study of lactic acid thermal behavior using...

Research ArticleStudy of Lactic Acid Thermal Behavior UsingThermoanalytical Techniques

Andrea Komesu1 Patricia Fazzio Martins Martinez1 Betacircnia Hoss Lunelli1

Johnatt Oliveira2 Maria ReginaWolf Maciel1 and Rubens Maciel Filho1

1School of Chemical Engineering University of Campinas (UNICAMP) Department of Process and Product DevelopmentAv Albert Einstein 500 13083-970 Campinas SP Brazil2Institute of Health Sciences Nutrition College Federal University of Para (UFPA) Augusto Correa St 0166073-040 Belem PA Brazil

Correspondence should be addressed to Andrea Komesu andrea komesuhotmailcom

Received 2 March 2017 Accepted 4 April 2017 Published 18 April 2017

Academic Editor Ewa Schab-Balcerzak

Copyright copy 2017 Andrea Komesu et alThis is an open access article distributed under theCreativeCommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Actually there is a growing interest in the biotechnological production of lactic acid by fermentation aiming to substitute fossil fuelroutes The development of an efficient method for its separation and purification from fermentation broth is very important toassure the economic viability of production Due to its high reactivity and tendency to decompose at high temperatures the studyof lactic acid thermal behavior is essential for its separation processes and potential application In the present study differentialscanning calorimetry (DSC) analyses showed endothermic peaks related to the process of evaporation Data of thermogravimetry(TGDTG) were correlated to Arrhenius and Kissinger equations to provide the evaporation kinetic parameters and used todetermine the vaporization enthalpy Activation energies were 5108 and 4837 kJsdotmolminus1 and frequency values were 85997 and96881 sminus1 obtained by Arrhenius and Kissinger equations respectively Thermogravimetry coupled with mass spectroscopy (TG-MS) provided useful information about decomposition products when lactic acid was heated at 573 K for approximately 30min

1 Introduction

Lactic acid or 2-hydroxypropionic acid an organic acidman-ufactured by fermentation from renewable sources such ascorn potato and other agriculture products is an alternativeto conventional petroleum raw materials routes It has awide variety of applications in cosmetics (moisturizers skin-lightening agents skin-rejuvenating agents pH regulatorsantiacne agents humectants and antitartar agents) in phar-maceutical products (dialysis solution mineral preparationspills prostheses surgical sutures and controlled drug deliv-ery systems) in chemistry (descaling agents pH regulatorsneutralizers chiral intermediates green solvents cleaningagents slow acid release agents and metal complexingagents) and in food (acidulants preservatives flavours pHregulators microbial quality improving agents and mineralfortification) [1 2] Furthermore it is used as precursor of sev-eral other products such as propylene oxide acetaldehyde

acrylic acid propionic acid 23-pentanedione ethyl lactateand polylactic acid [3] the latter is used for productionof biodegradable polymers with medical applications Overthe last decade more and more attention has been paidto its potential productivity due to its increasing demandin practice However it is still difficult to recover highquality lactic acid from a fermentation broth because of itscharacteristics such as high viscosity and thermal sensitivity[4]

The thermal sensitivity and high reactivity of lactic acidcan be explained due the presence of two adjacent functionalgroups acid and alcohol in a small molecule with only threecarbon atoms as well as their tendency to decompose athigh temperatures [5] However from literature review noaccurate study detailing the monomer lactic acid thermalbehavior could be found On the other hand the polylacticacid (PLA) polymer produced by polymerization of lacticacid has been extensively studied [6ndash10]

HindawiJournal of ChemistryVolume 2017 Article ID 4149592 7 pageshttpsdoiorg10115520174149592

2 Journal of Chemistry

The development of an efficient method for separationand purification of carboxylic acids from fermentation brothis very important to allow its biotechnological produc-tion in commercial scale since these steps are responsi-ble for 30ndash40 of the total production costs [11] How-ever for recovery and concentration of thermally unstablemolecules such as lactic acid it is essential to understandhow these molecules behave at high temperatures whichcan be achieved through thermal analyses as differen-tial scanning calorimetry (DSC) thermogravimetry (TG)and thermogravimetry coupled with mass spectroscopy(TG-MS)

DSC is performed by difference in energy supplied tothe sample and the reference pan in function of temper-ature By varying the energy of the sample as a functionof temperature physical and chemical phenomena can beobserved In general phase transitions dehydration reduc-tion and decomposition reactions produce endothermiceffects whereas crystallization oxidations and some decom-position reactions produce exothermic effects [12] DSC isoften used because of its speed simplicity and availability[13] Several reviews covering the fundamentals conceptsinstrumentation and general applications are available in theliterature [13ndash16]

TG is a technique that records variation of mass whilethe sample is heated The mass loss can be related to manyphenomena such as dehydration sublimation evaporationand decomposition TG has been used to estimate the kineticparameters such as activation energies reaction orders andthe Arrhenius preexponential factor of degradation [17]and evaporation processes [18] and to determine physi-cal properties as vapor pressure and vaporization enthalpy[19]

TG-MS is a powerful hyphenated technique combiningthe direct measurement of weight loss as a function oftemperature with the use of sensitive spectroscopic detec-tors Such detectors permit qualitative and quantitativedetermination of the evolved volatile products to providekinetic information about the specific reaction mecha-nisms [20] Other advantages are speed reduced samplehandling unique sample and absence of retention time[21] Research articles have been published about instru-mentation and applications of TG [22ndash24] and TG-MS[21 25 26]

So in this work the objective was to study the lacticacid thermal behavior usingDSC TGDTG andTG-MSTheobtained results provided a better understanding of the lacticacid thermal behavior allowing the development of adequateseparation processes

