayindistillationprocessesbyanelegantdescriptionthatmakesthe connections to the Type I to Type VI phase descriptions. The ethylene plant recoverysectionisusedasacasestudy.InChapter8,discussionsareextended to azeotropic mixtures and to the synthesis of solvents by computer-aided molecular design (MOLDES) to break up the azeotropes. As case studies, solvent design for recovery of aromatic fractions of reforming naphtha and high-pressure azeotropic separation of ethaneþCO mixtures by extractive 2 distillationusingn-butaneassolventarepresented. Chapter9isdevotedtogreenprocessesandhigh-pressuresupercriticalfluid solvents. Solvent tuning for systems displaying Type V (propaneþvegetable oil) and Type III (carbon dioxideþnatural oil) phase behavior are discussed indetail.Chapter10continuesthediscussionsontheuseofsupercriticalfluids in high-pressure fractionation and extraction of natural oils using orange oil deterpenation as a case study. Chapter 11 is devoted to reactive systems and supercriticalreactors,andthephasebehaviorofreactivemixturesandsolvents. Solvent selection strategies are discussed according to the reaction pathway using case studies such as selective hydrogenation of fatty acid methyl esters or hydrogenation of vegetable oils. Feasible or unfeasible operational regions arediscussedintermsoftheprevailingphasediagrams.Finally,Chapter12dis- cusses how phase equilibrium engineering is used in the conceptual process designusingproductionofbiodieselviatransesterificationofvegetableoilwith methanolandalcoholextractionanddehydrationasexamples. I trust you will find this volume with its application-oriented engineering approach to be of great value and interest. Erdogan Kiran Series Editor Blacksburg, Virginia December 2012 Preface Phase design engineering has valuable applications in a variety of chemical processes as well as in many other fields such as metallurgy, geology, clima- tology,materialsdesign,andoilreservoirengineering,tonameonlyafew.In this book, we explore the phase design of fluid systems and we apply it to a number of separation processes and chemical reactors. The design of the phase scenario that meets the process needs is what we have called a Phase Equilibrium Engineering (PEE) problem. We first used this terminology in a paper titled “Phase Equilibrium Engineering of Super- critical Reactors” published in 2002.1 This discipline combines methods of phase equilibrium thermodynamics with process requirements in order to obtain desired phase scenarios. The challenges posed by the phase design of a reactor that works under homogeneous conditions have all the elements of a chemical engineering design problem. Indeed, the solvent properties of supercritical fluids, highly dependent on pressure, temperature, and composi- tion, call for a systematic methodology for the design of the phase condition. ThedevelopmentofastrategyforPEEstartswiththeanalysisofthemix- ture components and their intermolecular forces. This volume thus begins with an introduction to the classification of industrial separation problems and explores the relationship between molecular interactions and separation technologies. The first part of the book also assesses the effect of molecular interactions on the general phase behavior and on the classification of binary and multicomponent mixtures. Thethermodynamicmodelingofphaseequilibriaisreviewedstartingwith idealmixturesandfollowingwithmodelsformixturesofincreasingdegreeof nonideality. The most popular models are presented and a strategy of model selection is discussed, taking into account the class of mixtures and their molecular interactions. The classification of molecules, separation processes, andthermodynamicmodelsconfirmsthatthemolecularnatureofthemixture is the key to determine an adequate thermodynamic model and a suitable technology. The above discussion is followed by the presentation of the GPEC pro- gram, a tool that proves useful to explore the effect of model parameters on thetopologicalphasebehaviorofbinarymixtures.TheGPECprogramisable to automatically compute the general phase diagrams of univariant lines of binary mixtures for the different types of phase behavior. 