Instant Controlled Pressure Drop technology: From a new fundamental approach of instantaneous transitory thermodynamics to large industrial applications on high performance–high controlled quality unit operations

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Instant Controlled Pressure Drop technology: From a new fundamental approach of instantaneous transitory thermodynamics to large industrial applications on high

performance–high controlled quality unit operations

Sabah Mounir, Tamara Allaf, Baya Berka, Aicha Hassani, Karim Allaf

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Sabah Mounir, Tamara Allaf, Baya Berka, Aicha Hassani, Karim Allaf. Instant Controlled Pressure Drop technology: From a new fundamental approach of instantaneous transitory thermodynamics to large industrial applications on high performance–high controlled quality unit operations. Comptes Rendus. Chimie, Académie des sciences (Paris), 2014, 17, pp.261-267. �10.1016/j.crci.2013.10.019�.

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Instant Controlled Pressure Drop technology: From a new fundamental approach of instantaneous transitory

thermodynamics to large industrial applications on high performance–high controlled quality unit operations

SabahMounirâ,b,TamaraAllaf^c,d,BayaBerkaâ,e,AichaHassaniê,KarimAllafâ,*

aUniversityofLaRochelle-LaSIE3474FRE-CNRS,17042LaRochellecedex01,France

bZagazigUniversity,FacultyofAgriculture,44115Zagazig,Egypt

cABCAR-DICProcess,BP12053,17010LaRochellecedex01,France

dUniversityofAvignon-INRA,UMR408,84000Avignon,France

eE´coleNormaleSupe´rieuredeKouba,BP92,Vieux-Kouba,16500Alger,Algeria

1. Introduction

Themainobjectiveofdifferentresearchworkscarried out on industrial unit operations is to improve both processperformanceandﬁnalproductquality.Itmeansto face the problematic of time and energy consumption, while preserving and even improving multi-criteria quality.Theglobalintensiﬁcation philosophyconsistsin

listingthedifferentprocesses,determiningtheirpossible interactionandconsideringbetweenthemainsuccessive processes, the limiting phenomena. This last should be intensiﬁedtoimprovetheglobalkineticsoftheoperation.

Thus, while empirical laws allow controlling operating parameters depending on various process performance and finalproductquality parameters usedas responses (dependentvariables)[1],onlyfundamental studiescan implydefiningintensificationprocesses.

Fundamental and experimental studies were carried outin thecase of variousconventional unit operations.

Whenmasstransferachievedthroughinternaldiffusionis ARTICLE INFO

Articlehistory:

Received1August2013

Acceptedafterrevision29October2013 Availableonline18January2014

Keywords:

SolventExtraction ProcessIntensiﬁcation

InstantControlledPressureDropDIC StartingaccessibilitydXs

EffectivediffusivityDeff

Yields Availabilityratio

ABSTRACT

Solventextractionprocesseshavebeenlargelyusedinvariousindustries.Theyrecently wereimprovedthroughnewphysicalconceptssuchasCO2SupercriticalFluidExtraction, Ultrasoundassistedprocess,Microwave-assistedextraction,InstantControlledPressure DropDIC-assistedextraction...Systematically,apretreatmentstageofgrindingtakes placein order to improve theexchangesurface increasing thestarting accessibility.

Swellingofthematerialstructureimpliesanincreaseoftheporositythusleadingtohigher solventdiffusivitywithinthesolidmatrix.Anewconceptofexpandedgranulepowderhas recentlybeendefinedusingInstantControlledPressureDropDICtechnology.Whatever thetypeofsolventis(evenCO2-SFE),suchaswelledstructuredramaticallyintensifiesthe kineticsthrough a higherspecific exchangesurfacethanks to theopenpores, while improvingthesolutionsolvent–solutediffusivitywithinthesolid.Coupledtoultrasound, theinternaltransferofsolute withinthepore solventcan likewisebe intensifiedby replacingmoleculardiffusionwithintheporesbyaneffectiveconvectiontransfer.Inthis work, we carried out a first approach of modelingof solvent extraction kinetics of expanded granules involving higher exchange surface and greater internal diffusion process.