2 Experimental

21 Material DL-lactic acid (molecular weight 9008 kgsdotmolminus1 CAS number 50-21-5) sim90 standard supplied bySigma-Aldrich (St Louis Missouri EUA) was used in thethermal analysis by DSC TGDTG and TG-MS withoutprior purification Water and residual substances are impu-rities reported by the supplier

22 Differential Scanning Calorimetry DSC experiment wascarried out using Shimadzu equipment (Japan) model DSC-50 A dynamic scan was performed at heating rate of10 Ksdotminminus1 over a temperature range from294K to 773KThesample was analyzed under a nitrogen dynamic atmosphereat flow rate of 50mLminminus1The experiments were carried outwith a sample size of sim7mg The samples were weighed intoopen aluminum pans and hermetically sealed

23 Thermogravimetry TG experiments were carried outusing Shimadzu thermal analyser (Japan) model TGA-50Constant heating rates of 5 10 15 20 25 and 30Ksdotminminus1were applied Data were collected in the temperature rangefrom 296K to 773K under a nitrogen dynamic atmosphere(50mLsdotminminus1)Themasses of samples were nearly 15mgTheequipment recorded TG and DTG (derivative thermogravi-metric analysis) data simultaneously Data obtained by TGwere used to determine evaporation kinetic parameters andevaporation enthalpy Data obtained by DTG were useful toshow the evaporation stages and the effect of heating rate

24Thermogravimetry Coupled withMass Spectrometer TG-MS analysis was carried out using Setaram SetSys Evolution1618 coupled with a mass spectrometer (MS) ThermostarPfeiffer Vacuum GSD 301T MS was responsible for mon-itoring the masses of compounds that have evolved fromthe sample during heating Initially the sample was heatedfrom 298K to 773K at heating rate of 10 Ksdotminminus1 undernitrogen atmosphere (16mLsdotminminus1) in order to observe thetemperature range in which the evolution of mass occurredAfterwards the analysis was performed with a mass spec-trometer coupled heating the sample from 293K to 573Kat heating rate of 10 Ksdotminminus1 under nitrogen atmosphere(16mLsdotminminus1) In addition an isothermal at 573K was builtduring 2 h In this case a scan of all fragments evolved fromthe sample during the heating time was used to obtain thethermal and mass spectrum Finally TG-MS was performedmonitoring fragments of higher intensity Data were collectedand used to obtain the lactic acid thermal behavior anddegradation products as a function of temperature and time

25 Kinetic Models Thermogravimetry is the most commontechnique used for kinetic analysis Sample mass variationby temperature data obtained by TGDTG was used todetermine evaporation kinetic parameters The frequencyfactor (119860) and activation energy (119864119886) were obtained usingArrhenius and Kissinger methods

Calculations are based on the following kinetic equation[18]

119889120572119889119905 = 119896 times (1 minus 120572)119899 (1)

where 120572 corresponds to the amount of vaporized material 119905is the time 119899 is the apparent reaction order and 119896 is the rateconstant

Journal of Chemistry 3

The amount of vaporized material (120572) is defined as

120572 = 1198980 minus 1198981199051198980 minus 119898119891 (2)

where1198980 is the sample initial mass119898119905 is the sample mass attime 119905 and119898119891 is sample final mass119896 depends on temperature following Arrhenius equation

119896 = 119860 exp(minus 119864119886119877119879) (3)

where 119860 is the frequency factor 119864119886 corresponds to theactivation energy and 119877 is the gas constant

Considering (1) and (3) the following expression isderived

119889120572119889119905 = 119860 exp (minus 119864119886119877119879) times (1 minus 120572)119899 (4)

26 Arrhenius Method This approach assumes Arrheniusbehavior and zero-order reaction kinetics Taking the naturallogarithm in (4) the following expression is derived

ln(119889120572119889119905 ) = ln119860 (1 minus 120572)119899 minus 119864119886119877119879 (5)

For zero-order reactions (119899 = 0) the equation becomes

ln 119889120572119889119905 = ln119860 minus 119864119886119877119879 (6)

119889120572119889119905 can be calculated by (7)The value of119889119898119889119905 is providedby DTG plot

119889120572119889119905 =

minus1198891198981198891199051198980 minus 119898119891 (7)

Thus plotting ln(119889120572119889119905) versus (1119879) and correlatingthe values by the least-square methods to obtain a straightline the slope will provide the activation energy after beingmultiplied by 119877 The intercept of this equation will beequivalent to ln11986027 Kissinger Method Kissinger developed a model-freenonisothermal method where there is no need to calculate119864119886 for each conversion value in order to evaluate kineticparameters [27]Thismethod is based on the study of the rateequation at the maximum reaction rate which means that11988921205721198891199052 is equal to zero Equation (4) can be written as

ln( 1205731198792119898) = ln(119860119877119864119886 ) minus119864119877119879119898 (8)

where 120573 is the heating rate (120573 = 119889119879119889119905) and 119879119898 is thetemperature peak of the DTG curve

The activation energy is determined from the TG dataat different heating rates by liner regression of the ln(1205731198792119898)versus 119879minus1119898 plot and the activation energy (119864119886) is calculatedfrom the slope of the resulting straight line

273 323 373 423 473 523 573 623 673 723 773

Temperature (K)minus33

minus28

minus23

minus18

minus13

minus8

minus3

2

Hea

t flow

(mW

)

darr Endo

Figure 1 DSC lactic acid profile

28 Vaporization Enthalpy Thermogravimetry is a rapid andconvenient technique used for determination of vaporizationenthalpy The theoretical basic of the TG procedure is theLangmuir equation [19]

