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JournalofAgriculturalChemistryandEnvironment,2022,11,143-162
ISSNOnline:2325-744X
ISSNPrint:2325-7458
ThermalDegradationProductsofα-Pineneina
TubularFurnaceintheTemperatureRange
from300˚Cto900˚C:ContributiontoWildfire
Flashovers
RawaaJamaladdeen1*,BrunoCoudour1,LaurentLemée2,Hui-YingWang1,Jean-PierreGaro1
1InstitutP’,ENSMAISAE,UniversitédePoitiers,Chasseneuil-du-Poitou,France
2IC2MP-UMRCNRS7285,UniversitédePoitiers,PoitiersCedex,France
Howtocitethispaper:Jamaladdeen,R.,Abstract
Coudour,B.,Lemée,L.,Wang,H.-
Garo,J.-P.(2022)ThermalDegradationInducedBVOCemissionsfrompyrolyzedplantsthatmayaccumulateincon-
Productsofα-PineneinaTubularFurnacefinedtopographieshavebeenacontroversyfortheirroleinwildfireeruptions
intheTemperatureRangefrom300˚-pinene(CH)isoneofthemostabundantmonoterpenes
900˚C:
JournalofAgriculturalChemistryandEn-
vironment,11,143-
/,thermaldegradationexperiments
Received:March24,2022wereperformedonα-pineneinatubularfurnaceinaninertatmosphereand
Accepted:May24,2022ahigh-temperaturerange(300˚C-900˚C).Thepyrolysisproductswereiden-
Published:May27,2022tifiedusinggaschromatography(GC)linkedtoatubularfurnaceoutletby
whichtheirretentiontimeswerecomparedwiththoseofreferencestandards.
Copyright©2022byauthor(s)and
,aliphatichydrocarbons(me-
ThisworkislicensedundertheCreativethane,ethane,ethene,propane,propene,1,3-butadiene,isoprene),andaro-
CommonsAttributionInternationalmatics(benzene,toluene)
License().ofthechemicalreactionsassociatedwiththeformationoftheproductsat
/
OpenAccessdifferentexperimentaltemperatureswereaddressedandcomparedwiththe
,butadiene,isoprene,aliphatichydrocarbons,andaro-
maticsformationsfromα--
er,evenifbenzenehasbeenidentifiedinourexperiments,wecannotsupport
withcertaintythemechanismsofitsformationdescribedintheliteraturesince
acetylenewasnotobserved.
Keywords
α-Pinene,BenzeneFormation,BVOCs,Diels-AlderReaction,Dimerization,
Isomerization,Isoprene,Pyrolysis,Rearrangement,TubularFurnace
DOI:.112010May27,2022143JournalofAgriculturalChemistryandEnvironment
:.
.
WildfireflashoversareformsofsuddenfireeruptionshostedprimarilybyMe-
diterraneanclimatewildlands[1][2]andhavebeenpreviouslyreportedbyfire-
fighterswhowereoverwhelmedbytheiroccurrencesinwildfires[3][4].They
arealsoreferredtobythescientificcommunityasAcceleratedForestFires(AFFs)
[5],eruptivefires[6],orgeneralizedblazefires(GBFs)[4].Flashoversinwild-
fires[7],occurwhenanaccumulatedmixtureofplantsemissionscomposedof
biogenicvolatileorganiccompounds(BVOCs)andtheirdegradationproducts,
(EF)
andemissionratios(ER)ofBVOCs[8][9]fromMediterraneanforestsinwild-
fireeventsbecauseoftheirroleinbio-sphere-atmosphereinteractions[10]and
globalwarming[11].However,asflashoversaremorecommonlywitnessedby
firefighters,itisinterestingtoanalysetheroleofBVOCsandtheirdegradation
products,asafavouringfactor.