ß2013Acade´miedessciences.PublishedbyElsevierMassonSAS.Allrightsreserved.

* Correspondingauthor.

E-mailaddress:[email protected](K.Allaf).

ContentslistsavailableatScienceDirect

Comptes Rendus Chimie

w ww . sc i e nce d i re ct . co m

1631-0748/$–seefrontmatterß2013Acade´miedessciences.PublishedbyElsevierMassonSAS.Allrightsreserved.

http://dx.doi.org/10.1016/j.crci.2013.10.019

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Version définitive du manuscrit publiée dans / Final version of the manuscript published in : Comptes Rendus Chimie (2014), Vol. 17, p. 261-267, DOI: 10.1016/j.crci.2013.10.019 Journal homepage: www.sciencedirect.com

the limiting process, Instant Controlled Pressure Drop (DIC) can systematically contribute to deﬁning new innovativeintensiﬁedoperations.Theexpandedstructures aswellastheinstantaneousautovaporizationinducedby DIC arenormally veryeffective. Otherexperimentsand operationsusingsuchtypesofinstantaneoustransforma- tions can systematically be more effective than quasi- statictransformations.Fromafundamentalpointofview, it was highlighted the inadequacy of the conventional quasi-staticthermodynamic laws of mass transfer phe- nomenatoexplainandcontrolamainpartofthetransfer phenomenaachievedthroughinstantaneousways.Three thermodynamic laws of instant phenomena were pro- posed[2]:

when a complex transformation is achieved instanta- neously,itgeneratesanulltotalentropy;

variousthermodynamicparametershavedifferentprio- ritieswhilereachingtheequilibriumstate;

thus,aone-variabletransformationcannotbeachieved inaninstantaneousway.

Thermodynamic analysis of various transformations shouldusuallyconsidersystemparticleswithpermanent, isotropic and random movement. The speciﬁc internal ﬂuctuationkineticenergyrevealsthesystemtemperature.

Insomeverylimitedcasesoftheinstantaneousoperations, suchas DIC, thesystemparticles can have a transitory anisotropicandunrandom/one-axismovement,duringa veryshorttime. Itnormallylastsforsomemilliseconds, whereonlythepartofthe2-otheraxisofinternalkinetic energyshouldconcerntheinternalﬂuctuation;tempera- tureis thenobservedtobemuchlower[3].Duringthis transitorystage,achievedbyinstantaneouslydroppingthe pressure,thesystemtemperatureismuchlowerthanthe equilibriumlevelandtheautovaporizationratioismuch superior.Such phenomenonhasbeenprovedtobevery effective in numerous industrial operations. Without increasing the energy consumption, the amount of evaporatedvolatilecompoundsisthenmuchhigher[4,5].

Thus,byachievinginstantaneouslyapressuredrop,the temperaturedecreasesfromitsinitiallevelTi,tocrossand beatT_flowerthan theequilibriumleveldeterminedby conventionalquasi-staticthermodynamics:Tf<Ts.Conse- quently,thelowerthevalueofTf,thehighertheamountof vapor m_v generated by autovaporization (Eq. 1). The evolutionof thesystemfromthelowesttemperatureTf

towardstheequilibriumlevelTsisaccomplishedrespect- ingusualnon-equilibriumquasi-staticthermodynamics:

m_v¼msðc_v_sþWc_v_wÞTfTi

L (1)

Insomespeciﬁccases,thecoolingissoinstantthatit wouldpreservethemolecularhightemperaturestructure ofthesolid[2].

These different fundamental studies were approved throughexperimentalapproaches.Theinstantaneitylaws, strictlylinkedtoaspecificbifurcation,contributetocarry out specific intensification processes. Various industrial unit operationswere achievedcoupling controlled high quality final products to the best performance of the

operation (energy consumption, environment impact, greatkinetics...)[6–8].

