Analysis of the Monochloroacetic Acid Crystallization Process by Entropic Modeling

Transcription

1 A ublication of 2071 VOL 32, 2013 CHEMICAL ENGINEERING TRANSACTIONS Chif Editors: Sauro Pirucci, Jiří J Klmš Coyright 2013, AIDIC Srvizi Srl, ISBN ; ISSN Th Italian Association of Chmical Enginring Onlin at: wwwaidicit/ct Analysis of th Monochloroactic Acid Crystallization Procss by Entroic Modling Thassio N Goms*, Hlno Biso, Nilton Silva, João Manzi *Dartmnt of Chmical Enginring, Fdral Univrsity of Camina Grand, Av Arígio Vloso, 882, Bodocongó, Camina Grand PB, , Brazil thassio_1@hotmailcom Th rocss of crystallization has always bn rgardd as a ky oration in th saration and urification of chmical roducts, articularly in fin chmistry and du to this, nw analytical tchniqus, nw control and otimization mthods hav bn dvlod Th analysis rsntd for th monochloroactic acid () crystallization systm has bn drivd from th mass and nrgy balancs associatd with th ntroy balanc, taking a solid-quilibrium diagram into account A mthodology that minimizs th ntroy roduction was usd to find th otimal orating conditions for th crystallization rocss, orating undr th minimum rat Th thortical rsults ar in good agrmnt with th xrimntal data, indicating that ntroy analysis is a siml mthodology, asy to aly and on which rquirs lss comutational ffort 1 Introduction Du its imortanc in th saration and urification of various chmical roducts, th crystallization rocss has bn th objct of svral studis with th aim of making it mor fficint and rofitabl Th classical analysis of crystallization rocsss has bn ld by modls basd on mass balancs and nrgy associatd with th oulation balanc (Randolh and Larson, 1971) Howvr it has bn vrifid, at last from th thortical oint of viw, that th bst orating conditions can b obtaind whn th ntroy conct is usd in association with such an analysis Thus, th mthodology alid for th analysis of th monochloroactic acid () crystallization rocss, rsntd in this ar, also known as ntroy gnration minimization (EGM), which combins th basic rincils of thrmodynamics, hat transfr and fluid mchanics (Bjan, 1996), has bn usd to dtrmin th otimal orating conditions Dsit th conct of ntroy conct having bn wll-stablishd for a long tim, it was only in th arly 1970s that an ntroy gnration minimization mthodology mad a significant mrgnc, with succssful alications in cryognics, hat transfr orations and th convrsion of solar nrgy (Bjan, 1996) In rcnt yars, considrabl rogrss has bn mad rlatd to ntroy gnration, and EGM can b considrd as a owrful tool for th analysis and otimization of ractiv or non-ractiv systms, as shown in th scific litratur (Andrsn, 2011) Th EGM has bn usd to stablish th otimum oration conditions of chmical ractors, and th rsults show thr ar nw orating conditions whrby th minimum ntroy gnration rat can b rachd, and this is mhasizd Such rsults hav bn rsntd by Manzi t al (2009), whr th analytical otntial of th rocdur can b vidncd, highlighting th flxibility and th as of us whn alid to ractiv systms Th uros of this ar is to stablish an analytical aroach for th crystallization rocss, by mans of dvloing and analyzing th ntroy roduction rat Using th rsults from such an analysis, th otimum orating conditions may b found and vrification undrtakn mad on whthr th rocss is orating undr th minimum ntroy gnration condition

2 Th Systm 21 Production of is normally usd as an intrmdiary in th chmical industry, bing alid in th synthsis of svral roducts, such as sticids, organic chmicals and harmacuticals Its main rout of manufactur is basd on th catalytic chlorination of actic acid whn actic anhydrid is usd as a catalyst, as shown by th following quation, cat CH3 COOH + Cl2 ClCH 2COOH + HCl (1) Th raction is carrid out in a smi-continuous ractor whr th chlorination of actic acid () is continuously rformd until th aroriat dgr of convrsion is rachd Th roduct obtaind from th raction is a solution of 68 %, 28 % actic acid and 4 % by-roducts, which is snt to a buffr tank and maintaind at 310 K With a viw to achiving saration of from th mothr liquor, th rocss of crystallization of is usd, sinc it is considrd to hav advantag ovr othr mthods du to its cost-bnfit, bsids safty factors, and th facility with which can b stord and transortd Th roduction rout of is shown in Figur 1 Figur 1 Diagram of th Monochloroactic acid roduction rocss Th hysical and chmical rortis and th data usd to simulat th systm ar listd in Tabl 1 Tabl 1: Orating conditions and aramtrs of th crystallizr alid to roduction of Paramtr Valu Units Paramtr Valu Units F 10 L s -1 V 100 L X 068 C 152 J g -1 K -1 T K Δ H c J g -1 ρ 158 g L -1 Δ Gc 1180 J g -1 ρ 137 g L -1 PM 9450 g mol -1