1. S.Pereda,S.B.Bottini,E.Brignole,Am.Inst.Chem.Eng.J.48(2002)2635–2645. xiii xiv Preface In the second part of the book, the principles of PEE are developed through the analysis of a series of case studies that look into the separation of heavy aromatic mixtures, the cryogenic processing of natural gas, and the separation of biodiesel mixtures obtained by supercritical alcoholysis. The useofmaterialandenergybalances,combinedwiththemethodologiesdevel- opedinthe firstpartofthe book, leadtothe formulationofan efficient strat- egy for phase design. The principles of PEE are applied to the tuning of thermodynamic models and to the analysis of thermodynamic sensitivity in thecontextoffractionaldistillationofsinglecolumnsandfractionationtrains. Thereafter,weexaminethequestionofsolvent selection forthe separation of highly nonideal mixtures as well as the computer-aided molecular design of solvents for liquid extraction and extractive distillation. Finally,westudythephasedesignofbothsupercriticalprocessingofnatural products (extraction and fractionation) and of supercritical reactors. In these two cases, the selection of solvents and the identification of optimal operating conditions are carried out while taking into account green chemistryprinciples for sustainable development. These principles call for the use of new reactants andcatalystsinordertoachievechemicalsynthesisthatresultsinimprovedatom efficiency,higheryieldsandselectivities,andsaferandenvironmentallyfriendly solvents.Thisdiscussionincludestwomorecasestudieswherethephasedesign leadstothedevelopmentofnewtechnologiesforbiofuelsproduction. PEE is thus the road that takes us in a systematic way from the molecular level of the mixture to the art of process synthesis, through (i) the process goals, (ii) thermodynamic modeling, (iii) algorithms for phase equilibrium calculations,(iv)phasescenarioandtechnologyselection,(v)sensitivityanal- ysis, and (vi) conceptual process design. Finally, this book highlights the fact that the answer to a successful phase design problem lies in the nature of the mixture we are working with. Thecasestudiespresentedinthisbookarebasedonthepersonalexperiences oftheauthorsandofmanyothercolleagues.Wewouldliketoparticularlythank andacknowledgethecontributionsofSusanaBottini,SoledadD´ıaz,Guillermo Mabe,GloriaFoco,PabloHegel,SusanaEspinosa,AlbertoArcodaci,Hernan- Gros, Ticiana Fornari, Marta Lacunza, Alberto Bandoni, Rube´n Debeistegui, Marcelo Zabaloy, Martin Cismondi, Olga Ferreira, Laura Rovetto, Nicola´s Gan˜an,Francisco Sa´nchez, Pedro Valle,andAlexisVe´lez.Our recognitionis alsoextendedtoCorPeters,PeterRasmussen,andthelateLilianaUrlic,Noemi Petracci,andAageFredenslund.Mostimportantly,thisbookwouldneverhave been possible without the encouragement received from the Editor of this Series,Prof.ErdoganKiran.Wethankhimdeeplynotonlyforsupportingthis bookprojectbutalsoforhisinsightfulcommentsandinvaluableeditinghelp. Esteban Brignole Selva Pereda Bah´ıa Blanca, Argentina December, 2012 Chapter 1 Phase Equilibrium and Process Development With this volume, we aim to fill the gap between the books on reactors and separations process design, and the chemical engineering thermodynamics. Ourgoalistochangethefocusfromtheuseofthermodynamicsrelationships to compute phase equilibria to the design and control of the phase conditions that a process needs. In this way, we can say that we put phase equilibrium thermodynamics to work. Phase equilibrium from a theoretical and experi- mental point of view belongs to the realm of thermodynamics. The ties to the fundamental laws of thermodynamics are so strong that the teaching of phase equilibria emphasizes more the relationships between the thermody- namicvariablesofeachphaseinequilibriumthanitsengineeringapplications. The main goal of phase equilibrium engineering is the design of the sys- temconditionstoachievethedesiredphaseequilibriumscenariothatthepro- cess at hand requires. The mixture under consideration and the process to be accomplished illuminate the search for the thermodynamic and process vari- ables that give the required phase conditions. The synthesis of new processes basedonthephasebehaviorisalsodiscussedinthisbook.Dealingwiththese types of problems, the engineer could make use of several design variables: pressureandtemperature,feedcomposition,entrainers,solvents,supercritical condition, etc. to modify the phase scenario. 