2. DICtreatmentinsolventextraction

DIC treatment is based on the thermo-mechanical effects issued from an abrupt pressure drop (DP/

Dt>0.5MPa/s) towardsa vacuum (about5kPa) taking place after a short-time/high-temperature and pressure stage (Figs. 1 and 2). In the processes of extraction of volatiles,DICcanbemainlyusedasanautovaporization procedure[5,6,9,10].

Theabruptpressuredropcausesinstantandreinforced cooling of the products, immediately stopping thermal degradation,swellingthetextureandevenbreakingcell walls,allowingvaluablecompoundstobemoreavailable and accessible. This operation completely modiﬁes the technologicalabilitiesofvariousplantsregardingheatand mass transfers. Powders issuedfrom thesetechnologies aredistinguishedbytheirspeciﬁcityasexpandedgranule texture,whichenables themtogetveryhighfunctional behavior.Openporesincreasetheexchangesurfaceand, thus, thestarting accessibility. While the new porosity issuedfromtherepartitionofsmallporesimplieshigher effectivediffusivity[11,12].

Fig.1.Schemeoflab-scaleDICequipment.

Fig.2.SchemeofDICprocess.

S.Mouniretal./C.R.Chimie17(2014)261–267 262

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Indeed,theDICexpansionenablesthevegetalmaterials to be much more adapted to solvent extraction; even supercritical CO2 becomes dramatically intensiﬁed [1,13,14]. The DIC-assisted extraction processes can be usedasasystemofbothautovaporizationandexpansion aspects [14]. The ﬁrst allows the volatile compounds (essentialoils...)tobedirectlyextractedinsomeminutes (1 to 4min) instead of some hours with conventional methods and some dozens of minutes with some

‘‘innovative’’ (microwave...)methods.Sincetheinternal high total pressure is much higher than the external vacuum pressure, the main part of the evaporated moleculesis transportedtowardsthesurroundingmed- ium using Darcy’s law with the gradient of the total pressureasdrivingforce[2,15].Theﬁnalessential-oil-in- waterstableemulsionweobtainedbyDICcanbeagood basisfortheconventionalnormalorvacuumdistillation (liquid–vapor interaction), for some speciﬁc uses. This essential oil emulsionDIC canalso bea good basisfor encapsulationprocess.

Using DIC as a pretreatment-expanding process,one cangreatlyintensifythesolid–ﬂuidinteractionsthrough thedeﬁnitionofnewphenomenasuchastheexpulsionby forcing out, the expansion preparing the product tobe moreadequatetopressingandbyincreasingthediffusivity of water and solvents within the solid matrix [8]. DIC expansionenablesthevegetalmaterialstobemuchmore adaptedtomasstransfer.

In terms of drying, coupled to conventional airflow drying,optimizedDICtreatmentcouldcompletelyremedy theshrinkageeffect,increase thekineticsofthesecond stageofdryingandimprovethetotalqualityofthefinal products. Airflow drying coupled to DIC treatment has alloweddefiningthenewoperationofswell-drying,used for producinghighquality,low energy-consumingdried fruitsandvegetables[12,16–18].

Another drying operation includes the properly said autovaporization;itcanbeusedtodeﬁneaveryeffective intermittentoperation:Multi-FlashDryingMFDorDehy- dration bySuccessive PressureDropsDDS [19,20].Both MFD and DDS operations are relevant answers to the paradoxical stage of various drying and Freeze–Drying operations.Oncetheproductreachestheglass-transition Tg,thedehydrationmainlyofthedesorptionstagecanbe achievedthroughDDS,whichallowsthevaportoremove usingthegradientoftotalpressureasdrivingforce(Darcy typemasstransfer).Totaldryingtimeisthenmuchlower aswellastheenergyconsumption.