(1119886)119889119898119889119905 = 119901120572radic

1198722120587119877119879 (9)

where 119889119898119889119905(119886) is the rate of mass loss per unit area(kg sminus1mminus2) 119901 is the vapor pressure (Pa)119872 is the molecularweight of the vapor of the evaporating compound (kgmolminus1)119877 is the gas constant (J Kminus1molminus1) 119879 is the absolute temper-ature and 120572 is the vaporization coefficient

Rearranging the Langmuir equation gives

119901 = 119896] (10)

where 119896 = radic2120587119877120572 and ] = (1119886)(119889119898119889119905)radic119879119872A plot of ln ] against 1119879 should give a straight line plot

of slope Δ1198671198773 Results and Discussion

31 Differential Scanning Calorimetry Analysis The DSCcurve of lactic acid is presented in Figure 1 From this figureit can be observed that two endothermic peaks are related tothe process of lactic acid and lactide evaporation at 44735 Kand 62524K respectively The double small peak in the firstpeak (44735 K) is noted it probably occurred because of thepresence of two isomers D(minus) and L(+) lactic acid present inthe sample

32 Thermogravimetry Analysis The TG and DTG thermalprofiles are shown in Figures 2(a) and 2(b)

The weight loss profile in Figure 2(a) shows the lossof mass with temperature at different heating rates As canbe seen in Figure 2(a) the curves do not show a plateauindicating thermal stability conversely evaporation processbegins at temperatures around the room temperature and


5Kminminus1

10 Kminminus1

15 Kminminus1

20 Kminminus1

25 Kminminus1

30 Kminminus1

0

10

20

30

40

50

60

70

80

90

100

Mas

s (

)

373 473 573 673 773273Temperature (K)

(a)

273 373 473 573 673 773


minus009

minus008

minus007

minus006

minus005

minus004

minus003

minus002

minus001

0

DTG

(mg

s)

5Kminminus1

10 Kminminus1

15 Kminminus1

20 Kminminus1

25 Kminminus1

30 Kminminus1

(b)

Figure 2 TG (a) and DTG (b) curves of lactic acid as a function of temperature and heating rates (5 10 15 20 25 and 30Ksdotminminus1)

proceeds rapidly with increasing temperature until about573K

The effect of heating rate is shown in Figures 2(a) and 2(b)Heating rates affect TG curve positions and shift maximumtemperature peaks (119879119898) towards higher temperatures Thisphenomenon can be explained on the basis of heat transferlimitation During the analysis at low heating rate a largerinstantaneous thermal energy is provided in the system anda longer time may be required for the purge gas to reachequilibrium with the temperature of the furnace or thesample While at the same time and in the same temperatureregion higher heating rate has a short reaction time and thetemperature needed for the sample to evaporate is also higher[27]

DTG profiles showed three evaporation stages Theevaporation stages (heating rate of 10 Ksdotminminus1) occurred atsim347K sim459K and sim612 K and mass loss percentage of12119 85520 and 1483 respectively First was the evap-oration of water and methanol impurities (sim347K) followedby lactic acid (sim459K) and probably lactide (sim612 K)

The Arrhenius plot for the calculation of activationenergy is shown in Figure 3(a) For a reaction to be consideredan evaporation process it is imperative that the mass lossaccording to the time or temperature should be a zero-order process [18] Lactic acid presented in this work showedthis behavior as show in Figure 3(a) using heating rate of10 Ksdotminminus1 The kinetic parameters determined from TGDTG data are shown in Table 1 The advantage of Arrheniusmodel is the ability to directly determine the kinetic parame-ters from a single TG measurement

Kissinger plot of ln(1205731198792119898) versus 119879minus1119898 is shown in Fig-ure 3(b)The kinetic parameters were calculated according to(8) and are given in Table 1 The advantage of the model-free

Table 1 Evaporation kinetic parameters of lactic acid by Arrheniusand Kissinger models

Model Heating rateKsdotminminus1 EakJsdotmolminus1 Asminus1 1198772Arrhenius 10 5108 85997 09962Kissinger 4837 96881 09712

analysis is founded on its simplicity and on the avoidance oferrors connected with the choice of a kinetic model [27]

The values of activation energy and frequency factorobtained from the Kissinger method are consistent with thevalues obtained by Arrhenius method (deviation less than10) Kinetic parameters of the lactic acid evaporation pro-cess have not been reported in literature review as describedin this work

The plot of ln ] against 1119879 for the calculation of vapor-ization enthalpy (Δ119867vap) is shown in Figure 4 using heatingrate of 30K minminus1 The vaporization enthalpy calculated was569 kJ molminus1 Experimental values for lactic acid vaporiza-tion enthalpy are very rare in the literature Emelrsquoyanenkoet al [28] reported a value of vaporization enthalpy of691 kJsdotmolminus1 at 29815 K using the transpiration method forthe L-lactic acid Comparing the results deviations are lowerthan 18 which is due to experimental errors and probablythe presence of the DL-lactic acid isomer used in this workalso influenced the results

33Thermogravimetry Coupled withMass Spectrometer Anal-ysis TG-MS analysis enabled the identification of vaporizedmolecules and thermal decomposition products from lacticacid at high temperatures TG-MS profiles are shown inFigure 5 From this figure it was observed that water (119898119911 =


1T (Kminus1)

00022 00023 00024 000250002 00021

ln(d120572dt)= minus61436 lowast (1T) + 67569

R2 = 09962

minus9

minus85

minus8

minus75

minus7

minus65

minus6

ln(d

120572d

t)

(a)

1T (Kminus1)