Bicyclicmonoterpenessuchasα-pinenepossesshighdensityof~·ml−1
[12],whichdoesn’tchangegreatlywithincreasingtemperatures[13].Therefore,
forexample,whenpyrolyzingplantsinawildfireemitα-pinene,itshigherden-
sityrelativetoairallowsittomigratedownwindatgroundlevelandconcentrate
innearbyconfinedtopographiessuchascanyons[14].Ifaccumulated,α-pinene
willdegradeunderthethermalstressesoftheapproachingfirefront[5].Nor-
mally,thethermaldegradationproductsofBVOCs(-pinene),formamix-
tureoftheirVOCisomersinadditiontoaliphaticandaromatichydrocarbons
[15][16].Whenanaccumulationofthesegasesisfavouredbyatmosphericcon-
ditions,itbecomespossibleforthemtoreachalowerflammabilitylimit(LFL)
[17],whichisdefinedasthelowestconcentrationinairatwhichacombustible
gasorvaporcanigniteandpropagateflameinthepresenceofanignition
source(spark,flame,heat),albeitsuchanignitionsourcewillnotbenecessary
iftheirLFLswerecoupledwiththeirauto-ignitiontemperatures(AIT).Nota-
bly,commonBVOCshaveanLFLoflowerthan1%volinair[18]andanauto
ignitiontemperature(AIT)of300˚C[19].α-Pinene,forexample,hasanLFL
˚C[20].Itremainsimportanttoidentifythethermal
degradationproductsoftheseBVOCs(-Pinene)inordertoalsolinktheir
flammabilitycharacteristics(LFL,UFL&AIT)totheprobabilityofaflashover
inawildfire.
Lowtemperatureanalyticalpyrolysisstudiesonα-pinenearemanyandthey
primarilyaddressitsisomerizationandrearrangementproductshowever,the
studiesidentifyingthetotalrangeofitsthermaldegradationproductsathigh
temperaturesareratherfew[21][22][23].Thisarticlecoversthetotalrangeof
thecompoundsemittedfromthethermaldegradationofα-pineneattempera-
turessimilartothosereachedinwildfiresanddescribestheprobablechemical
work,α-pinenewasthermallydegradedinaninertatmosphereusingatubular
ovensetatatemperaturerange(300˚C-900˚C).
DOI:.112010144JournalofAgriculturalChemistryandEnvironment
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Plants,particularlytrees,emitconsiderableamountsofdifferentconstitutive
biogenicvolatileorganiccompounds(BVOCs)withaglobalaverageof1150
Tg·C·year−1[24].PlantBVOCsaremainlyterpenoids(hemi-,mono-,sesqui-,
andditerpenes)[25],whichareinvolvedinplantgrowth,reproduction,defense,
andcommunicationwithinplantcommunities[26][27][28].Theyarealsostrongly
relatedtoplantflammability[29].The5-carbonsisomersisopentenylpyrophos-
phate(IPP)anddimethylallylpyrophosphate(DMAPP)areresponsibleforthe
biosynthesisofterpenoids[30].OnthebasisofC5unitsinvolvedintheirsyn-
thesis,terpenoidscanbeclassifiedintohemiterpenoidsorisoprene(C5H8),mo-
noterpenes(C10H16),sesquiterpenes(C15H24),diterpenes(C20H32),andotherpo-
lyterpenoids[31][32].Theproductionprecursorsandthefunctionalcharacte-
risticsofthemainBVOCsarereportedin(Table1).
Whenplantsareexposedtovariousabiotic(extremesintemperatures,Ozone
(O3),radiation,drought,etc.)orbiotic(fungi,bacteria,herbivores,etc.)stresses,
theirconstitutiveBVOCemissionsbecomeinduced(IBVOCs).Isoprenefol-
lowedbymonoterpenichydrocarbons(C10H16)dominatedbyα-pinene,have
beenreportedtobethemostabundantBVOCsemittedfromMediterranean
plantspeciesduringpyrolysistestingatmoderatetemperatureranges[33][34].
However,analysesofsmokesamplesfromwildfireplumesinMediterraneanfo-
rests,wheretemperaturesarelikelytoexceed900˚C,showedremarkablecon-
centrationsofBVOCs(isoprene,α-pinene,β-pinene)andaromatics(toluene
andbenzene),whencomparedtotheirconcentrationsinbackgroundair(Table
2).
Intheeventsofwildfires,IBVOCsoriginatefromplants’storagepoolsorde
novosynthesiswithproportionsdependingonthedurationandseverityofthe
thermalstresses,theplantspecies(withorwithoutBVOCstoragecompart-
ments),andtheBVOCvolatility[35].ThevolatilityofaBVOCisdefinedasthe
partitionbetweenitsliquidandgasphaseintheplantunderhightemperatures
anditismeasuredbyHenry’slawconstant(Kh)[36].Indeed,thecompounds
withalargerKhpartitionprimarilytothegasphasewhereasthosewithalowKh
partitionmainlytotheaqueousphase[37].TheKhofcommonBVOCsat25˚C
arelistedin(Table3).TheHenry’slawconstantofα-pineneat25˚Cis13590
Pa·m3·mol−--foldforevery10˚Cincreasein
temperature[38].Therefore,ourchoicetostudythethermaldegradationof
α-pineneisjustifiedbyitshighvolatility,coupledwithitshighestemissionrates
amongothermonoterpenesfromMediterraneanplantsduringwildfires[34]
[39].