DICtreatmentisanexceptionallyrelevantprocessfor themicrobiologicaldecontaminationofpowdersandsolid materials. Its effects are both thermal (similar to UHT treatment) andmechanical (expansion andexplosion of spores and vegetative microorganisms) [21]. The three operatingparametersoftemperature,treatmenttimeand numberofcyclescanbeusedtodeﬁnethisdecontamina- tionlevel.

3. Fundamentalapproachofsolventextraction

Beforestudyinganyintensiﬁcationoperation,onehas tostudythefundamentalsofextractionkinetics,tryingto

identifythelimitingphenomenon,whichﬁrstlyhastobe improved.

3.1. Mechanismsofmasstransfers

Itiswellknownthattheprocessofsolventextraction hasfourphysicalmechanismsofmasstransfer:

solventinteractionwiththematerialexchangesurface;

solventtransferwithintheproduct;itiscarriedoutin liquidformby variousprocesses,includingcapillarity, moleculardiffusivity;thegradientofsolventcontentis thedrivingforce;

solutetransferinthesolventwithintheproductpores;it iscarriedoutbymoleculardiffusivity;thegradientofits concentrationinthesolventisthedrivingforce;

solutetransportfromtheproductsurfacetotheexternal solventoutside.Whennoexternalagitationisoperated on thesolvent,this transporttakes placeby diffusion withthegradientofsoluteconcentrationinthesolvent asthedrivingforce.Bystirring,thistransportisdoneby convection.

Theappropriatesolventisnormallyidentiﬁedbasedon polarity,toxicity...; it isusually abletoinstantaneously dissolve the solute. The choice of the solvent (and the adequatetemperature)mayallowassumingtheinterac- tionbetweensolventandproducttoputinstantaneously thesoluteinsolution.

The agitation of the external environment solvent allowsthepartofthesolutem_Aaccessibleattheexchange surfacetobeeasilyandquicklyextractedandtransported fromtheexchangesurfacetotheoutsidebyconvection.

Thepartofsolutetobetransferredbydiffusionwithinthe materialandinsidethesolventisconsideredtobe(mi–mA).

Aresidualpartmrofthisdeepsolutemaybeunavailable forextractionbecauseofitslocationwithincellswithgreat wallandmembraneresistance.

Intermsofsolutedensities(gofsolute/100gDryBasis or%db),onecanconsider:

Xs:correspondstoms.Itisthepartofthesolutelocatedat the surface and initially accessible, quickly removed, mainlybyconvectionthankstothesolventagitationby interactionbetweenthesolventandthesurfaceofthe product;

(XiXs):correspondstotheinitialamountofthesolute (mims) ﬁrstly located as a supposed uniform and homogeneous density within the volume. It evolves overtimethankstovariousdiffusionprocesses.Attimet, itisindicatedbyX;

(XiX₁):correspondstotheamountofresidualsolutemr

unavailablefortheextraction(kgofsoluteperkgofdry matteror%db).

3.1.1. Washingstageofextractionprocess

Once the material granule is solvent logged, the extraction process begins by a starting fast extraction step [22]. Allaf [15] deﬁned this starting step as the washingstageofthesurface–solventinteraction(Fig.3):

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Version définitive du manuscrit publiée dans / Final version of the manuscript published in : Comptes Rendus Chimie (2014), Vol. 17, p. 261-267, DOI: 10.1016/j.crci.2013.10.019 Journal homepage: www.sciencedirect.com

Extractionrateofsolutefromsurface:

dms

dt ¼keESAð$s$solventÞ (2)

where:

ms:massofsoluteextractedbyinteractionbetweenthe solventandthesurfaceoftheproduct(kgofsolute);

k_e:interactioncoefﬁcientbetweenthesolventandthe surface,bydiffusionforthestaticcaseorbyconvection usuallyduetostirring(kgofsolventm²s¹);

ESA:exchangesurface areabetween solventand the product(m²);

$s:dissolvingcoefﬁcientatequilibrium(kgof solute kg¹ofsolvent);

$_solvent:soluteconcentrationinthesurroundingsolvent incontactwiththeexternalmaterialsurface(kgofsolute kg¹ofsolvent).