00019 0002 00021 00022 00023

= minus58174 lowast (1T) + 23018

R2 = 09712

minus108

minus106

minus104

minus102

minus10

minus98

minus96

minus94

minus92

minus9

minus88

ln(120573Tm2)

ln(120573

Tm

2)

(b)

Figure 3 Arrhenius plot (a) and Kissinger plot (b) for the calculation of the activation energy

= minus68523 lowast (1T) + 92093

R2 = 09922minus4

minus45

minus5

minus55

minus6

minus65

000

195

000

2

000

205

000

21

000

215

000

22

000

225

000

23

000

19

1T (Kminus1)

ln ]

ln]

(kg0

5sminus

1m

minus2m

ol05K0

5)

Figure 4The plot of ln ] against 1119879 for the calculation of vaporiza-tion enthalpy

18) hydroxyl (119898119911 = 17) and methanol (119898119911 = 32) werethemainmolecules eliminated during the heatingWater andmethanol are impurities from DL-lactic acid commerciallyproduced which has 90 of purity Probably water andmethanol come from fermentation and separation processesrespectively The hydroxyl group probably came from waterLactide is also an impurity which was observed inDSC curveThe presence of lactide in the commercial lactic acid may beexplained due to the tendency of lactic acid to polymerize inconcentrated solutions As described in the literature above30 of lactic acid concentration the presence of lactide isobserved [5] Other mass fragments monitored during thethermal analysis appeared in low ionic current values

Lactic acid can be conveniently converted into variousvalue-added products such as acrylic acid For acrylic acidproduction direct dehydration of lactic acid in high tempera-tures is an alternative For better understanding the lactic acidthermal behavior at high temperatures TG-MS isotherm oflactic acid at 573K was performed as shown in Figure 6 Theisothermprofiles were divided into parts (a) and (b) for bettervisualization

mz = 32

mz = 17

mz = 18

00E + 00

10E minus 07

20E minus 07

30E minus 07

50E minus 07

40E minus 07

Ion

curr

ent (

A)

392 492292Temperature (K)

Figure 5 TG-MS profiles of lactic acid

Figure 6 showed the fragments products of hydroxyl(119898119911 = 17) water (119898119911 = 18) methanol (119898119911 = 32)acetaldehyde orand carbon dioxide (119898119911 = 44) formate(119898119911 = 45) acrylic acid (119898119911 = 72) and propionic acid(119898119911 = 74) It can be concluded that various reactionsoccurred concurrently At approximately 30min of heatingthe presence of dehydration reactions (11) as well as reduction(12) and decarboxylation reactions (13) was observed

C3H6O3 997888rarr C3H4O2 +H2OLactic acid 997888rarr acrylic acid + water (11)

C3H6O3 997888rarr C3H6O2 + 12O2Lactic acid 997888rarr propionic acid + oxygen (12)


mz = 18

mz = 17

mz = 44

mz = 32

mz = 45

000E + 00

100E minus 07

200E minus 07

300E minus 07

400E minus 07

500E minus 07

Curr

ent i

onic

(A)

10 20 30 40 500Time (min)

(a)

10 20 30 40 500Time (min)

0000E + 00

500E minus 12

1000E minus 12

1500E minus 12

2000E minus 12

2500E minus 12

Curr

ent i

onic

(A)

mz = 72

mz = 74

(b)

Figure 6 TG-MS lactic acid isothermal at 573K during the time (a)119898119911 = 17 18 32 44 and 45 (b)119898119911 = 72 and 74The solid line in (b)is a type of noise from the equipment

C3H6O3 997888rarr C2H4O + CO2 +H2Lactic acid 997888rarr acetaldehyde + carbon dioxide + hydrogen (13)

According to the literature the formation of self-reactionproducts such as lactide which are subsequently morereadily decomposed into fragments (eg carbon monoxideacetaldehyde and water) is the main reaction that competeswith the dehydration process [29] Data obtained from TG-MS are in agreement with the literature

Additionally at the end of the analysis the sample wasfound graphitized indicating that a quantity of the samplewasreduced also confirming the analysis of the mass profiles Itcan be concluded that the decomposition process of lacticacid is related to temperature and the time of exposureto heat In addition only after 30min of heating at 573Klactic acid was decomposed into water hydroxyl methanolacetaldehyde orand carbon dioxide formate acrylic acidand propionic acid as can be seen by increasing the currentionic at 30min

Therefore it is important work with separation processeswhichminimize problems of thermal decomposition to avoidthe formation of byproducts Vacuum operations provide asubstantial decrease in the boiling points of substances dueto operating pressure reductionThis characteristic allows theseparation of compounds that would be destroyed if the mix-ture is processed at normal pressures [30]This characteristicis satisfied by the hybrid short path evaporation It has beenrecognized as a promising technology mainly because of itslow evaporation temperature and short residence time [31]

4 Conclusions

In this work thermal characterization of lactic acid usingthermoanalytical techniques was presented DSC analysesshowed endothermic peaks related to the process of evap-oration Effect of heating rate on TG and DTG curves

was also presented and the data were correlated to Arrhe-nius and Kissinger equations to provide the evapora-tion kinetic parameters Activation energies were 5108and 4837 kJsdotmolminus1 and frequency values were 85997 and96881 sminus1 obtained by Arrhenius and Kissinger equationsrespectively Enthalpy of vaporization calculated by TG was569 kJsdotmolminus1 TG-MS curve profiles showed many decom-position products when lactic acid was heated at 573K inapproximately 30min It can be concluded that decompo-sition process of lactic acid is related to temperature andthe time of exposure to heat Therefore separation andpurification processes which work with vacuum and shortresidence time are favored