DOI:.112010145JournalofAgriculturalChemistryandEnvironment
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.
-producedbiogenicvolatileorganiccompounds(BVOCs)
andtheirfunctionalcharacteristics,[25].
BVOCsandFunctionalCharacteristics
Compound
GroupPrecursorsFunctional
TypicalBVOCs
(derivedfrom)Characteristics
Tolerancetosunlight-
IsoprenoidsIsopreneIDP
inducedheating
β-Ocimene,β-Myrcene,Herbivore-inducedsignal
Monoterpenesα-/β-Pinene,Limonene,GDPAttractanttopollinator,
Linalool,Geraniolfragrance
β-Caryophyllene,
Herbivore-inducedsignal
Sesquiterpenesβ-Farnesene,FDP
Anti-microbialactivity
Farnesol,Nerolidol
(E,E)-Geranyl-
TMTT
HomoterpeneslinaloolHerbivore-inducedsignal
DMNT
(E)-Nerolidol
-
firesmokeplume,[8].
ConcentrationBVOCS
(ppbv)isopreneα-pineneβ-pinenebenzenetoluene
’slawconstants(Kh)at25˚CofcommonBVOCs.
CompoundClassBVOCNameKh(Pa·m3·mol−1)
Isoprene7789
AcyclicHydrocarbonsaMyrcene6300
β-Ocimene2507
α-Pinene13590
MonocyclicSabinene6451
Hydrocarbonsa
Limonene2850
α-Phellandrene5496
bβ-Caryophyllene2731
Sesquiterpenes
α-Cadrene3510
aCopoloviciandNiinemets,2005[38].bCopoloviciandNiinemets,2015[40].
-PineneintheLiterature
Accordingtotheliteraturedemonstratedinthissection,thepyrolysisofα-pinene
beginsbyitsisomerizationandrearrangementandisopreneformationatmod-
eratetemperaturesrangingfrom350˚Cto500˚C,followedbytheformationof
DOI:.112010146JournalofAgriculturalChemistryandEnvironment
:.
.
aliphatichydrocarbonsatelevatedtemperaturesfrom600˚Cto700˚C,andfi-
nallyaromatichydrocarbonsattemperaturesexceeding700˚C.
-PinenePyrolysistoIsoprene
TheworksofHlasiwetzandHinterberger,Schultz,Mokiewski,Tilden,andMah-
oodaboutthethermaldegradationofterpenichydrocarbons(mainlyα-pinene)
inthetemperaturerangefrom300˚Cto800˚C,weregatheredin[23].They
foundthatα-pinenedegradesinthetemperaturerangefrom300˚Cto450˚Cto
produceisoprene(C5H8)alsoknownas(2-methyl-1,3-butadiene).Isoprenereach-
esamaximumproductionbetween550˚Cand600˚Canddegradesafterthatto
˚Cto500˚C,isoprenegets
partiallypolymerizedtohigherunsaturatedhydrocarbonsofterpenicnature,
whileitstransformationfrom600˚Cto700˚Cisalmostcompletetoproduce
gasessuchashydrogen(H2),saturatedhydrocarbonssuchasmethane(CH4)
andunsaturatedhydrocarbonssuchasethylene(C2H4),propylene(C3H6),and
1,3-butadiene(C4H6).Aromaticcompoundssuchasbenzene(C6H6),toluene
(C7H8),andxylene(C8H10)begintoappearat700˚Candbecometheexclusive
productsabove800˚
isopreneinarangefrom400˚Cto800˚C,are:%unsaturatedhydrocarbons
asethylene,58%-%methane(CH4),%-%hydrogen,whilethe
tarcollectedcontained10gramsofbenzene,53gramsoftoluene,and21grams
ofnaphthalene(C10H8),[23].
-Pinene
Thethermalisomerizationofα-pinenehasbeenstudiedindetailattempera-
turesrangingfrom300˚Cto500˚Candleadtotheconclusionthattheproducts
aredipentene(racemiclimonene)andallo-ocimenethroughitsprecursoroci-
mene[41].Laterworksprovidedprecisiontothetemperaturevaluesresponsible
fortheevolutionoftheisomerizationproducts(-ocimene)
andtheirpercentages[42][43](Figure1).Thedegradationofα-pineneisneg-
ligibleat300˚C,thenitundergoesaconversionof25%and75%at360˚Cand
395˚C,respectively[42].Asshownin(Figure2),α-pineneconversioninthe
temperaturerangefrom350˚Cto500˚Cresultsprimarilyin45%oflimonene(4)
and2%ofreactiveocimene