Thedensityof theextractionrateof solutefromthe surfaceperunitofdrymatter:

dXs

dt ¼keSESAð$s$solventÞ (3)

SESA: speciﬁc exchange surface area between the solventandtheproductperunitofdrybasis(m²kg¹).

The totaleffect can beshown through the‘‘starting accessibility’’parameter,preferentiallyusinganeffective speciﬁcexchangesurfaceareaSESAeff:

Startingaccessibility:

dXs¼keSESAeffð$e$solventÞdt (4)

Usually,inkineticsstudies,thestartingaccessibilitydXs

doesnotinvolveanydiffusionsourceoreffect;itis the densityofsoluteperunitofdrymatterextractedbythe initialinteractionbetweenthesolventand theeffective exchangesurfaceoftheproduct.dXsisexpressedaskgof soluteperkgofdrymatteror%db.

3.1.2. Internaltransferbydiffusion

Aftertheﬁrstandquickwashingstageofextractionof superﬁcialsolute, theinternal mass transferwithin the

product mustpresentthehighest transferresistance. In suchconditions,themass transferwithintheexpanded granule controls the extraction kinetics; it is given by Allaf’spresentationofsimilarFickdiffusion[2]:

GeneralFickmasstransferlaw:

rs

rm

vs

!vm

¼Deffr^! rs

rm

(5) with:

rs:apparentdensityofsoluteinthematerial(kgm³),

rm:apparentdensityofdrymaterial(kgm³),

vs

!:absolutevelocityofsoluteﬂowwithintheporous medium(ms¹).

vm

!:absolutevelocityofsolidmedium(inms¹).

Deff: effective diffusivity of solvent within the solid medium(inm²s¹).

By neglecting the possible shrinkage or swelling process, onecan assumethat rm=constant and vm

! ¼0, itispossibletohave:

SimpliﬁedFickmasstransferlaw:

rsvs

!¼Deffr^!rs (6)

Usingthebalancemass,itispossibletoobtain:

SecondFickmasstransferlaw:

@rs

@t ¼r^! D_effr^!rs

(7) wheretisthetime.

Although the effective diffusivity Deff considerably varies versus the system temperature and porosity, it canbeassumedtobeconstantonlythroughthehypothesis ofbothstructuralandthermalhomogeneities.Byestimat- ingphysicalprocessesandcarryingoutﬁttingexperiments one can normally conﬁrm this hypothesis allowingthe equationtobecomethesecondFick’slaw:

@rs

@t ¼Deffr²rs (8)

And,foraunidirectionalradialﬂow,itbecomes:

@r_s

@t ¼Deff

d²r_s

dr² (9)

The solutions to provide to this diffusion equation closelydependontheinitialandboundaryconditions.The Crank’s solution [23] according tothe geometry of the sphericalexpandedgranulemaybeadopted,andbyusing theamountofextract,itispossibletoget:

X1X X1XA

¼X¹

1

A_ie^q²ⁱ^ð^tt⁰^Þ (10)

whereXistheamountofsoluteextractedattimet,andX1

is the amount of solute extracted at time t!1 (total yields). XA isan amountof solute extract attime t=to, whichischosenasatimeforwhichthestartingwashing stephascompletelydisappearedandthediffusionprocess is assumed to be the highest resistance of the solvent extraction.Byusingtheexperimentaldataforthediffusion model,onehastoexcludethevaluenearthestartingpoint (t<to).dXsisthencalculatedbyextrapolating(att=0)this Fig. 3.Kinetics of extraction of ﬂavonoids from buckthorn leaves:

phenomenologicalmodelingincludingwashingstepanddiffusionstep.

ModelparametersareDeff:theeffectivediffusivity(m²s¹);dXsandX1: thestartingaccessibilityandtheyieldsoravailabilityratio,respectively (EqmgMyricetin/gdb).

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