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

The authors are acknowledging the financial support fromSao Paulo Research Foundation (FAPESP) (Project nos 201217501-0 and 201512783-5)

References

[1] Y-J Wee J-N Kim and H-W Ryu Food Technology andBiotechnology vol 44 pp 163ndash172 2006

[2] R Datta and M Henry Journal of Chemical Technology andBiotechnology vol 81 pp 1119ndash1129 2006

[3] A Komesu P F Martins B H Lunelli et al ldquoLactic acid purifi-cation by hybrid short path evaporationrdquo Chemical EngineeringTransactions vol 32 pp 2017ndash2022 2013

[4] L Chen A Zeng H Dong Q Li and C Niu ldquoA novel processfor recovery and refining of l-lactic acid from fermentationbrothrdquo Bioresource Technology vol 112 pp 280ndash284 2012


[5] B H Lunelli Production and control of the acrylic acid ester syn-thesis through lactic acid fermentation [PhD thesis] Universityof Campinas Sao paulo Brazil 2010

[6] E Fortunati I Armentano A Iannoni and J M KennyldquoDevelopment and thermal behaviour of ternary PLA matrixcompositesrdquo Polymer Degradation and Stability vol 95 no 11pp 2200ndash2206 2010

[7] V S Giita Silverajah N A Ibrahim N Zainuddin W M ZWan Yunus and H A Hassan ldquoMechanical thermal and mor-phological properties of poly(lactic acid)epoxidized palm oleinblendrdquoMolecules vol 17 no 10 pp 11729ndash11747 2012

[8] V Speranza A De Meo and R Pantani ldquoThermal and hyd-rolytic degradation kinetics of PLA in themolten staterdquoPolymerDegradation and Stability vol 100 no 1 pp 37ndash41 2014

[9] S-L Yang Z-H Wu W Yang and M-B Yang ldquoThermaland mechanical properties of chemical crosslinked polylactide(PLA)rdquo Polymer Testing vol 27 no 8 pp 957ndash963 2008

[10] S Solarski M Ferreira and E Devaux ldquoCharacterization ofthe thermal properties of PLA fibers by modulated differentialscanning calorimetryrdquo Polymer vol 46 no 25 pp 11187ndash111922005

[11] C S Lopez-Garzon and A J J Straathof ldquoRecovery of car-boxylic acids produced by fermentationrdquo BiotechnologyAdvances vol 32 no 5 pp 873ndash904 2014

[12] M G Ionashiro Fundamentos da Termogravimetria e AnaliseTermica Diferencial e Calorimetria Exploratoria Diferencial GizEditorial Sao Paulo Brazil 2005

[13] K V Kodre S R Attarde P R Yendhe R Y Patil and V UBarge ldquoDifferential Scanning Calorimetry A Reviewrdquo Researchand Reviews Journal of Pharmaceutical Analysis vol 3 pp 11ndash22 2014

[14] S-D Clas C R Dalton and B C Hancock ldquoDifferentialscanning calorimetry applications in drug developmentrdquo Phar-maceutical Science and Technology Today vol 2 no 8 pp 311ndash320 1999

[15] B Z Chowdhry and S C Cole ldquoDifferential scanning calorime-try applications in biotechnologyrdquo Trends in Biotechnology vol7 no 1 pp 11ndash18 1989

[16] C G Biliaderis ldquoDifferential scanning calorimetry in foodresearch a reviewrdquo Food Chemistry vol 10 no 4 pp 239ndash2651983

[17] L Dai L-Y Wang T-Q Yuan and J He ldquoStudy on thermaldegradation kinetics of cellulose-graft-poly(l-lactic acid) bythermogravimetric analysisrdquo Polymer Degradation and Stabil-ity vol 99 no 1 pp 233ndash239 2014

[18] P F Martins P Sbaite C I Benites M R Wolf Maciel and RMaciel Filho in AIDIC Conference Series vol 10 pp 233ndash2422011

[19] S F Wright D Dollimore J G Dunn and K Alexander ldquoDe-termination of the vapor pressure curves of adipic acid and tri-ethanolamine using thermogravimetric analysisrdquoThermochim-ica Acta vol 421 no 1-2 pp 25ndash30 2004

[20] W H McClennen R M Buchanan N S Arnold J P Dworz-anski and H L C Meuzelaar ldquoThermogravimetrygas chro-matographymass spectrometry and thermogravimetrygaschromatographyFourier transform infrared spectroscopynovel hyphenated methods in thermal analysisrdquo AnalyticalChemistry vol 65 no 20 pp 2819ndash2823 1993

[21] K G H Raemaekers and J C J Bart ldquoApplications of simulta-neous thermogravimetry-mass spectrometry in polymer anal-ysisrdquoThermochimica Acta vol 295 no 1-2 pp 1ndash58 1997

[22] W Pu S Pang and H Jia ldquoUsing DSCTGDTA techniques tore-evaluate the effect of clays on crude oil oxidation kineticsrdquoJournal of Petroleum Science and Engineering vol 134 pp 123ndash130 2015

[23] S NMonteiro V Calado F MMargem and R J S RodriguezldquoThermogravimetric stability behavior of less common ligno-cellulosic fibers a reviewrdquo Journal of Materials Research andTechnology vol 1 no 3 pp 189ndash199 2012

[24] A W Coats and J P Redfern ldquoThermogravimetric analysis areviewrdquoThe Analyst vol 88 no 1053 pp 906ndash924 1963

[25] S Materazzi and R Risoluti ldquoEvolved gas analysis by massspectrometryrdquo Applied Spectroscopy Reviews vol 49 no 8 pp635ndash665 2014