3 Thortical Formulation Figur 1 shows that th roduct of th raction is continuously fd to th crystallizr rsulting in an outut stram consisting of th mothr liquor and crystals Th modling of th crystallization systm has bn dvlod basd on mass and nthaly balancs, taking a solid-liquid quilibrium diagram (s Sction 3 blow) into account to dtrmin th concntration of in th mothr liquor as a function of th tmratur It should b mhasizd that th quilibrium diagram of th systm - has bn thortically obtaind and is in vry good agrmnt with th xrimntal data 221 Mass balanc Considring that no raction occurs in th crystallizr, and having in mind that th fd stram consists solly of and, th mass balancs for th comonnts can b stablishd as r th following quations: dn X X PM = F ρ X FρX F ρ 1 X (2) dn PM = F ρ X FρX (3) 222 Enthaly balanc Sinc th nthaly (H) balanc can b givn by, dh ( s) s( l) s = H T ( ) H T H T Q (4) Givn that (H) is a function of tmratur and th numbr of mols of ach comonnt rsnt in th systm and considring th balancs stablishd by Eq (2) and (3), thn, basd on th conct of a total diffrntial, th following quation can b obtaind: dh H dt H dn H = + T n n + n i T, n T, n Substituting Eq (5) into Eq (4), rsults in, dn (5) ρ VC Sinc dt dh = H dt ( s) s( l) s T ( ) H T H T ~ = ρvc and H n i = H i H Q n T, n dn H n T, n rrsnting th artial molar nthaly, and taking into account mass balancs for ach comonnt givn by Eq (2) and (3), th nthaly balanc can b rwrittn as follows: ρvc dt whr V, X X = F ρ ΔH c + C( T T ) Q 1 X X, X, T, ρ, C, Δ H c ar, rsctivly, th crystallizr volum, th inlt mass fraction of, th mass fraction of in th mothr liquor, th crystallizr orating tmratur, scific gravity, scific hat and th hat of crystallization 222 Entroic modlling Th rat of ntroy gnration has bn dvlod in ordr to stablish th otimal oration conditions for th crystallization systm Thus, th following ntroy balanc must b considrd: ds ( s) s( l) s Q = S T ( ) S T S T + σ T (8) Sinc ntroy is a function of tmratur and of th numbr of mols of th comonnts involvd in th crystallization rocss, and taking into account th conct of a total diffrntial, th following rlation, givn by Eq (9), can b obtaind dn (6) (7)

4 2074 ds S dt S dn S dn = + + T n n n i T, n T, n (9) Considring th mass and nthaly balancs, Eqs (9) and (8), as wll as th rlations givn by ~ ds dt = ρvc T and S n i = S i whr S ~ i dnots th artial molar ntroy, thn Eq (10) is obtaind, which dscribs th ntroy gnration rat for th crystallization rocss σ = F X ρ 1 X X ΔG T c + C T T T T + ln T (10) 3 Rsults and Discussion 31 Analysis of th crystallization rocss By using th thrmodynamic critrion of quilibrium alid to a binary systm as r Nylvt (1985) it is asy to driv th quation that drivs th diagram of quilibrium for th crystallization rocss of, as shown blow: Figur 2: Diagram of solid-liquid quilibrium for th crystallization rocss of By analyzing th diagram of quilibrium, th orating oints for th crystallization systm can b found, for which, at first glanc, th bst rformanc can b obtaind For th cas in study, th fd solution containing 68 % and kt at 310 K is continuously coold until th concntration of in th mothr liquor rachs aroximatly 40 % by wight, corrsonding to a tmratur of around 273 K Figur 3:Dynamic bhavior of th concntration of

5 2075 Figur 4: Dynamic cooling of th crystallization systm Figurs 3 and 4 shows th dynamic bhavior of th concntration, as wll as th tmratur of th systm, which rachs 273 K, and which is considrd as th bst condition 32 Entroic Analysis Th analysis of th ntroy roduction rat givn by Equation (10) and dictd in Figur 5, considring th rang of tmratur for ractical alications, nabls th vrification that th oint of minimum ntroy gnration for th rocss can b stablishd whn th orating tmratur is qual to th tmratur of th utctic oint Figur 5: Th rsons surfac of th ntroy roduction for diffrnt valus of hat rmovd

6 2076 Figur 6: Bhavior of th ntroy roduction rat It can b vrifid from Figur 6 that th rduction in th ntroy gnration rat is associatd with th rduction of tmratur in th crystallizr, it bing obsrvd that th ntroy gnration rat rachs its minimum valu whn th tmratur of th systm is aroximatly 270 K In ractic, oration at this oint is inaroriat du to th ossibl occurrnc of both th and comonnts, in thir crystal stats Thrfor, it is ncssary to st som constraints on th tmratur so that th systm orats safly Thus, taking into account th limits imosd by th orational constraints, it can b vrifid that th otimal orating conditions whn th rocss is undr th minimum ntroy roduction ar found to b qual to 273 K and 40 % w/w, as shown in Figurs 3 and 6 It should b mhasizd that th ractical oration of an industrial lant follows th orating conditions that ar st out in this ar 4 Conclusion A modl for th ntroy gnration rat alid to th monochloroactic acid () crystallization rocss has bn dvlod from th mass, nthaly and ntroy balancs in addition to which a solidliquid quilibrium diagram has bn usd Th analysis of th modl basd on minimum ntroy was usd to stablish th otimal rocss conditions, and was shown to b in vry good agrmnt with th currnt modus orandi, thrby nabling th conclusion that, in ractic, th rocss orats undr th minimum ntroy gnration conditions Finally, this mthodology is asy to aly and can b don so at low comutational cost, and thus shows itslf as bing a owrful tool for analyzing th rocss Rfrncs Andrsn B, Currnt Trnds in Finit-Tim Thrmodynamics, Angw Chm Int Ed 2011, 50, Bjan A, Entroy gnration minimization Th mthod of thrmodynamic otimization of finit-siz systms and finit-tim rocsss, CRC Prss, Nw York, 1996 J Manzi R, Vianna, H Biso, Dirct ntroy minimization alid to th roduction of royln glycol, Chm Eng Proc 2009, 48 (1), Nývlt J, Söhnl O, Matuchová M, Broul M, Th kintics of industrial crystallization Ed Elsvir, Randolh A, Larson, M, Thory of Particulat Procsss, Acadmic Prss, Nw York, 1971