1.1 THE WORLD OF PHASE EQUILIBRIA IN CHEMICAL PROCESSES The world of applied phase equilibrium thermodynamics has four cardinal points:(1)thechemicalplantorprocess,(2)thelaboratory,(3)thethermody- namicmodelingofphaseequilibria,and(4)thesimulator.Howallthesecom- ponents can be focused and tuned in harmony to get the better design or operation is the ultimate goal of phase equilibrium engineering. Figure1.1illustratestheworldofphaseequilibriumandtheflowofinfor- mation between the main players and how each pair defines different realms. Theexchangeofinformationbetweenthechemicalplantandthelaboratoryis commonplace, as well as the interaction between the thermodynamic SupercriticalFluidScienceandTechnology,Vol.3.http://dx.doi.org/10.1016/B978-0-444-56364-4.00001-7 ©2013ElsevierB.V.Allrightsreserved. 1 2 PhaseEquilibriumEngineering Real world Chemical plant Laboratory P, T, z Data Industry Test plant data Phase equilibrium P, T, y, x Data Academy world Model and parameters Simulator Thermo modeling Modeling FIGURE1.1 Phaseequilibriumworlds:industryandacademyintherealandengineeringworld. modelingandthelab;however,theinformationonthechemicalplantprocess is seldom used in the modeling of phase equilibria. The parameterization of the thermodynamic models for phase equilibria is usually based on experi- mental binary information. These models and their parameters are available in the modern process simulators. On the other hand, the process simulator isnormallyusedintheindustrialplantwithoutpropertuningofthethermody- namic models to the process needs. In the industrial world, the virtual plant (the simulator) and the real process or chemical plant coexists, and often rather crude assumptions are made to match the simulator results with the plant data which could lead to serious errors in parameter estimation of plant units,revampingprojects,processoptimization,andnewdesigns.Goingback to Fig. 1.1, if we keep the game only on the sides, it will be a boring match andourmain “goal” willnotbeachieved. Onthe contrary,if the information flows from the plant or the actual process to the other players, that also exchangeinformationamongthem,veryfruitfulresultsinthedesignandopti- mizationoftheprocesswillbeobtained.Thedevelopmentofmodernprocess simulators with a large collection of thermodynamic models and parameters makes more critical the wise use of information from the real system to get the most from the process simulators, and to avoid critical errors in design, operation, and plant parameters estimation. 1.2 THERMODYNAMIC MODELING IN PROCESS DEVELOPMENT Theneedofinformationonphysicochemicalpropertiesofpurecompoundsand their mixtures isalways present inthe synthesis,design,simulation, debottle- necking,control,andoptimizationofchemicalplants.Fromthepointofview ofthemodernchemicalindustryandtheirsustainabledevelopment,theproper- tiesassociatedwiththeequilibriumbetweenphases,thatis,vapor–liquid(VL), Chapter 1 PhaseEquilibriumandProcessDevelopment 3 liquid–liquid (LL), gas–liquid (GL), and solid–liquid, play a dominant role. Otherpropertiesofinterestarerelatedtothethermodynamicenergyfunctions, transport,andvolumetricproperties. In the design or conception of a new process, a wealth of experimental information is required. This information comes from laboratory and bench scale studies, pilot plant, and industrial units. Even when a large amount of phase equilibrium and physical properties data is available, the need for ther- modynamicmodelpredictionsisalwayspresent.Thescenarioofphasecondi- tions in a plant is infinitely varied, and the experimental data will cover only some regions, hopefully the most critical, of the information required. The experimental data availableare like ascaffoldingthat supports the thermody- namicpredictionsofthevolumetricproperties,phaseequilibrium,andenergy functionsrequiredforthedesignandsimulationofalltheprocessunits.When moreabundantandreliablearetheexperimentaldata,betterpredictionsofthe physical and thermodynamic properties will be obtained from the selected thermodynamic model. Therefore, a well-tuned thermodynamic model for the mixture under the process conditions is a key engineering tool for the design and optimization oftheplantunits.Theprocessthermodynamicsensitivitywillprovideastrat- egy for parameter estimation of thermodynamic models, tailored to the pro- cess needs. On the other hand, models with qualitative