[26] B Roduit J Baldyga M Maciejewski and A Baiker ldquoInflu-ence of mass transfer on interaction between thermoanalyt-ical and mass spectrometric curves measured in combinedthermoanalyser-mass spectrometer systemsrdquo ThermochimicaActa vol 295 no 1-2 pp 59ndash71 1997

[27] K Slopiecka P Bartocci and F Fantozzi ldquoEnergy solutionsfor a sustainable worldrdquo in Proceedings of the 3rd InternationalConference onApplied Energy pp 1687ndash1698 Perugia Italy 2011

[28] V N Emelrsquoyanenko S P Verevkin C Schick E N Stepurko GN Roganov and M K Georgieva ldquoThe thermodynamic prop-erties of S-lactic acidrdquo Russian Journal of Physical Chemistry Avol 84 no 9 pp 1491ndash1497 2010

[29] X Xu J Lin and P Cen ldquoAdvances in the research anddevelopment of acrylic acid production from biomassrdquo ChineseJournal of Chemical Engineering vol 14 no 4 pp 419ndash427 2006

[30] P F Martins C Carmona E L Martinez P Sbaite R MacIelFilho and M R Wolf MacIel ldquoShort path evaporation formethyl chavicol enrichment from basil essential oilrdquo Separationand Purification Technology vol 87 pp 71ndash78 2012

[31] A Komesu P F Martins B H Lunelli J Oliveira R MacielFilho and M R Wolf Maciel ldquoEvaluation of lactic acidpurification from fermentation broth by hybrid short pathevaporation using factorial experimental designrdquo Separationand Purification Technology vol 136 pp 233ndash240 2014

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CatalystsJournal of


The development of an efficient method for separationand purification of carboxylic acids from fermentation brothis very important to allow its biotechnological produc-tion in commercial scale since these steps are responsi-ble for 30ndash40 of the total production costs [11] How-ever for recovery and concentration of thermally unstablemolecules such as lactic acid it is essential to understandhow these molecules behave at high temperatures whichcan be achieved through thermal analyses as differen-tial scanning calorimetry (DSC) thermogravimetry (TG)and thermogravimetry coupled with mass spectroscopy(TG-MS)

DSC is performed by difference in energy supplied tothe sample and the reference pan in function of temper-ature By varying the energy of the sample as a functionof temperature physical and chemical phenomena can beobserved In general phase transitions dehydration reduc-tion and decomposition reactions produce endothermiceffects whereas crystallization oxidations and some decom-position reactions produce exothermic effects [12] DSC isoften used because of its speed simplicity and availability[13] Several reviews covering the fundamentals conceptsinstrumentation and general applications are available in theliterature [13ndash16]

TG is a technique that records variation of mass whilethe sample is heated The mass loss can be related to manyphenomena such as dehydration sublimation evaporationand decomposition TG has been used to estimate the kineticparameters such as activation energies reaction orders andthe Arrhenius preexponential factor of degradation [17]and evaporation processes [18] and to determine physi-cal properties as vapor pressure and vaporization enthalpy[19]

TG-MS is a powerful hyphenated technique combiningthe direct measurement of weight loss as a function oftemperature with the use of sensitive spectroscopic detec-tors Such detectors permit qualitative and quantitativedetermination of the evolved volatile products to providekinetic information about the specific reaction mecha-nisms [20] Other advantages are speed reduced samplehandling unique sample and absence of retention time[21] Research articles have been published about instru-mentation and applications of TG [22ndash24] and TG-MS[21 25 26]

So in this work the objective was to study the lacticacid thermal behavior usingDSC TGDTG andTG-MSTheobtained results provided a better understanding of the lacticacid thermal behavior allowing the development of adequateseparation processes

2 Experimental

21 Material DL-lactic acid (molecular weight 9008 kgsdotmolminus1 CAS number 50-21-5) sim90 standard supplied bySigma-Aldrich (St Louis Missouri EUA) was used in thethermal analysis by DSC TGDTG and TG-MS withoutprior purification Water and residual substances are impu-rities reported by the supplier

22 Differential Scanning Calorimetry DSC experiment wascarried out using Shimadzu equipment (Japan) model DSC-50 A dynamic scan was performed at heating rate of10 Ksdotminminus1 over a temperature range from294K to 773KThesample was analyzed under a nitrogen dynamic atmosphereat flow rate of 50mLminminus1The experiments were carried outwith a sample size of sim7mg The samples were weighed intoopen aluminum pans and hermetically sealed

23 Thermogravimetry TG experiments were carried outusing Shimadzu thermal analyser (Japan) model TGA-50Constant heating rates of 5 10 15 20 25 and 30Ksdotminminus1were applied Data were collected in the temperature rangefrom 296K to 773K under a nitrogen dynamic atmosphere(50mLsdotminminus1)Themasses of samples were nearly 15mgTheequipment recorded TG and DTG (derivative thermogravi-metric analysis) data simultaneously Data obtained by TGwere used to determine evaporation kinetic parameters andevaporation enthalpy Data obtained by DTG were useful toshow the evaporation stages and the effect of heating rate

24Thermogravimetry Coupled withMass Spectrometer TG-MS analysis was carried out using Setaram SetSys Evolution1618 coupled with a mass spectrometer (MS) ThermostarPfeiffer Vacuum GSD 301T MS was responsible for mon-itoring the masses of compounds that have evolved fromthe sample during heating Initially the sample was heatedfrom 298K to 773K at heating rate of 10 Ksdotminminus1 undernitrogen atmosphere (16mLsdotminminus1) in order to observe thetemperature range in which the evolution of mass occurredAfterwards the analysis was performed with a mass spec-trometer coupled heating the sample from 293K to 573Kat heating rate of 10 Ksdotminminus1 under nitrogen atmosphere(16mLsdotminminus1) In addition an isothermal at 573K was builtduring 2 h In this case a scan of all fragments evolved fromthe sample during the heating time was used to obtain thethermal and mass spectrum Finally TG-MS was performedmonitoring fragments of higher intensity Data were collectedand used to obtain the lactic acid thermal behavior anddegradation products as a function of temperature and time

25 Kinetic Models Thermogravimetry is the most commontechnique used for kinetic analysis Sample mass variationby temperature data obtained by TGDTG was used todetermine evaporation kinetic parameters The frequencyfactor (119860) and activation energy (119864119886) were obtained usingArrhenius and Kissinger methods

Calculations are based on the following kinetic equation[18]

119889120572119889119905 = 119896 times (1 minus 120572)119899 (1)

where 120572 corresponds to the amount of vaporized material 119905is the time 119899 is the apparent reaction order and 119896 is the rateconstant



120572 = 1198980 minus 1198981199051198980 minus 119898119891 (2)


119896 = 119860 exp(minus 119864119886119877119879) (3)





ln(119889120572119889119905 ) = ln119860 (1 minus 120572)119899 minus 119864119886119877119879 (5)


ln 119889120572119889119905 = ln119860 minus 119864119886119877119879 (6)


119889120572119889119905 =

minus1198891198981198891199051198980 minus 119898119891 (7)


ln( 1205731198792119898) = ln(119860119877119864119886 ) minus119864119877119879119898 (8)



273 323 373 423 473 523 573 623 673 723 773


minus28

minus23

minus18

minus13

minus8

minus3

2

Hea

t flow

(mW

)

darr Endo



(1119886)119889119898119889119905 = 119901120572radic

1198722120587119877119879 (9)



119901 = 119896] (10)







5Kminminus1

10 Kminminus1

15 Kminminus1

20 Kminminus1

25 Kminminus1

30 Kminminus1

0

10

20

30

40

50

60

70

80

90

100

Mas

s (

)

373 473 573 673 773273Temperature (K)

(a)

273 373 473 573 673 773


minus009

minus008

minus007

minus006

minus005

minus004

minus003

minus002

minus001

0

DTG

(mg

s)

5Kminminus1

10 Kminminus1

15 Kminminus1

20 Kminminus1

25 Kminminus1

30 Kminminus1

(b)














1T (Kminus1)

00022 00023 00024 000250002 00021


R2 = 09962

minus9

minus85

minus8

minus75

minus7

minus65

minus6

ln(d

120572d

t)

(a)

1T (Kminus1)

00019 0002 00021 00022 00023

= minus58174 lowast (1T) + 23018

R2 = 09712

minus108

minus106

minus104

minus102

minus10

minus98

minus96

minus94

minus92

minus9

minus88

ln(120573Tm2)

ln(120573

Tm

2)

(b)


= minus68523 lowast (1T) + 92093

R2 = 09922minus4

minus45

minus5

minus55

minus6

minus65

000

195

000

2

000

205

000

21

000

215

000

22

000

225

000

23

000

19

1T (Kminus1)

ln ]

ln]

(kg0

5sminus

1m

minus2m

ol05K0

5)




mz = 32

mz = 17

mz = 18

00E + 00

10E minus 07

20E minus 07

30E minus 07

50E minus 07

40E minus 07

Ion

curr

ent (

A)







mz = 18

mz = 17

mz = 44

mz = 32

mz = 45

000E + 00

100E minus 07

200E minus 07

300E minus 07

400E minus 07

500E minus 07

Curr

ent i

onic

(A)

10 20 30 40 500Time (min)

(a)

10 20 30 40 500Time (min)

0000E + 00

500E minus 12

1000E minus 12

1500E minus 12

2000E minus 12

2500E minus 12

Curr

ent i

onic

(A)

mz = 72

mz = 74

(b)






4 Conclusions





Acknowledgments


References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



120572 = 1198980 minus 1198981199051198980 minus 119898119891 (2)


119896 = 119860 exp(minus 119864119886119877119879) (3)





ln(119889120572119889119905 ) = ln119860 (1 minus 120572)119899 minus 119864119886119877119879 (5)


ln 119889120572119889119905 = ln119860 minus 119864119886119877119879 (6)


119889120572119889119905 =

minus1198891198981198891199051198980 minus 119898119891 (7)


ln( 1205731198792119898) = ln(119860119877119864119886 ) minus119864119877119879119898 (8)



273 323 373 423 473 523 573 623 673 723 773


minus28

minus23

minus18

minus13

minus8

minus3

2

Hea

t flow

(mW

)

darr Endo



(1119886)119889119898119889119905 = 119901120572radic

1198722120587119877119879 (9)



119901 = 119896] (10)







5Kminminus1

10 Kminminus1

15 Kminminus1

20 Kminminus1

25 Kminminus1

30 Kminminus1

0

10

20

30

40

50

60

70

80

90

100

Mas

s (

)

373 473 573 673 773273Temperature (K)

(a)

273 373 473 573 673 773


minus009

minus008

minus007

minus006

minus005

minus004

minus003

minus002

minus001

0

DTG

(mg

s)

5Kminminus1

10 Kminminus1

15 Kminminus1

20 Kminminus1

25 Kminminus1

30 Kminminus1

(b)














1T (Kminus1)

00022 00023 00024 000250002 00021


R2 = 09962

minus9

minus85

minus8

minus75

minus7

minus65

minus6

ln(d

120572d

t)

(a)