predictive capacity are needed in development studies. A well-tuned thermodynamic model allows studying different pressure and temperature conditions of operation, exploring new phase scenarios to carry out the reactions, as well as, testing new separation techniques. The likelihood of finding the required information generally is limited to pure compounds or binary mixtures. Modern equations of state, on the basis of pure component physical constants and a few empirical parameters, are used to obtain PVT relations for pure compounds and their mixtures. In gen- eral, the mixture phase equilibria can be estimated on the basis of limited experimental information using the tools of classical thermodynamics, com- bined with the predictions of PVT properties from equations of state. Also, group contribution models can be applied to extend the scarce information available, to systems for which no experimental information has been measured. 1.3 DEFINITION OF PHASE EQUILIBRIUM ENGINEERING Thechemicalandpharmaceuticalindustryisblamedforitsnegativeenviron- mentalimpact.TheGreenChemistryprinciplesforasustainabledevelopment of the chemical industry claim for new reactants and catalyst for chemical synthesis with improved atom efficiency, higher yields and selectivities, pro- cess intensification and simplification, less waste, and safe and environmen- tally friendly solvents. Among the benign solvents, the supercritical fluids 4 PhaseEquilibriumEngineering (SCFs) have an increasing role. SCFs are classified as low or high critical temperature(T )solvents.LowT SCFs,likeCO andethane,offeringeneral c c 2 low solvent power, unless very high pressures are applied. In addition, these solvents are selective for compounds of low to moderate polarity and low molecular weight.High T SCFs have highsolventpowerbutlow selectivity. c Typical examples of high T solvents are supercritical water or toluene. c The SCFs have very attractive physical properties and exceptionally tune- able solvent power. SCFs add a new dimensionto conventional solvents, that is, the density-dependent solvent power, as the density of SCFs is very sensi- tive to changes in pressure, temperature, and composition. The design of the phase scenario that meets the process needs is what we call a phase equilibrium engineering problem. This discipline combines the methods of phase equilibrium thermodynamics with the process requirements to obtain the desired phase scenario and thermodynamic properties. We may look for homogeneous conditions in a supercritical reactor, for phase split and selectivity in a separation process, or a tuneable phase condi- tiontoachievebothreactionandseparationprocess inasinglestep.Foreach problem, there will be a set of specifications which represent the process restrictions. For instance, if we need to operate a reactor under homogeneous conditions, we specify the reactants, degree of conversion, and the operating temperature. Phase equilibrium engineering, by systematic analysis, develops criteria for selecting the right solvent, the solvent-to-feed ratio, and the pres- sure of operation, to keep the whole reaction trajectory in a single phase region [1]. Amulticomponentfluidmixturecanbeinahomogenousphaseatsupercrit- icalconditionsorasasubcooledliquidorsuperheatedvapor,orinaheteroge- neousVLorLLphasecondition.Thephaseenvelopeorpressure–temperature diagramisausefulplotforagivenmixturecomposition;itpresentsthebubble anddewpointphasetransitioncurvesaswellasthemixturecriticalpoint.The regionunderthecurveisheterogeneous.Abovethemaximumpressureatany temperature,wewillhaveasinglephase. Figure 1.2 presents a phase envelope sketch for a given mixture where three typical phase scenario requirements are indicated. Of course, during the course of a reaction or a separation process, with the change in composi- tions, different phase envelopes will be obtained, and the process trajectory should be always in the specified phase scenario: homogeneous or heterogeneous. 1.4 PHASE SCENARIOS IN SEPARATION, MATERIALS, AND CHEMICAL PROCESSES Allsortsofphasescenariosarepresentinnature,inlivingorinertbodies:the exchange of oxygen and carbon dioxide in our lungs (GL), the formation of clouds and ice in the atmosphere, the evaporation of water from oceans and

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