1T (Kminus1)

00019 0002 00021 00022 00023

= minus58174 lowast (1T) + 23018

R2 = 09712

minus108

minus106

minus104

minus102

minus10

minus98

minus96

minus94

minus92

minus9

minus88

ln(120573Tm2)

ln(120573

Tm

2)

(b)


= minus68523 lowast (1T) + 92093

R2 = 09922minus4

minus45

minus5

minus55

minus6

minus65

000

195

000

2

000

205

000

21

000

215

000

22

000

225

000

23

000

19

1T (Kminus1)

ln ]

ln]

(kg0

5sminus

1m

minus2m

ol05K0

5)




mz = 32

mz = 17

mz = 18

00E + 00

10E minus 07

20E minus 07

30E minus 07

50E minus 07

40E minus 07

Ion

curr

ent (

A)







mz = 18

mz = 17

mz = 44

mz = 32

mz = 45

000E + 00

100E minus 07

200E minus 07

300E minus 07

400E minus 07

500E minus 07

Curr

ent i

onic

(A)

10 20 30 40 500Time (min)

(a)

10 20 30 40 500Time (min)

0000E + 00

500E minus 12

1000E minus 12

1500E minus 12

2000E minus 12

2500E minus 12

Curr

ent i

onic

(A)

mz = 72

mz = 74

(b)






4 Conclusions





Acknowledgments


References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


5Kminminus1

10 Kminminus1

15 Kminminus1

20 Kminminus1

25 Kminminus1

30 Kminminus1

0

10

20

30

40

50

60

70

80

90

100

Mas

s (

)

373 473 573 673 773273Temperature (K)

(a)

273 373 473 573 673 773


minus009

minus008

minus007

minus006

minus005

minus004

minus003

minus002

minus001

0

DTG

(mg

s)

5Kminminus1

10 Kminminus1

15 Kminminus1

20 Kminminus1

25 Kminminus1

30 Kminminus1

(b)














1T (Kminus1)

00022 00023 00024 000250002 00021


R2 = 09962

minus9

minus85

minus8

minus75

minus7

minus65

minus6

ln(d

120572d

t)

(a)

1T (Kminus1)

00019 0002 00021 00022 00023

= minus58174 lowast (1T) + 23018

R2 = 09712

minus108

minus106

minus104

minus102

minus10

minus98

minus96

minus94

minus92

minus9

minus88

ln(120573Tm2)

ln(120573

Tm

2)

(b)


= minus68523 lowast (1T) + 92093

R2 = 09922minus4

minus45

minus5

minus55

minus6

minus65

000

195

000

2

000

205

000

21

000

215

000

22

000

225

000

23

000

19

1T (Kminus1)

ln ]

ln]

(kg0

5sminus

1m

minus2m

ol05K0

5)




mz = 32

mz = 17

mz = 18

00E + 00

10E minus 07

20E minus 07

30E minus 07

50E minus 07

40E minus 07

Ion

curr

ent (

A)







mz = 18

mz = 17

mz = 44

mz = 32

mz = 45

000E + 00

100E minus 07

200E minus 07

300E minus 07

400E minus 07

500E minus 07

Curr

ent i

onic

(A)

10 20 30 40 500Time (min)

(a)

10 20 30 40 500Time (min)

0000E + 00

500E minus 12

1000E minus 12

1500E minus 12

2000E minus 12

2500E minus 12

Curr

ent i

onic

(A)

mz = 72

mz = 74

(b)






4 Conclusions





Acknowledgments


References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


1T (Kminus1)

00022 00023 00024 000250002 00021


R2 = 09962

minus9

minus85

minus8

minus75

minus7

minus65

minus6

ln(d

120572d

t)

(a)

1T (Kminus1)

00019 0002 00021 00022 00023

= minus58174 lowast (1T) + 23018

R2 = 09712

minus108

minus106

minus104

minus102

minus10

minus98

minus96

minus94

minus92

minus9

minus88

ln(120573Tm2)

ln(120573

Tm

2)

(b)


= minus68523 lowast (1T) + 92093

R2 = 09922minus4

minus45

minus5

minus55

minus6

minus65

000

195

000

2

000

205

000

21

000

215

000

22

000

225

000

23

000

19

1T (Kminus1)

ln ]

ln]

(kg0

5sminus

1m

minus2m

ol05K0

5)




mz = 32

mz = 17

mz = 18

00E + 00

10E minus 07

20E minus 07

30E minus 07

50E minus 07

40E minus 07

Ion

curr

ent (

A)







mz = 18

mz = 17

mz = 44

mz = 32

mz = 45

000E + 00

100E minus 07

200E minus 07

300E minus 07

400E minus 07

500E minus 07

Curr

ent i

onic

(A)

10 20 30 40 500Time (min)

(a)

10 20 30 40 500Time (min)

0000E + 00

500E minus 12

1000E minus 12

1500E minus 12

2000E minus 12

2500E minus 12

Curr

ent i

onic

(A)

mz = 72

mz = 74

(b)






4 Conclusions





Acknowledgments


References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


mz = 18

mz = 17

mz = 44

mz = 32

mz = 45

000E + 00

100E minus 07

200E minus 07

300E minus 07

400E minus 07

500E minus 07

Curr

ent i

onic

(A)

10 20 30 40 500Time (min)

(a)

10 20 30 40 500Time (min)

0000E + 00

500E minus 12

1000E minus 12

1500E minus 12

2000E minus 12

2500E minus 12

Curr

ent i

onic

(A)

mz = 72

mz = 74

(b)






4 Conclusions





Acknowledgments


References










































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

study of lactic acid thermal behavior using...

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